Rotary engines were invented by Felix Wankel which is why they are also known as Wankel rotary. This new internal combustion engine was patented in 1929 and it was first of its kind because it didn’t require a piston to work. But then World War 2 happened and the development of the engine was stopped. Once the war was over, the development was kick-started again at NSU which was a German manufacturer that later become Audi.
It was the 1960’s when Mazda and NSU came together to further develop and work on the Rotary engine. The first car to be sold with a Rotary engine was the NSU Spider but they weren’t able to capture the market because of the reliability issues. Even the Chevrolet tried their hands on the Rotary engines but they weren’t able to pull it off. It was the Mazda that was successful with its Rotary engines specifically used in their RX model range. They were able to do this because they took their own sweet time to correct the problems that the other manufacturers faced. There are many advantages of using a Rotary engine instead of a piston one.
Advantages of Rotary engines
The rotary engine has lesser moving parts such as there is no need for camshafts, pistons, and connecting rods. The engine moves in a circular motion which makes for a smoother movement and refined engine.
If you are an automotive enthusiast then you know you can get goosebumps with engines that rev high. Rotary engines are high revving because they do not have a reciprocating force, there is just rotational mass which helps the engine to rev higher. For instance, the Mazda RX-8 revved to a screaming 9,000rpm.
A rotary engine is a much more compact in size when compared to a traditional piston engine. This means that the manufactures can tightly package the internals of the car and the engine weighs less which means the weight of the car will also be less.
High power output
A full rotation of the engine needs three turns of crankshaft due to which the rotary engines produce more power when compared to a similar displacement engine. For instance, the Mazda RX-8 produced 232bhp from a tiny 1.3-liter engine.
Even after having certain advantages, the rotary engines died. No one in the automotive industry is using a rotary engine nowadays. The last car that sold with a rotary engine was the Mazda RX-8 which too was discontinued way back in 2011. So, why the Rotary engines died?
Poor fuel economy
The Rotary engines have a low compression ratio which often leads to not burning the fuel completely. Because of this, the unburned fuel travels to the exhausts, and the mileage of the vehicle drops. Even after using two spark plugs, the manufacturers were not able to achieve complete combustion and the unburnt fuel economy also leads to low thermal efficiency.
The unburned fuel travels through the exhausts and may produce flames which we agree would look very cool. But, because of this, it makes it very difficult for the engine to pass the emission regulations.
One of the biggest challenges with the rotary engine was how to keep it sealed. The combustion occurs only on one side of the engine due to which the temperature of the combustion chamber is significantly higher than the other. Because of this thermal expansion occurs which means that the metal parts can increase or decrease in size which can mess up the rotor seals.
As we learnt that creating a perfect seal was very difficult with the Wankel engines. To overcome this, Mazda came up with a way of inserting oil into the engine to help maintain the longevity of the apex seals. This further increases the exhaust emissions because some oil is burnt to keep ensure that the engine is sealed and lubricated. This requires the owner to add oil periodically.
These were the major drawbacks why the manufacturer had to kill the rotary engine in the first place. Even after being so many drawbacks, there are still some true enthusiasts who still love the rotary engines for its screaming soundtrack and linear power delivery. We can only hope that some manufacturers sometime in the future revive the beloved rotary engines.