Comparison between RCCI and Conventional Diesel. Cooper ... oot [g/k gf]. Experiment. Simulation. 8. DEER 10/18/2012. Comparison at 5 Modes. 5 imode.
Comparison of Conventional Diesel and Reactivity Controlled Compression Ignition (RCCI) Combustion in 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 1
DEER 10/18/2012
Reactivity Controlled Compression Ignition - RCCI • HCCI Combustion offers high efficiency & low PM and NOx emissions, 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 fuel into combustion chamber later during compression (as in diesel engines) – Optimized fuel blending in-cylinder H/PCCI
- Emissions regs. met in-cylinder - No Diesel Exhaust Fluid tank!
RCCI
2
DEER 10/18/2012 Gasoline Diesel
Optimized Reactivity Controlled Compression Ignition Port injected gasoline
Direct injected diesel
Gasoline
Injection Signal
Gasoline
Squish Conditioning
-80 to -50
Ignition Source Diesel
-45 to -30
Crank Angle (deg. ATDC)
Diesel
CFD plus Genetic Algorithms used to optimize multiple injection strategy 3
DEER 10/18/2012
Dual fuel RCCI combustion – controlled HCCI Kokjohn, IJER 2011
Heat release occurs in 3 stages Cool flame reactions from diesel (n-heptane) injection First 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
AHRR [J/o]
150
95 Cool Flame
PRF Burn
Primarly n-heptane
n-heptane + entrained iso-octane
Iso-octane Burn
Delivery Ratio [% iso-octane]
200
Primarly iso-octane
100 50 0
RCCI
-20
-10
0 o Crank [ ATDC]
10
90 85 80 75 70 65
4
RCCI SOI = -50 ATDC
60 55
20
d( D el i ver yRati o) = 0 4 per cent : d(CA50=2 I nt:Temp:) ˚ ATDC K
80
90
100 110 120 130 140 150 160 170 4 Intake Temperature [oC]
DEER 10/18/2012
Light-duty automotive drive-cycle performance • 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 Diesel fuel injector specifications Bosch common rail Included angle 155° Number of holes 7 Hole size (µm) 141 Type
5
Kokjohn, PhD thesis 2012
Combustion chamber geometry
Engine specifications Base engine Bore (mm) Stroke (mm) Connecting rod (mm) Squish height (mm) Displacement (L) Compression ratio Swirl ratio IVC (°ATDC) EVO (°ATDC)
GM 1.9 L 82 90.4 145.5 0.617 0.4774 16.7:1 1.5 - 3.2 -132° 112°
DEER 10/18/2012
Comparison between RCCI and Conventional Diesel
Cooper, SAE 2006-01-1145 (assumes 3500lb Passenger Car)
• Evaluate NOx / fuel efficiency tradeoff using SCR for CDC Assumptions • Diesel exhaust fluid (DEF) consumption 1% per g/kW-hr NOx reduction
12 10
IMEPg [bar]
• Five operating points of Adhoc fuels working group • Tier 2 bin 5 NOx targets from:
8 6
Ad-hoc fuels working group SAE 2001-01-0151
4
4
2
2
1
0
5
Size shows weighting
1000
Speed Mode (rpm) Johnson, SAE 2011-01-0304 1 1500 • No DPF regeneration penalty 2 1500 • UHC and CO only lead to 3 2000 4 2300 reduced work 5 2600 *Baseline CDC Euro 4: SAE 2012-01-0380 6
3
1500 2000 Speed [rev/min]
IMEP (bar) 2 3.9 3.3 5.5 9
2500
3000
CDC Baseline NOx NOx (g/kgf) Target * (g/kgf) 1.3 0.2 0.9 0.4 1.1 0.3 8.4 0.6 17.2 1.2
DEER 10/18/2012
Euro 4 operating conditions - Conventional Diesel
50
Mode 2
Mode 3
6
Experiment Simulation
5
2 3.9 1500 9.5 60 1 38 400 -7.2 0 16 60
Experiment Simulation
4
40
30
3
30
20
2
20 10
10
0
0
0 -30
100
50
40
-20
-10
0 10 20 30 Crank [deg. ATDC]
40
50
30
-20
-10
0 10 20 30 Crank [deg. ATDC]
40
3 3.3 2000 8 70 1 42 500 -8.2 1.6 15
50
*Baseline CDC Euro 4: SAE 2012-01-0380 7
Mode 4
80
4 5.5 2300 13.3 67 1.3 25 780 -11.7 -0.1 10
Experiment Simulation
Mode 5
5 9 2600 20.9 64 1.6 15 1100 -15.4 -2.6 5 100
Experiment Simulation
80
60
60
40
40
20
20
0 -30
0 -20
-10
0 10 20 30 Crank [deg. ATDC]
40
5030
-20
-10
0 10 20 30 Crank [deg. ATDC]
DEER 10/18/2012
40
50
AHRR [J/deg.]
Cylinder Pressure [bar]
60
1 2.3 1500 5.6 60 1 47 330 -5.8 1.6 34
Cylinder Pressure [bar]
Mode IMEPg (bar) Speed (rev/min) Total Fuel (mg/inj) Intake Temp. (C) Intake Press. (bar abs) EGR Rate (%) CR Inj. Pressure (bar) Pilot SOI (° ATDC) Main SOI (° ATDC) DI fuel in Pilot (%)
CDC Operating Conditions *
AHRR [J/deg.]
Model validation
Model Validation (Euro 4) Cycle average emissions and performance Cycle EINOx and EISoot [g/kgf]
Experiment Simulation
20 10
EISoot [g/kgf]
0 1
0.5
3
40
2.5 2
Tier 2 Bin 5
1.5 1
Experiment Simulation
38 36 34 32
0.5 0
30
EISoot
EINOx
GIE
Optimized CDC with SCR for Tier 2 Bin 5
0
100
40 35 30 1
2
Weighted average:
3 Mode
4 5
Ecycle =
∑
5
Cylinder Pressure [bar]
45 GIE [%]
42
Experiment Simulation
Experiment-Euro 4 Simulation - Euro 4 CDC - Peak GIE
80
100
Mode 3
80
60
60
40
40
20
20
0
0
EimodeWeightimode
imode=1 5
∑
imode=1
Weightimode
-20
-10
8
20 10 0 Crank [deg. ATDC]
30
AHRR [J/deg.]
EINOx [g/kgf]
30
3.5
Cycle GIE [%]
Comparison at 5 Modes
CDC optimized GIE has higher allowable PPRR (advanced SOI) than Euro 4 calibration
40
DEER 10/18/2012
Comparison between RCCI and CDC plus SCR CDC (with SCR) • Main injection timing swept DEF consumption 1% per 1 g/kW-hr reduction in NOx GIETotal
CDC optimization with SCR
Euro 4
Work−180 to 180 × 100 ( mDEF + mFuel ) * LHVFuel
• Peak efficiency at tradeoff between fuel consumption (SOI timing) and DEF consumption (engine-out NOx) 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
9
DEER 10/18/2012
Comparison of Efficiency, NOx and PRR RCCI meets NOx Tier 2 Bin 5 targets without DEF DEF NOx after-treatment has small efficiency penalty at light-load and moderate EGR (~40%) DEF penalty larger above 5 bar IMEP
10
DEER 10/18/2012
Cycle averaged NOx, Soot and GIE 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 in fuel consumption over CDC+SCR RCCI soot is an order of magnitude lower than CDC+SCR RCCI HC is ~5 times higher than CDC+SCR Crevice-originated HC emissions Splitter, SAE 2012-01-0383 11
DEER 10/18/2012
Future research directions 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 Φ (lower temps) – Lower swirl reduces convective heat transfer losses – Higher wall temps improve combustion efficiency (steel piston) 15 bar/°
11 bar/° 8.8 bar/° 6.7 bar/°
15%
15 bar/° 18 bar/°
Mode 5
Numbers show Peak PRR
9.4bar/° Selected
12
Kokjohn, PhD thesis 2012
DEER 10/18/2012
Summary and Conclusions • 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 consumption over 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! 13
DEER 10/18/2012
Comparison between RCCI and Conventional Diesel 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 Mode IMEPg (bar) Speed (rev/min) Total Fuel (mg/inj.) Intake Temp. (deg. C) Intake Press. (bar abs.) EGR Rate (%) Premixed Gasoline (%) CR Inj. Pressure (bar)
CDC
RCCI
1 2.3
2 3.9
CDC
RCCI
3 3.3
CDC
RCCI
4 5.5
CDC
5 9
RCCI
1500
2000
2300
2600
5.6 60 1
9.5 60 1
8 70 1
13.3 67 1.3
20.9 64 1.6
61 0 500 -33/ -8
Percent of DI fuel in Pilot
20
DEF (%)
0.9
SOI (° ATDC) Peak GIE
RCCI
1500
47 0 330 -5.8/ 1.6 -14.4/ -6
SOI (° ATDC) Baseline
CDC
38 0 400 -7.2/ 0 -20.2/ -5
0 80 500 -58/ -37
42
15
0
0.8
N/A
42 0 500 -8.2/ 1.6 -15.8/ -6
0 55 500 -58/ -37
60
15
0
0.7
N/A
14
25 0 780 11.7/ 0 -17.6/ -6
0 80 500 -58/ -37
60
10
0
3
N/A
15 0 1100 -18.6/ -2.6 -23/ -7
36 89 500 -58/ -37
0
10
60
0
4.6
0
N/A
DEER 10/18/2012
N/A
RCCI Model Validation IMEPg (bar) Speed (rev/min) Total Fuel (mg/inj.) Intake Temp. (deg. C) Intake Press. (bar abs.) EGR Rate (%) CR Inj. Pressure (bar) Pilot SOI (°CA) (actual) Main SOI (° ATDC) (actual) Percent of DI fuel in Pilot (%)
Kokjohn et al. SAE 2011-01-0375
15
9 1900 20 36 1.86 41 500 -56 -35 60%
DEER 10/18/2012