present 2002 deer dec

8/13/2019 Present 2002 Deer Dec

1/16

John E. Decand

Magnus SjbergSandia National Laboratories

Sponsor: U.S. Dept. of Energy, OTT, OAAT and OHVT

Program Managers: Kathi Epping and Gurpreet Singh

HCCI Combustion: the Sources of Emissions atLow Loads and the Effects of GDI Fuel Injection

8th Diesel Engine Emissions Reduction Workshop

August 25-29, 2002


2/16

Introduction

HCCI engines are a low-emissions alternative to diesel engines.

Provide diesel-like or higher efficiencies.

Very low engine-out NOXand PM emissions.

Research is required in many areas to resolve technical barriers tothe development of HCCI engines by industry.

The objective of our work is to help provide this understanding.

Establish a laboratory to investigate HCCI combustion fundamentals.

All-metal engine: fully operational result are subject of presentation.

Optically accessible engine: examine in-cylinder processes (end of 02).

CHEMKIN kinetic-rate computations

Guide experiments

Assist in data analysis

Show limiting behavior


3/16

Engine and Operating Conditions

Six-cylinder diesel engine converted forbalanced, single-cyl., HCCI operation.

Versatile facility to investigate variousoperational and control strategies.

Compression ratios from 13 - 21(18)*Swirl ratios from 0.9 - 3.2; 7.2(0.9)*Speeds to 3600 rpm(600 - 1800 rpm)*Multiple fueling systems.

> Fully premixed(curr.)*> Port fuel injection (PFI)

> Direct injection, gasoline-type(curr.)*

> Direct injection, diesel-type

Liquid or gas-phase fuels(iso-octane)*

Complete intake charge conditioning.

Intake temperatures to 180C.(varies)*

Intake pressures to 4 bars.(varies)*

Simulated or real EGR.(none)*

HCCI All-Metal Engine

* Values in(red)are used for current work.Based on Cummins B, 0.98 ltr./cyl.


4/16

Engine Appears to be Working Well

88

90

92

94

96

98

100

90 100 110 120 130 140 150Intake Temperature [C]

Combustionefficien

cy[%]

36

38

40

42

44

46

48

Thermalefficiency

[%]

Combustion efficiency

Thermal efficiency

CR = 18;= 0.24; Pin= 120 kPa;1200 rpm; Well-Mixed Charge

Large squish clearance.Ring-land crevice 1% of TDC vol.Various compression ratios

0

25

50

75

100

125

150

175

200


CO&HC[g/kg

fuel]

0

100

200

300

400

500

600

700

800

NOx[mg/kgfuel]

CO

HC

NOx

0

50

100

150

200

250

300

350

400


IMEPg[kPa]

0

0.5

1

1.5

2

2.5

3

3.5

4

Std.

Dev.

ofIME

Pg[%]

IMEPg

Std. Dev. IMEPg


5/16

Computational Approach

Senkin application of the CHEMKIN-III kinetics rate code.

Single-zone model with uniform properties and no heat transfer.

Allows compression and expansion with slider-crank relationship.

Full chemistry for iso-octane (Westbrook et al., LLNL).

Great oversimplification of a real engine. Model cannot reproduceall real-engine behavior.

Model is well suited for investigating certain fundamental aspects ofHCCI combustion.

Allows the effects of kinetics and thermodynamics to be isolated andevaluated without complexities of walls, crevices, and inhomogeneities.

> Assists in analysis of experimental data by separating chemical-kineticand physical effects.

Represents the adiabatic limit for bulk-gas behavior in real engines.

Guide experiments by showing approximate trends in ignition timing &temperature compensation with changes in operating conditions.


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0.0 0.1 0.2 0.30

20

40

60

80

100

120

Equivalence Ratio (Phi)

Combustion

Efficiency(%)

0.0 0.1 0.2 0.3 0.4 0.51e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

Equivalence Ratio (Phi)

MoleFraction/Phi

HCOHCHC + OHCCO

100 ppm for = 1.0

Below= 0.2, emissions rise followed by a drop in combustion efficiency.

Temperatures are too low to complete reactions, especially CO CO2.

Indicates high emissions of OHC as well as CO and HC.

OHC not well-detected by standard FID HC detector, and they can be harmful.

Results for bulk-gas alone, in the absence of heat transfer.

Occurs in range of interest (typical diesel idle conditions are = 0.10 - 0.12).

In real engine, heat transfer will shift onset of incomplete reactions to higher .

Walls & crevices also add to emissions.

CHEMKIN predicts incomplete bulk-gas reactions at low loads.

Iso-Octane; 1800 rpm; CR = 21; Tin= 380 K; Pin= 1 atm.

SAE Paper 2002-01-1309


7/16

Vary: Experiment and CHEMKIN

Iso-Octane ; CR = 18; 1200 rpm;Pin= 120 kPa; Pre-Mixed

Intake temperature adjusted for

50% burn at TDC for = 0.14.Experiment: Tin= 140C

CHEMKIN: Tin= 117C

Experiment shows greatervariation in combustion phasing.

Heat transfer and residuals.

Advanced timing at higherloads has little effect on

emissions.

Timing retard at low loads issmall and has little effect onemissions.

40

60

80

100

120

Pressure

(Bars)

MotoredPhi = 0.06Phi = 0.10Phi = 0.14Phi = 0.18Phi = 0.22Phi = 0.26

CHEMKIN

Tin= 117C

340 350 360 370 380 390 40020

30

40

50

60

70

80

90

100

Crank Angle (Degrees)

Pressure(Bars)

MotoredPhi = 0.06Phi = 0.10Phi = 0.14Phi = 0.18Phi = 0.22Phi = 0.26

Experiment

Tin= 140C


8/16

Emissions: Experiment and CHEMKIN

1200 rpm; CR = 18; Pin= 120 kPa;Pre-Mixed Fueling

Experimental Tinwas increasedto maintain near-TDC ignition.

Compensate for heat transfer. Experimental emissions match

model closely.

CO levels match closely ~65%

> Bulk-gas source.HC, rise for < 0.2 is similar to

model indicates bulk-gassource at low.

> Near-constant baseline

level for > 0.2 suggestcrevice source.

Missing carbon in experimentindicates presence of OHCs.

> Similar to model, but lower

due to FID response.

0

10

20

30

40

50

60

70

80

90

100

0.02 0.06 0.1 0.14 0.18 0.22 0.26

Equivalence Ratio []

FuelCarbonintoEmissions[%]

CO

CO2

HC

OHC

CHEMKIN

Tin= 117C

0

10

20

30

40

50

60

70

80

90

100

0.02 0.06 0.1 0.14 0.18 0.22 0.26


FuelCarboninto

Emissions[%]

CO

CO2

HC

OHC

Experiment

Tin= 140C


9/16

0

10

20

30

40

50

60

70

0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3


FuelCarbonintoCO[%]

CHEMKIN, Tin = 117C

Experiment, Tin = 118C




Interpolated 50% HR@TDC

Comparison of CO Emissions with at Various Tin

Magnitude of increase in CO with decreasingagrees well with theCHEMKIN results. Shows incomplete bulk-gas reactions are the cause.

Onset of rise in CO levels is shifted to higher in engine due to heat transfer.

Rise in CO shifts to progressively higher as Tinis reduced (lower Tcombustion.).

Engine data also show a large drop in combustion efficiency at low loads,corresponding to the increase in CO.


10/16

-50

0

50

100

150

200

250

300

350

0.02 0.06 0.1 0.14 0.18 0.22 0.26Equivalence Ratio []

IMEPg

[kPa]

0

2

4

6

8

10

12

14

16

Std.

Dev.

IMEP

g[kPa&%]IMEPg [kPa]

Std. Dev. IMEPg [kPa]

Std. Dev. IMEPg [%]

Efficiencies and Combustion Stability

Combustion efficiency dropsfrom 95% to 60% as fuel isreduced to low-idle,= 0.1.

Similar drop in pressure-indicated thermal efficiency.

Commensurate with therapid rise in CO.

Std. Dev. of IMEP is 2 4kPa for all fueling rates ().

Increase at = 0.16 due thisbeing in the middle of the

rapid rise in CO.

NormalizedIMEPincreases below = 0.1because IMEP is near zero.

Std. Dev. of IMEPg 2.6%from= 0.1 to = 0.26.

0

10

20

3040

50

60

70

80

90

100

0.02 0.06 0.1 0.14 0.18 0.22 0.26


Combustio

nefficiency[%]

0

5

10

1520

25

30

35

40

45

50

ThermalEfficiency[%]

Combustion efficiency [%]

Thermal efficiency [%]

CR = 18; Pin= 120 kPa;Tin= 140C; Pre-Mixed


11/16

Effect of Intake Pressure

1200 rpm; CR = 18; Pre-Mixed

Changing Pinfrom 101 to 120

kPa has little effect on onset ofincomplete bulk-gas reactionswhen combustion phasing ismaintained.

Experiment and CHEMKIN

both show slightly lower COvalues during rapid rise.

Tinadjusted for 50% burn at

TDC for = 0.14.

101 kPa: Tin= 157C 120 kPa: Tin= 140C

0

10

20

30

40

50

60

70

0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3


FuelCarbo

nintoCO[%]

1.0 bar, Expr. Tin = 157C

1.2 bar, Expr. Tin = 140C

1.0 bar, CHEMKIN, Tin = 121C

1.2 bar, CHEMKIN, Tin = 117C

0

10

20

30

40

50

60

70

80

90

100

0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3


FuelCarbonintoEmissions[%]

CO2 100 kPa

CO2 120 kPa

CO 100 kPa

CO 120 kPa

HC 100 kPaHC 120 kPa

OHC 100 kPa

OHC 120 kPa


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0

10

20

30

40

50

60

70

0.02 0.06 0.1 0.14 0.18 0.22 0.26


FuelCintoCO&HC[%]

30

40

50

60

70

80

90

100

Combustion

efficiency[%]

CO 600 rpmCO 1200 rpmCO 1800 rpmHC 600 rpm

HC 1200 rpmHC 1800 rpmCE 600 rpmCE 1200 rpmCE 1800 rpm

Effect of Engine Speed on Bulk-Gas Reactions

Tinadjusted to maintain combustion phasing at TDC for= 0.14.Higher compression temperatures compensate for reduced time for reactions.

Engine speed has little effect on the fueling rate at which the onset ofincomplete bulk-gas reactions occurs for iso-octane.In agreement with CHEMKIN computations.

Results suggest that special combustion strategies will be required forlow-load operation.


13/16

GDI Fueling: Vary Injection Timing

Early Injection

Provides a fairly uniform mixture.

Can lead to incomplete bulk-gas

reactions at low loads, aspredicted by CHEMKIN.

Late Injection

Can provide partial charge

stratification.Mixture locally richer for the

same fueling rate.

Offers the potential to mitigateincomplete bulk-gas reactions at

light loads.

Also, could prevent fuel fromreaching ring-land crevice.

Reduce baseline emissions.


14/16

Variation in Injection Timing: = 0.1

Tin= 142C; Pin= 120 kPa;1200 rpm; GDI fueling

Early injection (0-90aTDC

intake) provides a well-mixedcharge.

High CO and low combustionefficiency for = 0.1.

Retarding injection improvescombustion and emissions forlow-load operation.

Injection at 290reduces COand HC emission substantially

with only about 1g/kg-fuel NOX(4 ppm).

Combustion efficiencyincreases from 59% to 82%.

Further improvements possiblewith optimized stratification.

0

10

20

30

4050

60

70

80

90

100

0 45 90 135 180 225 270 315 360

Injection Timing [deg. CA]

IMEPg

[kPa]&

Combustion

efficiency[%]

0

2

4

6

810

12

14

16

18

20

Std.

Dev.of

IMEPg[%]

IMEPg [kPa]

Combustion efficiency [%]

Std. Dev. IMEPg [%]

0

200

400

600

800

1000

1200

1400

0 45 90 135 180 225 270 315 360

Injection Timing [deg. CA]

CO&HC[g/kgfuel]

0

5

10

15

20

25

30

35

NOx,

50x

Soot[g/kgfuel]

CO HC

Soot NOx


15/16

Summary and Conclusions - 1

Metal HCCI research engine appears to be functioning well.

At fully combusting conditions: thermal~ 46%, IMEP < 1%, CO < 65g/kg (1000 ppm), HC < 35 g/kg (1200 ppm), NOX~ 0.06 g/kg (1 ppm).

CHEMKIN results show that for fuel loads below ~ 0.16, bulk-gasreactions are incomplete, even for an idealized adiabatic engine.

Significant combustion inefficiencies, very high CO, and increased HC.

> Temperatures are too low to complete reactions, mainly COCO2.Indicate that significant OHC emissions should occur. (OHC is ~2x HC).

Experimental data show a very similar trend to the changes inemissions and combustion efficiency as fuel loading is reduced.

CO levels match very closely with those of the model (~65% of fuel C).> Bulk-gas must be the source.

Onset of incomplete bulk-gas reactions occurs at higher~ 0.2 due toheat transfer cooling the charge.


16/16

Summary and Conclusions - 2

The missing carbon in the emissions measurements matches theexpected OHC trends.

HC detector (FID) has low sensitivity to OHC.

Combustion stability was good even at idle loads, IMEP 2.6%.

Increasing Pinfrom 1.0 to 1.2 bars had little effect on the onset ormagnitude of incomplete bulk-gas reactions when ignition timing

was maintained.

Changing speed from 600 to 1800 rpm has almost no effect on theonset or magnitude of incomplete bulk-gas reactions for iso-octane.

Increased compression temperatures required to maintain ignitiontiming compensate for reduced time to complete reactions.

Partial charge stratification by late-cycle fuel injection appears tohave a strong potential for mitigating the difficulties of low-load

operation.

present 2002 deer dec

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