1/23

The Reactivity Controlled Compression Ignition Engine:

Simulating Performance in a Changing Fuel Environment

Rolf D. ReitzEngine Research Center

University of Wisconsin-Madison

UNIVERSITY OF WISCONSIN - ENGINE RESEARCH CENTER

Acknowledgements: Diesel Engine Research Consortium (DERC)DOE Sandia Labs & University Project EE0000202Sage Kokjohn, Derek Splitter, Reed Hanson

3rd MACCCR FUELS RESEARCH MEETINGPrinceton, NJ

September 20, 2010

2/23

Outline

• RCCI background

• Experimental engines - HD Caterpillar SCOTE- LD GM 1.9L SCE

• Results- RCCI for high efficiency, low emissions- Fuel effects

• Comparison of RCCI and conventional diesel

• Conclusions

3/23

• SI gasoline engine with 3-Way Catalyst: Thermal Efficiency ~30%

• Diesel engines are the most efficient engines in existence: Thermal Efficiency ~ 40-50%

• Widely used commercially• Can efficiencies be increased?

DOE “SuperTruck” Goal HD 55% BTE• Stringent emission standards

IC Engine thermal efficiency = work output/energy input

4/23

New combustion regimes

HCCI

High EfficiencyClean Regime

Cylinder Temperature [K]

Equ

ival

ence

Rat

io

0.0

0.5

1.0

1.5

2.0

1400 1600 1800 2000 2200 2400

NOx

Soot

CO HCCI

Requires precise charge preparation and combustion control mechanisms

(for auto-ignition and combustion timing)

KIVA Simulations – Park & Reitz CST 2007

*Singh, Musculus, Reitz: Combust&Flame, 2009

5/23

Diesel fuel ignites easily – difficult to vaporizeGood for low load premixed operationCauses combustion to occur too early at high load load limit

Gasoline is difficult to ignite – vaporizes easilyAllows extension to higher loadPoor combustion at low load

Both have benefits and drawbacks

What is the best fuel for kinetics controlled PCCI?

Dual-fuel CI combustion

Gasoline Diesel- Emissions regs. met in-cylinder- No Diesel Exhaust Fluid tank!

1. Diesel + O2 Ketone + ‘some’ heat 2. Ketone Products + heat

6/23SENKIN Predictions (ERC PRF chemistry mechanism): Po= 70 bar, Φ= 0.5

Fuel effects on ignition delay time – charge preparation

Adding varying amounts of gasoline to diesel could help control ignition time

40

7/23

CFD used for charge preparation optimization

Dual fuel operation

reactivity stratificationDirectinjectiondiesel

Port injected gasoline

Simulation tools• KIVA-3V CFD code• ERC grid independent

spray models• ERC PRF chemistry

mechanisms* (~44 species, 130 react)

• Multi-objective GeneticAlgorithm optimizationNSGA-II

• UW CONDOR 4,000computer pool

* Ra and Reitz, Combustion & Flame, In press., 2010

8/23

* Kokjohn et al. SAE 2009-01-2647

RCCI dual fuel – port gasoline, direct diesel injection

KIVA CFD plus Genetic Algorithm optimization used to choose injection parameters*

- Red: Gasoline (Iso-octane)- Blue: Diesel (n-heptane)- Green: optimum blend

80% gasoline/20% diesel- SOI1 ~ -60°ATDC- SOI2 ~ -33°ATDC- 60% of diesel fuel

in first injection

Gasoline

Diesel

9/23

Multiple injection strategy for dual-fuel RCCI combustion

*ENGINE COMBUSTION CONTROL VIA FUEL REACTIVITY STRATIFICATIONWARF US Patent Application: 09820924-P100054, 2/2010

Gasoline

Diesel

Gasoline-diesel“cocktail”

http://www.engr.wisc.edu/news/headlines/2009/Aug03.html

10/23

Reactivity Controlled Compression Ignition (RCCI)

• Combustion phasing controlled by most reactive regions: gasoline-to-diesel fuel ratio

• Combustion duration controlled by fuel reactivity gradient

• Low temperature combustion

-20 -15 -10 -5 0 5 10 15 201E-6

1E-5

1E-4

1E-3

co

oh

ch2o

nc7h16

ic8h18

HRR

Crank [°ATDC]

Mol

e Fr

actio

n [-]

Temp.

0

200

400

600

800

1000

1200

1400

1600

HR

R [J

/°] a

nd A

vera

ge T

empe

ratu

re [K

]

n-heptane iso-octane formaldehydeTemperature

11/23Single inject IMEP=5.5 bar, 2300 rev/min

Reactivity vs. Equivalence Ratio stratification

Controlled combustion timing and duration

12/23

Heavy- and light-duty experimental diesel enginesEngine Heavy Duty Light Duty

Engine CAT SCOTE GM 1.9 LDispl. (L/cyl) 2.44 0.477Bore (cm) 13.72 8.2Stroke (cm) 16.51 9.04Squish (cm) 0.157 0.133CR 16.1:1 15.2:1Swirl ratio 0.7 2.2IVC (°ATDC) -85 and -143 -132EVO(°ATDC) 130 112Injector type Common railNozzle holes 6 8Hole size (µm) 250 128

LDHD

Engine size scalingStaples et al.SAE 2009-01-1124

13/23

RCCI Experimental Validation - ERC Caterpillar SCOTE

IMEP (bar) 9

Speed (rpm) 1300

EGR (%) 43

Equivalence ratio (-) 0.5

Intake Temp. (°C) 32

Intake pressure (bar) 1.74

Gasoline (% mass) 76 82 89

Diesel inject press. (bar) 800

SOI1 (°ATDC) -58

SOI2 (°ATDC) -37

Fract. diesel in 1st pulse 0.62

IVC (ºBTDC)/Comp ratio 143/16

• Computer predictions confirmed!• Combustion timing and Pressure Rise Rate control with diesel/gasoline ratio

Effect of gasoline percentage

* Hanson et al. SAE 2010-01-0864

• Dual-fuel can be used to extend load limits of either pure diesel or gasoline

14/23

RCCI Experimental Validation - ERC Caterpillar SCOTE

IMEP (bar) 9

Speed (rpm) 1300

EGR (%) 43

Equivalence ratio (-) 0.5

Intake Temp. (°C) 32

Intake pressure (bar) 1.74

Gasoline (% mass) 76 82 89

Diesel inject press. (bar) 800

SOI1 (°ATDC) -58

SOI2 (°ATDC) -37

Fract. diesel in 1st pulse 0.62

IVC (ºBTDC)/Comp ratio 143/16

Not only improved fuel efficiency -ALSO NOx & soot below EPA 2010!No exhaust after-treatment required

• PRR < 10 bar/deg and net ISFC of 158 g/kW-hr!

Conventional diesel

15/23

Optical validation of RCCI – in-cylinder FTIR

2300 2700 3100 3500 3900

Reactants

A

Wavelength (nm)

-11 deg ATDCProducts

B

2300 2700 3100 3500 3900

Reactants

A

Wavelength (nm)

-7 deg ATDCProducts

B

2300 2700 3100 3500 3900

Reactants

A

Wavelength (nm)

-3 deg ATDCProducts

B

2300 2700 3100 3500 3900

Reactants

A

Wavelength (nm)

3 deg ATDCProducts

B

2300 2700 3100 3500 3900

Reactants

A

Wavelength (nm)

16 deg ATDCProducts

B

Fuel decomposition and combustion products form at slower rate at location B,extending combustion duration

Splitter et al. SAE 2010-01-0345

Squish

Bowl

16/23

Load sweep - gasoline/diesel and E85/diesel*

0 0

0.1

0.2

0.3 0.000

0.005

0.010

0.015

0.020140

150

160

170

180 0.45

0.50

0.55

0.60

2010 HD limit

NO

x (g

/kW

-hr)

2010 HD limit

PM (g

/kW

-hr)

E-85/diesel gasoline/diesel

ISFC

(g/k

W-h

r)

ηg (-

)

4 6 8 10 12 14 16 180.00.20.40.60.81.0

01020304050600

Φ (

−)

IMEPg (bar)

EGR

(%)

N O

* 9 bar optimum injection parameters usedSplitter et al. THIESEL, 2010

59% GITE• Use any two fuels with different reactivities

• US EPA 2010 HD emissions met in-cylinder without after-treatment, whileachieving ~53-59% thermal efficiency

• Stable combustion and phasing control atboth high and low engine loads with PRR <10 bar/deg.

17/23

Fuel Reactivity Effects

E-85 Gasoline

• 9.6 bar IMEPg condition• KIVA simulation PRF distribution,

just prior to combustion• E-85 increases reactivity

stratification

E85/Diesel

Gas/Diesel

18/23

Effect of fuel - RCCI GDI engine? Additized gasoline*

• Engine does not run without DTBP• DI gasoline plus 1.75% additive same

performance as DI dieselDTBP dosing ~0.2% of total fuel rate

• NOx, soot below EPA 2010• ISFC 145 g/kW-hr, 56% TE

* Splitter et al. 2010-01-2167

DI gasoline w/ cetane improver DTBP: di-tert-butyl peroxide

19/23

Outline

• RCCI background

• Experimental engines - HD Caterpillar SCOTE- LD GM 1.9L SCE

• Results- RCCI for high efficiency, low emissions- Fuel effects

• Comparison of RCCI and conventional diesel

Conclusions

20/23

Caterpillar SCOTE energy budgets (9 bar IMEP)

Fuel-MEP

Q-MEP

CL-MEP

HT-MEP

Ex-MEP

I-MEPg

I-MEPn

F-MEPBMEP

B F P Ex Ht C

I-MEPg

47% 48% 53% 55% 59%

36% 37% 34% 31% 26%

16% 14% 12% 12% 11%

Conv. Diesel: SAE 2009-01-1124; LTC Diesel: Hardy SAE 2006-01-0026; Gasoline PCCI: Hanson SAE 2009-01-1442 Dual fuel PCCI: Hanson SAE 2010-01-0864; E85 DF PCCI: Splitter THIESEL 2010

21/23

• Thermal efficiency improved by ~7% over conventional diesel combustion

– Reduced heat transfer loss compared to early injection conventional diesel

– Improved combustion phasing and end-of-combustion compared to late injection conventional diesel

• RCCI NOx and soot emissions are near zero due to highly dilute charge

Comparison of Conventional and RCCI Combustion

22/23

Temperature contours near CA50

Comparison of Conventional and RCCI Combustion

• High temperature in conventional diesel next to piston bowl surface

• Highest temperature for RCCI in center of chamber (adiabatic core)

• Region near liner has similar temperatures– Heat transfer differences are at piston bowl surface

23/23

• An optimized dual-fuel PCCI concept, RCCI, is proposed

• Port fuel injection of gasoline (cost effective) Direct injection of diesel or additized gasoline (low injection pressure). Diesel or GDI (w/spark plug) operation retained.

• RCCI engine experiments performed in HD and LD engines

• Near zero NOx and soot achieved in-cylinder in both engines

• High efficiency achieved in both engines (>50% TE)– However, heavy-duty engine has ~5% greater thermal efficiency

• Thermal efficiency improved via reduction in heat transfer losses and improvements in combustion phasing

• RCCI technology provides practical low-cost pathway to >20% improved fuel efficiency (lower CO2), while meeting emissions mandates in-cylinder

Summary and Conclusions