Generally it is an engine that does not have reciprocating pistons, but instead has rotors that look like big triangles with seals at the apexes. The rotors rotate in the engine along a sort of oval barrel on a eccentric drive shaft in such a way that the 3 faces of the rotor make an expanding and collapsing chamber with intake and exhaust ports. If you search youtube you will find some 3d models that show you how it works. There are other rotary engines that operate on different but similar principles too..

You could argue that any engine not driven by pistons going up and own in cylinders is a rotary engine (e.g. a gas turbine engine or a radial engine as used in some aircraft) but the name is usually used for wankel engines in which the cylinders are replaced by an irregularly shaped chamber and the job of pistons and of the 'induction/compression/ignition/exhaust cycle is done by a three pointed rotor that moves within the chamber.

In the UK, such rotary engines were first used in the NSU Ro80 car but it proved a disaster, most engines being replaced with conventional Ford engines. Mazda perfected the rotary engine and used/use it successfully in a a few models.

I am sure you are referring to a Wankel rotary engine as used in Mazda automobiles. It is a non reciprocating engine, instead of pistons in cylinders driving a crank, it uses a rotor, and the combustion occurs in spaces not cylinders. Due to the non reciprocating design they can develop very high RPM. They give large horsepower for their size, but they use a similar amount of fuel as a piston engine of similar HP rating. They were quite popular in Can Am racing when that was a popular sport, Can Am had no HP limit, so combining 3 Wankel engines together resulted in 1000-1200 hp beast engines no larger than a big block V-8 http://en.wikipedia.org/wiki/Wankel_engi...

Other rotary engines were primarily used in aviation, the cylinders are arranged in a circle fashion around the crankshaft, in some cases the crank was stationary and the cylinders rotated, some the crank rotated.

No. Although wankel and radial engines might be thought to be rotary, the correct meaning is that the crankshaft stays still and the cylinders rotate around it.

http://en.m.wikipedia.org/wiki/Rotary_en...

Go on-line and see how a Wankel Engine operates.

Its also known as a wankel engine and Im not kidding.

http://en.wikipedia.org/wiki/Rotary_engi...