clues for improvements in i. c. engine design p m v subbarao professor mechanical engineering...
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Clues for Improvements in I. C. Engine Design
P M V SubbaraoProfessor
Mechanical Engineering Department
Future Direction for Better Performance !!!
Clues for Improvement- reduce heat loss
• Heat losses caused by high engine turbulence level
• Need high turbulence to
• Wrinkle flame (premixed charge, gasoline)
• Disperse fuel droplets (nonpremixed charge, Diesel)
• "Inverse-engineer" engine for low-turbulenc
• Gasoline - electrically-induced flame wrinkling?
• Diesel - electrostatic dispersion of fuel in chamber?
Clues for Improvement - 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 densitydensity through decrease in pressurepressure ( PP = RT)
• Throttling losses substantial at part load
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Fraction of maximum load
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Natural gasGasolineTheory
Eff
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iency (
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ttle
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Load (fraction of maximum)
Clues for Improvement for improvements : Reduce Friction Losses
• Programmable intake/exhaust valve timing
• Electrical/hydraulic valve actuation
• Choose open/close timing to optimize power, emissions, efficiency - can eliminate throttling loss
The Art of Down Sizing an Engine
Clues for Improvement for improvements : Down Sizing
Clues for Improvement : Reduce NOx
• Homogeneous ignition engine - controlled knocking
• Burn much leaner mixtures - higher efficiency, lower Nox
• Need to abandon traditional combustion control strategy
Ideas - improved lean-limit operation
• Recent experiments & modelling suggest lean-limit rough operation is a chaoticchaotic 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
Fuel Savings due to down sizing + +
Conclusions
• IC engines are the non-ideal 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)
– SensorsSensors (especially in-cylinder temperature, pressure)
– ActuatorsActuators (especially intake valves)
Development of Power Plant for A Vehicle
P M V SubbaraoProfessor
Mechanical Engineering Department
Matching the horse to the Cart …..
TRACTIVE FORCE REQUIREMENTS
• Vehicles require thrust forces, generated at the tires, to initiate and maintain motion.
• These forces are usually referred to as tractive forces or the tractive force requirement.
• If the required tractive force (F) is broken into various components.
Major Force Components Demanding Trctive Force
• Resistance
• Tractive effort
• Vehicle acceleration
• Braking
• Stopping distance
Resistance Force : Ra
• The major components of the resisting forces to motion are comprised of :
• Aerodynamic loads (Faero) • Acceleration forces (Faccel = ma & I forces)• Gradeability requirements (Fgrade)• Chassis losses (Froll resist ).
grraero FFFmaF
Aerodynamic Force : Flow Past A Bluff Body
Composed of:
1. Turbulent air flow around vehicle body (85%)
2. Friction of air over vehicle body (12%)
3. Vehicle component resistance, from radiators and air vents (3%)
Aerodynamic Resistance on Vehicle
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VF = P designd ,
Dynamic Pressure:
Drag Force:
Aero Power