The Wankel Rotary Engine

The loyalty of the Japanese car company Mazda to the Wankel rotary engine is one of curious quirks of the automotive world.  In a way, this makes sense—the Wankel rotary engine is compact and lightweight.  Smaller and lighter engines help produce better fuel efficiency.  It is therefore perfectly suited for a company manufacturing cars for a country like Japan, where gas is expensive and space is precious.  The Wankel rotary engine, however, operates utterly, completely differently from regular internal combustion piston engines, and thus is often poorly understood.  This article will help explain the basic operation of the rotary engine, hopefully with a minimum of technical jargon and in simple enough laymen’s terms to be easily understood by anyone.

The key to understanding the difference between a piston engine and a rotary engine is this: In a regular piston engine, the piston cylinder performs four different jobs in sequence—intake, compression, combustion, and exhaust—that all take place within the cylinder to more the piston.  In a Wankel rotary engine, each function occurs in its own separate part of the engine (that performs only that one job) arranged in a sequential circle around the ‘piston’ (in this case, a triangular rotor).  The ‘piston’ then continually rotates (yes, I said the piston moves) around to the four different parts of the engine to achieve intake, compression, combustion, and exhaust.

In a piston engine, the engine harnesses the pressure, trapped within the cylinder, created by detonating a mixture of fuel and air to move the pistons back and forth.  Connecting rods and crankshafts convert the back-and-forth motion of the pistons into rotational motion used to run the car.

In a Wankel rotary engine, the engine harnesses the pressure of the detonation, trapped in the space between one side of the triangular rotor and the wall of the detonation chamber, to turn the triangular rotor and push it on to the next stage of the ignition sequence (in this case, exhaust).  This spinning rotor is what runs the car—there is no need for connecting rods and crankshafts to convert it into rotational motion—it’s already rotating!

As the triangular rotor turns, first it passes by the intake valve, and the gaseous fuel-air mixture is injected into the space between one side of the triangular rotor and the chamber wall and trapped there.  Second, as the rotor continues to turn, the space between the chamber wall and the rotor side shrinks, and the fuel-air gas is compressed.  Third, as the rotor continues to turn, it drags this compressed fuel-air gas past spark plugs in the chamber wall.  This ignites the fuel-air gas, and the pressure released by the combustion turn the rotor (in fact, pressure from previous detonations is what has been turning the rotor this whole time).  Fourth and finally, as the rotor continues to turn, the exhaust fumes left over from the detonated fuel-air gas is dragged past the exhaust valve and removed from the engine.

Well, that’s the basic operation of the Wankel rotary engine.  Of course, there’s a lot more to the rotary engine—entire books could be (and have been) written on this topic.  Hopefully, this article explained it to you plainly enough to help you understand this brilliant and efficient engine.