[InitialBP]

Mazda hasn't sold a production car with a rotary engine in a while, I believe since the RX-8 went out of production. Due to the nature of rotary engines they inherently have worse emissions (more like a 2-stroke than a 4-stroke) and while people have been hoping for another production rotary from Mazda it's unclear if they will build another one or not.

[elihu]

I'm kind of hoping the LiquidPiston design works out, since in theory it should fix a lot of the fuel economy and emissions issues (combustion chamber is closer to the ideal round shape), and maybe even be lower maintenance (apex seals move to the non-moving part of the engine, where they can be lubricated more easily). It's not owned by Mazda, though, so even if it works it's anyone's guess if Mazda would even be able or want to license it. Or if gas engines in general will be effectively obsolete by the time the technology matures.

I love the idea of rotary engines, but environmentally they're a disaster (at least in their current form), and even if the problems are fixed they'll still not be significantly cleaner than any other gas engine.

(I'm currently working on trying to covert an RX-8 to electric.)

[iagovar]

There's a development here in Spain that seems pretty interesting for range-extenders, by InnEngine. They seem to be in the prototype phase, it's also a pretty interesting design.