Ship’s Prime Mover
Ships will stay at standstill in the absence of its prime mover. It becomes derelict even with complete machines including propulsion systems. Without a ship's prime mover, it’s just a gargantuan log floating in the ocean at the mercy of winds, waves and tides because the prime mover is where the shaft and propeller are connected to complete the propulsion system. There are types of prime movers that are presently used.
Types of Ship’s Prime Movers
- Internal Combustion Engine (Diesel Engine)
- Steam Turbine
- Gas Turbine or Tri-fuel
- Fuel cell
- Bio-diesel
- Solar
- Water jet
- Nuclear
- Wind
- Electricity driven (Electric Motor)
We will try to discuss parts and construction, models, operation, maintenance and available troubleshooting procedures for each type of ship’s prime mover.
The Diesel Engine
This type of prime mover employed in the main propulsion system is described as the pure internal combustion engine. It can tolerate low-grade fuel, and ignites the fuel directly inside the cylinder without the assistance coming from the outside. This happens when the piston goes up and compresses the air (oxygen) within the cylinder and high temperature is attained when exactly a finely atomized fuel is injected inside and mixes with the high temperature air causing an ignition (explosion inside) thus power is created and produces work.
There are two major kinds of diesel engine based on how they operate.
Four-stroke diesel engine
Principle of Operation of the Four-Stroke Cycle Diesel Engine
This kind of engine produces power in two complete revolutions of the crankshaft in one cycle comprising the four-strokes of the piston. within that two revolutions namely:
- Suction or intake stroke
- Compression stroke
- Power stroke
- Exhaust stroke
Let us examine how these four strokes (series of events) of the piston play to fill up the two revolutions of the crankshaft (one cycle) which produces power.
The image above illustrates the series of events how the four-stroke diesel produces power.
The marine diesel prime mover. - The four stroke plant
Stroke 1 the intake/inlet valve is open letting the ambient air enter the cylinder. This time the exhaust valve is closed. The arrow shows that the piston is moving downwards from the top most of its travel (TDC).
- Stroke 2 both the intake/inlet and exhaust valves are closed and the piston is moving upwards after it reaches the bottom most (BDC) of its travel. This is the compression stroke. As the piston travels closer and closer to the top the trap air becomes hotter and hotter.
- Stroke 3 purely atomized fuel is injected. This mixes with the very hot air and ignition takes place creates power. Intake and exhaust valves are still closed.
- Stroke 4 due to massive pressure upon ignition, the piston travels downwards while the intake valve is still closed and the exhaust valve begins to open. This will allow burnt gases to escape. The next cycle of operation will begin.
The video below shows how a Four-stroke cycle diesel engine works just click the video link.
How Diesel Engines Work - Part - 1 (Four Stroke Combustion Cycle)