Rotary Piston Engine (Wankel Engine)

The rotary piston engine is an internal combustion engine which operates on the same general principle as the conventional petrol engine.

In the latter, however, a rotary motion is produced by an oscillating piston and connecting rod, whereas the rotary piston engine produces this motion by means of a rotating ‘piston’. This means that there are no oscillating masses which have to be alternately accelerated and retarded, as occurs when an ordinary piston moves to and fro.

Consequently, the forces of inertia associated with the oscillatory motion are obviated in the rotary piston engine. As a result, higher speeds of rotation are possible.

The edges of the rotating piston open and close ports in the cylinder wall, so that the piston itself controls the ‘breathing’ of the engine, without the aid of valves. The triangular piston with convex sides rotates in a housing whose internal cross-section presents an oval shape slightly constricted in the middle (epitrochoid).

When the piston rotates, the seals mounted at its three corners continuously sweep along the wall of the housing. The three enclosed spaces formed between the piston and the wall successively increase and decrease in size with each revolution.

These variations in the spaces are utilised for drawing in the fuel-and-air mixture, for compressing this mixture, for combustion, and for discharging the burned gases, so that the full four-stroke working cycle is performed.

One of the major problems in the construction of the rotary piston engine is the sealing of the three chambers in relation to one another. Intercommunication between these chambers would be detrimental to the proper functioning of the engine.

This problem has been solved by means of a system of sealing strips.

How it operates - The operation of a Rotary Piston Engine