It's starting to look more and more likely that the Wankel rotary engine could have a future as an electric vehicle range extender. Felix Wankel's original concept was once seen as having great potential because of its high power density compared to piston engines. Unfortunately, the manufacturing processes available in the 1960s and 1970s made it difficult to achieve adequate durability without high oil consumption and excessive emissions.
The combination of high precision machining, new materials and technologies like direct injection can help overcome many of those issues. Add in the ability to optimize the engine to operate within a narrow speed range as a range extender and this could be a winning combination. Wankels are also well suited for use with alternative fuels, including hydrogen.
Powertrain engineering firm AVL has built a prototype Mini with an ER-EV powertrain that uses a 254 cc single-rotor Wankel to produce 15 kilowatts at 5,000 rpm or 25 kW at 7,000 rpm. The 10 kilowatt-hour battery gives the car a 19-mile electric range and a 2.6-gallon gas tank extends the range to 124 miles. The complete package of rotary, generator, power electronics and cooling weighs just 143 pounds. By comparison, the more powerful 75 kW 1.4-liter inline-four in the Chevrolet Volt weighs approximately 200 pounds for the engine alone. Even a more powerful complete Wankel setup could probably still come in below the weight of the piston engine.
[Source: Ward's Auto World]