10-12-2012, 03:06 PM
PRESENTATION ON DIESEL ENGIN
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Introduction of Diesle Engine
Diesel engine is a type of internal-combustion engine used chiefly for heavy-duty work. Diesel engines drive huge freight trucks, large buses, tractors, and heavy road-building equipment. They are also used to power submarines and ships, and the generators of electric-power stations in small cities. Diesel engines have a high thermal efficiency, or ability to convert the stored chemical energy in the fuel into mechanical energy, or work.
DIESEL CYCLE:
Diesel cycle is an ideal cycle for reciprocating compression (CI) engines. It was proposed by Rudolph Diesel.
WORKING OF A DIESEL ENGINE
DIESEL ENGINE IS MAINLY WORKED ON BELOW STROKES.
SUCTION STROKE :-
In this stroke,the piston moves down from the top dead centre.As a result,inlet valve opens and air is drawn into the cylinder.After sufficient quantity of air with pressure is drawn,suction valve closes at the end of the stroke.The exhaust valve remains closed during this stroke
Compression Stroke:-
In this stroke,piston moves up from the bottom dead centre.During this stroke both inlet and exhaust valve are closed.The air drawn into the cylinder during suction stroke,is entrapped inside the cylinder and compressed due to upward movement of the piston.In diesel engine,the compression ratio used is very high as a result,the air is finally compressed to a very high pressure up-to 40 kilogram per centimeter square,at this pressure,the temperature of the air is reached to 1000 degree centigrade which is enough to ignite the fuel.
EXPANSION STROKE:
In this stroke both valves are closed. In this piston at TDC is pushed to BDC by expansion of burning gases. Actual work is obtained during this stroke due to force obtained by high pressure burning gases. That’s why this stroke is also called as POWER STROKE OR WORKING STROKE
Exhaust Stroke:-
In this stroke,the piston again moves upward.The exhaust valve opens,while inlet and fuel valve are closed.A greater part of the burnt fuel gases escape due to their own expansion.The upward movement of the piston pushes the remaining gases out through the open exhaust valve.Only a small quantity of exhaust gases stay in the combustion chamber.At the end of exhaust stroke,the exhaust valve closes and the cycle is thus completed.
KINDS OF DIESEL ENGINES
There are two main types of diesel engines. They differ according to the number of piston strokes required to complete a cycle of air compression, exhaust, and intake of fresh air. A stroke is an up or down movement of a piston. These engines are (1) the four-stroke cycle engine and (2) the two-stroke cycle engine.
FOUR STROKE ENGINE
In a four-stroke engine, each piston moves down, up, down, and up to complete a cycle. The first down stroke draws air into the cylinder. The first upstroke compresses the air. The second down stroke is the power stroke. The second upstroke exhausts the gases produced by combustion. A four-stroke engine requires exhaust and air-intake valves.