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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


2/15

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


3/15

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


4/15

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


5/15

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


7/15 7 DEER 10/18/2012

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


8/15

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


9/15 9 DEER 10/18/2012

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


10/15 10 DEER 10/18/2012

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


11/15 11 DEER 10/18/2012

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


12/15 12 DEER 10/18/2012

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


13/15 13 DEER 10/18/2012

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


14/15 14 DEER 10/18/2012

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


15/1515 DEER 10/18/2012

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

deer12 reitz

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