Internal Combustion Engines: The Internal Combustion Engines: The Worst Form of Vehicle Propulsion - Worst Form of Vehicle Propulsion -

Except for All the Other FormsExcept for All the Other Forms

A primer on IC engines A primer on IC engines and their alternativesand their alternatives

Paul D. RonneyPaul D. RonneyDeparment of Aerospace and Mechanical EngineeringDeparment of Aerospace and Mechanical Engineering

University of Southern CaliforniaUniversity of Southern California

Download this presentation: Download this presentation: http://ronney.usc.edu/WhyICEngines-expanded.ppthttp://ronney.usc.edu/WhyICEngines-expanded.ppt

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OutlineOutline Automotive enginesAutomotive engines

Definition of Internal Combustion Engines (ICEs)Definition of Internal Combustion Engines (ICEs) Types of ICEsTypes of ICEs History and evolution of ICEsHistory and evolution of ICEs Things you need to know before…Things you need to know before… Gas turbinesGas turbines What are the alternatives to ICEs?What are the alternatives to ICEs?

The nitty grittyThe nitty gritty How they workHow they work Why they’re designed that wayWhy they’re designed that way Gasoline vs. dieselGasoline vs. diesel Practical perspectivePractical perspective

SummarySummary

Part 1:Part 1:

Automotive engines:Automotive engines:how and whyhow and why

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IntroductionIntroduction Hydrocarbon-fueled ICEs are the power plant of choice for vehicles Hydrocarbon-fueled ICEs are the power plant of choice for vehicles

in the power range from 5 Watts to 100,000,000 Watts, and have in the power range from 5 Watts to 100,000,000 Watts, and have been for 100 yearsbeen for 100 years

There is an unlimited amount of inaccurate, misleading and/or There is an unlimited amount of inaccurate, misleading and/or dogmatic information about ICEsdogmatic information about ICEs

This seminar’s messagesThis seminar’s messages Why ICEs so ubiquitousWhy ICEs so ubiquitous Why it will be so difficult to replace them with another technologyWhy it will be so difficult to replace them with another technology What you will have to do if you want to replace themWhat you will have to do if you want to replace them

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Classification of ICEsClassification of ICEs

Definition of an ICE: a Definition of an ICE: a heat engineheat engine in which the heat source is in which the heat source is a a combustible mixturecombustible mixture that that also serves as the working fluidalso serves as the working fluid

The working fluid in turn is used either toThe working fluid in turn is used either to Produce shaft work by pushing on a piston or turbine blade Produce shaft work by pushing on a piston or turbine blade

that in turn drives a rotating shaft orthat in turn drives a rotating shaft or Creates a high-momentum fluid that is used directly for Creates a high-momentum fluid that is used directly for

propulsive forcepropulsive force

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What is / is not an ICE?What is / is not an ICE?

ISIS Gasoline-fueled Gasoline-fueled

reciprocating piston reciprocating piston engineengine

Diesel-fueled Diesel-fueled reciprocating piston reciprocating piston engineengine

Gas turbineGas turbine RocketRocket

IS NOTIS NOT Steam power plantSteam power plant Solar power plantSolar power plant Nuclear power plantNuclear power plant

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ICE family treeICE family tree

TurboshaftAll shaft work to drive propeller,

generator, rotor (helicopter)

TurbofanPart shaft, part jet -"ducted propeller"

TurbojetAll jet except for work needed to

drive compressor

Gas TurbineUses compressor and turbine,

not piston-cylinder

RamjetNo compressor or turbine

Use high Mach no. ram effect for compression

Solid fuelFuel and oxidant are premixed

and put inside combustion chamber

Liquid fuelFuel and oxidant are initially separatedand pumped into combustion chamber

RocketCarries both fuel and oxidantJet power only, no shaft work

Steady

Two-strokeOne complete thermodynamic cycle

per revolution of engine

Four-strokeOne complete thermodynamic cycle

per two revolutions of engine

Premixed-chargeFuel and air are mixed before/during compression

Usually ignited with spark after compression

Two-strokeOne complete thermodynamic cycle

per revolution of engine

Four-strokeOne complete thermodynamic cycle

per two revolutions of engine

Non-premixed chargeOnly air is compressed,

fuel is injected into cylinder after compression

Non-steady

Internal Combustion Engines

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Largest internal combustion engineLargest internal combustion engine

Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel, built in Finland, Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel, built in Finland, used in container shipsused in container ships

14 cylinder version: weight 2300 tons14 cylinder version: weight 2300 tons; ; length 89 feet; height 44 feet; max. length 89 feet; height 44 feet; max. power 108,920 hp @ 102 rpm; max. torque 5,608,312 ft lb @ 102 RPMpower 108,920 hp @ 102 rpm; max. torque 5,608,312 ft lb @ 102 RPM

Power/weight = Power/weight = 0.024 hp/lb0.024 hp/lb Also one of the most efficient IC engines: 51%Also one of the most efficient IC engines: 51%

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Most powerful internal combustion engineMost powerful internal combustion engine Wartsila-Sulzer RTA96-C is the Wartsila-Sulzer RTA96-C is the largestlargest IC engine, but the Space Shuttle IC engine, but the Space Shuttle

Solid Rocket Boosters are the Solid Rocket Boosters are the most powerfulmost powerful (≈ 42 (≈ 42 millionmillion horsepower ( horsepower (32 32 hp/lbhp/lb); not shaft power but kinetic energy of exhaust stream)); not shaft power but kinetic energy of exhaust stream)

Most powerful shaft-power engine: Siemens SGT5-8000H stationary gas Most powerful shaft-power engine: Siemens SGT5-8000H stationary gas turbine (340 MW = 456,000 HP) (turbine (340 MW = 456,000 HP) (0.52 hp/lb0.52 hp/lb) used for electrical power ) used for electrical power generationgeneration

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Smallest internal combustion engineSmallest internal combustion engine

Cox Tee Dee 010Cox Tee Dee 010Application: Application: model airplanesmodel airplanesWeight: Weight: 0.49 oz.0.49 oz.Displacement: Displacement: 0.00997 in0.00997 in33

(0.163 cm(0.163 cm33))RPM: RPM: 30,00030,000Power:Power: 5 watts5 wattsIgnition: Glow plug

Typical fuel: castor oil (10 - 20%), nitromethane (0 - 50%), balance methanol

Good power/weight (Good power/weight (0.22 hp/lb0.22 hp/lb) but poor performance) but poor performance Low efficiency (< 5%)Low efficiency (< 5%) Emissions & noise unacceptable for many applicationsEmissions & noise unacceptable for many applications

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History of automotive enginesHistory of automotive engines 1859 - Oil discovered at Drake’s Well, Titusville, 1859 - Oil discovered at Drake’s Well, Titusville,

Pennsylvania (20 barrels per day) Pennsylvania (20 barrels per day) - 40 year supply- 40 year supply 1876 - Premixed-charge 4-stroke engine - Otto1876 - Premixed-charge 4-stroke engine - Otto

1st practical ICE1st practical ICE Power: 2 hp; Weight: 1250 poundsPower: 2 hp; Weight: 1250 pounds Comp. ratio = 4 (knock limited), 14% efficiency Comp. ratio = 4 (knock limited), 14% efficiency

(theory 38%)(theory 38%) Today CR = 9 (still knock limited), 30% efficiency Today CR = 9 (still knock limited), 30% efficiency

(theory 55%)(theory 55%) 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

1901 - Spindletop Dome, east Texas - Lucas #1 1901 - Spindletop Dome, east Texas - Lucas #1 gusher produces 100,000 barrels per day - ensures gusher produces 100,000 barrels per day - ensures that “2nd Industrial Revolution” will be fueled by that “2nd Industrial Revolution” will be fueled by oil, not coal or wood oil, not coal or wood - 40 year supply- 40 year supply

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History of automotive enginesHistory of automotive engines

1921 - Tetraethyl lead anti-knock additive discovered at 1921 - Tetraethyl lead anti-knock additive discovered at General MotorsGeneral Motors Enabled higher compression ratio (thus more power, better Enabled higher compression ratio (thus more power, better

efficiency) in Otto-type enginesefficiency) in Otto-type engines 1952 - A. J. Haagen-Smit, Caltech1952 - A. J. Haagen-Smit, Caltech

NO + UHC + ONO + UHC + O22 + sunlight + sunlight NONO22 + O + O33

(from exhaust) (from exhaust) (brown) (irritating)(brown) (irritating)

(UHC = unburned hydrocarbons)(UHC = unburned hydrocarbons)

1960s - Emissions regulations1960s - Emissions regulations Detroit won’t believe itDetroit won’t believe it Initial stop-gap measures - lean mixture, EGR, retard sparkInitial stop-gap measures - lean mixture, EGR, retard spark Poor performance & fuel economyPoor performance & fuel economy

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

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History of automotive enginesHistory of automotive engines

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 Then we found that MTBE pollutes groundwater!!!Then we found that MTBE pollutes groundwater!!! Alternative “oxygenated” fuel additive - ethanol - very attractive Alternative “oxygenated” fuel additive - ethanol - very attractive

to powerful senators from farm statesto powerful senators from farm states

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History of automotive enginesHistory of automotive engines

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 Plug-in hybrid: half-way between conventional hybrid and Plug-in hybrid: half-way between conventional hybrid and

electric vehicleelectric vehicle Recent study in a major consumer magazine: only 1 of 7 Recent study in a major consumer magazine: only 1 of 7

hybrids tested show a cost benefit over a 5 year ownership hybrids tested show a cost benefit over a 5 year ownership period if tax incentives removedperiod if tax incentives removed» Dolly Parton: “You wouldn’t believe how much it costs to look Dolly Parton: “You wouldn’t believe how much it costs to look

this cheap”this cheap”» Paul Ronney: “You wouldn’t believe how much energy some Paul Ronney: “You wouldn’t believe how much energy some

people spend to save a little fuel”people spend to save a little fuel”

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

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

Room for improvement - factor of less than 2 in efficiencyRoom for improvement - factor of less than 2 in efficiency Ideal Otto cycle engine with compression ratio = 9: 55%Ideal Otto cycle engine with compression ratio = 9: 55% 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

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

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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

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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

»How to increase air flow?How to increase air flow?• Larger enginesLarger engines• Faster-rotating engines Faster-rotating engines • Turbocharge / superchargeTurbocharge / supercharge• Avoid stop/start cycle of reciprocating piston engines - how?Avoid stop/start cycle of reciprocating piston engines - how?

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Basic gas turbine cycleBasic gas turbine cycle

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TurbofanTurbofan

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Why gas turbines?Why gas turbines?

GE CT7-8 turboshaft (used in GE CT7-8 turboshaft (used in helicopters)helicopters)

http://www.geae.com/engines/http://www.geae.com/engines/commercial/ct7/ct7-8.htmlcommercial/ct7/ct7-8.html

Compressor/turbine stages: 6/4Compressor/turbine stages: 6/4 Diameter 26”, Length 48.8” = 426 liters Diameter 26”, Length 48.8” = 426 liters

= = 5.9 hp/liter5.9 hp/liter Dry Weight 537 lb, max. power 2,520 hp Dry Weight 537 lb, max. power 2,520 hp

((power/wt = 4.7 hp/lbpower/wt = 4.7 hp/lb)) Pressure ratio at max. power: 21 (ratio Pressure ratio at max. power: 21 (ratio

per stage = 21per stage = 211/61/6 = 1.66) = 1.66)   Specific fuel consumption at max. Specific fuel consumption at max.

power: 0.450 (units not given; if lb/hp-hr power: 0.450 (units not given; if lb/hp-hr then corresponds to 29.3% efficiency)then corresponds to 29.3% efficiency)

Cummins QSK60-2850 4-stroke Cummins QSK60-2850 4-stroke 60.0 60.0 liter (3,672 inliter (3,672 in33)) V-16 2-stage V-16 2-stage turbocharged diesel (used in mining turbocharged diesel (used in mining trucks)trucks)

http://www.everytime.cummins.com/http://www.everytime.cummins.com/

assets/pdf/4087056.pdfassets/pdf/4087056.pdf 2.93 m long x 1.58 m wide x 2.31 m high = 2.93 m long x 1.58 m wide x 2.31 m high =

10,700 liters = 10,700 liters = 0.27 hp/liter0.27 hp/liter Dry weight 21,207 lb, 2850 hp at 1900 Dry weight 21,207 lb, 2850 hp at 1900

RPM (RPM (power/wt = 0.134 hp/lb = 35x lower power/wt = 0.134 hp/lb = 35x lower than gas turbinethan gas turbine))

Volume compression ratio ??? (not Volume compression ratio ??? (not given)given)

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Ballard HY-80 “Fuel cell engine”Ballard HY-80 “Fuel cell engine” http://www.ballard.com/resources/http://www.ballard.com/resources/

transportation/XCS-HY-80_Trans.pdf (no transportation/XCS-HY-80_Trans.pdf (no longer valid link!)longer valid link!)

Volume 220 liters = 0.41 hp/literVolume 220 liters = 0.41 hp/liter 91 hp, 485 lb. (91 hp, 485 lb. (power/wt = 0.19 hp/lbpower/wt = 0.19 hp/lb)) 48% efficiency (fuel to electricity)48% efficiency (fuel to electricity) Uses hydrogen only - NOT hydrocarbonsUses hydrogen only - NOT hydrocarbons Does NOT include electric drive systemDoes NOT include electric drive system (≈ (≈

0.40 hp/lb) at ≈ 90% electrical to mechanical 0.40 hp/lb) at ≈ 90% electrical to mechanical efficiency efficiency (http://www.gm.com/company/gmability/adv(http://www.gm.com/company/gmability/adv_tech/images/fact_sheets/hywire.html) (no _tech/images/fact_sheets/hywire.html) (no longer valid)longer valid)

Fuel cell + motor overall 0.13 hp/lb at 43% Fuel cell + motor overall 0.13 hp/lb at 43% efficiency, not including Hefficiency, not including H22 storage storage

Why gas turbines?Why gas turbines?

Lycoming IO-720 11.8 liter (720 cu in) 4-Lycoming IO-720 11.8 liter (720 cu in) 4-stroke 8-cyl. gasoline engine stroke 8-cyl. gasoline engine ((http://www.lycoming.com/engines/series/pdfs/Specialty%20insert.pdf))

Total volume 23” x 34” x 46” = 589 liters = Total volume 23” x 34” x 46” = 589 liters = 0.67 hp/liter0.67 hp/liter

400 hp @ 2650 RPM400 hp @ 2650 RPM Dry weight 600 lb. (Dry weight 600 lb. (power/wt = 0.67 hp/lb = power/wt = 0.67 hp/lb =

7x lower than gas turbine7x lower than gas turbine)) Volume compression ratio 8.7:1 (= Volume compression ratio 8.7:1 (=

pressure ratio 20.7 if isentropic)pressure ratio 20.7 if isentropic)

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Why gas turbines?Why gas turbines? Why does gas turbine have much higher power/weight & Why does gas turbine have much higher power/weight &

power/volume than recips? power/volume than recips? More air can be processedMore air can be processed since since steady flow, not start/stop of reciprocating-piston enginessteady flow, not start/stop of reciprocating-piston engines More air More air more fuel can be burned more fuel can be burned More fuel More fuel more heat release more heat release More heat More heat more work (if thermal efficiency similar) more work (if thermal efficiency similar)

What are the disadvantages?What are the disadvantages? CompressorCompressor is a is a dynamicdynamic device that makes gas move from low device that makes gas move from low

pressure to high pressure without a positive seal like a pressure to high pressure without a positive seal like a piston/cylinderpiston/cylinder» Requires very precise aerodynamicsRequires very precise aerodynamics» Requires blade speeds ≈ sound speed, otherwise gas flows back to Requires blade speeds ≈ sound speed, otherwise gas flows back to

low P faster than compressor can push it to high Plow P faster than compressor can push it to high P» Each stage can provide only 2:1 or 3:1 pressure ratio - need many Each stage can provide only 2:1 or 3:1 pressure ratio - need many

stages for large pressure ratiostages for large pressure ratio Since steady flow, each component sees a constant temperature Since steady flow, each component sees a constant temperature

- at end of combustor - - at end of combustor - turbineturbine stays hot continuously and must stays hot continuously and must rotate at high speeds (high stress)rotate at high speeds (high stress)» Severe materials and cooling engineering required (unlike recip, Severe materials and cooling engineering required (unlike recip,

where components only feel where components only feel average gas temperature during cycleaverage gas temperature during cycle))» Turbine inlet temperature limit ≈ 1600K = 2420˚F - limits fuel inputTurbine inlet temperature limit ≈ 1600K = 2420˚F - limits fuel input

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Why gas turbines?Why gas turbines? As a result, turbines require more maintenance & are more As a result, turbines require more maintenance & are more

expensive for same power (so never used in automotive expensive for same power (so never used in automotive applications… but is used in modern military tanks, because of applications… but is used in modern military tanks, because of power/volume, NOT power/weight)power/volume, NOT power/weight)

Simple intro to gas turbines: Simple intro to gas turbines: http://geae.com/education/engines101/http://geae.com/education/engines101/

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Alternative #1 - external combustionAlternative #1 - external combustion Examples: steam engine, Stirling cycle engineExamples: steam engine, Stirling cycle engine

Use any fuel as the heat sourceUse any fuel as the heat source Use any working fluid (high Use any working fluid (high , e.g. helium, provides better efficiency), e.g. helium, provides better efficiency)

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 W/mK2.5 W/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 = 2 m/s = 60,300,000 W/m60,300,000 W/m22 - - 321x higher!321x higher! CONCLUSION: HEAT TRANSFER IS TOO SLOW!!!CONCLUSION: HEAT TRANSFER IS TOO SLOW!!! That’s why 10 large gas turbine engines ≈ large (1 gigawatt) coal-That’s why 10 large gas turbine engines ≈ large (1 gigawatt) coal-

fueled electric power plantfueled electric power plant

k = gas thermal conductivity, T = temperature, x = distance, k = gas thermal conductivity, T = temperature, x = distance, = density, Y = density, Yff = =

fuel mass fraction, Qfuel mass fraction, QRR = fuel heating value, S = fuel heating value, STT = turbulent flame speed in = turbulent flame speed in

engine engine

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Alternative #2 - Electric Vehicles (EVs)Alternative #2 - Electric Vehicles (EVs) Why not generate electricity in a large central power plant Why not generate electricity in a large central power plant

and distribute to charge batteries to power electric motors?and distribute to charge batteries to power electric motors? EV NiMH battery - 26.4 kW-hours, 1147 pounds = EV NiMH battery - 26.4 kW-hours, 1147 pounds = 1.83 x 101.83 x 1055

J/kgJ/kg (http://www.gmev.com/power/power.htm) (http://www.gmev.com/power/power.htm) Gasoline (and other hydrocarbons): Gasoline (and other hydrocarbons): 4.3 x 104.3 x 1077 J/kg J/kg Even at 30% efficiency (gasoline) vs. 90% (batteries), Even at 30% efficiency (gasoline) vs. 90% (batteries),

gasoline has gasoline has 78 times higher energy/weight than batteries! 78 times higher energy/weight than batteries! 1 gallon of gasoline ≈ 481 pounds of batteries for same 1 gallon of gasoline ≈ 481 pounds of batteries for same

energy delivered to the wheelsenergy delivered to the wheels Other issues with electric vehiclesOther issues with electric vehicles

"Zero emissions” ??? - EVs "Zero emissions” ??? - EVs exportexport pollution pollution Replacement cost of batteriesReplacement cost of batteries Environmental cost of battery materialsEnvironmental cost of battery materials Possible advantage: EVs make smaller, lighter, more Possible advantage: EVs make smaller, lighter, more

streamlined cars acceptable to consumersstreamlined cars acceptable to consumers

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““Zero emission” electric vehiclesZero emission” electric vehicles

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Ballard HY-80 “Fuel cell engine” Ballard HY-80 “Fuel cell engine” ((power/wt = 0.19 hp/lbpower/wt = 0.19 hp/lb))

48% efficient (fuel to electricity)48% efficient (fuel to electricity) MUST use hydrogen (from where?)MUST use hydrogen (from where?) Requires large amounts of platinum Requires large amounts of platinum

catalyst - extremely expensivecatalyst - extremely expensive Does NOT include electric drive systemDoes NOT include electric drive system

(≈ 0.40 hp/lb thus fuel cell + motor (≈ 0.40 hp/lb thus fuel cell + motor at ≈ 90% electrical to mechanical efficiency)at ≈ 90% electrical to mechanical efficiency)

Overall system:Overall system: 0.13 hp/lb at 43% efficiency (hydrogen) 0.13 hp/lb at 43% efficiency (hydrogen) Conventional engine: ≈ 0.5 hp/lb at 30% efficiency (gasoline)Conventional engine: ≈ 0.5 hp/lb at 30% efficiency (gasoline) Conclusion: fuel cell engines are only marginally more efficient, Conclusion: fuel cell engines are only marginally more efficient,

much heavier for the same power, and require hydrogen which is much heavier for the same power, and require hydrogen which is very difficult and potentially dangerous to store on a vehiclevery difficult and potentially dangerous to store on a vehicle

Prediction: even if we had an unlimited free source of hydrogen Prediction: even if we had an unlimited free source of hydrogen and a perfect way of storing it on a vehicle, and a perfect way of storing it on a vehicle, we would still burn it, we would still burn it, not use it in a fuel cellnot use it in a fuel cell

Alternative #3 - Hydrogen fuel cellAlternative #3 - Hydrogen fuel cell

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Hydrogen storageHydrogen storage Hydrogen is a great fuelHydrogen is a great fuel

High energy density (1.2 x 10High energy density (1.2 x 1088 J/kg, ≈ 3x hydrocarbons) J/kg, ≈ 3x hydrocarbons) Much faster reaction rates than hydrocarbons (≈ 10 - 100x at same T)Much faster reaction rates than hydrocarbons (≈ 10 - 100x at same T) Excellent electrochemical properties in fuel cellsExcellent electrochemical properties in fuel cells

But how to store it???But how to store it??? Cryogenic (very cold, -424˚F) liquid, low density (14x lower than water)Cryogenic (very cold, -424˚F) liquid, low density (14x lower than water) Compressed gas: weight of tank ≈ 15x greater than weight of fuelCompressed gas: weight of tank ≈ 15x greater than weight of fuel Borohydride solutionsBorohydride solutions

» NaBHNaBH44 + 2H + 2H22O O NaBO NaBO22 (Borax) + 3H (Borax) + 3H22

» (mass solution)/(mass fuel) ≈ 9.25 (mass solution)/(mass fuel) ≈ 9.25 Palladium - Pd/H = 164 by weightPalladium - Pd/H = 164 by weight Carbon nanotubes - many claims, few facts…Carbon nanotubes - many claims, few facts… Long-chain hydrocarbon (CHLong-chain hydrocarbon (CH22))xx: (Mass C)/(mass H) = 6, plus C atoms : (Mass C)/(mass H) = 6, plus C atoms

add 94.1 kcal of energy release to 57.8 for Hadd 94.1 kcal of energy release to 57.8 for H22!! MORAL: MORAL: By farBy far the best way to store hydrogen is to attach it to the best way to store hydrogen is to attach it to

carbon atoms and make hydrocarbons, even if you’re not going to use carbon atoms and make hydrocarbons, even if you’re not going to use the carbon as fuel!the carbon as fuel!

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Alternative #4 - Solar vehicleAlternative #4 - Solar vehicle 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 mi/hr / 20 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 (4.3 x 10mi/gal) x (6 lb/gal) x (kg / 2.2 lb) x (4.3 x 1077 J/kg) x (hr / 3600 sec) J/kg) x (hr / 3600 sec) = = 97 kilowatts97 kilowatts

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

Do you want to drive this car every day (but never at night?)Do you want to drive this car every day (but never at night?)

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Alternative #5 - nuclearAlternative #5 - nuclear Who are we kidding ???Who are we kidding ??? Higher energy density thoughHigher energy density though

UU235235 fission: fission: 8.2 x 10 8.2 x 101313 J/kg ≈ 2 million x hydrocarbons! J/kg ≈ 2 million x hydrocarbons! Radioactive decay much less, but still much higher than Radioactive decay much less, but still much higher than

hydrocarbon fuelhydrocarbon fuel

Part 2:Part 2:

The nitty grittyThe nitty gritty

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Power and torquePower and torque

Engine performance is specified in both in terms of power and Engine performance is specified in both in terms of power and engineengine torque - which is more important? torque - which is more important? Wheel torque = engine torque x gear ratioWheel torque = engine torque x gear ratio tells you whether you tells you whether you

can climb the hillcan climb the hill Gear ratio in transmission typically 3:1 or 4:1 in 1st gear, 1:1 in Gear ratio in transmission typically 3:1 or 4:1 in 1st gear, 1:1 in

highest gear; gear ratio in differential typically 3:1highest gear; gear ratio in differential typically 3:1» Ratio of engine revolutions to wheel revolutions varies from 12:1 in Ratio of engine revolutions to wheel revolutions varies from 12:1 in

lowest gear to 3:1 in highest gearlowest gear to 3:1 in highest gear Power Power tells you how fast you can climb the hilltells you how fast you can climb the hill Torque can be increased by transmission (e.g. 2:1 gear ratio Torque can be increased by transmission (e.g. 2:1 gear ratio

ideally multiplies torque by 2)ideally multiplies torque by 2)

Power can’t be increased by transmission; in fact because of Power can’t be increased by transmission; in fact because of friction and other losses, power will decrease in transmissionfriction and other losses, power will decrease in transmission

Power tells how fast you can accelerate or how fast you can Power tells how fast you can accelerate or how fast you can climb a hill, but power to torque ratio ~ N tells you what gear climb a hill, but power to torque ratio ~ N tells you what gear ratios you’ll need to do the jobratios you’ll need to do the job

€

P (in horsepower) ≡N (revolutions per minute, RPM) x Torque (in foot pounds)

5252

3333

How much power does an engine make?How much power does an engine make?

€

Power = η th˙ Q = η th ˙ m fuelQR = η th

˙ m air f

1+ fQR

˙ m air = η vρ airVd N /n

η th = thermal efficiency ≡Power output

˙ m fuelQR

η v = volumetric efficiency ≡˙ m air (actual)

˙ m air (theoretical)

ff Fuel mass fraction in mixture (---)Fuel mass fraction in mixture (---)Air mass flow rate (kg/s)Air mass flow rate (kg/s)Fuel mass flow rate (kg/s)Fuel mass flow rate (kg/s)

NN Engine rotational speed (revolutions per second)Engine rotational speed (revolutions per second)nn Parameter = 1 for 2-stroke engine, = 2 for 4-strokeParameter = 1 for 2-stroke engine, = 2 for 4-stroke

Heat transfer rate (Watts)Heat transfer rate (Watts)QQRR Fuel heating value (J/kg)Fuel heating value (J/kg)

VVdd Displacement volume (mDisplacement volume (m33))

airair Air density (= 1.18 kg/mAir density (= 1.18 kg/m33 at 298K, 1 atm) at 298K, 1 atm)

€

˙ m a

€

˙ m f

3434

Fuel propertiesFuel properties

Fuel Heating value, QR

(J/kg)

f at stoichiometric

Gasoline 43 x 106 0.0642

Methane 50 x 106 0.0550

Methanol 20 x 106 0.104

Ethanol 27 x 106 0.0915

Coal 34 x 106 0.0802

Paper 17 x 106 0.122

Fruit Loops

16 x 106 Probably about the same as paper

Hydrogen 120 x 106 0.0283

U235 fission

82,000,000 x 106

1

3535

Volumetric efficiencyVolumetric efficiency Volumetric efficiency (Volumetric efficiency (vv) = (mass of air actually drawn into cylinder) / ) = (mass of air actually drawn into cylinder) /

(mass of air that ideally could be drawn into cylinder) (mass of air that ideally could be drawn into cylinder)

where where airair is at ambient = P is at ambient = Pambientambient/RT/RTambientambient and R - 287 J/kgK for air and R - 287 J/kgK for air Volumetric efficiency indicates how well the engine “breathes” - what Volumetric efficiency indicates how well the engine “breathes” - what

lowers lowers vv below 100%? below 100%? Pressure drops in intake system (e.g. throttling) & intake valvesPressure drops in intake system (e.g. throttling) & intake valves Temperature rise due to heating of air as it flows through intake Temperature rise due to heating of air as it flows through intake

systemsystem Volume occupied by fuelVolume occupied by fuel Non-ideal valve timingNon-ideal valve timing ““Choking” (air flow reaching speed of sound) in part of intake system Choking” (air flow reaching speed of sound) in part of intake system

having smallest area (passing intake valves)having smallest area (passing intake valves) See figure on p. 217 of Heywood (Internal Combustion Engine See figure on p. 217 of Heywood (Internal Combustion Engine

Fundamentals, McGraw-Hill, 1988) for good summary of all these effectsFundamentals, McGraw-Hill, 1988) for good summary of all these effects

€

v ≡˙ m air (measured)

ρ airVd N /n

3636

ExampleExample

How much power does a 5.7 liter (= 0.0057 mHow much power does a 5.7 liter (= 0.0057 m33) Hemi ) Hemi 4-stroke (n = 2) gasoline engine at 6000 RPM (N = 4-stroke (n = 2) gasoline engine at 6000 RPM (N = 100/sec) with thermal efficiency 100/sec) with thermal efficiency thth = 30% = 0.30 and = 30% = 0.30 and

volumetric efficiency volumetric efficiency vv = 85% = 0.85 generate? = 85% = 0.85 generate?

€

˙ m air = η vρ airVd N /n = 0.85( )1.18kg

m3 0.0057m3( )

100

sec

1

2=

0.286kg

sec

Power = η th

˙ m air f

1+ fQR = 0.30( )

0.286kg

sec0.0642

1+ 0.0642

4.3 ×107 J

kg

= 2.22 ×105Whp

746W= 298hp

3737http://static.howstuffworks.com/flash/engine.swf

4-stroke premixed-charge piston engine4-stroke premixed-charge piston engineMost common type of IC engineMost common type of IC engineSimple, easy to manufacture, Simple, easy to manufacture,

inexpensive materialsinexpensive materialsGood power/weight ratioGood power/weight ratioExcellent flexibility - works Excellent flexibility - works

reasonably well over a wide range reasonably well over a wide range of engine speeds and loadsof engine speeds and loads

Rapid response to changing Rapid response to changing speed/load demandspeed/load demand

““Acceptable” emissionsAcceptable” emissionsWeaknessesWeaknesses

Fuel economy (compared to Diesel, Fuel economy (compared to Diesel, due lower compression ratio & due lower compression ratio & throttling losses at part-load)throttling losses at part-load)

Power/weight (compared to gas Power/weight (compared to gas turbine)turbine)

3838

4-stroke premixed-charge piston engine4-stroke premixed-charge piston engine Animation: http://auto.howstuffworks.com/engine3.htmAnimation: http://auto.howstuffworks.com/engine3.htm

Note: ideally combustion occurs in zero time when piston is at the top of its travel between the Note: ideally combustion occurs in zero time when piston is at the top of its travel between the compression and expansion strokescompression and expansion strokes

Intake (piston Intake (piston moving down, moving down, intake valve intake valve open, exhaust open, exhaust valve closed)valve closed)

Compression Compression (piston moving (piston moving up, both valves up, both valves closed)closed)

Expansion Expansion (piston moving (piston moving down, both down, both valves closed)valves closed)

Exhaust (piston Exhaust (piston moving up, intake moving up, intake valve closed, valve closed, exhaust valve open)exhaust valve open)

3939

ThrottlingThrottling When you need less than the maximum torque available When you need less than the maximum torque available

from a premixed-charge engine (which is most of the time), a from a premixed-charge engine (which is most of the time), a throttlethrottle is used to control torque & power is used to control torque & power

Throttling adjusts torque output by reducing intake density Throttling adjusts torque output by reducing intake density through decrease in pressure Throttling loss significant at through decrease in pressure Throttling loss significant at light loads (see next page)light loads (see next page)

Control of fuel/air ratio can adjust torque, but cannot provide Control of fuel/air ratio can adjust torque, but cannot provide sufficient range of control - misfire problems with lean sufficient range of control - misfire problems with lean mixturesmixtures

Diesel - nonpremixed-charge - use fuel/air ratio control - no Diesel - nonpremixed-charge - use fuel/air ratio control - no misfire limit - no throttling neededmisfire limit - no throttling needed

4040

ThrottlingThrottling Throttling loss increases from zero at wide-open throttle (WOT) to about Throttling loss increases from zero at wide-open throttle (WOT) to about

half of all fuel usage at idle (other half is friction loss)half of all fuel usage at idle (other half is friction loss) At typical highway cruise condition (≈ 1/3 of torque at WOT), about 15% At typical highway cruise condition (≈ 1/3 of torque at WOT), about 15%

loss due to throttling (loss due to throttling (side topic: throttleless premixed-charge enginesside topic: throttleless premixed-charge engines)) Throttling isn’t always bad, when you take your foot off the gas pedal & Throttling isn’t always bad, when you take your foot off the gas pedal &

shift to a lower gear to reduce vehicle speed, you’re using throttling loss shift to a lower gear to reduce vehicle speed, you’re using throttling loss

(negative torque) and high N to maximize negative power(negative torque) and high N to maximize negative power

K = IMEP/P intake =

9.1FMEP = 10 psi

Pambient = 14.7 psi0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

BMEP / BMEP at wide open throttle

Efficiency (with throttle) / Efficiency (without throttle)

Typical highway cruise condition ≈ 1/3 of maximum BMEP

≈ 0.85

Double-click plotDouble-click plotTo open Excel chartTo open Excel chart

4141

ThrottlingThrottling

Another way to reduce throttling losses: close off some Another way to reduce throttling losses: close off some cylinders when low power demand cylinders when low power demand Cadillac had a 4-6-8 engine in the 1981 but it was a mechanical Cadillac had a 4-6-8 engine in the 1981 but it was a mechanical

disaster disaster GM uses a 4-8 “Active fuel management” (previously called GM uses a 4-8 “Active fuel management” (previously called

“Displacement On Demand”) engine “Displacement On Demand”) engine http://www.gm.com:80/experience/technology/news/2006/2007_powertrain_http://www.gm.com:80/experience/technology/news/2006/2007_powertrain_

051806.jsp051806.jsp Mercedes has had 4-8 “Cylinder deactivation” engines for Mercedes has had 4-8 “Cylinder deactivation” engines for

European markets since 1998:European markets since 1998:http://www.answers.com/topic/active%20cylinder%20controlhttp://www.answers.com/topic/active%20cylinder%20control

Many auto magazines suggest this will cut fuel usage in half, Many auto magazines suggest this will cut fuel usage in half, as though engines use fuel based only on displacement, not as though engines use fuel based only on displacement, not RPM (N) or intake manifold pressure - more realistic articles RPM (N) or intake manifold pressure - more realistic articles report 8 - 10% improvement in efficiencyreport 8 - 10% improvement in efficiency

4242

2-stroke premixed-charge engine2-stroke premixed-charge engine Source: http://static.howstuffworks.com/flash/two-stroke.swfSource: http://static.howstuffworks.com/flash/two-stroke.swf

4343

2-stroke premixed-charge engine2-stroke premixed-charge engine Most designs have fuel-air mixture Most designs have fuel-air mixture

flowing first INTO CRANKCASE (?)flowing first INTO CRANKCASE (?) Fuel-air mixture must contain Fuel-air mixture must contain

lubricating oil lubricating oil On down-stroke of pistonOn down-stroke of piston

Exhaust ports are exposed & Exhaust ports are exposed & exhaust gas flows out, crankcase is exhaust gas flows out, crankcase is pressurizedpressurized

Reed valve prevents fuel-air mixture Reed valve prevents fuel-air mixture from flowing back out intake from flowing back out intake manifoldmanifold

Intake ports are exposed, fresh fuel-Intake ports are exposed, fresh fuel-air mixture flows into intake portsair mixture flows into intake ports

On up-stroke of pistonOn up-stroke of piston Intake & exhaust ports are coveredIntake & exhaust ports are covered Fuel-air mixture is compressed in Fuel-air mixture is compressed in

cylindercylinder Spark & combustion occurs near top Spark & combustion occurs near top

of piston travelof piston travel Work output occurs during 1st half Work output occurs during 1st half

of down-strokeof down-stroke

4444

2-stroke premixed-charge engine2-stroke premixed-charge engine

2-strokes gives ≈ 2x as much power2-strokes gives ≈ 2x as much power since only 1 crankshaft since only 1 crankshaft revolution needed for 1 complete cycle (vs. 2 revolutions for revolution needed for 1 complete cycle (vs. 2 revolutions for 4-strokes)4-strokes)

Since intake & exhaust ports are open at same time, some Since intake & exhaust ports are open at same time, some fuel-air mixture flows directly out exhaust & some exhaust fuel-air mixture flows directly out exhaust & some exhaust gas gets mixed with fresh gasgas gets mixed with fresh gas

Since oil must be mixed with fuel, oil gets burnedSince oil must be mixed with fuel, oil gets burned As a result of these factors, As a result of these factors, thermal efficiency is lower, thermal efficiency is lower,

emissions are higher, and performance is near-optimal for a emissions are higher, and performance is near-optimal for a narrower range of engine speedsnarrower range of engine speeds compared to 4-strokes compared to 4-strokes

Use primarily for small vehicles, leaf blowers, RC aircraft, Use primarily for small vehicles, leaf blowers, RC aircraft, etc. where power/weight is the overriding concernetc. where power/weight is the overriding concern

4545

Rotary or Wankel engineRotary or Wankel engine Uses non-cylindrical combustion chamberUses non-cylindrical combustion chamber Provides one complete cycle per engine revolution without “short circuit” flow of 2-Provides one complete cycle per engine revolution without “short circuit” flow of 2-

strokes (but still need some oil injected at the rotor apexes)strokes (but still need some oil injected at the rotor apexes) Simpler, fewer moving parts, higher RPM possibleSimpler, fewer moving parts, higher RPM possible Very fuel-flexible - can incorporate catalyst in combustion chamber since fresh gas Very fuel-flexible - can incorporate catalyst in combustion chamber since fresh gas

is moved into chamber rather than being continually exposed to it (as in piston is moved into chamber rather than being continually exposed to it (as in piston engine) - same design can use gasoline, Diesel, methanol, etc. engine) - same design can use gasoline, Diesel, methanol, etc.

Very difficult to seal BOTH vertices and flat sides of rotor!Very difficult to seal BOTH vertices and flat sides of rotor! Seal longevity a problem alsoSeal longevity a problem also Large surface area to volume ratio means more heat lossesLarge surface area to volume ratio means more heat losses

http://static.howstuffworks.com/flash/rotary-engine-exploded.swf

4747

Rotary or Wankel engineRotary or Wankel engine Source: Source: http://static.howstuffworks.com/flash/rotary-engine-animation.swf http://static.howstuffworks.com/flash/rotary-engine-animation.swf

4848

4-stroke Diesel engine4-stroke Diesel engine

Conceptually similar to 4-Conceptually similar to 4-stroke gasoline, but only stroke gasoline, but only air is compressed (not air is compressed (not fuel-air mixture) and fuel fuel-air mixture) and fuel is injected into is injected into combustion chamber combustion chamber after air is compressedafter air is compressed

Key advantagesKey advantages Higher compression Higher compression

ratio possible because ratio possible because no knock (only air is no knock (only air is compressed)compressed)

No throttling losses No throttling losses since always operated at since always operated at atmospheric intake atmospheric intake pressurepressure

http://static.howstuffworks.com/flash/diesel2.swf

4949

Premixed vs. non-premixed charge enginesPremixed vs. non-premixed charge engines

Flame front Fuel spray flame

Premixed charge(gasoline)

Non-premixed charge(Diesel)

Spark plug Fuel injector

Fuel + air mixture Air only

5252

2006 GM Northstar 4.6 Liter V8 (LD8);2006 GM Northstar 4.6 Liter V8 (LD8);r = 10.5; variable valve timingr = 10.5; variable valve timing

Comparison of GM truck engines - gasoline vs. DieselComparison of GM truck engines - gasoline vs. Diesel

Recall Power (hp) = Torque (ft lb) x N (rev/min) Recall Power (hp) = Torque (ft lb) x N (rev/min) 5252 5252 Gasoline: Torque ≈ constant from 1000 to 6000 RPM; power ~ NGasoline: Torque ≈ constant from 1000 to 6000 RPM; power ~ N Turbo Diesel: Torque sharply peaked; much narrower range of usable N Turbo Diesel: Torque sharply peaked; much narrower range of usable N

(1000 - 3000 RPM) (P(1000 - 3000 RPM) (Pintakeintake not reported on website but maximum ≈ 3 atm not reported on website but maximum ≈ 3 atm

from other data)from other data) Smaller, non-turbocharged gasoline engine produces almost as much Smaller, non-turbocharged gasoline engine produces almost as much

power as turbo Diesel,power as turbo Diesel, largely due to higher N largely due to higher N

2006 GM Duramax 6.6 liter V8 2006 GM Duramax 6.6 liter V8 turbocharged Diesel (LBZ); r = 16.8turbocharged Diesel (LBZ); r = 16.8

5353

Ronney’s catechism (1/4)Ronney’s catechism (1/4) Why do we throttle in a premixed charge engine despite the throttling Why do we throttle in a premixed charge engine despite the throttling

losses it causes?losses it causes? Because we have to reduce power & torque when we don’t want the Because we have to reduce power & torque when we don’t want the

full output of the engine (which is most of the time in LA traffic, or full output of the engine (which is most of the time in LA traffic, or even on the open road)even on the open road)

Why don’t we have to throttle in a nonpremixed charge engine?Why don’t we have to throttle in a nonpremixed charge engine? Because we use control of the fuel to air ratio (i.e. to reduce power & Because we use control of the fuel to air ratio (i.e. to reduce power &

torque, we reduce the fuel for the (fixed) air mass)torque, we reduce the fuel for the (fixed) air mass) Why don’t we do that for the premixed charge engine and avoid throttling Why don’t we do that for the premixed charge engine and avoid throttling

losses?losses? Because if we try to burn lean in the premixed-charge engine, when Because if we try to burn lean in the premixed-charge engine, when

the equivalence ratio (the equivalence ratio () is reduced below about 0.7, the mixture ) is reduced below about 0.7, the mixture misfires and may stop altogethermisfires and may stop altogether

Why isn’t that a problem for the nonpremixed charge engine?Why isn’t that a problem for the nonpremixed charge engine? Nonpremixed-charge engines are not subject to flammability limits like Nonpremixed-charge engines are not subject to flammability limits like

premixed-charge engines since there is a continuously range of fuel-premixed-charge engines since there is a continuously range of fuel-to-air ratios varying from zero in the pure air to infinite in the pure fuel, to-air ratios varying from zero in the pure air to infinite in the pure fuel, thus someplace there is a stoichiometric (thus someplace there is a stoichiometric ( = 1) mixture that can burn. = 1) mixture that can burn. Such variation in Such variation in does not occur in premixed-charge engines since, does not occur in premixed-charge engines since, by definition, by definition, is the same everywhere. is the same everywhere.

5454

Ronney’s catechism (2/4)Ronney’s catechism (2/4) So why would anyone want to use a premixed-charge engine?So why would anyone want to use a premixed-charge engine?

Because the nonpremixed-charge engine burns its fuel slower, since Because the nonpremixed-charge engine burns its fuel slower, since fuel and air must mix before they can burn. This is already taken care of fuel and air must mix before they can burn. This is already taken care of in the premixed-charge engine. This means lower engine RPM and thus in the premixed-charge engine. This means lower engine RPM and thus less power from an engine of a given displacement less power from an engine of a given displacement

Wait - you said that the premixed-charge engine is slower burning. Wait - you said that the premixed-charge engine is slower burning. Only if the mixture is too lean. If it’s near-stoichiometric, then it’s faster Only if the mixture is too lean. If it’s near-stoichiometric, then it’s faster

because, again, mixing was already done before ignition (ideally, at because, again, mixing was already done before ignition (ideally, at least). Recall that as least). Recall that as drops, T drops, Tadad drops proportionately, and burning drops proportionately, and burning velocity (Svelocity (SLL) drops exponentially as T) drops exponentially as Tadad drops drops

Couldn’t I operate my non-premixed charge engine at overall stoichiometric Couldn’t I operate my non-premixed charge engine at overall stoichiometric conditions to increase burning rate? conditions to increase burning rate? No. In nonpremixed-charge engines it still takes time to mix the pure No. In nonpremixed-charge engines it still takes time to mix the pure

fuel and pure air, so (as discussed previously) burning rates, flame fuel and pure air, so (as discussed previously) burning rates, flame lengths, etc. of nonpremixed flames are usually limited by mixing rates, lengths, etc. of nonpremixed flames are usually limited by mixing rates, not reaction rates. Worse still, with initially unmixed reactants at overall not reaction rates. Worse still, with initially unmixed reactants at overall stoichiometric conditions, the last molecule of fuel will never find the stoichiometric conditions, the last molecule of fuel will never find the last molecule of air in the time available for burning in the engine - one last molecule of air in the time available for burning in the engine - one will be in the upper left corner of the cylinder, the other in the lower will be in the upper left corner of the cylinder, the other in the lower right corner. That means unburned or partially burned fuel would be right corner. That means unburned or partially burned fuel would be emitted. That’s why diesel engines smoke at heavy load, when the emitted. That’s why diesel engines smoke at heavy load, when the mixture gets too close to overall stoichiometric.mixture gets too close to overall stoichiometric.

5555

Ronney’s catechism (3/4)Ronney’s catechism (3/4) So what wrong with operating at a maximum fuel to air ratio a little lean So what wrong with operating at a maximum fuel to air ratio a little lean

of stoichiometric?of stoichiometric? That reduces maximum power, since you’re not burning every That reduces maximum power, since you’re not burning every

molecule of Omolecule of O22 in the cylinder. Remember - O in the cylinder. Remember - O22 molecules take up a molecules take up a lot more space in the cylinder that fuel molecules do (since each Olot more space in the cylinder that fuel molecules do (since each O22 is attached to 3.77 Nis attached to 3.77 N22 molecules), so it behooves you to burn every molecules), so it behooves you to burn every last Olast O22 molecule if you want maximum power. So because of the molecule if you want maximum power. So because of the mixing time as well as the need to run overall lean, Diesels have mixing time as well as the need to run overall lean, Diesels have less power for a given displacement / weight / size / etc.less power for a given displacement / weight / size / etc.

So is the only advantage of the Diesel the better efficiency at part-load So is the only advantage of the Diesel the better efficiency at part-load due to absence of throttling loss?due to absence of throttling loss? No, you also can go to higher compression ratios, which increases No, you also can go to higher compression ratios, which increases

efficiency at any load. This helps alleviate the problem that slower efficiency at any load. This helps alleviate the problem that slower burning in Diesels means lower inherent efficiency (more burning at burning in Diesels means lower inherent efficiency (more burning at increasing cylinder volume)increasing cylinder volume)

Why can the compression ratio be higher in the Diesel engine?Why can the compression ratio be higher in the Diesel engine? Because you don’t have nearly as severe problems with knock. Because you don’t have nearly as severe problems with knock.

That’s because you compress only air, then inject fuel when you That’s because you compress only air, then inject fuel when you want it to burn. In the premixed-charge case, the mixture being want it to burn. In the premixed-charge case, the mixture being compressed can explode (since it’s fuel + air) if you compress it too compressed can explode (since it’s fuel + air) if you compress it too muchmuch

5656

Ronney’s catechism (4/4)Ronney’s catechism (4/4) Why is knock so bad?Why is knock so bad?

It causes intense pressure waves that rattle the piston and leads to It causes intense pressure waves that rattle the piston and leads to severe engine damagesevere engine damage

So, why have things evolved such that small engines are usually premixed-So, why have things evolved such that small engines are usually premixed-charge, whereas large engines are nonpremixed-charge?charge, whereas large engines are nonpremixed-charge? In small engines (lawn mowers, autos, etc.) you’re usually most In small engines (lawn mowers, autos, etc.) you’re usually most

concerned with getting the highest power/weight and power/volume concerned with getting the highest power/weight and power/volume ratios, rather than best efficiency (fuel economy). In larger engines ratios, rather than best efficiency (fuel economy). In larger engines (trucks, locomotives, tugboats, etc.) you don’t care as much about size (trucks, locomotives, tugboats, etc.) you don’t care as much about size and weight but efficiency is more criticaland weight but efficiency is more critical

But unsteady-flow aircraft engines, even large ones, are premixed-charge, But unsteady-flow aircraft engines, even large ones, are premixed-charge, because weight is always critical in aircraftbecause weight is always critical in aircraft You got me on that one. But of course most large aircraft engines are You got me on that one. But of course most large aircraft engines are

steady-flow gas turbines, which kill unsteady-flow engines in terms of steady-flow gas turbines, which kill unsteady-flow engines in terms of power/weight and power/volume.power/weight and power/volume.

5757

Practical alternatives… discussion pointsPractical alternatives… discussion points Conservation!Conservation! Combined cycles: use hot exhaust from ICE to heat water for Combined cycles: use hot exhaust from ICE to heat water for

conventional steam cycle - can achieve > 60% efficiency but not conventional steam cycle - can achieve > 60% efficiency but not practical for vehicles - too much added volume & weightpractical for vehicles - too much added volume & weight

Natural gasNatural gas 4x cheaper than electricity, 2x cheaper than gasoline or diesel for 4x cheaper than electricity, 2x cheaper than gasoline or diesel for

same energysame energy Somewhat cleaner than gasoline or diesel, but no environmental Somewhat cleaner than gasoline or diesel, but no environmental

silver bulletsilver bullet Low energy storage density - 4x lower than gasoline or dieselLow energy storage density - 4x lower than gasoline or diesel

5858

Practical alternatives… discussion pointsPractical alternatives… discussion points Fischer-Tropsch fuels - liquid hydrocarbons from coal or natural gasFischer-Tropsch fuels - liquid hydrocarbons from coal or natural gas

Competitive with $75/barrel oilCompetitive with $75/barrel oil Cleaner than gasoline or dieselCleaner than gasoline or diesel … … but using coal increases greenhouse gases!but using coal increases greenhouse gases!

Coal : oil : natural gas = 2 : 1.5 : 1Coal : oil : natural gas = 2 : 1.5 : 1 But really, there is no way to decide what the next step is until it is But really, there is no way to decide what the next step is until it is

decided whether there will be a tax on COdecided whether there will be a tax on CO22 emissions emissions Personal opinion: most important problems are (in order of priority)Personal opinion: most important problems are (in order of priority)

Global warmingGlobal warming Energy independenceEnergy independence EnvironmentEnvironment

5959

Summary of advantages of ICEsSummary of advantages of ICEs 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 (4.3 x 104.3 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 Relative safety of hydrocarbons compared to hydrogen or Relative safety of hydrocarbons compared to hydrogen or

nuclear energynuclear energy Conclusion #1: IC engines are the worst form of vehicle Conclusion #1: IC engines are the worst form of vehicle

propulsion, except for all the other formspropulsion, except for all the other forms Conclusion #2: Oil costs way too much, but it’s still Conclusion #2: Oil costs way too much, but it’s still

very cheapvery cheap

6060

Sidebar: Throttleless Premixed-Charge Engine (TPCE)Sidebar: Throttleless Premixed-Charge Engine (TPCE)

E. J. Durbin & P. D. Ronney, U.S. Patent No. 5,184,592 E. J. Durbin & P. D. Ronney, U.S. Patent No. 5,184,592 http://ronney.usc.edu/Research/TPCE/TPCE_patent.pdfhttp://ronney.usc.edu/Research/TPCE/TPCE_patent.pdf

Use intake temperature increment via exhaust heat transfer to reduce air Use intake temperature increment via exhaust heat transfer to reduce air density, thus IMEP/torque/powerdensity, thus IMEP/torque/power

Keep PKeep Pintakeintake (= P (= P22 in our notation) at ambient in our notation) at ambient (no throttling loss)(no throttling loss) Increasing TIncreasing Tintakeintake = (T = (T22 in our notation) leads to leaner lean misfire limit in our notation) leads to leaner lean misfire limit

(lower f) - use air/fuel ratio AND T(lower f) - use air/fuel ratio AND T intakeintake to control power/torque to control power/torque Lean limit corresponds ≈ to constant TLean limit corresponds ≈ to constant Tadad (= T (= T44 in our notation) in our notation) TT44 = T = T33 + fQ + fQRR/C/Cvv = T = T22rr

-1-1 + fQ + fQRR/C/Cvv can get lean-limit T can get lean-limit T44 through various through various

combinations of Tcombinations of T22 & f & f Higher THigher T22 & lower f & lower f lower IMEP lower IMEP

Higher THigher Tintakeintake increases knock tendency, but increases knock tendency, but Lean mixtures much less susceptible to knockLean mixtures much less susceptible to knock Alternative fuels (natural gas, methanol, ethanol) betterAlternative fuels (natural gas, methanol, ethanol) better

Retrofit to existing engines possible by changing only intake, exhaust, & Retrofit to existing engines possible by changing only intake, exhaust, & control systemscontrol systems

€

IMEPg =Pintake

RTintake

η th,i,gη v fQR = ρ intakeη th,i,gη v fQR

6161

TPCE operating limitationsTPCE operating limitations

6262

Test apparatusTest apparatus Production 4-cylinder engines Production 4-cylinder engines Maximum Brake Torque (MBT) spark timingMaximum Brake Torque (MBT) spark timing For simplicity, electrical heating, not exhaust heat transfer in For simplicity, electrical heating, not exhaust heat transfer in

test enginetest engine

6363

ResultsResults Substantially improved fuel economy (up to 16 %) compared Substantially improved fuel economy (up to 16 %) compared

to throttled engine at same power & RPMto throttled engine at same power & RPM EmissionsEmissions

Untreated NOUntreated NOxx performance performance

< 0.8 grams per kW-hr< 0.8 grams per kW-hr> 10 x lower than throttled engine )> 10 x lower than throttled engine )< 0.2 grams per mile for 15 hp road load @ 55 mi/hr< 0.2 grams per mile for 15 hp road load @ 55 mi/hr

CO and UHC comparable to throttled engineCO and UHC comparable to throttled engine May need only inexpensive 2-way oxidizing catalyst for CO & May need only inexpensive 2-way oxidizing catalyst for CO &

UHC in TPCE enginesUHC in TPCE engines All improvements nearly independent of RPMAll improvements nearly independent of RPM Good knock performance of lean mixtures, even with Good knock performance of lean mixtures, even with

gasoline, instrumental to TPCE performancegasoline, instrumental to TPCE performance

6464

TPCE performance TPCE performance

1

10

0 0.2 0.4 0.6 0.8 1

Throttled engineTPCE engine

Engine load (fraction of maximum)

1

1.05

1.1

1.15

1.2

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Natural gasGasolineTheory

Engine load (fraction of maximum)

6565

TPCE implementation conceptTPCE implementation concept Branched intake manifold with diverter valve to control intake Branched intake manifold with diverter valve to control intake

TT