It's architecture enables it to make huge amounts of power in a tiny, lightweight package with almost no vibration. On the other hand they weren't particularly efficient and had durability issues early on.
Despite the pitfalls, Mazda has stuck by Felix Wankel's concept since the 1960s. While the last current rotary-powered machine, the Mazda RX-8 will soon cease production, the Wankel has in recent years found favor as a potential range extender in series hybrid vehicles like the +Chevrolet Volt. Audi built a fleet of A1 e-trons with tiny rotaries running a generator and several other companies have experimented with the layout.
For a decade Mazda has also been testing rotaries running on hydrogen. The rotary layout works particularly well with the rapid combustion characteristics of hydrogen. Now Mazda is apparently looking at using a hydrogen-fueled rotary as a range extender. Unlike the Volt, a hydrogen rotary ER-EV would actually be a full time zero-emissions vehicle since burning H2 produces water and no CO2.
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Green Car Congress: Mazda to use hydrogen rotary engine for EV range extender
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I love the rotary. And it does make sense to use it with hydrogen. And they have been testing it for quite a while. However: You need a range extender because people want to drive further than the limited battery range currently 30-150 miles. You can fill up your tank at any one of tens of thousands of gas stations and drive as long as you wish… But if your range extender needs H2, whose filling stations in the entire country you can count on your fingers and toes … I don't see as how that helps much…
Not only that, unless you store your H2 at something like 900psi (which would be extremely dangerous), you won't get very much range for a tank anyway.
Actually most automakers are using 700 psi storage (although Honda has stuck with 350 psi for the FCX Clarity) for hydrogen in fuel cell vehicles. These tanks have gone through all of the crash testing required of other vehicles and been certified for road use.
A small single rotor Wankel optimized for steady-state operation (as used for a range extender) and hydrogen fuel could probably get you 200-300 miles of range on a 3-4 kg of hydrogen.