To some, it’s known as that “tiny little engine with the funny name.” To others, it’s the key that unlocks driving nirvana. It is, of course, the Wankel rotary engine.
The legendary Wankel engine is a piston-less internal combustion engine, which was first prototyped in the 1950s by German engineer Felix Wankel. However, despite those German roots, it would be given its most prolific existence under the hood of Mazda sports cars—in particular the RX-7 and RX-8—and to great effect.
But just how does a Wankel rotary engine work? Take a look at the animation, below.
Forget the pumping pistons of the conventional reciprocating piston engine, in simplest form, the Wankel engine consists of a triangular-shaped rotor, which is encased within an engine housing and rotates around a central “eccentric” shaft. As the rotor moves around its axis, its shape creates different sized pockets of air between it and the housing wall. These pockets are integral to creating the four strokes of the Wankel engine—induction, compression, power, and exhaust.
First, one side of the rotor (let’s call it side “A”) passes by an intake port, located in the wall of the housing. As the rotor rotates, the space between side “A” of the rotor and the housing wall increases, which draws the fuel-air mixture into the engine. As the rotor continues to spin, side “A” moves closer to the housing wall, compressing that air into a smaller pocket, which is met with a spark plug.
The compressed mixture is ignited, rapidly expands, and forces the rotor to continue its spinning motion during this power stroke. The final exhaust stroke occurs when side “A” of the rotor expels the spent gases through the exhaust port, and rotates once again to meet the intake port—repeating the cycle. With three sides per rotor, each of these strokes occurs simultaneously inside each housing.
In order to minimize vibration, a second rotor commonly operates in an additional housing next to the first, connected to the same eccentric shaft. Early Wankel engine examples utilized just a single rotor. By comparison, high-powered race cars such as the Mazda 787B have utilized four rotors…and produced over 700 horsepower in the process. Yikes.
The Wankel rotary engine configuration is lauded for its high-rev performance, high power for its relatively small size and weight, as well as operational smoothness. However, Wankel engines tend to be thirstier than their piston-pushing cousins.
At the moment, there are no mass market automobiles that rely solely on Wankel rotary engines. The Mazda RX-8 (pictured above) bowed out in 2012. However, Mazda has stated it isn’t done with Wankel rotary engine power yet. In 2013, Mazda revealed it was experimenting with using the engine setup as a range-extender for electric vehicles. With the adoption of similar gas-powered range extenders in EVs, perhaps this layout could still happen.