FRANKFURT: The Wankel rotary engine, named after its German inventor, Felix Wankel, is simple, reliable and durable but Mazda is the only carmaker to have overcome the challenge it poses to achieve volume production.
The motor has some disadvantages too but Mazda has persevered for decades and nearly 20 years after the Mazda R8 sports car was supposed to have signalled a Wankel revival, the Japanese manufacturer is poised to launch a new rotary-powered car.
Dubbed the MX-30, the unique sports utility mates the engine to an electric motor and is due to appear in 2022.
Felix Wankel was a pioneer and for a while his engine was seen as the way forward. Electric cars were a long way off in the 1960s and NSU's introduction in 1963 of the little Prinz III Spyder saw the first production car to use the Wankel engine.
NSU later produced the handsome Ro80 saloon before the company was swallowed up by Audi but rotary technology was not a game-changer and enthusiasm soon waned.
Rotary development continued on three continents with truck and bus maker MAN, Rolls-Royce, Porsche, Nissan, Suzuki, Ford, Kawasaki und Yamaha all buying licenses. Wankel engines found their way into aeroplanes and even lawnmowers but in the end only Mazda forged ahead with fitting rotary combustion engines into cars.
The RX-8, which was dropped in 2012, was the last production car with a Wankel engine and for most engineers the cons of its construction outweighed the pros. On the plus side the engine has only a handful of parts, compared with about 40 components which make up a typical four-cylinder piston engine.
A triangular piece of metal called the central rotor revolves in a chamber and does the work of reciprocating pistons. In a regular four-stroke piston engine, valves move up and down to bring air in and let burnt gases out. The rotor of a Wankel engine allows the four strokes to occur at the same time.
As the rotor turns, it uncovers slots in the housing, admitting air and releasing spent exhaust. The lack of components makes the rotary engine very light and powerful for its size.
Mercedes-Benz manage to wring 350hp from the Wankel motor used in the revolutionary C111 sports car but fuel consumption was the big bugbear with all rotary engines. The Wankel used more petrol than heavy V8 engines with more than four times the same displacement.
Imperfect seals led to fuel leakage and the rotary blasted far too many carbon monoxide and unburned hydrocarbons into the atmosphere, making it a no go for environmentalists. So what is new?
"The advantages of the rotary motor lie in its compact form and low vibration level," said Stefan Pischinger, who head a university chair for combustion engine technology in the German city of Aachen. That makes it ideal as a range extender for electric cars.
The scientist claims the Wankel problems are challenging but "can be solved". The motor’s fuel thirst can also be eliminated by using hydrogen which burns six times faster than petrol.
The rotary motor in the MX-30 will drive a generator at a constant speed which then charges the batteries during driving or sends the energy directly to electric motor. The motor is near silent and can burn CNG, LPG gas fuels or hydrogen, said Mazda’s Jochen Muenzinger.
Mazda said the Wankel will make the MX-30 a long-distance electric car which should overcome the range anxiety of many would-be buyers who have so far shied away from going electric.
The developments come as little surprise to Ro80 expert Matthias Steil who regularly answers the technical queries of the car club’s 1,000 members. He knows every nut and bolt of the NSU rotary engine and claims that many of its alleged faults have been exaggerated.
Steil said the Wankel engine runs so smoothly that a coin placed vertically on top of an engine at tickover will not fall over. He also blames the excessive fuel consumption on the standard automatic transmission of the day.
