PM Emissions from HCCI Engines

Transcription

1 PM Emissions from HCCI Engines H.M. Xu, J. Misztal, M.L. Wyszynski University of Birmingham P. Price, R. Stone Oxford University J. Qiao Jaguar Cars Particulate matter and measurement Cambridge University, 16 May 2008

2 Presentation outline Background PM with Gasoline HCCI Varied valve timing Varied injection timing Effect of air temperature Comparison with SI combustion Effect of diesel addition Summary and conclusions

3 HCCI a generic name for new combustion mode SI combustion Diesel combustion spontaneous multiple-point ignition (Oxford Lasers) Homogeneous Charge Compression Ignition typically, rather homogeneous mixture and temperature distributions capable of running with extremely lean mixtures (AFR>80) load can be controlled by fuel quantity or air-egr dilution

4 Advantages of HCCI/CAI combustion Extremely low (1-5% of SI) NOx emissions - absence of high temperature regions High fuel economy (approach Diesel s ) - un-throttling, lean combustion possible, increased heat release rate, removal of knock tendency, high CR possible Very low cycle-by-cycle variations? - multipoint flame initiation Smokeless? Combustion images Wilson et al SAE Paper

5 How much PM is HCCI producing The first measurement of HCCI PM by Ford was surprising, although clearly HCCI smoke numbers will be low compared to diesel Kaiser et al, 2002 Kalghatgi et al, 2007

6 Comparison of PM for different combustion systems Stability limit for GDI SI Motored condition The load of the GDI engine is regulated by air fuel ratio and stratified charge is used for low load - Data measured at Tsinghua University Xu et al, 2008 SAE HCCI Symposium

7 Extension of the low load HCCI boundary by Dieseline PM mass fraction (10-6 ) Load regulated by air fuel ratio HCCI(D0) HCCI(D10) HCCI(D20) TSDI Two-stage injection For lowest low load TSDI (gasoline swirl injector!) Knocking Knocking Gasoline direction IMEP IMEP / (bar) :59:49 Dieseline- Mixture of gasoline and diesel fuels - Data measured at Tsinghua University Xu et al, 2008 SAE HCCI Symposium

8 Jaguar HCCI engine Base Engine Bore Stroke Compression Ratio Con Rod Length Fuel 3.0L V6 89 mm 79.5 mm mm UL95 gasoline Dual Variable Cam Timing (VCT) Dual Cam Profile Switching (CPS) Direction injection

9 Emission measurement system

10 Emission characteristics of the Jaguar HCCI engine Higher PM Price et al SAE paper

11 PM comparison for HCCI and SI 1. At a higher load condition for IMEP of bar, PM with HCCI shows a lower level in both accumulation mode and nucleation mode than SI 2. Varied injection timing (-300 or -340) can make a big difference, greater for that in the case of varied valve strategies (A or B) or SI Xu et al, 2008 SAE HCCI Symposium

12 PM for varied injection timings - HCCI HCCI rpm; λ = 1.0; IVO = 60CAaTDC; EVC = 86CAbTDC Total Mass [ a. u. ] Total [ MN/cc ] NOx/100 [ppm] Mass [ a. u. ] HCCI - En.Speed = 1500rpm; λ = 1.0; IVO = 60CAaTDC; EVC = 86CAbTDC Number [ MN/cc ]; NOx [ ppm ] ºbTDCc - 340ºbTDCc - 320ºbTDCc - 300ºbTDCc - 260ºbTDCc 0.0 Matching of the injection and the intake valve timing may be important Xu et al, 2008 SAE HCCI Symposium

13 PM for lean burn with boosting - HCCI 1.E+07 HCCI : IMEP = 5.2 bar - En. Speed = 1500rpm 1.E+06 dn/dlogdp (1/cm3) 1.E+05 1.E+04 1.E+03 λ NA_λ=1.0 BP=0.2_λ=1.3 BP=0.4_λ= Dp (nm) λ lean burn significantly reduces PM over the full spectrum Xu et al, 2008 SAE HCCI Symposium

14 PM for lean burn with boosting - HCCI 2.0 Total Mass [ a.u. ] 40 Total Number [ MN/cc ] NOx/10 [ppm] 35 Mass [ a. u. ] HCCI - NMEP = 5.2 bar - En. Speed = 1500rpm Number [ MN/cc ]; NOx [ ppm ] NA_λ=1.0 BP=0.2_λ=1.3 BP=0.4_λ=1.6 0 lean burn significantly reduces PM, both in mass and number Xu et al, 2008 SAE HCCI Symposium

15 PM may approach SI for smaller load 1.E+08 Eng Speed = 1500 rpm; NMEP = 4.2 bar IMEP=3.9bar IMEP=4.3bar 1.E+07 dn/dlogdp (1/cm3) 1.E+06 1.E+05 SI - IVO=5CAaTDC, EVC=3CAaTDC, EOI=250CAbTDC SI - IVO=25CAaTDC, EVC=3CAaTDC, EOI=250CAbTDC HCCI - IVO=65CAaTDC,EVC=98CAbTDC,EOI=350CAbTDC 1.E+04 HCCI - IVO=80CAaTDC,EVC=89CAbTDC,EOI=350CAbTDC Dp (nm) There are relatively more larger size of PMs with HCCI at lower load (increase of accumulation mode fractions). Xu et al, 2008 SAE HCCI Symposium

16 PM may approach SI for smaller load 0.30 Total Mass [ a.u ] 20 Total Number [ MN/cc ] Total Mass [ a.u. ] NOx/100 [ ppm ] Total Number [ MN/cc ]; NOx/10 [ ppm ] HCCI - IVO=65CAbTDCHCCI - IVO=80CAbTDC SI - IVO=5CAaTDC SI - IVO=25CAaTDC 0 In one case, PM mass even exceeded SI case for the same load Xu et al, 2008 SAE HCCI Symposium

17 PM with split injection 1.E+08 En. Speed = 1500 rpm; IVO = 60CAaTDC, EVC = 89 CAbTDC - NMEP = bar 1.E+07 IMEP=4.7bar IMEP=4.85bar dn/dlogdp (1/cm3) 1.E+06 1.E+05 IMEP=4.9bar IMEP=5.2bar 1.E+04 1.E+03 40%-EOI=250ºbTDCc 60%-EOI=250ºbTDCc EOI=350ºbTDCc EOI=250ºbTDCc Dp (nm) PM will fall between the boundaries for one injection in recompression or late induction Xu et al, 2008 SAE HCCI Symposium

18 PM with split injection 0.5 En. Speed = 1500 rpm; IVO = 60CAaTDC, EVC = 98 CAbTDC - NMEP = bar Total Mass [ a. u. ] Total Mass [ a.u. ] Total Number [ MN/cc ] NOx/10 [ppm] Total Number [ MN/cc ]; NOx/10 [ ppm ] %-EOI=250ºbTDCc 60%-EOI=250ºbTDCc EOI=350ºbTDCc EOI=250ºbTDCc 0 More pilot injection may increase PM Xu et al, 2008 SAE HCCI Symposium

19 Effect of intake air temperature A thermal management system incorporating electrical heaters and an intercooler bypass was used to control the intake air temperature. Varied valve timings are used to regulate the engine load Ambient Charge Air Ambient Charge Air Heated Charge Air Cooled Charge Air TEST NMEP dp/θ IVO EVC T_In T_Ex PM No nm PM Mass nm bar bar/deg. ºaTDC ºbTDC º C º C MN/cc a. u. % % % N N H C EGR η vol η comb

20 Effect of intake air temperature (1) N normal, H heated, C cooled inlet air Higher intake temperature seems to increase the number of PM in nuclei mode

21 Effect of intake air temperature (2) The effect of intake temperature on the mass of PM is limited, but apparently more on the number

22 Summary and conclusions 1. Particulate emissions from HCCI engines are not negligible, especially when taking the number of smaller sized particulates into consideration. 2. In the HCCI engine with NVO, PM varies with valve timing for a given engine speed and relates to engine load and internal EGR rate. When the valve overlap is reduced, both NOx and PM levels increase with engine load.. 3. For a given valve timing for the GDI engine, HCCI PM varies with injection timing. A later injection around the time of intake MOP gives lower PM and NOx emissions, while pilot injection with impingement may increase PM. 4. Particulate emissions from HCCI engines are affected by air-fuel ratio and intake temperature, while the number of smaller sized particulates is more sensitive to engine conditions.

23 Acknowledgement The authors gratefully acknowledge relevant research funding from EPSRC and former DTI, industrial support from Jaguar Land Rover Research and Shell Global Solutions, and contributions to the related research from the Birmingham, Oxford and JLR teams including colleagues and students who are currently with us or have moved.

24 Gasoline and Diesel Engine Technologies are merging CR Conventional compression engines New fuel management 10 Conventional spark-ignition Engines Optimized Combustion Engine In-direct injection Direct injection High EGR Complex-injection

25 Multi-fuel injection system the future of new engines? A computer controlled colour printer can print colourful pictures using 3 original coloured inks If we have 3 different type of fuels, why cant a CPU controlled fuel injection system supply a required fuel colour (property) for printing a beautiful picture for optimised engine operation at varied conditions? Simply, a multi-channel fuel nozzle is required at gas stations to supply the fuels as for printer cartridges!