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What is an engine?
Engine is the heart of any automobile. It converts the Chemical Energy (heat energy) into Mechanical Energy.
Automotive engines are called internal-combustion (IC) engines, because the fuel that runs them, is burned inside the engines.
The fuel in the IC engine can either be ignited by a spark, or by high compression of air.
Classification of Automobile Engines
1.Fuel Used
Petrol Engine (or Gasoline Engine)
Diesel Engine
Gas Engine
Petrol Engine
The petrol engine uses petrol which is a hydrocarbon for its running action.
Air-petrol mixture is sucked into the cylinder during the suction stroke of the piston.
The correct air-petrol mixture is obtained from the carburettor.
The mixture is compressed during the compression stroke, ignited during the power stroke and the exhaust gases pushed out during the exhaust stroke.
A spark plug is fitted at the top of the cylinder which sparks to ignite the fuel-air mixture.
In the diesel engine, only air is sucked into the cylinder during the suction (intake) stroke and compressed to high pressure, the compression ratio is as high as 22:1. Its temperature also rises by about 530°C.
Diesel Engine
At the end of the compression stroke the diesel is injected by an injector.
The injected fuel burns due to the high temperature of the compressed air.
The burnt gases expand pushing the piston down during the power stroke.
Finally, the gases are pushed out during the exhaust stroke.
2.No. of Strokes Per Cycle
Two Stroke Engine
Four Stroke Engine
Four-stroke Petrol Spark Ignition engine
Two-stroke engine
The two-stroke engine completes a cycle of operations with the two-piston strokes.
In the two-stroke engine, the intake and compression strokes combined in Up-stroke.
The power and exhaust strokes are combined in the down stroke.
Thus, during every one revolution of the crankshaft, there is one power stroke of the piston.
Therefore, a two-stroke engine produces twice as much horsepower as a four-stroke engine of the same size, running at the same speed.
3.Types of Ignition
Spark Ignition (SI) Engine
Compression Ignition (CI) Engine
4.No. of Cylinders
Single-cylinder Engine
Six-cylinder Engine
Two-cylinder Engine
Eight-cylinder Engine
Three-cylinder Engine
Twelve-cylinder Engine
Four-cylinder Engine
Sixteen-cylinder Engine
5.Arrangement of Cylinders
Inline Vertical Engine
Opposed cylinder Engine
Horizontal Engine
Radial Engine
V-type Engine
6.Type of Cooling
Air-cooled Engine
Water-cooled Engine
7.Method of Fuel Injection
Air Injection Engine
Airless or Solid Injection Engine
Carburettor Engine
8.Special Type Engine
Wankel Engine
Automotive Gas Turbine
Radial Engine
Technical Terms Used In Engine
A number of basic terms are used to describe and compare engines. A few commonly used terms are described here.
Top Dead Centre (T.D.C): This refers to the position of the crankshaft when the piston is in its top most position i.e. the position closest to the cylinder head.
Bottom Dead Centre (B.D.C): This refers to the position of the crankshaft when the piston is in its lowest position i.e. the position farthest from the cylinder head.
Bore: Diameter of the engine cylinder is referred to as the bore.
Stroke: Distance travelled by the piston in moving from T.D.C. to the B.D.C is called ‘stroke’.
Clearance Volume: The volume of cylinder (including the combustion chamber) above the piston when it is in the T.D.C. position is referred to as ‘clearance volume’ (Vc).
Piston Displacement: This is the volume swept by the piston in moving from T.D.C. to B.D.C. This is also called ‘swept volume’.
Engine Capacity: This is the total piston displacement or the Swept volume of all the cylinders. If ‘n’ is the number of cylinders and Vs is the piston displacement, then ‘engine displacement’ or engine capacity Vd, is given by Vd = Vs.n
Compression Ratio:This indicates the extent to which the charge in the engine is compressed. This is calculated as the ratio of the volume above the piston at B.D.C. to the volume above the piston at T.D.C. If ‘y’ is the compression ratio, then For petrol engines, compression ratios are about 8 to 9.5 : 1, whereas for diesel engines, these vary from 16 to 22.
Power: It is the work done in a given period of time. Doing the same amount of work in a lesser time would require more power.
Horse Power (H.P.): This is the amount of energy required to do 4500kgm. of work in one minute.
Indicated Horse Power (I.H.P): The power developed within the engine cylinders is called indicated horse power. This is calculated from the area of the engine indicator diagram.
Brake Horse Power (B.H.P): This is the actual power delivered at the crankshaft. It is obtained by deducting various power losses in the engine from the indicated horse power.
Friction Horse Power (F.H.P.): This is the power lost due to friction present between different matching components. F.H.P = I.H.P – B.H.P
Engine Torque: It is the force of rotation acting about the crankshaft axis at any given instant of time. It is expressed in newton-metre (Nm). Engine torque goes through the vehicle transmission system, to the road wheels and is responsible for rotation of the latter and hence for pulling of the vehicle.
***End of session -3 of unit 1***
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