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

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The Evolution of the Internal Combustion Engine
and Future Design ChallengesPerformance,
Efficiency, Emissions

• Paul D. Ronney
• Dept. of Aerospace Mechanical Eng.
• University of Southern California
• Los Angeles, CA 90089-1453 USA
• http//carambola.usc.edu

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Outline

• Why gasoline-fueled premixed-charge IC engines?
• History and evolution
• Things you need to understand about IC engines
  before ...
• Ideas for improvements
• Conclusions

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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 (gt100 miles per gallon)

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Zero emission electric vehicles
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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

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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

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Premixed vs. non-premixed charge engines
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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 wont believe it
• Initial stop-gap measures - lean mixture, EGR,
  retard spark
• Poor performance fuel economy
• 1973 1979 - The energy crises
• Detroit takes a bath

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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!!!

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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

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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

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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

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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

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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

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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?

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Electrostatic sprays
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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

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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

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TPCE implementation concept
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Results

• Substantially improved fuel economy (up to 16 )
  compared to throttled engine at same power RPM

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Results

• NOx performance
• lt 0.8 grams per kW-hr (10 x lower than throttled
  engine )
• lt 0.2 grams per mile for 15 hp road load _at_ 55
  mi/hr - half of California 2001 standard
• CO and UHC comparable to throttled engine

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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

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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

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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

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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)

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Thanks to ...

• USC Dept. of Aerospace Mechanical Engineering
• Gas Research Institute
• South Coast Air Quality Management District
• and especially METRANS