Marine engines on ships are responsible for propulsion of the vessel from one port to another. Whether it’s of a small ship plying in the coastal areas or of a massive one voyaging international waters, a marine engine of either 4-stroke or 2-stroke is fitted onboard ship for the propulsion purpose.
The marine engines are heat engines used for converting heat, which is generated by burning fuel, into useful work, i.e. developing thermal energy and transforming it into mechanical energy. The engines used onboard ships are internal combustion engines (a type), in which, the combustion of fuel takes place inside the engine cylinder and the heat is generated post the combustion process.
Ship Engine Working Principle
Engines are mainly used for marine propulsion and power generation purpose. The working of the marine engine can be explained by the following procedure:
– The fuel is injected at a controlled amount at high pressure
– A mixture of fuel and air is compressed inside the engine cylinder with the help of piston, which results in the explosion of the mixture when pressurized due to compression. As a result, heat is released which increases the pressure of the burning gas
– The sudden increase in the pressure pushes the piston downwards and transmits the transverse motion into the rotary motion of the crankshaft using connecting rod arrangement. The explosion is repeated continuously for maintaining the power output depending upon the type of marine engine and its usage.
Types of marine diesel engines:
The two basic types of marine diesel engines are –
4 stroke engine
2 stroke engine
A 4 stroke engine can be installed on the ship to produce electrical power and also to propel the ship (usually in small size vessel). This engine takes 4 cycles to complete the transfer of power from the combustion chamber to the crankshaft.
The 2 stroke engines are used for vessel propulsion and are bigger in size as compared to the 4 stroke engines. In this engine, the complete sequence is complete in two cycles i.e.
- Suction and compression stroke – which is the upward movement of the piston to draw fresh air inside and to compress the air-fuel mixture
- Power and exhaust – which is the downward movement of the piston due to an explosion inside the chamber followed by removal of exhaust through the exhaust valve fitted on the top of the cylinder. A stuffing box is used which separates and seals the crankcase against the combustion chamber.