VALVE TIMING DIAGRAM :-
The above diagram is for a Caterpillar series 3600 turbo charged after cooled engine. As can be seen from the timing diagram, the induction stroke commences when the inlet valve opens 10° before TDC when air is drawn into the cylinder as the piston moves down. The inlet valve closes 1° before BDC.
The air is now trapped in the cylinder and as the piston rises on the compression stroke, the air is compressed. As the air is compressed, it rises in temperature. When the piston reaches 19° before TDC, the injection of fuel commences and continues until 73° after TDC.
The heat in the compressed air ignites the fuel and combustion takes place. The gases expand forcing the piston down on the power stroke.
The exhaust valves opens at 26° before BDC and the exhaust gases commence and are discharged as the piston rises on the exhaust stroke. Most of the exhaust gases have been discharged as the piston nears TDC. However, at 10° before TDC, the inlet valve opens and air enters the cylinder and helps discharge any remaining exhaust gases until the exhaust valve closes at 3° after TDC.
The whole cycle is then repeated.
Both the exhaust valve and inlet valve are open from 10° before TDC to 3° after TDC, an overlap of 13°. This is referred to as “valve overlap” and ensures that all the exhaust gases are discharged from the cylinder and the cylinder receives a fresh charge of air to make it more efficient when combustion next takes place.
Therefore there is one power stroke for every cycle or two revolutions of the crankshaft.
The above diagram is for a Caterpillar series 3600 turbo charged after cooled engine. As can be seen from the timing diagram, the induction stroke commences when the inlet valve opens 10° before TDC when air is drawn into the cylinder as the piston moves down. The inlet valve closes 1° before BDC.
The air is now trapped in the cylinder and as the piston rises on the compression stroke, the air is compressed. As the air is compressed, it rises in temperature. When the piston reaches 19° before TDC, the injection of fuel commences and continues until 73° after TDC.
The heat in the compressed air ignites the fuel and combustion takes place. The gases expand forcing the piston down on the power stroke.
The exhaust valves opens at 26° before BDC and the exhaust gases commence and are discharged as the piston rises on the exhaust stroke. Most of the exhaust gases have been discharged as the piston nears TDC. However, at 10° before TDC, the inlet valve opens and air enters the cylinder and helps discharge any remaining exhaust gases until the exhaust valve closes at 3° after TDC.
The whole cycle is then repeated.
Both the exhaust valve and inlet valve are open from 10° before TDC to 3° after TDC, an overlap of 13°. This is referred to as “valve overlap” and ensures that all the exhaust gases are discharged from the cylinder and the cylinder receives a fresh charge of air to make it more efficient when combustion next takes place.
Therefore there is one power stroke for every cycle or two revolutions of the crankshaft.
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