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: Radial Engines: Around the common crankshaft, the cylinders are positioned radially and evenly spaced.Opposed Cylinder Engines: On opposing sides of the engine, two rows of cylinders are placed.V Engines: Two rows of cylinders are positioned at an angle to one another.Inline Engines: A single row of cylinders is placed in a line.The investigation of the specifics of combustion is essential for modifying the engine’s power.Īs a result of these factors, the engine, whether 2-stroke or 4-stroke, is constructed according to the valve timing diagram, so that the piston moves from TDC to BDC is accompanied by the optimal timing of the intake and exhaust valves opening and closing.Ĭonfiguration of petrol and diesel engines.The cleaning of the engine cylinder improves combustion quality and reduces wear and tear inside the cylinder.To burn the fuel, a high compression ratio is necessary, especially in the case of a diesel engine, which is accomplished by overlapping the valve closings.The timing of the opening and closing of the intake and outlet valves is perfect, which protects the engine against knocking and explosion.Allow the combustion residue to leave so that the engine can complete its next cycle.When the engine requires it (at the moment of suction), provide it with a mixture of air and fuel or air in the case of a diesel engine.Complete seizure of the combustion chamber at the point when the air-fuel combination is ignited, as leaking can harm the engine and be dangerous.Synchronization between the phases of an engine cycle, from the air-fuel ratio intake through the residual combustion exhaust.Why do We Need a Valve Timing diagram?īecause a single cycle (from the intake of the air-fuel mixture to the exhaust of the combustion residue) of an internal combustion engine completes roughly 100000 cycles per minute, it is important to be provided with an effective system that can operate. This diagram is known as the valve timing diagram. The timing of these sequences of events can be shown graphically in terms of crank angles from the dead center position. The ignition timing is also timed to occur a little before the top dead center.

The valves operate to some degree before or after the dead centers. But, in actual practice, they do not open and close instantaneously at dead centers. We consider that for the valve timing diagram, the valves open and close at the dead center positions of the piston.

Pin Valve arrangements in a 4 Stroke engine What is the valve timing diagram?

Valve and ignition timing diagram