Four Stroke Cycle Petrol Engine

How does the petrol engine of your vehicle work? It has become the most promising question to you. Let us take a look at the operation and engine cycle of a petrol engine. Theoretically, a petrol engine cycle is also known as the Otto cycle. Your petrol powered engine requires four strokes of the engine piston to complete a cycle.  These four strokes are discussed below:

a. Suction Stroke: At the very beginning of the suction stroke, the inlet valve of your engine opens. As the piston moves downward from TDC, it aids to suck the air fuel mixture into the cylinder. The valve remains open until the piston reaches the BDC.

b. Compression Stroke: This is one of the most important strokes of an engine operation. In this stroke, both valves (Inlet and Outlet) of your engine remain closed. Here, the piston moves from BDC to TDC, and the charge gets compressed in the cylinder. As you know, temperature of any gas mixture increases with the increased pressure. To complete this stroke your engine crankshaft gives one revolution of 180o.

c. Expansion Stroke: You can also say it the working stroke of an engine. In this stroke the combustion of air-fuel mixture takes place. Shortly before the piston reaches the TDC during the compression stroke, the air fuel mixture gets ignited by means of a spark plug. Then, the pressure and temperature of the cylinder increases significantly. But, the volume the volume remains constant. This increased pressure creates a thrust to the piston that moves from TDC to BDC, and the crankshaft gets a revolution of 180o. As the piston of your engine moves at high speed, the flue gas expands. During the expansion of gases, the heat energy gets converted into mechanical energy. All valves remain closed in this stroke.

d. Exhaust Stroke: This is the final stroke of your four stroke cycle petrol engine. In this stroke, the outlet valve opens and the inlet valve remains closed. From the timing diagram you can see that the piston moves from BDC to TDC in this stroke, and the burnt gases escapes from the engine cylinder due to the push of the piston. With the completion of this stroke, the engine completes a successful operation cycle. Then, your engine gets ready to such fresh charge again. This is how your petrol engine works by completing the engine operation cycle.