• Jul 16th 2010 at 5:02PM
  • 52
It's starting to look more and more likely that the Wankel rotary engine could have a future as an electric vehicle range extender. Felix Wankel's original concept was once seen as having great potential because of its high power density compared to piston engines. Unfortunately, the manufacturing processes available in the 1960s and 1970s made it difficult to achieve adequate durability without high oil consumption and excessive emissions.

The combination of high precision machining, new materials and technologies like direct injection can help overcome many of those issues. Add in the ability to optimize the engine to operate within a narrow speed range as a range extender and this could be a winning combination. Wankels are also well suited for use with alternative fuels, including hydrogen.

Powertrain engineering firm AVL has built a prototype Mini with an ER-EV powertrain that uses a 254 cc single-rotor Wankel to produce 15 kilowatts at 5,000 rpm or 25 kW at 7,000 rpm. The 10 kilowatt-hour battery gives the car a 19-mile electric range and a 2.6-gallon gas tank extends the range to 124 miles. The complete package of rotary, generator, power electronics and cooling weighs just 143 pounds. By comparison, the more powerful 75 kW 1.4-liter inline-four in the Chevrolet Volt weighs approximately 200 pounds for the engine alone. Even a more powerful complete Wankel setup could probably still come in below the weight of the piston engine.

[Source: Ward's Auto World]

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    • 1 Second Ago
      • 4 Years Ago
      EVrangeExtender.com and BatteryrangeExtender may be available. http://dld.bz/anTMD
      • 5 Years Ago
      The oil companies must love this. The point of a range extender engine is to be able to economically extend the range.
      If you spend large amounts of money to reduce fuel consumption, what is the point in throwing it away when you actually want to use it?
      The Lotus Range Extender blows the Wankel away IMO:
      • 5 Years Ago
      So their prototype gets 40mpg. That's interesting but not any better than current hybrid technology. The mini might not be the best test platform as the car is not aerodynamic or lightweight.
      • 5 Years Ago
      2.6-gallon gas tank extends the range to 124 miles. == 47 mpg with the range extender.

      • 5 Years Ago
      Series hybrids so far have shown themselves to be less efficient than series-parallel or parallel. There's just too many losses when you do all the conversions. Series hybrids will likely always show a comparative weakness in fuel efficiency once the stored grid charge is depleted and the petrol fuel in the tank is the source of onboard energy.

      I wouldn't expect to see anything different from the Volt (i.e. 50 mpg city/hwy combined in CS mode ain't going to happen).

      Still, it's possible that a Series-hybrid done right (perhaps with a compact, low cost range extender like this one) could be produced cheap enough and at the end of the year will have burned very little gas for the miles travelled.

      IMO -- The Volt in it's current form will have a limited production run until the whole thing is redisigned into something radically different (i.e. cost competitive/viable).

        • 8 Months Ago
        "I wouldn't expect to see anything different from the Volt (i.e. 50 mpg city/hwy combined in CS mode ain't going to happen).


        Wow - you must really be an awesome clairvoyant - I am truly impressed by your foresight into the future!!

        Or not - do you really think that you are so intellectually superior to all of the highly experienced engineers at GM that you can easily make such a pronouncement that will sway all of the people who are following this development?

        Seriously, stop being so anal retentive - we in the US have enormous engineering talent that can exceed anything that an 'AUTOBLOG Green highly qualified commenter" can think up.

        WTF Dud?
        • 8 Months Ago

        You don't need an special powers to realize that A is more efficient than B:

        A: Mechanically connecting engine to wheels.
        B: Connecting engine to generator, converting mechanical to electrical energy, convert electrical energy back into mechanical energy in EV motor, connect EV motor to wheels.

        Defenders of B will often point out that you can run engine in optimal range, but that only happens if you buffer the energy in the batter then you lose even more with energy conversions to and from chemical potential energy.

        The Prius isn't going to lose it's MPG crown to a serial hybrid, especially not one powerd by a rotary.
        • 8 Months Ago
        GM themselves have said that they will only produce the car in limited numbers and expect to loose money.
        They used an off-the-shelf engine adapted as a range extender.
        Do you think any of this supports your thesis?
        • 8 Months Ago
        The original post by Carcus which you took exception to said:
        'IMO -- The Volt in it's current form will have a limited production run until the whole thing is redisigned into something radically different (i.e. cost competitive/viable).'

        From your latest post it appears that you do not seriously disagree with this, and so I am at a loss to account for the rather intemperate nature of your original response.

        Your issue seems to be the narrower one of the possible efficiency/inefficiency of the present engine. and your dislike of any critique on the grounds that commentators do not have access to all information.

        On the first count the engine is hardly likely to be optimal, since it was taken as far as possible off the shelf.
        It also appears that the GM engineers are very much of this opinion, as in the next version they are considering all sorts of options including the Wankel, which they would hardly do if they thought that their present configuration left a lot to be desired.

        On the second count, we are all more or less limited in our information, and any comments here are of course subject to later revision as more data becomes available.
        A number of the commentators here are however engineers, and so not totally unqualified to comment.

        Without in any way claiming to be qualified I would express a personal preference for the hybrid 4 system with an electric motor driving one axle and an ICE the other, rather than either the series hybrid GM configuration or the planetary gear parallel system on the Prius, because it is simpler. It is far too early to draw definitive conclusions though.

        However, both because it is a newer system and from the remarks GM themselves have made it seems reasonable to think that there is a lot more room for optimisation in the GM system than in the Toyota.

        • 8 Months Ago
        @ David Martin -

        The Volt in the first generation configuration likely will not be a money maker - however, they are hard at work on Gen 2, and the technology advancements that are being implemented for future gen vehicles are all building on what they have already accomplished - which is significant. I have ridden in several Volts and the previous Cruze based Volt mules and can state unequivocally that I have seen significant advances in driving characteristics; change over from regen to regular braking and the feel of the range extender starting have felt much better, from the passenger seat - haven't driven one yet :-(.

        That said, I don't see any reason why the range extender would not be able to attain 50 mpg rather easily - and cannot understand why someone like Carcus could possibly think that they have superior knowledge compared to the HUNDREDS of engineers GM has working on this and the many other hybrid vehicles currently under development.

        I mean seriously - a hobbyist is no match for a global engineering team, wouldn't you agree? And lots of these engineers also worked on the EV1 program, development from that early generation vehicle program was transferred. The biggest changes are in the battery technology, electronics and control system advancements. Modeling capabilities especially have had huge advancements over the last ten or so years (HIL, MIL, SIL), enabling large strides.

        My ICE is mid-sized, has a 2.4L DOHC with VVT and a six speed automatic. My average fuel economy over @ 24K miles ranges from 29-31 MPG.

        When running 70 MPH on a level freeway, it is easy (and fun) to keep the instantaneous fuel economy between 50-60 MPG. Why would a 1.4L running at a consistent speed not be able to do the same?

        The other thing that many of the naysayers don't understand is that too small of an engine for it's load requirements is generally less fuel efficient than one that is correctly sized. I'm not saying that the 1.4L is optimally sized - I don't know enough to have an opinion one way or the other on that. Do you think that anyone who posts here is sufficiently knowledgeable about the load characteristics of the generator in the Volt to really have a valid opinion on that? Highly doubtful.

      • 5 Years Ago
      The system makes more sense in a vehicle with a larger battery where the engine behaves more as a "get me home box" than as primary means of propulsion. That is an area where space considerations will matter more than the efficiency of the engine. I would expect at a minimum to have similar electric only range as the Volt.
      • 5 Years Ago
      Wankel engines are quite reliable as long as they aren't overheated or lacking lubrication. I've known of several wankel powered cars achieving over 300K miles with original internal components. They are most reliable when naturally aspirated and rotating at a somewhat constant rpm(powering a generator). The combustion chamber is not shaped optimally, but it does provide for better heat distribution for Hydrogen applications. Additionally, direct injection would greatly reduce fuel atomization problems and aid in a more even and complete combustion(thus reducing consumption). New metal coatings have greatly diminished oil consumption in experimental wankel style internal combustion motors, and pumps.
      • 5 Years Ago
      I'm still waiting for a MYT-Engine as range extender to come along.

      Seems less vapor-ish than EESTOR anyway.

        • 8 Months Ago
        nah the obtuse inventor still hasn't even run it on any type of fuel. just powered it with compressed air. it might have some use but there is absolutely no development coming out of them for years.
      • 5 Years Ago
      The cutaway photo shows a single piston rotary engine.
      Hello? There are no pistons in a rotary engine.
      It is called simply a rotor or rotar in some badly translated texts on the subject.
      I digress though even as a fan of the NSU/Wankel this is not very impressive either in power or efficiency.
      I guess you have to start somewhere,so,cheers!
        • 8 Months Ago
        The rotor IS the piston.
      • 5 Years Ago
      better technology: http://wankelsupertec.de/

      ....and multi fuel
      • 5 Years Ago
      RX-7 :)
      • 5 Years Ago
      Wankel engine is flawed, too much heat losses due too much surface, too much friction, sub-optimal combustion chamber shape that result in poor combustion, last but not least inherent radial displacement of the piston that unavoidably result in loss of efficiency.
      Lubrication and reliability have been only partially solved by Mazda.

      I don't buy it, a 2 stroke 2 cylinder engine would do better
        • 8 Months Ago

        Ricardo’s Wolverine 4, a 300-cm3 horizontally opposed, liquid-cooled, compression-ignition four-stroke rated at 25 hp (18.6 kW), is under development for a larger, higher performance UAV.

        Also the Lotus omnivore engine looks like it would make a good range extender.
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