HYDROGEN-FUELED SPARK IGNITION ENGINE

HYDROGEN-FUELED SPARK IGNITION
ENGINE--ITS PERFORMANCE AND
EXHAUST EMISSION CHARACTERISTICS
By
PRITHVI RAJ KHAJURIA
A Thesis
aubmitted in fulfilment of the requirements
of the degree of
DOCTOR OF PHILOSOPHY
in the Faculty of engineering
Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY, NEW DELHI (INDIA)
July, 198,1
ii
CERTIFICATE
I, the undersigned, certify that the thesis entitled,
'Hydrogen-Fueled Spark Ignition Engine - Its Performance
and Exhaust Emission Characteristics' which is being submitted by Mr. P.R. Khajuria, in fulfilment of the requirements fol.‘ , the award of the degree of 'Doctor of Philosophy'
in the Faculty of Engineering of the Indian Institute of
Technology, New Delhi, is a record• :of candidate's own bonafide research work carried out under my guidance. The matter
embodied in this thesis has not been submitted in part or
full, elsewhere for the award of any degree.
(Dr. H.B.athul
fcT-Professor and He ad
Department of Mechanical Engineering,
Indian Institute of Technology, Delhi.
ACKNOWLEDGEMENTS
The author is extremely grateful to Dr. H.B. Mathur,
Professor and Head of Mechanical Engineering Department, for
his able guidance, encouragement, fruitful suggestions and
helpful attitude during the course of this research work.
The valuable help extended by Dr. M.K. G. Babu of Centre
of Energy Studies during computational and experimental work
is gratefully acknowledged.
Sincere thanks are due to the technical staff of the
'Engines and Unconventional Fuels Laboratory' of Centre of
Energy Studies and the 'I.C. Engines Laboratory' of Mechanical
Engineering Department for their valuable assistance during
experimental work. Thanks are also due to Mr. V.P. Gulati
for typing the manuscript and to Mr. N.K. Choudhary for making
drawings.
The financial assistance made available under Q.I.P. by
the Ministry of Education, Government of India, is gratefully
acknowled ged.
Finally, the author wishes to offer sincere gratitude and
appologies to his family for patiently enduring certain
difficulties wkiich resulted from his long absence from home
for completing this research work.
(P. R. KHAJURI A )
iv
ABSTRACT
V
The economic and industrial growth of a nation is
greatly dependent upon modern means of surface transport.
This is all the more so for developing countries like India
where the demand for automobiles and other light vehicles
is growing rapidly with the pace of economic development and
industrralization. These vehicles are powered by spark
ignition engines which are quite reliable and efficient. In
fact presently there is no other power-plant in sight for
light vehicles which can compete with spark-ignition (S.I.)
engine in cost, size, flexibility and reliability. It
appears that at least for next few decades the S.I. engines
will continue to have monopoly in the field of automobiles
and other light vehicles,.
The S.I. engine uses gasoline as fuel which was both
plentiful and reasonably cheap in the world market upto
1 973. The situation has since drastically changed and gaso-
line prices have incre ased manifold causing great scarcities
and an unbearable strain on the economy of developing countries which have been depending on. imports to meet their motor
fuel requirements. Moreover, the resources of petroleum fuels
are fast depleting, making the availability of gasoline
supplies in future a matter of serious concern.
Apart from their irreplaceable nature, and growing
scarcity another problem associated with the use of petroleum
vi
based fuels is the nature of their combustion products which
cause environmental pollution. Gasoline powered vehicles
are the main contributors to atmospheric carbon monoxide
pollution in metropoliton cities. The hazardous effects of
automobile exhaust pollution on human health, plant and animal
life are well known.
These problems of fast dwindling resources of petroleum
fuels and the hazard of environmental pollution caused by
their combustion have focused the attention on the task of
finding alternate 'clean' burning renewable fuels for use in
automobiles. Broadly two types of alternative fuels have
been under investigation for use in automobiles. These are
the two types of alcohols (ethanol, methanol) and hydrogen.
Alcohols are conveniently handled liquids and are
already operational fuels. They can be obtained from
renewable store of raw materials, organic matters including
lignite, wood, coal, oil shale, natural gas and indirectly
from punicipal and farm wastes. However, their wide spread
use in chemical industry makes it difficult to spare them
for burning in automobiles on a large scale.
From many technical and economic considerations hydrogen seems to be the most suitable candidate fuel to substitute
gaPotine .Hydrogen can be manufactured from nuclear
energy through electrolysis or thermal, decomposition of water
vii
and it has been suggested as the most feasible future fuel.
Tasteless, Odourless and non—toxic by itself, hydrogen
produces just clean energy- and water vapours upon combustion
with air, thus restoring quantitatively to the environment
the water from which it is produced. Hence, there would never
be a 'resource depletion' when hydrogen is burned as a fuel.
Hydrogen would be a particularly good fuel for spark
ignition engines, because its wide flammability limit would
permit high efficiency and unthrottled engine operation.
Engine emissions of hydrocarbons, c arb onmonoxide and carb on
dioxide would be completely eliminated,
Hydrogen mixes easily with air and the mixture is quite
stable at room temperature, however, the ignition energy of
hydrogen is low compared to other gaseous and liquid fuels
and it is ignitable at very low equivalence rati os. The
flammability limits of hydrogen vary between 4 and 74 per cent
by volume in air at room temperature and pressure. One of the
consequences of this is the wide range of flame speeds and
temperatures obtainable from hydrogen—air mixture.
3:I, engines using gasoline as fuel must be run very
close to stoichiometric or richer mixtures thus producing
conditions favourable to the formation of nitrogen oxides,
unburned hydrocarbons and carbon monoxide in the exhaust.
Hydrogen, on the other hand, may be burned so lean as to
viii
reduce peak temperatures to values at which dramatically less
NO is produced and of course it is no source of hydrocarbons
or carbon monoxide.
In addition to the favourable aspects of the properties
of 'hydrogen noted above, its exceptionally high flame velocity
le 3d6'` to such rapid combustion that the linstant-combustion'
idealization of the Otto cycle is approached, which should
lead to higher thermal efficiency. However, it could also
cause rough running of the engine, and result in other
associated combustion problems. These and other aspects of
hydrogen utilisation as spark ignition engine fuels are
matters of considerable current research interest.
In the work reported here, detailed analytical and
experimental investigations of hydrogen as an S.I. engine
fuel have been carried out. The analytical study involves
application of a combustion model to predict combustion
characteristics of hydrogen and a nitric oxide emission model
to predict emission characteristics. The experimental
investigations have been carried out using a single-cylinder,
Varimax variable compression ratio engine modified to run on
hydrogen. Both aspects of investigation have focused particular attention on the unthrottled pre-mixed hydrogen engine.
Model calculations and experimental results are described and
compared.
ix
An engine combustion model has been formulated to
determine the combustion rate with hydrogen fuel. Using this
model the cylinder pressures and temperatures have been predicted and cylinder pressure crank angle traces have been
compiled.
In the formulation of the combustion model the cylinder
has been divided into two zones, one composed of burnt gases
in chemical equilibrium and the other composed of unburned
fuel air mixture along with residual gases. The flame front
area has been found by assuming spherical propagation outward
from the ignition point. By applying mass and energy balance
equations, the temperature and pressure after each increment
of flame advance have been determined for each zone. Temperature and composition dependent thermodynamic properties have
been used and all processes except combustion have been assumed
to be isentropic.
This combustion model has been employed to account for
the hydrogen-air combustion process over a wide range of
stoichiometry and spark advance for the Varimax engine operating at various speeds and compression ratios. Based on the
computed results various graphs have been plotted showing the
variation of combustion crank angle and flame speed with fuel
air equivalence ratio, engine speed, compression ratio, etc.
In addition pressure-time traces for various fuel-air e qui-
valence ratios and compression ratios have been prepared.
Plots for peak pressure and temperature variations across the
cylinder for various equivalence ratios have also been obtained.
Although a spark ignition engine fueli with hydrogen
would be free from carbon monoxide and hydrocarbon emissions,
nitric oxide (NO)would still be a potential exhaust pollutant
requiring control. In order to estimate the exhaust nitric
oxide concentration an analytical model has been evolved.
This is based on the experimental observations of Zeldovich
and his co—workers, that the NO formation rate is much slower
than the combustion rate and that most of the NO formation is
after the completion of combustion. Using the 'frozen'
expansion concept, the exhaust nitric oxide concentration has
been computed by integrating the chemical rate equation. The
burnt gases have been assumed to remain unmixed and they have
been divided into a series of discret adiabatic zones of
equal pressure but different temperature. The nitric oxide
production has been computed for each zone during the entire
expansion stroke till the opening of the exhaust valve. At
this point the exhaust NO concentration has been arrived at
by summing the contribution from all zones. On the basis of
this model exhaust nitric oxide emissions for hydrogen fueled
spark ignition varimax engine have been calculated for a wide
variety of engine operating conditions, and variations of
xi
exhaust NO emissions with equivalence ratio at various
x
speeds have been plotted.
In order to check on the analytical re sults and to know
how to ad apt spark ignition engine s for operation of hydrogen
fuel detailed experimental investigations have been carried
out using Vari max research engine. The engine performance
data over its entire operating range of speeds and loads has
been collected at different compression ratios , spark timings,
etc. using hydrogen as fuels. various graphs showing the nature of engine performance characteristics wi th
hydrogen fuel have been plotted.
Experimental plots of the rmal efficiency variation with
equivalence ratio at different engine speeds and compression
rati os show that use of hydrogen as fuel can result in significantly higher cycle efficiencies. Hydrogen' s extremely
broad le an flammability limit enables power output regulation
by mixture control rather than by throttling. Graphs showing
the variation of me an effective press ure wi th equivalence
ratio and specific fuel consumpti on have been plotted for
different engine speeds and compression ratios. They indicate
the feasible range of engine speeds and compression ratios
for best results with hydrogen operation of the engine.
In order to assess the NO/NOx emission characteristics
of the engine extensive experiments have been carried out
xii
using a chemiluminescent NO/NOx analyser. The experimental
results have been plotted showing variation of exhaust NO/NOx
with equivalence ratio and compression ratio. It has been
found that NO emission is maximum at an equivalence ratio of
around 0.8 and it is extremely low for very lean mixtures.
NO formation process depends upon the available oxygen
and the prevailing temperatures, and they occur in post flame
gases. The type of fuel used effects the flame temperatures
and through the stoichi ome try the available oxygen. For
equivalence ratios lower than 0.8 the NO formation is
controlled by quenching of formation reactions during the
expansion stroke, while for richer mixtures NO concentrations
are primarily determined by the quenching of decomposition
reactions during the expansion process. The experimentally
determined trends of NO/NOx emissions are in good agreement
with the theoretically predicted results.
On the basis of the work reported here, it can be
safely concluded that hydrogen—fueled S.I. engine is a feasible proposition. Such an engine having quality governing
can operate with very lean mixtures giving much higher
efficiency as compared to gasoline engine. It would have
the additional advantage of emitting a cleaner exhaust free
from hazardous carbon containing pollutants and as much as
about ninety per cent lower exhaust NO emissions.
At higher outputs and higher equivalence ratios,
charge dilution is one of the measures to ensure smoother
operations. Narrower spark plug gap would have to be employed
to account for hydrogen' s 'low quench' distance and low
ignition energy-. These coupled with deposit free combustion
chamber could ensure smoother operation without the problem
of flashback past the intake valve an.d preigniti on during
compression.
=00=
xiv
CON NT.S
PAGE
m•-•-1.-•■••••■••••■
Certificate
Acknowledgements
Abstract
..
••
Contents
xiv
List of Figures
CHAPTEA-1
IN TRODUC TI ON
xviii
.. 1-10
1.1
Energy Crisis and Internal
Combustion aagines
••
2
1.2
Alternate Engine Fuels
..
3
1.3
Hydrogen as a S.I . Engine Fuel
..
4
1.4
Statement of Problem
..
9
CHAPTER-2
HYDROGEN AS S . I . ENGINE
FUEL
..11-38
2.1
Historic al Review
2.2
Current Status of Hydrogen
..16
2.3
Combustion Characteristics of
Hydrogen
..21
2.4
Problems Connected with Hydrogen
On Board Storage of Hydrogen
i
2.4.2 Safety Consideration
2.4 . 1
2.4.3
Cost Benefit An
2.5
Concludin: Remarks
. •.
..
12
6
27
..32
..37
XV
PAGE
CHAPTER-3
,,_,-...._ THEORETICAL ,. IN YES TI GAT IONS
ANDCOiskUTATI ON AL TECHNI.2039-84 .
3.1Basic Appro ach and Equations• •40
3.1. 1 Temperature Derivative
• •41
3. 1. 2 Heat Transfer Coefficient• •44
3. 2Engine C omb us ti on Model • •46
3. 2. 1 Expression for Flame Velocity. •50
3.2. 2 Expression for He at Rele as e..53
3.2.3 Expression for the Rate of Change
in Unburnt Gas Temperature• •55 .
3.2.4 Expressi on for the Rate of Burnt
Volume Change
3.2.5 Expressi on for the Rate of Change
of Burnt Mass
.•
3. 2.6 Expression for the Rate of Change
of Pressure
• •56
.
.
• •
56
59
3. 2. 7 Expressi on for the Burnt Volume
• •
60
3. 2.8 Es ti mati on of the Rate of Pressure
rise and Rate of Change of Mass
• •
61
3.3Expansion Process
• •
63
3. 3. 1 Computation of Equilibrium Gas
Composi ti on
• •
63
3.3. 2 Red uc ti on in Number of Equati ons
• •
66
3.3.3
3.3.4
Mole Fractionn Computati on
Equati ons
• •
Initial Estimation of Mole
Fractions
• •
67
69
.
XVi
PAGE
3.3.5Partial Derivatives of Mole
Fr ac ti on s
• •71
3. 3. 6Enthalpy and Internal Energy•••74
3.4Oxides of Ni Urogen Formati on
Model
3.5Computer Program
CHAPTER.4
EXPERI TAI, EsnalEN
AN- D
4.1Introduction
4. 2The Variable aompression Engine
System
• •7 6
• •80
• •85 -1 10
• •86
..8 6
4.2.1Vari max Engine
• •86
• •93
4. 2. 2Engine Dynamometer
4.2.3Fuel and ai r-Fl ow Measurement• •94
4.2.4Cylinder Pressure Me asuring Setup ..97
4.2.5Crank Angle Timing Marker• •9 7
4.3Instrument for Measuring NOx
Emission
• •97
4.3.1Chemiluminescent NO Analyser• •97
4.4Experimental Techni que
4.4.1Performance a:-ad Fuel Economy
Tests
4.4. 2Exhaust Emission Tests
Appendix to Chapter-4
• •103
, •103
• •107
• •108
xvii
PAGE
Tp. w.MI
CHAPTER-5
--____
DISCUSSION OF RESULTS
111-211
5.1
Introduction
••
112
5.2
••
113
5.3
Engine Performance
.
Engine Emissi on
••
149
5.4
Analytical Results
••
168
C H AP TER. -6
CONCLUSIONS
REFERENCES
••
212- 21 7
• •218-229