Fishing Craft Technology

Unit 5 - Marine Engine and propulsion system

5.3.Components of Engines

Cylinder:
It is the heart of engine. Here only fuel is burnt and power is developed. The inner side of cylinder is formed by liner or sleeve, made of nickel chromium alloy steel. The inner diameter of cylinder is called bore of cylinder.

Cylinder head:
It is usually a single piece of casting made of alloy iron, bolted to the top of the engine. It covers the top end of cylinder and has provision for fitting inlet and exhaust value arrangement.

Piston:
It is fast moving part inside the cylinder which converts thermal energy into useful mechanical energy.

Piston ring:
These are rings fitted to the body of the piston. Piston rings are classified into compression ring and oil ring according to their purpose. Compression rings are fitted to the top of the body provides a seal to maintain power developed. Oil rings are used for circulating lubrication oil over the entire body of the piston and cylinder to reduce wear and tear.

Connecting rod:
This is tapering rod with small end connected to the piston and big end connected to the crankshaft. The small end is connected to the piston by means of piston pin. The big end is split in two halves to facilitate fixing with the crankshaft. This connecting rod converts reciprocating motion of piston into rotary motion of crankshaft.

Cam shaft:
It consists of cams arranged on it with suitable phase difference in order to control the opening of the valves at different times as and when required. It gets its drive from the crankshaft by suitable gear and chain mechanism.

Cam:
These are the parabolic projections machined on a cam shaft or ellipsoidal metal pieces attached to the cylindrical shaft in such way that there is parabolic projection. This projection lifts the cam follower thereby opening the corresponding valve.

Cam follower:
This is flat piece attached to end of push rod which transmits the motion from cam to push rod.

Push rod:
This is rod which transmits motion to the rocker arm assembly by a suitable ball and socket arrangement.

Rocker arm:
This is actuated by the suitable lifting of push rod which in turn opens the valve.

Valve spring:
When the cam is released, the opened valve is closed back into position by the tension in the spring.

Crank shaft:
This is output shaft, which delivers the useful work to the driven shaft. It is supported by two bearings fixed in the crank case. To one end of the shaft a fly wheel is attached.


Fly wheel:
It takes care of fluctuation of the cyclonic vibration in speed. It stores energy during power stroke and release during other stroke, thus giving fairly constant output torque.

Cooling water jackets:
To cool the cylinders head and wall a jacket is provided to circulate the cooling water.

Fuel nozzle:
Fuel is delivered by this nozzle in a fine spray under pressure in diesel engine. This is an optional part of diesel engine.

Spark plug:
At the end of the compression stroke, the air fuel-mixture supplied to the engine cylinder is ignited by an electric spark, produced by spark plug. This is an optional part in petrol engine.

Inlet Valve:
To supply air at the suction stroke.

Exhaust Valve:
To remove the exhaust gas at the exhaust stroke.