Indicator Diagram or P-V Diagram (Actual) for a Four Stroke Cycle Petrol Engines

Indicator Diagram or P-V Diagram (Actual) for a Four Stroke Cycle Petrol Engines. Points : Indicator Diagram or P-V Diagram (Actual) for a Four Stroke Cycle Petrol Engines. The indicator diagram of a four stroke cycle petrol engine. The suction stroke by the line 1-2, which lies below the atmospheric pressure line. It is this pressure difference, which makes the fuel air mixture to flow into the engine cylinder. The inlet valve offers some resistance to the incoming charge. That is why, the charge cannot enter suddenly into the engine cylinder. As a result of this, pressure inside the cylinder remains somewhat 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(I.V.C.) a little beyond 2(i,e.BDC). At the end of this stroke, there is an increase in the pressure inside the engine cylinder. Shortly before the end of compression stroke (i.e. TDC.), the charge is ignited (IGN) with the help of spark plug as shown in the figure. The sparking suddenly increases pressure and temperature of the products of combustion. But the valve, practically, remains constant as shown by the line 3.4. The expansion stroke is shown by the line 4-5, in which the exit valve opens (EVO) a little before 5 (i.e. B.D.C). Now the burnt gases are exhausted into the atmosphere through the exit valve. The exhaust stroke is shown by the line 5-i, which lies above the atmospheric pressure line. It is this pressure difference, which makes the burnt gases to flow out of, the engine cylinder. As a result of this, pressure inside the cylinder remains somewhat above the atmospheric pressure line during the exhaust stroke.