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.
There are numerous companies working on hydrogen-fueled internal combustion engines, most notably BMW with its Hydrogen7. Mazda however, is uniquely positioned to take advantage of hydrogen as a combustion fuel. They are, after all, the only manufacturer currently building Wankel rotary engines. The nature of the rotary engine - where the intake and combustion chambers are separate - makes the design well suited to the rapid burn characteristics of hydrogen. Mazda is also using direct injection