WORKING OF I.C. ENGINE

Basically there are 2 types of internal combustion engines; the two stoke type and the 4-stroke type. A brief description of these is given below:

1.      TWO STROKE PETROL ENGINE: The air fuel mixture from the carburettor enters the crank case through the inlet port during the upward movement of the piston. At the same time the mixture in the cylinder is compressed, which is ignited when the piston is just at T.D.C. the combustion takes place and the piston is just at T.D.C. the combustion takes place and the piston moves imparting motion to the crankshaft. During the downward movement of the piston the mixture in the crankshaft is compressed and pushed into the cylinder through the transfer port, which pushes out the exhaust through the exhaust port, at the same time filling the cylinder with a new charge. This process is called cross-flow scavenging. Thus the whole cycle is completed in two strokes, one revolution of the crankshaft.

2.       FOUR STROKE PETROL ENGINE

The cycle of events that take place in 4-stroke petrol engine is shows the suction of air-fuel mixture in the cylinder during the downward movement of the piston. The piston moving away from the cylinder head creates a pressure reduction or depression reaching maximum of 30 k (0.3bar) below atmospheric pressure at one third of the piston stroke. The actual depression reaching depends upon the speed and load on the engine. This depression is responsible for sucking the air-fuel mixture in the engine cylinder. The engines in which air-fuel mixture is introduced only by the depression in the cylinder are called 'normally aspirated' or 'naturally aspirated' engines. The compression stroke in which both the inlet and exhaust valves are closed and at the end of which the typical cylinder pressures will be which both the inlet and exhaust valves are closed and at the end of which the typical cylinder pressure will be from 800 to 1300 K Pa (8 to 13 bars) with the engine running under load. Towards the end of combustion stroke, the combustion of the charge ignited by a spark plug occurs. This generator generates the heat and a rapid in the pressure occurs which may reach as high as 6000kpa (60 bars) under full-load. The burning gases then expend pushing the piston away from the cylinder head. This is called the power-stroke or expansion -stroke at the end of which the pressure may drop to as low as 400kpa (4 bars). At the end of the power stroke the inlet value remains closed but the exhaust valve opens, the piston moves towards the cylinder head expelling most of the burnt gases to the atmosphere. At the end of this stroke, called the exhaust stroke, the cylinder pressure may drop down to atmospheric or even less. In this way, the entire cycle is completed in four strokes, two crankshaft revolutions.