Future Fuels and Reactivity Controlled Compression Ignition (RCCI ...

Future Fuels and Reactivity Controlled 

Compression Ignition (RCCI) 

Rolf D. Reitz, 

Reed M. Hanson, Sage L. Kokjohn, Derek A. Splitter, 

Adam Dempsey, Bishwadipa Das Adhikary, Sandeep 

Viswanathan, ERC Students and Staff 

Engine Research Center, University of 

Wisconsin-Madison 

Acknowledgments 

DERC Member Companies 

DOE/Sandia National Labs 

Oak Ridge National Labs 

June 9, 2011 

1 ERC Symposium - Future Engines and Their Fuels

Outline 

• RCCI combustion background 

• Experimental engines 

• Modeling and experimental results 

• Comparison of RCCI and conventional diesel 

• Use of renewable fuels – hydrated ethanol/diesel 

• Conclusions 


IC engine combustion regimes 

• Gasoline engine spark-ignition with flame propagation: 

High turbulence for high flame speed heat losses, NOx and UHC/CO 

knock (CR, fuels), throttling losses low thermal efficiency TE ~25% 

• Diesel engine with spray (diffusion) combustion: 

Rich mixtures (soot), high temperatures (NOx) higher TE ~45% 

• H/Premixed Charge Compression Ignition – LTC, chemistry controlled: 

Sensitive to fuel, poor combustion/load control, low NOx-soot TE ~50% 

spark-ignition 

diesel 

H/PCCI 


Dual fuel Reactivity Controlled Compression Ignition 

• Addition of second fuel allows 

significant control over autoignition 

characteristics 

• Optimized stratification of fuel 

reactivity allows control of 

combustion duration 

2˚ 

Single injection SOI = -55 o 

12% direct injected n-heptane, PRF=0 

88% premixed iso-octane, PRF=100 

8˚ 

IMEP=5.5 bar, 2300 rev/min 


RCCI combustion – Offers transient control 

• Heat release occurs in 3 stages (SAE 2010-01-0345) 

– Cool flame reactions result from n-heptane (diesel) injection 

– First energy release occurs where both fuels are mixed 

– Final energy release occurs where lower reactivity fuel is located 

• Changing fuel ratios changes relative magnitudes of stages 

• Fueling ratio provides “next cycle” CA50 transient control 

AHRR [J/ o ] 

200 

150 

100 

50 

0 

Cool Flame 

Primarly 

n-heptane 

PRF Burn 

n-heptane 

+ entrained 

iso-octane 

Iso-octane Burn 

-20 -10 0 10 20 

Crank [ o ATDC] 

Primarly 

iso-octane 

Delivery Ratio [% iso-octane] 

95 

90 

85 

80 

75 

70 

65 

60 

55 

♎ ♓␛♋♓ 

♎❄ CA50=2 ˚ ATDC 

♍ 

 

80 90 100 110 120 130 140 150 160 170 

Intake Temperature [ o C] 

RCCI 

SOI = -50 ATDC 

5 ERC Symposium - Future Engines and Their Fuels 

5

Multiple injections for optimized RCCI 

Port injected gasoline 

Direct injected diesel 

Gasoline 

Injection 

Signal 

Squish 

Conditioning 

-80 to -50 -45 to -30 

Crank Angle (deg. ATDC) 

KIVA plus Genetic Algorithms used 

to optimize multiple injection strategy 

Ignition 

Source 

Gasoline 

Diesel 

Diesel 


RCCI high speed 

combustion 

luminosity 

imaging 

Load: 4.2 bar IMEP 

Kokjohn, S. 

GDI SOI: -240°ATDC 

Musculus, M.P.B 

Speed: 1200 rpm CR SOI: -57°/-37°ATDC 

Reitz, R.D., 

Intake Temperature: 90°C 

ILASS-2011 

Equivalence ratio: 0.42 

Intake Pressure: 1.1 bar abs. Iso-octane mass %: 64 

Bowl window 

Squish (upper) window 


Heavy- and light-duty ERC experimental engines 

Engine Heavy Duty Light Duty 

Engine CAT SCOTE GM 1.9 L 

Displ. (L/cyl) 2.44 0.477 

Bore (cm) 13.72 8.2 

Stroke (cm) 16.51 9.04 

Squish (cm) 0.157 0.133 

CR 16.1:1 15.2:1 

Swirl ratio 0.7 2.2 

IVC (°ATDC) -85 and -143 -132 

EVO(°ATDC) 130 112 

Injector type 

Common rail 

Nozzle holes 6 8 

Hole size (µm) 250 128 

Engine size scaling 

Staples et al. 

SAE 2009-01-1124 

HD 

LD 


RCCI experimental validation 

- HD 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 1 st pulse 0.62 

IVC (ºBTDC)/Comp ratio 143/16 

Pressure [MPa] 

10 

8 

6 

4 

2 

Effect of gasoline percentage 

14 Experiment 

Simulation 

12 

Neat 

Diesel Fuel 

76% 

82% 

89% 

89% 

Gasoline 

Neat 

Gasoline 

0 

0 

-30 -20 -10 0 10 20 30 

Crank [°ATDC] 

* Hanson et al. 

SAE 2010-01-0864 

1400 

1200 

1000 

800 

600 

400 

200 

Apparent Heat Release Rate [J/°] 

• Computer modeling predictions confirmed 

• Combustion timing and Pressure Rise Rate control with diesel/gasoline ratio 

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


RCCI – high efficiency, low emissions, fuel flexibility 

• Indicated efficiencies of 59% 

achieved with E85/diesel 

• Emissions met in-cylinder, 

without need for after-treatment 

• Considerable fuel flexibility, 

including ‘single’ fuel operation 

• Diesel can be replaced with 

Comparison of conv. diesel and RCCI - KIVA CFD 

Pressure [bar] 

Average Temperature [K] 

140 

120 

100 

80 

60 

40 

20 


Diesel 

-20 

-16 

-12 

TDC 

0 

0 

-20 -15 -10 -5 0 5 10 15 20 25 30 

2700 

2400 

2100 

1800 

1500 

1200 

900 

9 bar IMEP, 

1300 rpm, 

41% EGR 

-20 

-8 

-4 


-16 

-12 

+4 

Diesel SOI 

Retard 

600 

-20 -15 -10 -5 0 5 10 15 20 25 30 

-8 

-4 


TDC 

+4 


Diesel 

1500 

1200 

900 

600 

300 

Heat Release Rate [J/°] 

Peak Temperature [K] 

• Sharp end-of-combustion 

• Peak temperatures reduced 

significantly compared to 

conventional diesel combustion 

• Difference between peak and 

average temperatures very small 

for RCCI combustion 

2700 

2400 

2100 

1800 

1500 

1200 

– Well mixed combustion event 

-20 

-16 

-12 

900 


Diesel 

600 

-20 -15 -10 -5 0 5 10 15 20 25 30 


-8 

-4 

TDC 

+4 

Crank [°ATDC]

Comparison of conv. diesel 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 

Temperature contours near CA50, Crank = 6.1 deg ATDC 


Comparison of conv. diesel and RCCI - KIVA CFD 

Gross Indicated Efficiency [%] 

57 

54 

51 

48 

45 

42 

39 

SOI -20° ATDC 


7% of 

fuel energy 

High EGR Diesel Pinj 800 bar 

High EGR Diesel Pinj 1800 bar 

RCCI Combustion 

-10 -5 0 5 10 15 20 25 

CA50 [°ATDC] 

RCCI: 

- Similar pressure rise rates 

- Significantly lower NOx and soot 

- 16% higher thermal efficiency 

- Reduced heat losses (~50%) 

- Improved end-of-combustion phasing 

Fuel Energy [%] 


(800 bar) 

High-EGR 

Diesel 

(1800 bar) 

Ringing (MW/m 2 ) 3.8 2.8 

Max PRR (bar/deg) 10.3 8.9 

Gross Indicate TE (%) 54.3 48.5 

Combustion Loss (%) 1.3 0.7 

ISNOx (g/kW-hr) 0.006 0.97 

ISsoot (g/kW-hr) 0.01 0.1 

100 

90 

80 

31.6 

41.5 

33.4 38.1 

70 

60 19.2 10.9 

50 

40 

54.3 61.9 

30 

57.9 

Comb. Loss 

48.5 

Exhaust 

20 

Heat Loss 

10 

GIE 

0 

With HT Adiabatic With HT Adiabatic 

SOI -12 o 13 ERC Symposium - Future Engines and Their Fuels 

High-EGR Diesel 

RCCI

Collaboration with Oak Ridge - Parks et al. DOE ACE031-2011 


RCCI low emissions – HC reduced with DOC 


Fuel flexibility and the future – renewable fuels 

“The fuel of the future is going to come from fruit like that sumac out by the 

road, or from apples, weeds, sawdust – almost anything. 

There is fuel in every bit of vegetable matter that can be fermented.” 

– Henry Ford, 1925 

http://www.energyfuturecoalition.org/biofuels/fact_ethanol.htm 

37% of fuel energy consumed 

in distillation-dehydration. 

Use of hydrated EtOH can give 

significant net energy gain 


16

Can “Wet” ethanol be used with RCCI? 

• Cannot be used with SI engines due to lower flame speeds, misfire, 

condensation problems, phase separation of water with EtOH-gasoline 

• Cannot be used with diesel engines due to high EtOH octane number 

• Has been proposed for use in HCCI engines – Berkeley, LLNL* 

High heat of vaporization: 

Gasoline = 308 kJ/kg 

EtOH = 924 kJ/kg 

H 2 O = 2400 kJ/kg 

GT-Power predicted 

IVC temperature 

- port injected wet 

ethanol/gasoline 

7 

o 

9 bar IMEP 

20 

o 

52 o 

compression 

*Flowers et al. “Improving Ethanol 

Life Cycle Energy Efficiency by Direct 

Utilization of Wet Ethanol in HCCI 

Engines, SAE 2007-01-1867 


Can “Wet” ethanol be used with RCCI? 

CHEMKIN HCCI simulations - mixtures of hydrated ethanol and 20% diesel 

5 bar 9 bar 

• Use constant intake 

temperature 

• Water mainly effects 

intake temperature 

13.5 bar 16 bar 

Dempsey et al. ASME 2011 


Fuel reactivity stratification - EtOH/H 

2 O & DI diesel 

KIVA CFD simulation 

1300 rpm, 9 bar IMEP 

Fuel reactivity stratification with 

premixed Wet ethanol and DI diesel 

Wet ethanol gives large 

reactivity gradients 

reduces pressure rise rate 


Cylinder pressure and heat release with EtOH/H 

2 O 

5 bar IMEP 

9 bar IMEP 

13.5 bar 16 bar 


Thermal efficiency &emissions with 70% EtOH/H 

2 O 

Diesel amount varied to control combustion phasing with 0% EGR 


21

Summary and conclusions 

RCCI offers practical low-cost pathway to >15% improved diesel 

engine fuel efficiency (lower CO 2 ) + meet emission mandates in-cylinder 

Inconvenience of two fuels already accepted by diesel industry (diesel/urea) 

RCCI is cost effective: 

- low cost port-injected less reactive fuel (e.g., gasoline, E85, “wet” EtOH, C/LNG) 

with optimized* low pressure DI of more-reactive fuel (e.g., diesel/additized gas) 

- Diesel or GDI (w/spark plug) operation can be retained (limp home). 

RCCI offers great fuel flexibility and transient response: 

- proportions of low and high reactivity fuels can be changed dynamically, based 

on fuels used with same/next-cycle combustion feedback control 

RCCI can be used with alternative fuels, including hydrated “wet” ethanol 

- significantly shifts net energy gain of bio-ethanol fuel production 

(75% of total distillation energy to remove last 20% of water in EtOH/H 2 O) 

- intake charge cooled significantly less charge air cooling with boosting 

- combustion is retarded due to water addition less EGR required 

- with a single grade of hydrated ethanol (70% ethanol-in-water) and 0% EGR, 

low NOx and soot predicted from 5 to 16 bar IMEP with peak GTE > 55% 

* WARF Patents pending 


Future Engines and their Fuels in Sweden – today! 

http://www.greencarcongress.com/2011/05/volvo-20110531.html 


Thank you for your attention! 


Thermal efficiency &emissions with 70% EtOH/H 

2 O 

EGR varied to control combustion phasing with 20% diesel injection 


25

RCCI particulate matter reduced by DOC 


RCCI low particle number – by 2 orders of magnitude 


RCCI – provides high efficiency, low emissions 

HD engine gasoline/diesel 

RCCI gives near zero NOx 

and soot and peak gross 

thermal efficiency of 56% 

Pressure [bar] 

AHRR [J/deg] 

140 

120 

100 

80 

60 

40 

20 

0 

Experiment = Solid 

Simulation = Dash 

800 4.6 bar 

700 

600 

500 

400 

5.9 bar 

9.3 bar 

11.6 bar 

14.6 bar 

300 

200 

100 

0 

-20 -15 -10 -5 0 5 10 15 20 25 30 


Kokjohn et al. IJER 2011 

Hanson et al. SAE 2010-01-0864 

Splitter et al. THIESEL 2010 

NOx 

[g/kW-hr] 

Soot 

[g/kW-hr] 

Gross Ind. 

Efficiency [%] 

Ringing Int. 

[MW/m 2 ] 

1300 rev/min 

0.3 

0.2 

0.1 

0.0 

0.02 

0.01 

0.00 

56 

54 

52 

50 

48 

4 

2 

0 

2010 EPA HD Limit 

2010 EPA HD Limit 

Experiment 

Simulation 

4 6 8 10 12 14 16 

IMEPg [bar]

Future Fuels and Reactivity Controlled Compression Ignition (RCCI ...

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