The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression. Hence diesel engines are also called as Compression ignition (C.I) engines.

The deformation of the bar, per unit length in the direction of the force (i.e. δl/l) is known as primary strain or linear strain.

When a change in length takes place, the strain is known as linear strain.

The deformation of the bar per unit length in the direction of the force is known as linear strain.