Rotary-powered cars which made it as far as the showroom.
The Wankel engine was a revolutionary design that made the reciprocating internal combustion engine created by Nikolaus Otto in 1876 seem more like a product born in the white hot heat of the industrial revolution.
A Wankel engine is about as simple as it gets in engineering terms, as power in a rotary powerplant is produced by a troichidal shaped rotor orbiting an eccentric shaft in the centre of an epitrochodal shaped housing.
As the rotor orbits the housing, it creates a large odd shaped combustion chamber and even with two spark plugs firing the mixture, not all the fuel is burnt. This leads to a high level of noxious fumes exiting the exhaust, a situation that's compounded by a rotary engine's fondness to consume engine oil.
Wankel engines are high revving due to the triangular rotor firing three times every time it orbits the housing. To lubricate the hard-working apex seals on the rotor's three tips, a small amount of oil is injected into the engine but this does little to improve the Wankel's reputation as a 'dirty' engine, as surplus lubricant is burned in the combustion process.
The apex seals on the rotor tips work like piston rings in a conventional reciprocating piston engine and have to provide a gas tight seal under extreme pressures and temperatures. Failing apex seals are the primary reason a Wankel engine has to be rebuilt and back in the late 1960s premature seal wear on the futuristic looking NSU Ro 80’s twin-rotor power unit proved a massive problem that essentially bankrupted the company.
Over the years several vehicle manufacturers have invested millions of dollars and no doubt an equal amount of man-hours researching and refining the Wankel internal combustion engine. These companies include Citroën with its Ami-based single rotor powered M35 and Chevrolet with an interesting looking quad-rotor Aerovette XP-985. In the 1970s Mazda built a Wankel powered pickup truck marketed as ‘The Pickup with Pickup’, while Rolls-Royce developed a two-stage rotary engine with low and high pressure rotors.
Other applications included Curtis-Wright Wankel aircraft engines and back on terra firma NSU and Norton produced rotary powered motorbikes. A host of small air-cooled rotary engines have powered snowmobiles and chainsaws and in 1991 Mazda won Le Mans with the 787B Wankel powered racer. Several rotary powered Mazda saloons also went racing and in 1970 Mercedes-Benz produced a concept C111 with a fuel-injected four-rotor Wankel engine. Although we’re unlikely to see the launch of a new Wankel powered car in the near future, the rotary engine could make a comeback in a range of hydrogen fuelled hybrids.
A Wankel engine is at its most efficient when running at a constant speed and back in 2010, Audi experimented using a compact 110bhp Wankel unit in its A1-Etron hybrid concept to extend the range of the batteries. Although a new generation of bi-fuelled Wankel engines could be used to generate power in future hybrid vehicles, the following panels describe the main rotary powered cars that actually went into production.