Toyota`s High Efficiency Diesel Combustion Concept

2015 Engine Research Center Symposium University of Wisconsin-Madison
Toyota’s High Efficiency Diesel Combustion Concept
Takeshi HASHIZUME
Toyota Motor Corporation
Toyota’s High Efficiency Diesel Combustion Concept
1
Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
2
Example of heat balance of diesel engine
Most of the energy was wasted in heat loss
Input Energy
Output
Pumping
Friction
Cooling
Heat
Loss
Exhaust
Brake thermal
efficiency
43%
For T/C, EGT*
Large part of this waste energy
*)Turbo Charger
Exhaust Gas Treatment
Develop a new combustion concept which improves
thermal efficiency by reducing cooling heat loss.
Toyota’s High Efficiency Diesel Combustion Concept
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Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
4
Factors of cooling heat loss in diesel engine
Injection nozzle
Cylinder head
Radiation
Convective
heat transfer
Heat loss
to engine oil
Coolant
In-cylinder flow
Cylinder block
Luminous flame
Heat loss to
coolant
To clarify the influence of each heat transfer. We measured
the radiant and convective heat flux using a RCM
Toyota’s High Efficiency Diesel Combustion Concept
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Rapid Compression Machine (RCM)
Thin film
thermocouple
6
Radiant heat flux sensor
Fuel spray
Combustion chamber
Piston
Air cylinder
Cam
Thermocouple and radiant heat flux sensor were equipped.
Convective and Radiant heat flux can be measured.
Toyota’s High Efficiency Diesel Combustion Concept
Radiant and total heat flux measured using RCM
(MW/m2)
15
10
Radiant
heat flux
Total heat flux
5
0
-10
(kJ/s)
Heat release rate Local heat flux
Injection quantity : 40mm3
250
200
150
100
50
0
-10
Small amount
0
10
20
0
10
20
Time after compression end (end)
The main cause of cooling heat loss is
convective heat transfer in diesel engine
Toyota’s High Efficiency Diesel Combustion Concept
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Approach to reduce the cooling heat loss
The local heat flux transfer from in-cylinder gas to the chamber wall
Heat flux = α × (Tg -Tw)
(Heat loss)
α : heat transfer coefficient
Tg : in-cylinder gas temp.
Tw : chamber wall temp.
Diesel engine has a strong swirl and squish flow
to improve mixture formation
α is high
To reduce the cooling heat loss Toyota applied
Strategy
Method
Reducing
heat transfer
coefficient
Reduction of
in-cylinder
gas velocity
Toyota’s High Efficiency Diesel Combustion Concept
Engine design
Lower swirl flow
Lower squish flow
8
Low cooling heat loss combustion concept
9
Weaken in-cylinder flow
+ Cooling loss reduction
- Fuel-air mixing (Smoke)
Promote
fuel-air mixing
Maximized advantage,
minimized disadvantage
Highly dispersed sprays
+ Smoke reduction
- Maximum torque
(weaken penetration)
Lowering cooling heat
loss Increase
in-cylinder temp.
Low comp. ratio
Advancing
injection timing
+ Maximum torque
- Cold startability
Adopting a weak in-cylinder flow, highly dispersed sprays
and lower comp. ratio realized maximized advantage.
Toyota’s High Efficiency Diesel Combustion Concept
Estimation of in-cylinder gas velocity
2400rpm Pme=1.1MPa
Results at 20°ATDC
0
10
10
20
Gas velocity m/s
Low flow combustion
Conventional combustion
cooling heat loss
was reduced
Lowering gas flow
・swirl
・squish
Re-entrant chamber
Lip-less shallow dish chamber
Swirl ratio = 2.2
Swirl ratio = 0.3
φ0.10mm x 10hole
φ0.08mm x 16hole
Analyzed using STAR-CD
With the low flow combustion gas velocity is lower than conventional.
This result indicates cooling heat loss is decreased
Toyota’s High Efficiency Diesel Combustion Concept
Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
11
Specifications of test engine
12
Low flow combustion
Conventional
Engine type
4 cylinder DI diesel
Displacement L
2.231
Bore x stroke mm
86 x 96
0.3
Swirl ratio
2.2
(Straight port)
Combustion chamber
diameter mm
Re-entrant
φ 58
Lip-less shallow
φ 61
Compression ratio
15.8 : 1
14.0 : 1
Nozzle specification
580 cc
φ 0.10 mm x 10 hole
spray angle 155ﾟ
580 cc
φ 0.08 mm x 16 hole
140°
With low flow concept, swirl ratio is 0.3, combustion chamber is lip-less
shallow, injection nozzle with smaller diameter and larger number of holes.
Toyota’s High Efficiency Diesel Combustion Concept
Engine system
Straight port
13
EGR valve
Inter
cooler
HPL-EGR
Highly dispersed spray
DPF
Lip-less cavity
EGR valve
Turbo charger
LPL-EGR
EGR cooler
In order to reduce in-cylinder gas flow, straight port
and lip-less cavity piston were equipped.
Toyota’s High Efficiency Diesel Combustion Concept
Summary of the combustion photograph
14
Start of main injection Conventional: TDC, New concept: 3 BTDC
Crank
angle
4 ATDC
10 ATDC
20 ATDC
30 ATDC
40° ATDC
Conv.
A large amount of luminous flame forms
luminous flame disappears
Low flow
Eventually, reaches an equivalent low level of smoke.
With low flow combustion, the in-cylinder gas flow can be restricted
without deteriorating smoke emission.
Toyota’s High Efficiency Diesel Combustion Concept
Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
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Cooling heat loss 1600rpm-0.3MPa
80
70
Cooling loss depends on combustion timing
Under same combustion timing.
Conventional
200
Cooling
heat loss (J)
ROHR (J/)
60
Low flow
50
40
30
Same ignition timing
40%
150
100
20
50
0
20
NOx (ppm)
10
0
-10
-30
16
-20
-10
0
10
20
30
Crank angle ( ATDC)
10
0
Conventional Low flow
Under same smoke emission
Low flow combustion concept can be reduced 40%
of cooling heat losses without increase in NOx emission
Toyota’s High Efficiency Diesel Combustion Concept
Effect of load on cooling heat loss reduction
Cooling loss reduction rate %
(Compared to conventional)
60
Larger cooling loss reduction
at low load
50
40
30
Reduction rate decreases
at high load conditions
20
10
0
0
0.5
1
BMEP MPa
The following section describes this mechanism
and ways to reduce the cooling heat loss further
Toyota’s High Efficiency Diesel Combustion Concept
1.5
17
Reason for a cooling heat loss increase at high load18
2100rpm-1.1 MPa
The low flow combustion
High heat flux region
The gas flow was restricted by
Lip-less cavity
Near zero swirl ratio.
0
25
Heat flux MW/m2
Flow at upper portion of the
piston side wall was still high
0
20
Velocity m/s
High temperature gas moves
close to the side wall.
600
2800
Temperature K
Calculated by STAR-CD
If the reverse squish flow can be restricted, the heat transfer
coefficient will decrease, and the heat loss can be improved.
Toyota’s High Efficiency Diesel Combustion Concept
Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
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The method to restrict the reverse squish flow
In-cylinder gas
velocity
Restrict the reverse
squish flow by
・Allowing wider gap
between piston
and cylinder head.
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Standard
Wider gap
(Case1)
12
Motoring
Engine speed : 1600 rpm
Crank angle : 10deg. ATDC
Tapered
piston
(Case3)
Tapering piston bowl restricts the reverse squish flow
from the piston wall side to cylinder head .
Toyota’s High Efficiency Diesel Combustion Concept
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Velocity (m/s)
Stepped
piston
(Case2)
Heat flux measurement of the tapered piston
2100rpm-1.1MPa under the same heat release rate
ROHR J/°
150
100
Measured at
cylinder head
50
Heat flux MW/m2
at squish area
0
less taper
20
10
0
-20
with taper
reduced
0
20
40
Heat flux
(squish area)
60
Crank angle ° ATDC
Tapered piston bowl reduced the heat flux in the squish area,
which makes a large contribution to the cooling heat loss reduction.
Toyota’s High Efficiency Diesel Combustion Concept
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Improvement of fuel economy in NEDC
5.1
Equivalent NEDC
Under same smoke emission
Conventional combustion
5.0
Fuel consumption
(L/100 km)
22
3%
4.9
5%
Low flow combustion
4.8
Low flow combustion
w/ tapered shallow dish
4.7
4.6
4.5
0
0.02
0.04
0.06
0.08
NOx (g/km)
Low flow combustion reduced the fuel consumption by 3% .
The adoption of taper shallow dish reduced fuel
consumption by 5% under equivalent emissions.
Toyota’s High Efficiency Diesel Combustion Concept
Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine (mass production)
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
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Specifications of smaller bore engine
Conventional
24
Low flow combustion
Engine type
4 cylinder DI diesel 2 valves
Displacement L
1.364
Bore x stroke mm
73 x 81.5
Swirl ratio
2.2
2.2
Combustion chamber
Re-entrant
Lip-less shallow
Compression ratio
16.9 : 1
16.4 : 1
Nozzle specification
525 cc
φ 0.10 mm x 8 hole
525 cc
φ 0.10 mm x 8 hole
Low flow combustion concept was applied
to Mass-produced small engine with 2 valves
Toyota’s High Efficiency Diesel Combustion Concept
Application of low flow concept to two valve engine
Large squish area
Center of bore
Small squish area
Center of chamber
Lip-less shallow dish
Lip-less shallow dish
Smoke FSN
For 2 valves engine
Cooling heat loss %
Effect of low flow chamber in 2 valves engine
Re-entrant
NOx g/h
NOx g/h
Gas flow is fast
in large squish area
Rich mixture is remained
in small squish area
Large squish area
Gas flow is fast
Increase of cooling heat loss
Small squish area
Rich mixture is remained
Injection nozzle
Increase of smoke emission
0
15
Velocity m/s
Rich
Lip-less shallow dish
Toyota’s High Efficiency Diesel Combustion Concept
φ
Lean
25
Improvement of combustion chamber for 2 valves
1. Reduction of heat loss
Taper
Chamber
Reducing heat
transfer coefficient
Weaken squish flow
2. Decrease of smoke
Improve the mixture
formation
Mixture introduction
to large squish area
3. Decrease of smoke
Large
squish area
Small
squish area
Large taper
Small taper
Center of bore
Reduction of fuel at
squish area
Keep the squish
flow
Center of chamber
Lip-less chamber + Bore-centered taper
(Eccentric tapered shape)
Improved combustion chamber with eccentric tapered shape
is applied to lower squish flow and fuel distribution
Toyota’s High Efficiency Diesel Combustion Concept
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Simulated distribution of gas flow velocity
TDC
5
27
10
15
Taper could weaken gas flow velocity
Eccentric
Tapered
shape
Large
squish area
Small
squish area
Low flow velocity
Re-entrant
High flow velocity
Velocity m/s
0
Taper could weaken the gas flow velocity in large squish area.
The cooling heat loss was reduced with Eccentric tapered chamber.
Toyota’s High Efficiency Diesel Combustion Concept
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Simulated distribution of equivalence ratio
TDC
7
15
28
25
Taper could spread fuel mixture gas
Eccentric
Tapered
shape
Large
squish area
Small
squish area
Spread to whole cylinder area
Re-entrant
φ
0
The lower squish flow and the improvement of air-fuel mixing
can be realized simultaneously with eccentric tapered chamber.
Toyota’s High Efficiency Diesel Combustion Concept
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Effect of the eccentric tapered chamber
29
2000rpm/0.7MPa
1800rpm/0.1MPa
Smoke FSN
Cooling heat loss %
Conventional
18%
New chamber
(0.5g/kWh)
Smoke 0.5FSN
Conventional
(0.5FSN)
New chamber
NOx g/kWh
(0.5g/kWh)
NOx g/kWh
Both reduction of cooling heat loss and smoke emission
could be realized using conventional nozzle spec. and swirl ratio
Toyota’s High Efficiency Diesel Combustion Concept
Content
1. Introduction
2. Combustion Concept
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
4. Conclusion
Toyota’s High Efficiency Diesel Combustion Concept
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Conclusion
31
This research aimed to reduce cooling heat loss.
The heat transfer coefficient was reduced by lowering gas flow.
As a result, the cooling heat loss was reduced.
A large amount of cooling heat loss was generated by strong squish
flow. The cooling heat loss was reduced further by tapered piston bowl
For application of this concept to a small engine with two valves,
providing an eccentric tapered combustion chamber achieved a proper
squish flow.
Simultaneous reduction of cooling heat loss and smoke emission can
be achieved without micro multi-hole injector with eccentric tapered
combustion chamber.
Toyota’s High Efficiency Diesel Combustion Concept
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Thank you for your attention
Toyota’s High Efficiency Diesel Combustion Concept