The Evolution of the Internal
Combustion Engine and Future
Design Challenges:
Performance, Efficiency, Emissions
Paul D. Ronney
Dept. of Aerospace & Mechanical Eng.
University of Southern California
Los Angeles, CA 90089-1453 USA
http://carambola.usc.edu
Outline
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Why gasoline-fueled premixed-charge IC engines?
History and evolution
Things you need to understand about IC engines before ...
Ideas for improvements
Conclusions
University of Southern California - Department of Aerospace and Mechanical Engineering
Why premixed-charge IC engines?
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Alternatives
• External combustion - "steam engine," "Stirling cycle"
» Heat transfer is too slow (≈ 100x slower than combustion)
» 10 B-747 engines ≈ large coal-fueled electric power plant
• Electric vehicles (EVs)
» Batteries are heavy ≈ 1000 lbs/gal of gasoline equivalent
» Fuel cells better, but still nowhere near gasoline
» "Zero emissions" myth - EVs export pollution
» Environmental cost of battery materials
» Possible advantage: makes smaller, lighter, more
streamlined cars acceptable to consumers
» Prediction: eventual conversion of electric vehicles to
gasoline power (>100 miles per gallon)
University of Southern California - Department of Aerospace and Mechanical Engineering
“Zero emission” electric vehicles
University of Southern California - Department of Aerospace and Mechanical Engineering
Why premixed-charge IC engines?
• Alternatives (continued…)
• Solar
» Need ≈ 30 ft x 30 ft collector for 15 hp (Arizona, high
noon, mid-summer)
• Nuclear
» Who are we kidding ???
• Moral - hard to beat gasoline-fueled IC engine for
• Power/weight & power/volume of engine
• Energy/weight & energy/volume of liquid hydrocarbon fuel
• Distribution & handling convenience of liquids
University of Southern California - Department of Aerospace and Mechanical Engineering
History and evolution
• 1859 - Oil discovered in Pennsylvania
• 1876 - Premixed-charge 4-stroke engine - Otto
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1st practical IC engine
Power: 2 hp; Weight: 1250 pounds
Comp. ratio = 4 (knock limited), 14% efficiency (theory 38%)
Today CR = 8 (still knock limited), 30% efficiency (theory 52%)
• 1897 - Nonpremixed-charge engine - Diesel - higher efficiency
due to
• Higher compression ratio (no knock problem)
• No throttling loss - use fuel/air ratio to control power
University of Southern California - Department of Aerospace and Mechanical Engineering
Premixed vs. non-premixed charge engines
Spark plug
Flame front
Fuel + air mixture
Premixed charge
(gasoline)
Fuel injector
Fuel spray flame
Air only
Non-premixed charge
(Diesel)
University of Southern California - Department of Aerospace and Mechanical Engineering
History and evolution
• 1923 - Tetraethyl lead - anti-knock additive
• Enable higher CR in Otto-type engines
• 1952 - A. J. Haagen-Smit
• NO + UHC +
(from exhaust)
O2 + sunlight  NO2 +
O3
(brown) (irritating)
• 1960s - Emissions regulations
• Detroit won’t believe it
• Initial stop-gap measures - lean mixture, EGR, retard spark
• Poor performance & fuel economy
• 1973 & 1979 - The energy crises
• Detroit takes a bath
University of Southern California - Department of Aerospace and Mechanical Engineering
History and evolution
• 1975 - Catalytic converters, unleaded fuel
• Detroit forced to buy technology
• More “aromatics” (e.g., benzene) in gasoline - high octane but
carcinogenic, soot-producing
• 1980s - Microcomputer control of engines
• Tailor operation for best emissions, efficiency, ...
• 1990s - Reformulated gasoline
• Reduced need for aromatics, cleaner(?)
• ... but higher cost, lower miles per gallon
• Now we find MTBE pollutes groundwater!!!
University of Southern California - Department of Aerospace and Mechanical Engineering
Things you need to understand before ...
…you invent the zero-emission, 100 mpg 1000 hp
engine, revolutionize the automotive industry and
shop for your retirement home on the French Riviera
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Room for improvement - factor of 2 in efficiency
• Ideal Otto cycle engine with CR = 8: 52%
• Real engine: 25 - 30%
• Differences because of
» Throttling losses
» Heat losses
» Friction losses
University of Southern California - Department of Aerospace and Mechanical Engineering
Things you need to understand before ...
• Room for improvement - infinite in pollutants
• Pollutants are a non-equilibrium effect
» Burn: Fuel + O2 + N2  H2O + CO2 + N2 + CO + UHC + NO
OK OK OK Bad Bad Bad
» Expand: CO + UHC + NO “frozen” at high levels
» With slow expansion, no heat loss:
CO + UHC + NO  H2O + CO2 + N2
...but how to slow the expansion and eliminate heat loss?
• Worst problems: cold start, transients, old or out-of-tune
vehicles - 90% of pollution generated by 10% of vehicles
University of Southern California - Department of Aerospace and Mechanical Engineering
Things you need to understand before ...
• Room for improvement - very little in power
• IC engines are air processors
» Fuel takes up little space
» Air flow = power
» Limitation on air flow due to
• “Choked” flow past intake valves
• Friction loss, mechanical strength - limits RPM
• Slow burn
• Majority of power is used to overcome air resistance smaller, more aerodynamic vehicles beneficial
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas for improvement - alternative fuels
• Natural gas
+ Somewhat cleaner than gasoline, non-toxic
+ High octane without refining or additives (≈ 110)
+ No cold start problem
+ Abundant, domestic supply
+ Cheap (≈ 1/5 gasoline)
+ Half the CO2 emission of EVs charged with coal-generated
electricity
+ Dual-fuel (gasoline + natural gas) easily accommodated
- Lower energy storage density (≈ 1/4 gasoline)
- Lower power (≈ 7% less)
Attractive for fleet vehicles with limited territory
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas for improvement - alternative fuels
• Alcohols
+ Slightly cleaner than gasoline
+ High octane (≈ 95)
- Not cost-effective without price subsidy
- Lower storage density (methanol ≈ 1/2 gasoline)
- Toxic combustion products (aldehydes)
Attractive to powerful senators from farm states
• Hydrogen
+ Ultimate clean fuel
+ Excellent combustion properties
+ Ideal for fuel cells
- Very low storage density (1/10 gasoline)
- Need to manufacture - usually from electricity + H2O
Attractive when we have unlimited cheap clean source of
electricity and breakthrough in hydrogen storage technology
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas for improvements - reduce heat loss
• Reduction of heat losses
• Heat losses caused by high engine turbulence levels
• Need high turbulence to
» Wrinkle flame (premixed charge, gasoline)
» Disperse fuel droplets (nonpremixed charge, Diesel)
• "Inverse-engineer" engine for low-turbulence
» Gasoline - electrically-induced flame wrinkling?
» Diesel - electrostatic dispersion of fuel in chamber?
University of Southern California - Department of Aerospace and Mechanical Engineering
Electrostatic sprays
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas - reduce throttling loss
• Premixed-charge IC engines frequently operated at lower
than maximum torque output (throttled conditions)
• Throttling adjusts torque output of engines by reducing
intake density through decrease in pressure ( P = rRT)
• Throttling losses substantial at part load
1
Efficiency (throttled) /
Efficiency (no throttle)
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
Fraction of maximum load
0.8
1
University of Southern California - Department of Aerospace and Mechanical Engineering
The TPCE concept
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Throttleless Premixed-charge Engine (TPCE)
U. S. Patent No. 5,184,592
Supported by SCAQMD School Clean Fuels Program
Preheat air using exhaust heat transfer to reduce r
Preheat provides leaner lean misfire limit - use air/fuel
ratio AND intake temperature to control torque
• Provides Diesel-like economy with gasoline-like power
• Retrofit to existing engines possible by changing only
intake, exhaust, & control systems
University of Southern California - Department of Aerospace and Mechanical Engineering
TPCE implementation concept
FUEL
CARBURETOR
DIVERTER VALVE
ADJUSTABLE
FUEL CONTROL VALVE
AIR
EXHAUST
HEAT EXCHANGER
CONVENTIONAL
4-STROKE ENGINE
University of Southern California - Department of Aerospace and Mechanical Engineering
Results
• Substantially improved fuel economy (up to 16 %)
compared to throttled engine at same power & RPM
Efficiency (best TPCE) / Efficiency (throttled)
1.2
Natural gas
Gasoline
Theory
1.15
1.1
1.05
1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Load (fraction of maximum)
University of Southern California - Department of Aerospace and Mechanical Engineering
Results
• NOx performance
< 0.8 grams per kW-hr (10 x lower than throttled engine )
< 0.2 grams per mile for 15 hp road load @ 55 mi/hr - half of
California 2001 standard
• CO and UHC comparable to throttled engine
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas for improvements
• Programmable intake/exhaust valve timing
• Electrical/hydraulic valve actuation
• Choose open/close timing to optimize power, emissions,
efficiency - can eliminate throttling loss
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas for improvements
• Homogeneous ignition engine - controlled knocking
• Burn much leaner mixtures - higher efficiency, lower NOx
• Need to abandon traditional “Hail, Mary” combustion control
strategy
University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas - improved lean-limit operation
• Recent experiments & modelling suggest lean-limit rough
operation is a chaotic process
• Feedback via exhaust gas residual
• Could optimize spark timing on a cycle-to-cycle basis
• Need to infer state of gas & predict burn time for next
cycle - need in-cylinder sensors
University of Southern California - Department of Aerospace and Mechanical Engineering
Conclusions
• IC engines are the worst form of vehicle propulsion,
except for all the other forms
• Despite over 100 years of evolution, IC engines are far
from optimized
• Any new idea must consider many factors, e.g.
• Where significant gains can & cannot be made
• Cost
• Resistance of suppliers & consumers to change
• Easiest near-term change: natural-gas vehicles for fleet &
commuters
• Longer-term solutions mostly require improved (cheaper)
• Sensors (especially in-cylinder temperature, pressure)
• Actuators (especially intake valves)
University of Southern California - Department of Aerospace and Mechanical Engineering
Thanks to ...
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USC Dept. of Aerospace & Mechanical Engineering
Gas Research Institute
South Coast Air Quality Management District
… and especially METRANS
University of Southern California - Department of Aerospace and Mechanical Engineering