We haven’t seen the last of the spinning triangles.
Back in March, Martijn ten Brink, Mazda Motor Europe's vice president of sales and customer service, when he told Dutch auto news outlet ZERauto that the Wankel rotary engine will return to production.
Specifically, ten Brink said the rotary could become a range extender for an electric car in 2019, and for now that’s just a rumor. Mazda Motor of America won't discuss or confirm ten Brink's comments, telling us only that “Mazda hasn't announced any specific products featuring a rotary engine at this time. Mazda remains committed to working on rotary engine technologies, however.”
So what's so special about this legendary engine that’s got everyone so excited for its return? And why might things be different this time around?
How It Works
A rotary engine is a barrel-shaped internal combustion engine that lacks many of the major parts you’d find in a conventional piston engine. For one thing, there are no pistons chugging up and down. Rather, rounded triangular rotors—most often two, but sometimes one or three—spin around a shaft through the hollow barrel.
Fuel and air are pumped into the spaces between the rotors' sides and interior walls of the barrel, where they ignite. The rapid expansion of exploding gases turns the rotors, thus generating power. The rotors fulfill the same task as pistons in a piston engine, but with far fewer moving parts, making a rotary engine lighter and smaller than a piston engine of equivalent displacement.
The basic design is a century-old one. Felix Wankel himself was a German engineer who came up with his version of a rotary engine in the 1920s. Being busy with warmongering on behalf of the Nazi party, however, he didn't get the chance to develop his vision too far until 1951, when German automaker NSU invited him to design a prototype.
Wankel’s complex design actually lost out to a simpler prototype developed by engineer Hanns Dieter Paschke, whom NSU had also invited to take a crack at Wankel's original concept. Paschke's is the engine Mazda would come to own and champion into the 21st century. Thus, the modern Wankel is not quite a Wankel.
Naming concerns aside, Wankel is the most common and successful rotary engine design, and the only one to make it into mass production. Back in the early '60s, NSU and Mazda had a friendly, collaborative competition to sell the first Wankel-powered car as they worked the kinks out of the immature design. NSU was the first to market in 1964, but it destroyed its reputation over the next decade as frequent engine failures sent owners into the shop again and again. Soon it wasn't rare to find an NSU Spider or Ro 80 that'd been through three or more engines.
The problem was the apex seals—thin strips of metal between the spinning rotors' tips and the rotor housings. NSU made them out of three layers, which caused irregular wear that made them grenade. Mazda figured out apex seals by making them out of a single layer, and introduced its Wankel in the 1967 Cosmo sports-luxury car.
In the early 70s, Mazda envisioned an entire lineup of Wankel-powered cars, a dream that was smashed by the 1973 oil crisis. But the rotary became the sole power plant for three generations of sporty Mazda RX-7s from 1978 though 2002, a period that made the Wankel engine both revered and reviled.
Loved and Loathed
Gearheads love the rotary in part because it’s different. Car enthusiasts have always had a soft spot for an engine that, aside from burning gasoline internally, hardly resembles a conventional piston engine. The rotary delivers power linearly all the way to 7,000 or 8,000 RPM, depending on engine specifics, and that flat power band sets it apart from rev-happy piston engines that too often pour on the power at high RPM while feeling gutless at low RPM.
Carmakers also liked the rotary for its smoothness. Rotors spinning around a central axis make for a sweet lack of vibration compared to a piston engine, whose up-and-down piston motion is more jarring. But an unusual engine is an unfamiliar animal, which is why the polarizing Wankel also inspires its share of loathing among car fan and mechanics. It's a simple design – no timing belt, no camshaft, no rocker arms – but unfamiliarity creates mistrust, and the Wankel has quirks that cry for attention.
The rotary burns oil by design, pumping small amounts of motor oil into the combustion chambers to lubricate the rotors, creating a customary stream of blue smoke puffs out the tailpipe when you crank the car. Frankly, it freaks people out—blue exhaust smoke is a distress signal when it comes from a piston engine.
Rotaries also prefer mineral oil to synthetic, and their design means you must top off the oil periodically because the engine is constantly drinking it. Those apex seals don't tend to last long before they need replacing, either. Rebuilding a Wankel at 80,000-100,000 miles is typical, and earlier than most piston engine need such exhaustive work.
Modern drivers are also most sensitive to the rotary’s other disadvantages, poorer emissions and fuel economy due to the engine’s tendency not to completely burn the fuel-air mixture before sending it out the exhaust. For the RX-8, Mazda alleviated these problems by placing the exhaust ports on the sides of the combustion chambers. Fuel emissions have gotten stricter over the years, too. That's part of the reason the RX-8, the last Wankel-powered car, went on sale in 2002 and was phased out in 2012.
Time for a Second Spin
Back to Mazda VP Martijn ten Brink's rumor, that Mazda could use some kind of rotary engine as a range extender for an electric car. It'd make sense. Back in 2012, Mazda leased 100 Demio EV electric cars in Japan, but the car's short 124-mile range was a sore point. So in 2013, Mazda created a prototype that incorporated a rotary range extender to nearly double that range and called it the Mazda2 RE Range Extender (Mazda2 is what the Demio is called outside Japan). The prototype's wheels were driven via an electric motor, and a 0.33-liter 38-horsepower rotary engine would spool up to recharge the electric motor's batteries if they ran low and there was nowhere nearby to recharge.
Because the rotary engine couldn't power the wheels, the Mazda2 RE wasn't a hybrid like the Volt or Prius. The Wankel was more of an onboard generator that added to the car's range. The same compactness and light weight that made the Wankel a great motor for a sports car like the RX-7 also make it ideal as a range-extending generator on a car, especially one that already has electric motors and batteries competing for space and can’t afford to take on too much weight. But the range extender concept didn't make it into production, and Mazda didn't hasn't sold any electric vehicles since those 100 Demio EVs.
Still, the rotary built its reputation mainly as a sports car motor, not as a generator lugged around by electric motors. As long as rumors of a rotary revival endure, car lovers will dream of this fussy, quirky engine once again powering the wheels of a torquey, rev-happy ride.