Indicator diagram or P.V diagram (actual) of four Stroke Cycle Diesel Engines

Indicator diagram or P.V diagram (actual) of four Stroke Cycle Diesel Engines Points : Indicator diagram or P.V diagram (actual) of four Stroke Cycle Diesel Engines Shows the indicator diagram of a four stroke cycle diesel engine. The suction stroke is shown by the line 1-2 which lies below the atmospheric pressure line. It is this pressure difference, which makes the fresh air to flow into the engine cylinder. The inlet valve offers some resistance to the incoming air. That is why, the air cannot enter suddenly into the engine cylinder. As a result of this, pressure inside the cylinder remains some what below the atmospheric pressure during the suction stroke. The compression stroke is shown by the line 2.3 which shows that the inlet valve closes (IVC) a little beyond 2 (i.e. BDC). At the end of this stroke, there is an increase of pressure inside the engine cylinder shortly before the end of compression stroke (i.e. TDC fuel valve opens (FVO) and the fuel is injected into engine cylinder. The fuel is ignited by high temperature of the compressed air. The ignition suddenly increases volume and temperature of the products of combustion. But the pressure, practically, remains constant as shown by the line 3.4. The expansion stroke is shown by the line 4.5 in which they exist valve opens a little before 59i.e. BDC). Now the burnt gases are exhausted into the atmosphere through the exit valve. The exhaust stroke is shown by the line 5-1, which lies above the atmospheric pressure line. It is this pressure difference, which makes the burnt gases to flow out of the engine cylinder. They exist valve offers some resistance to the outgoing burnt gases. That is why, the burnt gases cannot escape suddenly from the engine cylinder. As a result of this pressure inside the cylinder remains somewhat above the atmospheric pressure line during the exhaust stroke.