Why Mazda's Revival Of The Rotary For The MX

Mazda brought back the legendary rotary engine, but now how it was expected

Mazda’s Rotary engine is nothing new. It was invented by Felix Wenkel, a German engineer, in the early 1950s. But a masterpiece doesn’t have to be new to be admired. It offered an elegant alternative to the common four-cycle internal combustion engine (ICE). It had an innovative approach, and fewer moving parts. And as is the case with most things different, it had some advantages, and disadvantages to the usual four-cycle ICE. For quite some time, the advantages seemed to overcome the disadvantages. And with good reason too. The Wenkel Rotary engine allowed for more power, and more RPMs, with a more compact, smaller displacement engine. A four-cycle ICE needs 720 degrees of rotation to complete one thermodynamic cycle. That’s the same as saying it needs two complete revolutions of the crankshaft. With the rotary engine, for every 360 degrees of rotation, two faces of the rotor go through a full combustion cycle. In a way, it is similar to the power output of a two-stroke engine.

Related: Why Mazda's First EV, The MX-30, Failed In Its First Attempt

The Rotary design allows for the air and fuel intake cycle, the compression cycle, the thermodynamic cycle, and the exhaust cycle, to happen simultaneously. Inside the legendary Mazda 13B rotary engine, for example, you have only three moving parts. Two Rotors, and the eccentric shaft, which is the rotary engine equivalent of the crankshaft. On a usual four-cycle ICE, you have parts like the piston, crankshaft, connecting rods, camshaft, inlet valves, outlet valves, valve springs, and the flywheel. Not only that, on a rotary engine, you have rotational mass as opposed to reciprocating mass on a four-cycle ICE. Instead of going up and down like the valves (which can cause valve float), and pistons, generating ever stronger reciprocating forces as the engine’s RPMs rise, the rotational mass of the rotary engine allows for higher revs, and fewer vibrations.

Check this slow-motion, see-through video, of how the rotary engine works. This is a 3D printed, one-third scale model of the 13B rotary engine. Try selecting a slower view speed to make it even easier to see, and understand all the cycles happening inside the combustion chamber.

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Some engineering challenges exist in the rotary engine, and they are not easy to tackle. One of them is that, by design, the rotary engine is not very thermally efficient. The engine has trouble burning all the mixture during the combustion cycle. This is bad for fuel efficiency, and emissions. If you’ve ever seen a Mazda spitting fire through the exhaust, that’s wasted fuel being burned after the combustion cycle happened.

Also, due to the shape of the combustion chamber, you will always have the thermodynamic cycle happening on one side of the chamber, making it very hot. At the same time, the other side of the chamber will be colder, since it will be dealing with air, and fuel intake. The difference in temperature makes it so that the metal will tend to expand at different rates. This makes sealing difficult. You don’t want to mix gasses from one chamber to another. For this reason, you have apex seals, face seals, and side seals to try and prevent gasses from escaping into other chambers. To further ensure good sealing, you have oil injected directly inside the combustion chamber. This means the engine burns oil by design. Because of this, you will have even worse emissions. And the emissions are a major part of the reason the rotary engine was discontinued. That is until recently.

Related: Mazda's Rotary Engine Could Have A Much More Exciting Future

The first-ever fully-electric vehicle from Mazda, the MX-30 is a bit of a conundrum. For starters, it only offers a 100-mile range with a price tag starting at around $35,000. For the first year of production, Stateside, it’s supposed to be released only in California. And that with a very limited production of only 560 units. It is also supposed to be an SUV/Crossover of sorts but only comes with front-wheel drive.

But then, as if to end the range anxiety of their own creation, Mazda announced a hybrid that will bring the rotary engine back. But this is not the application motor enthusiasts were hoping for. The Mazda MX-30 e-Skyactive R-EV is a plug-in hybrid model that uses a rotary engine not to drive power to the wheels. But simply as a generator to top off the 17.8 kWh battery as needed. The single rotor rotary is 0.8 liter (5.65 cubic inches), and with a 13.2-gallon fuel tank, it provides a total range of up to 372 miles. The electric motor makes 160 horsepower and 192 pound-feet of torque. These are figures for everyday use, but they don’t really make much sense for the price. And, the fact that this car has a rotary engine used as a glorified generator hurts the legacy and moniker of the once legendary rotary engine.

Related: Mazda's Rotary Engine Could Have A Much More Exciting Future

To be fair, the rotary engine is smaller, and lighter than regular four-cycle ICEs. And the idea of using an ICE as a range extender for EVs didn't come as a big surprise. Also, this single-rotor rotary of the MX-30 E-Skyactive R-EV has an exhaust gas recirculation system, and a three-way catalytic converter with a gasoline particle filter. This ensures it is up to the current emission standards. And the fact that the engine will function at a lower RPM, without being pushed too hard, means it's going to be reliable and durable. It will also run very silently, and with very low vibrations which is a design characteristic of this engine as explained before. Since the rotary engine will be so discreet, the experience of driving the MX-30 e-Skyactive R-EV is very much similar to driving an all-electric EV. This unfortunately brings us back to how this doesn’t do the rotary justice.

We could still have hope for the future though. Some speculate that Mazda is bringing back the rotary engine in this way to get dealerships reacquainted with them. And maybe the future will bring back a true Mazda sports car powered by a rotary engine such as an RX-9, for example. And maybe even a hybrid powertrain, but like the ones used by sports cars where the main propulsion comes from the ICE, and the electric motors are there to improve performance. Maybe we will hear those rotaries screaming again someday.

A car and motorcycle enthusiast, Bruno enjoys writing about and following up on what's happening in the industry. He's easy and friendly. Known to drop the bass on occasion.