Question

Describe the principle operation of four-stroke cycle engine.

Answer 1

1. Induction stroke cycle
   • The piston moves down the cylinder causing the inlet valve to open and outlet valve closes. This causes the drawing in of fresh petrol vapour and air into the cylinder.
2. Compression stroke;
   • Both inlet and outlet valves are closed and the piston moves up the cylinder. This causes compression of the fresh fuel mixture in the combustion chamber.
3. The power stroke cycle;
   • The fuel air mixture is fully compressed and a spark is produced at the spark plug.
   • This causes the fuel mixture to ignite and expand resulting in high pressure that cause/force the piston to move down the cylinder.
4. The Exhaust stroke cycle;
   • This is the last stroke where the piston moves up the cylinder to eliminate the burned fuel mixture through an open exhaust valve.