Operating Cycles

OTTO CYCLE (Constant Volume Combustion Cycle).

• It is the ideal air standard cycle for Petrol engine, the gas engine and the high-speed oil engine.
• The engines based on this cycle have high thermal efficiency but noisiness results particularly at higher power due to higher pressures in the cylinders.

DIESEL CYCLE (Constant Pressure Combustion Cycle).

• It is the ideal Air standard cycle for Diesel Engine, especially suitable for low speed Diesel Engine but not for high speed Diesel Engine.
• The thermal efficiency is lower than Otto cycle engines but engines run smoothly due to lower pressures in the cylinder.

DUAL COMBUSTION CYCLE (Constant Pressure and Constant Volume Combustion Cycle).

• Modern Diesel Engines do not operate purely on constant pressure combustion cycle but some part of combustion process takes place at constant volume while the rest is completed at constant pressure.
• In general, this cycle resembles Constant volume combustion Cycle more than constant pressure combustion cycle. It is suitable for modern Medium and High Speed Diesel Engines.
• The thermal efficiency is more than Diesel Cycle but less than Otto cycle. Also noise level is in between the two. This is a more practical engine.