The Evolution of the Internal Combustion Engine and Future Design Challenges: Performance, Efficiency, Emissions

1. 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

2. Outline • 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

3. Why premixed-charge IC engines? • 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

4. “Zero emission” electric vehicles University of Southern California - Department of Aerospace and Mechanical Engineering

5. 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

6. History and evolution • 1859 - Oil discovered in Pennsylvania • 1876 - Premixed-charge 4-stroke engine - Otto • 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

7. Premixed vs. non-premixed charge engines University of Southern California - Department of Aerospace and Mechanical Engineering

8. History and evolution • 1923 - Tetraethyl lead - anti-knock additive • Enable higher CR in Otto-type engines • 1952 - A. J. Haagen-Smit • NO + UHC + O2 + sunlight  NO2 + O3 (from exhaust) (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

9. 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

10. 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 • 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. Electrostatic sprays University of Southern California - Department of Aerospace and Mechanical Engineering

17. 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 University of Southern California - Department of Aerospace and Mechanical Engineering

18. The TPCE concept • 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

19. TPCE implementation concept University of Southern California - Department of Aerospace and Mechanical Engineering

20. Results • Substantially improved fuel economy (up to 16 %) compared to throttled engine at same power & RPM University of Southern California - Department of Aerospace and Mechanical Engineering

21. 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

22. 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

23. 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

24. 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

25. 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

26. Thanks to ... • 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