much simpler design to be adopted to conventional powertrains. Wankel engine development Felix Wankel designed a rotary compressor in the 1920s, and received his first patent for a rotary type of engine in 1934. He realized that the triangular rotor of the rotary compressor could have intake and exhaust ports added producing an internal combustion engine. Eventually, in 1951, Wankel began working at German firm NSU Motorenwerke to design a rotary compressor as a supercharger for NSU's motorcycle engines. Wankel conceived the design of a triangular rotor in the compressor. With the assistance of Prof. from Stuttgart University of Applied Sciences, the concept was defined mathematically. The supercharger he designed was used for one of NSU's 50 cm³ one-cylinder two-stroke engines. The engine produced a power output of at 12,000rpm. In 1954, NSU agreed upon developing a rotary internal combustion engine with Felix Wankel, based upon Wankel's design of the supercharger for their motorcycle engines. Since Wankel was known as a "difficult colleague", the development work for the DKM was carried out at Wankel's private Lindau design bureau. According to John B. Hege, Wankel received help from his friend Ernst Höppner, who was a "brilliant engineer". The first working prototype, DKM 54 (see figure 2.), first ran on 1 February 1957, at the NSU research and development department Versuchsabteilung TX. It produced . Soon thereafter, a second prototype of the DKM was built. It had a working chamber volume Vk of 125 cm³ and also produced at 17,000rpm. It could even reach speeds of up to 25,000rpm. However, these engine speeds caused distortion in the outer rotor's shape, thus proving impractical. According to Mazda Motors engineers and historians, four units of the DKM engine were built; the design is described to have a displacement Vh of 250 cm³ (equivalent to a working chamber volume Vk of 125 cm³). The fourth unit built is said to have received several design changes, and eventually produced at 17,000/min; it could reach speeds up to 22,000/min. One of the four engines built has been on static display at the Deutsches Museum Bonn (see figure. 2). Due to its complicated design with a stationary center shaft, the DKM engine was not practical. explicitly mentions that proper engine cooling cannot be achieved in a DKM engine, and argues that this is the reason why the DKM design had to be abandoned. NSU engineer Walter Froede solved