The differences between low-speed, medium-speed and high-speed marine diesel engines:

1. Marine diesel engine parts Low-speed diesel engines are mostly two-stroke engines, medium-speed diesel engines are mostly four-stroke engines, and high-speed diesel engines are both. The scavenging forms of the marine two-stroke diesel engine include reflux scavenging, port-valve DC scavenging and opposed piston port scavenging. Heavy-duty medium and low-speed diesel engines widely use heavy oil as fuel, while high-speed diesel engines still use light diesel.

2. The low-speed diesel engine directly drives the propeller. In order to make the propeller have higher propulsion efficiency, the diesel engine accessories require a lower speed. The medium and high-speed diesel engines drive the propeller through the gear reduction box. The gear box is generally equipped with a reverse car mechanism to achieve the propeller reversal, but the low-speed diesel engine and some medium-speed diesel engines can reverse themselves. Medium and high speed diesel engines are also electrically driven by generator-motor-propellers.

The diesel engine has high thermal efficiency, good economy, easy start, and great adaptability to various types of ships. It was soon used as a propulsion power for ships. By the 1950s, in newly constructed ships, diesel engines almost completely replaced steam engines. Marine diesel engine has been the main power of civil ships, small and medium-sized ships and conventional submarines (see marine power plant). Marine diesel engines can be divided into main engines and auxiliary engines according to their role in ships. The main engine is used as the propulsion power of the ship, and the auxiliary engine is used to drive the generator, air compressor or water pump.