Diesel engines are internal combustion engines which are also known as CI engines or compression-ignition engines. In these engines the ignition of the fuel is initiated by a high temperature caused by a gas that is greatly compressed.
This is different than spark-ignition engines such as gas engines and petrol engines where a spark plug ignites an air-fuel mixture.
Nevertheless, diesel engines come in four-stroke and two-stroke versions. You can learn all about their basic components in the video below. Check it out!