Potential of the Mild HCCI Combustion for Worldwide Applications

Transcription

1 Potential of the Mild HCCI Combustion for Worldwide Applications Future Fuels for IC Engines ERC Research Symposium Madison June 6-7, 2007 P.Gastaldi M.Besson JP.Hardy Renault Powertrain Division

2 Overview The Diesel engine : a customer oriented product within the planetary challenge for reducing CO2 Potentials and threatens The Mild HCCI as a promising Low Temperature Combustion system. Mild HCCI and available fuels Future combustion systems for future fuels or future fuels for future combustion systems? P / 2

3 Part 1 The Diesel engine : a customer oriented product within the planetary challenge for reducing CO2 P / 3

4 Satisfying customers is the main task for automotive manufacturers P / 4

5 The Diesel Engine : a large success in Europe linked to upgraded technologies Technological advances deeply linked to customer requirements 60% European Diesel market share (data from ACEA) 50% 40% 30% 20% 10% 0% Fuel Economy Performances Turbo DI Variable Turbo Noise Common rail 1 st gen. Emissions Common rail 2 nd gen P / 5

6 The Diesel engine and the environment By its high fuel efficiency, the Diesel engine is up to now the best contributor for reducing the CO2 rejections due to road transport P / 6

7 Improvement of averaged CO2 emissions (Western Europe ACEA data) Contribution of both Higher market share CO2 (g/km) % 50% and % gasoline Diesel total Diesel market share % 20% 10% 0% Stronger reduction of the fuel consumption P / 7

8 Part2 : Potentials and threatens CO2 Driving pleasure Low noise And threatens Potentials Cost P / 8

9 A challenge for the future : protecting the environment at an acceptable cost 25% of the engine cost is due to the after-treatment NOx & 10*PM (g/km) 0,8 0,7 0,6 0,5 0,4 0,3 0,2 Oxycat Euro 3 NOx Soot CSF NOx trap? Euro 4 Euro 5? after treatment Injection system turbocharger Base engine 0, ? 0 Euro 3 Euro 5 Euro 3 Euro MPI 1.5 dci 72kW / 127Nm 66kW / 200Nm Two different strategies for the future Strategies for Euro5/6/US Advanced aftertreatment NOx-trap, SCR Reduction of Engine out Emissions New combustion P / 9

10 on worldwide markets Low CO2 High performances High fuel quality High torque SUV Very low emissions Difficult conditions Low cost low fuel quality The combustion system must be compatible with worldwide applications to reduce costs P / 10

11 Part 3 The Mild HCCI as a promising Low Temperature Combustion system P / 11

12 A low temperature combustion : the key for the future? Local Equivalence Ratio [-] 5 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 Rich Stability, #2 cold & HC stratified Lean #3 cold & lean Soot "conventional" combustion #1 rich Material reliability & hot NO x Combustion temp. [K] Only solution #3 seems to be feasible in the near future P / 12

13 The split injection as a way of realising a low temperature combustion Fuel vaporised during the second injection is cooling the first combustion Combustion due to the first injection Combustion due to the second injection BTC Heat release Fuel quantities and respective phasing of the two injections are governing the noise/soot trade off The combustion is actively controlled by the injection P / 13

14 Mechanism of the split injection dq (kj/m3.deg) SOI after TDC (CA) (2nd injection) Cool flame -5,0 2,5 10,0 17,5 25,0 32,5 40,0 Crank Angle CA Mass burnt rate late fully premixed combustion 2nd diffusive combustion High cooling due to 2nd injection 2 almost independent combustions 2nd one late in burnt gases P / 14

15 Mild HCCI definition HCCI because a noticeable part of the fuel is injected early in the compression cycle to get a homogeneous mixture and to secure a quasi fully premixed combustion mild because the second part of the fuel is injected later on in the cycle and can burn as a diffusive flame associated to a quite conventional Euro4 chamber design and therefore allowing competitive full load performances P / 15

16 Mild HCCI results: simulation on a NMVEG cycle (hot) Renault Laguna, 6 gear manual transmission Euro4 / 10 ppm S Calculated engine out emissions noise level equivalent to Euro4 version (rough estimation of transitions between combustion modes) NOx IOF HC CH4 CO CO2 f.c.(l/100km ) conventional Mild HCCI HCCI strategy is successfully reducing both NOx and soot Engine Out Emission High penalty on hydrocarbons and especially methane Fuel consumption must be reduced P / 16

17 Part 4 Mild HCCI and available fuels P / 17

18 Mild HCCI and worldwide representative fuels Test engine : 4 cylinder 2.0 liter 84x90 mm CR 16 engine with HP and LP EGR Fuels Euro 4 US Euro 3 B30 (30% Diester) Heating value (MJ/kg) Cetane Sulfur level (ppm) O/C % vaporized ( C) P / 18

19 Full load results No noticeable difference between Euro4, Euro3 and US fuels even with the same tuning For B30, low reduction of performance ( ~3%) due to a lower heating Value but lower smoke level at 4000 rpm ( ~0.5 FSN) P / 19

20 Detailed comparison between US and Euro4 at 4000 rpm full load Same injection timing Th2dQ1 [kj/m3deg] EVL1 [V] D D Gazole US Euro4 The longer delay due to the low CN is compensated by the higher combustion velocity in pre-mixed mode Th2Int1 [kj/m3] Angle vilebrequin [deg] Same smoke vs equiv.ratio Fumée [FSN] Eur o4 0.5 Gazole US 0 P / R 0.8

21 Part load results US versus Euro4 analysis at 2000 rpm 6 bars BMEP same engine tuning same moderate EGR rate Th2dQ1 [kj/m3deg] EVL1 [V] D D gazole Euro4 gazole US Angle vilebrequin [deg] Two injections Th2Int1 [kj/m3] With Euro4 fuel, the first combustion is effectively slowed down by the second injection With US fuel, the low cetane leads to a high delay => there s only one retarded combustion US versus Euro4 : - 25% NOx - 10 dba % HC + 15% BSFC Too late combustion leading to unacceptable BSFC P / 21

22 Conclusion for US fuel This late combustion leads to a poor acceptance of EGR rates compatible with a fuel neutral target > necessity to move to earlier injection timing for the 2 injections NOx [g/kwh] NOx target Covariance PME Sigma BMEP CO2rg [%] CO2rg [%] Combustion becomes unstable with US fuel P / 22

23 Part load results Euro3 versus Euro4 analysis at 1750 rpm 7 bars BMEP same engine tuning same moderate EGR rate Very close combustion Behavior no difference for emissions and BSFC soot +30% due to Sulfur level P / 23

24 Conclusion for Euro3 fuel 5 4 IOFCL [mg/s] NO4.0 x[mg /s] Euro4 Euro NOx [mg/s] For Euro3 fuel, high EGR rates are forbidden due to important soot emissions NOx reduction and compliance with Fuel Neutral is impossible Engine tuning has to be modified P / 24

25 Part load results B30 versus Euro4 analysis at 2000 rpm 6 bars BMEP same engine tuning same moderate EGR rate Th2dQ1 [kj/m3deg] EVL1 [V] D D B30 iso CO2rg=4,6% Euro4 iso CO2rg=4,6% Th2Int1 [kj/m3] Reduced ignition delay for the first combustion Slightly higher noise level (+ 2 dba) Lower smoke level due to Oxygen in the fuel BSFC higher with B30 but efficiency is the same Angle vilebrequin [deg] 450 Engine tuning could be common for both Euro4 and B30 fuels P / 25

26 B30 fuel results: simulation on a NMVEG cycle (hot) Renault Laguna, 6 gear manual transmission NOx level compatible with fuel neutral hypothesis Noise level equivalent to Euro4 30% 25% 20% 15% 10% 5% 0% -5% -10% B30/Euro4 optis B30/Euro4 optis Nox IOF HC CO CO2 CH4 CSE But lower spec.heating value > same efficiency Only one penalty on CH4 > oxycat light off to be secured P / 26

27 Part load optimisation with Euro4 and US fuels analysis at 2000 rpm 6 bars BMEP constant very low NOx level Retarded combustion for Euro4 fuel Slightly higher BSFC Roughly one advanced combustion allowed by the low soot level for US Low cetane and high volatility compensates the earlier injection P / 27

28 Part load optimisation with Euro4 and US fuels analysis at 2000 rpm 6 bars BMEP constant very low NOx level tuning US Timing inj.1 dwell y = x R 2 = y = x R 2 = Slightly delayed inj1 timing for US 5 0 tuning Euro Linear correction on injection timing easily achievable in the ECU P / 28

29 US fuel results: simulation on a NMVEG cycle (hot) Renault Laguna, 6 gear manual transmission NOx level compatible with fuel neutral hypothesis Noise level equivalent to Euro4 120% US versus EU4 fuel 100% 80% US/Euro4 at NOx target 60% 40% 20% 0% -20% Nox IOF HC CO CSE HC and CO penalties on cycle (overmixing effect due to a high volatility?) P / 29

30 Part load optimisation with Euro4 and Euro3 fuels analysis at 2000 rpm 6 bars BMEP constant very low NOx level Timing inj1 dwell y = x R 2 = Euro3 tuning y = x R 2 = NOx level compatible with fuel neutral hypothesis Noise level equivalent to Euro4 0 Euro4 tuning Ti1/Ti Linear corrections for Euro3 versus Euro4 tuning Euro3 tuning y = x R 2 = Euro4 tuning P 2.00 / 30

31 Conclusion The mild HCCI combustion system is compatible with fuels representative of worldwide availability as with 1st generation bio. ones At full load eg for down-sizing strategies within a fuel neutral hypothesis (simulation result transitions to be optimised) HC, CH4 and CO have nevertheless to be secured, especially for cold start Fuel consumption has still to be reduced for all the fuels (Euro4 vehicles still the target) P / 31

32 Fuels and combustion for the future The Well to Wheel approach is the key parameter to quantify the actual interest on new fuels as for the currently existing B30 (tests achieved on a Renault Megane on New European Driving Cycle) P / 32

33 Part 5: New combustion systems and new fuels are like tango couples They could be the best if they remain together But they still have to be performant if they change partner and orchestra Thank you for your attention P / 33

34 Fun to drive and economic Improved technologies and down-sizing Vehicle Performance index 40% 30% 20% K9K 1.5l DI TC 106ch 10% 0% -10% G8T 2.2l IDI NA 87ch F9Q 1.9l DI TC 100ch -20% -30% Fuel Consumption Euro2 (1996) Euro3 (2002) Euro4 (2007) Euro5? (???) P / 34