PETROL ENGINE(Gasoline Engine)

                     The engine which gives power to to propel the vehicle is a petrol-burning, spark-ignition, four-stroke cycle, internal combustion engine . Petrol is a liquid fuel and is also called by the name gasoline. that is why the petrol engines are also known as gasoline engines. The ability of petrol to furnish power rests on the two basic principles of physics :

• burning or combustion is always accompanied by the production of heat.
• when a gas is heated, it expands. if the volume remains constant, the pressure rises according to Charles's law.

                 The operation of petrol engine in the production of power may be described as, during the downward motion of the piston, the air fuel mixture is sucked from the carburetor into the cylinder. During the upward motion the mixture is compressed by the piston in the cylinder and ignited by an electric spark. When the mixture is compressed by the piston in the cylinder and ignited by an electric spark. When the mixture is burned in the cylinder, the resulting heat causes the gases to expand which exert pressure on the cylinder walls and on the piston. The piston, being movable, is pushed downward by this pressure to the full length of its stroke.
                 The pressure exerted on the piston is transmitted through the connecting rod to the crankshaft that is made to revolve. The crankshaft turns through one half of a resolution as the piston moves downward. A fly wheel attached to the crankshaft stores up energy. The momentum of the flywheel carries the piston through the balance of its motion until it receives another power impulse. The process is repeated over and over again the crankshaft is turning continuously and the engine is running.
                 The events that are repeated make up the cycle of the engine. The number of strokes of the piston required to complete the cycle varies with the type of engine. In modern vehicles, the cycle is extended through four-strokes of the piston or two revolutions of the crankshaft. This is called a four-stroke cycle engine. in two stroke cycle engines, the cycle is completed in two-strokes of the piston or one revolution of the crankshaft.
In four stroke cycle engine, the four strokes are named suction, compression, power and exhaust in accordance with the operation of the cycle which occur during each particular stroke.