Compression-ignition is a type of internal combustion engine operation where fuel ignites due to the heat generated by compressing air in the cylinder. In this process, air is compressed to a high pressure, raising its temperature. When fuel, typically diesel, is injected into the hot, compressed air, it ignites spontaneously without the need for a spark plug. This method is commonly used in diesel engines, which are known for their efficiency and durability. Compression-ignition engines are often found in heavy-duty vehicles, such as trucks and buses, as well as in some ships and generators, due to their ability to produce high torque and operate on less fuel.