Lesson 2.   The Four-stroke Cycle

         四冲程循环

Anyone familiar with the working of the ordinary petrol engine is aware that the motive power is produced by igniting above the piston in each cylinder a mixture of petrol vapour and air, the resultant combustion of which causes an expansion of gases exerting pressure on the top of the piston.

By this means the heat released by the fuel is transformed into work, the rec