Are gasoline engines limited to spark igntion?

[454Casull]

Can the combustive mixture be ignited the same way as in a diesel engine? Would there be any disadvantages to igniting the mix through that method?

[arcadiabc]

When an engine ignites the mixture on pressure not from a spark, you would get uncontrolled combustion known as "knock", that is when the fuel ignites before the spark. Engines mostly do that when you don’t put the right fuel with the correct Octane level. Octane helps the piston be compress more. That’s why is not good to put 87 octane fuel on a sports car.

[SaabJohan]

I can't se no reason why this shouldn't be possible. The question is rather why it should be done?

In a direct injected combustion ignited engine there cannot be any preignition or knocking as in a spark ignited engine.

There is howevers something that is called diesel knock but that is bit different compared with a "normal knock".

If compression ignition is used, the cetane number is what is important, not octane.

[ivymike1031]

arcadiabc, knock is not "when the fuel ignites before the spark." Knock is the name given to the explosive combustion of a pre-mixed charge due to excessive pressure&temperature. It most often happens many crank degrees AFTER the spark plug has fired.

454, you ask if the "mixture" can be ignited the same way as in a diesel engine, so I'm guessing that you're picturing a pre-mixed charge (like a typical gas engine) rather than a direct-injection setup. The key difference is that a pre-mixed charge contains a fairly uniform mixture of fuel and air, while an injector plume contains a large region of fuel alone, surrounded by a smaller mixed region. Only the fuel in the mixed region can burn, so there is little risk of knock.

HCCI is the name given to a premixed charge, compression ignition engine (Homogenous Charge Compression Ignition). If you search online you may find interesting info about such engines. The ones I'm aware of all run on natural gas, but I don't know a fundamental reason why you couldn't run one on gasoline given enough development.