What is the mode of operation of a four stroke petrol engine?

Not sure what you are asking here... But here goes: Stroke 1: Intake stroke. The intake valve is open, and fuel air mixture is sucked into the cylinder as the piston moves down. Stroke 2: The intake valve is closed, and the fuel air mixture is compressed as the piston moves up. Stroke 3: The power stroke. The compressed fuel air mixture is ignited by the spark plug. The resulting explosion forces the piston down, providing power. Stroke 4: The exhaust valve is opened, and the spent fuel air mixture (now exhaust) is pushed out of the cylinder by the rising piston. Repeat indefinitely...