Friday, 18 April, 2014

Published December 07, 2013
Simply electric
The Mazda2 electric vehicle uses a small rotary engine to double its range. By Samuel Ee
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MAZDA may have stopped selling cars with rotary engines but that doesn't mean it will stop making these small but punchy motors. When it comes to the rotary engine, no one else has more experience than Mazda. Or made it more cool. Think back to the Cosmo and RX-7, those low-slung sports models powered by this brilliant little engine.

Now, the Japanese carmaker is applying its expertise in rotary engines to electric vehicles and portable generators. For over a year now, Mazda has been operating a fleet of Mazda2 electric vehicles (EVs) in Hiroshima, where Japan's fifth largest carmaker is based. These 100 pure EVs are currently leased to corporations and Mazda collects data on their performance as they run around the southern Japanese city,

With a 75 kW motor and 20 kWh litihium-ion battery, the electric Mazda2, or Demio as it is called in Japan, has a range of about 200 km. But with a petrol-driven rotary engine as an onboard generator, that is effectively doubled to approximately 400 km. The concept of this Mazda2 Range Extender or RE is simple - a compact 330 cc single rotor engine drives a generator to produce additional electricity on board the electric vehicle when its battery runs out of juice. The 22 kW rotary engine spinning at a constant 4,500 rpm is fuelled by a nine-litre tank.

Placed horizontally with a belt to drive an electric generator beside it, the whole assembly is able to achieve a thin system height. It is bolted under the rear bumper of a basic Mazda2 and other than adding 100 kg to the electric car's weight, no other changes are made.

During a recent drive of the Mazda2 RE, the quiet rotary engine emitted only a low hum when it kicked in. Mazda engineers tuned the system to work under the vehicle noise level so that it will be acceptable to the occupants. In fact, they say the rotary engine achieves better sound levels than any conventional diesel or petrol engine, thus making it the perfect partner for EVs. One interesting result with the addition of the range extender is that the Mazda2 RE has become even more fun to drive.

With a conventional petrol engine, this small hatchback has a front/rear weight distribution of 70:30 and is a zippy performer. When there is a battery under the rear seat, the Mazda2 pure EV's weight distribution improves to 50:50. Bolt on the range extender assembly of rotary engine, generator and fuel tank, and the Mazda2 RE achieves dynamic rear-biased performance - even though it is a front-wheel-driven car.

Also interesting is that Mazda believes the concept of the rotary-engined range extender can be extended to that of a portable electric generator. The company says there is a clear market niche for such compact but high-powered generators with multiple fuel capabilities, for example as backup generators or for small businesses like convenience stores. Whatever the application, it is still good news because it means the rotary engine is back.