27-07-2012, 12:10 PM
ENGINE ppt
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An Engine is a device or motor that coverts thermal energy to mechanical energy, or an engine is a mechanical device that produces some form of output from a given input.In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft There are two types of engines; Two stroke engines (petrol engine) and Four stroke engines (petrol and diesel engines). Two stroke engines are built for high speed and performance while Four stroke engines are fuel efficient. Four stroke engines are more preferred than Two stroke engines.
STROKE
A stroke is a single action of certain engines, or A Stroke is a half revolution of an engine during which the piston travels from one extreme of its range to the other.
TYPES OF ENGINES
Four Stroke engine
An internal combustion engine (type of engine in which burning of fuel takes place within the engine)in which the entire engine cycle is completed in four piston strokes. In this type of engine with a single intake of fuel the engine can run four strokes [3+1(fuel intake)]. Four stroke engine includes the following strokes;
1. Intake or Suction Stroke
2. Compression Stroke
3. Power or Combustion Stroke
4. Exhaust stroke
Four stroke engine can be further divided on the bases of fuel, i.e. Four Stroke Diesel engine and Four Stroke Petrol engine.
Four stroke Petrol engine
The four stroke internal combustion engine which uses petrol as the burning fuel is known as four stroke petrol engine. The fuel actually used in the engine is the mixture of petrol and air (oxygen, used to ignite petrol).
WORKING
The cycle begins at top dead center (TDC), when the piston is farthest away from the axis of the crankshaft.
Intake or Suction Stroke
The piston starts at TDC, the intake valve opens and the piston moves down to let the engine to take in a cylinder-full of fuel (mixture of air and petrol). This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. The piston is connected to crankshaft with the help of connecting rod. This crankshaft is further transforms the mechanical work into desired output.
Compression Stroke
Then in the compression stroke the pistonmoves back up to the extreme top position which compress the fuel (air + petrol mixture). The use or benefit of compression is to make the explosion more powerful. This stroke increases the temperature of fuel which produces large amount of heat during ignition.
Power or Combustion Stroke
Then in the Power stroke, the fuel is then ignited near the end of the compression stroke, with the help of spark plug. The spark plug ignites the spark right before the power stroke which burns the fuel. The resulting pressure of burning fuel pushes the piston back to the extreme end or down position.
Exhaust stroke
In the exhaust stroke, once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out through the exhaust pipe which is attached to exhaust valve.
Now the engine is ready for the next cycle, so it intakes another charge of fuel and repeats the entire process.