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Chapter: Mechanical Engineering : Internal Combustion Engines

Four Stroke Cycle Petrol Engines

Construction and Working of Four Stroke Petrol Engine

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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Mechanical Engineering : Internal Combustion Engines : Four Stroke Cycle Petrol Engines |


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