Transcript
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
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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
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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
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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
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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
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Low cooling heat loss combustion concept
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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
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Specifications of test engine
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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
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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
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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
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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)
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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
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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
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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
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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
