German engineer Felix Wankel came up with the idea of an internal combustion engine with a three-sided rotor rather than reciprocating pistons way back in 1929, but it took him until 1951 to get NSU interested in the concept.
The first engine ran in 1957 and the first rotary-powered car, the NSU Spider, went on sale in 1964, followed by the NSU Ro80 and the Mazda Cosmo 110S in 1967. Early problems with premature seal wear were quickly solved and it seemed as if the compact, smooth-running rotary - simpler and more powerful than a piston engine double its size - was the engine of the future.
Everybody scrambled on to the rotary bandwagon; they powered motorcycles (Norton, Suzuki, Hercules and Van Veen) snowmobiles (Arctic Cat), aircraft (Curtiss-Wright, Diamond) and tractors (John Deere). Even Roll-Royce experimented with a two-stage diesel rotary engine.
But a rotary is not as clean-burning as a four-stroke piston engine and uses more fuel to make the same power; the 1973 oil crisis and new emissions regulations suddenly made the Wankel engine less attractive.
GM found that, kilowatt for kilowatt, rotaries were more expensive to make than conventional engines and by 1990, the only manufacturer still selling Wankel-engined cars was Mazda, which felt that the rotary fitted perfectly with its “zoom-zoom” marketing strategy.
The RX-8 coupé, its Renesis rotary able to (just) meet current emissions standards thanks to improved port design, was introduced in 2004 and remains Mazda's only rotary model.
But the RX-8 will be discontinued at the end of this year, and product planning and development boss Kiyoshi Fujiwara has admitted there is fierce debate at Mazda about the future of rotary development.
There was a next-generation rotary under development for release in 2017, according to Ward's Auto, but the programme has been halted and corporate bean-counters, looking for ways to cut costs in the wake of the recession, are considering axing rotary development altogether.
But Fujiwara insists the technology is a part of Mazda's DNA, and that Mazda has already solved two of the rotary's three big problems, although he wouldn't give details. He said recently: “Rotary engines literally are part of our soul.”
However, there may be a way out - in an electric car. Rotary engines are at their most efficient running at constant speed and load; that, together with their compact size and smooth, quiet power delivery, makes them ideal as the power generator for an extended-range electric vehicle such as the Chevrolet Volt.
The Volt uses a 1.4-litre piston engine to generate power for its electric drivetrain, and that's something a rotary could do even better, according to Mazda US vice-president Robert Davis.
“If you build a rotary that's tuned to a very specific load and rpm,” he said, “it runs very efficiently. Certainly, we've looked at that.”
According to Ward's, he's not the only one. Audi, with the help of AVL Powertrain Engineering is reportedly considering using a rotary in an extended-range battery car, mostly because conventional engines are simply too bulky.