Four cycles, three chambers, 60 (and 50) years: dual anniversaries for the Wankel rotary engine

Original DKM Wankel-designed engine prototype. Photo by Ralf Pfeifer.

As the world waits on Mazda to maybe possibly announce that it will resurrect the rotary engine, the compact pistonless internal combustion engine marks twin anniversaries this year: 60 years since one first ran and 50 years since Mazda first offered its take on the rotary.

Commonly called the Wankel engine after German Felix Wankel, an early member of the Nazi party in Germany who went on to work for NSU after the war, the pistonless rotary engine we know today wasn’t actually Wankel’s design. Wankel, who conceived the pistonless rotary in 1919 and patented it in 1929, proposed a well-balanced but also highly complicated version in which both the rotor and its housing ran on different axes called the DKM. That engine first ran in February 1957.

Wankel’s colleague at NSU, Hanns Dieter Paschke, believed the DKM, due to its complications, would not make for a good production engine, so he simplified it with a fixed housing in a design called the KKM, which also first ran in 1957.

In both designs, the same principle applied: While the engine relied on the four-stroke Otto cycle, it did so in a rotary motion rather than a reciprocating motion using a tri-lobed rotor. With all four cycles taking place in each spin of the rotor, the pistonless rotary offered a higher power-to-weight ratio, smoother operation, a simpler design, and a more compact package than traditional reciprocating internal combustion engines. The tradeoffs: higher fuel consumption, rapid wear of the apex seals at the tip of each rotor lobe, and (as engineers would come to find out later) worse emissions than a traditional internal combustion engine.

Regardless of Paschke’s contribution to the design, Wankel’s name still sat atop the pistonless rotary engine’s design. And regardless of the Wankel engine’s drawbacks, NSU pushed forward with the engine’s development, partly to build Wankel rotary engines of its own to put into production cars of its own (in the process earning the distinction of first automaker to offer a rotary engine in a production automobile in 1964) but largely to license the engine technology.

Early Mazda rotary engine. Photo by Taisyo.

Curtiss-Wright first took up NSU on the licensing offer in 1960, and a number of other companies followed suit over the next couple of decades, among them GM, AMC, Toyota, Ford, Alfa Romeo, Yamaha, and Rolls-Royce. The fourth company to do so, Mazda, reached its agreement with NSU in 1961. Only the year before did Mazda build its first passenger car, but, within six years, Mazda would not only solve apex seal problems that plagued other rotary manufacturers – thanks to the work of Kenichi Yamamoto and the Rotary Engine Development Committee – it would also introduce its first rotary-powered (Mazda preferred not to use the Wankel name) car, the Cosmo Sport 110S, powered by a 110-horsepower 982-cc 10a two-rotor engine.

The Cosmo remained a low-production luxury sport coupe throughout its existence, but it proved the rotary’s capability as a high-performance engine and thus paved the way for Mazda to install rotaries in many of its cars and trucks, including the RX line of sport sedans sold in the United States starting in 1970.

While the 12A, an 1,146-cc version of the 10A, came to prominence with the RX line, the 13B would go on to become Mazda’s most prolific and adapted engine, starting with the 1973 RX-4 and continuing on through the 2002 RX-7, over time gaining fuel injection and turbochargers to produce as much as 280 horsepower. Mazda sold so many rotaries during that period that the company and the technology almost became inseparable.

However, as pointed out in an April 2007 article on the rotary in Hemmings Motor News, “Emissions were the Mazda rotary engine’s Achilles’ heel. Overlapping intake and exhaust ports were unable to allow the engine to pass increasingly stringent emissions requirements without the use of extensive exhaust work. Later RX-7s featured twin pre-catalysts, and a final catalytic converter to tame the heavy emissions, which proved both problematic and expensive to replace.”

While Mazda updated the 13B as the Renesis for the RX-8 in 2003, that car and engine lasted only until 2012. Rumors swirl about Mazda announcing yet another rotary resurrection, this time known as the 16x, but as of this writing the company has made no such announcement.

Audi, however, has put together a tribute to the pistonless rotary engine in observation of the engine’s anniversaries at its Ingolstadt museum. In addition to various Wankel-powered NSUs, the exhibit will also include rotary-powered Mazdas, Citroens, motorcycles, snowmobiles, and even power saws.

For more information on the Audi Museum exhibition, visit Audi.com.