Question

Why are high-compression ratios not used in spark ignition engines?

Answer 1

In spark ignition engines,there is no need for high compression ratios because there is a spark to ignite the fuel.High compression ratio-ed engine are used when the fuel can be ignited by merely applying some pressure.
Let take an eample to understand it better.Take a diesel engine.Diesel can be ignited by merely applying some pressure.or in other words there i no need for a spark to ignite diesel in engine.so, a diesel engine will be a high compression engine owing to the nature of the fuel used.But,in a petrol engine,things are different.petrol cannot be ignited using mere pressure.u need a bit more energy to light it up.so,u need park to do o.In whichever case u need a spark to ignite it right?so,it' uneconomical to use a high compression ratio engine coz u can do the act same without one.
This i the reason why u dont need high compression ratio in spark ignition engine