The rotary engine is known for many good things. It’s compact and lightweight. It’s super smooth. It’s happy to rev to outrageous revs. It even won the 24 Hours of Le Mans. What’s the twist Not Known for being eco-friendly. In fact, rotary pistons are notoriously thirsty for fuel. but Mazda tries to change this reputation. It just started the MX-30 R-EVa series plug-in hybrid with a power-generating Wankel engine. And for years decadesbefore this little one crossing, the Hiroshima-based company has tried to make the gyroscope green. One could argue that this has been the case from the start of the work to make the regular gas-powered rotary lobes more efficient, but even the most efficient production rotary lobes, the RX-8‘s Renesis engines have never been economical. And the ethanol-powered engines like that in the sweetly-freaky Furai concept weren’t particularly green either. So we’re looking specifically at the larger trials: Mazda’s hydrogen and range extender projects.
Mazda’s green rotary development has long focused on hydrogen hybrids. Mazda introduced a concept called the HR-X back in 1991, which is shown here. It had a smooth, organic shape, characteristic of that time, especially Mazda, which was undoubtedly intended to give the hydrogen engine the best opportunities for efficiency as well. It was followed in 1993 by an HR-X2 with a slightly more angular design. Both ran existing Wankel engines that were converted to hydrogen. Mazda also had a 1993 Miata prototype with one of these hydrogen engines, and in 1995 it began testing a few Capella charge (Mazda626) station wagons with them.
One of the reasons Mazda experimented with hydrogen in rotary pistons was that they have an inherent advantage over piston engines when burning hydrogen. Hydrogen ignites easily, sometimes too easily, so pre-ignition is a real problem. This can cause a reciprocating engine to misfire if it’s early enough. This is much less likely with rotors that are constantly spinning in one direction rather than going back and forth. Also, because combustion takes place in only one section of the rotor case, due to the design of the rotary engine, the intake area is kept much cooler, reducing the risk of pre-ignition when hydrogen is introduced into the air-fuel mixture.
The next major milestone for the hydrogen rotor came in the mid-2000s. Mazda had unveiled the latest iteration of the gas model, the Renesis, and once again developed a hydrogen variant. What was particularly nice about the engine was that it was designed to run on either hydrogen or gasoline. It wasn’t limited to one flashy concept either. The engine was first shown in 2003 and then appeared in a few cars, the RX-8 and premature birth (Mazda5) in 2005. The former wasn’t just a show car like it was available for either rent as of 2006. Some were even sent to Norway for naval service.
With the RX-8, the powertrain did not differ much from a regular automatic RX-8. In fact, at 207 hp on petrol, it was just a few hp less (the regular automatic version made 212 hp). The big difference was that four injectors, two for each rotor, were added at the top of the rotor cases for hydrogen operation. The dual injectors were necessary to provide enough hydrogen for adequate performance. Emphasis on “sufficient”. Running on hydrogen reduced power to 108 hp.
Although the RX-8 featured both a gas tank and high-pressure tanks for hydrogen, it still retained all four passenger seats. However, it lost pretty much all of its cargo space to the hydrogen tanks. The range was fairly short, however, at just around 60 miles, likely a combination of the low energy density of hydrogen and tanks constrained by the RX-8’s relatively small package and having to save room for some gasoline.
The Premacy was originally shown with the same engine but with an additional 40hp electric motor to turn it into a hybrid. As well as the obvious efficiency benefits of partially electric operation, the electric motor likely contributed to the off-the-line performance as rotators are notoriously lacking in torque. On the Premacy, the entire powertrain was transverse, driving the front wheels like a standard model. The lithium ion battery Pack was under the second row of seats and the hydrogen tank was behind the third row. Although later Mazda simply showed it as a double-breasted suit with the tanks behind the second row and cargo hold behind both. The supremacy began Road testing in 2008and it entered fleet service in 2009. The range was around 120 miles on hydrogen.
This was about the point at which Mazda’s hydrogen rotary development peaked, at least publicly. Rumors have come and gone over the years that the company is working on more modern hydrogen rotations, but nothing has really surfaced. Some of these rumours The engine was used as a range extender, and while hydrogen hasn’t been involved yet, Mazda has definitely experimented with the range extender idea.
In 2013 Mazda showed a Mazda2 electric car with a tiny Wankel engine that supplies electricity as soon as the on-board battery is empty. We also mean tiny, as it only had a displacement of 330cc, half the displacement allowed Japan’s Microcars in the no Class. It only produced 30 hp, but only had to generate electricity. The actual drive came from the 100 hp electric motor driving the front wheels, which had about the same power as the conventional one Mazda2 did. The range-extended electric Mazda2 battery lasted about 124 miles. The small gyro and its 2.6 gallon gas tank gave it a range of up to 250 miles. Using our math, that means the gas engine got about 48mpg.
Which of course brings us to today with the Mazda MX-30 R-EV. The electric-to-gas ratio is slightly more gas-focused than the extended-range Mazda2 model. Its 17.8kWh battery is half the size of the regular electric and offers a range of around 50 miles. But the remaining space makes room for a 13.2-gallon gas tank. Nevertheless, the basic idea is the same. The 168 hp electric motor provides all the propulsion, and the 830 cc, 75 hp single-rotor engine generates power on demand. The rotary engine uses side intake and exhaust ports like the RX-8’s Renesis engine, but uses an aluminum rotor case and direct fuel injection.
As for the future of Rotary, it’s hard to say. Fully electric cars have steadily gained momentum, making the future of the internal combustion engine look bleak. Still, there are automakers that continue to pursue the use of hydrogen, even in combustion. That’s probably the best case for the rotating, possibly as a power generator like in the MX-30, or maybe for limited production enthusiast models. But if anyone can find a future for the gyroscope, it’s Mazda.