2. How it works

2.1 4-stroke cycle

The vast majority of AC motors operate on the 4-stroke cycle, which lasts 2 motor revolutions and has the following characteristic phases (figure 11 ).

• Time 1. Admission

It occurs as the piston descends from TDC to BDC, creating a vacuum in the cylinder and drawing in the fuel mixture, or air in the case of direct-injection engines. Gas velocities are quite high (the speed of sound can be reached when passing through valves) and the inertia of gaseous masses cannot be neglected. As a result, and also because there are pressure losses in the intake circuit (throttle, valves, etc.), the cylinders are not completely...