Valve Timing Diagram for a 4-stroke cycle SI (Petrol) Engine

The petrol engines are also known as spark ignition (SI) engines. The valve timing diagram for a 4-Stroke cycle petrol engine is shown in below.

The following particulars are important for a four stroke cycle petrol engine regarding valve timing diagram.

• T.D.C - Top dead center

• B.D.C - Bottom dead center

• I.V.O - Inlet valve opens at 10^o - 20^o before T.D.C

• I.V.C - Inlet valve closes at 30^o - 40^o after B.D.C
• I.G.N - The ignitions of charge takes place at 20^o - 30^o before T.D.C
• E.V.O - The Exhaust valve opens at 30^o - 50^o before B.D.C
• E.V.C -  The Exhaust valve closes at 10^o - 15^o after T.D.C

Important Notes:

(i) The inlet valve of a 4-stroke I.C engine remains open for 230^o.

(ii) The charge is compressed when both the valves are closed.

(iii) The charge is ignited with the help of a spark plug.

(iv) The pressure inside the engine cylinder is above the atmospheric pressure during the exhaust stroke.