The Wankel Rotary Engine — A Postmortem

September 26, 2022

Since the automobile's beginning, the percentage of cars built with gasoline-powered, piston engines approaches 100 percent even though recently we are seeing electric and hybrid cars make a dent. The only other significant departure from the tried and true piston engine was a promising upstart that emerged in the 1960s: the Wankel rotary engine.

The rotary engine was a radically new concept that was born in Germany and perfected in Japan. While using the same four-stage Otto process for gasoline combustion as its piston counterpart, it did so in a way that had many advantages. Rotary engines are more compact and lighter for a superior power-to-weight ratio. They are simpler, cheaper to produce, and more balanced. 

Despite these inherent plusses, in 2012 it was laid to rest when Mazda ceased production of the RX-8. (Yes, they are still in use in various applications including motorsports -- I'm just referring to mass-produced cars here.) Let’s investigate the birth, life, and death of the rotary engine to see the causes of its early demise.

Born in Post-War Germany

The father of the rotary engine is Felix Wankel, a German mechanical engineer, who conceived of the idea when he was a mere 17 years old. The gifted Wankel took a few more years to develop a design in 1924 for which he was issued a patent in 1929 when was just 27 years old. 

As Germany went to war, his talents were put to use developing seals and rotary valves for the German military. It is worth noting that he was very active in the Nazi party and anti-semitic organizations before and during WWII, not a great thing. After the war, Wankel was put under house arrest and his engineering lab was shut down and confiscated by the French. 

As Germany rebuilt, he went to work for NSU Motorenwerke in 1951, where he was finally able to develop the rotary engine and see his dream come to fruition. Wankel built a prototype while an NSU counterpart named Hanns Dieter Paschke made an alternative version of his own design. In a  twist of irony, the engine we all refer to today as the Wankel rotary engine was in fact the one that Paschke built. 

The prototype, DKM 54, first ran on February 1, 1957 -- now the official birthday of the rotary engine -- and produced 21 bhp. Once word got out, however, there was a strong demand to license the new design. 

The first customer was America’s Curtiss-Wright, which wanted to put the new design to use in aviation and industrial applications. However, car manufacturers were also clamoring for it. Alfa Romeo, American Motors, Citroën, Ford, GM, Mercedes-Benz, Nissan, Porsche, Rolls-Royce, Suzuki, and Toyota all contracted with NSU to use the revolutionary engine design. 

GM even began a project for a rotary-engined Corvette. However, only one car manufacturer ended up producing rotary engines in mass quantities: Mazda.

1964 NSU Spider, the first production car with a Wankel rotary engine.

Mazda Goes ‘All In’

The year was 1961, and NSU and Mazda agreed to team up to bring the first rotary engine-powered car to market. NSU debuted the NSU Spider at the 1964 Frankfurt Auto Show. It was a two-seater with a charming body by Bertone, powered by a 498cc rear-mounted rotary engine. The NSU Spider was the first production car with a rotary engine, and it eventually sold 2,400 units during its run that ended in 1967.

Meanwhile, Mazda was ramping up for bigger things in Japan. They made huge engineering investments in the rotary engine which they saw as a significant differentiator from other Japanese carmakers. 

1967 Mazda Cosmo

At the 1964 Tokyo Motor Show, they displayed the futuristic-looking Cosmo sports car. It wasn’t until 1967, however, that the Cosmo went into full production with a two-rotor engine that produced 110 bhp. The Cosmo was well-received but had low production numbers of less than 1,200 units. 

NSU still had designs on its own line-up of Wankel rotary-powered cars. They came out with a four-door luxury sedan called the Ro80 in 1967. This would be the model that led to NSU’s demise, as the engines were poorly designed with bad seals and poor lubrication, resulting in very high warranty costs.

NSU also had a short-lived venture with Citroen called Comotor which built a rotary engine that appeared in the experimental Citroen M35 and GS Birotor. The historic firm, founded in 1873, was bought by Volkswagen AG in 1969 and rolled into Audi. The NSU brand stopped being used in 1977. 

Mercedes-Benz even showed intent when it featured a three-rotor Wankel engine in the first model in its C111 line of prototype automobiles. The C111 had a mid-engine configuration, gullwing doors, and a fiberglass body. Mercedes even tested the C111 with a four-rotor engine, but ultimately pursued other powerplants, including a diesel version.

Mazda had solved all of the problems that NSU had not taken the time to fix. With NSU’s demise, Mazda became the only automotive company producing Wankel rotary engines. They developed two-, three-, and four-rotor versions over the years, as well as adding turbochargers. 

The rotary engine was not fuel-efficient and had high emissions, so it suffered during the oil crisis of the early 70s. It was subjected to tightening standards meant to bring about less polluting cars on the road. At this point, Mazda opted to reintroduce piston-engined cars back into its line-up and focused the rotary engine on the performance market. 

1978 Mazda RX-7

In 1978, Mazda introduced the groundbreaking RX-7 sports car which was a blockbuster. It was a regular on “best car” lists and throughout its 17-year run, Mazda produced more than 800,000 RX-7s.

Astonishingly in 1991, Mazda entered the 787B, a four-rotor prototype sports car, in the 24 Hours of Le Mans. It famously won the event overall and is the only non-piston racecar to win at Le Mans. The 787B program also marked the first time a Japanese manufacturer won the legendary endurance race. Mazda’s creation was a sensation, and its banshee scream of the engine remains the stuff of legends. (Le Mans subsequently banned rotary engines for the 1992 race, otherwise, Mazda may have had more of an impact. Jerk move, imho.)

Mazda 787B that won the 1991 24 Hours of LeMans

The Cause of Death

After the RX-7, Mazda introduced the RX-8 as its successor in 2003. However, the RX-8 was not as popular and had trouble meeting emissions standards. In 2012, the RX-8 stopped production. It was the last production car to have a rotary engine.

The Wankel rotary engine had a lot going for it. However, despite the sporting and performance success with Mazda, it was always an oddity and curiosity. For all of the pluses, the list of minuses was equally long. 

The true cause of death was that its design was inherently less efficient at burning the fuel-air mixture than piston engines. A flaw of the rotary design is its thermal efficiency. The larger surface area of the combustion chamber absorbs more heat, which makes the engine less efficient. Also, to keep the seals lubricated, the engine burned oil at a high rate, resulting in more pollutants. The result was poor gas mileage and, worse yet, bad emissions. 

Finally, rotary engines needed more maintenance than their piston counterparts and were costly to maintain. Ironically, the Wankel engine had fewer parts, but since Mazda was the sole producer, they were expensive to source and few mechanics knew how to work on them. Problems that may have not arisen had other manufacturers jumped on the rotary engine bandwagon.

A Future Yet?

It may be a bit premature to write off the rotary engine entirely as they may get a lifeline from clean cars. Just this year, Mazda announced it is producing a small rotary engine for the Mazda MX-30 as a range extender. 

The real opportunity is with alternative fuels. It turns out rotary engines are optimal for hydrogen-powered ICEs. The thermal properties that were detrimental in gas cars are a huge asset when burning hydrogen. There are even prototypes of rotary-engine cars that can switch between gasoline and hydrogen. 

The Wankel rotary engine will likely remain a great idea that just didn’t get liftoff. It’s a shame, as it is generally beneficial to have alternative technologies competing in the marketplace. We shall see if it can make a meaningful comeback in the “clean fuel revolution,” but until then, the Wankel rotary engine’s performance and incredible sound will always have its devotees. 

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