Even people who aren’t gearheads tend to be at least provisionally aware that the Mazda RX-7 and RX-8 used a very different sort of engine than pretty much every other car. While the rest of the auto world had long since settled on a piston-and-cylinder design, the RX cars used something else: the Rotary or Wankel engine.
I knew this, too, and even had a vague idea how it actually worked — just a lot MORE vague than my understanding of conventional cylinder engines. However, if you’re curious, this excellent video runs down exactly how rotaries work by walking you through the actual parts involved (in this case, from a 1985 Rx-7). It’s pretty awesome.
You may have also noticed that, well, not only were the Mazda RX cars the only cars to use these things, but not even Mazda makes them anymore. Why is that? Well, fortunately, the same guy also made a video about why the rotary engine is dead. Again, I knew some of this, but not the underlying causes for them. Great, very accessible work here.
The tl;dr here, though, is kind of simple: because of the way the engine works, there’s an irregularly shaped combustion chamber, and that leads to inefficient combustion. A rotary is absolutely going to end up emitting unburnt fuel, which is terrible for fuel economy and terrible for emissions. The problem is exasperated by the fact that combustion only happens on one side of the chamber, which leads to enormous temperature differentials, which leads to problems in sealing, which means inefficient combustion, which means bad emissions and bad fuel economy again.
But watch the videos. He explains is really well.