The marine diesel engine is an internal combustion engine that uses diesel oil as a combustible. There are three principal kinds of diesel propulsion engines: high- speed, medium-speed and low-speed.
High-speed engines are found in small vessels, such as harbor tugboats. Medium-speed versions are used in various mid-sized ships. Low-RPM engines are normally installed in ships over 30,000 dwt
The marine diesel engine is an internal combustion engine that does not use a spark to ignite the fuel. Instead, it achieves ignition by compressing the fuel in the combustion chamber. The high- and medium-speed engines drive the propeller after being reduced in RPM in a reduction gearbox, while the drive shaft of low-speed diesel engines (installed on merchant ships) is directly coupled to the propeller.
The criterion for the choice among engine types, apart from vessel size, available space and required power, is the fuel which can be used. Diesel oil (MDO) is best, burns cleaner, but is expensive. Heavy fuel oil (HFO) is much cheaper, but requires additional systems, such as pre-filtering and heating.
