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Happy Birthday Felix Wankel: How Does the Rotary Engine Work, Anyway?

Posted in Car Tech, Design, Guide, History, Mazda, Videos by Vito Rispo | August 12th, 2008 | 11 Responses |

All the major parts of the Mazda RX-8 Renesis engine disassembled.

Today in history – Felix Wankel, the inventor of the Wankel rotary engine, was born. I’m a Wankel freak. I love Wankel rotary engines, I think they’re one of the most beautiful mechanical devices of all time. Call me a geek, call me a weirdo…whatever, I love it when you talk dirty.

When I was young, I saw the innards of an old, junked Mazda Cosmo at my fathers salvage yard. I heard about this crazy motor out in the yard and decided to check it out; I knew the basics of how piston engines worked, and figured this strange thing would be pretty fun to mess around with. But sitting there, with it’s seals broken and rotors immovable, it blew my mind. It was just an oval with a triangle in it. That’s it. I had no idea how it worked or how it moved or anything. How could this thing power a car?

The Mazda Cosmo was the first 2-rotor rotary engine powered car.

So I looked up and read everything I could find about Wankel engines and about Felix Wankel, and that really blew my mind. The Wankel engine has basically one moving part, and it just spins. And it has a higher power to weight ratio than any traditional engine.

So why aren’t more automakers producing Wankel powered cars?
Because they already have a motor that works. The traditional piston engine does it’s job well, and these are hefty multi-billion dollar companies. It would be near impossible to steer these behemoths away from something that works and towards some weirdo engine with a cult following.

As I read about the rotary engine, I learned that the inside chamber isn’t an oval, it’s an epitrochoid. And the triangle rotor isn’t just a triangle, it’s what’s called a curve of constant width, or a Reuleaux polygon. Wankel engines are serious business. Instead of just a cylinder inside another cylinder, which is a very primal design for humans, the Wankel is pure simplicity via mathematical precision.

This is why most mechanics and engineers who understand Wankel engines are so enamored with them. They appeal to mechanically minded people because they’re such an elegant solution to a complex problem. Instead of having three separate pistons and all the bits associated with them, the rotary engine just has a triangle rotor, and each side works as a combustion chamber. It just spins. Quiet, harmonious, elegant spinning.

In contrast to the Wankel engine, the piston engine has a veritable army of moving parts. Cylinders, connecting rods, crankshafts, timing belt, camshaft, rocker arms, valves. There are countless little bits and pieces flickering away under the hood of the average car, creating that violent shaking. Meanwhile, the Wankel just spins around the eccentric shaft. That’s the only moving part. Really.

A Wankel rotor with the apex seals and side chamber seals removed and displayed.

The common objections to Wankel engines are ‘fuel efficiency’ and ‘reliability’, and those issues really just boil down to one thing, the seals. The combustion chambers inside the Wankel are constantly moving, so the seals (the apex seals and the seals against the chamber ends) are of major importance. Those are problems, not huge ones, but problems nonetheless. They’re nothing that a few years of competing automotive firms couldn’t fix, though.

You have to realize that Wankel’s are still on the fringes, despite the RX-7s and RX-8s, they’re essentially ignored by everyone else. They never really had a chance to get the kinks worked out by competition. Competition gets lots of minds working on the same problems, and that’s how you get real progress.

But, the first step in trying to change something is education. So, in honor of Felix Wankel’s 106th birthday today, August 13th, 2008; let’s get educated.

How it works:

And illustrated example of the Wankel engine in action.

Just about all internal combustion engines today are four-stroke engines. The four strokes are intake, compression, combustion and exhaust.

A traditional piston engine performs them all in each piston. The piston moves down, a camshaft opens the intake valve, and the air/fuel mixture gets sucked in. The piston moves up, compressing the mixture into a very small space. The spark plugs fire, creating combustion, which pushes the piston downwards, creates the force that moves the car; and turns the camshaft, which opens the exhaust valve. Lots of moving parts, still pretty simple. But that cycle takes place separately in each cylinder.

In a Wankel rotary engine, on the other hand, each side of the triangular rotor acts like a cylinder in a piston engine. As one side of the rotor is sucking in the air/fuel mixture, the other side is compressing another air/fuel mixture and getting ready for combustion; and the third side is expelling the exhaust from combustion that has already happened in that chamber. As the rotor moves, it closes off the intake or exhaust port, making camshafts and valves irrelevant. A Wankel engine car with two rotors (3 sides on each rotor = 6 sides or 6 combustion chambers) is equivalent to a traditional V6 car (6 cylinders = 6 combustion chambers).

It sounds complicated, but it’s not really. If you’re still having problems visualizing it, this should offer some clarification:

So, it’s a badass machine. It’s beautiful, it’s elegant, and it works perfectly. Hopefully Mazda will keep the dream alive and keep producing cars in their RX series, like the awesome 2009 Mazda RX-8. Thanks Felix.

Felix Wankel was born in Lahr, Germany in 1902. He never went to college, never got a degree in engineering, and was never even able to become an engineers apprentice. He taught himself engineering and was able to put together the first prototype Wankel rotary engine in the mid 1950s.
Happy Birthday.

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11 Responses

  1. fmfm says:

    I agree with you that rotary engine is a mechanic marvel.

    But… to considered as every day average auto industry engine is not easy. the main disadvantage of this engine is the fraction, where you can see that other than the traditional engine the rotors have great are of contact with the housing, this is not good on the long run.

    But still we hope to see new technologies applied to make the rotary engine more reliable.

  2. Joe says:

    fmfm–as I see it, and I could be wrong because this engine has always been something like understanding the meaning of life, but aren’t the apex or side chamber seals what is in constant contact with the housing? Similiar to the piston rings in a traditional engine? In addition, aren’t LESS parts better than MORE parts? I mean, common sense would indicate that if there’s less pieces to break then there will be LESS BROKEN PIECES should something break.

    Vito–God damn—you’ve just explained the meaning of life to me, or well at least how one of those damn rotary engines work anyway. Something I haven’t had the time to look into in the 30 years or so that I’ve been around cars. And that guy that made that video gets big ups from me too. That was sweet.

    I imagine that if Felix Wankel had been trained in a traditional (college) setting he might have never thought so far “out of the box.”

    Good shit— I’m now reading your stuff right after checking my mail. Keep this stuff coming!!

  3. nocode says:

    Rotary Engine really is a work of ART!
    Makes you wonder who would want to use a two/four stroke engine!!??
    Just think of the efficiency!! Two/Four stroke engine the piston would have to stop 2x or 4x just to complete a cycle!! What a waste of efficiency!! The world/universe is round! (If you believe the Big Bang thoery that the entire universe is expanding like a balloon) And it is evidently clear that the most energy efficient things in nature all comes in spherical shape, continuous………..around and around!!

  4. bigobe charles says:

    I think Felix Wankel was a wiser man because my observations:
    1-He solved the problem of engine timing
    2-He solved the problem of costly fuel like petrol
    3-He also reduced on the weight of the engine by using only two ports and using a rotor isteady of crankshaft and others

  5. Mike says:

    I thought that rotaries consumed more fuel than a standard piston engine.

  6. yo says:

    That vid was mazing i have confidence in a rebuild now

  7. J.H. Chapdelaine says:

    For the first time I think I am getting to understand your engine and it seem to be prety sharp. How come we do not see many of them in automobiles. To expensive ?? Blackballed from the industries ?? Or what ??
    If you do have some free publications to give awayn well I would be gratefull to received some.
    Yours truly J.H. Chapdelaine, 7782 rue des Terrasses du Fleuve
    Trois-Rivières, Qc. Canada G9B 1L2

  8. cars lover says:

    Felix Wankel what amazing great man really with very outrageous engine ???!!!! rest in peace great man!!!!

  9. SB says:

    The rotary is such an amazing work of machinery. I’m trying to get an FC RX7 as a first car and for a while I was intimidated by the rotary design. I’ve spent the last week wrapping my head around the design and it all makes sense now. The rotary engine is a marvel. Thanks for your contribution to the automotive world, Mr. Felix. Also, Wankel has the same birthday as my grandmother. How weird is that?

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  11. kyle says:

    felix wankel is the greatest who invented the rotary engine.
    1; genius idea using rotors inted of crank shafts.
    2; more high rpm power than any other engine,
    should be a cocaine powered car on how expensive it is on fuel lol.
    i wish i could take felix wankel for a drive in my 12a brideport.