Rotary Engine Evolution - Tech

Rotary Evolution: Part 1
Most Japanese performance car enthusiasts are familiar with the 13B twin-rotor engine Mazda equipped the RX-7 and RX-8 with. But unless you've owned and modified an RX of some type, chances are you have only a basic understanding of how this unique type of combustion engine differs from a more traditional piston engine. If the name Dr. Felix Wankel means nothing to you, then here's your chance to learn everything you ever wanted to know (and more) about rotary engines. Spend a few minutes reading this story and you may just find yourself falling in love with this strangely ingenious engine design and looking at rotary-powered Mazdas like the RX-7 and RX-8 in a whole new light.

A (Not So) Brief History The history of the rotary engine is a strange and wonderful tale that dates back as far as 1588 when Ramelli invented the first rotary-piston-type water pump. Almost 200 years later James Watt, a Scottish inventor and mechanical engineer whose pioneering work with steam engines helped drive the Industrial Revolution, invented the first rotary steam engine in 1769. So although we motorheads (and rotorheads) tend to give Dr. Felix Wankel (1902-88) sole credit as the inventor of the rotary engine, the truth is that rotary engine design goes back much further than this 20th century German engineer.

The first working rotary engine prototype, the type DKM, was designed by Dr. Wankel and built by automaker NSU.

The first working rotary engine prototype, the type DKM, was designed by Dr. Wankel and bu

Still, Wankel's story is a fascinating one. His obsession with the idea of building a rotary engine began in 1919 when, at the ripe old age of 17, he had a strangely prophetic dream that he invented an engine that was half-turbine, half-reciprocating in design. With no formal training (he was granted an honorary doctorate later in life), Wankel set up his own research lab at the age of 22 and began pursuing his dream. Fast-forward to World War II when, as a member of the Nazi party, Wankel continued his work with the support of the German Aviation Ministry and private funding from the corporate sector, both of which believed that the development of a rotary engine would give the nation and its industries an advantage over its enemies. After the war Wankel was eventually able to re-establish himself (having been imprisoned for a short time by the allies, his lab closed and research confiscated), starting the Technical Institute of Engineering Study, where he continued his rotary engine R&D. Shortly after, in 1951, Wankel partnered with motorcycle and car manufacturer NSU and just six years later he and NSU completed a prototype rotary engine called the DKM. This first working prototype used a rotating cocoon-shaped rotor housing and a triangular rotor, but it was the KKM with its static rotor housing - completed a year later in 1958 - that's considered the true forefather of the modern rotary engine.

It wasn't until 1963 that the first rotary-powered car hit the streets as a '64 model year NSU Wankel-Spider. Then, in 1967, NSU released the Ro-80 sedan with a two-rotor 113hp Wankel engine and earned Car of the Year accolades in the European press. But because of the extremely costly development of the rotary engine and damage done to the brand's reputation by rotor apex seal reliability problems, NSU was taken over by the Volkswagen Group in 1969 (which merged NSU with Auto Union to form Audi) and the use of Wankel rotary engines was phased out.

But before NSU's merger with Auto Union, as joint patent-holders Dr. Wankel and NSU sold licenses to other automakers to develop their own versions of the rotary engine. Most major automakers bought a license during the '60s and began rotary-engine development programs of their own (the smooth and quiet operation and fewer moving parts of a rotary engine having strong appeal), but as you know it was the relatively small Japanese car company by the name of Mazda that eventually emerged as the only automaker able to mass-produce reliable and cost-effective versions of Wankel's design.

Mazda's journey into the world of rotary engines began in 1961 when then president Tsuneji Matsuda personally negotiated a licensing agreement with NSU. As part of this agreement, Mazda obtained a prototype of an NSU-built single-rotor engine and first learned of the "chatter mark" problem. These chatter marks, something Mazda's engineers nicknamed "nail marks of the Devil," presented themselves as wavy traces of abnormal wear on the rotor housing, causing the seals and the housing itself to significantly deteriorate. This was a major roadblock to the practical and widespread use of rotary engines and it was Mazda's own engineers - having formed its RE (Rotary Engine) Research Department - that eventually solved the problem.

By David Pratte

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