The engine cycle begins with this stroke, when the inlet valve opens as the piston advances from TDC to BDC, allowing air-fuel mixture in petrol engines and fresh air in diesel engines to enter the cylinder until the piston reaches BDC. The crank angle between the inlet valve opening and exhaust valve closing is known as the angle of valve overlap. The period between the inlet valve opening and exhaust valve closing is known as the valve overlap period. Before it closes, the inlet valve opens 10–30° before the t.d.c. The exhaust valve closes 8–20° after the t.d.c. The exhaust gases are forced out of the cylinder till the exhaust valve closes. The exhaust valve opens 30–60° before the b.d.c. The burning gases expand till the exhaust valve opens. The burning gases expand and force the piston to do useful work. This gives sufficient time for the fuel to burn. The spark is produced at 20–40° before the t.d.c. Until the spark happens, the air-fuel mixture is compressed. After reaching the bottom dead center position, the input valve shuts 30–40 degrees or even 60 degrees. Until the intake valve shuts, the air-fuel mixture is sucked into the 4 stroke cycle engine cylinder. The input valve opens 10–30 degrees before the top dead center. Pin The valve timing diagram for 4 stroke engine The theoretical valve timing diagram for 4 stroke enginesĪ valve timing diagram for a 4 stroke cycle petrol engine is shown in the diagram. The airfuel mixture is compressed till the spark occurs. The inlet valve closes 30–40°, or even 60° after the bottom dead center position. The air fuel mixture is sucked into the engine cylinder till the inlet valve closes. The inlet poppet valve opens 10–30° before the top dead center position. The diagram shows the valve timing diagram for a four-stroke cycle petrol engine. Pin Types of Engine The valve timing diagram for 4 stroke petrol engine:
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