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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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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Drag Force:

Aero Power