The tiny single-rotor 330cc engine generates 30bhp at 4,500rpm and, via a belt drive, can maintain a continuous electric output of 20kw. The compact size of rotary engines makes them perfectly suited to range extender applications, while their low vibration and minimal noise characteristics further add to their suitability for the task of maintaining battery charge on electric vehicles.
Plus, by running constantly at optimal revs, the high fuel and oil consumption issue that can trouble rotary engines is negated. Cleverly designed as flat as possible within a modular frame, the engine, electric generator, nine-litre fuel tank and ancillaries weigh just 100kg and are designed to attach underneath an electric car, without reducing boot space or requiring expensive redesigning of the body shell.
A brief drive of the Mazda 2 EV being used as a test bed confirmed the unit is quiet – it’s only in the back seat that you can hear it running. We didn’t drive the prototype long enough to establish what kind of effect the extra 100kg hanging behind the rear axle has on handling but Mazda’s engineers claimed that in theory the range extender would double the range of the Mazda 2 EV before needing its small fuel tank filled up.
At this early stage Mazda is coy about the exact capabilities of the engine and the timescale before we see a production Mazda range-extender EV. Currently, the firm has no electric cars in its range – just a small fleet of pure EV Mazda 2s being tested by government agencies in Japan. However, Powertrain Development Program manager Takashi Suzuki confirmed that the aim was for the rotary to achieve a 13g/km output, just like the BMW i3 range extender engine.
Interestingly, Mazda’s engineers explained that the rotary power pack was so compact that it could have non-automotive uses, including being used as an emergency back up generator. With this purpose in mind it could be adapted to run on Butane or Propane, in addition to petrol.
But more tantalisingly for sportscar fans, Mazda insiders also hinted that rotary engine development isn’t strictly limited to range extender units, and that oil and fuel consumption gains could be implemented in a larger capacity rotary engine for a future Mazda RX-8 successor.