Vankel's Rotary engines: All you need to know

Have you ever wanted to know more about these strange Wankel rotary engines?Here's our complete guide to one of the most controversial engines ever created.

Although the Wankel rotary engine is over 60 years old, its concept is still often misunderstood. If you've spent any time in the automotive internet space, you know that rotary engines have a reputation for being unreliable. However, as we will now show, this reputation is not entirely fair. Don't get us wrong though, there are other downsides to be aware of. But before we get to that, let's get you up to speed on what a Wankel rotary engine is...

Content:

• How does a Wankel rotary engine work?
• History of Wankel rotary engines
• Mazda's association with Wankel rotary engines
• Advantages of Wankel rotary engines
• Disadvantages of Wankel rotary engines
• Economy and ecology

How does a Wankel rotary engine work?

Admission

As the name suggests, Wankel rotary engines use curved triangular rotors instead of pistons. They are located vertically in an oval-shaped housing and rotate around the output shaft. As the rotor rotates, it creates oscillating air pockets between itself and the housing walls at various locations around the inner perimeter of the housing. The vacuum in these pockets draws the air and fuel mixture into the housing. Think of it as the equivalent of the intake stroke of a piston engine.

Burning

After that, the second "top" of the triangular rotor closes the path of the air-fuel mixture as it passes the intake port. As the rotor continues to rotate, the space between it and the housing wall decreases. As a result, the air-fuel mixture is pressed against the wall of the opposite side of the housing. There is a certain part of the wall where the compression will be maximum during the rotation cycle of the rotor, and there you will find a pair of spark plugs. They ignite a highly compressed mixture of air and fuel, and voila, combustion occurs.

Exhaust

A mini-explosion from the combustion sets the rotor in motion, continuing its cycle. As the rotor continues to rotate around the housing, its first peak will soon meet the exhaust port. As the peak passes the hole, it opens a channel for the exhaust gases to escape. And here it is, a complete combustion cycle of a rotary engine.

In fact, the designers increased the size of the rotor and its body in such a way that while the exhaust process is taking place, the third tip of the rotor will already be near the intake opening, drawing in another portion of the air-fuel mixture. And so the cycle continues, driving the rotor, which in turn drives the "eccentric output shaft" (essentially a crankshaft), which transmits the engine's power through the transmission to the wheels.

History of Wankel rotary engines

If you ask enthusiasts which cars they most associate rotary engines with, they will most likely say Mazda's RX sports cars. However, the Japanese brand was not the first to use rotary technology in its production cars. This honor was awarded to the now defunct German brand NSU.

German origin

In the 1950s, an engineer named Felix Wankel worked at NSU, and as the name suggests, he was the first to come up with the idea of ​​the Wankel rotary engine. Due to the complexity of the development process, the first car with a rotary engine appeared only in 1964:NSU Spider. This two-door roadster was soon followed by the NSU Ro80 sedan, and on first impressions the Ro80 won many fans. Moreover, in 1968 it even became the European car of the year.

However, as is often the case with innovative technologies, the design of early rotary engines soon began to show flaws. This resulted in a rather short life for the Ro80, effectively leading to the demise of the NSU altogether.

It would not be surprising if the history of the rotary engine ended there. However, despite the demise of NSU, Mazda decided to adopt the technology and invest in Wankel and his ideas.

Mazda's association with Wankel rotary engines

The rest of this story, I'm sure, will be familiar to many of you. It's a venture that ultimately led to Mazda's RX line of sports cars, most famously the RX-7 and RX-8. The RX-7, in particular, is a true automotive icon. On the track, the first generation won the grueling 24 Hours of Le Mans (quite a feat for a car with a reputation for being unreliable), and later models became icons of modification and tuning.

These RX-7s and RX-8s use a twin-rotor design known to enthusiasts as the "13B" engine. The two rotors are 180 degrees apart, meaning they complement each other in the combustion cycle. In other words, as soon as the peak of one rotor enters and passes the combustion stage, the second rotor is slightly behind, ready to take on the load as the first rotor transitions to exhaust.

In rare cases, 3- and 4-rotor Wankel engines can also be purchased for additional power. A larger number of rotors means less time between the combustion stages of each rotor, which ensures a smooth and powerful supply of energy. Four-rotor engines in the past were usually installed on racing cars, in particular, onMazda 787B, which won an absolute victory in Le Mans. However, these days we are starting to see extreme tuner builds with these almost mythical "20B" four-rotor engines.

Advantages of Wankel rotary engines

There are many reasons beyond the simple novelty factor why some people like these rotary engines. To begin with, one rotor effectively performs the work of three pistons: intake, combustion and exhaust occur almost simultaneously. In practice, this means more power from a relatively small and light engine.

Another distinctive feature of Wankel rotary engines is that their rotors move in only one direction. Therefore, compared to the jerky reciprocating motion of piston engines, healthy rotary cars will have a much smoother start-up and power transfer while driving. Moreover, the absence of reciprocating masses means that rotary engines can develop very high revolutions without much problem.

Disadvantages of Wankel rotary engines

Of course, we're not going to pretend that rotary engines are perfect. After all, there is a reason they are so rare.

Mechanical defects

In the early days of NSU, when the Ro80s were starting to "die like flies", Wankel realized that the vacuum chambers created during each part of the combustion cycle could lose compression due to poor rotor sealing. The addition of apex seals, of course, greatly helped to solve this problem, but Wankel had to find a way out of the heating problem.

If the intake, combustion and exhaust processes take place in the same housing, the result is that the parts of the rotor and the walls of the housing reach very different temperatures. And as your high school physics class will tell you, metals can change shape slightly at different temperatures. Therefore, in a scenario that relies on a perfect seal between the rotor and the housing walls, this can be problematic. To alleviate this problem, the Wankel company introduced cooling "scars" along the perimeter of the body walls, but in the end this problem cannot be solved perfectly. Physics simply won't allow it.

Moreover, during the combustion cycle, a huge amount of friction occurs as the rotor passes the casing walls. Therefore, rotary engines drink motor oil like alcoholics at Oktoberfest, which means they require much more maintenance compared to conventional engines.cars with a piston engine. Perhaps this is where the main argument about unreliability comes from. Among RX owners, there were many who did not know about the tougher requirements of these cars or were indifferent to them. If they are neglected, it won't take long for your rotor to fail.

Economy and ecology

That's not all that's wrong with Wankel rotary engines. Compared to piston engines, they do not have better thermal efficiency, due to the peculiar shape of the space in which combustion takes place. As a result, unburnt fuel often enters the exhaust system, resulting in flashbacks and suboptimal fuel economy.

Now we turn to environmental problems. More oil burned means more tailpipe emissions, which is bad news for the health of our planet. In fact, environmental regulations are a big part of the reason the Mazda RX-8 was discontinued in the early 2010s. In the end, Mazda simply couldn't find a way to bring the rotary engine's exhaust emissions up to Euro 5 standards.

Conclusion

So, the Wankel rotary engine has a lot of advantages in terms of performance. Higher specific power, smooth torque delivery and relative weightlessness - all these characteristics will appeal to car enthusiasts like you and me.

But the Internet is not entirely wrong. These engines really do have an Achilles heel, and in order for them to last as long as possible, you'll need to take their maintenance more seriously than any other vehicle. However, for some people, that's a price worth paying for the pleasure you'll get behind the wheel.

Plus, even though the RX-8 ended its existence in 2012, it looks like rotary powertrains still have a future despite their decade-long hiatus. Emissions laws will block any future full rotary models, but Mazda has just announced its intentions to use rotary technology as a hybrid EV range extender. So who knows, maybe there will be a place in our electrified future for a revived RX sports car...