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Approaches Air-Standard cycle analysis

Fuel-Air cycle analysis

Actual cycle analysis

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Basic Thermodynamic Cycles

Otto Cycle

Diesel Cycle

Dual Combustion Cycle

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Air-Standard cycle analysis to perform elementary analyses of IC

engine cycles

simplifications include:  fixed amount of air (ideal gas) for working

fluid

 combustion process not considered

 intake and exhaust processes not considered

 engine friction and heat losses not considered

 specific heats independent of temperature

 all processes are reversible

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Otto Cycle

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Diesel Cycle

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Dual Combustion Cycle

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Comparison of cyclesSame Compression ratio & Heat addition

diesl dual otto       

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Comparison of cyclesSame Max.pressure & Heat addition

ott dual diesel        

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 Fuel-Air Cycles: Significancefactors taken into account actual composition of cylinder gases

variation of specific heat w.r.ttemperature

effect of dissociation

variation in the no of moleculesAnalysis gives effect of variation ofF/A ratio and compression ratio

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 Fuel-Air Cycles : assumptions no chemical change in fuel/air prior to

combustion

charge is in chemical equilibrium

compression and expansion are adiabatic &frictionless

fluid motion inside cylinder is ignored

fuel is completely vaporized and perfectlymixed with air (for Otto cycle)

burning takes place instantaneously (forOtto cycle)

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Fuel air cycle- Otto

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Fuel air cycle- Diesel

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Composition of Cylinder gases A/F ratio changes during engine

operation

Thus affects composition of gasesbefore & after combustion Amount of exhaust gases in clearance

varies with load

Analysis which includes this, needsnumerical techniques (computeranalysis)

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Variable Specific heats  p-V  

diagram

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Effect of dissociation on Temp

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Dissociation in  p-V  diagram

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Actual CyclesOTTO DIESEL

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Reasons for the deviation Mixing of A/F mixture with products of

combustion from the previous cycle

Change in chemical composition of mixture

Variation of specific heats with temperature

Gas leakage, fluid friction

Not instantaneous combustion

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Loss of power in Actual

Cycles Time loss

Heat loss

Exhaust blow down loss

Pumping loss

Friction loss

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Time loss

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Time loss Increases Loss on compression

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Time loss Decreases Loss on compression

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Heat loss, Blow down loss and

Pumping loss Heat loss during combustion and expansion

(to components, cooling medium,lubricant)

Reduces max.temp & contributes 12% Blow down loss due to early opening of

exhaust valve

contributes 2%

Pumping loss due to pumping gas fromlower inlet pressure to higher exhaustpressure

contributes 2% and increases with speed

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Effect of losses on  p-v diagram