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ENGINES

In an internal combustion engine, fuel is burnt in air to provide heat that produces the engine power.
The combustion of fuel occurs inside the chambers of the engine and because the combustion is internal, such engine are referred to as internal combustion engines.

In practical cycle of a reciprocating ICE, the fuel and air are burnt and consumed and the products of combustion will need to be cleared or exhausted from the engine’s chamber before a  fresh air/fuel charge can be induced for the next cycle.

The reciprocating type internal combustion engine consist of a piston which moves back and forth in a cylinder in a gas tight combination. The  connecting rod connects the piston to a crank shaft.
The piston and connecting rod arrangement therefore translates the back and forth motion also known as reciprocating motion of the piston, to a rotary motion of the crankshaft.
In a multi-cylinder engine, the angular position are such that the cylinders contribute their power strokes in a selected and regular sequence.

CLASSIFICATION OF INTERNAL COMBUSTION ENGINES
Engines exist in various types and arrangement. Because of this, some classification is necessary to fully describe an engine for a fuller understanding of the engine we are dealing with. Three means by which engines are classified is as follows:

BY FUEL USED
Engines may be classified by the fuel used. Thus where the fuel is gas, petrol or diesel, we can classify the engines accordingly.

BY THE MODE OF COMBINATION OF THE FUEL
The means by which the combination is initiated or effected is also used to classify engines. For instance, IC engines where the ignition of the fuel/ air mixture is brought about by a spark are known as Spark Ignition (SI) engines. In these engines, fuel and air charge is premixed in the right proportion before being introduced into the engine combustion chamber where the charge is compressed and subsequently spark-ignited.
Usually, gas and petrol engines are spark ignition engines, in contrast, engines that are diesel fuel, have their combustion initiated by means or phenomenon of initiating combustion is known as compression ignition engines.

BY THE ARRANGEMENT OF THE CYCLE OF PROCESS
In the reciprocating internal combustion engine, there are usually four processes that make up the engine cycle. Also, the engine cycle requires a definite number of strokes of the piston to complete it. Reciprocating  IC engines are thus classified according to the number of strokes of the piston that are required to complete the engine cycle of the processes  are referred to as four stroke engine, while those that use two strokes of the piston to complete the cycle of the processes are reffered to as two stroke engine.

ENGINE PARAMETER AND DETAILS
There are some imperative parameters or engine details which we mist be familiar with our study of the reciprocating internal combustion engines, as follows.

1.THE PISTON STROKE
The piston stroke is the distance traveled by the piston between its outermost position and its innermost position in the cylinder. The innermost position and the innermost position of the piston in a gas or petrol engine, are reffered to as the top dead center (TDC) and bottom dead center (BDC) respectively.
Theses positions of the piston for diesel or oil engine are known as Inner Dead Center (IDC) and Outer Dead Center(ODC) respectively.

THE CLEARANCE VOLUME
There is usually a small space between the piston and the cylinder head when the piston is at the innermost point in the cylinder. This space is necessary son that the piston does not make contact with the injector nozzle, as the case may be. This space between the piston and the cylinder head when the piston is at its innermost point in the cylinder, is known as the clearance volume(CV).

SWEPT VOLUME
The swept volume of the engine is the volume of the cylinder corresponding to the stroke of the piston.

ENGINE CAPACITY
The engine capacity is the total sum of the swept volume of the engine cylinders. For an engine of ‘n’ cylinders, the engine capacity is thus n x swept volume of a cylinder. Also it must be remembered that where the bore of the cylinder or piston diameter is ‘d’.

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