Two Stroke Diesel Engine Working Principle and Diagram

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2-stroke diesel engine is widely applied to ship engines and locomotives engines, while for smaller vehicles such as trucks and pick-ups use 4-stroke diesel.

Just for knowledge, you might don’t know what a 2-stroke diesel engine is and how it works.

Therefore, today Autoexpose will explain the working principle of 2-step diesel engines and process diagrams.


What is a 2-stroke diesel engine?

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As with gasoline engines, a 2-stroke diesel engine is a machine that has a combustion every revolution of the crankshaft. That is, in one cycle there are only two piston steps namely the piston step up and the piston step down.

From these two steps, the name 2 stroke diesel was taken.

What are the advantages?

The two stroke diesel engine only has advantages in the power sector that is larger than the four stroke type. That is because on a 4-stroke diesel engine, combustion appears every two revolution of crankshaft.

While the two stroke diesel has a combustion each revolution of crankshaft, that means the 2-stroke diesel has power twice than 4 stroke.

In addition to profits, this type turns out to have many disadvantages;


  • Bad emissions
  • Wasteful fuel
  • Less efficient


That reason makes this type not widely applied to commercial vehicles.

Then what is the working principle?

Two Stroke Diesel Engine Working Principle


Before going any further, you must understand some of the main components;

  • Piston, used as a regulator of combustion chamber volume
  • Cylinder block, used as a piston moving track
  • Blower, functions as a turbocharger to supply air to the combustion chamber
  • Inlet hose, channel on the cylinder wall as a place for air to entering the combustion chamber
  • Exhaust valve, a valve to remove combustion residual gas
  • Connecting rod & crankshaft, used to change the direction of movement of the piston into rotary motion
  • injector, a component to spray diesel fuel into the combustion chamber


For the working principle, there are only two steps. However, technically this two stroke engine also has 4 processes, where each step will take 2 processes

1. Upward stroke


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The upward stroke is a step that piston move upward from BDC (bottom dead center) to TDC (top dead center). In this stroke there are two steps, the intake step and compression step.

The intake step is the process of entering air into the engine cylinder, while the compression step is the process of compressing air into a denser form so that the air pressure and temperature increases.

On a 4 stroke engine, these two processes are located in different steps. But in a 2 stroke system, these two steps occur in one step alternately.

It start when piston on the BDC, in this condition the air will enter through the air hose around the cylinder wall. This air can be pushed in because the intake channel has a blower or turbo that pushes the air towards the engine.

Then the piston will move up, this movement will make the air hole covered by the piston wall. As a result, when the new piston moves ¼ upward the compressed air will begin.

When the piston reaches TDC, the air has been successfully compressed so the pressure and temperature rises and is ready for combustion.

2. Downward stroke



The downward stroke is a step that piston moving down from TDC to BDC. In this stroke there are 2 steps, combustion step and exhaust step.

The combustion step is the burning process of the compressed air and fuel, while the exhaust step is the process of removing combustion residual gas from the engine to the exhaust.

The combustion step will occur when the piston reaches TDC at the end of the compression step, at this time the injector will atomize some of the diesel fuel into the high pressure air. The result is the diesel fuel will burn by itself.

Why can diesel fuel burn?

This is because the temperature in the compressed air exceeds the diesel fuel flash point. So that, diesel fuel will burn instantly when it is put into the high temperature air.

The result of combustion will cause expansion power that pushes the piston to move down to the BDC. Before the piston reaches BDC, the exhaust valve will open. In this position, the air outlet will also open because the piston position is below. So that the air exhaled by the blower will push the combustion residual gas to pass through the exhaust valve.

Then, the exhaust valve will be closed when the piston move upward. When the exhaust valve closed, the engine running in one cycle. This cycle will continue until the diesel fuel supply is stopped.

Lastly, what should not be forgotten is the piston movement. From the explanation above, the main energy of the piston is power expansion. But the piston only moves vertically.


To change the direction of piston movement from vertical to rotation, it uses the crankshaft mechanism and connecting rod. In this case, the mechanism is the same as a bicycle that changes the upward movement down the foot into a round movement.