How is fuel ignited in a Diesel engine?

In a Diesel engine, fuel is ignited primarily through a process known as compression ignition. This method differs significantly from gasoline engines, which rely on spark plugs for ignition. In a Diesel engine, air is compressed to a very high pressure inside the cylinder, which raises its temperature significantly. When the diesel fuel is injected into this highly compressed and heated air, the heat causes the fuel to ignite spontaneously without the need for a spark.

This process is essential for the function of a Diesel engine, as it allows for greater efficiency and power output compared to other ignition methods. The high compression ratio in Diesel engines typically ranges from about 14:1 to 25:1, contributing to the engine's overall performance and fuel efficiency. Understanding this fundamental operation helps clarify why compression and heat are the primary means of ignition in Diesel engines, as opposed to methods such as electric ignition systems or spark plugs.