Transcript Presenting a Technical Report
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
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External combustion - "steam engine," "Stirling cycle"
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Heat transfer is too slow (≈ 100x slower than combustion)
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10 B 747 engines ≈ large coal-fueled electric power plant
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Electric vehicles (EVs)
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Batteries are heavy ≈ 1000 lbs/gal of gasoline equivalent
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Fuel cells better, but still nowhere near gasoline
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"Zero emissions" myth - EVs export pollution Environmental cost of battery materials Possible advantage: makes smaller, lighter, more streamlined cars acceptable to consumers
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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?
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Alternatives (continued…)
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Solar
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Need ≈ 30 ft x 30 ft collector for 15 hp (Arizona, high noon, mid-summer)
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Nuclear
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Who are we kidding ???
Moral - hard to beat gasoline-fueled IC engine for
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Power/weight & power/volume of engine
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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
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1859 - Oil discovered in Pennsylvania 1876 - Premixed-charge 4-stroke engine - Otto
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1st practical IC engine
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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
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Higher compression ratio (no knock problem)
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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 injector Fuel spray flame Fuel + air mixture Air only Premixed charge (gasoline) Non-premixed charge (Diesel) University of Southern California - Department of Aerospace and Mechanical Engineering
History and evolution
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1923 - Tetraethyl lead - anti-knock additive
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Enable higher CR in Otto-type engines 1952 - A. J. Haagen-Smit
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NO + UHC + O 2 + sunlight
NO 2 + O 3 (from exhaust) (brown) (irritating) 1960s - Emissions regulations
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Detroit won’t believe it
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Initial stop-gap measures - lean mixture, EGR, retard spark Poor performance & fuel economy 1973 & 1979 - The energy crises
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Detroit takes a bath University of Southern California - Department of Aerospace and Mechanical Engineering
History and evolution
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1975 - Catalytic converters, unleaded fuel
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Detroit forced to buy technology
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More “aromatics” (e.g., benzene) in gasoline - high octane but carcinogenic, soot-producing 1980s - Microcomputer control of engines
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Tailor operation for best emissions, efficiency, ...
1990s - Reformulated gasoline
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Reduced need for aromatics, cleaner(?)
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... 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
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Ideal Otto cycle engine with CR = 8: 52% Real engine: 25 - 30% Differences because of
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Throttling losses
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Heat losses
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Friction losses University of Southern California - Department of Aerospace and Mechanical Engineering
Things you need to understand before ...
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Room for improvement - infinite in pollutants
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Pollutants are a non-equilibrium effect
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Burn: Fuel + O 2 + N 2
H 2 O + CO 2 + N 2 + CO + UHC + NO
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OK OK OK Bad Bad Bad Expand: CO + UHC + NO “frozen” at high levels
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With slow expansion, no heat loss: CO + UHC + NO
H 2 O + CO 2 + N 2 ...but how to slow the expansion and eliminate heat loss?
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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 ...
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Room for improvement - very little in power
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IC engines are air processors
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Fuel takes up little space
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Air flow = power
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Limitation on air flow due to
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“Choked” flow past intake valves
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Friction loss, mechanical strength - limits RPM
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Slow burn
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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
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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 CO 2 electricity emission of EVs charged with coal-generated + 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
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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
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Hydrogen + Ultimate clean fuel + Excellent combustion properties + Ideal for fuel cells - Very low storage density (1/10 gasoline) - Need to manufacture - usually from electricity + H 2 O
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
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Reduction of heat losses
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Heat losses caused by high engine turbulence levels
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Need high turbulence to
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Wrinkle flame (premixed charge, gasoline)
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Disperse fuel droplets (nonpremixed charge, Diesel)
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"Inverse-engineer" engine for low-turbulence
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Gasoline - electrically-induced flame wrinkling?
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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
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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 =
r
RT) Throttling losses substantial at part load 1 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
ADJUSTABLE FUEL CONTROL VALVE
AIR EXHAUST
CARBURETOR DIVERTER VALVE HEAT EXCHANGER CONVENTIONAL 4-STROKE ENGINE
University of Southern California - Department of Aerospace and Mechanical Engineering
Results
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Substantially improved fuel economy (up to 16 %) compared to throttled engine at same power & RPM
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
Load (fraction of maximum) 0.9
1
University of Southern California - Department of Aerospace and Mechanical Engineering
Results
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NO x 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
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CO and UHC comparable to throttled engine University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas for improvements
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Programmable intake/exhaust valve timing
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Electrical/hydraulic valve actuation
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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
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Homogeneous ignition engine - controlled knocking
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Burn much leaner mixtures - higher efficiency, lower NO x
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Need to abandon traditional “Hail, Mary” combustion control strategy University of Southern California - Department of Aerospace and Mechanical Engineering
Ideas - improved lean-limit operation
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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
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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.
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Where significant gains can & cannot be made
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Cost Resistance of suppliers & consumers to change Easiest near-term change: natural-gas vehicles for fleet & commuters Longer-term solutions mostly require improved (cheaper)
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Sensors (especially in-cylinder temperature, pressure)
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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