Question

For internal combustion engines found that the cycle thermal cffciency would increase with an increase in compression ratio of the cycle. Discuss the factors that limit us in taking advantage of this fact and this explains the higher efficiencies of compression ignition engines

type the anser plase not hand writing thank you

Answer 1

As thermal efficiency increases with increase in compression ratio but we can increase compression only up to a certain value which is known as KNOCK LIMITED COMPRESSION RATIO.

After this compression ratio, knocking inside the engine increases which results in poor thermal efficiency and low power output.

Secondly when the compression ratio increases then the pressure inside the combustion chamber increases and the parts like piston, connecting rod, crankshaft are design to sustain a particular value of load above that value these part fails. Hence in this way it limits the compression ratio.

Efficiency is basically defined for two particular condition that is PART LOAD CONDITION and FULL LOAD CONDITION. Part load efficiency of CI engine is higher than SI engine because in CI engine there is no throttle valve hence there is no obstruction in the path of incoming air. Thus the losses reduces.

Full load efficiency of SI engine is higher than CI engine because in SI engine we get a complete combustion and almost negligible unburnt hydrocarbons are present in exhaust. In CI engine we never get a complete combustion hence always we get a overlean mixture and unburnt hydrocarbons in exhaust that's why it's efficiency is poor at Full load condition as compared to SI Engine.