See-Through Rotary Engine Reveals Wankel Magic

The Wankel rotary engine is known for its troubled life in the mainstream automotive industry, its high power-to-weight ratio, and the intoxicating buzz it makes at full tilt. Popular with die-hard enthusiasts and punishing to casual owners, it stands as perhaps the most popular alternative internal combustion design to see the light of day. There are myriad diagrams out there to explain its operation, but what if you could see inside?

The video comes courtesy of [Warped Perception], and features a small Wankel rotary engine intended for model aircraft. The engine’s end plate is removed and replaced with a transparent plate, making the combustion process visible. Add in a high-speed camera, and you’ve got a recipe for a great technical video.

It starts with a basic explanation of how the Wankel rotary power cycle operates, before cutting to the glorious slow-motion shots of the engine in operation. It also highlights several techniques useful for producing this type of video, such as painting surrounding components black to make it easier to image the parts of interest. The visuals are amazing and very clearly show the  manner in which the intake, compression, power and exhaust strokes function in the engine.

We’re big fans of the rotary engine, and it’s amazing to see how they really work in such great detail. If you’ve yet to learn about the rich story of the Wankel rotary engine, don’t worry – we’ve got you covered.

25 thoughts on “See-Through Rotary Engine Reveals Wankel Magic

    1. Probably not, but they’re also having a lot of trouble getting it to run steady because there’s little to no flywheel to help the engine turn over.

      This application uses a glow plug so the timing is going to be a little random until the fuel mixture gets steady and the engine runs a constant speed. Between changing the temperature of the glow plug and adjusting compression ratio (which can’t be done on this particular engine) you can vary the timing a bit.

      1. It’s not just that. In the slow mo you can see lots of unburnt liquid fuel both in the chamber and the exhaust. It’s mostly a side effect his setup and not letting the engine get up to stable operating speeds / temperature. But these small model engines have a reputation for running dirty, so much so they used to get referred to as ‘slimers’ in much of the RC community from the trail of slime left on the aircraft after a day of flying.

    1. I was wondering that too. If it’s sealed well enough to contain the combustion I’d expect it to get oily and/or scratched. Maybe this is one of the reasons it doesn’t run that well.

      1. In a “real” automotive wankel, there are a bunch more seals on the rotor than on this model engine. You’ve got apex seals to seal the three combustion “chambers” against the main housing and rim seals on both sides of the rotor to seal against the two end-plates. Then there are two ring seals on each side around the center hole of the rotor.

        Lubrication is achieved by injecting oil into the housing and thus the combustion chamber. It’s one of the reasons, why the rotary has gone off the market, right next to bad economy. Emissions are just way too bad.

        On model engines, it’s slightly different. The one shown in the video doesn’t have any rim or ring seals. Lubrication is achieved via the fuel itself, which is also the reason why it has to run rich.

  1. I owned an RX4 and RX3 with a Mazda 13B and 12A. Both were great cars, bought at end of life of course, but were great running engines. Wish the technology had not gone away as it has.

      1. That’s really nice. On the other hand they are launching the Skyactiv-X compression ignition engine right now, with 40% efficiency. How does a Wankel fit into that?

      2. Mazda has not announced a new Wankel. They are just rumors. I drive a Wankel daily, a 2008 RX8. I get about UK 25 MPG, which is not great when other cars easily get 40MPG with similar performance. They could not be sold in Europe after 2010 due to CO2 being above the minimum. They could make a good auxiliary charger on an electric vehicle, due to high power to weight ratio and small size.

        My car reached 180,000km 110,000 miles (10 years of age) before it needed to be rebuilt at a cost of €3000.
        It was not the seals which wore, but instead the rotor tips snapped due to fatigue. It may have also been due to main bearing wear, which causes wobble and wear elsewhere. I use 2 stroke premix in the petrol to reduce wear and carbon build up, and also high revs once per journey to remove carbon build up. There are work abounds and fixes to most of the issues with these vehicles. The main bad reputation comes from those who have not applied any of the recommendations and have typical problems.

        It has similar reliability to any specialist sports car, if not looked after, it is likely to fail, and high milers need work.
        Main issues like any performance car are insurance costs, fuel costs, and government taxes, and aging parts.

        1. I’m a huge Wankel fan, but I wouldn’t agree that an RX8 has similar reliability to other sports cars. MX-5s, S2000s, 350Zs and all manner of others have far superior reliability.

  2. I have been interested in Wankel engines for many years. The primary issue with them is the large surface to volume ratio of the combustion chamber, especially with high compression ratios. This causes fuel to condense out and large heat losses. All is not lost, though, as they have a characteristic that makes them an excellent candidate for stratified charge where fuel is injected directly into the combustion chamber at a rate to match the burn. This allows much higher engine efficiency and eliminates unburned fuel. Wankel engines inherently sweep the mixture in the combustion chamber past a fixed point where fuel can be injected and ignition initiated. Piston engines require carefully controlled swirl to enable this. That is very hard to do. I have been waiting for the time when direct injection is sufficiently developed to make this economically viable in a Wankel. A turbocharged, direct injection, stratified charge Wankel engine should be capable of diesel like efficiency, without the NOX issues of diesel, in a very small package. This would be an ideal power unit for a hybrid vehicle. I suspect Mazda may be near to having such an engine.

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