On this episode of Engineering Explained, Jason Fenske explains how the wankel rotary engine works. Using a 3D-printed 1/3 scale model of a 13B-REW engine from an FD Mazda RX-7, we get a closer look at how rotaries function. The wankel rotary engine was first used by Mazda when the company debuted the Cosmo back in 1967. It was later used in pickup trucks, but didn’t gain popularity until it found its way into the first generation RX-7 in 1978. From there, rotary engines and the RX-7 name became synonymous until the final production of the RX-8 in 2012.
Gallery: 3D printed Mazda rotary engine
Unlike conventional piston-pumping internal combustion engines, the wankel engine instead contains a rotor inside. Looking at the model of the 13B-REW, you can see inside the rotor housing where all the fun happens. The tortilla crisp-shaped rotor inside is the key to making power and rotates with the help of the eccentric shaft. The shaft and rotors spin together as opposed to a four-stroke engine, which uses reciprocating motion.
During the rotation of the rotor, all three chambers of the combustion process are active: intake stroke, power stroke, and exhaust stroke. With the 13B engine having two rotors, that means six cycles are occurring simultaneously. This combustion process allows the rotary engine to create a lot of power compared to a similar four-stroke engine. Not having to deal with reciprocating mass going up and down, rotary engines can rev up to 9,000 rpm no problem due to the rotational inertia.
Due to the long shape of the combustion chamber, there is often unburnt fuel exiting the exhaust, which isn’t very efficient. By design, rotary engines burn oil to help seal the combustion chamber. This is why most RX-7 owners carry quarts of oil in the boot. Rumours of the Mazda RX-7’s return surface every year, but will it ever really happen? Only time will tell.