Fun with Mechanical Engineering:

1. Engineering scrutiny2. History of internal combustion

engines

http://ronney.usc.edu/AME436S05

Paul D. RonneyUniversity of Southern California, USA

National Central UniversityJhong-Li, Taiwan, October 3, 2005

Travel supported by the Combustion InstituteTravel supported by the Combustion Institute

University of Southern CaliforniaUniversity of Southern California Established 125 years ago Established 125 years ago this week!this week! ……jointly by a Catholic, a Protestant and a Jew - USC has always jointly by a Catholic, a Protestant and a Jew - USC has always

been a multi-ethnic, multi-cultural, coeducational universitybeen a multi-ethnic, multi-cultural, coeducational university Today: 32,000 students, 3000 facultyToday: 32,000 students, 3000 faculty 2 main campuses: University Park and Health Sciences2 main campuses: University Park and Health Sciences USC Trojans football team ranked #1 in USA last 2 yearsUSC Trojans football team ranked #1 in USA last 2 years

USC Viterbi School of EngineeringUSC Viterbi School of Engineering Naming gift by Andrew & Erma ViterbiNaming gift by Andrew & Erma Viterbi Andrew Viterbi: co-founder of Qualcomm, co-inventor of CDMAAndrew Viterbi: co-founder of Qualcomm, co-inventor of CDMA 1900 undergraduates, 3300 graduate students, 165 faculty, 30 1900 undergraduates, 3300 graduate students, 165 faculty, 30

degree optionsdegree options $135 million external research funding$135 million external research funding Distance Education Network (DEN): 900 students in 28 M.S. Distance Education Network (DEN): 900 students in 28 M.S.

degree programs; degree programs; 1171 MS degrees awarded in 200571 MS degrees awarded in 2005 More info: More info: http://viterbi.usc.eduhttp://viterbi.usc.edu

Paul RonneyPaul Ronney B.S. in Mechanical Engineering, UC BerkeleyB.S. in Mechanical Engineering, UC Berkeley M.S. in Aeronautics, CaltechM.S. in Aeronautics, Caltech Ph.D. in Aeronautics & Astronautics, MITPh.D. in Aeronautics & Astronautics, MIT Postdocs: NASA Glenn, Cleveland; US Naval Research Lab, Postdocs: NASA Glenn, Cleveland; US Naval Research Lab,

Washington DCWashington DC Assistant Professor, Princeton UniversityAssistant Professor, Princeton University Associate/Full Professor, USCAssociate/Full Professor, USC Research interestsResearch interests

Microscale combustion and power generation Microscale combustion and power generation (10/4, INER; 10/5 NCKU)(10/4, INER; 10/5 NCKU)

Microgravity combustion and fluid mechanics Microgravity combustion and fluid mechanics (10/4, NCU)(10/4, NCU) Turbulent combustion Turbulent combustion (10/7, NTHU)(10/7, NTHU) Internal combustion enginesInternal combustion engines Ignition, flammability, extinction limits of flames Ignition, flammability, extinction limits of flames (10/3, NCU)(10/3, NCU) Flame spread over solid fuel bedsFlame spread over solid fuel beds Biophysics and biofilms Biophysics and biofilms (10/6, NCKU)(10/6, NCKU)

Paul RonneyPaul Ronney

““Engineering scrutiny” 1. Smoke testEngineering scrutiny” 1. Smoke test

Equivalent in building electronics: turn the power switch on Equivalent in building electronics: turn the power switch on and see if it smokesand see if it smokes

For analysis: For analysis: check the unitscheck the units - this will catch 90% of your - this will catch 90% of your mistakes mistakes

Example: I just derived the ideal gas law as Pv = R/T, Example: I just derived the ideal gas law as Pv = R/T, obviously units are wrongobviously units are wrong

Other rulesOther rules Anything inside a square root, cube root, etc. must have units Anything inside a square root, cube root, etc. must have units

that is a square (e.g. mthat is a square (e.g. m22/sec/sec22) or cube, etc.) or cube, etc. Anything inside a log, exponent, trigonometric function, etc., Anything inside a log, exponent, trigonometric function, etc.,

must be dimensionlessmust be dimensionless Any two quantities that are added together must have the Any two quantities that are added together must have the

same unitssame units

““Engineering scrutiny” 2. Function testEngineering scrutiny” 2. Function test

Equivalent in building electronics: does the device do what Equivalent in building electronics: does the device do what it was designed it to do, e.g. the red light blinks when I flip 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.switch on, the bell rings when I push the button, etc.

For analysis: does the result gives sensible predictions?For analysis: does the result gives sensible predictions? Determine if sign (+ or -) of result is reasonable, e.g. if Determine if sign (+ or -) of result is reasonable, e.g. if

predicted absolute temperature is –72 K, obviously it’s predicted absolute temperature is –72 K, obviously it’s wrongwrong

Determine whether what happens to y as x goes up or down Determine whether what happens to y as x goes up or down is reasonable or not. For example, in the ideal gas law, Pv = is reasonable or not. For example, in the ideal gas law, Pv = RT:RT: At fixed v, as T increases then P increases – At fixed v, as T increases then P increases –

reasonablereasonable At fixed T, as v increases then P decreases – At fixed T, as v increases then P decreases –

reasonablereasonable Etc.Etc.

““Engineering scrutiny” 2. Function testEngineering scrutiny” 2. Function test

Determine what happens in the limit where x goes to special Determine what happens in the limit where x goes to special values, e.g. 0, 1, ∞ as appropriatevalues, e.g. 0, 1, ∞ as appropriate

Example: entropy change (SExample: entropy change (S22 - S - S11) of an ideal gas) of an ideal gas

For TFor T22 = T = T11 and P and P22 = P = P11 (no change in state) then S (no change in state) then S22 – S – S11 = 0 or = 0 or

SS22 = S = S11

Limit of SLimit of S22 = S = S11, the allowable changes in state are, the allowable changes in state are

which is the isentropic relation for ideal gas with constant which is the isentropic relation for ideal gas with constant specific heatsspecific heats

€

S2 − S1 =CP lnT2

T1

⎛

⎝ ⎜

⎞

⎠ ⎟− R ln

P2

P1

⎛

⎝ ⎜

⎞

⎠ ⎟

€

T2

T1

⎛

⎝ ⎜

⎞

⎠ ⎟=P2

P1

⎛

⎝ ⎜

⎞

⎠ ⎟

RCP

=P2

P1

⎛

⎝ ⎜

⎞

⎠ ⎟

γ −1γ

““Engineering scrutiny” 3. Performance testEngineering scrutiny” 3. Performance test

Equivalent in building electronics: how fast, how Equivalent in building electronics: how fast, how accurate, etc. is the deviceaccurate, etc. is the device

For analysis: how accurate is the result?For analysis: how accurate is the result? Need to compare result to something else, e.g. a Need to compare result to something else, e.g. a

“careful” experiment, more sophisticated analysis, “careful” experiment, more sophisticated analysis, trusted published result, etc.trusted published result, etc.

Example, I derived the ideal gas law and predicted Pv = Example, I derived the ideal gas law and predicted Pv = 7RT - passes smoke and function tests, but fails the 7RT - passes smoke and function tests, but fails the performance test miserably (by a factor of 7)performance test miserably (by a factor of 7)

Why internal combustion engines?Why internal combustion engines?

Alternatives - external combustion - "steam engine," "Stirling Alternatives - external combustion - "steam engine," "Stirling cycle”cycle”

Heat transfer, gasoline engineHeat transfer, gasoline engine Heat transfer per unit area (q/A) = k(dT/dx)Heat transfer per unit area (q/A) = k(dT/dx) Turbulent mixture inside engine: k ≈ 100 kTurbulent mixture inside engine: k ≈ 100 kno turbulenceno turbulence ≈ 2.5 ≈ 2.5

W/mKW/mK dT/dx ≈ dT/dx ≈ T/T/x ≈ 1500K / 0.02 mx ≈ 1500K / 0.02 m q/A ≈ 187,500 W/mq/A ≈ 187,500 W/m22

Combustion: q/A = Combustion: q/A = YYffQQRRSSTT = (10 kg/m = (10 kg/m33) x 0.067 x (4.5 x 10) x 0.067 x (4.5 x 1077 J/kg) x J/kg) x

2 m/s = 60.3 x 102 m/s = 60.3 x 1066 W/m W/m22 - - 321x higher!321x higher! CONCLUSION: HEAT TRANSFER IS TOO SLOW!!!CONCLUSION: HEAT TRANSFER IS TOO SLOW!!! That’s why 10 Boeing 747 engines ≈ large (1 gigawatt) coal-fueled That’s why 10 Boeing 747 engines ≈ large (1 gigawatt) coal-fueled

electric power plantelectric power plant

k = gas thermal conductivity, T = temperature, x = distance, k = gas thermal conductivity, T = temperature, x = distance, = = density, Ydensity, Yff = fuel mass fraction, Q = fuel mass fraction, QRR = fuel heating value, S = fuel heating value, STT = =

turbulent flame speed in engine turbulent flame speed in engine

Why internal combustion engines?Why internal combustion engines? Alternatives - electric vehiclesAlternatives - electric vehicles

Why not generate electricity in a large central power plant (Why not generate electricity in a large central power plant ( ≈ 40%), distribute to charge batteries to power electric ≈ 40%), distribute to charge batteries to power electric motors (motors ( ≈ 80%)? ≈ 80%)?

Car battery, lead acid: 100 amp-hours, 12 volts, 20 kg; Car battery, lead acid: 100 amp-hours, 12 volts, 20 kg; energy/mass = 100 A * 12 V * 3600 sec / 20 kg = energy/mass = 100 A * 12 V * 3600 sec / 20 kg = 2 x 102 x 1055 J/kg J/kg

Gasoline (and other hydrocarbons): Gasoline (and other hydrocarbons): 4.5 x 104.5 x 1077 J/kg J/kg Batteries are heavy ≈ 1000 lbs/gal of gasoline equivalentBatteries are heavy ≈ 1000 lbs/gal of gasoline equivalent Fuel cell systems better, but still nowhere near gasolineFuel cell systems better, but still nowhere near gasoline "Zero emissions" myth - EVs "Zero emissions" myth - EVs exportexport pollution pollution Environmental cost of battery materialsEnvironmental cost of battery materials Possible advantage: makes smaller, lighter, more Possible advantage: makes smaller, lighter, more

streamlined cars acceptable to consumersstreamlined cars acceptable to consumers Prediction: eventual conversion of electric vehicles to Prediction: eventual conversion of electric vehicles to

gasoline power (>100 miles per gallon)gasoline power (>100 miles per gallon)

““Zero emission” electric vehiclesZero emission” electric vehicles

Why internal combustion engines?Why internal combustion engines? Alternatives - solarAlternatives - solar

Arizona, high noon, mid summer: solar flux ≈ 1000 W/mArizona, high noon, mid summer: solar flux ≈ 1000 W/m22

Gasoline engine, 20 mi/gal, 60 mi/hr, thermal power = (60 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 10mi/hr / 20 mi/gal) x (6 lb/gal) x (kg / 2.2 lb) x (4.5 x 1077 J/kg) x J/kg) x (hr / 3600 sec) = 102 kW (hr / 3600 sec) = 102 kW

Need ≈ 100 mNeed ≈ 100 m22 collector ≈ 32 ft x 32 ft - lots of air drag, what collector ≈ 32 ft x 32 ft - lots of air drag, what about underpasses, nighttime, bad weather, about underpasses, nighttime, bad weather, northern/southern latitudes, etc.?northern/southern latitudes, etc.?

Why internal combustion engines?Why internal combustion engines? Alternatives - nuclearAlternatives - nuclear

Who are we kidding ???Who are we kidding ??? Higher energy density thoughHigher energy density though

»UU235235 fission: 3.2 x 10 fission: 3.2 x 10-11-11J/atom * (6.02 x 10J/atom * (6.02 x 102323 atom / 0.235 kg) atom / 0.235 kg)

= = 8.2 x 108.2 x 101313 J/kg ≈ 2 million x hydrocarbons! J/kg ≈ 2 million x hydrocarbons!»Radioactive decay less, but still much higher than Radioactive decay less, but still much higher than hydrocarbon fuelhydrocarbon fuel

Moral - hard to beat liquid-fueled internal combustion Moral - hard to beat liquid-fueled internal combustion engines forengines for Power/weight & power/volume of enginePower/weight & power/volume of engine Energy/weight (Energy/weight (4.5 x 104.5 x 1077 J/kg J/kg assuming only fuel, not air, assuming only fuel, not air,

is carried) & energy/volume of liquid hydrocarbon fuelis carried) & energy/volume of liquid hydrocarbon fuel Distribution & handling convenience of liquids Distribution & handling convenience of liquids

Conclusion: IC engines are the worst form of vehicle Conclusion: IC engines are the worst form of vehicle propulsion, except for all the other formspropulsion, except for all the other forms

History of automotive enginesHistory of automotive engines

1859 - Oil discovered in Pennsylvania1859 - Oil discovered in Pennsylvania 1876 - Premixed-charge 4-stroke engine - Otto1876 - Premixed-charge 4-stroke engine - Otto

1st practical IC engine1st practical IC engine Power: 2 hp; Weight: 1250 poundsPower: 2 hp; Weight: 1250 pounds Comp. ratio = 4 (knock limited), 14% efficiency (theory Comp. ratio = 4 (knock limited), 14% efficiency (theory

38%)38%) Today CR = 8 (still knock limited), 30% efficiency Today CR = 8 (still knock limited), 30% efficiency

(theory 52%)(theory 52%) 1897 - Nonpremixed-charge engine - Diesel - higher 1897 - Nonpremixed-charge engine - Diesel - higher

efficiency due toefficiency due to Higher compression ratio (no knock problem)Higher compression ratio (no knock problem) No throttling loss - use fuel/air ratio to control powerNo throttling loss - use fuel/air ratio to control power

History and evolutionHistory and evolution 1923 - Tetraethyl lead - anti-knock additive1923 - Tetraethyl lead - anti-knock additive

Enable higher CR in Otto-type enginesEnable higher CR in Otto-type engines 1952 - A. J. Haagen-Smit1952 - A. J. Haagen-Smit

NO + UHC + ONO + UHC + O22 + sunlight + sunlight NO NO22 + O + O33

(from exhaust) (brown) (irritating)(from exhaust) (brown) (irritating)UHC = unburned hydrocarbonsUHC = unburned hydrocarbons

1960s - Emissions regulations1960s - Emissions regulations Detroit won’t believe itDetroit won’t believe it Initial stop-gap measures - lean mixture, EGR, retard Initial stop-gap measures - lean mixture, EGR, retard

sparkspark Poor performance & fuel economyPoor performance & fuel economy

1973 & 1979 - The energy crises1973 & 1979 - The energy crises Detroit takes a bathDetroit takes a bath

History and evolutionHistory and evolution 1975 - Catalytic converters, unleaded fuel1975 - Catalytic converters, unleaded fuel

Detroit forced to buy technologyDetroit forced to buy technology More “aromatics” (e.g., benzene) in gasoline - high octane but More “aromatics” (e.g., benzene) in gasoline - high octane but

carcinogenic, soot-producingcarcinogenic, soot-producing 1980s - Microcomputer control of engines1980s - Microcomputer control of engines

Tailor operation for best emissions, efficiency, ...Tailor operation for best emissions, efficiency, ... 1990s - Reformulated gasoline1990s - Reformulated gasoline

Reduced need for aromatics, cleaner(?)Reduced need for aromatics, cleaner(?) ... but higher cost, lower miles per gallon... but higher cost, lower miles per gallon Now we find MTBE pollutes groundwater!!!Now we find MTBE pollutes groundwater!!! Alternative “oxygenated” fuel additive - ethanol - very Alternative “oxygenated” fuel additive - ethanol - very

attractive to powerful senators from farm statesattractive to powerful senators from farm states 2000’s - hybrid vehicles2000’s - hybrid vehicles

Use small gasoline engine operating at maximum power Use small gasoline engine operating at maximum power (most efficient way to operate) or turned off if not needed(most efficient way to operate) or turned off if not needed

Use generator/batteries/motors to make/store/use surplus Use generator/batteries/motors to make/store/use surplus power from gasoline enginepower from gasoline engine

More efficient, but much more equipment on board - not clear More efficient, but much more equipment on board - not clear if fuel savings justify extra cost if fuel savings justify extra cost

Things you need to understand before ...Things you need to understand before ...

……you invent the zero-emission, 100 mpg 1000 hp you invent the zero-emission, 100 mpg 1000 hp engine, revolutionize the automotive industry and engine, revolutionize the automotive industry and shop for your retirement home on the French Rivierashop for your retirement home on the French Riviera

Room for improvement - factor of 2 in efficiencyRoom for improvement - factor of 2 in efficiency Ideal Otto cycle engine with CR = 8: 52%Ideal Otto cycle engine with CR = 8: 52% Real engine: 25 - 30%Real engine: 25 - 30% Differences because ofDifferences because of

»Throttling losses Throttling losses »Heat lossesHeat losses»Friction lossesFriction losses»Slow burningSlow burning»Incomplete combustion is a very minor effectIncomplete combustion is a very minor effect

Things you need to understand before ...Things you need to understand before ...

Room for improvement - infinite in pollutantsRoom for improvement - infinite in pollutants Pollutants are a Pollutants are a non-equilibriumnon-equilibrium effect effect

»Burn: Fuel + OBurn: Fuel + O22 + N + N22 H H22O + COO + CO22 + N + N22 + CO + UHC + NO + CO + UHC + NO

OK OK OK Bad Bad BadOK OK OK Bad Bad Bad»Expand: CO + UHC + NO “frozen” at high levelsExpand: CO + UHC + NO “frozen” at high levels»With slow expansion, no heat loss:With slow expansion, no heat loss:

CO + UHC + NO CO + UHC + NO H H22O + COO + CO22 + N + N22

...but how to slow the expansion and eliminate heat loss?...but how to slow the expansion and eliminate heat loss? Worst problems: cold start, transients, old or out-of-Worst problems: cold start, transients, old or out-of-

tune vehicles - 90% of pollution generated by 10% of tune vehicles - 90% of pollution generated by 10% of vehiclesvehicles

Things you need to understand before ...Things you need to understand before ...

Room for improvement - very little in powerRoom for improvement - very little in power IC engines are air processorsIC engines are air processors

»Fuel takes up little spaceFuel takes up little space»Air flow = powerAir flow = power»Limitation on air flow due toLimitation on air flow due to• ““Choked” flow past intake valvesChoked” flow past intake valves• Friction loss, mechanical strength - limits RPMFriction loss, mechanical strength - limits RPM• Slow burnSlow burn

Majority of power is used to overcome air resistanceMajority of power is used to overcome air resistance - - smaller, more aerodynamic vehicles beneficialsmaller, more aerodynamic vehicles beneficial