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1 DEER 10/18/2012
Comparison of Conventional Diesel and
Reactivity Controlled Compression Ignition
(RCCI) Combustionin a Light-Duty Engine
Rolf D. Reitz and Sage L. Kokjohn
Engine Research Center,
University of Wisconsin-Madison
2012 Directions in Engine-Efficiency
and Emissions Research
(DEER) Conference
(Thursday, October 18th )
Acknowledgements: DOE Sandia labs,
Direct-injection Engine Research Consortium
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2 DEER 10/18/2012
HCCI Combustion offers high efficiency & low PM and NOxemissions, but is sensitive to fuel properties, is limited to low
load and has no direct means to control combustion phasing Control can be provided by varying fuel reactivity using TWO
fuels with different reactivities - dual-fuel PCCI = RCCI:
Port fuel injection of gasoline
(mixed with intake air, as in spark-ignition engines)
Multiple direct-injections of diesel fuelinto combustion
chamber later during compression (as in diesel engines)
Optimized fuel blending in-cylinder
Reactivity Controlled Compression Ignition - RCCI
Gasoline Diesel
- Emissions regs. met in-cylinder- No Diesel Exhaust Fluid tank!
H/PCCI RCCI
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3 DEER 10/18/2012
Direct injected dieselPort injected gasoline
Diesel-80 to -50 -45 to -30
Crank Angle (deg. ATDC)
Injection
Signal Squish
Conditioning
Ignition
Source
Gasoline
Diesel
Gasoline
Optimized Reactivity Controlled Compression Ignition
CFD plus Genetic Algorithms used
to optimize multiple injection strategy
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Dual fuel RCCI combustion controlled HCCI
Heat release occurs in 3 stages
Cool flame reactions from diesel (n-heptane) injectionFirst energy release where both fuels are mixed
Final energy release where lower reactivity fuel is located
Changing fuel ratios changes relative magnitudes of stages
Fueling ratio provides next cycle CA50 transient control
4
-20 -10 0 10 200
50
100
150
200
Crank [
o
ATDC]
AHRR
[J/o]
Primarlyiso-octane
n-heptane+ entrained iso-octane
Iso-octane BurnPRF BurnCool Flame
Primarly n-heptane
80 90 100 110 120 130 140 150 160 17055
60
65
70
75
80
85
90
95
Intake Temperature [o
C]
DeliveryRatio
[%iso-octane]
d(Deli ver yRatio)
d(I nt:Temp:) = 0:4
per cent
K
CA50=2ATDC
RCCI
SOI = -50 ATDC
RCCI
4 DEER 10/18/2012
Kokjohn, IJER 2011
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Compare conventional diesel
combustion (CDC) and Reactivity
Controlled Compression Ignition(RCCI) combustion
Same operating conditions
(CR, boost, IMT, swirl..)
ERC KIVA-Chemkin Code- Reduced PRF model for diesel
and gasoline kinetics
- Improved ERC spray models
Base engine GM 1.9 LBore (mm) 82Stroke (mm) 90.4Connecting rod (mm) 145.5
Squish height (mm) 0.617Displacement (L) 0.4774Compression ratio 16.7:1Swirl ratio 1.5 - 3.2IVC (ATDC) -132
EVO (ATDC) 112
TypeBosch common
railIncluded angle 155Number of holes 7
Hole size (m) 141
Engine specifications
Diesel fuel injector specifications
Combustion chamber geometry
Light-duty automotive drive-cycle performance
Kokjohn, PhD thesis 2012
5 DEER 10/18/2012
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6 DEER 10/18/2012
1000 1500 2000 2500 30000
2
4
6
8
10
12
Speed [rev/min]
IMEP
g[bar]
4
32
5
1
Five operating points of Ad-
hoc fuels working group
Tier 2 bin 5 NOx targets from:
(assumes 3500lb Passenger Car)
Evaluate NOx / fuel efficiency
tradeoff using SCR for CDCAssumptions
Diesel exhaust fluid (DEF)
consumption 1% per g/kW-hr
NOx reduction
No DPF regeneration penalty
UHC and CO only lead to
reduced work
Size shows
weighting
Mode Speed(rpm) IMEP(bar)
CDC
Baseline
NOx (g/kgf)*
NOx
Target(g/kgf)
1 1500 2 1.3 0.2
2 1500 3.9 0.9 0.4
3 2000 3.3 1.1 0.3
4 2300 5.5 8.4 0.6
5 2600 9 17.2 1.2*Baseline CDC Euro 4: SAE 2012-01-0380
Comparison between RCCI and Conventional Diesel
Cooper, SAE 2006-01-1145
Johnson, SAE 2011-01-0304
Ad-hoc fuels working group
SAE 2001-01-0151
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CDC Operating Conditions *
Mode 1 2 3 4 5
IMEPg (bar) 2.3 3.9 3.3 5.5 9Speed (rev/min) 1500 1500 2000 2300 2600
Total Fuel (mg/inj) 5.6 9.5 8 13.3 20.9
Intake Temp. (C) 60 60 70 67 64
Intake Press. (bar abs) 1 1 1 1.3 1.6
EGR Rate (%) 47 38 42 25 15CR Inj. Pressure (bar) 330 400 500 780 1100
Pilot SOI ( ATDC) -5.8
-7.2
-8.2
-11.7
-15.4
Main SOI ( ATDC) 1.6 0 1.6 -0.1 -2.6
DI fuel in Pilot (%) 34 16 15 10 5
Euro 4 operating conditions - Conventional Diesel
Model validation
*Baseline CDC Euro 4: SAE 2012-01-0380
-30 -20 -10 0 10 20 30 40 50
0
20
40
60
80
100
Crank [deg. ATDC]
CylinderPressure[bar]
Experiment
Simulation
0 -20 -10 0 10 20 30 40 50
Crank [deg. ATDC]
0
20
40
60
80
100
AHRR[J/deg.]
Experiment
Simulation
-30 -20 -10 0 10 20 30 40 50
0
10
20
30
40
50
60
Crank [deg. ATDC]
CylinderPressure[bar]
Experiment
Simulation
0 -20 -10 0 10 20 30 40 50
Crank [deg. ATDC]
0
10
20
30
40
50
60
AHRR[J/deg.]
Experiment
Simulation
Mode 4 Mode 5Mode 3Mode 2
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EINOx EISoot0
0.5
1
1.5
2
2.5
3
3.5
CycleEINOxandEISoot[g/k
gf]
Experiment
Simulation
8 DEER 10/18/2012
Comparison at 5 Modes
5
imode imode
imode=1
5
imodeimode=1
cycle
E Weight
E
Weight
=
Weighted
average:
Cycle average emissions and performance
Tier 2 Bin 5
-20 -10 0 10 20 30 40
0
20
40
60
80
100
Crank [deg. ATDC]
CylinderPressure
[bar]
0
20
40
60
80
100
AHRR[J/deg.]
Experiment-Euro 4
Simulation - Euro 4
CDC - Peak GIE
Optimized CDC with SCR for Tier 2 Bin 5
CDC optimized
GIE has higherallowable PPRR
(advanced SOI)
than Euro 4
calibration
Mode 3
Model Validation (Euro 4)
0
10
20
30
EINOx[g/kgf]
0
0.5
1
EISoot[g/k
gf]
1 2 3 4 530
35
40
45
GIE[%]
Mode
ExperimentSimulation
GIE30
32
34
36
38
40
42
CycleGIE[%]
Experiment
Simulation
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CDC (with SCR)
Main injection timing swept
DEF consumption 1% per 1
g/kW-hr reduction in NOx
Peak efficiency at tradeoffbetween fuel consumption (SOI
timing) and DEF consumption
(engine-out NOx)
( )180 to 180
100*
Total
DEF Fuel Fuel
WorkGIE
m m LHV
=
+
CDC optimization with SCR
Comparison between RCCI and CDC plus SCR
Euro 4
RCCI (No SCR needed)
Gasoline amount controls CA50
to meet NOx/PRR constraints
Mode 1 uses diesel LTC (no
gasoline and EGR)
Mode 5 has EGR for CA50 control
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RCCI meets NOx Tier 2 Bin 5 targets
without DEF
DEF NOx after-treatment has smallefficiency penalty at light-load and
moderate EGR (~40%)
DEF penalty larger above 5 bar IMEP
Comparison of Efficiency, NOx and PRR
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RCCI and CDC compared at
baseline and Tier 2 Bin 5 NOx
CDC NOx-GIE tradeoff controlled
by main injection timing
RCCI meets NOx targets without
after-treatment
RCCI gives ~7% improvement infuel consumption over CDC+SCR
RCCI soot is an order of magnitude
lower than CDC+SCR
RCCI HC is ~5 times higher thanCDC+SCR
Crevice-originated HC emissions
Cycle averaged NOx, Soot and GIE
Splitter, SAE 2012-01-0383
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LD RCCI improved by relaxing constraints (Euro 4 boost, IMT, swirl..)
Peak efficiency at Mode 5 is 46.1%CFD predicts increase to ~53%
7% + 15% ~ DOE goals of 20-40% improvement
Higher boost (1.86 bar vs. 1.6 bar) allows CA50 advance with same
PRR, lowers heat transfer losses due to lower (lower temps)
Lower swirl reduces convective heat transfer losses
Higher wall temps improve combustion efficiency (steel piston)
Future research directions
15 bar/11 bar/ 8.8 bar/
6.7 bar/
9.4bar/
Selected
15 bar/
Numbers show
Peak PRR
18 bar/
15%
Kokjohn,
PhD thesis
2012
Mode 5
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RCCI yields clean, quiet, and efficient combustion over wide
load/speed ranges (HD: 4 to 23 bar IMEP, 800 to 1800 rev/min).
HD: EPA 2010 NOx/PM emissions met in-cylinder with GIE >55%
LD: Low NOx and PM emissions with less EGR over FTP cycle.
Suggested RCCI strategy: Optimized high EGR CDC combustion
at low load (idle) and no EGR up to Mode 5 (~9 bar IMEP).
RCCI LD modeling indicates ~7% improved fuel consumptionover CDC+SCR over FTP cycle using same engine/conditions.
RCCI meets Tier 2 bin 5 without needing NOx after-treatment or
DPF, but DOC will likely be needed for UHC reduction
Further RCCI optimization possible with:higher boost pressure, higher piston temps,
reduced swirl, surface area, optimized crevice
RCCI experiments/modeling: optimized pistons,
alternative fuels .. and vehicle testing!
Summary and Conclusions
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CDC and RCCI efficiency sensitive to selected value of peak PRR
Maximum allowable PRR of CDC points set at 1.5 times higher than for RCCI
Comparison between RCCI and Conventional Diesel
CDC RCCI CDC RCCI CDC RCCI CDC RCCI CDC RCCI
Mode 1 2 3 4 5
IMEPg (bar) 2.3 3.9 3.3 5.5 9
Speed (rev/min) 1500 1500 2000 2300 2600
Total Fuel (mg/inj.) 5.6 9.5 8 13.3 20.9
Intake Temp. (deg. C) 60 60 70 67 64Intake Press. (bar abs.) 1 1 1 1.3 1.6
EGR Rate (%) 47 61 38 0 42 0 25 0 15 36
Premixed Gasoline (%) 0 0 0 80 0 55 0 80 0 89
CR Inj. Pressure (bar) 330 500 400 500 500 500 780 500 1100 500
SOI ( ATDC) Baseline-5.8/
1.6
-33/
-8
-7.2/
0
-58/
-37
-8.2/
1.6
-58/
-37
11.7/
0
-58/
-37
-18.6/
-2.6
-58/
-37
SOI ( ATDC) Peak GIE-14.4/
-6N/A
-20.2/
-5N/A
-15.8/
-6N/A
-17.6/
-6N/A
-23/
-7N/A
Percent of DI fuel in Pilot 20 42 15 60 15 60 10 0 10 60
DEF (%) 0.9 0 0.8 0 0.7 0 3 0 4.6 0
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RCCI Model Validation
IMEPg (bar) 9
Speed (rev/min)
1900
Total Fuel (mg/inj.) 20
Intake Temp. (deg. C)
36
Intake Press. (bar abs.) 1.86
EGR Rate (%)
41
CR Inj. Pressure (bar) 500
Pilot SOI (CA) (actual) -56
Main SOI (ATDC) (actual) -35
Percent of DI fuel in Pilot (%)
60%
Kokjohn et al. SAE 2011-01-0375
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