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Engine

Engine is a machine for converting energy into motion or mechanical work. The energy is usually supplied in the form of a chemical fuel, such as oil or gasoline, steam, or electricity, and the mechanical work is most commonly delivered in the form of rotary motion of a shaft.

 

There are two types of engines:

1. External combustion engines
2. Internal combustion engines

EXTERNAL COMBUSTION ENGINES

There is such a thing as an external combustion engine. A steam engine in old-fashioned trains and steam boats is the best example of an external combustion engine. The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine. Internal combustion is a lot more efficient (takes less fuel per mile) than external combustion, plus an internal combustion engine is a lot smaller than an equivalent external combustion engine. This explains why we don't see any cars from Ford and GM using steam engines.

"In an internal combustion engine, the burning of fuel is carried out inside the engine, while in an external combustion engine, the process of burning of the fuel is carried out separately in another chamber."

The important type of engines, however, is the internal combustion engine, mostly used in sophisticated automobile engines. We take up this type in the further discussion.

Internal combustion engines (I.C. engines)

Internal combustion engines are the most important type of engines. In these engines, the fuel is burnt inside the engine cylinder either by compressing air and fuel mixture and igniting it with a spark or by compressing air and spraying fuel directly on the compressed air.

Before going in any further detail let us first define some common terms related to engines

Important terms related to the engines

The engine is the heart of your car, but instead of pumping blood, the engine pumps air and fuel.  The engines main function is to convert air and fuel into rotary motion so it can drive the wheels of the car.  How does it do that ??.... well let's start with a cutaway of the engine and see all the major parts then we will get into the actual mechanics.

      
 

Engine cylinder: The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures.

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   Combustion chamber: The combustion chamber is the area in which the air or the charge is compressed and ignited. The high energy gases at very high temperature and pressure expand rapidly and cause the piston to move out (making the power stroke). the combustion chamber is very small portion of the engine cylinder and is also called the clearances volume.

   Pistons: Most common engines have 4, 6, or 8 pistons which move up and down in the cylinders.  On the upper side of the piston is what is called the combustion chamber where the fuel and air mix before ignited.  On the other side is the crankcase which is full of oil.  Pistons have rings which serve to keep the oil out of the combustion chamber and the fuel and air out of the oil. Piston Rings serve very important purposes that include the lubrication of the moving components and the cooling of the different parts

   Crankshaft:  The crankshaft is connected to the pistons via a connecting rod.  As the piston moves up and down in the cylinder it rotates the crankshaft and converts the straight line motion into rotary motion.

   Valvetrain:  The valvetrain consists of valves, rocker arms, pushrods, lifters, and the cam shaft. The valvetrain's only job is that of a traffic cop.  It lets air and fuel in and out of the engine at the proper time.  The timing is controlled by the camshaft which is synchronized to the crankshaft by a chain or belt. In the case of the two stroke engine, the function of the valvetrain is fulfilled by the piston itself, which while its up and down movement, cover and uncover different ports.

Fuel injection nozzle/ Spark plug: the purpose of a fuel injection nozzle is to inject the fuel in to the cylinder containing highly compressed air in the case of a C.I. engine, while a spark plug gives a timed spark for the ignition of the compressed charge in the case of a S.I. engine

  Normally, an internal combustion engine consists of more than one cylinders. The timing of processes in different cylinders is  so arranged that there is no unnecessary pressure on the crankshaft.

This can be clearly understood from the following animation.

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In the modern engines, the number of cylinders is from four to six normally.

      Now we go into the details of the I.C. engines and see what are the major classifications of these engines

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