Two Stroke Cycle Diesel Engines

TWO STROKE CYCLE DIESEL ENGINES- CONSTRUCTION

Construction :

•           Two stroke cycle diesel engines require air supply

•         This air is used to blow out the exhaust gases and to fill the cylinder with clean air

•         This air is supplied by a blower or air compressor which is driven by engine itself.

•         These engines may be valve or port type.

•         A plate is provided in the crank case to admit air into the crank case.

•         Transfer and exhaust ports are provided in the cylinder.

•         These ports are covered and uncovered by the moving piston.

First Stroke (Upward Stroke of the piston)

(a) Compression and inductance:

•         The piston moves upwards from Bottom Dead Centre (BDC) to Top Dead Centre (TDC).

•         Both transfer and exhaust ports are covered.

•         Air which is transferred already into the engine cylinder is compressed by moving piston.

•         The pressure and temperature of the air increases.

•         At the same time, fresh air is admitted into the crankcase through the plate valve (reed valve)

First Stroke (Upward Stroke of the piston)

(b) Ignition and inductance.

•         Piston almost reaches the top dead centre.

•         The fuel is injected into the hot compressed air inside the cylinder. The fuel mixed with hot air and burns.

•         The admission of fresh air into the crankcase continues till the piston reaches the top centre.

Second Stroke (Downward Stroke of the piston)

(c) Expansion and crank case compression:

•         The burning gases expand in the cylinder.

•         Burning gases force the piston to move down. Thus useful work is obtained.

•         At the same time, the air in the crank case is compressed by the movement of piston.

•         All the ports and the plate valve are in closed position

Second Stroke (Downward Stroke of the piston)

(d) Exhaust and Transfer:

•           At the end of expansion, the exhaust port is uncovered.

•         The burnt escape to the atmosphere through the exhaust port.

•         Transfer port is also uncovered shortly after the exhaust port is opened.

•         The partially compressed air from crank case enters the cylinder the transfer port.

•         This air is deflected upwards by the deflected shape of the piston.

•         Thus the entering air helps in forcing out the combustion products from the cylinder

•         The plate valve remains during this period.