IM T
Improving the Spark-Ignition Engine
John B. HeywoodSun Jae Professor of Mechanical Engineering
Director, Sloan Automotive LaboratoryM.I.T.
Engine Research Center - 2005 SymposiumUniversity of Madison, Wisconsin
June 8-9, 2005
Theme
6/8/05
“Why can’t a spark-ignition engine be more like a diesel?”
2
Key Diesel Characteristics
6/8/05
1. High compression ratio
2. Operates lean
3. Operates unthrottled
4. Usually turbocharged
3
Contributors
6/8/05
Ferran Ayala, Mike Gerty, Josh Goldwitz,Ziga Ivanic, Bridget Revier, Dan Sandoval,Jenny Topinka
This presentation includes results from severalof my graduate students:
4
Comparison: Spark-Ignition and Diesel Engine
6/8/055
1. Lean operation vs. stoichiometric (EGR): Efficiency/emissions trade-off
2. Benefits of higher compression ratio
3. Reducing throttling losses
4. Turbocharging and downsizing
5. Dealing with knock constraint
Agenda: Improving the Spark-Ignition Engine
6/8/056
Definitions
6/8/057
Definitions (Continued)
6/8/058
SI Engine Friction
6/8/05
50
100
150
200
250
300
0 1000 2000 3000 4000 5000 6000 7000
Speed (rpm)
FM
EP
(kP
a)
Friction Model
Ford 2.0L engine
Mechanical plus accessory friction mep vs. speed (Sandoval, Ivanic)
9
1. Vehicle performance
• Maximum torque/brake power
• Vary engine displaced volume
bmep = x torque/displaced volume• Then,
imep = bmep + fmep
2. Simpler: Cylinder volume• Net imep constant
• Brake performance: subtract friction
Comparisons: What Hold Constant?
06/08/05
4!
10
6/8/05
1. Gasoline spark-ignition engine• Operate stoichiometric• Use three-way catalyst: 98% effective• Probably meet PZEV emissions
2. High-speed direct-injection diesel• Particulate and NOx exhaust treatment
technology?• “Active” control system required• Reducing agents for NOx: 5 % fuel penalty• Are PZEV levels feasible?
U.S. Emissions Requirements
11
Change Dilution:Air and/or EGR
06/08/0512
Lean, EGR: Effects on Burn Rate
06/08/05Source: Ayala
15
20
25
30
35
40
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Thermal Dilution Parameter (TDP)
10-9
0%
Bu
rn D
ura
tio
n (
CA
D)
Air
EGR
3.5 bar NIMEP
Rc=11.6
13
Lean, EGR: Effects on Efficiency, COV IMEP
06/08/05
Source: Ayala
0.28
0.29
0.30
0.31
0.32
0.33
0.34
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Thermal Dilution Parameter (TDP)
En
gin
e n
et
ind
ica
ted
eff
icie
nc
y
0
2
4
6
8
10
12
CO
V o
f N
IME
P (
%)
Efficiency - Air
Efficiency - EGR
COV - Air
COV - EGR
3.5 bar NIMEP
Rc=11.6
14
Explanation: Dilution Efficiency Limit
06/08/05
Source: Ayala15
25%
27%
29%
31%
33%
35%
37%
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
Relative Air/Fuel Ratio
Eff
icie
ncy
Lengthening Burn Duration
Gamma + Heat Transfer
Gamma + Heat Transfer + Pumping
DataAll Effects
Baseline Efficiency
Compression Ratio Effects
06/08/05
Change in net efficiency with compression ratio for arange of loads; (Gerty).! = 1.0
0.2
0.22
0.24
0.26
0.28
0.3
0.32
0.34
0.36
0.38
9 10 11 12 13 14
Rc
Ne
t In
dic
ate
d E
ffic
ien
cy
NIMEP = 2.0 bar, 1500 rpm
NIMEP = 2.0 bar, 2500 rpm
NIMEP = 4.0 bar, 1500 rpm
NIMEP = 4.0 bar, 2500 rpm
NIMEP = 8.0 bar, 1500 rpm
NIMEP = 8.0 bar, 2500 rpm
16
Compression Ratio, Boost, and Downsizing
06/08/05
Increases in net and brake efficiency with rc and boost, withEngine downsizing for constant max. torque. 2.6 bar bmep,1500 rpm, (Gerty).
0
2
4
6
8
10
12
9 10 11 12 13 14
Rc
Ch
an
ge in
Bra
ke E
ffic
ien
cy (
%)
Without Downsizing
With Downsizing
0
4
8
12
16
20
0 10 20 30 40 50
NIMEP Boost Level (%)
Ch
an
ge in
Eff
icie
ncy (
%)
Net Efficiency
Brake Efficiency
! = 1.017
1. Knock is the process that produces an audible(sharp, clanging) sound outside the engine.
2. Caused by rapid autoignition of the unburnedend-gas in a fraction of the engine’s cycles.
3. Onset first occurs at time of peak pressure.
4. Key variables are end-gas temperature,pressure and composition; time/speed; fueloctane rating.
Knock Constraint
6/8/0518
Knock: Sensitivity to Air and Fuel Flow
6/8/05
Octane requirement map: primary reference fuels (Topinka)19
6
7
8
9
10
11
12
13
0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Intake Manifold Pressure [bar]
IPW
[ms]
(mea
sure
of f
uel f
low
)
Constant OutputConstant FuelConstant MAPConstant Lambda
9696 10098
999896
94
90
92
92
85
90 Boxed Numbers = ONR
1. Significantly increases WOT bmep
2. At constant vehicle performance allows enginedownsizing
3. At typical part load (25% of max. torque), bmepis then higher
4. Part-load brake efficiency increases due toreduced pumping work AND increasedmechanical efficiency
Benefits of Turbocharging
6/8/0520
Benefits of Turbocharging (Continued)
6/8/05
Performance maps of naturally aspirated and turbochargedengines. (Gerty).21
Bm
ep, b
ar
1. Higher octane (e.g. premium) gasoline
2. With VVT, delay intake valve closing
3. Homogeneous gasoline direct injection
4. Variable compression ratio engine
5. Increase mixture octane with H2 plus CO fromon-board reformer
6. Direct injection of ethanol
Dealing with Knock
6/8/0522
Gains from Engine Boosting and Downsizing
6/8/05
Reduction Fuel economy, in Vd Test efficiency, gain
Study % cycle %
Ivanic (MIT) 30 U/H FTP 10 - 20
Gerty (MIT 30 light load 16
FEV (Lang, et al) 30 NEDC 15 - 22
Ricardo (Web) 10 - 30 engine data 6 - 17
IFP (Lecointe) 40 DI engine 25
“Average” 30 15 - 20
23
Diesel More Efficient Than SI Engine
6/8/05
Typical driving, diesel mpg some 50 percent higherthan SI engine mpg.
Higher fuel energy/gallon 8%Lean operation (above EGR) 5%Compression ratio higher 5%High levels of boost 20%Combustion efficiency 6%
_____
Total ~ 50%24
1. The biggest opportunity for improving the spark-ignition engine is boosting and downsizing.
2. Stoichiometric operation enables very low airpollutant emissions.
3. Many other design variables could contribute:e.g. increase compression ratio, variable valvecontrol, lower friction
4. The major challenge is controlling knock
5. 20 - 30% higher part-load efficiency plausible
Summary
6/8/0525
