Toyota s High Efficiency Diesel Combustion Concept

Transcription

1 2015 Engine Research Center Symposium University of Wisconsin-Madison 1 Takeshi HASHIZUME Toyota Motor Corporation

2 Content 2 1. Introduction 2. Combustion Concept 3. Results Combustion characteristics Cooling heat loss analysis Cooling heat loss reduction Application to smaller bore engine 4. Conclusion

3 Exhaust Cooling Friction Pumping Output Example of heat balance of diesel engine 3 Most of the energy was wasted in heat loss Input Energy Brake thermal efficiency Heat Loss 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.

4 Content 4 1. Introduction 2. Combustion Concept 3. Results Combustion characteristics Cooling heat loss analysis Cooling heat loss reduction Application to smaller bore engine 4. Conclusion

5 Cylinder block Coolant Factors of cooling heat loss in diesel engine 5 Injection nozzle Luminous flame Cylinder head Radiation Convective heat transfer In-cylinder flow Heat loss to engine oil Heat loss to coolant To clarify the influence of each heat transfer. We measured the radiant and convective heat flux using a RCM

6 Rapid Compression Machine (RCM) 6 Thin film thermocouple Fuel spray Radiant heat flux sensor Combustion chamber Piston Air cylinder Cam Thermocouple and radiant heat flux sensor were equipped. Convective and Radiant heat flux can be measured.

7 Heat release rate (kj/s) Local heat flux (MW/m 2 ) Radiant and total heat flux measured using RCM 7 Injection quantity : 40mm Radiant heat flux Small amount Total heat flux Time after compression end (end) The main cause of cooling heat loss is convective heat transfer in diesel engine

8 Approach to reduce the cooling heat loss 8 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 Engine design Reducing heat transfer coefficient Reduction of in-cylinder gas velocity Lower swirl flow Lower squish flow

9 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 Lowering cooling heat loss Increase in-cylinder temp. Highly dispersed sprays + Smoke reduction - Maximum torque (weaken penetration) Advancing injection timing Low comp. ratio + Maximum torque - Cold startability Adopting a weak in-cylinder flow, highly dispersed sprays and lower comp. ratio realized maximized advantage.

10 Estimation of in-cylinder gas velocity rpm Pme=1.1MPa Results at 20 ATDC Conventional combustion 0 10 Gas velocity m/s Low flow combustion 20 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

11 Content Introduction 2. Combustion Concept 3. Results Combustion characteristics Cooling heat loss analysis Cooling heat loss reduction Application to smaller bore engine 4. Conclusion

12 Specifications of test engine 12 Engine type Displacement L Bore x stroke mm Conventional Low flow combustion 4 cylinder DI diesel x 96 Swirl ratio (Straight port) Combustion chamber diameter mm Compression ratio Nozzle specification Re-entrant φ 58 Lip-less shallow φ : : cc φ 0.10 mm x 10 hole spray angle 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.

13 Engine system 13 Straight port EGR valve HPL-EGR Highly dispersed spray Inter cooler 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.

14 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.

15 Content Introduction 2. Combustion Concept 3. Results Combustion characteristics Cooling heat loss analysis Cooling heat loss reduction Application to smaller bore engine 4. Conclusion

16 Cooling Cooling heat loss 1600rpm-0.3MPa 16 ROHR (J/ ) Conventional Low flow Same ignition timing Crank angle ( ATDC) Cooling loss depends on combustion timing Under same combustion timing. heat loss (J) NOx (ppm) Conventional 40% Low flow Under same smoke emission Low flow combustion concept can be reduced 40% of cooling heat losses without increase in NOx emission

17 Cooling loss reduction rate % (Compared to conventional) Effect of load on cooling heat loss reduction Larger cooling loss reduction at low load Reduction rate decreases at high load conditions BMEP MPa The following section describes this mechanism and ways to reduce the cooling heat loss further

18 Reason for a cooling heat loss increase at high load 2100rpm-1.1 MPa 18 The low flow combustion The gas flow was restricted by Lip-less cavity Near zero swirl ratio. High heat flux region Flow at upper portion of the piston side wall was still high 0 25 Heat flux MW/m 2 High temperature gas moves close to the side wall Velocity m/s If the reverse squish flow can be restricted, the heat transfer coefficient will decrease, and the heat loss can be improved Temperature K Calculated by STAR-CD

19 Content Introduction 2. Combustion Concept 3. Results Combustion characteristics Cooling heat loss analysis Cooling heat loss reduction Application to smaller bore engine 4. Conclusion

20 Velocity (m/s) The method to restrict the reverse squish flow 20 In-cylinder gas velocity Restrict the reverse squish flow by Allowing wider gap between piston and cylinder head. Standard Wider gap (Case1) Motoring Engine speed Crank angle : 1600 rpm : 10deg. ATDC Stepped piston (Case2) Tapered piston (Case3) 12 0 Tapering piston bowl restricts the reverse squish flow from the piston wall side to cylinder head.

21 at squish area ROHR J/ Heat flux measurement of the tapered piston rpm-1.1MPa under the same heat release rate Heat flux MW/m less taper with taper reduced Crank angle ATDC Measured at cylinder head Heat flux (squish area) Tapered piston bowl reduced the heat flux in the squish area, which makes a large contribution to the cooling heat loss reduction.

22 Fuel consumption (L/100 km) Improvement of fuel economy in NEDC Under same smoke emission Equivalent NEDC 5.0 Conventional combustion Low flow combustion Low flow combustion w/ tapered shallow dish 3% 5% 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.

23 Content 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

24 Specifications of smaller bore engine 24 Engine type Displacement L Bore x stroke mm Swirl ratio Conventional Low flow combustion 4 cylinder DI diesel 2 valves x Combustion chamber Re-entrant Lip-less shallow Compression ratio 16.9 : : 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

25 Cooling heat loss % Smoke FSN Application of low flow concept to two valve engine 25 Effect of low flow chamber in 2 valves engine For 2 valves engine Lip-less shallow dish Lip-less shallow dish Large squish area Small squish area Re-entrant Center of bore Center of chamber 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 φ Lean

26 Improvement of combustion chamber for 2 valves Reduction of heat loss Reducing heat transfer coefficient Weaken squish flow 2. Decrease of smoke Improve the mixture formation Mixture introduction to large squish area Taper Large squish area Large taper Small squish area Small taper Chamber 3. Decrease of smoke Reduction of fuel at squish area Keep the squish flow Center of bore 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 Center of chamber

27 Simulated distribution of gas flow velocity 27 TDC Eccentric Tapered shape Large squish area Small squish area Taper could weaken gas flow velocity Low flow velocity Re-entrant High flow velocity Velocity m/s 0 20 Taper could weaken the gas flow velocity in large squish area. The cooling heat loss was reduced with Eccentric tapered chamber.

28 Simulated distribution of equivalence ratio 28 TDC Taper could spread fuel mixture gas Eccentric Tapered shape Large squish area Small squish area Spread to whole cylinder area Re-entrant φ 0 2 The lower squish flow and the improvement of air-fuel mixing can be realized simultaneously with eccentric tapered chamber.

29 Cooling heat loss % Smoke FSN Effect of the eccentric tapered chamber rpm/0.1MPa 2000rpm/0.7MPa Conventional 18% Smoke 0.5FSN Conventional (0.5FSN) New chamber (0.5g/kWh) New chamber (0.5g/kWh) NOx g/kwh NOx g/kwh Both reduction of cooling heat loss and smoke emission could be realized using conventional nozzle spec. and swirl ratio

30 Content Introduction 2. Combustion Concept 3. Results Combustion characteristics Cooling heat loss analysis Cooling heat loss reduction Application to smaller bore engine 4. Conclusion

31 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.

32 32 Thank you for your attention