Useful Car Tips

Wankel Rotary Engines Explained

June 27, 2020
You’ve probably heard the term “internal combustion engine” or ICE before. Most vehicles on the road are powered by internal combustion engines with notable exceptions being electric vehicles—which of course rely on motors powered by electric batteries. But have you ever heard of a Wankel rotary engine? All internal combustion engines work in a similar fashion: fuel (and an oxidizer such as air is combusted (burned) in a combustion chamber. The expansion of high-pressure gasses generated by this combustion process then directly applies force to some component of the engine—typically the pistons as is the case in most ICE vehicles. This is where the major distinction between standard IC engines and Wankel rotary engines (named after their creator, German engineer Felix Wankel) lies. Instead of these high-pressure gasses acting on a series of reciprocating pistons as in a typical IC engine, they instead act upon a rotor in a Wankel rotary engine. Confused? Let’s take a closer look.


Now that we’ve established that Wankel rotary IC engines (and rotary engines in general) use rotors in lieu of traditional reciprocating pistons, you may be wondering what this really means—what purpose do these rotors actually serve and how do they work inside the engine? Modern vehicles almost exclusively use engines with a four-stroke cycle: intake, compression, combustion, and exhaust. Four-stroke piston engines complete one combustion stroke per cylinder for every two rotations of the crankshaft (the component in an engine which converts reciprocating motion into rotational motion). The same volume of space in the cylinder is alternately used for these four sequential processes. While Wankel rotary engines similarly perform these four sequential functions, there are two fundamental differences versus their reciprocating piston counterparts. Firstly, each combustion chamber in a Wankel engine generates one combustion stroke per driveshaft rotation. Secondly, these four processes happen in separate parts of the engine housing instead of in just one space. Still a little confused? Check out these handy animations: one featuring a typical four-stroke reciprocating engine and the other featuring a Wankel engine, with accompanying diagrams and further explanations under each animation.


All of this begs the question: why? Why do we need Wankel rotary engines when the vast majority of ICE vehicles use traditional reciprocating designs? Far from merely being an exercise in novel engineering, Wankel engines have several advantages—and naturally, disadvantages—as compared to reciprocating engines. For one, there aren’t as many moving parts in a Wankel engine, which means that there are less components which can break or malfunction. A rotary engine can have as few as three moving parts as compared to the dozens of moving components in a reciprocating engine. Due to this lightweight and compact design, Wankel engines often have excellent power-to-weight ratios. Inherent to the Wankel design is a smoothness unmatched by other ICE engines. With no reciprocating mass, the engine can rev extremely high—one variant of the Mazda RX-8 had a Wankel tuned to rev up to a blistering 9,000 revolutions per minute. High rpm also means a lot of power, something which enthusiasts welcome with open arms, and the unique sound of rotary engines only adds to the overall experience. As with any design however, Wankel engines are not without their cons as well. They tend to deliver poor fuel economy and emissions which makes it harder for manufacturers to meet or exceed evermore stringent emissions regulations. Not only do they consume a lot of fuel, but oil falls victim to their design as well. In fact, Wankel engines are designed to burn oil, which lubricates the engine but results in the consumption of more oil than you’re likely used to. Lastly are some practical issues; mainly their tendency to require frequent maintenance and their further unfortunate tendency to require costly repairs (provided the owner does not have the necessary knowledge to work on the engine themselves). Owners must be diligent with checking not only oil levels but for the presence of oil leaks, which tend to plague Wankel engines.


Despite their finicky nature concerning oil consumption and possible costly repairs, Wankel rotary engines nonetheless have a devoted cult following among enthusiasts. Such legendary cars as the Mazda RX-7 (FB through FD generations) and Mazda RX-8 have used rotary engines to great acclaim. While these are road cars, we would be remiss if we did not mention the legendary Mazda 787 race car and its derivative 787B—the latter of which famously took the overall victory at Le Mans in 1991. To date, this remains the only victory at Le Mans by a car not using a reciprocating engine. Although production of the FD RX-7 ended in 2002 and production of its RX-8 successor ended in 2012, there is yet still hope for rotary lovers. For several years, rumors have swirled that Mazda would bring a new rotary-powered sports car to the market. Although Mazda has mostly been tight-lipped about this, executives have hinted that consumers may see some form of rotary technology from the brand in the future. Although nearly a decade has passed since the RX-8 was discontinued, enthusiasts will forever dream that their favorite spinning Dorito-like engine will make its triumphant return.
Previous Article Next Article