一. some differences between low speed, medium speed and high speed Marine diesel engines:

1. Low-speed diesel engines are mostly two-stroke engines, medium-speed diesel engines are mostly four-stroke engines, while high-speed diesel engines have both.The scavenging forms of Marine two-stroke diesel engines include reflux scavenging, vent-valve dc scavenging and piston scavenging.Heavy oil is widely used as fuel in high power medium - and low-speed diesel engines.

2. The low-speed diesel engine drives the propeller directly. In order to make the propeller more efficient, it requires a lower speed.Medium and high speed diesel engine through the gear reducer drive screw, gear box are equipped with reverse mechanism to realize the reverse screw, but low speed diesel engine and parts of medium speed diesel engine itself can reverse itself.Medium and high speed diesel engines are also driven by generators, motors and propellers.

二.Second, diesel engine has high thermal efficiency, good economic efficiency, easy starting and great adaptability to various kinds of ships. It will be used as ship propulsion power soon after its introduction.By the 1950s, diesel engines had almost completely replaced steam engines in newly built ships.Marine diesel engines have become the main power for civil ships, small and medium sized vessels and conventional submarines (see ship power plant).Marine diesel engine can be divided into main engine and auxiliary engine according to its function in ship.The main engine is used as the propulsion power of the ship. The auxiliary engine is used to drive generators, air compressors, water pumps, etc.