Diesel Engine

• Designed by Rudolf Diesel in 1892.
• Here the air is working substance and diesel is fuel.
• The cylinder is provided with three valves namely inlet valve, oil supply valve and the exhaust valve.
• The valves are opened and closed at proper moments by suitable mechanisms.

Working of Diesel Engine

a) Suction stroke:

• Air valve is opened and pure air at atmospheric pressure is drawn into the cylinder by the outward motion of the piston.

b) Compression stroke:

• All the valve are closed, as the piston starts moving inwards.
• Air is compressed adiabatically to about 1/17^th of its initial volume by the inward suction of the piston.
• Temperature is raised to about 1000⁰

c) Working Stroke:

• The oil valve is opened and diesel oil is forced in under pressure.
• At high temperature, the oil burns spontaneously.
• The supply of oil is so regulated that during combustion, as the piston moves forward, the pressure remains constant.
• The burning fuel supplies heat to the air at constant pressure.
• At a certain stage when the temperature has reached max. value, about 2000 K, the supply of oil is cut off.

d) Exhaust stroke:

• As the piston moves inward, exhaust valve is opened and the useless gas mixture is forced out of cylinder and the apparatus becomes ready for fresh cycle.

Efficiency of diesel engine

• It is calculated by:

η = 1- Q₂/Q₁