## Firing order of engine

The sequence in which the power impulses occur in an engine is called the firing order. The firing order,or order in which the cylinders deliver their power strokes, is selected as a part of the engine design to obtain the best engine performance.

When the cylinders are in line, the cylinder nearest to the radiator is designated as No.1 the one directly behind it is No.2, and so on. The firing order is shown by the sequence of the number of cylinders in which the cyinders deliver the power strokes. For example, the firing order of a four cylinder engine will be written as

1---2---4---3

This means that the firing will take place in the sequence of first , second, fourth and third cylinder respectively in a four cylinder engine.

Engine balancing firing order:

Engine balancing is related to firing order. One cylinder engine, working on four stroke cycle, has only one power impulse for every two revolutions of the crankshaft. Hence it will not run smoothly and quietly, inspite of the compensating effect f a large flywheel. The opertaion will be very rough, and to withstand it, the engine parts must be made large and heavy. Hence single cylinder engine working on four stroke cycle is not used in automobiles.

Scooters and motorcycles use two stroke single cylinder engines. Heavy vehicles adopt two-, four-, six- and eight-cylinder engines. By increasing the number of cylinders, the power impulses for each revolution of the crankshaft also increase, giving a more uniform torque and smoother operation. Above four cylinders there is no period during which some cylinder is not delivering power, and there is no time at which the flywheel must supply all the power required to maintain the engine speed. The more cylinders in an engine, the more continuous the flow of power, if the power impulses are spaced eqally, the less work is to be done by wheel in storing and releasing energy, and the less is the vibration. A lighter fly wheel can serve the purpose in multi cylinder engines.

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