• Compression induced swirl is a method of generating swirl by which an organized rotation of charge about the cylinder axis is achieved.
• In this method the swirl is modified by the combustion chamber cavity as the piston approaches the Top Dead Centre position during the compression stroke. The piston approaching the TDC forces the rotating air into the piston bowl. The rotational force is modified by the reduced diameter of the piston bowl. Higher swirl rates can be achieved by using thin and deep bowls.

• A swirl chamber or divided chamber is required for producing compression swirl. In such chambers the combustion space is divided into distinct compartments, which have throats or restrictions between them, small enough to allow pressure differences to occur during combustion. It is a type of indirect injection combustion chamber.
• The swirl chamber consists of a spherical shaped chamber separated from engine cylinder and located in the cylinder head. About 50% of air is transferred in this chamber during the compression stroke. The chamber is connected to cylinder via a throat which enters the chamber in a tangential direction. This causes the entering air to undergo a strong rotary movement inside the chamber and the products after combustion to rush back into the cylinder at a much higher velocity through the same throat. Schematic of swirl or divided combustion chamber is shown in figure.

Advantages:

1. Injection pressure required is low.
2. Direction of spraying is not very important.
3. Single orifice injector is sufficient.
4. Greater air utilization due to strong swirl leading to smaller and cheaper engine.
5. Swirl is proportional to speed, so suitable for variable speed operation.
6. Smooth engine operation.

Disadvantages:

1. Poor cold starting performance requiring heater plugs.
2. Specific fuel consumption is higher because there is loss of pressure due to air motion through the duct and heat loss due to large heat transfer area.
3. Mechanical efficiency is lower.
4. Indicated thermal efficiency is lower because of lower air fuel ratio.