How Two Stroke and Four Stroke Engines Work

Two-Stroke Engine

A Two-Stroke Engine is that kind of Internal Combustion Engine which can produce a Power Cycle in 2-Strokes, or we can say that a type of Internal Combustion Engine in which the starting of the Compression Stroke and finishing of Combustion Stroke happens simultaneously.




There are basically there are two different types of Engines.
1. Internal Combustion Engines.
2. External Combustion Engines.

Difference between two-strokes and four-stroke Engine

In two-stroke engines, the cycle is completed in one revolution of the crankshaft. The main difference between the Two-stroke and Four-stroke engines is in the method of charging the fresh air-fuel mixture and removing the burnt gases outside from the cylinder. on the other hand in Four-stroke engines, these operations are performed by the engine piston during the suction and exhaust strokes respectively. In a Two-stroke engine, the filling process accomplished by the charge compressed in the crankcase or by the blower. The induction of the compressed charge moves out the product of combustion through the exhaust valve. Thus, not any separate piston strokes are required for these two operations. Two strokes are sufficient to complete the cycle, one for compressing the fresh charge and the other for expansion or power stroke. The inlet spring loaded valve let the charging of air-fuel mixture into the crankcase, and it happens when the piston moves upwards and the pressure of the crankcase gets reduced during the compression stroke. After the compression and ignition, expansion takes place in the usual way.

Click here to know how Four Stroke engine work

During the expansion stroke, the charge in the crankcase is compressed. Near the end of the expansion stroke, the piston uncovers the exhaust ports and the cylinder pressure drops to atmospheric pressure as the combustion products leave the cylinder. After small movement of piston transfer ports are opened and the compressible air-fuel mixture will now reach into the cylinder through these ports. The piston top usually has a projection to deflect the exhaust ports. This serves the double purpose of scavenging the combustion products from the upper part of the cylinder and preventing the combustion products from the upper part of the cylinder and preventing the fresh charge from flowing out directly through the exhaust ports.

What is Four-Stroke Engine

A Four-Stroke Engine is that kind of Internal Combustion Engine which can produce power cycle in

Four-Strokes, these four strokes are comprised of different process and reactions inside the Engine.

The Four Stroke Engines are further classified as:

1. Compression Ignition 4-Stroke Engines
2. Spark Ignition 4- Stroke Engines

The main difference between the CI and SI engines is that in CI engines fuel is ignited by compression under high pressure, but in SI engines fuel is ignited with compression and a spark is produced with the help of a Spark Plug.

Compression Ignition Four Stroke Internal Combustion Engine
The different strokes in the Engine are:
1. Suction Stroke
2. Compression Stroke
3. Power Stroke
4. Exhaust Stroke

In the Suction Stroke the initial position of the Piston is at the top dead centre, now as the Piston will start to move in downward direction towards the bottom dead centre the inlet valve will be opened and the air is sucked or charged inside the cylinder, the valve remains open as the piston will reach the bottom dead centre, at the final position now the inlet valve will be closed automatically and finally air is sucked and kept inside the cylinder, this is the completion of the first stroke of piston.

In the Compression Stroke, now the Piston is at the bottom dead centre so it will start moving upwards towards the top dead centre and will tend to compress the air at very high pressure, one important thing is that both the inlet and outlet valves are closed in the compression stroke, as when the piston reaches nearly at the top dead centre the air is compressed at such a high pressure that it became hot red and will definitely get ignited very easily by charging fuel, this is the completion of the second stroke.

In the Expansion stroke, both the valves are closed during the complete stroke.

Fuel is charged with nozzle for a small time from the cylinder head at the end of compression stroke and the beginning of the exhaust stroke, when this fuel gets in contact of hot red highly compressed air it will ignite with a blast inside the cylinder at constant pressure,  so due to this blast the ignited products will now expand and tends to move the piston in the downward direction towards the bottom dead centre. This is the completion of the third stroke of the piston.

In the Exhaust Stroke, the piston now moves from the bottom dead center to the top dead center and the outlet valve is opened at the same time the product of the combustion is released through the outlet valves. The inlet valve remains closed during this stroke. Here is the completion of the final stroke or fourth stroke. How Two Stroke and Four Stroke Engines Work

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I have uploaded an article on the complete Internal Combustion Engine Working, IC engine Classification, types of internal combustion engines. Everything you need to know about the Engines.

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