experiments and modeling of two-stage combustion in … · experiments and modeling of two-stage...

1 DEER, August 4, 2008

Experiments and Modeling of TwoExperiments and Modeling of Two--Stage Combustion in Stage Combustion in LowLow--Emissions Diesel EnginesEmissions Diesel Engines

August 4, 2008

Rolf D. Reitz, Sage L. Kokjohn, Thaddeus A. Swor, and Michael J. Andrie*

Engine Research Center, University of Wisconsin-Madison

DOE/Sandia National Labs

Diesel Emissions Reduction Consortium

(DERC)

Acknowledgments:


Presentation OutlinePresentation Outline•

Motivation and background

•

Numerical models and validation•

Simulation results and discussion

•

Experimental setup•

Experimental results and discussion

•

Conclusions


Motivation and BackgroundMotivation and Background•

Emissions standards are becoming more and more stringent

•

A focus on the reduction of greenhouse gases has driven a need for increased efficiency

•

HCCI can yield high efficiency, low NOx & PM

•

Y. Sun used the TSC concept to expand operating range of HCCI combustion in a heavy-duty engine (SAE 2008-01-0058)

•

HCCI problems and solutions–

Ignition control•

EGR & VVA

–

Excessive pressure rise rates•

Two-stage combustion (TSC)

–

Spray-wall impingement resulting

from early injection

•

Adaptive injection strategies (AIS) (Kamimoto, Akihama, Pickett)


AIS (Yong Sun SAE 2008AIS (Yong Sun SAE 2008--0101--0058)0058)•

Low-pressure (<50MPa, 5~25MPa) narrow-angle injection--

Early injection: intake or early compression stroke HCCI, PCCI combustion--

Post injection: late expansion or exhaust stroke DPF, LNT regeneration

•

High-pressure (>50MPa, above 100MPa) wide-angle injection--

Late injection: late compression or early expansion stroke conventional diesel, PCCI combustion

•

Low load: HCCI combustion early injection

•

Medium load: Two-Stage Combustion (TSC) early + late injections--

Sun, Y., SAE 2006-01-0027•

High load: conventional diesel combustion late injection

TDC BDC TDC BDC TDC


Engine Specifications

Base engine type GM1.9 LBore 8.2 cmStroke 9.04 cmConnecting Rod Length 16.1 cmSquish height 0.0617 cmDisplacement 0.4774 LCompression ratio 16.5:1Swirl ratio 2.2Bowl type re-entrantIntake valve opening 344º

ATDC FiringIntake valve closing -132º

ATDC FiringExhaust valve opening 112º

ATDC Firing Exhaust valve closing 388º

ATDC Firing

Injector typeHigh-pressure

solid-coneManufacturer BoschInjection pressure 860 barIncluded angle 155°Number of holes 7Nozzle hole diameter 141 μm

Injector Specifications

SpecificationsSpecifications


Numerical ModelsNumerical Models•

KIVA-3V Release 2 code coupled with CHEMKIN II–

39 species and 131 reaction n-heptane mechanism

•

RNG k-ε turbulence model

•

Gasjet theory used to model near nozzle droplet/gas relative velocity (SAE 2008-01-0970)

•

KH-RT break up model

•

Unsteady droplet vaporization

•

Drop collision and coalescence

•

Multi-objective genetic algorithm (MOGA) optimization


Model ValidationModel Validation

-50 -40 -30 -20 -10 0 10 20 30 40 500

2000

4000

6000

8000

10000

12000

0

30

60

90

120

150

Cyl

inde

r Pre

ssur

e [k

Pa]

Crank [degrees]

Experiment Simulation

SOI -29.2 dATDC

Hea

t Rel

ease

Rat

e [J

/deg

]•

Validation was performed against PCCI experiments of Opat et al. (SAE 2007-01-0193)

•

Engine was operated at the F4 condition

Engine speed (rev/min) 2000Nominal IMEP (bar) 5.5Fuel flow rate (kg/hr) 0.895EGR rate (%) 65IVC Temperature (K) 350IVC Pressure (bar) 1.91SOI (ºATDC) -16.2 to -34.2

0.0

0.1

0.2

0.3

0.4

-39 -36 -33 -30 -27 -24 -21

0.100.150.200.25

Soot

[g/k

gf] experiment

simulation

NO

x [g

/kgf

]

SOI (°aTDC)


Preliminary investigationPreliminary investigation•

Fixed parameters to those of TSC case found by Kokjohn and Reitz (2008-01-2412)

•

Swept early injection timing at two injection pressures–

100 bar and 860 bar

•

Low pressure early injection showed a significant reduction in spray-wall impingement

Simulation Results & Discussion Simulation Results & Discussion

IVC Pressure (bar) 1.74EGR rate (%) 54SOLI timing (ºATDC) 2.9Late injection pressure (bar) 860Early injection fueling (mg) 5.36Late injection fueling (mg) 9.54

High pressure early injection Low pressure early injection

0.00.20.40.60.8

0.0

0.1

0.2

0

100

200

100

150

200

200

250

300

-100 -90 -80 -70 -60 -50 -40 -30234

NO

x[g

/kgf

]so

ot[g

/kgf

]H

C[g

/kgf

]C

O[g

/kgf

]IS

FC[g

/kW

-hr]

PRR

[bar

/deg

]

start of early injection [deg. ATDC]


0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14Generation [-]

Nor

mal

ized

Con

verg

ence

[-]

AIS OptimizationAIS Optimization•

Multi-Objective Genetic Algorithm (MOGA)

•

Seven optimization parameters •

Minimize six objectives–

NOx, soot, HC, CO, ISFC, and PRR

•

13 generations with a population size of 24–

20 hours/case on 3.0 GHz AMD Athalon™

processor–

Monitored convergence by comparing

location of current generation Pareto

front to the location of all other Pareto solutions

( )( )( )

( )1

tFit i

t

dC P

F== ∑

( ) ( ) 2*

max min1 1minP M

k ki j k k k

f i f jd

f f==

−⎛ ⎞= ⎜ ⎟−⎝ ⎠

∑

Early inj. pressure 100 ~ 1500 bar

Late inj. pressure 600 ~ 1500 bar

Early inj. timing IVC ~ (SOLI-30) ºATDC

Late inj. timing -10 ~ 25 ºATDC

IVC pressure 1.67 ~ 3.0 bar

Fuel split 10 ~ 90 % total fuel

EGR rate 0 ~ 65 %


AIS OptimizationAIS Optimization•

Two promising types of combustion strategies found by GA optimization

•

Both strategies utilize low pressure early injections

1) Split Heat Release–

~50% fuel split –

Moderate EGR (43%)–

Very retarded second injection2) Single Heat Release

–

30% fuel injected early –

Second injection near TDC–

Similar to UNIBUS strategy

Parameters ObjectivesEarly Late

SOEI SOLIIVC

Press.

fra

c EGR IVC

Max

PRR

Net ISFC soot NOx CO HCInj. Pres. Inj. Pres

bar bar °ATDC °ATDC bar - % °ATDC bar/deg g/kW-hrSplit HR 110 774 -49.7 7.5 2.5 0.5 43 -100 4.8 194 0.68 0.1 45 7.0

Single HR 563 1384 -43.1 -1.3 2.4 0.3 54 -104 6.7 196 0.21 0.1 23 8.4Baseline-LTC 860 NA -28.2 NA 1.91 1 65 -132 5.5 199 0.004 0.004 46 9.0

02468

10

0306090

120

-50 -40 -30 -20 -10 0 10 20 30 40 500

200400

Pre

ssur

e [M

Pa] Split HR

Single HR

HR

R [J

/deg

]

Inj.

Vel

. [m

/s]

Crank [°ATDC]


Engine Specifications

Base engine type GM1.9 LBore 8.2 cmStroke 9.04 cmConnecting Rod Length 16.1 cmSquish height 0.0617 cmDisplacement 0.4774 LCompression ratio 16.5:1Swirl ratio 2.2Bowl type reentrantIntake valve opening 344º




ATDC Firing


solid-coneManufacturer BoschIncluded angle 155°Number of holes 7Nozzle hole diameter 141 μm

Injector Specifications

Base engine type GM1.9 LBore 8.2 cmStroke 9.04 cmConnecting Rod Length 16.1 cmSquish height 0.11 cmDisplacement 0.4774 LCompression ratio 15.5:1Swirl ratio 2.2Bowl type Mexican-hatIntake valve opening 344º




ATDC Firing


solid-coneManufacturer DensoIncluded angle 155°Number of holes 8Nozzle hole diameter 128 μm

•

Hardware limitations prohibited use of VVA

•

Lower compression ratio•

Mexican-hat combustion chamber

•

8 hole Denso injector

Adaptation of AIS for ExperimentsAdaptation of AIS for Experiments


Variable Pressure Pulse SystemVariable Pressure Pulse System•

Low pressure early injection and high pressure secondary injection

•

Achieved by switching between a low and high pressure system

0 10 20 30 40 50 60 70 800

5

10

15

20

25800 bar

Inje

ctio

n R

ate

[mg/

ms]

Crank [degrees]

Shape 1 Shape 2 Shape 3 Shape 4 Shape 5

150 bar


Variable Pressure Pulse SystemVariable Pressure Pulse System•

Consists of:–

High Pressure Common Rail

–

Low Pressure Fuel System–

Switching Solenoid

–

Needle Valve–

Relief Orifice

–

PFIM controller•

Synchronize the solenoid and injector


AIS Experimental ResultsAIS Experimental Results

0.00.20.40.60.8

0.0

0.4

0.8

180

210

240

4 5 6 7 8 9 10 11 12 130

2

4

NO

x[g

/kW

-hr]

soot

[g/k

W-h

r]

Net

ISFC

[g/k

W-h

r]

PR

R[b

ar/d

eg]

Start of Late Injection Timing [°ATDC]

•

Simulations capture emissions trends and magnitudes very well

•

GA optimum shows that significant

improvements in NOx and ISFC are possible with higher boost and early fueling

Experiments/Simulations

GA Optimum Split Heat Rel.

Early inj. pressure 150 bar 110 bar

Late inj. pressure 800 bar 740 bar

Early inj. timing -53 ºATDC -49 ºATDC

Late inj. timing 5.8 ~ 12.8 ºATDC 7.5 ºATDC

Boost 1.55 bar 2.35 bar

IVC timing -132 ºATDC -100 ºATDC

Total Fuel 13 mg/stroke 14.9 mg/stroke

Early Inj. Fuel 40 % 50 %

EGR rate 47 % 43 %

Nominal IMEP 4.3 bar 5.5 bar

Split Heat Release Cases

Experiment SimulationSimulation optimum

ExperimentSimulation


AIS Experimental ResultsAIS Experimental Results

•

Emissions trends are captured, but simulations over predict peak PRR

and under predict NOx

•

GA optimum shows that significant

improvements in NOx and ISFC are possible with higher boost and early fueling

Experiments/Simulations

GA Optimum Single Heat Rel.

Early inj. pressure 150 bar 560 bar

Late inj. pressure 1000 bar 1400 bar

Early inj. timing -53 ºATDC -43 ºATDC

Late inj. timing -3 ~ 3 ºATDC -1 ºATDC

Boost 1.62 bar 2.32 bar

IVC timing -132 ºATDC -104 ºATDC

Total Fuel 14.9 mg/stroke 14.9 mg/stroke

Early Inj. Fuel 10 % 30 %

EGR rate 57 % 54 %

Nominal IMEP 5.5 bar 5.5 bar

Single Heat Release

Cases

0.000.15

0.30

0.45

0.000.080.160.24

180

210

240

-3 -2 -1 0 1 2 32468

10

NO

x[g

/kW

-hr]

soot

[g/k

W-h

r]

Net

ISFC

[g/k

W-h

r]

PR

R[b

ar/d

eg]

Start of Late Injection Timing [°ATDC]

Experiment SimulationSimulation optimum

ExperimentSimulation


Summary and ConclusionsSummary and Conclusions•

Significant reductions in ISFC and NOx were observed through the

use of low-pressure early injection and high boost pressure –

Net ISFC ~ 194 g/kW-hr and NOx ~ 0.1 g/kW-hr•

VVA has been shown to provide a means for premixed combustion phasing control

•

A split heat release strategy (TSC) was used control pressure rise rate and reduce engine noise –

Peak PRR ~ 4 bar/deg•

Low pressure early injections were shown to reduce spray-wall impingement, resulting in improved ISFC and HC emissions

•

A variable injection pressure system was developed and used to validate the AIS/TSC computational results

•

Future work will include validation of GA optimum points when VVA system is available

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