By on August 29, 2012

The rotary engine and Mazda have had a tumultuus, on-and-off relationship that rivals an Old Hollywood marriage. Market conditions and government regulations have made mass production of the rotary a constant challenge, and the death of the Mazda RX-8 looked like the final nail in the Wankel’s coffin.

It turns out that Mazda is not only reviving the rotary, but the rumors of its use as a range extender have been confirmed by Mazda head Takashi Yamanouchi, who spoke briefly at the Moscow Auto Show regarding its future.

Yamanouchi revealed that the next-generation rotary car would be a plug-in vehicle that would only be available for lease in Japan. Regarding the rotary’s use, Yamanouchi said

“The rotary has very good dynamic performance, but if you accelerate and brake a lot there are efficiency disadvantages. The range extender overcomes that. We can keep it spinning at it’s most efficient 2000rpm while also taking advantage of it’s size.”

Better a range-extending rotary than no rotary at all, right?

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29 Comments on “Mazda Boss Reveals More About Rotary Range Extender...”

  • avatar

    A small rotary optimized for generating electricity is a good idea. Few moving parts, compact size, and high power to displacement ratio means a smaller engine can be built to specs. This would be simpler that the Atkins engine being used at the moment

  • avatar

    Yes, but a small Diesel is even easier to optimize to run at a specific RPM.

  • avatar

    The largest problem with wankel engines have been that they are inefficient at low loads due to the inability to achieve ideal air-fuel mixtures. Direct injection would help, but just as importantly, wankels would be good match for hybrid/PHEV applications where range of loads are more limited.

    The other benefit obviously is weight & packaging. Wankel would allow for more space and weight for batteries. There already are some Wankel generators on the market, one 16Kw/24hp wankel generator that weighs just around 40lbs.

    Both GM & VW have recently discussed the possibility of wankel engine rage extenders. GM discussed the possibility for a wankel range extender to replace the inline-4 in their next Volt. VW actually showed a working Audi A1 eTron concept; the 60hp wankel generator was mounted below the boot floor.

    Mazda, who has sunk billions in R&D over the last few decades, would be an ideal candidate to make a rotary range extender.

    • 0 avatar

      nice paraphrase

    • 0 avatar

      They are inefficient no matter what the load. If the hemi is the most efficient configuration for a combustion chamber, the Wankel’s more pancake-shaped combustion chamber is the worst, and there’s almost nothing you can do about that. There are several other efficiency problems that are related to the restraints imposed by Wankel’s simplicity. That’s why the RX-8 got really crummy mileage (18-20ish) whereas the much much more powerful Corvette could actually get 30 on the highway.

      If they are serious about using it as a range extender, my guess is that the large amount of power per size and weight that you can get out of this thing trumps the inefficiency disadvantage in that role.

      • 0 avatar

        The combustion chamber argument isn’t really apples to apples since we’re talking about two completely different types of engines that would likely have widely different dynamic compression curves.

        The hemi combustion chamber works well, but is more marketing than anything at this point since there are pentroof designs that perform better – at least when using more than two valves per cylinder. The hemi design appeals to nostalgia I guess.

        I believe they can tune a limited range rotary to be much more efficient than we’re used to, but it’ll be interesting to see how the emissions compare to its piston powered cousins. When used over a wide dynamic range the fuel inefficiency really can’t be argued. They definitely are fun to rev out though. :)

      • 0 avatar

        Yup, the hemi combustion chamber was high tech in 1948, when two valve engines and 7.5 to 1 compression ratios were normal. The Jaguar XK engine comes to mind. With way higher CRs today, there is no room for a hemi chamber, and pent-roof chambers with 4 valves per cylinder have become the norm in piston engines. Chrysler’s Hemi is name only as the combustion chamber resembles an orangine rind in shape.

        The latest thing is playing with connecting rod length and cylinders offset from the crankshaft in an attempt to maximize the time the piston remains almost stopped at Top Dead Center and just beyond. The reason for this is to maintain a predetermined combustion chamber space as closely as possible for maximum combustion efficiency. Honda 4 cylinder engines are like this, Toyota Yaris engines, BMWs new N20 and many more. It all started with the old flathead Ford V8 and was then forgotten for decades.

        The Wankel has a completely constantly changing combustion space due to its rotary nature, and is unlikely to ever match the piston engine for complete burn. This may be why Mazda is running the range extender at such a slow speed, 2000rpm, to minimize combustion inefficiencies. However, 2000 rpm is very slow and thus the engine will have to be relatively large in displacement to produce the desired horsepower.

        Add to that the need to lubricate the moving parts with a total loss oiling system, which contaminates the exhaust, and you really have to wonder – why? Why bother with the deck stacked against the rotary? Mazda must just not want to lose face, because there’s no technically compelling reason to go this way.

        A piston engine optimized to run at a given rpm can be made very smooth if it has at least two cylinders. Welcome ONAN generator. What’s old can be new again, especially as they can run on natural gas.

  • avatar

    I can see the benefits, but I can’t shake the thought that overall efficiency will drive the application more than weight or space. I can’t say I know enough about Wankels, but I have a hard time believing that even at the right conditions they would be more efficient than the alternatives.

  • avatar

    Mazda is throwing a bone to their development engineers after the demise of the RX-8.

    Those who can take some joy in designing a tiny one-speed engine for niche applications will be OK. Those who prefer the challenges of sports car development won’t be so happy.

  • avatar

    The rotary engine’s main benefit is its small size for the horsepower output. And it is the one thing that Mazda steadfastly FAILED to capitalize on. The RX8’s engine bay looks like it was made for the 2.3 turbo (which it should have had to begin with). Mazda should be making sports cars the size of Lotus Elises in order to take advantage of the packaging advantage of the rotary engine.

    I do like the idea of a rotary engined hybrid though. The torque characteristics would be perfectly complimentary.

    • 0 avatar

      Exactly. The rotary would have been perfect for a high strung track day car like an Elise. The poor fuel economy and reliability issues would be worth the marginal weight savings and the packaging advantages in a car like that. In a 3,000 pound 4-door grand touring coupe (the RX-8) the rotary made no sense. Especially since Mazda used a conventional inline-4 for the 2,450 pound roadster (the Miata) that it built using the same basic platform.

  • avatar
    bill h.

    I believe small gas turbines have also been looked at for range extender/battery recharging purposes in a series-type hybrid vehicle. What’s not clear to me is whether a very small turbine would have an efficiency advantage (and perhaps fewer moving parts) vs. a Wankel, though there would be other complications in using one. I think a big payoff would be a fuel burning recharging system that allows a carmaker to forego a conventional liquid radiator/water pump cooling system and its associated weight penalties. I’m not sure if either of these options allows that in a car, but aircraft turbines in APUs seem to be a reasonable engineering precedent.

    • 0 avatar

      The closest that a mirco-turbine has come to becoming a range-extender has been the Jaguar C-X75, which used a mircoturbines from a small UK outfit called Bladen Jets.

      But the final car ditched the turbines for a more classic 1.6L engine. Obviously, there was a reason for this.

      I think there are several large hurdles for turbines and range-extenders. Primary of which is if it can reliably operate for 100-200k miles and 10+ years, with the amount of maintenance that a normal consumer puts into the engine of their car.

      There is also the issue of emissions. Turbines operate at high temperatures, meaning that Nox and particulate emissions may be a problem. How well, and economically, microturbines will fit into global emissions regulations is still a question.

      Wankel too has its own set of issues. But unlike the turbine has been continuously used and developed in automobiles for a very long time. Meaning that a lot of those variables are accounted for.

      • 0 avatar

        Volvo has shown a couple turbine powered concepts over the years, the more interesting of them is a large commercial truck. I suspect the turbine has a future directly driving electric motors for heavy hauling, or in a more interesting alternative, being used to charge a hydrostatic setup (a la INGOCAR).

        As the Bladon Jet powered Jaguar is concerned, Ratan Tata is a large investor in the company, so showing off the engine in the C-X75 was keeping it in the family. It’s not out of the question that a very limited number of cars could be turbine powered, as Jag has hinted at as much. Keep your fingers crossed…

        A hurdle I’ve often heard thrown around against the engine’s use is the expensive and heavy gearbox needed to step down it’s high rotational speeds. For this reason, the traction drive of a Rotrex supercharger should be ideal because of it’s ability to deal with speeds as high as 200,000 rpm. Like a turbo, the supercharger can and has been configured as a fuel burning power source, and has been tested at outputs up to 100 Kw. It seems like only a matter of time until it’s developed for this use, as Lotus has already used the units in a traditional role to increase the power output of a proprietary three cylinder generator.

        As a bonus, a turbine can burn a very wide variety of fuels.

      • 0 avatar

        The turbine would never work as a direct drive engine in an automobile due to the reduction gearing (that is one of the primary reasons that the M1’s are used as little as possible in training (95% + of tank crew training takes place in simulators), b/c of maint. cost related). However used as a generator/hybrid set-up the benefits seem to make perfect sense, especially if used with a magnetic flywheel KERS system so that the turbine could be spun upto optimal rpm’s electronically before re-ignition for stop/start purposes.

  • avatar

    Volvo had a concept car in the 90s that used a Turbine to power the electric drive. I never saw any write-up of its strengths and weaknesses.

  • avatar

    As a biased lover (as in emotional, willing to overlook warts and scars) of the Rotary, I say unto thee, I’d rather walk than drive a clattery piston ICE after experiencing the buttercream deliciousness of a Wankel, whether at 2k rpm or 10k.

  • avatar

    derek, your statement that mazda is reviviing the rotary is a bit misleading, as we’ve known for the better part of two years now that mazda has been working on this skyactiv(back then anyways) rotary for future hybrid use. and mazda hasn’t really been shy about talking about it either.

  • avatar

    Same old engineering compromises Cost Size Weight Efficiency Durability, etc, again, still! Oh, I forgot buttercream deliciousness :-)

  • avatar

    So far, range extender applications haven’t been very impressive. Once you get the Fixker or Volt onto full *parallel hybrid* mode, where the ICE engine directly powers the drive motors instead of charging a battery, the efficiency becomes very mundane. I can’t see how a rotary would be any better… Sure, it would be smaller and lighter, but the key point is that in present form, the engine has a hard time harnessing all of the combustion and converting it into torque. You can get a lot of power in a small package because revs are free, but the design is essentially akin to a very short stroke Otto engine, like a sportbike engine or the S2000…. it’s all about the revs, efficiency is secondary.

    • 0 avatar

      No one said that using a rotary that you would have to go into a parallel hybrid mode. The reason the Volt does it is because it is more efficient with the 4 cyl engine. If it isn’t the same for the rotary engine, then it won’t go into that mode. But all of this relies upon what is more efficient.

      Once you consider the weight savings of the engine over how often you would go into range extending mode, packaging concerns, might allow for a little bigger battery, you never know, it might make more sense to go with it. But don’t assume that the rotary would be used in a parallel mode like todays ranger extenders.

  • avatar
    el scotto

    I wan an electric Batmobile with a turbine range extender.

  • avatar

    The advantages are that it’s simple, light, and compact- perfect for a range extender. It means you’re carrying around less dead weight, and can tuck it away in some corner.

    The disadvantages of the rotary are emissions, efficiency and reliability. Believe it or not, these don’t matter much in a range extender, because the extender will seldom be used. After 100k miles, your range extender might have 15k miles on it. Design it light at the expense of reliability. And, for that few miles, efficiency isn’t that big of a deal. Again- keep it light to increase your electric efficiency and decrease your battery size.

    • 0 avatar

      I hadn’t thought of this but it makes sense. If I am someone who does a lot of city driving but has the occasional highway jaunt this makes sense. If the apex seals are good for 100k (100k on the motor, not the chassis) then in this application they should long outlast the batteries.

      The flip side is that the Wankel is needy…you don’t maintain it it dies early. In an enthusiast marketed car like the RX8 this is less of an issue…the buyers tend to pay attention to that. Now take those same traits and market them to a Prius or car as an appliance type and I’m not sold.

      • 0 avatar

        The engine has to be self maintaining.. anyways using it as a genset in a serial hybrid overcomes all the problems of a Wankel.. probably optimized to 60hp and 30hp in two speeds

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