Everything You Need to Know about Rotary Engines

Once considered a highly efficient option, rotary engines were replaced by piston engines almost a decade back. However, we still see variations of the same type of engine in some cars, especially in the hybrid ones. In this blog, we take you through all the details pertaining to the rotary engine history and how certain auto manufacturers are developing a new kind of rotary engine for hybrid vehicles. 

Rotary Engine – What is it?

Rotary engines have been around for a while and were the most commonly used types of engines till the 1920s. A rotary engine was a kind of internal combustion engine that powers all types of vehicles. Not just cars and trucks, rotary engines were also used to power planes and boats.

Rotary engines carried out the task to power up a vehicle similar to a conventional piston engine. That said, the mechanism of the engine was slightly different. 

Here is step by step look into the combustion cycle of a rotary engine:

Intake – Similar to a piston engine, the intake valve draws air into the engine before pumping it in the interior chamber via the engine intake port.

Compression – as for compression, a rotor shaped like a triangle can be found inside the chamber. This chamber makes three gas-tight seals that perform the same functions as pistons in a normal engine. 

Combustion – at the highest level of pressure inside each gas chamber, the fuel-air mix is ignited, making power that is transferred to the drivetrain via the output shaft.

Exhaust – exhaust gasses are emitted out through an exhaust port in the engine housing with a standard tailpipe.

Similar to a standard piston engine, a rotary engine’s temperature is controlled by a cooling system, where the coolant passageways face the outside shell of the combustion housing. The circulation of oil also takes place in similar passages, lubricating the moving parts of the rotor, output shaft and valves.

Components of a Rotary Engine

Below we explain the rotary engine parts in detail to help you understand how it works.

Rotor

The rotor is a component with three sides that are concave. These are designed to give a gas-tight seal when pressed against the side of the housing. An inlet is present on each face of the rotor allowing for more volume of gas inside the housing. This effectively increases the displacement rate of the engine.

The rotor spins on gears attached to a shaft in the centre. When the rotor spins, each side touches the housing in a way that three different combustion pockets are maintained.

Housing

The main structure that holds the rotary engine is the housing. Made with an oval shape, the housing by design maximizes the displacement of the engine while simultaneously enabling the rotor to spin with its edges in constant contact with the inner wall of the housing.

Each gas packet undergoes four steps of the combustion cycle: intake, compression, combustion and exhaust. The fuel injectors and spark plugs are injected through the housing wall directly. Meanwhile, outside channels pass oil and coolant through the system, maintaining its temperature.  

Output Shaft

The purpose of the output shaft is to transfer energy generated by compression and combustion to the drivetrain, powering the wheels. Round lobes are mounted on the shaft. These lobes come in contact with the rotor, enabling the shaft to spin.

Are There Any Benefits to Rotary Engines in Cars?

Rotary engines are a thing of the past century and were replaced by piston engines because they were not all that economical owing to lower thermodynamic efficiency due to the size of the combustion chamber and low compression ratio.

That said, a rotary engine had benefits to offer when compared to a piston engine. Rotary engine advantages include:  

Smooth and quiet – the movement of a rotary engine is smoother than the movement of pistons. This leads to a quieter and more refined feel on the road. Moreover, the counterbalances on the outside of the rotary housing are designed in a way that help dampen vibration and make up for smooth performance.

Fewer moving parts – when compared with conventional engines, rotary engines have fewer moving parts. This makes up for more reliability, and it also means affordable maintenance and upkeep in the long term.

Slower internal movement – the internal movement to power the car with piston engines has to be fast and intense. As a result, the internal parts are under a lot of pressure. Without regular maintenance, this pressure on internal parts may lead to premature degradation. 

On the other hand, rotary engines are slower, with a single movement in one direction. As a result, their parts are under less pressure while the long-term reliability improves.

Which Cars Have a Rotary Engine?

At present, just a handful of modern cars work with a rotary engine. Because a rotary engine is less economical and comes with a higher manufacturing cost, car makers generally stick with piston-powered engines. 

In the 1960s, Japanese car brand Mazda started experimenting with rotary-engined cars. The carmaker got its first success in 1967 with the Cosmo Coupé – a car renowned for its ultra-smooth and efficient rotary engine. Since then, the carmaker developed a few rotary-powered models, including the RX-7, RX-8 and a rotary version of the Mazda 2, which was launched in 2013.

After several years, Mazda has announced its plans to build a whole new rotary engine. They plan on using the engine along with an electric motor as a range extender for hybrid-electric vehicles. According to Mazda, a rotary unit is a perfect match for a hybrid car, delivering a reliable performance that is expected to be more refined than a standard piston engine.

Moreover, rotary engines are known to work well with next-generation fuels, such as hydrogen. The longer duration for air intake by a rotary engine is very efficient at mixing air and fuel. 

This means that higher quantities of hydrogen can be injected for the correct fuel-air mix, enhancing efficiency and performance. Both hybrid and electric vehicles promise lower emissions. That said, automakers are looking to utilize rotary engines in hybrid vehicles. For the 21^st century, the rotary engine is expected to have a new look.

That is all about rotary engines. If you want an in-depth analysis of rotary engines and piston engines, read this comparison of rotary vs piston engines.

Stay tuned to your favourite car blog for more on various car parts.