6.2.3 Fishing boat Engines

Fishing boat Engines


  1. 1.       How many types of combustion engines are there? What are they?

There are two types of combustion engines

i.            Internal combustion engine,

ii.            External combustion engine.

  1. 2.       What is meant by internal combustion engines?

Burns oil inside the engine is called internal combustion engine.

  1. 3.       Write the classification of internal combustion engine according to the fuel they burn?
  • Gas engine,
  • Petrol engine,
  • Kerosene engine,
  • Diesel engine,
  • Gas turbines.
  1. 4.    Describe the operation of a 2-stroke Diesel engine Or Describe the working principles of a 2-stroke Diesel engine.

It performs the intake, compression and exhaust stroke.

There are no independent intake and exhaust stroke.

A special method is necessary to supply air to the cylinder.

Working principle

  • The piston moves down
  • Then the scavenging port is opened
  • The clean air is enter into the cylinder
  • Next the piston moves up
  • The exhaust port is closed
  • Then  the trapped air is compressed
  • Next the fuel is injected into the combustion chamber
  • The combustion takes place inside the chamber
  • Next the combusted gas expands
  • Then the combusted gas moves the piston down
  • The exhaust port is opened
  • Finally the combusted gas is exhausted
  1. 5.       Define the following terms
    1. Stroke: each movement of the piston is called one stroke
    2. 2-storke engine: an engine that carries out one cycle with every 2-storkes of the piston is called 2-storke engine.
    3. 4-stroke engine: an engine that carries out one cycle for every 4-storkes of the piston is called a 4-stroke engine.
  1. 6.       Name the four strokes in order of their sequence in one cycle?
    1. Induction or intake,


Power or expansion,


  1. 7.       Explain the following strokes of an engine

Induction: clean air is drawn into the cylinder through the open inlet value as the piston

moves down on the induction stroke

Compression: The inlet valve closes and as the piston moves up the trapped air is compressed.

  • Near the end of the stroke fuel oil is sprayed into a combustion chamber as fine     spray.
  • In the case of petrol engine the fuel air mixture is ignited by an electric spark.
  • In diesel engines the spray vaporizes and begins to burn.

Power: as combustion continues the pressure in the cylinder rises very rapidly and the piston is forced down turning the crankshaft

  • Towards the end of the stroke the exhaust valve opens to allow the waste products of combustion to escape.

Exhaust: with the exhaust valve open the cylinder is completely emptied of the waste products as the piston rises for second time.

  1. 8.       Write the differences between the petrol and diesel engines.


Petrol engine Diesel engine
Induction stroke or

intake stroke

Air and fuel is taken into the combustion chamber and cylinder

Piston moves down

Ari only is taken into the cylinder

Piston moves down

Compression stroke Piston moves up

Fuel, air mixture is compressed

Raising temperature pressure

Piston moves up

Air is compressed

Rises the temperature

Power stroke or

expansion stroke

Fuel air mixture is ignited


Gases expand

Forces the piston down

A fuel injector sprays fuel into the hot cylinder where it burns
Exhaust stroke Products of combustion are pushed out from the cylinder by piston moving up The combusted gas are pushed out of the cylinder by the piston
Weight light Very heavy
Fuel Expensive

Highly combustible


Not highly combustible

Ignition Spark plugs required Spark plugs not required
Maintenance More complicated easier
Air mixing with fuel Fuel mix with air in carburetor. No carburetor present, so diesel never mix with air.
Repairs Difficult or complicated Easy
price costly Cheaper

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