Four Stroke Cycle Petrol Engines

PETROL ENGINES

Classification of Petrol Engines 

•         Two Stroke cycle Petrol Engines 

•         Four Stroke cycle petrol Engines

FOUR STROKE CYCLE PETROL ENGINES 

Construction :

•         A piston reciprocates inside the cylinder 

•         The piston is connected to the crank shaftby means of a connecting rod and crank. 

•           The inlet and exhaust valves are Mounted on the cylinder head. 

•         A spark is provided on the cylinderHead. 

•           The fuel used is petrol

Four Stroke Petrol Engine- Working

(a) Suction Stroke (First Stroke of the Engine)

•         Piston moves down from TDC to BDC 

•         Inlet valve is opened and the exhaust valve is closed. 

•         Pressure inside the cylinder is reduced below the atmospheric pressure. 

•         The mixture of air fuel is sucked into the cylinder through the inlet valve.

(b)   Compression Stroke : (Second Stroke of the piston)

•         Piston moves up from BDC to TDC 

•         Both inlet and exhaust valves are closed. 

•         The air fuel mixture in the cylinder is compressed.

(c) Working or Power or Expansion Stroke: (Third Stroke of the Engine)

•         The burning gases expand rapidly. They exert an impulse (thrust or force) on the piston. The piston is pushed from TDC to BDC 

•         This movement of the piston is converted into rotary motion of the crankshaft through connecting rod.

•         Both inlet and exhaust valves are closed.

(d) Exhaust Stroke (Fourth stroke of the piston)

•         Piston moves upward from BDC 

•         Exhaust valve is opened and the inlet valve is closed. 

•         The burnt gases are forced out to the atmosphere through the exhaust valve (Some of the burnt gases stay in the clearance volume of the cylinder)

•         The exhaust valve closes shortly after TDC 

•         The inlet valve opens slightly before TDC and the cylinder is ready to receive fresh charge to start a new cycle.

Summary : 

•         Compression ratio varies from 5 to 8 

•         The pressure at the end of compression is about 6 to 12 bar. 

•         The temperature at the end of the compression reaches 250o C to 350o C

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