Final Report

Transcription

Final Report

The Application of Woodward’s Diesel Burner System
to a Low-Temperature Duty Cycle Application Using
Tenneco’s ELIM-NOx SCR System
Final Report
for:
New Technology Research and Development Program
N-16
Submitted to:
Houston Advanced Research Center
Submitted by:
Woodward Governor Company
Principal Investigators:
Dr. Michael B. Riley
Ed VanDyne
February 28, 2009
The preparation of this report is based on work funded
by the State of Texas through a grant from
the Texas Environmental Research Consortium, with funding
provided by the Texas Commission on Environmental Quality
Table of Contents
1.
Executive Summary................................................................................................................. 6
2.
Introduction ............................................................................................................................. 8
3.
Project Objectives/Technical Approach ................................................................................ 11
3.1.
4.
Exhaust Temperature Limitations and the Exhaust Heat Exchanger ............................. 13
Tasks ...................................................................................................................................... 17
4.1.
Phase 1............................................................................................................................ 17
4.1.1.
Phase 1 Task 1 NOx Aftertreatment Alternatives ................................................... 17
4.1.2.
Task 2 Fuel Economy Effects of Thermal Regulation Approaches ....................... 18
4.1.3.
Task 3 Possible Hydrocarbon Poisoning of SCR at Low Exhaust Temperatures .. 18
4.2.
Phase 2............................................................................................................................ 19
4.2.1.
Task 1 Selection of Candidate Engine .................................................................... 19
4.2.2.
Task 2 Procurement of SCR System Components ................................................. 20
4.2.3.
Task 3 Computational Fluid Dynamics (CFD) Analysis ........................................ 21
4.2.4.
Task 4 Burner Control Software Development ...................................................... 22
4.2.5.
Task 5 Proof-of-Concept System Fabrication......................................................... 23
4.2.6.
Task 6 Engine Testing ............................................................................................ 27
5.
Finance and Schedule ............................................................................................................ 42
6.
Discussion/Observations ....................................................................................................... 45
6.1.
Objectives vs. Results .................................................................................................... 45
6.2.
Critical Issues ................................................................................................................. 46
6.3.
Technical and Commercial Viability of the Proposed Approach .................................. 46
6.4.
Scope for Future Work ................................................................................................... 46
7.
Intellectual Properties/Publications/Presentations ................................................................. 48
8.
Summary/Conclusions ........................................................................................................... 49
9.
Acknowledgements ............................................................................................................... 50
10.
References .......................................................................................................................... 51
11.
Appendices ......................................................................................................................... 52
11.1.
Appendix 1: Comparison of NOx reduction technologies, report from project N-1252
Final Report NTRD Program N-16
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11.2.
Appendix 2: Poisoning in SCR Systems ................................................................... 68
11.3.
Appendix 3: SwRI Testing Report of Woodward’s Burner System ......................... 74
Table of Figures
Figure 1: Technologies Used by US Heavy Duty Engine Manufacturers in the 1980’s to 1990’s 8
Figure 2: Profile of exhaust temperatures in a trash truck with a diesel engine over an urban cycle
......................................................................................................................................................... 9
Figure 3: Exhaust temperature occurrence levels in a trash truck with a diesel engine over an
urban cycle ...................................................................................................................................... 9
Figure 4: NOx conversion efficiency as a function of exhaust gas temperature at two different
ratios of NO to NO2 (and ammonia) ............................................................................................ 10
Figure 5: Light-off with ionization signal and temperature in burner ......................................... 11
Figure 6: Flame-out with ionization signal and temperatures in burner ....................................... 12
Figure 7: Woodward burner system for control of DPF ............................................................... 13
Figure 8: Engine exhaust temperatures into heat exchanger as tested in Loveland, Colorado ..... 14
Figure 9: Schematic of double-sided heat exchanger showing flow paths ................................... 14
Figure 10: Double-sided heat exchanger on test in Loveland, CO ............................................... 15
Figure 11: Measured test engine exhaust outlet temperatures after heat exchanger ..................... 16
Figure 12: Schematic of test setup ................................................................................................ 24
Figure 13: Burner system on test engine at Woodward ................................................................ 25
Figure 14: Burner system on test engine at SwRI......................................................................... 26
Figure 15: Woodward test engine performance characteristics and SCR test points ................... 27
Figure 16: Burner inlet temperatures (left) and SCR inlet temperatures (right) from SCR testing
at Woodward, October 2008 ......................................................................................................... 28
Figure 17: NOx levels entering SCR (left) and exiting SCR (right) from SCR testing at
Woodward, October 2008 ............................................................................................................. 29
Figure 18: NOx reduction percentages with burner preheating exhaust prior to SCR from testing
at Woodward, October 2008 ......................................................................................................... 29
Figure 19: Schematic representation (left) and graphic representation (right) of energy input and
losses between burner inlet and SCR inlet. ................................................................................... 30
Figure 20: Energy balance between burner inlet and SCR inlet from testing at Woodward,
October 2008 ................................................................................................................................. 31
Figure 21: Ideal consumption of diesel fuel into the burner to raise exhaust temperatures to
300°C. Heat losses and heating of burner fuel and air ignored. .................................................. 32
Figure 22: Scaled, measured flow rates of diesel fuel into the burner to raise exhaust
temperatures to 300°C. Heat losses and heating of burner fuel and air included. ....................... 33
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Figure 23: Impact on fuel economy of heating exhaust flow to 300°C at the inlet of the SCR.
Data scaled from measured data with slightly varying burner outlet temperature. Thermal and
other losses included. .................................................................................................................... 34
Figure 24: Impact on fuel economy of heating exhaust flow to 300°C at the inlet of the SCR.
Data calculated only. Thermal and other losses are not included. ............................................... 35
Figure 25: Torque curve of Detroit Diesel Series 60 engine with speed/load points at which SCR
testing was conducted. .................................................................................................................. 36
Figure 26: Exhaust temperatures during SwRI testing for the inlet and outlet of the exhaust heat
exchanger. ..................................................................................................................................... 36
Figure 27: SCR inlet temperatures with burner on during SwRI testing of Woodward burner
system ........................................................................................................................................... 38
Figure 28: NOx levels entering and exiting the SCR with burner on during SwRI testing of
Woodward burner system ............................................................................................................. 39
Figure 29: NOx reduction efficiencies with burner on during SwRI testing of Woodward burner
system ........................................................................................................................................... 39
Figure 30: Ratio of NO2 to NOx at SCR inlet with the burner off (left) and on (right) during
SwRI testing of Woodward burner system. .................................................................................. 40
Figure 31: Ammonia slip from SCR with burner on during SwRI testing of Woodward burner
system. Actual test data shown in white squares ......................................................................... 41
Figure 32: Monthly project costs for N-16 ................................................................................... 42
Figure 33: Cumulative project costs for N-16 .............................................................................. 43
Figure 34: Transient performance of a burner system during Woodward testing (different system
than reported here.) ....................................................................................................................... 47
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Table of Tables
Table 1: Tube diameters to fabricate double-sided heat exchanger .............................................. 15
Table 2: Speed and load points for testing burner and SCR system at SwRI ............................... 37
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1. Executive Summary
Diesel NOx emissions have been the subject of intense research over the past two decades.
Approaches have concentrated on either in-cylinder reductions or aftertreatment. Of the
aftertreatment approaches SCR systems have gained the greatest support, promising NOx
mitigation up to 90% in certain circumstances. An added benefit with aftertreatment systems is
that the base engine is not affected, and a wide range of engines can be serviced by a relatively
small number of sizes of SCR systems. The downside of this strategy is that occasional
maintenance by the engine owner is required to ensure an uninterrupted urea supply, and the
engine owner must bear that cost.
SCR systems work very effectively when the exhaust gases are in the range of 300°C to 450°C.
When exhaust gas temperatures are below this range some form of thermal regulation is
required. Woodward has developed proprietary technology around combustion ion-feedback
sensing with a controller and a burner that can provide the degree of thermal regulation required
to ensure the temperatures of exhaust gases are elevated to the range of efficient operation of the
SCR, while simultaneously promising to minimize ammonia slip while providing high levels of
NOx reduction.
The Engine Systems Research group within Woodward has been developing a diesel burner for
use in exhaust systems to facilitate regeneration of particulate traps. In RFGA-06 the Texas
Environmental Research Consortium (TERC) was seeking technologies that would allow diesel
engines operating on low-temperature duty cycles to reduce NOx effectively. The requirements
for low exhaust temperatures presented a key challenge for lab testing and evaluation of the
burner. For testing purposes only, a custom-design air-to-air heat exchanger was added to the
exhaust system upstream of the burner to simulate the low-temperature duty cycles. This method
of achieving low exhaust temperatures was selected solely to demonstrate the capabilities of the
burner, not to optimize the system for fuel economy. The heat exchanger would never be
included in a real-world burner system design. Woodward has demonstrated a practical diesel
exhaust burner system that is capable of heating low-temperature exhaust to 300°C from idle
to rated speed and 50% load. (Beyond these levels the exhaust gas temperatures exceeded
300°C even with the heat exchanger.)
Selective catalyst reduction (SCR) systems are effective in reducing NOx in diesel exhaust
systems only if the exhaust temperature is sufficiently high, typically above 250 - 275°C.
Woodward’s burner was designed to elevate exhaust temperatures up to 650°C to allow diesel
particulate filters (DPFs) to regenerate. This system was modified to operate continuously at
300°C for efficient SCR operation while allowing the higher temperatures required for DPF
regeneration.
An air-to-air heat exchanger was designed and fabricated to ensure exhaust temperatures
reaching the burner were sufficiently reduced to be representative of low-temperature duty
cycles. The duty cycles that TERC references are usually the result of transient operation, where
the vehicle is driven in such a way that there is significant idle time between periods of
reasonably high load. Examples include school buses and trash trucks. Under this mode of
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operation the exhaust temperature may rarely exceed 225°C, preventing SCR systems from
operating effectively.
Duplicating such an operating cycle in the laboratory would be challenging for developing a
burner, so the approach used was to operate at steady-state speed and load points, and remove
sufficient heat from the exhaust gases to fall below 225°C. The focus of the program was to
prove the capability of the burner to maintain close to 300°C at the inlet of the SCR, so the heat
exchanger subsystem was operated at a high rate of heat rejection. The subsequent effects on
fuel economy must not be taken as a measure of the performance of the burner in real-world
applications. The correlation between engine speed and load, exhaust mass flow and exhaust
temperature would require measurement in real-world applications to understand the fuel
economy impacts more thoroughly.
A proof-of-concept system was assembled and tested on a 12.6 L diesel engine at Woodward’s
Loveland test facility with Woodward’s burner heating the now-cooled exhaust into a Tenneco
ELIM-NOx SCR system. The system was calibrated and debugged, and testing was conducted
over a wide range of speeds and loads where the temperatures into the burner were at or below
225°C. The exhaust was heated with the burner so that exhaust temperatures into the SCR were
maintained between 297°C and 335°C. Urea dosing levels were conservative as Woodward does
not have the capability to measure ammonia emissions. Overall NOx reduction under these
conditions was approximately 55%.
After testing at Woodward the complete system was shipped to SwRI where it was installed on a
Detroit Diesel Series 60 engine. The burner controller and SCR system were recalibrated for the
different engine and the engine was run with and without the burner at a number of steady-state
test points, comparing the NOx reduction in both cases.
The overall NOx reduction from the Detroit Diesel Series 60 engine when operating with
temperatures below 225°C was 75%. Ammonia slip was below 10 ppm for 16 of the 21 test
points, with higher speed and load points showing slip between 10 and 21 ppm. Tenneco
engineers on-site during part of the SwRI testing indicated that the SCR catalyst was undersized.
More refinement of the calibrations and an appropriately sized catalyst would allow ammonia
slip levels to be reduced below 10 ppm while maintaining a NOx reduction efficiency in the 75%
range.
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2. Introduction
NOx emissions are directly linked to ground-level ozone, one of the principal components in
smog [1]. The high efficiencies of diesel engines, resulting from high combustion temperatures,
make them one of the major sources of NOx emissions. Over the past twenty years a number of
new technologies have been introduced to meet ever-tightening emissions standards, as shown
below [2].
Figure 1: Technologies Used by US Heavy Duty Engine Manufacturers in the 1980’s to 1990’s
The general trend of the technologies listed in Figure 1 is to reduce engine-out emissions, that is,
emissions that are generated in-cylinder. There are several new and existing technologies that
are effective in reducing NOx from diesel engines. Techniques for reducing NOx in-cylinder
that use conventional diesel combustion include charge-air cooling, retarded injection timing
(with variable injection timing (VIT) for minimal fuel economy impact) and cooled exhaust gas
recirculation (EGR.) More sophisticated approaches modify the combustion modes, including
homogeneous charge combustion ignition (HCCI) and low temperature combustion (LTC.)
These latter approaches are still being researched and have not made it into widespread use at
this stage.
The alternative to in-cylinder NOx reduction approaches is to treat the exhaust gas after it has
been released from the cylinder. Aftertreatment approaches include lean NOx traps (LNT) and
selective catalyst reduction (SCR.) Particulates are reduced with aftertreatment using diesel
particulate filters (DPF).
Significant reductions in NOx in diesel engine exhausts can be achieved with an SCR system,
but this requires exhaust temperatures above certain thresholds for effective operation. If the
temperature of the exhaust stream is too low then heat addition is required. This implies the need
to control the heat added, as well as the quantity of urea injected. Heat addition may be
accomplished via electric resistance heating elements (not regarded seriously at this stage), with
a diesel oxidation catalyst (DOC) provided exhaust temperatures are sufficiently high, or with
burners. Using burners implies the need for accurate delivery of fuel and air, especially through
transient operation.
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An example of anticipated exhaust system temperatures from urban-cycle driving is shown in
Figure 2 [3].
Figure 2: Profile of exhaust temperatures in a trash truck with a diesel engine over an urban cycle
The frequency with which the temperatures in Figure 2 are exceeded is shown in Figure 3.
Figure 3: Exhaust temperature occurrence levels in a trash truck with a diesel engine over an urban cycle
In this case the exhaust temperatures were below 225 C over 80% of the time.
NOx is made up of NO and NO2. Catalyst performance depends on the ratio of NO and NO2,
exhaust gas temperature and catalyst formulation. SCR systems require exhaust temperatures to
be above certain levels for efficient operation. Figure 4 shows the effects of varying temperature
and NO:NO2 ratio on the reduction of NOx [4] for a particular catalyst formulation. The
implication is that a higher proportion of NO2 in the exhaust allows catalyst function to be more
efficient at lower inlet temperatures. Conversion of NO to NO2 facilitates this process.
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Figure 4: NOx conversion efficiency as a function of exhaust gas temperature at two different ratios of NO to NO2 (and
ammonia)
DPFs for reduction of particulate emissions also require thermal regulation to ensure that
temperatures are high enough to burn the trapped particulates during their intermittent
regeneration cycles. In the case of diesel fueled burners, diesel fuel and air are supplied to the
burner, which is located just before the DPF. Accurate control of the fuel quantity injected and
air delivered is essential to control combustion in the burner for a low emission flame, to
generate temperatures that both minimize fuel consumption and optimize emissions, and to be
independent of the condition of the exhaust stream. Woodward’s development of ion sensing for
combustion feedback provides the instantaneous control required.
Where control of both particulates and NOx is required, a DPF and an SCR system may be used
sequentially. The thermal characteristics of the two systems are different. An SCR system
operates between 300 C and 700 C and is endothermic, while the DPF operates between 600 C
and 900 C without a catalyst, or 450 C to 900 C with a catalyst, and is exothermic. The
temperatures achieved at the output of a DPF may exceed the maximum operating temperatures
of an SCR system, so tight control over burner outlet temperatures is required to regulate both
processes with only one burner over a wide range of engine operating conditions. The control
logic developed by Woodward allows accurate control of the exit temperatures to protect the
SCR catalyst.
There are still several challenges remaining to make this system viable for retrofit applications.
These include cost reductions and more compact air sources, both of which are being addressed
aggressively.
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3. Project Objectives/Technical Approach
The objective of this project was to demonstrate the combination of a diesel burner and
controller capable of elevating the temperature of sub-225°C diesel exhaust to 300°C within a
small margin.
Woodward has developed a proprietary ion sensing technology for application to both
compression- and spark-ignited engines for a variety of combustion diagnostics and control. The
ion sensing system is well suited for application to a diesel burner in engine exhausts to control
temperatures, allowing optimal operation of catalysts and/or DPFs. The ability of the ion sensing
system to provide accurate feedback of the combustion process means that hydrocarbon spikes
due to delayed light-off of the burner, unstable combustion or failing to identify a flame-out are
essentially eliminated. This tight control over the combustion process ensures the inlet
temperature to the SCR is maintained at appropriate levels, providing high levels of NOx
reduction.
Figure 5 shows temperatures and the ionization signal in a burner developed by Woodward for a
diesel application. The plot shows burner light-off, and how the ion signal reacts almost
instantaneously to the start of combustion, while the thermocouples take an additional half a
second to register any change. This demonstrates the advantage of measuring ionization in
combustion over temperature, which is a consequence of combustion. Further, in transient
applications exhaust temperatures change with engine load, making it difficult to separate the
effects of combustion from those of engine load change.
Figure 5: Light-off with ionization signal and temperature in burner
The process is similar when the flame is extinguished. Figure 6 shows this phenomenon in the
same diesel burner. Again the lag between flame-out and the thermocouple reaction is
significantly longer than that with the ionization signal.
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Figure 6: Flame-out with ionization signal and temperatures in burner
It is obvious from the traces in Figure 5 and Figure 6 that the ionization signal is a more
immediate measure of combustion than temperature measurement, so when used in conjunction
with a burner and an SCR, the ion sensing system would reduce the risks of a hydrocarbon spike
both at the start and end of combustion.
Woodward has developed this system to work with a burner as a temperature controller for a
DPF.
Figure 7 shows a schematic of such a system, although with a DPF.
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Figure 7: Woodward burner system for control of DPF
3.1. Exhaust Temperature Limitations and the Exhaust Heat Exchanger
The overriding requirement for this project was to test the capabilities of the Woodward burner
with exhaust temperatures below 225°C over a significant portion of the operating map of the
test engine. To achieve these low temperatures Woodward designed and fabricated an air-to-air
heat exchanger.
The space limitations of test cells at both Woodward and SwRI dictated that a double-sided heat
exchanger of limited length be used. Sizing of the heat exchanger was estimated knowing the
exhaust temperature range and the exhaust mass flow rates at different conditions. A fixed air
flow using blower fans was selected, and the exhaust temperatures were allowed to find their
equilibrium level at each speed and load point.
Figure 8 shows the normal exhaust temperatures for the 12.6 L test engine operating over its
speed and load range as tested in Woodward’s Loveland dyno facility. The area of the curve
with temperatures below 225°C is only a very small fraction of the operating map.
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Figure 8: Engine exhaust temperatures into heat exchanger as tested in Loveland, Colorado
Commercially available blowers were used to pipe cooling air into the heat exchanger, flowing
either side of, and in the opposite direction to the exhaust flow. (Two blowers with combined
flow of approximately 1000 CFM were used.) Figure 9 shows a schematic of the cooling
passages of the heat exchanger.
Figure 9: Schematic of double-sided heat exchanger showing flow paths
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Diameters of the constituent pipe sections making up the plug, exhaust flow area and cooling
flow areas were evaluated to determine the effects on exhaust temperature out and pressure drop
in the exhaust. Detailed optimization was not carried out as it was not felt to be necessary. The
following table lists the tube diameters for commercially available stainless steel tubing, which
were considered to be a reasonable compromise between cooling capacity and overall system
bulk:
Table 1: Tube diameters to fabricate double-sided heat exchanger
Description
Outermost tube
Outside of exhaust section
Inside of exhaust section
Innermost tube
Tube OD
9”
8”
7”
6”
Figure 10 shows a photo of the heat exchanger on-engine during testing at Woodward’s
Loveland, CO facility.
Figure 10: Double-sided heat exchanger on test in Loveland, CO
The additional piping required to duct the exhaust gas to and from the heat exchanger was also
helpful in reducing overall exhaust temperatures.
Figure 11 shows the measured exhaust outlet temperatures with an overall heat exchanger length
of 2.0 m.
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Figure 11: Measured test engine exhaust outlet temperatures after heat exchanger
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4. Tasks
The following list of phases and tasks was produced at the start of the project.
Phase 1: NOx aftertreatment alternatives, fuel economy consequences of heating exhaust
gases, and potential SCR poisoning
 Task 1: NOx aftertreatment alternatives
 Task 2: Fuel economy effects of thermal regulation approaches
 Task: Possible hydrocarbon poisoning of SCR at low exhaust temperatures
Phase 2: Construct proof-of-concept NOx reduction system and perform preliminary
testing






Task 1: Selection of candidate engine
Task 2: Procurement of SCR system components
Task 3: Computational fluid dynamics (CFD) analysis
Task 4: Burner control software development
Task 5: Proof-of-concept system fabrication
Task 6: Engine testing
4.1.Phase 1
4.1.1. Phase 1 Task 1 NOx Aftertreatment Alternatives
4.1.1.1.
Phase 1 Task 1 Objective
The goal of this task was to outline the different alternatives available to engine manufacturers to
reduce NOx levels from diesel engines.
4.1.1.2.
Phase 1 Task 1 Technical Details
This task had already been completed by one of the principal investigators for project N-12. The
report included in-cylinder and aftertreatment approaches used by many researchers investigating
methods to reduce NOx levels. Emphasis was given to the in-cylinder effects of variable
injection timing, as that was one of the main thrusts of project N-12.
SCR systems appear to offer the best option of NOx reduction, especially when fuel
consumption was considered. The studies referenced in this report were not specifically for
engine duty cycles with low-temperature exhaust entering the SCR, so the fuel economy benefits
may not relate directly to this project.
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4.1.1.3.
Phase 1 Task 1 Major Issues/Critical Paths
This task was a literature study. There were no major issues or critical paths.
4.1.1.4.
Phase 1 Task 1 Deliverables
The deliverable from this task is the report given in Appendix 1.
4.1.2. Task 2 Fuel Economy Effects of Thermal Regulation Approaches
4.1.2.1.
The goal of this task was to investigate the effects of providing heat by combustion and electric
resistance methods on fuel economy.
4.1.2.2.
Discussions were held with HARC personnel about this task after the program was awarded. It
was agreed that there was little benefit in carrying out this task. Combustion systems deliver
almost 100% of the energy value of the fuel as heat into the exhaust, as where electricity
produced by the engine’s electrical system delivers around 30% of the energy as heat in optimal
circumstances. In addition this approach appears to have attracted little interest from
manufacturers, so it was agreed to delete this task.
4.1.2.3.
4.1.2.4.
None.
None.
4.1.3. Task 3 Possible Hydrocarbon Poisoning of SCR at Low Exhaust Temperatures
4.1.3.1.
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The goal of this task was to conduct a literature survey to investigate mechanisms by which SCR
performance is degraded during operation.
4.1.3.2.
A literature study was undertaken to review work performed by others in investigation of
reduced SCR performance Mechanisms for performance degradation include contamination by
sulfur, hydrocarbons, minerals in blow-by oil, crystallized urea, as well as thermal aging. Both
contamination by hydrocarbons (exiting the burner) and thermal aging (if the SCR is located
after an SCR in the exhaust) are potential hazards to SCR systems with a burner.
4.1.3.3.
This task was a literature study, so there were no major issues or critical paths.
4.1.3.4.
The deliverable from this task is the report given in Appendix 2.
4.2.Phase 2
4.2.1. Task 1 Selection of Candidate Engine
4.2.1.1.
The goal of this task was to select an appropriate candidate engine to demonstrate the
effectiveness of the burner to maintain a 300°C outlet temperature from sub-225°C exhaust
temperatures. This task turned out to require two engines, one for testing at Woodward in
Colorado, and the other at SwRI in San Antonio, Texas.
4.2.1.2.
The choice of engine (size, power, NOx levels) determined the size of burner to be designed and
built. Woodward has been working with a manufacturer who provided an engine of suitable size
for burner development, but who would prefer to remain anonymous. This engine is a 2004
model, 6-cylinder, turbocharged diesel engine of 12.6 L swept capacity.
The engine selected for testing at SwRI was a 1998-calibration Detroit Diesel Series 60 engine.
It is also a 6-cylinder, turbocharged diesel engine of 12.7 L swept capacity.
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4.2.1.3.
Testing at Woodward was uneventful in terms of communications of the burner controller with
the engine controller. Testing at SwRI was delayed for a short period due to the inability to
communicate over the CAN bus to read speed and load settings on the engine. These values
were entered manually into the controller software to ensure correct burner operation. This
process was acceptable during the steady-state testing conducted, but would not be practical for
transient testing.
4.2.1.4.
The deliverables for testing purposes were a suitable engine for burner and SCR installation at
Woodward’s test facility in Colorado, and the Detroit Diesel Series 60 engine at SwRI in Texas.
4.2.2. Task 2 Procurement of SCR System Components
4.2.2.1.
The goal of this task was to select and procure a suitable SCR system to apply to the candidate
engine(s). A mandatory requirement of this equipment is the ability to program the SCR system
to achieve correct urea dosing under all engine operating conditions.
4.2.2.2.
Woodward’s partner in the development of the burner system, Tenneco, markets the ELIM-NOx
SCR system, so the choice of SCR system was obvious.
The ELIM-NOxTM SCR system is designed to reduce NOx emission from on-road and non-road
construction equipment. It meters precise amounts of the urea solution into the exhaust stream of
the diesel engine. Once in the exhaust, the reagent vaporizes, mixes with the oxides of nitrogen
and passes over a catalyst to turn the ozone-forming oxides of nitrogen (NOx) into water,
nitrogen, and CO2. The system includes a reagent storage tank, pump, motor and filter, a
patented return flow urea injector, SCR catalyst, dedicated electronic control unit (ECU) and
various sensors to monitor and control the process. The system is modular, compact and
packaged for quick retrofit installation.
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4.2.2.3.
During testing at SwRI there was agreement between Tenneco and SwRI engineers familiar with
SCR systems that the catalyst used on this program was undersized for the engines tested. The
recommended catalyst size would be approximately twice the volume of the catalyst used for
testing. This size difference was thought to contribute to ammonia slip in some test conditions.
The catalyst sizing was not considered to be an impediment for this program however.
Maximum exhaust flow during testing for peak torque output for the engine tested at
Woodward’s facility in Colorado was approximately 450 g/s, while the peak flow during SCR
testing was 207 g/s, under 50% of the peak flow.
4.2.2.4.
The deliverable for this task was a complete ELIM-NOx SCR system from Tenneco for
installation on the test engines.
4.2.3. Task 3 Computational Fluid Dynamics (CFD) Analysis
4.2.3.1.
The goal of this task was to determine the appropriate mixing length for location of the urea
injection nozzle in the entry pipe to the SCR.
4.2.3.2.
Urea injected into the inlet pipe of the SCR must be uniformly distributed, and preferably fully
evaporated before it enters the SCR. Failure to achieve either of these objectives may result in
underutilizing the reaction sites of the SCR. Prior to identifying the Tenneco ELIM-NOx system
as the preferred solution it was thought that several CFD models would have to be investigated to
determine the optimal location of the nozzle. Discussions with a Tenneco engineer familiar with
the system resulted in recommendations for placement that obviated the need for this analysis.
The recommendations for mixing length were: 18” for adequate mixing, 24” for good and 30”
for complete mixing.
4.2.3.3.
None.
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4.2.3.4.
The deliverable for this task was a recommended mixing length for the location of the urea
injector nozzle. The range of acceptable locations was decided from discussions with an
experienced Tenneco engineer rather than CFD analysis. That recommendation was that the
injector should be located at least 18” from the inlet of the SCR.
The test installation included locating the injector approximately 42” from the SCR inlet.
4.2.4. Task 4 Burner Control Software Development
4.2.4.1.
The goal of this task was to develop control software to allow the burner to maintain a prescribed
temperature to the inlet of the SCR.
4.2.4.2.
At the start of project N-16 Woodward had developed the basic software to control the burner for
light-off, ramp-up to temperature, temperature control, ramp-down and shut-off. The software
monitored engine speed and load, several temperatures and the pressure drop across the DPF.
Numerous set points and ramp rates were controllable in the user interface for the development
work. The primary difference between controller operation for DPF regeneration and SCR
operation was the desired outlet temperature. This was set initially at the outlet of the burner, but
later was set to the inlet to the SCR for tighter control.
Testing in this phase was at steady state only. The software has been developed for DPF
regeneration to handle engine transients, but this feature was not exercised during SCR testing
either at Woodward or SwRI.
4.2.4.3.
Testing at Woodward was conducted with correct communications between the control module
for the burner and the engine ECU. The engine used CANbus communications for speed and
load between the controllers. Communications between the Detroit Diesel at SwRI and the
burner ECU were not feasible over the early CANbus on that engine. Scheduled testing was for
steady-state points, so the decision was made not to install speed and load sensors to deliver that
information to the burner ECU. As a consequence the control software interface was modified to
allow user input of speed and load.
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For future activities the effects of the thermal mass of a diesel exhaust with a DPF should be
modeled and evaluated experimentally. This may require modifications to the control algorithms
to ensure sufficiently accurate temperature tracking at the SCR inlet.
4.2.4.4.
The deliverable for this task was control software to allow the burner to provide the required
inlet temperatures to the SCR. In addition the software allowed manual entry of engine speed
and load for steady-state testing.
4.2.5. Task 5 Proof-of-Concept System Fabrication
4.2.5.1.
The goal of this task was to assemble the complete exhaust system, including air-to-air heat
exchanger, burner, DPF and SCR systems, along with all the required sensors, controller,
mounting hardware and data acquisition system.
4.2.5.2.
A 2004 model 12.6 L test engine was mounted on a dynamometer at Woodward’s Loveland test
facility. The engine was fitted with the exhaust air-to-air heat exchanger described above. The
burner was installed after the heat exchanger, and DPF and SCR systems were installed after the
burner. The installation was instrumented to record temperatures into the burner and SCR, and
NOx emissions entering and exiting the SCR. There was no facility to measure ammonia slip.
A schematic of the installation is shown in Figure 12. (The ammonia sensor is shown here,
although it was not installed until the system was tested at SwRI.) As is obvious from the photo
in Figure 10 there is a substantial length of exhaust pipe both before and after the heat exchanger,
further contributing to reducing the exhaust temperatures entering the burner.
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Figure 12: Schematic of test setup
The exhaust system is shown on-engine during Woodward testing in Figure 13. The engine is on
the lower right.
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Figure 13: Burner system on test engine at Woodward
The exhaust system was assembled in a modular fashion so that it could be shipped to SwRI for
installation on a 1998 Detroit Diesel Series 60 engine. The layout could be modified somewhat
for the geometry of the test cell, but the components and distances between them remained the
same. The SwRI installation is shown in Figure 14.
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Figure 14: Burner system on test engine at SwRI
4.2.5.3.
Incorporating the air-to-air heat exchanger in the exhaust created some issues with the volume it
occupied in the dyno cell during the fabrication/installation stage.
4.2.5.4.
The deliverable for this task was a complete exhaust system that included the air-to-air heat
exchanger, burner and controller, DPF, SCR system and all sensors. This system was modular to
allow disassembly after testing at Woodward, and reassembly for testing on a different engine at
SwRI.
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4.2.6. Task 6 Engine Testing
4.2.6.1.
The goal of this task was to demonstrate that the Woodward burner could heat incoming exhaust
gases below 225°C into a burner to 300°C at the inlet of an SCR. All testing at this stage is
steady-state.
4.2.6.2.
4.2.6.2.1.
Engine Performance Characteristics and Data Points for SCR
Operation During Testing At Woodward
Figure 15 shows the torque curve for the test engine used at Woodward. The curve show peak
torque from the manufacturer. The filled circles show the speeds and torques at which SCR
testing was performed. The shaded area shows the bounding box of subsequent contour plots.
Figure 15: Woodward test engine performance characteristics and SCR test points
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4.2.6.2.2.
Control of Exhaust Temperatures During Testing At Woodward
The temperatures into the SCR inlet were maintained within a tight range around 300°C. Figure
16 shows the temperature into the burner on the left, and into the SCR on the right.
Figure 16: Burner inlet temperatures (left) and SCR inlet temperatures (right) from SCR testing at Woodward, October
2008
The burner was able to hold inlet temperatures at the SCR within a close margin over the entire
test range with exhaust temperatures considerably lower than most engine applications. Testing
was performed with control on the burner-out temperature. At higher speeds and loads the SCR
inlet temperature drifted upwards because thermal losses from the DPF and piping did not
increase as rapidly as the exhaust enthalpy.
4.2.6.2.3.
Performance of ELIM-NOx System During Testing At Woodward
The calibration of the urea injection system was carried out with an awareness of the lack of
ammonia measurement capability. Accordingly NOx reduction levels were kept well below the
maximum achievable. Figure 17 shows NOx levels before and after the SCR catalyst.
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Figure 17: NOx levels entering SCR (left) and exiting SCR (right) from SCR testing at Woodward, October 2008
The overall NOx percentage reduction is shown in Figure 18.
Figure 18: NOx reduction percentages with burner preheating exhaust prior to SCR from testing at Woodward, October
2008
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The use of a more appropriately sized injector at low speeds and loads would improve NOx
reduction.
4.2.6.2.4.
Energy Balance on Burner System During Testing At Woodward
The additional fuel consumed in the burner must be compared to the heat addition to raise the
exhaust temperature to the required level for efficient SCR operation. Figure 19 shows a
schematic representation of the heat exchanger-burner-piping-DPF system, from the inlet of the
burner to the inlet of the SCR, with the sources of energy input and thermal losses. The input
and losses are also shown qualitatively in the accompanying bar graph. Figure 20 shows the
actual gains/losses at the different test points. The energy (rate) balance on the burner system is
split into five components:
: fuel energy (rate) added to the burner
: energy (rate) to raise the temperature of the air and fuel delivered to
the burner to the SCR inlet temperature
: heat losses (rate) from the outside of the piping, burner and DPF
: thermal energy (rate) to vaporize the urea
: energy (rate) to raise the exhaust temperature to the SCR inlet temperature.
Figure 19: Schematic representation (left) and graphic representation (right) of energy input and losses between burner
inlet and SCR inlet.
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Energy Balance between Burner and SCR
Project N-16, Low Temperature NOx Reduction, October 2008
40000
35000
30000
Power (W)
25000
Q urea
20000
Q loss
15000
Q into air, fuel
Q into exhaust
10000
5000
0
RPM/Torque (ft-lb)
Figure 20: Energy balance between burner inlet and SCR inlet from testing at Woodward, October 2008
It is evident from Figure 20 that reducing thermal losses from the system is critical to minimizing
the fuel consumption increase.
4.2.6.2.5.
Correlation Between Exhaust Temperature and Mass Flow for Heat
Addition
The thermal input required to raise exhaust temperature to 300°C is a function of the exhaust
mass flow rate and its temperature. Figure 21 shows this relationship for the ideal case of no
thermal or other losses.
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Figure 21: Ideal consumption of diesel fuel into the burner to raise exhaust temperatures to 300°C. Heat losses and
heating of burner fuel and air ignored.
Real systems will have thermal losses between the inlet of the burner and the inlet of the SCR, so
the thermal input will be higher than this theoretical figure. In addition the different rates of heat
transfer from the exhaust gases inside the piping and DPF relative to the outside will skew the
shape of the contours. Figure 22 shows the fuel flow to the burner from measured data during
experimentation at Woodward, scaled to an inlet temperature of 300°C at the SCR.
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Figure 22: Scaled, measured flow rates of diesel fuel into the burner to raise exhaust temperatures to 300°C. Heat losses
and heating of burner fuel and air included.
4.2.6.2.6.
Fuel Economy Impact to Raise Exhaust Temperature to 300°C
The thermal input required to raise exhaust temperature to 300°C is a function of the exhaust
mass flow and the exhaust temperature into the burner. The exhaust cooling system employed
for this project was designed to remove more heat from the exhaust than absolutely necessary
to ensure sub-225°C temperatures into the burner. This design overkill imposes an additional
fuel economy penalty on the burner system.
Figure 23 shows the impact on overall fuel economy of the burner operating with the system
tested at Woodward. The increase ranges from a low of 2.9% at high speed, high load, to a
maximum of 47% at idle over the engine speeds and loads tested and for the rate of exhaust heat
removal achieved with the exhaust heat exchanger.
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Figure 23: Impact on fuel economy of heating exhaust flow to 300°C at the inlet of the SCR. Data scaled from measured
data with slightly varying burner outlet temperature. Thermal and other losses included.
The effects of thermal losses as well as the heating of the air and fuel supplied to the burner
obviously increase fuel consumption. To gauge the impact of thermal and other losses on fuel
economy, an ideal burner system is shown in Figure 24.
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Figure 24: Impact on fuel economy of heating exhaust flow to 300°C at the inlet of the SCR. Data calculated only.
Thermal and other losses are not included.
4.2.6.2.7.
Burner and SCR Testing at SwRI
The entire exhaust system comprised of the heat exchanger, burner, DPF and SCR were shipped
to SwRI for installation on a Detroit Diesel Series 60 engine, vintage 1998. The engine
performance was mapped for basic characteristics, and to ensure that exhaust temperatures were
similar to testing at Woodward.
A plot of the engine peak torque curve, overlaid with the test points selected for evaluating the
SCR system is shown in Figure 25.
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Figure 25: Torque curve of Detroit Diesel Series 60 engine with speed/load points at which SCR testing was conducted.
4.2.6.2.8.
Control of Exhaust Temperatures During Testing at SwRI
The heat exchanger and piping were installed on the Detroit Diesel engine, and the burner
controller was recalibrated to hold tighter values at the SCR inlet. The exhaust temperatures
were mapped with and without the burner operating. The results are shown in Figure 26.
Figure 26: Exhaust temperatures during SwRI testing for the inlet and outlet of the exhaust heat exchanger.
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The range of speed and load values over which the exhaust temperatures are below 225°C is
broader than for testing at Woodward.
A range of engine speeds and loads was selected for testing the burner and SCR system. These
points are shown in Table 2.
Table 2: Speed and load points for testing burner and SCR system at SwRI
Operation of the burner during steady-state testing at the points in Table 2 produced inlet
temperatures to the SCR that were close to the 300°C target, as shown in Figure 27.
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Figure 27: SCR inlet temperatures with burner on during SwRI testing of Woodward burner system
4.2.6.2.9.
NOx Reduction with Woodward Burner System During Testing at
SwRI
Tenneco’s ElimNOx system was recalibrated for operation on the Detroit Diesel engine. The
engine was then operated over the range of speed and load points in Table 2, and the NOx
emissions before and after the SCR were measured. The emissions levels are shown in Figure
28.
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Figure 28: NOx levels entering and exiting the SCR with burner on during SwRI testing of Woodward burner system
NOx reduction efficiency is shown in Figure 29.
Figure 29: NOx reduction efficiencies with burner on during SwRI testing of Woodward burner system
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4.2.6.2.10.
Effect of Burner on NO:NO2 Ratio During Testing at SwRI
Increasing the ratio of NO2 to NO increases the activity of some catalysts at lower temperatures
[4]. Figure 4 shows this trend. An alternative perspective on Figure 4 is that a percentage of
NO2 to NOx approaching 50% aids in lower temperature NOx conversion. Figure 30 shows the
percentage of NO2 to NOx for the Detroit Diesel engine both with and without the burner
operating.
Figure 30: Ratio of NO2 to NOx at SCR inlet with the burner off (left) and on (right) during SwRI testing of Woodward
burner system.
With burner operation the ratio of NO2 to NOx is close to 50%, which should allow improved
catalyst function at lower temperatures.
4.2.6.2.11.
Ammonia Slip from SCR with Woodward Burner During Testing at
SwRI
The availability of ammonia slip measurement during SwRI testing allowed more optimal urea
calibrations of the ElimNOx system compared to testing at Woodward. Ammonia slip levels
were set at 10 ppm for testing, corresponding to the level set by the California Energy
Commission in a modification made to conditions for certification AQ-48 made on August 8,
2007 [5].
Ammonia slip during testing is shown in Figure 31.
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Figure 31: Ammonia slip from SCR with burner on during SwRI testing of Woodward burner system. Actual test data
shown in white squares
The labels in Figure 31 show that five of twenty-one test points had ammonia levels above 10
ppm, the highest being 20.9 ppm. (Recalibration of the SCR system was undertaken to reduce
these levels, but during this process there was contamination of the SCR with diesel fuel as a
result of a power supply failure to the air pump for the burner. There was insufficient time left at
the end of testing to resolve the issue, so the recalibration and retesting were not carried out in
this program. See the Discussion section below.)
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5. Finance and Schedule
The monthly expenditures for project N-16 are shown in Figure 32.
N-16 Monthly Project Costs
$140,000
$120,000
$100,000
$80,000
$60,000
$40,000
$20,000
$0
Monthly NTRD
Monthly Cost Share
Monthly Project Cost
Figure 32: Monthly project costs for N-16
The cumulative costs are shown in Figure 33.
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N-16 Cumulative Project Costs
$900,000
$800,000
$700,000
$600,000
$500,000
$400,000
$300,000
$200,000
$100,000
$0
Monthly NTRD
Monthly Cost Share
Monthly Project Cost
Figure 33: Cumulative project costs for N-16
The initial contract period for project N-16 was from 11/28/2006 to 8/31/2007. Several
extensions were granted. They were:
Grant Amendment #1: Extension: to 5/31/2008 – due to burner development process
Grant Amendment #2: Extension: to 12/31/2008 – due to project progress and third party
testing schedule
There were several revisions to the budget. These included:
June 2008
o Budgeted items under Equipment were transferred to Supplies and Materials and
Personnel Costs
o Adjustments made within Supplies and Materials no changes to the bottom line
December 2008
o Remaining budgeted balances transferred to Personnel Costs
Explanatory notes for budget changes:
January 2008: activity increase in burner development work
May – June 2008: activity increase due to supplies and materials purchases
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July 2008 – NTRD Personnel Costs budgeted amount depleted, and costs were absorbed
by cost share
October 2008: increase due to Cost Share and first SwRI testing payment
November: increase due to travel and testing at SwRI – second testing payment
December: approval to portion remaining funds to Personnel Costs. Cost share from
July and August Personnel Costs removed, recalculated and added back in for final
invoicing
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6. Discussion/Observations
6.1.Objectives vs. Results
The objective of this project was to demonstrate the combination of a diesel burner and
controller capable of elevating the temperature of sub-225°C diesel exhaust to 300°C within a
small margin. This goal was met completely (see Figure 16 and Figure 27.)
A follow-on metric of the success of the burner performance was the level of NOx reduction
with the elevated exhaust temperatures. These levels differed between testing at Woodward and
at SwRI based on the ability to measure ammonia slip, which may become more important in the
calibration phase of the SCR dosing system.
Testing at Woodward was conducted without the ability to differentiate between NO and NO2,
nor to measure ammonia slip. However measurements were taken of the effect on fuel economy
to raise exhaust temperatures to 300°C at the SCR inlet. With overall NOx reduction levels of
55% the fuel economy penalty ranged from 3% to 47%, depending on speed and load, and with
the level of exhaust cooling applied during lab testing. These figures are difficult to interpret
without integrating the effect over a realistic operating cycle to determine the effect on fuel
economy. However it is realistic to point out that reductions in thermal losses off the exhaust
system would reduce the fuel consumption penalty by 50% or more (see Figure 23 and Figure
24.)
Initial sizing of the SCR system was made for a 2004-calibration 12.6 L engine at Woodward,
with engine-out NOx levels some 25% lower than the NOx levels on the Detroit Diesel engine
used for testing at SwRI. Based on observations from both Tenneco and SwRI engineers the
recommended SCR volume on the Detroit Diesel should be approximately twice that of the
current system. For the range of speeds and loads tested (due to the sub-225°C exhaust
temperature requirement, and the use of an exhaust heat exchanger) this was not considered to be
an issue. The exhaust flow over the range tested was below half that of peak output, mitigating
the effect of the undersized SCR. Having said that though, the higher ammonia slip numbers
occurred at higher speed/load points (see Figure 31), indicating that a larger SCR volume, and
thus more reaction sites in the catalyst, would aid in meeting the 10 ppm target.
The ammonia slip measurements were made on a system that has not been optimized. There
were five of twenty-one test points with ammonia slip above the self-imposed 10 ppm limit. The
highest value was 21 ppm, at a speed and load where the SCR system was thought to be near its
capacity for efficient NOx reduction. Had the SCR system been sized correctly this issue may
not have occurred. These points were to be retested, but during this process there was a failure
of the power supply to the air pump for the burner. Normal overrides were not in place with the
burner due to the experimental nature of the testing, the recalibrations to the ELIM-NOx
controller, and the need to make minor modifications to air/fuel ratios with the cooled exhaust.
As a consequence of the power supply failure to the air pump raw fuel was injected into the
burner can before the pump failure was detected. When the air pump was operational again the
process of relighting the burner resulted in combustion that sprayed raw diesel fuel downstream
into the SCR. Subsequent attempts to heat the SCR system to a high enough temperature to
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drive out the diesel were unsuccessful. (The exhaust cooler was operated during the process to
avoid potential cracking of the cooler with high temperature gradients.) The major goals of the
program had been achieved to that point, and the test cell was needed for other programs, so the
testing was halted.
6.2.Critical Issues
The primary approximation made for this project was to design and build an air-to-air heat
exchanger to reduce exhaust temperatures, to demonstrate the capabilities of the burner and
controller. It is difficult to determine whether the steady-state temperatures resulting from the
heat exchanger are representative of the exhaust temperatures that would be seen in real-world
testing. It is uncertain whether the effect on fuel economy was realistic, and fuel economy is an
important operating characteristic. Future testing should be done on an application where the
actual field conditions can be replicated.
Heat loss between the engine and the SCR should be minimized in a vehicle setup that represents
field conditions.
6.3.Technical and Commercial Viability of the Proposed Approach
There is little doubt that Woodward’s burner and controller system is capable of providing the
required heat addition and thermal regulation to enable low-temperature duty cycle engines to
work effectively with SCR systems for NOx reduction. Validation of the ability of the burner
and controller to provide robust performance under transient operation in conjunction with an
SCR system still remains to be proven. (See the next section regarding transient performance.)
The commercial viability of the technology depends on a number of factors, not the least of
which is the cost of verification. It is unclear how the EPA would want to verify the
performance of the burner, as it does not reduce emissions by itself, but rather it allows adjunct
systems (DPF, SCR) to perform more effectively. If several different sizes of burner could be
tested independent of these other systems, then the path to commercialization is relatively
straightforward. However if specific combinations of these systems are required to undergo
verification the economic opportunity may be very limited.
6.4.Scope for Future Work
There are several steps that are required moving forward. The first is to validate performance of
the burner and controller under transient load conditions.
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Testing of the burner system for the SCR was conducted at steady-state conditions only. The
Woodward burner system has been tested over transient cycles in other applications, and has
been shown to hold a target temperature with close tolerances. Figure 34 shows a plot of a
transient performance test on a different burner system at Woodward performed outside of this
program. The burner was operated over a 20-minute transient cycle, then switched off. (Details
of the plot have been suppressed for confidentiality.)
Figure 34: Transient performance of a burner system during Woodward testing (different system than reported here.)
Similarly the ELIM-NOx system has been designed for transient operation on diesel engines.
Transient operation may result in slightly lower NOx reduction percentages to avoid ammonia
slip.
As suggested above, testing should be carried out on an appropriate transient duty cycle
application, where exhaust temperatures are representative of real-world driving conditions.
Identification of suppliers for components should be carried out, and the resulting system should
be prepared for verification testing.
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7. Intellectual Properties/Publications/Presentations
There are no intellectual property developments as a result of this project.
Woodward is planning to prepare a paper for publication in a suitable refereed forum in the next
six months. The forum has not been selected at this stage.
Woodward made a presentation at a HARC workshop in Houston in February of 2008.
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8. Summary/Conclusions
The following conclusions may be drawn from the data presented:
1. With exhaust temperatures at or below 225°C the burner system has shown its capability
to maintain temperatures into the SCR inlet of 300°C with a tight tolerance.
2. The burner system is capable of heating the exhaust flow at idle to 300°C.
3. NOx reductions of 75% or more appear achievable over most of the speed/load range
with burner inlet temperatures below 225°C.
4. The fuel penalty measured is almost certainly higher than will be experienced in real
world applications. Exhaust temperatures entering the burner during these tests are felt
to be unrealistically low with the high-heat rejection heat exchanger in the exhaust
system. Therefore the energy input to raise exhaust temperatures back to 300°C for the
SCR inlet is unrealistically high.
5. Minimization of thermal losses off the exhaust system is critical. At most speeds and
loads these losses account for a third or more of the burner fuel requirement.
6. The fuel economy impact is high for such low exhaust temperatures. Operation of the
SCR at lower temperatures would improve this penalty, but the NOx conversion
efficiency may suffer.
7. Ammonia slip levels below 10 ppm appear feasible over the operating range tested.
Results from testing show this burner-controller combination to be a viable solution for the
problems of low-temperature duty cycle engine applications. There are commercially available
burners used for active regeneration, but mainly used for diesel particulate filters, and mainly
developed in-house for the OEM’s own use. The technology is becoming more mature and more
sales and marketing information is available, but it is difficult to benchmark other technologies at
this point. Based on literature searches, Woodward believes that there are no other fuel-based
burner systems for supplemental heat for SCR systems in production. Woodward’s application
is unique because it uses ion sensing in closed loop control to detect combustion. Other
technologies sense temperature and seem to have difficulty differentiating a transient exhaust
temperature from actual flame light-off or blow-out.
Woodward is working with Tenneco to release a product for Tier 4 emission regulations. In
first- fit applications, the OEM will certify the system with the EPA. For retrofit, the
manufacturer of record would bring this to the EPA. Woodward has not selected a delivery
partner for retrofit and the timeline for the EPA verification has not been defined. Woodward has
tested the burner design on many applications, including trucks, with minimal changes to the
design.
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9. Acknowledgements
The preparation of this report is based on work funded in part by the State of Texas through a
grant from the Texas Environmental Research Consortium with funding provided by the Texas
Commission on Environmental Quality.
The SCR system was procured through Tenneco, whose personnel assisted with their experience
and knowledge in the commissioning and calibration of the SCR system.
The advice, efforts and experience of the personnel at SwRI under Dr. Magdi Khair were greatly
appreciated. Dr. Qilong Lu at SwRI worked tirelessly to ensure consistent and complete results
from testing at SwRI.
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10.
References
1. http://www.ci.austin.tx.us/airquality/ozone.htm, All About Ozone
2. Engine Design for Low Emissions, DieselNet 2003
3. DSNY and Cummins Inc.: A Collaboration Towards Cleaner Air. A
Demonstration of Diesel Particulate Filter Emission Control Technologies on
Refuse Collection Trucks and Deployment of Natural Gas Powered Street
Sweepers. Project Summary Report, October 2005.
www.nescaum.org/documents/cummins_dsny_report_final.pdf/
4. W. Addy Majewski, “Selective Catalyst Reduction,” DieselNet.com
5. Letter from California Energy Commission, “Midway Sunset Cogeneration Project
(85-AFC-3C), Staff Analysis of Request to Increase Ammonia Slip”, August 2007,
http://www.energy.ca.gov/sitingcases_pre-1999/midway_sunset/2007-0810_STAFF_ANALYSIS_OF_REQUEST_MIDWAY.PDF
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11.
Appendices
11.1.
Appendix 1: Comparison of NOx reduction technologies, report
from project N-12
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Funding Opportunity RFGA-03
Area of Interest:
Development and Testing of Engine Upgrade/Retrofit
Kit for Existing Engines
Applicant:
Motive Engineering Co.
19 Old Town Square
Suite 238
Fort Collins, CO 80524
Point of contact:
Michael B. Riley, President
Telephone:
(970) 221-9600 / (970) 218-0141
Fax:
(970) 221-3863
Email:
miker@mec.com
Project Title:
A Novel Method of Mechanical Variable Injection
Timing to Reduce NOx Emissions
Date:
January 11, 2007
Phase 1: Benefits of Variable Injection Timing
Phase 1 Report Grant N-12
Page 1/15
Benefits of Variable Injection Timing
When emissions standards for heavy-duty diesel engine manufacturers tightened in 1991
the industry made the transition from mechanical, fixed injection timing, meaning fixed
start of injection (SOI), to more expensive electronically varied SOI. This report seeks to
summarize research work conducted both before and after that time to quantify the
benefits of variable injection timing (VIT.)
There are numerous studies that report the effects of variable SOI [1, 2, 3, 4, 5.] The
studies cited from 1981 to 2002, and generally measure the effect of SOI change on fuel
consumption and NOx emissions.
Locomotive Application
In [1] the authors studied the emissions and fuel economy effects on locomotive engines.
Of particular interest is the GE 7FDL locomotive engine whose unit pump injection
system is a good candidate for MEC’s eccentric sleeve phasing (ESPi™) system for
variable SOI. These engines are normally tested over an eight-point duty cycle, but to
reduce total testing time their timing sweeps for determining the effects on fuel economy
and emissions were conducted at three points. The points chosen were at idle, notch 5
and notch 8. Results quoted are weighted with 50% at the idle condition, and 25% each
to the other two points. Extrapolating from the data in the paper they indicate that a
reduction of 25% in NOx would require the SOI to be retarded by just over 6° crank, with
corresponding drop in fuel economy of just over 3%.
Midrange
The engine tested in [2] was a 9.5 L truck engine certified to Euro 2 emissions. The aim
of the study was to determine the emissions from different diesel fuel formulations,
however by testing at the stock, fixed timing, and one other setting with constant NOx
output, useful extrapolations could be made on their reference fuel. Testing was
conducted over a 13-mode European cycle, again averaging the results. One of the fuels
used represented a low-sulfur European fuel, and results using this fuel are referenced.
The engine used a fixed SOI of 10° BTDC for the baseline tests. SOI was then altered to
produce a fixed NOx level of 6.3 g/kW-hr, or a reduction of 7%. While extrapolating
these results to a 25% reduction in NOx may not be linear it points to fuel consumption
worsening by approximately 4%, with retarding the SOI by some 5° crank.
Initially it appears that it is possible to reduce NOx by 25%, simply by retarding SOI by
an average of 5° to 6° crank, but the penalty is paid in fuel economy. In most references
[1, 2, 4, 5] data reported are averaged over some sort of representative cycle, disguising
the effects of SOI change at different speeds and loads. In [3] however, specific
examples are given of these effects, as shown in Figure 1 below.
Page 2/15
Figure 1: Test results reported in [3] for BSFC vs. SOI at different speeds and loads
Heavy Duty
Testing was performed on a single-cylinder test engine, representing a heavy duty truck
application. Data for 25%, 50% and 100% load were taken at 1130 and 1420 rpm. Like
all other studies reported they show that advancing SOI at all speeds and loads results in
increasing NOx output as shown in Figure 2 below. The effect on fuel economy is more
varied. In this case it is obvious from Figure 1 that the location of optimal timing for fuel
consumption shifts significantly with load, and somewhat with speed. Further, at some
load conditions the effect on fuel consumption appears flat over a wide range of timing,
allowing timing selection to be made to minimize NOx emissions.
Figure 2: Test results reported in [3] for BSNOx vs. SOI at different speeds and loads
Assuming that static SOI would occur at 16° BTDC it is possible to estimate the changes
in BSFC, BSNOx and, to a certain extent, particulates. (The scale chosen for the
particulate plots made it difficult to determine changes in emissions with any degree of
accuracy.)
Page 3/15
For the case of full load at 1130 rpm, the NOx level was 12 g/kW-hr. Reducing the NOx
level to 9 g/kW-hr required a 7.5° timing retard, and fuel consumption worsened by
1.5%. However at 25% load the initial NOx level was 31 g/kW-hr. When this was
reduced by 25% to 23 g/kW-hr the timing retard was 4°, and fuel consumption improved
by 1.6%. In this case it was more beneficial to retard the timing further, by 10°, which
gave an improvement in fuel consumption of almost 4%.
With different SOI values feasible at different speeds and loads it may be possible to
reduce overall NOx emissions by the 25% target required while having little impact, if
any, on fuel consumption. As an example the 1420 rpm data could be considered at full
load. In Figure 1 it is apparent that the fuel consumption varies very little between 14°
BTDC and 11° BTDC. (There is no data at the 16° BTDC point.) However the NOx
level falls off by 12%. Depending on the duty cycle of the engine concerned this may be
a suitable trade-off between NOx emissions and fuel economy over the entire cycle while
the overall target of 25% is achieved. From all the data found so far in the literature it
appears that preserving fuel economy is not feasible with a fixed SOI retard.
Mechanical Injector Design Considerations
Dual and Single Helix Pumps
The data in Figure 2 show that NOx increases significantly as load decreases with fixed
SOI timing. This is due to the excess air in unthrottled diesel engines at part load. To
counteract this tendency, as NOx emissions regulation began, many non-electronic (or
mechanical-only) fuel systems changed to modified designs known as “dual helix”
plungers to retard SOI timing as fueling decreases. Mechanical-only systems control SOI
and how much fuel is injected by machined cuts in the outer cylindrical surface of the
injection plunger. As the injection plunger begins to move upward, fuel flows through
the cut plunger passages into a “spill port” in the pump barrel until the lower edge of the
cut is reached, which closes the port, and traps fuel in the pumping volume. This trapped
volume is then pressurized by the plunger upward motion for injection. End of injection
(EOI) occurs when another cut in the plunger connected to the pressurized injection
volume reaches the spill port and releases the fuel pressure. A “single helix” plunger has
a horizontal edge cut for (fixed timing) SOI, and regulates the amount of fuel injected by
rotating the plunger so that a helical cut ends injection, with the amount injected a
function of the distance between the SOI horizontal cut and the EOI helical cut at the spill
port position. A “dual helix” plunger has a second helical edge cut (instead of horizontal)
for SOI so that as the plunger is rotated to regulate fuel quantity, the SOI timing is also
modified.
SOI Lag Due to Line Length
Although dual helix plunger systems have much less variation in NOx versus engine
load, the SOI timing is still a direct function of the amount of fuel injected and does not
change with engine speed. With pump/line/nozzle (PLN) systems, using either a single
multicylinder inline pump assembly, or several separated single cylinder unit pumps,
there is still a significant delay between the beginning of an injection pulse at the pump
Page 4/15
and the resulting pulse reaching the injector tip, due to the speed of sound in the fuel and
the distance along the length of the injection line and through the injector. These delays
in each line and nozzle are nearly constant in absolute time (seconds), meaning that the
delay in engine crank angle (degrees) varies with engine speed. Thus SOI timing retards
as speed is increased. For example, for a 720 mm line length, the delay can increase from
2.6 deg at 800 RPM to 7.2 deg at 2200 RPM, causing a 5.6 deg retard in SOI at 2200 vs.
800. This runs opposite to the desired trend in SOI versus speed, where for constant
BSNOx, SOI timing is usually advanced as engine speed increases.
Resulting Compromises in SOI Timing
Thus even with a dual helix system, the phasing of the injection pump and resulting SOI
timings are usually limited by one or only a few speed/load regions at which the highest
NOx is produced, usually at the lower speed and high load ranges. With a single helix
system, the phasing is often limited by the very high NOx lower speed and lower load
ranges. All other points then are not optimized in SOI timing for the best BSNOx vs.
BSFC tradeoff. This results in higher overall fuel consumption throughout the full
speed/load range, which is magnified if the application duty cycle requires significant
amounts of time in the higher speed range. With VIT, the SOI timings can be
independently tailored so that in the highest NOx regions, SOI timing is retarded, and in
the lower NOx regions, SOI timing is advanced. Thus overall NOx can be reduced
without a significant penalty in fuel consumption, and even sometimes an improvement,
depending on application duty cycle.
Summary statement
Fixed retard of SOI for NOx reduction of 25% results in a fuel economy penalty of 3 –
4%. VIT can achieve the same level of NOx reduction with a fuel economy penalty that
is much lower, and may sometimes even be an improvement, depending on the duty
cycle.
EFI Conversion Cost Estimates
Finding suitable cost information for comparison purposes has been difficult. Some
information has been found on the difference in cost between mechanical injection
systems, and their subsequent model electronic versions, and will be summarized here.
Some of this information has been provided through personal contacts, and should be
regarded as approximate. Other numbers are for retail systems that may be purchased
through distributors. However there are no readily available cost numbers that allow
direct costing of converting existing mechanical injection systems to electronically
controlled, fully variable SOI timing systems.
The initial cost information is for replacing a mechanical in-line pump for 6-cylinder
heavy-duty diesel engines with an electronically controlled pump. This comparison is
made difficult by the difference in architecture between this style of pump, and the MEC
ESPi™ system which is intended for applications using unit pumps.
Page 5/15
The mechanical in-line pump units are estimated to cost $1,000 to $1,200 to the engine
manufacturer. A replacement electronically controlled pump (for varying SOI) is
estimated to cost $2,200. (Note that this cost comparison assumes that a direct
replacement pump is available for the particular engine under consideration. If a generic
electronic pump replaces an existing tailored unit the costs are certain to be considerably
higher.) The estimated OEM cost of the appropriate engine control module (ECM) is
$400 to $450. If the markup for retail sale is in the range of 50 – 100%, then the
additional cost of variable SOI to the end customer is in the range of $2,100 to $3,300 for
the components alone for a six-cylinder, in-line diesel engine. The cost of labor for
removal of the old system and installation of the new system must be added to these
numbers, and the cost of replacement nozzles should be added as well.
In comparison, the cost of hardware for the MEC ESPi™ system for this engine type to
vary SOI timing only is estimated to be $3,400 (including modified unit pumps) from the
information given in the proposal application. As above, labor is additional, but should
be comparable. Timing maps for different speed/load conditions for a 25% NOx
reduction will have to be generated during the verification stage of the MEC ESPi™
system. These costs have not been included here. They are difficult to estimate due to
uncertainty in the numbers of possible candidate engines. However they should be
comparable to conversion costs to electronic systems if they were not tailored to the
candidate engine.
Current retail prices for heavy duty unit injectors (with wiring) for electronically (spill
valve) controlled systems are in the range of $400 per injector or $2,400 for a 6-cylinder
engine. The ECM for these systems is estimated to cost $1,500. Sensors ($300) and a
gear pump for pressurizing the fuel ($300) would bring the hardware cost estimate for
this type of system up to $4,500. It is not clear whether EFI conversions require different
cam profiles, necessitating either replacing or modifying the existing camshaft. If so this
cost would be additional, and is not included here.
If suitable solenoid controlled injectors are not available for older, candidate engines then
the conversion cost to the MEC ESPi™ system should be considerably lower than
electronically controlled SOI injection systems. In the case where such injectors are
available, the hardware cost estimates for replacement hardware to convert existing
mechanical injection systems to electronically controlled SOI timing appear to be in the
same range, or slightly more expensive, than the proposed MEC system.
NOx Reduction Approaches
NOx is formed in-cylinder as a consequence of the combustion process. There are two
general areas to reducing NOx, and techniques in these areas may be used in tandem.
The first is in-cylinder, where the conditions that lead to the formation of NOx are
modified so that there is less NOx produced. VIT is one of the techniques that can
achieve this, but there are others, as described below.
Page 6/15
The second approach is to accept the levels of NOx produced in-cylinder and then
chemically reduce it in the exhaust. Such aftertreatment approaches may be used in
conjunction with in-cylinder techniques to lower the overall NOx output. Their
combined use is more a matter of economics than practicality.
Available Technologies – In-Cylinder
The previous section described the effects of variable SOI on NOx emissions, fuel
economy and particulates. The use of higher injection pressures can assist in reducing
NOx if later SOI is used with the resulting smaller fuel particles [6]. The following plot
[7] contains a concise summary of the different technologies for dealing with NOx and
particulates. For in-cylinder technologies the plot demonstrates the effect of SOI on
NOx and particulates (more advanced timing leads to higher NOx and lower
particulates), and the effects of EGR (more EGR leads to higher particulates and lower
NOx.) Meanwhile a combination of aftertreatment approaches helps engine
manufacturers in achieving the 2007 emissions standards (shown in the lower left hand
corner of the plot.)
Figure 3: Summary of in-cylinder and aftertreatment technologies
from [7] in reducing emissions
Besides new combustion system approaches like HCCI (homogeneous charge
compression ignition) and PCC (partial HCCI) the primary technique used to reduce NOx
in-cylinder is exhaust gas recirculation (EGR), which, to be most effective, requires
cooling. This approach requires external valving and piping, and a cooler for the exhaust
gas. (HCCI and PCCI will not be addressed here. For older engines where retrofit
Page 7/15
technologies are being considered it is highly likely that these new combustion systems
would require greater changes to the engine than would be economic.)
EGR works by displacing oxygen in the intake charge with relatively inert gases. With
less oxygen available the combustion process will be somewhat slower, leading to lower
temperatures. In addition the added CO2 and water vapor in the exhaust stream affects
the rate of temperature rise due to their high thermal capacitance relative to other gases.
It is also the lower oxygen levels of the intake charge that reduces the oxidation of soot
particles, leading to higher PM emissions.
The following diagram [8] show the effect of cooled vs. uncooled EGR on NOx,
particulates and intake manifold temperature. While the effect of cooling the EGR has
little effect on NOx, the effect is substantial on particulates.
Figure 4: Effect of EGR temperature on NOx, PM and
intake manifold temperature from [8]
EGR approaches usually increase the load on the engine cooling system, and impose a
fuel economy and particulates penalty [9, 10], although the latter may be mitigated if
combined with a diesel particulate filter (DPF.) A further constraint that will apply to
retrofit applications is whether the engine is turbocharged or not, and whether a highpressure or low-pressure loop is selected for returning the EGR to the cylinder, as shown
in the following diagram.
Page 8/15
Figure 5: High pressure EGR loop (left) and low pressure EGR (right) from [8]
EGR has certain drawbacks though. With higher particulates the gas stream diverted
back to the engine will increase wear. (If used with a DPF this is not as much of an issue,
although the low pressure loop must be used, incurring a fuel economy penalty to
recompress the EGR, and adversely affecting transient response. Also the combination
would be expensive for retrofitting older engines.) During transients the volume of EGR
in the piping and heat exchanger will cause additional particulates due to the rate of
fueling exceeding the available air even more than a non-EGR engine. Piping, heat
exchanger and valving for EGR can be cumbersome and expensive.
Available Technologies – Aftertreatment
There are a number of aftertreatment technologies available for reduction of both NOx
and particulates. These technologies are:
• SCR – selective catalyst reduction
• LNT – lean NOx trap
• DPF – diesel particulate filter
• DOC – diesel oxidation catalyst
Technologies that reduce particulates are included in this study because both VIT and
EGR impact particulates. If particulate levels are worse due to reduced NOx (and
possibly improved fuel economy) there will be a trade-off at some point to maintain air
quality.
SCR Technology
This approach introduces a reducing agent into the exhaust stream, either by the addition
of urea or ammonia directly, or the addition of extra fuel to provide the reducing reagent
[9, 11, 12, 13.] The resulting chemical reaction reduces NOx to oxygen and nitrogen.
This approach has been used in stationary power plants for some time. Efficiencies are
very high for engines that operate under constant conditions, but are lower for operation
under transient conditions. (Model-based algorithms are under development to allow
more accurate prediction of the amount of ammonia required when the anticipated
quantity of NOx changes with load and speed.)
Page 9/15
Of potential concern is ammonia slip, where some of the reducing agent escapes the
exhaust system into the atmosphere. The major logistical problems are that an additional
storage tank is required on each vehicle, and a refilling infrastructure is required.
The promise of significant reductions in NOx means that SOI can be advanced again for
improved efficiency, resulting in better fuel economy than other approaches. Particulates
are also improved with this approach. However, in certain applications the temperature
of the exhaust stream may be too low for effective operation of the catalytic reaction. In
those cases an additional heat source may be required, either a burner or an electric
heating element. Either of these options will result in a reduction of fuel economy of the
engine.
There is potentially a 6% improvement in fuel economy, although this is offset by the
cost of urea. One study [13] found that urea must cost less that $1.50 per gallon for there
to be an equivalent fuel economy benefit using an SCR.
A schematic of a system developed by Bosch is shown below.
Figure 6: A commercial SCR system with a DOC as shown in [14]
LNTs
LNTs adsorb NOx and oxygen during lean operation modes, then during occasional rich
operation the NOx is catalyzed to nitrogen. Sulfur in the exhaust causes performance
degradation over time [12] so that periodic desulfation is required. There are some
operational issues with these NOx adsorbers for the regeneration phase. Either a dual-leg
layout is needed where one of the two legs may be regenerated while the other continues
to adsorb NOx, or a single-leg layout requires periodic injection of diesel fuel into the
exhaust to facilitate the reduction process. Using fuel as a reductant has a substantial fuel
economy penalty. Schematics of the two approaches are shown below.
Page 10/15
Figure 7: Single and double leg LNT systems from [10]
DPF Technology
This consists of a closed filter that physically traps particulates then oxidizes them. The
oxidation process requires a particular temperature range, which is often controlled by a
burner, impacting fuel economy. Some filters are catalytic, reducing the fuel economy
impact. They also trap ash from combustion of engine oil, which cannot be oxidized.
Consequently they require periodic cleaning.
DOC Technology
This approach is similar to the use of catalyst in automotive applications, except that it
does not reduce NOx emissions due to the oxygen-rich environment. These oxidize
unburned hydrocarbons and carbon monoxide as well as some particulates (although not
as effectively as DPFs for the latter.) They are passive devices with no maintenance
required.
The following table shows a summary of the effectiveness of both in-cylinder and
aftertreatment approaches on emissions, including a range of costs for retrofit situations,
based on the references given at the end of this report.
Page 11/15
Table 1: NOx reduction alternatives at a glance
Technology
NOx
Reduction
PM
Reduction
HC
Reduction
CO
Reduction
Effect on Fuel Economy
Estimated Cost 1
VIT
Up to 50%
-
-
Less than fixed retard, may
even be neutral
$7,400
EGR (cooled)
40 – 60%
Increased
Increased
1 – 4% worse
$13,000 – 15,000
SCR
60 – 90%
Could
increase
50%
Could
increase
300%
20 – 30%
99%
76%
$10,500 - $50,000
LNT
>80%
-
-
-
Possibly up to 6% improved,
but have reductant
costs/consumption
3 – 7% worse
DOC
-
10 – 50%
50%
40%
-
$500 - $2,000
DPF
-
80 – 90%
85%
85%
Depending on heat source for $5,000 - $10,000 2
activation
1
2
Estimates based on 10 – 15 L heavy duty diesel engine
Requires ULS diesel
Page 12/15
$5,000 - $10,000
The following diagram from [7] gives a good comparison of EGR, SCR and NOx
adsorber approaches on other performance issues. As noted above, the advantage that
SCRs have with fuel economy is somewhat negated by the need to recharge the reductant
tank periodically. The alternative approach of on-board reforming to provide the
reductant reduces this advantage somewhat.
Figure 8: Performance effects of different NOx reducing technologies from [7]
Another potential NOx reducing technology is that of the lean NOx catalyst.
Unfortunately to date there have been no successful, durable lean NOx catalysts that can
reduce NOx under the typical oxygen-rich environment of a diesel engine exhaust. Even
if one is found, there is expected to be a fuel economy penalty of 3% or more due to the
addition of a suitable reductant [10, 12].
Page 13/15
Summary of Retrofits
Each of the technologies listed above has a number of advantages and disadvantages.
The table below is intended to offer a summary of the pros and cons of applying these
systems as retrofits to older diesel engines for the purposes of NOx reduction.
Table 2: Pros and cons of different NOx reduction alternatives
Technology Advantages
Mechanical
VIT
Cooled EGR
Transparent to user
Constant over engine life
Little impact on fuel economy
Effective NOx reduction
No user intervention required
SCR
NOx reduction high
Potentially best fuel economy
LNT
Potentially high NOx reduction
DOC
Low cost control of HC, CO,
PM
Reduces PM with timing retard
DPF
Disadvantages
May be invasive in engine
May require higher injection pressures
PM, HC, CO worse
Additional engine wear
Higher PM during transients
Hardware packaging
Additional cooling system demands
Requires reductant
User intervention required
Hardware packaging
Expensive
High fuel economy penalty
Hardware packaging
Does nothing for NOx
Does nothing for NOx
Requires heat source
Hardware packaging
Summary
A low-cost VIT solution may be a very attractive approach for older diesel engines to
achieve a 25% reduction in NOx emissions. While there are other approaches that reduce
NOx further they appear to be substantially more expensive, and in some cases require
user intervention.
Further VIT appears to offer very good fuel economy results for the cost, an issue that is
sure to be of concern to users of older engines who will see no economic benefit to lower
NOx emissions.
Page 14/15
References
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
V. O. Markworth, S. G. Fritz, G. R. Cataldi, “The Effect of Injection Timing
Enhanced Aftercooling, and Low-Sulfur, Low-Aromatic Diesel Fuel on
Locomotive Exhaust Emissions,” Transactions of the ASME, pp. 488 – 495,
Vol. 114, July 1992
R. Stradling, P. Gadd, M. Signer, C. Operti, “The Influence of Fuel Properties
and Injection Timing on the Exhaust Emissions and Fuel Consumption of an
Iveco Heavy-Duty Diesel Engine,” SAE Paper 971635, 1997.
D. A. Kouremenos, D. T. Hountalas, K. B. Binder, A. Raab, M. H. Schnabel,
“Using Advanced Injection Timing and EGR to Improve DI Diesel Engine
Efficiency at Acceptable NO and Soot Levels,” SAE Paper 2001-01-0199,
1999.
P. Lauvin, A. Loffler, A. Schmitt, W. Zimmermann, W. Fuchs,
“Electronically Controlled High Pressure Unit Injector System for Diesel
Engines,” SAE Paper 911819, 1991.
R. C. Yu, S. M. Shahed, “Effects of Injection Timing and Exhaust Gas
Recirculation on Emissions from a D.I. Diesel Engine,” SAE Paper 811234,
1981.
J. M. Desantes, J. V. Pastor, J. Arregle, S. A. Molina, “Analysis of the
Combustion Process in a EURO III Heavy-Duty Direct Injection Diesel
Engine,” ASME J. Eng. Gas Turbines Power, 124, pp. 636-644
M. Schittler, “State-of-the-Art and Emerging Technologies,” 9th Diesel Engine
Emissions Reductions Conference, August 2003
“Exhaust Gas Recirculation,” DieselNet Technology Guide, Engine Design
for Low Emissions, 2005
“Overview of Clean Diesel Requirements and Retrofit Technology Options,”
F. J. Acevedo, Michigan Clean Fleet Conference, March 2006
G. Weller, “EPA Engine Implementation Workshop – 6/7 August 2003, 2007
Technology Primer,” Presentation by Ricardo
“Diesel Powered Machines and Equipment: Essential Uses, Economic
Importance and Environmental Importance,” Diesel Technology Forum, June
2003
H. Hu, J. Reuter, J. Yan, J. McCarthy Jr., “Advanced NOx Aftertreatment
System and Controls for On-Highway Heavy Duty Diesels,” SAE Paper 200601-3553, 2006
R. Krishnan, T. J. Tarabulski, “Economics of Emission Reduction for HeavyDuty Trucks,” DieselNet Technical Report, January 2005
W. Addy Majewski, “SCR Systems for Mobile Engines,” DieselNet Technical
Report, 2006
Page 15/15
11.2.
Appendix 2: Poisoning in SCR Systems
Woodward
Page 68
ENGINE SYSTEMS, AFTERTREATMENT SYSTEMS GROUP
Phase 1: Literature Study
Contract# N-16 Project# 89016
March 11, 2008 authored by Dan Mastbergen
Poisoning in SCR Systems
1 ABSTRACT
In this study, a review of SCR degradation mechanisms has been performed to assess longterm SCR system efficiency. This study has also focused on the specific issue of hydrocarbon
poisoning which plays a larger role in a fuel-fired heater-SCR system. There have been a
number of papers published in the past few years regarding SCR performance degradation as
more long-term field/lab experience comes in. Reductions in conversion efficiency can come
from thermal aging, poisoning, and hydrocarbon adsorption/coking. Typical causes of
poisoning in after-treatment systems come from minerals in the fuel or oil such as sulfur,
potassium, calcium, zinc [2], and urea related by-products [3][4].
2 BACKGROUND
In recent years, the ground level ozone concentrations in a number of US cities have
exceeded EPA limits. This results in negative health effects for the residents, and severe fines
for the city governments. In the state of Texas, four cities have exceeded the ozone levels
several times. The key contributors to ozone formation are NOx, hydrocarbons, and sunlight.
Emissions levels for new engines being produced over the next decade will have to reduce
NOx levels by roughly an order of magnitude (depending on engine size). However, many
engines in fleet vehicles (delivery trucks, trash haulers, etc) will not be replaced by these
newer engines for some time. Because these vehicles are significant contributors to NOx
within the city, a retrofit technology is required to bring these cities into compliance. Currently
the most efficient and cost effective means for lowering NOx is Selective Catalytic Reduction
(SCR). SCR systems have been implemented commercially in Europe now for two years, with
positive results. For a successful retrofit, the SCR system must maintain a high conversion
efficiency long enough to make a contribution to NOx reduction within that city.
Typically SCR systems are very efficient at reducing NOx, however, the conversion efficiency
is very temperature dependant. In order to exceed 80% conversion efficiency, the exhaust
temperature must be above 300-400 C (depending on the catalyst material). For inner city
vehicles following stop-and-go driving cycles, the exhaust temperature may rarely, if ever,
exceed these temperatures. Therefore, for these applications it is also necessary to have an
auxiliary exhaust heater in-line to increase the exhaust temperatures. Currently Woodward
Governor is developing an exhaust heater capable of heating exhaust temperatures at idle up
to 650 C. The inclusion of a heater into SCR systems is a newer development, since most
systems to date have been installed on on-highway vehicles where exhaust temperatures are
typically high. As a part of this study the issue of hydrocarbon poisoning has received focused
attention since additional hydrocarbon emissions can be emitted from the fuel-fired heater.
3 THERMAL AGING
Thermal aging of the catalyst can have a significant effect on conversion efficiency, special
high temperature cycles. The main cause of thermal deactivation is metal sintering and
1/5
dealumination [6]. The effect of thermal aging on catalyst performance is very complex and
hard to predict since it depends on the time-temperature history of the substrate. It also
depends largely on the substrate material. High temperature Zeolite catalysts have much
higher temperature capability than Vanadium, however, they also require higher temperature
operation to be efficient.
Cavataio et al. performed an extensive study of thermal aging on different catalyst materials at
varying temperatures[5]. The majority of the work was on Cu-zeolites and Fe-zeolites. The
Cu-zeolite showed an approximately 5% reduced (peak) efficiency at 120k miles, while the Fezeolite showed almost no drop in performance at 120k miles (120k miles simulated as 64
hours at 670 C). The same test was performed after aging at a lower temperature (550C) for
2000 hours. In this test the Cu-zeolite showed a roughly 15% reduction in peak efficiency
while the Fe-zeolite again showed negligible reductions in peak efficiency. An additional study
was performed by exposing the catalyst to high temperatures for one hour. The reductions in
maximum efficiency for the Cu-zeolite were around 10% at 800C, 60% at 900 C, and 80% at
950 C. For the Fe-zeolite the reduction in maximum efficiency was 1% at 800 C, 5% at 900
C, and 6% at 950 C.
Houel et al. performed a comparison of Cu-Zeolite and Ag/Alumina. The two substrates were
aged at 700 C for 72 hours. The peak conversion efficiency in the Ag/alumina system shifted
from 400 C to 300c, and was reduced from 90% to 60%. The Cu-zeolite peak efficiency was
reduced from 80% to 30%.
Although these results are specific to the catalyst material used for the test, it serves as a
good example of the time/temperature sensitivity on SCR catalyst aging.
4 POISONING
4.1 SULFUR POISONING
Unlike other after-treatment devices, SCR systems are fairly insensitive to sulfur poisoning.
Sulfur in the fuel can result in ammonium sulfate that can foul the SCR catalyst. This reduces
the low temperature (< 300 C) conversion efficiency. Fortunately, after bringing the substrate
up to high temperatures (650 C) the sulfur poisoning is purged and the performance is
returned to normal[1][5]. In general, the effects of sulfur poisoning are less detrimental than
thermal aging, especially on the Cu-zeolite system[6]. However, Houel et al. found that the
effect of sulfur poisoning is very detrimental on the Ag/Alumina system. No data was shown
as to whether this damage could be reversed by a thermal regeneration.
4.2 OIL DERIVED POISONING
Poisoning can also be caused by minerals contained in the motor oil that make it into the
catalyst such as Potassium, Calcium, and Zinc[2]. Trace amounts of these substances were
observed on the catalyst after 120k miles of service. However, the contribution of these
poisons to the overall deactivation could not be separated from the thermal aging effect.
4.3 UREA BYPRODUCT POISONING
It is also possible for deposits of urea to build up on the catalyst and impact conversion
efficiency. This can occur if the SCR system is run at low temperatures and the urea dosing
system does not sufficiently atomize the urea solution. The result is a build up of crystallized
2/5
urea on the face of the catalyst that will plug the channels, resulting in reduced efficiency. At
temperatures less than 250 C large deposits of urea were formed (when dropping aqueous
urea directly on the substrate). It was also found that once the substrate was heated above
350 C the deposits would be vaporized[4].
5 HYDROCARBON EFFECTS
The issue of hydrocarbon poisoning is very important in a fuel-fired heater-SCR system since
there is the possibility of much higher hydrocarbon emissions entering the SCR system than
with a stand alone SCR. The effects hydrocarbons can be broken into three regimes:
instantaneous effects, short-term effects, and long-term effects.
During times when the SCR is in operation (dosing urea), the presence of hydrocarbons can
reduce the efficiency of the SCR system. It should be noted that hydrocarbons can act as the
reducing agent in place of urea/NH3, however, the efficiency of hydrocarbon reduction is lower
than for urea/NH3 [5][6]. In fact, Hoeul et al. experimented with using diesel fuel as the
reducing agent and showed conversion efficiencies up to 60% (above 450 C). However, at
lower temperatures (<300) the conversion efficiency using diesel fuel is less than 10 %[6].
When hydrocarbons are present in an SCR system made to operate on urea/NH3, the
hydrocarbons directly interfere with the reaction of NH3, reducing the overall conversion
efficiency. Cavatio et al. showed that the conversion efficiency of a Cu-zeolite catalyst at 300
C dropped from 95% to 85% with 225 ppm Benzene and to 50% with 50 ppm n-Decane. At
200 C the efficiency dropped from 80% to 75% with 225 ppm Benzene and to 30% with 50
ppm n-Decane[5]. This reduced efficiency can also lead to increased ammonia slip since the
hydrocarbons are blocking the reaction of the ammonia.
Gieshoff et al showed the conversion efficiency on a Vanadia based catalyst with varying
concentrations of n-decane. Above 400 C there is negligible effect of 30 ppm n-Decane.
Below 300 C the conversion efficiency is roughly cut in half for 30 ppm n-Decane.
Hydrocarbons can also lead to medium-term deactivation if they are adsorbed to the
substrate, or if coking occurs. This would cause the catalyst to continue to operate at a
reduced efficiency until the exhaust temperature got high enough to free and burn the
hydrocarbons. The temperature required for regeneration is around 400 C[5]. At this
temperature the recovery was nearly instantaneous. Houel et al also saw a recovery from
coking at 500 C[6].
Within the sources reviewed here, there has been no mention of long term poisoning effects of
hydrocarbons, assuming they can be periodically purged completely from the system. Any
mineral left behind (such as sulfur) would be present in the exhaust stream regardless of what
form the hydrocarbons are in.
6 SUMMARY
There are many potential causes for reduced efficiency in SCR systems including thermal
aging, sulfur poisoning, oil-derived compound poisoning, urea crystallization, and hydrocarbon
poisoning. The most severe and most permanent is thermal aging, however, this can be
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minimized by selecting the appropriate material for the application and by not exceeding
“maximum” thresholds. Reductions in efficiency from thermal aging should be less than 15%
per 120k miles for a well designed system. The effect of sulfur poisoning is significant for nonzeolite catalysts. However, poisoning due to sulfur can be reversed by regenerating the
catalyst. Poisoning by oil-derived minerals has also been observed, but its effects are not well
quantified. Poisoning by crystallized urea is possible at low temperatures, but is quickly
vaporized once the temperature exceeds 350 C. Hydrocarbons can reduce the instantaneous
efficiency by inhibiting the reaction with ammonia. This could lead to increased ammonia slip
from the catalyst. The substrate can also temporarily absorb hydrocarbons for continued
lower efficiency. Once again, this type of poisoning can be reversed by increasing the
temperature above 400 C. Hydrocarbons do not appear to contribute to any long-term
degradation.
7 REFERENCES
[1]
Majewski a, “Selective Catalytic Reduction” on www.dieselnet.com 2005
[2]
Cheng Y, Xu L, Hanngas J, Jagner M, Lambert C, “Laboratory Postmortem Analysis of
120k mi Engine Aged Urea SCR Catalyst” SAE Publication 2007-01-1579
[3]
Kim J, Cheng Y, Patterson J, Laing P, Lambert C, “Modeling Study of Urea SCR
Catalyst Aging Characteristics” SAE Publication 2007-01-1580
[4]
Xu L, Watkins W, Snow R, Graham G, McCabe, Lambert C, Carter R, “Laboratory and
Engine Study of Urea-Related Deposits in Diesel Urea-SCR After-Treatment Systems”
SAE Publication 2007-01-1582
[5]
Cavatio G, Girard J, Patterson J, Montreuil C, Cheng Y, Lambert C, “Lab Testing of
Urea-SCR Formulations to Meet Tier 2 Bin 5 Emissions” SAE Publication 2007-01-1575
[6]
Houel V, James D, “A Comparison of the Activity and Deactivation of Ag/Al2O3 and
Cu/ZSM-5 for HC-SCR Under Simulated Diesel Exhaust Emission Conditions” Journal
of Catalysis, Feb 2005 Vol 230(1), p. 150-157
[7]
Pieterse J, Top H, “Selective Catalytic Reduction of NOx in Real Exhaust Gas of Gas
Engines Using Unburned Gas: Catalyst Deactivation and Advances Toward Long Term
Stability” Chemical Engineering Journal, July 2006 Vol 120, issue 1-2, p. 17-23
[8]
Block M, Clark N, Wayne S, Nine R, Miller W, “An Investigation into the Emissions
Reduction Performance of an SCR System Over Two Years IN-Use Heavy-Duty
Vehicle Operation” SAE Publication 2005-01-1861
[9]
Gieshoff J, et al “ Improved SCR Systems for Heavy Duty Applications” SAE Publication
2000-01-0189
4/5
5/5
11.3.
Appendix 3: SwRI Testing Report of Woodward’s Burner System
Woodward
Page 74
IMPROVING DIESEL SCR LOW TEMPERATURE
PERFORMANCE USING A BURNER SYSTEM
― PROOF-OF-CONCEPT EVALUATION
FINAL REPORT
SwRI® Project No. 03.14560
Prepared for:
Woodward Governor Company
3800 North Wilson Avenue
Loveland, CO 80538
Prepared by:
Qilong Lu
Senior Research Engineer
December 16, 2008
S A N
A N T O N I O ,
HOUSTON, TEXAS
!
T E X A S
WASHINGTON, DC
TABLE OF CONTENTS
Page
1.0
INTRODUCTION .............................................................................................................. 1
2.0
EXPERIMENTAL DETAILS AND TEST PROCESS...................................................... 2
2.1
Test Engine ..................................................................................................................... 2
2.2
Test Fuel and Lube Oil ................................................................................................... 3
2.3
Test Procedures............................................................................................................... 3
2.4
Installation of Woodward’s Aftertreatment System ....................................................... 6
2.5
Test Engine Instrumentation ........................................................................................... 7
3.0
EMISSION TEST RESULTS AND ANALYSIS .............................................................. 8
iii
TABLE OF FIGURES
Page
Figure 1. Photograph of DDC Series-60, 12.7L Engine Installed in Test Cell.............................. 3
Figure 2. FTIR System Setup......................................................................................................... 5
Figure 3. Schematic of CVS Emissions Sampling System............................................................ 5
Figure 4. Test Parameter Denotation of Special Measurement Required by Woodward.............. 6
Figure 5. Installation of the Woodward Aftertreatment System.................................................... 7
Figure 6. SCR Inlet Temperature Comparison ............................................................................ 13
Figure 7. NO2/NOx Ratio Comparison ....................................................................................... 14
Figure 8. SCR NOx Reduction Efficiency and NH3 Slip............................................................ 15
iv
LIST OF TABLES
Page
Table 1. DDC Series-60, 12.7L Engine Specifications ................................................................. 2
Table 2. Final Test Points .............................................................................................................. 8
Table 3. Diluted Tailpipe Measurement Without Burner Operation ............................................. 9
Table 4. FTIR Measurement Before and After SCR Catalyst Without Burner Operation .......... 10
Table 5. Diluted Tailpipe Measurement With Burner Operation ................................................ 11
Table 6. FTIR Measurement Before and After SCR Catalyst With Burner Operation ............... 12
v
1.0
INTRODUCTION
The project was conducted at Southwest Research Institute (SwRI) on behalf of
Woodward Governor Company (Woodward). The objective of this program was to evaluate the
effectiveness of the Woodward burner to improve an SCR system performance measured
through its NOx reduction efficiency, especially at low exhaust temperatures.
SwRI conducted this project on a 1998 model year, Detroit Diesel Series-60, 12.7L,
diesel engine. ULSD fuel was used for all the emissions tests. NO, NO2 and NH3 upstream and
downstream of the SCR catalyst were measured by a FTIR analyzer. Regulated emissions of HC,
CO, NOx, and PM were also measured for each test by a dilute constant volume sampling (CVS)
system. This work was performed under SwRI Project No. 03-14560. The project leaders were
Dr. Magdi Khair and Dr. Qilong Lu.
This final report contains experimental details, test procedures, installation of test engine
and Woodward’s aftertreatment system, and emission test results and analysis.
1
2.0
EXPERIMENTAL DETAILS AND TEST PROCESS
This section of the report provides an overview of the equipment, fuel, and test
procedures used during the project.
2.1
Test Engine
The test engine was a 1998 model year, Detroit Diesel Series-60, 12.7L, diesel engine.
The engine’s specifications are given in Table 1. A side view of the engine installed in the test
cell is given in Figure 1.
Table 1. DDC Series-60, 12.7L Engine Specifications
Item
Description/Specification
Engine Type
In-line, 6-Cylinder
Engine Model
DDC Series-60, 12.7 L
Model Year
1998
Serial Number
06R0422316
Engine Displacement
12.7 L/775 CID
Rated Speed
1800 rpm
Rated Power
405 hp
Peak Torque Speed
1200 rpm
Peak Torque
1625 lb-ft
Aspiration
Turbocharged - Aftercooled
Fuel Injection System
EUI System
2
Figure 1. Photograph of DDC Series-60, 12.7L Engine Installed in Test Cell
2.2
Test Fuel and Lube Oil
Emission tests in this project were conducted using USLD fuel. The fuel was coded as
EM-6406-F at SwRI. The lube oil used was Shell Rotella T Multi-Grade Triple Protection SAE
15W-40 API CJ-4 diesel engine oil.
2.3
Test Procedures
The project objective was to evaluate the effectiveness of the Woodward burner to
improve a SCR system performance at low exhaust temperatures. The test procedures to achieve
the project goal were described as follows:
1, SwRI installed the test engine and Woodward’s aftertreatment system in a test cell
equipped with a dilution tunnel. Preliminary verification of engine performance was carried out.
2, Experiments were conducted to determine final test points by changing engine speed
from idle to 1800rpm in 200 rpm increments and load from 0 to rated in 200 lb-ft increments.
The temperature downstream of Woodward heat exchanger was set as the selection criterion.
3
3, SwRI provided emission test benches. NOx emissions such as NO and NO2 and
ammonia (NH3) before and after the SCR catalyst were measured by a Fourier transform
infrared (FTIR) system as shown in Figure 2. Regulated emissions of HC, CO, NOx, and PM
were measured using a CVS system. Figure 3 shows a schematic diagram of the CVS system. In
the system, the exhaust gases are diluted with conditioned air to maintain a constant total flow
rate under all engine operating conditions. A portion of the diluted exhaust gases is taken for
emissions measurement. HC was measured using a heated flame ionization detector (FID). CO
and CO2 were determined by a non-dispersive infrared analyzer (NDIR). NOx was measured
via chemiluminescence instruments (CLD). PM levels were determined by collecting particulate
matter on 90 mm Pallflex filters which were weighed before and after each test mode after
conditioning in a temperature and humidity controlled environmental chamber.
4, Test parameters denoted in Figure 4 were documented for all the final test points.
5, Woodward burner system and Tenneco Elim-NOx SCR system were calibrated by
Woodward and Tenneco personnel for operation with the test engine.
6, Initially, the Woodward burner system was not operated. SCR dosing system was
controlled by Tenneco Elim-NOx controller. Emissions were measured when the engine and
aftertreatment system reached thermal equilibrium for all the final test points.
7, Subsequently, the Woodward burner system was operated. SCR inlet temperature was
increased to 300 °C and maintained during emissions measurement for each test point. SCR
dosing system was controlled by its controller. Emissions were measured when the engine and
aftertreatment system reached thermal equilibrium for all the final test points.
4
Heated Sampling Lines
FTIR Console
Switch Valve
Figure 2. FTIR System Setup
Aftertreatment
System
Note: NO Analyzer was
not used in this project.
Figure 3. Schematic of CVS Emissions Sampling System
5
10
8
1 2
3
4
5
6
9
7
1, Turbo Outlet Temp.
2, Heat Exchanger Inlet Temp.
3, Heat Exchanger Outlet Temp. /Burner Inlet Temp.
4, Burner Outlet Temp. /DPF Inlet Temp.
5, DPF Outlet Temp. 6, SCR Inlet Temp. 7, SCR Outlet Temp.
8, SCR Inlet FTIR Measurement
9, SCR Outlet FTIR Measurement
10, Diluted Tailpipe Emission Measurement
Figure 4. Test Parameter Denotation of Special Measurement Required by Woodward
2.4
Installation of Woodward’s Aftertreatment System
SwRI received the Woodward’s aftertreatment system which consisted of an exhaust heat
exchanger, a 10" Woodward burner, a DPF, and a SCR system as shown in Figure 4. Figure 5
shows the aftertreatment system installation at SwRI.
6
Airless Urea Injector
SCR
FTIR Sampling Probes
Exhaust Pipe
to CVS System
DPF
Burner
Heat Exchanger
Figure 5. Installation of the Woodward Aftertreatment System
2.5
Test Engine Instrumentation
For each test engine used for emissions measurement, SwRI provides the engine with an
extensive list of instrumentation to monitor test engine performance. In this project, the test cell
was equipped with thermocouples and pressure transducers for monitoring coolant inlet and
outlet temperatures, oil temperature, intake air temperature, fuel temperature, exhaust
temperature, intercooler inlet and outlet temperatures, inlet air restriction, exhaust back pressure,
boost pressure, intercooler restriction, oil pressure, etc.
7
3.0
EMISSION TEST RESULTS AND ANALYSIS
After the installation of the test engine, its performance at rated as well as peak torque
was validated. The rated power was 420 bhp at 1800rpm and the peak torque was 1612 lb-ft at
1200rpm. Both observed rated power and peak torque agreed well with the engine performance
specifications.
By changing engine speed from idle to 1800rpm in 200 rpm increments and load from 0
to rated in 200 lb-ft increments, sweep experiments were conducted in order to determine final
test points for the SCR system performance evaluation. By considering lower exhaust
temperature into the SCR catalyst and wider engine operating range, Woodward engineers
determined the 21 modes listed in Table 2 as the final speed and load points for the test matrix.
Table 2. Final Test Points
Mode No.
Speed (rpm)
Load
(lb-ft)
1
1800
20
109
2
1600
20
99
3
1400
20
89
4
1200
20
78
5
1000
20
69
6
700
20
59
7
1800
200
188
8
1600
200
167
9
1400
200
148
10
1200
200
135
11
1000
200
117
12
1800
400
250
13
1600
400
235
14
1400
400
216
15
1200
400
195
16
1000
400
172
17
1600
600
295
18
1600
500
268
19
1400
600
270
20
1200
600
258
21
1000
800
280
Temp. after Heat Exchanger (°C)
Following the determination of the test matrix and the calibrations of the burner system
and the SCR system, SwRI conducted emissions measurement for all those 21 test points. Tests
were firstly performed when the burner system was not operated while the SCR dosing system
was controlled by its own controller. Tables 3 and 4 summarize the test results of diluted tailpipe
8
measurement and FTIR measurement before and after SCR catalyst. And then, tests were
conducted when the burner system was triggered and SCR inlet temperature was increased to
300 °C. Emission test results are tabulated in Tables 5 and 6.
Table 3. Diluted Tailpipe Measurement Without Burner Operation
Temperature Distribution (°C)
Mode
No.
Speed
(rpm)
Load
(lb-ft)
Diluted Tailpipe Measurement (g/hp-hr)
Turbo
Outlet
HX
Inlet
HX
Outlet
Burner
Outlet
DPF
Outlet
SCR
Inlet
SCR
Outlet
HC
CO
NOx
PM
CO2
1
1800
20
162
156
109
NA
100
100
99
5.04
84.45
40.61
0.113
3965
2
1600
20
149
144
99
NA
91
90
90
4.56
59.38
27.51
0.365
2765
3
1400
20
139
134
89
NA
82
82
81
4.63
48.79
24.15
0.015
2285
4
1200
20
125
120
78
NA
73
74
72
6.31
55.54
25.25
0.092
2321
5
1000
20
114
109
69
NA
63
64
63
4.23
39.75
34.60
0.165
2144
6
700
20
109
103
59
55
52
55
54
0.71
14.51
21.34
0.027
1240
7
1800
200
279
268
188
NA
168
163
163
0.22
1.71
7.36
0.035
598
8
1600
200
258
246
167
NA
149
145
145
0.14
2.02
7.13
0.004
584
9
1400
200
239
228
148
NA
132
130
128
0.15
2.17
8.48
0.006
569
10
1200
200
234
221
135
NA
118
115
114
0.15
2.00
8.82
0.009
548
11
1000
200
216
203
117
NA
102
102
100
0.15
1.70
12.05
0.013
546
12
1800
400
360
344
250
NA
223
216
215
0.07
0.15
6.08
0.008
512
13
1600
400
354
336
235
NA
209
202
201
0.03
0.05
5.42
0.005
496
14
1400
400
342
324
216
NA
191
185
184
0.02
0.06
6.14
0.001
484
15
1200
400
329
309
195
NA
172
168
166
0.06
0.34
6.59
0.002
478
16
1000
400
319
296
172
NA
149
146
144
0.04
0.31
10.10
0.004
466
17
1600
600
432
410
295
NA
261
251
251
0.02
0.10
5.68
0.002
470
18
1600
500
396
377
268
NA
239
233
232
0.01
0.01
5.59
0.001
479
19
1400
600
420
395
270
NA
235
226
226
0.01
0.01
6.30
0.000
459
20
1200
600
423
395
258
NA
223
215
215
0.01
0.00
6.17
0.000
457
21
1000
800
495
454
280
NA
236
222
224
0.01
0.01
7.77
0.000
453
9
Table 4. FTIR Measurement Before and After SCR Catalyst Without Burner Operation
SCR Inlet (ppm)
Mode
No.
Speed
(rpm)
SCR Outlet (ppm)
Load
(lb-ft)
NO
NO2
NOx
NO2/NOx(%)
NH3
NO
NO2
NOx
NO2/NOx (%)
NH3
1
1800
20
150
60
210
28.6
0
153
38
191
19.9
0
2
1600
20
144
59
202
29.2
0
137
42
179
23.5
0
3
1400
20
134
60
194
30.9
0
136
45
181
24.9
0
4
1200
20
129
54
183
29.5
0
131
40
171
23.4
0
5
1000
20
191
52
243
21.4
0
191
39
230
17.0
0
6
700
20
235
41
276
14.9
4.9
211
16
227
7.0
4.7
7
1800
200
479
31
511
6.1
0
500
1.6
502
0.3
0
8
1600
200
435
48
483
9.9
0
448
30
478
6.3
0
9
1400
200
498
59
557
10.6
0
505
45
549
8.2
0
10
1200
200
559
59
618
9.5
0
562
48
610
7.9
0
11
1000
200
749
63
812
7.8
0
752
55
807
6.8
0
12
1800
400
652
33
685
4.8
1
671
0
671
0.0
0
13
1600
400
600
20
620
3.2
0
613
1
614
0.2
0
14
1400
400
702
9
711
1.3
0
711
1
712
0.1
0
15
1200
400
754
17
771
2.2
0
747
16
763
2.1
0
16
1000
400
1202
46
1248
3.7
0
1210
38
1248
3.0
0
17
1600
600
791
45
836
5.4
2
815
1
816
0.1
0
18
1600
500
687
28
715
3.9
0
698
15
713
2.1
0
19
1400
600
903
32
935
3.4
0
917
22
939
2.3
0
20
1200
600
933
23
956
2.4
0
940
16
956
1.7
0
21
1000
800
1489
38
1528
2.5
0
1491
29
1520
1.9
0
10
Table 5. Diluted Tailpipe Measurement With Burner Operation
Temperature Distribution (°C)
Mode
No.
Speed
(rpm)
Load
(lb-ft)
Diluted Tailpipe Measurement (g/hp-hr)
Turbo
Outlet
HX
Inlet
HX
Outlet
Burner
Outlet
DPF
Outlet
SCR
Inlet
SCR
Outlet
HC
CO
NOx
PM
CO2
1
1800
20
168
162
115
315
321
307
308
0.17
1.17
40.12
0.096
6927
2
1600
20
159
153
107
313
319
306
305
0.04
0.29
2.77
0.059
3401
3
1400
20
143
137
93
315
320
304
303
0.08
0.33
2.72
0.092
4556
4
1200
20
132
126
83
313
320
301
300
0.01
0.38
1.31
0.098
3593
5
1000
20
114
109
70
315
319
297
296
0.00
0.49
1.93
0.344
5785
6
700
20
104
98
59
321
320
291
290
0.00
0.53
0.13
0.273
4660
7
1800
200
279
267
189
318
318
309
305
0.00
0.04
0.22
0.010
770
8
1600
200
262
251
172
317
318
308
304
0.00
0.04
0.54
0.021
761
9
1400
200
241
228
150
317
318
305
301
0.00
0.06
0.91
0.003
779
10
1200
200
230
217
134
317
318
303
300
0.00
0.06
1.04
0.003
770
11
1000
200
220
207
120
319
319
301
297
0.00
0.05
3.77
0.005
766
12
1800
400
360
344
245
319
318
310
304
0.00
0.02
0.44
0.007
583
13
1600
400
357
340
235
319
318
308
304
0.00
0.02
0.25
0.004
572
14
1400
400
347
328
215
318
318
306
301
0.00
0.02
1.11
0.001
569
15
1200
400
334
313
193
319
318
304
299
0.00
0.03
1.27
0.002
575
16
1000
400
316
294
168
321
319
302
299
0.00
0.01
4.39
0.146
576
17
1600
600
428
407
294
319
318
309
304
0.00
0.01
1.27
0.000
506
18
1600
500
398
378
267
319
318
309
303
0.00
0.01
0.47
0.001
532
19
1400
600
425
400
275
319
318
308
302
0.01
0.09
1.43
0.007
506
20
1200
600
419
392
252
319
319
305
301
0.00
0.00
2.01
0.000
511
21
1000
800
409
377
223
319
319
303
297
0.00
0.03
2.96
0.004
494
11
Table 6. FTIR Measurement Before and After SCR Catalyst With Burner Operation
SCR Inlet (ppm)
Mode
No.
Speed
(rpm)
SCR Outlet (ppm)
NO
NO2
NOx
NO2/NOx
(%)
NH3
NO
NO2
NOx
NO2/NOx
(%)
NH3
NOx Conv.
Efficiency
(%)
Torque
(lb-ft)
1
1800
20
90
127
217
58.5
59
15
36
57
63.2
2.4
74
2
1600
20
91
127
218
58.3
68
11
37
48
77.1
2.6
78
3
1400
20
82
124
206
60.2
81
7
13
20
65.0
2.0
90
4
1200
20
79
131
210
62.4
97
6
6
12
50.0
2.6
94
5
1000
20
70
136
206
66.0
129
7
2
9
22.2
2.9
96
6
700
20
62
153
215
71.2
165
7
1
8
12.5
6.8
96
7
1800
200
199
239
438
54.6
196
8
38
46
82.6
3.5
89
8
1600
200
184
229
413
55.4
179
8
38
46
82.6
6.0
89
9
1400
200
213
273
486
56.2
188
9
63
72
87.5
6.0
85
10
1200
200
220
289
509
56.8
194
8
72
80
90.0
5.5
84
11
1000
200
291
358
649
55.2
183
53
168
221
76.0
1.7
66
12
1800
400
352
278
630
44.1
252
28
3
30
10.0
10.6
95
13
1600
400
291
268
559
47.9
283
17
8
25
32.0
6.3
96
14
1400
400
325
278
603
46.1
220
66
65
131
49.6
8.2
78
15
1200
400
347
332
679
48.9
299
45
64
109
58.7
6.4
84
16
1000
400
582
446
1028
43.4
254
235
176
411
42.8
6.6
60
17
1600
600
469
266
735
36.2
158
163
13
176
7.4
14.3
76
18
1600
500
381
279
660
42.3
309
220
51
271
18.8
9.8
59
19
1400
600
440
419
860
48.7
321
118
103
221
46.6
20.7
74
20
1200
600
830
465
1295
35.9
361
435
143
578
24.7
13.1
55
21
1000
800
758
613
1371
44.7
496
305
164
469
35.0
20.9
66
12
The weight factor of each test mode was considered as the same for this emission
analysis. When the SCR inlet temperature was not regulated by the burner, the total NOx
emission results of the 21 modes was considered as a baseline. The NOx baseline emission was
283.14 g/hp-hr, which was the sum of all modal NOx contribution listed in Table 3. When the
burner was operated to maintain the SCR inlet temperature at the level of 300 °C, the total NOx
emission was reduced to 71.05 g/hp-hr, which was the sum of all modal NOx contribution listed
in Table 5. Thus, the overall SCR NOx reduction efficiency was 74.9 % with the aid of the
burner.
SCR inlet temperature of each test mode was summarized and plotted in the Figure 6.
With the exception of Mode 17, all other SCR inlet temperatures were below 250 °C and 18
modes were below 225 °C. When the burner was operated, the SCR inlet temperatures of all the
21 modes were well controlled at 300 °C within ±3.5% steady-state errors.
SCR Inlet Temperature
400
Temp. Not Regulated By Burner
Temp. Regulated by Burner
T [degC]
300
200
100
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Engine Mode Points
Figure 6. SCR Inlet Temperature Comparison
13
17
18
19
20
21
Upstream of the SCR catalyst, a significant difference of NO2/NOx ratios was observed
for the two comparison conditions as shown in Figure 7. The greatest NO2/NOx ratio was 31%
at Mode 3 and most other modes had much lower NO2/NOx ratios when the burner was not used.
When the burner was operated, the NO2/NOx ratios were for all modes higher than 40% with the
exception of Modes 17 and 20.
NO2/NOx Upstream of SCR Catalyst
80
Temp. Not Regulated by Burner
Temp. Regulated by Burner
NO2/NOx [%]
60
40
20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Engine Mode Points
Figure 7. NO2/NOx Ratio Comparison
14
16
17
18
19
20
21
When the burner was operated to raise the exhaust gas temperature, an overall 74.9%
NOx reduction efficiency was achieved based on the diluted tailpipe emission results. Figure 8
further shows the reduction rate for each test mode based on FTIR NOx measurement before and
after the SCR catalyst. The reduction rates varied in the range of 55% to 96%. The NH3 slip
concentrations are also plotted in Figure 8 for all the 21 modes. The NH3 slip for all modes was
below 25ppm. In Modes 12, 17, 19, 20, and 21 the NH3 slip was above 10ppm. All other modes
had NH3 slip below 10ppm. Modes with high NH3 slip had relatively higher exhaust flow than
other modes due to higher speed, higher load or both. This might indicate that the SCR catalyst
used in the tests was undersized so that NH3 could not get enough storage space and became
susceptible to slip when exhaust space velocity increased. It is worth noting that there exists an
opportunity to further optimize the urea dosing calibration.
SCR NOx Reduction Efficiency and NH3 Slip
NOx Reduction [%]
100
80
60
40
20
30
0
NH3 Slip [ppm]
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Engine Mode Points
Figure 8. SCR NOx Reduction Efficiency and NH3 Slip
15
18
19
20
21

Final Report

Transcription

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