PM Emissions from HCCI EnginesH.M. Xu, J. Misztal, M.L. Wyszynski

University of BirminghamP. Price, R. Stone

Oxford University

J. QiaoJaguar Cars

Particulate matter and measurement

Cambridge University, 16 May 2008

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

HCCI – a generic name for new combustion mode

• spontaneous multiple-point 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

Diesel combustion Homogeneous ChargeCompression Ignition

SI combustion(Oxford Lasers)

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 2005-01-2129

How much PM is HCCI producing

Kaiser et al, 2002 Kalghatgi et al, 2007

The first measurement of HCCI PM by Ford was ‘surprising’, although clearly HCCI smoke numbers will be low compared to diesel

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

Dieseline- Mixture of gasoline and diesel fuels - Data measured at TsinghuaUniversity Xu et al, 2008 SAE HCCI Symposium

0 1 2 3 4 50

50

100

150

TSDI

Knocking

2007-7-3 13:59:49

HCCI(D0) HCCI(D10) HCCI(D20)

PM

mas

s fra

ctio

n (1

0-6)

IMEP / bar

Knocking

TSDI

Extension of the low load HCCI boundary by Dieseline

IMEP (bar)

Two-stage injectionFor lowest low load Gasoline direction

Load regulated by air fuel ratio

(gasoline swirl injector!)

Direction injection

Dual Cam Profile Switching (CPS)

138.1 mmCon Rod Length

Dual Variable Cam Timing (VCT) UL95 gasolineFuel

11.3 Compression Ratio

79.5 mmStroke89 mmBore3.0L V6 Base Engine

Jaguar HCCI engine

Emission measurement system

Emission characteristics of the Jaguar HCCI engine

Higher PM

Price et al SAE paper 2007-01-0209

PM comparison for HCCI and SI

1. At a higher load condition for IMEP of 5.2-5.4bar, 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

PM for varied injection timings - HCCIHCCI - 1500rpm; λ = 1.0; IVO = 60CAaTDC; EVC = 86CAbTDC

Matching of the injection and the intake valve timing may be important

Xu et al, 2008 SAE HCCI Symposium

0.0

0.5

1.0

1.5

2.0

2.5

3.0

- 350ºbTDCc - 340ºbTDCc - 320ºbTDCc - 300ºbTDCc - 260ºbTDCc0.0

1.5

3.0

4.5

6.0

7.5

9.0Total Mass [ a. u. ]Total [ MN/cc ]NOx/100 [ppm]

HCCI - En.Speed = 1500rpm; λ = 1.0; IVO = 60CAaTDC; EVC = 86CAbTDC

Mas

s [ a

. u. ]

Num

ber [

MN

/cc

]; NO

x [ p

pm ]

PM for lean burn with boosting - HCCI

lean burn significantly reduces PMover the full spectrum

λ λ

Xu et al, 2008 SAE HCCI Symposium

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1 10 100 1000Dp (nm)

dN/d

LogD

p (1

/cm

3)

NA_λ=1.0 BP=0.2_λ=1.3 BP=0.4_λ=1.6

HCCI : IMEP = 5.2 bar - En. Speed = 1500rpm

PM for lean burn with boosting - HCCI

lean burn significantly reduces PM, both in mass and number

Xu et al, 2008 SAE HCCI Symposium

0.0

0.5

1.0

1.5

2.0

NA_λ=1.0 BP=0.2_λ=1.3 BP=0.4_λ=1.60

5

10

15

20

25

30

35

40Total Mass [ a.u. ]Total Number [ MN/cc ]NOx/10 [ppm]

HCCI - NMEP = 5.2 bar - En. Speed = 1500rpm

Mas

s [ a

. u. ]

Num

ber [

MN

/cc

]; N

Ox

[ ppm

]

PM may approach SI for smaller load

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

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1 10 100 1000Dp (nm)

dN/d

LogD

p (1

/cm

3)

SI - IVO=5CAaTDC, EVC=3CAaTDC, EOI=250CAbTDC

SI - IVO=25CAaTDC, EVC=3CAaTDC, EOI=250CAbTDC

HCCI - IVO=65CAaTDC,EVC=98CAbTDC,EOI=350CAbTDC

HCCI - IVO=80CAaTDC,EVC=89CAbTDC,EOI=350CAbTDC

Eng Speed = 1500 rpm; NMEP = 4.2 barIMEP=3.9bar

IMEP=4.3bar

PM may approach SI for smaller load

In one case, PM mass even exceeded SI case for the same load

Xu et al, 2008 SAE HCCI Symposium

0.00

0.05

0.10

0.15

0.20

0.25

0.30

HCCI - IVO=65CAbTDCHCCI - IVO=80CAbTDC SI - IVO=5CAaTDC SI - IVO=25CAaTDC0

5

10

15

20Total Mass [ a.u ]Total Number [ MN/cc ]NOx/100 [ ppm ]

Tota

l Num

ber [

MN

/cc

]; N

Ox/

10 [

ppm

]

Tota

l Mas

s [ a

.u. ]

PM with split injection

PM will fall between the boundaries for one injection in recompression or late induction

Xu et al, 2008 SAE HCCI Symposium

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1 10 100 1000Dp (nm)

dN/d

LogD

p (1

/cm

3)

40%-EOI=250ºbTDCc 60%-EOI=250ºbTDCcEOI=350ºbTDCc EOI=250ºbTDCc

En. Speed = 1500 rpm; IVO = 60CAaTDC, EVC = 89 CAbTDC - NMEP = 4.7 - 5.2 bar

IMEP=4.7bar

IMEP=5.2barIMEP=4.9bar

IMEP=4.85bar

PM with split injection

More pilot injection may increase PM

Xu et al, 2008 SAE HCCI Symposium

0.0

0.1

0.2

0.3

0.4

0.5

40%-EOI=250ºbTDCc 60%-EOI=250ºbTDCc EOI=350ºbTDCc EOI=250ºbTDCc0

5

10

15

20

25

Total Mass [ a.u. ]Total Number [ MN/cc ]NOx/10 [ppm]

En. Speed = 1500 rpm; IVO = 60CAaTDC, EVC = 98 CAbTDC - NMEP = 4.7 - 5.2 bar

Tota

l Num

ber [

MN

/cc

]; N

Ox/

10 [

ppm

]

Tota

l Mas

s [ a

. u. ]

Effect of intake air temperature

bar bar/deg. ºaTDC ºbTDC º C º C MN/cc a. u. % % %

N - 2 4.8 6.0 60 86 56 412 0.90 0.69 41.3 60.9 93.6

N - 3 4.8 4.2 80 81 61 430 0.65 0.36 40.5 60.3 93.5

H - 4 4.8 5.8 60 91 87 391 0.29 0.18 44.3 53.1 93.6

C - 3 4.8 2.4 80 86 45 438 0.57 0.31 50.3 56.0 92.7

TEST

Ambient Charge AirAmbient

Charge AirHeated Charge

AirCooled Charge

Air

ηcombPM No.

50-300nmPM Mass50-300nm ηvolT_In T_ExIVO EGREVCNMEP dp/Θ

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

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

Effect of intake air temperature (2)

The effect of intake temperature on the mass of PM is limited, but apparently more on the number

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 withinjection 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.

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.

New fuel management

OptimizedCombustion

Engine

OptimizedCombustion

Engine

Conventional compression engines

Conventional spark-ignition Engines

In-direct injection Direct injection High EGR Complex-injection

CR

20

10

15

Gasoline and Diesel Engine Technologies are merging

Multi-fuel injection system – the future of new engines?

• A computer controlled colour printer can printcolourful 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!