The operation of a diesel engine is completed by four processes: suction, compression, power generation, and exhaust, which constitute a working cycle. A four stroke diesel engine is a diesel engine in which the piston travels through four processes to complete one working cycle.

Turbocharged diesel engines have high thermal efficiency, good economy, easy starting, and great adaptability to various types of ships. After their release, they were quickly used as propulsion power for ships. By the 1950s, diesel engines had almost completely replaced steam engines in newly built ships. Turbocharged diesel engines have become the main power source for civilian ships, small and medium-sized vessels, and conventional submarines. Turbocharged diesel engines can be divided into main engines and auxiliary engines based on their role in ships. The main engine is used as the propulsion power for ships, while the auxiliary engine is used to drive generators, air compressors, or water pumps, etc.