Mazda 2 EV gets new rotary range extender engine

25 Nov, 2013 2:59pm Owen Mildenhall

We've driven the latest Mazda 2 EV to test a new range-extending rotary engine

Mazda gave us a glimpse into its future by revealing a new rotary range extender engine and allowed us a very brief drive in a modified Mazda 2 EV to experience it in action.

Mazda 2 review

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.

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Mazda really are on a roll these days. Some great technical developments like the above. Impressive stuff from a relatively small car maker.

Engine will need a rebuild at 60k along with a new battery pack though......Id rather see a small version of their high compression sky engines in place of a rotary. Would instantly put me off being sold with a rotary even though as an engineer I can see the benefits (which is why a gas turbine is ideal for this roll).

They said they fixed the rotary issues on the RX8 and look how that worked out. I like the new direction of Mazda and I am tempted by a 6. Rotary though, no chance

It amazes me that after so many years of electric vehicles, most of the major manufacturers are still at such an early development stage.

What a shame - this sounds like a very effective solution.

Sounds very good - but why does it have such a small petrol tank ?
Why not 20 or 30L ?
They you would have 300-400 mile range.

Also, it is tempting to wonder how much a 40Kw charger would weigh ? Hardly twice the 20Kw one.

IMO, they should license this design to everyone, and then start a range of 20, 25, 30, 40 Kw range extenders (though 20Kw should be enough for most people living in reasonably flat areas).

Back in the 1930's 15BHP was enough to transport a family of 4 on holiday in an Austin 7. 30BHP just for a range extender - where did we go wrong

It takes only 25 to 30hp to propel a large American car down the highway at 70mph. Yet they put engines in them that can output 150 to 200hp. Most of that output is for acceleration and heavy loads. Highly inefficient.

The great thing about a series-hybrid is that the generating engine works totally independent of the demands of the electric driving motor, enabling maximum efficiency when running. This means the generating engines can be greatly downsized. The battery acts as an energy buffer to give acceleration boosts.

As the engine is only periodically used, the life of the engine is greatly extended. Also newer metallurgic techniques are being used to make the engines. Additional, the engines will run at a constant speed. Constant speed engines running at ideal conditions last far longer than accelerating and decelerating engines. I can see at least 150,000 mile life out of these engines and more if direct injection and laser ign is used.
Changing batteries at 60K miles - you made that up.

All this has been known for the past 30 years. A Wankel engine with direct injection running at a constant speed turning a genny which power small electric motors was suggested long ago. Ferdinand Porche's first car in 1909 was a series-hybrid. Batteries are advancing at a rapid rate and more importantly supercapacitors are. Supercaps can replace batteries entirely if recent lab results are converted into products. An EV can be transformed by a battery replacement. The life of the cars will go way into 20 to 30 years by just replacing or uprating batteries. If Supercaps are introduced, they will last the life of the car.

Direct fuel injection and laser ign will improve the Wankel considerably when introduced. The problem of unburnt fuel in the exhaust will be eliminated improving emissions and fuel consumption. The engine performs very, very well in fuel consumption and emissions running at a constant speed turning a generator - its "sweet spot". Wankels lose efficiency dramatically when they are revved up and down as when directly driving a car. The engine has a vastly superior power-weight ratio and is about one third of the size and weight of a piston engine for a similar power output.

All these positive attributes combine to make a superb range extender. If a car is plugged in each night and uses grid power to run most of the time, then wear on these units will be negligible. Even when batteries are depleted, the Wankel can provide enough electricity to power the car and still be economical.

The first ever series-hybrid plane flew in June 2013 - using a Wankel engine because of its small size and light weight, and an electric prop. The makers say it can be scaled up to around a 100-150 seater plane. The Wankel engine(s) can be in the fuselage for better weight distribution with small electric motors on the wings giving lighter, and cheaper, wings. About 5 companies still make Wankels engines for special purposes such as drones.

The sooner they are introduced in road vehicles in series-hybrid the better. The Wankel has finally met its niche.