Working of Four Stroke Diesel Engine.

 CONSTRUCTION AND WORKING OF FOUR STROKE DIESEL ENGINE

    Diesel engine works on diesel cycle.
    In petrol engine, mixture of air and fuel is ignited with production of spark, but in diesel engine fuel is ignited by injecting it into the engine cylinder, containing air compressed to a very high pressure.
    The injected diesel immediately vaporizes forming air-fuel mixture, at a temperature more than flash and fire point. Due to this, it instantly explode without need of spark.
    Thus, in a diesel engine combustion takes place due to compression, therefore it is called as ' compression ignition engine'.
    There is no spark plug in diesel engine.Temperature of compression air is sufficiently high to ignite the fuel, which sprayed in the form of fine spray.

Working of Four Stroke Diesel Engine.

    Diesel cycle consists of following four strokes.

1. Suction.
2. compression
3. Expansion or Power
4. Exhaust.

      These are explained below in detail.

This GIF shows how strokes can be worked.

• Suction Stroke:-

        During this stroke piston moves from TDC to BDC. The air is drawn into cylinder through the inlet valve. The exhaust valve remains closed. 

• Compression Stroke:-

        In compression stroke the piston moves up from the BDC to TDC.

        During compression stroke, both the inlet and exhaust valve remains closed.

        The air sucked during the suction stroke is compressed as the piston moves to TDC.

        The rise in temperature and pressure of the air at end of compression depends on the compression ratio. The compression ratio of diesel engine is higher than that of petrol engine.

        Few degree before the completion of compression stroke, a fine spray of diesel is injected into the compressed air which is at high temperature. The fuel ignites spontaneously. The injection of fuel into combustion chamber is assumed to occur at constant pressure.

•  Expansion stroke:-

        During expansion stroke both the inlet and exhaust valve remains closed and piston is forced to move to BDC due to thrust of explosion.

        The heat energy released by the combustion fuel, results in the rise in pressure of the gases. This high pressure product of combustion gives downward thrust to piston producing some useful work. This is the only stroke during which power is produced.

• Exhaust stroke:-

        During exhaust stroke, piston moves from BDC to TDC.

        The inlet valve remains closed whereas the exhaust valve is opened

        The upward movement of the piton expels the burnt gases out of the cylinder through the exhaust valve.