Rotary engines had a radical departure from traditional Otto cycle engines and the Wankel design was a paradigm shift in the internal combustion engine design. Unfortunately rotary engines did not gain in popularity.
Traditional otto cycle engines have pushed rotary engines into the background but it is worth having a look.
Mazda’s 26B racing car won the Le Mans 1991 competition using a Wankel engine. The RX 7 became a cult model followed by the RX-8 but emission norms made Mazda put a stop to their production though development continues.
For practical purposes the rotary engine can be classified into two types:
The eccentric gear in the rotor also serves as the internal timing gear. The fixed pinion gear is the fixed timing gear, both of which are connected to ignition.
The intake stroke is when there is a vacuum in the cylinder that opens the intake valve to let in fuel-air mixture. Next is the compression stage when the fuel air mixture is compressed as piston moves up in the cylinder, just a little bit before the top dead center position. The spark plug ignites the mixture, and the resulting explosion is the power stroke, during which the outlet valve also opens. The last stroke is the exhaust stroke in which piston pushes out the exhaust burnt gases.
The triangular rotor assembly is fixed around a ring gear that meshes with a gear attached to a fixed pinion. The rotor moves in an eccentric pattern within the epitrochoid chamber in which there are intake and exhaust ports as well as the spark plugs. As the rotor moves, it uncovers the inlet port and lets in the fuel-air mixture. Rotor pushes the air mix in the lobe to the next stage of compression while sealing the intake port. As the rotor turns, the space in one lobe is greatly reduced, resulting in compression of the fuel air mixture and, in the next stage, when fuel is fully compressed, ignition occurs in the chamber. The moving rotor pushes the burnt gas mixture to the exhaust port from where it is expelled.
The challenges are to make the Wankel more fuel efficient and less polluting.
Apex seals of the rotor in the Wankel Rotary Engine are the main problem areas at times. These seals need to be kept well-lubricated with oil. A regular check on the oil squirting system helps keep the engine in check.