Close-up of rotary engine cutaway

How Does a Rotary Engine Work?

If you know a bit about cars, you probably have a general idea of how a conventional combustion engine works. But, did you know that throughout the years other engine designs have been imagined and manufactured with varying degrees of success? The rotary engine is one unique example that still has relevance today, yet remains an obscurity. So, how does a rotary engine work, and is there room for this design in the future of the automotive industry?

How Does a Rotary Engine Work?

First off, it’s important to understand that the term “rotary engine” can be used to describe different types of engines that involve rotary movement. In the automotive world, the term is mostly synonymous with the Wankel engine.

Chances are, the car you drive has a conventional combustion engine, in which a specific number of cylinders move up and down creating intake, compression, combustion and exhaust strokes. These phases ultimately pull air and fuel into the combustion chamber, compress it, ignite it and expend what’s left as the pistons reciprocate in a linear path.

Rotary engines use some of the same basic concepts, but with a different spin. Did you ever make a Spirograph as a kid? It’s a little like that. Here’s how it works:

  1. You start with a triangular part that rotates in an oblong space. The triangle acts like a piston, and the spaces created as it moves act as combustion chambers.
  2. Since the space is oval, the triangle creates areas with more and less space as it turns, causing a vacuum to pull in air and fuel.
  3. It then compresses the air and fuel and ignites it before expelling the exhaust.
  4. This cycle continues on each full turn of the triangle.How Does a Rotary Engine Work?

What Goes Around…

Rotary engines do have a few benefits. As one of my fellow mechanics noted, “They are cool,” which isn’t something I can argue with. In addition to their being unique and clever, they’re also simpler than conventional engines with fewer parts. This means they have less opportunity for broken parts, and are lighter overall. The rotary motion is also a smoother operation that doesn’t fight itself the way reciprocation does, and produces impressive horsepower as a result.

However, these benefits are offset by the fact that rotary engines require more fuel and burn it less efficiently, so mileage suffers and emissions can get ugly. They also consume more oil, which tends to leak. Furthermore, they’re rare, which means getting parts and finding a knowledgeable mechanic can get pricey.

Rotary Club

On the whole, these design limitations have outweighed the potential benefits and kept most manufacturers from using them in vehicles. Except for Mazda, who used and then scrapped a rotary engine from the 1970s to 2012, but has teased that it may be brought back in a new electric vehicle as a range extender. Time will tell if they’ve innovated the design enough to make it a competitive and viable technology.

Check out all the Mazda engines, parts and gaskets available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on engines, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

about author

Blair Lampe

Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter.  In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.

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