Internal combustion engines have been powering cars since the mid-1800s. The inherent reliability, efficiency, and power are what made them the standard for car manufacturers. The automotive industry has had its fair share of fuel-chugging machines with different designs over the years, and while some were iconic, others have become a bit controversial.
Speaking of controversy, let’s discuss one well-respected engine design that was heavily criticized due to its negative impact on the environment—the rotary engine.
While Mazda usually comes to mind when the name “rotary engine” is mentioned, there are a number of other carmakers that have tried to use the design, such as Chevrolet in its Aerovette and Vega models. However, only Mazda was able to find a good use for the distinct engine design for years.
What is a rotary engine and when was it invented?
The rotary engine, which is also referred to as a Wankel engine, was invented by German mechanical engineer Felix Wankel in 1954. Ironically and contrary to popular belief, the rotary engines commonly found on cars weren’t actually derivatives of Wankel’s “Drehkolben Maschine” (DKM) model.
Wankel began working on the rotary engine in 1951, but it was seen as unprofitable by most. Hanns Dieter Paschke improved and reworked the DKM, calling his version the Kreiskolbenmotor (KKM). Paschke’s KKM eventually became the basis of the modern Wankel rotary engine.
Unlike traditional combustion engines that use pistons, rotary engines utilize rotors that spin inside an oval housing. The three processes known as intake, compression, and ignition happen almost simultaneously inside a rotary engine.
A bit of trivia: Skoda was the first carmaker that toyed around with the rotary engine. The Czech automaker experimented with single-rotor rotary engine-powered 1000 MB models in the early ‘60s. Unfortunately, these never made it to market, as most of the units were scrapped after the test. NSU Motorenwerke AG went on to make its own version, which was fitted under the hood of the Wankel Spider model shortly after.
How does a rotary engine work?
As stated earlier, there are three main parts of the rotary engine: the housing, the rotor, and the eccentric shaft.
Inside the oval housing, a rounded triangular rotor spins around a shaft. This housing is composed of an inlet and an outlet port. The inlet is where the fuel and air mixture enters the chamber where the rotor’s rotation helps suck the mixture in.
As the rotor spins, the area where the mixture is contained gets smaller, compressing the fuel and air in the process. The part where the fuel gets compressed is where you’ll find the spark plug, which ignites the fuel as it goes through the process.
The combusted fuel, now mostly gas, leaves the chamber through the exhaust port. The rotor spins so fast that the inner sidewall of the housing becomes prone to friction damage. This problem, however, was solved by attaching apex seals on each tip of the rotor, while an oil injector sprays oil inside the chamber to lubricate the wall.
How Mazda fell into the rotary engine realm
Mazda first used the rotary engine in the Cosmo, which was later dubbed as the Japanese carmaker’s halo car. The success of the Cosmo, which was the first mass-produced car with a rotary engine, further drove Mazda’s interest towards the unconventional engine design.
The second-generation Cosmo was sold internationally as the RX-5 coupe in 1975 and came with 1.2 and 1.8-liter rotary engine options. Mazda then discontinued the RX-5 in favor of the RX-7 sports car, which is where the rotary engine buzz got louder.
Why people fell in love with the Mazda rotary engine
Even though Mazda wasn’t the first to use the rotary engine, it managed to scale its sales up. People saw the potential of the new engine design and favored it quickly. In its golden days, the Mazda RX-7 rotary engine was admired due to a number of reasons:
1. It’s extremely compact.
The first thing that caught the interest of buyers was its compact size. A rotary engine is only a third of the size of its piston engine equivalent, which was a crucial trait particularly in Japan, where owners of cars with displacements under one liter paid lower taxes.
Because of this, Mazda capitalized on rotary engines and even introduced an RV van named Parkway.
2. It’s lightweight.
Since rotary engines are small, it leaves more room in the engine bay to fit more components. They are also relatively lightweight, leading to a better power-to-weight ratio. This is one of the many traits that helped Mazda go as far as being the first automaker to win Le Mans with a rotary engine.
3. It boasts unparalleled simplicity.
A piston engine has roughly 40 moving parts inside, which means there is a higher chance of failure due to wear and tear. In contrast, a rotary engine only has two moving parts, namely the rotor and eccentric shaft.
4. It’s capable of higher revolutions per minute (RPM).
Since there is no reciprocating mass due to a piston’s movement, rotary engines operate way smoother than its piston-engine counterparts. This aspect also helps the engine achieve higher RPM compared to piston engines.
5. It has a distinct aggressive sound even without forced induction devices.
Sound is debatable, especially when it’s from a controversial engine that has been the subject of harsh criticisms. If you’re a sucker for V10s, then you probably won’t like the sound of the rotary.
It may not be the best-sounding engine to have ever roamed the streets, but it’s distinct and has character.
Why do other people hate the Wankel engine?
There’s a large chunk of the population that hate the rotary engine, and they have all the right to do so. Despite all the good stuff that rotary engines had to offer, there are the notable disadvantages that eventually caused its demise:
1. It threatens the environment with horrific emissions.
The number one enemy of the rotary engine was the poor emission rating that no one succeeded in solving. Even Mazda had to abandon its dream engine to escape the horrendous consequences of continuing with this engine.
The reason behind its unpleasant emission rating lies within its design. Rotary engines are notorious for spewing out unburned fuel out of the exhaust. Those flame-spitting stunts you see on videos and car shows contain hydrocarbons that are a threat to your well-being and to the environment.
2. It has the worst fuel economy.
Due to spitting out unburned fuel, Wankel engines had the worst fuel economy rating—an issue that no one was able to resolve (not even Mazda). A rotary engine with a smaller displacement could rate far worse than a piston engine with a larger displacement.
This was a problem that Americans didn’t want to face, especially when oil prices were high.
One factor that made the rotary engine unappealing is the mere fact that it burns more fuel during combustion. To lubricate the rotor, fuel is injected directly inside the chamber, which gets burned along with the fuel and air mixture during the ignition phase.
Aside from adding up to the bad emissions, burning oil means you have to top up more frequently than in piston engines.
3. Ever heard of blown apex seals?
Apex seals are tiny strips of metal that slide into the tip of the rotor. This acts as a scraper of the fuel from the wall of the chamber as the rotor spins. Due to rapid changes in temperature inside a Wankel engine, apex seals tend to expand and contract, causing it to blow and fail.
A blown apex seal won’t be able to scrape all the fuel residue on the wall. This leads to inefficient power output as some of the fuel is left unburned. Also, a blown apex seal causes the engine to lose compression ratio, leading to misfiring, rough idling, power reduction, and difficulty starting the engine in cold weather.
Mazda rotary engine’s new promise
If you follow automotive news, you probably have come across reports that Mazda is currently developing a new Wankel engine. There was a time when the Japanese automaker hinted at a rotary engine comeback, claiming that it would be resurrected under the hood of the RX-9—the successor to the RX-8. However, it was found out that the rotary engine everyone initially expected was simply a range extender for the hybrid RX-9.
The Mazda RX-8 rotary engine was the last of Mazda’s attempts to market the Wankel engine. It was controversial enough to cause mixed emotions for RX line-up followers, rotary engine worshippers, and skeptics.
The RX-8, the last Mazda model to bear the rotary engine, was discontinued in 2012 due to poor sales and reliability issues. However, the Japanese carmaker continued experimenting with the rotary engine in some of its concept vehicles after the RX-8.
Will we see a standalone rotary engine in newer Mazda offerings? Perhaps. While the carmaker admits to developing a new and improved rotary engine, whether or not we’ll see one under the hood of their upcoming models remains to be seen—so keep your ears to the ground!