Difference Between two and four stroke Marine Diesel Engine


One of the most common questions in Interview and discussions; “What are the difference between two and four stroke Marine Diesel Engine”? We all heard about it, we all learn about it. Yet at the time of necessity we always forget one or two main points to say. So to brush up your knowledge and get you prepared for that next opportunity lets begin with its basics.

2 Stroke Engine / 4 Stroke Engine = 2/4 + Stroke + Engine.

What is Engine?

An Engine is a machine that converts the heat energy of fuel into the mechanical energy. Fuel is burned in the combustion space which is then used to create force using pistol, connecting rod and crankshaft. It can be then classified on the basis of design, fuel, stroke, number and position of cylinder.

An engine can also be studied on the basis of its parts such as cylinder head, exhaust valves, inlet valves (2 stroke ), scavenge space, liner, crankshaft, connecting rod, piston rod, piston, gudgeon pin and many more. With all such components working in an order it became the heart of the ship.

What is stroke?

Even being used a lot many times in engineering (Mechanical + Marine). There are always some engineers who remain doubtful to what it is ! A stroke in a I.C (Internal Combustion) Engine is the distance traveled by the piston from top to bottom dead center and vice versa. In other words, They are the distance traveled by the piston in the 1800 revolution of crank angle.

Difference Between two and four stroke Marine Diesel Engine

A combustion cycle is the complete process of induction, compression, ignition and exhaust. The difference between two and four stroke engine arise with the time taken by combustion process to complete. It depends on the number of times the piston moves up and down (stroke) in the cylinder during one cycle.

 S. No.
Four Stroke Engine
Two Stroke Engine
For one power stroke it takes 2 revolution

of crankshaft.

For one power stroke it takes one revolution

of crankshaft.

Complicated Engine design due to intake and exhaust valve mechanism.
Comparatively easier and simpler design.
It require heavy and bigger flywheel due to uneven forces on the crankshaft.
It require Small and light flywheel due to even forces on the crankshaft.
High Power to weight ratio.
Produce High torque and power.
Exhaust and inlet valves are mounted along with the fuel injectors on the cylinder head.
Exhaust valves may or may not be mounted along with the fuel injectors on cylinder head.
Low initial cost.
High Initial Cost
High Maintenance and fuel cost.
Low maintenance and Fuel cost.
Lub-Oil Consumption is high.
Lub-oil consumption is low.
Engine requires Less Space
Engine requires more space.
Are generally medium and high speed engines.
Are generally Slow speed engines.
Low stroke to bore ratio ( 1.5 – 2.5 :1 )
High stroke to bore ratio ( 4.2:1 )
Difficulty burning lower quality fuels.
Compatible with cheap/low quality fuels.
Require Gear assembly.
 Are generally direct Drive.
Contains unique Parts such as Rocker arm, Inlet valve, Gudgeon pin and complex lubrication and cooling assembly.
Contains unique parts such as piston rod, scavenge space, scavenge ports with simple cooling and lubrication assembly.

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  1. Janush Jinu

    Thank you for information very good to learn and keep in remember all those

    1. Amit

      Welcome. Its really happy to see that you like the post.

  2. Ajay Kotian

    Nice and simple explanation. Thanks.

  3. argenis

    excelent information..

  4. Romel A Caranel

    Verry usefull information.thanks


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