What is a Rotary Engine?

When you hear the term “rotary engine,” think of an internal combustion engine like the engine in most cars, but with a unique twist.

Your car (which we’re assuming is not completely electric) most likely uses a piston engine. Integral to the piston engine is the cylinder, where the intake, compression, combustion and exhaust processes happen. Intake involves taking in the fuel, compression involves mixing the fuel with the appropriate amount of air, combustion involves burning the air and exhaust involves getting rid of the unnecessary byproducts of the chemical reaction responsible for making your car move.

rotary engine2In a rotary engine, all these four processes still occur, but not within one cylindrical housing. Instead, each process occurs in its own part of the housing. It’s kind of like having four cylinders, each of which is dedicated to one of the four jobs. The piston then moves continuously from one cylinder to the next.

The rotary engine design was thought up by engineer Dr. Felix Wankel, prompting it to be called a Wankel engine or Wankel rotary engine.

Ok so back to basics: Much like a piston engine, Wankel or rotary engines need to create pressure by combining air and fuel and the burning that combination. Piston engines contain that pressure in the cylinder and then forces pistons to move back and forth. The pistons are connected to rods and crankshafts which then turn the piston motion into rotational motion that forces the wheels to roll.

In a rotary motion, the pressure of combustion is contained in a chamber that is sealed by one face of a triangular rotor, which takes the place of the pistons. The rotor is in motion in such a way that each of its three peaks are always in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. This expansion and contraction creates the vacuum that allows for air and fuel to enter the engine, the compression that allows for the appropriate amount of pressure to build up to the point of powering the car, and the expulsion that leads to the exhaust.

mazda rotary engineThe Maza RX-8 has a rotary engine and Mazda in general has been a pioneer in the production of rotary engines for consumer markets. The RX-7 hit the market back in 1978 and became likely the most widely sold rotary-engine car to date. Even before the RX-7, there had been the production of successful rotary-engine cars, trucks and busses since 1967.

Now the newer Mazda RX-8 (released circa 20011) has an award winning rotary engine called the RENESIS that won International Engine of the Year. It had a naturally aspirated, two-rotor engine that produced 250 horsepower, making it truly a one-of-a-kind vehicle.

So who knows, maybe rotary engines will be the way of the future. It’s worth considering that the Mazda RX-8 gets about 16 mpg in the city and 23 in the highway, so if the rotary engine doesn’t offer fuel efficiency there may not be a place for it in our future.


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