Eighty-five years on from the night when Dr Felix Wankel allegedly dreamed of piloting his own car powered by an engine that was half turbine and half reciprocating, the rotary engine has conspicuously failed to evolve as quickly or successfully as its piston-equipped counterparts. But the rotary engine has inherent attributes that could make it eminently suitable for running on hydrogen. Mazda is seriously looking into it. Jesse Crosse reports.