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
As mentioned earlier, IC (Internal combustion) 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.
The crankshaft is connected via a flywheel, either to the alternator or to a propeller arrangement for doing the mechanical work. To obtain continuous rotation of the crankshaft the explosion has to be repeated continuously.
Before the next explosion, the used gases are drawn out from the cylinder through an exhaust valve and fresh air is supplied, which helps to push the used gas and also to provide fresh air for next combustion process.
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.
Diesel Marine Engine Components
The field of diesel marine engines is quite vast and the engine itself is made up of several components. These components have been discussed individually in different articles at this website and we have articles on theoretical cycles upon which these engines are designed and operate, and various components such as the crankshaft, bedplate, pistons, liner & head. You can also check out the procedure of taking indicator diagrams and read about the job profile of personnel working on these engines right from the junior engineer to the chief engineer. Infact there is also an article which describes the tips to buy used engines in case you want to buy a used diesel marine engine.