What ever happened to the Wankel engine?

At a meeting with fellow community-garden oriented neighbors, we met a really neat gentleman who filled our imaginations with all sorts of interesting things. From a high-tech neighborhood of underground homes in North Texas to rotating watering schedules, we were transfixed. But the really remarkable bit of information was the mystery of the Wankel engine. What ever happened to this engine which promised to make the use of hydrocarbon fuels more efficient over 50 years ago? Why don’t we use it in cars today? “School” today consisted in our efforts to solve the mystery of the Wankel engine.

First we needed to know more about the kind of engines we use today. We reviewed the six types of simple machines to get a sense of context for our mechanics exploration. (Little “Millers”, as Tino calls her, conducted her own exploration of the inclined plane, a simple machine, by running up and down our garage ramp.)

Then, I asked him to create a sheet of paper that explains the four-stroke engine to someone like me- someone who doesn’t know much about mechanics or engineering. His simple description (accompanied by a Max sketch):

Split-second timing is essential for smooth running in a car engine. This is achieved by a car engine’s cams and cranks together. As pistons move up and down, they drive the wheels. But, through a chain link, they also drive the cams. As the cams move, they open and close the valves. They do this in step to the four-stroke cycle.

The process involved in the two-stroke engine is internal combustion. But there is another internal combustion engine that could be used in cars. The Wankel engine, also known as a rotary engine, was envisioned and developed by Felix Wankel. We watched a 2-minute video showing how Wankel engines work. How does internal combustion work differently in the two engines? We found a good answer here:

In a piston engine, the same volume of space (the cylinder) alternately does four different jobs — intake, compression, combustion and exhaust. A rotary engine does these samĀ­e four jobs, but each one happens in its own part of the housing. It’s kind of like having a dedicated cylinder for each of the four jobs, with the piston moving continually from one to the next.

Of course I can’t really “see” this in my mind without a sketch. Thankfully, Max is the consummate sketcher.

Max’s comparison of internal combustion engines.


Fold a sheet of paper in half. Then draw a piston engine on one half and a rotary engine on the other half. For assistance in sketching, you can refer to this piston engine diagram or this rotary engine diagram. Now create a key using crayons or markers. Use yellow to designate “intake”, orange to designate “compression”, purple to designate “combustion”, and green to designate “exhaust”. Draw little dots or shade the corresponding parts of each engine according to this key.