Variations of compression ratios

[mech-eng]

Hi,all. What changes the variations of compression rations in diesel and otto cycles which are
always used in the engines. Are there any cycles used in automobile engines other than otto, diesel or seillinger?

 

[Baluncore]

In a petrol engine, the fuel must not ignite under compression until the spark occurs.
So compression ratio must be below about 10:1 for high octane and 8:1 for ULP.

Diesel fuel must ignite as it is injected so it needs about 20:1 compression to get high temperature.
If a charger is used to boost input air pressure then only about 16:1 will be needed to get same pressure.