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Fun with Mechanical Engineering: 1. Engineering scrutiny 2. History of internal combustion engines http://ronney.usc.edu/AME436S05 Paul D. Ronney University of Southern California, USA National Central University Jhong-Li, Taiwan, October 3, 2005 Travel supported by the Combustion Institute.
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Fun with Mechanical Engineering:1. Engineering scrutiny2. History of internal combustion engines http://ronney.usc.edu/AME436S05Paul D. RonneyUniversity of Southern California, USANational Central UniversityJhong-Li, Taiwan, October 3, 2005Travel supported by the Combustion Institute
University of Southern California • Established 125 years ago this week! • …jointly by a Catholic, a Protestant and a Jew - USC has always been a multi-ethnic, multi-cultural, coeducational university • Today: 32,000 students, 3000 faculty • 2 main campuses: University Park and Health Sciences • USC Trojans football team ranked #1 in USA last 2 years
USC Viterbi School of Engineering • Naming gift by Andrew & Erma Viterbi • Andrew Viterbi: co-founder of Qualcomm, co-inventor of CDMA • 1900 undergraduates, 3300 graduate students, 165 faculty, 30 degree options • $135 million external research funding • Distance Education Network (DEN): 900 students in 28 M.S. degree programs; 171 MS degrees awarded in 2005 • More info: http://viterbi.usc.edu
Paul Ronney • B.S. in Mechanical Engineering, UC Berkeley • M.S. in Aeronautics, Caltech • Ph.D. in Aeronautics & Astronautics, MIT • Postdocs: NASA Glenn, Cleveland; US Naval Research Lab, Washington DC • Assistant Professor, Princeton University • Associate/Full Professor, USC • Research interests • Microscale combustion and power generation (10/4, INER; 10/5 NCKU) • Microgravity combustion and fluid mechanics (10/4, NCU) • Turbulent combustion (10/7, NTHU) • Internal combustion engines • Ignition, flammability, extinction limits of flames (10/3, NCU) • Flame spread over solid fuel beds • Biophysics and biofilms (10/6, NCKU)
“Engineering scrutiny” 1. Smoke test • Equivalent in building electronics: turn the power switch on and see if it smokes • For analysis: check the units - this will catch 90% of your mistakes • Example: I just derived the ideal gas law as Pv = R/T, obviously units are wrong • Other rules • Anything inside a square root, cube root, etc. must have units that is a square (e.g. m2/sec2) or cube, etc. • Anything inside a log, exponent, trigonometric function, etc., must be dimensionless • Any two quantities that are added together must have the same units
“Engineering scrutiny” 2. Function test • Equivalent in building electronics: does the device do what it was designed it to do, e.g. the red light blinks when I flip switch on, the bell rings when I push the button, etc. • For analysis: does the result gives sensible predictions? • Determine if sign (+ or -) of result is reasonable, e.g. if predicted absolute temperature is –72 K, obviously it’s wrong • Determine whether what happens to y as x goes up or down is reasonable or not. For example, in the ideal gas law, Pv = RT: • At fixed v, as T increases then P increases – reasonable • At fixed T, as v increases then P decreases – reasonable • Etc.
“Engineering scrutiny” 2. Function test • Determine what happens in the limit where x goes to special values, e.g. 0, 1, ∞ as appropriate • Example: entropy change (S2 - S1) of an ideal gas • For T2 = T1 and P2 = P1 (no change in state) then S2 – S1 = 0 or S2 = S1 • Limit of S2 = S1, the allowable changes in state are which is the isentropic relation for ideal gas with constant specific heats
“Engineering scrutiny” 3. Performance test • Equivalent in building electronics: how fast, how accurate, etc. is the device • For analysis: how accurate is the result? • Need to compare result to something else, e.g. a “careful” experiment, more sophisticated analysis, trusted published result, etc. • Example, I derived the ideal gas law and predicted Pv = 7RT - passes smoke and function tests, but fails the performance test miserably (by a factor of 7)
Why internal combustion engines? • Alternatives - external combustion - "steam engine," "Stirling cycle” • Heat transfer, gasoline engine • Heat transfer per unit area (q/A) = k(dT/dx) • Turbulent mixture inside engine: k ≈ 100 kno turbulence ≈ 2.5 W/mK • dT/dx ≈ T/x ≈ 1500K / 0.02 m • q/A ≈ 187,500 W/m2 • Combustion: q/A = YfQRST = (10 kg/m3) x 0.067 x (4.5 x 107 J/kg) x 2 m/s = 60.3 x 106 W/m2 - 321x higher! • CONCLUSION: HEAT TRANSFER IS TOO SLOW!!! • That’s why 10 Boeing 747 engines ≈ large (1 gigawatt) coal-fueled electric power plant k = gas thermal conductivity, T = temperature, x = distance, = density, Yf = fuel mass fraction, QR = fuel heating value, ST = turbulent flame speed in engine
Why internal combustion engines? • Alternatives - electric vehicles • Why not generate electricity in a large central power plant ( ≈ 40%), distribute to charge batteries to power electric motors ( ≈ 80%)? • Car battery, lead acid: 100 amp-hours, 12 volts, 20 kg; energy/mass = 100 A * 12 V * 3600 sec / 20 kg = 2 x 105 J/kg • Gasoline (and other hydrocarbons): 4.5 x 107 J/kg • Batteries are heavy ≈ 1000 lbs/gal of gasoline equivalent • Fuel cell systems 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)
Why internal combustion engines? • Alternatives - solar • Arizona, high noon, mid summer: solar flux ≈ 1000 W/m2 • Gasoline engine, 20 mi/gal, 60 mi/hr, thermal power = (60 mi/hr / 20 mi/gal) x (6 lb/gal) x (kg / 2.2 lb) x (4.5 x 107 J/kg) x (hr / 3600 sec) = 102 kW • Need ≈ 100 m2 collector ≈ 32 ft x 32 ft - lots of air drag, what about underpasses, nighttime, bad weather, northern/southern latitudes, etc.?
Why internal combustion engines? • Alternatives - nuclear • Who are we kidding ??? • Higher energy density though • U235 fission: 3.2 x 10-11J/atom * (6.02 x 1023 atom / 0.235 kg) = 8.2 x 1013 J/kg ≈ 2 million x hydrocarbons! • Radioactive decay less, but still much higher than hydrocarbon fuel • Moral - hard to beat liquid-fueled internal combustion engines for • Power/weight & power/volume of engine • Energy/weight (4.5 x 107 J/kg assuming only fuel, not air, is carried) & energy/volume of liquid hydrocarbon fuel • Distribution & handling convenience of liquids • Conclusion: IC engines are the worst form of vehicle propulsion, except for all the other forms
History of automotive engines • 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
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) UHC = unburned hydrocarbons • 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
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!!! • Alternative “oxygenated” fuel additive - ethanol - very attractive to powerful senators from farm states • 2000’s - hybrid vehicles • Use small gasoline engine operating at maximum power (most efficient way to operate) or turned off if not needed • Use generator/batteries/motors to make/store/use surplus power from gasoline engine • More efficient, but much more equipment on board - not clear if fuel savings justify extra cost
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 • Slow burning • Incomplete combustion is a very minor effect
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
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