LiquidPiston's X Mini engine isn't new, but it is endlessly fascinating. It's a rotary, but it doesn't have much in common with the best-known rotary, the Wankel engine popularized by Mazda. The LiquidPiston engine uses an oval rotor that spins eccentrically in a triangular housing. A Wankel, by contrast, uses a triangular rotor spinning in an oval housing.

To show off the engine again (and keep interest on simmer), LiquidPiston shoved one into a go-kart to help demonstrate the power density. It's rated at three horsepower at 10,000 rpm and weighs just four pounds, which is significantly lighter than the 40-pound horizontal reciprocating piston engine it's replacing in the go-kart.

It'd just be nice, and more impressive, if LiquidPiston was comfortable showing the kart moving at something more than just off-idle speed. The video simply doesn't demonstrate much except that the engine runs, at what seems to be steady throttle inputs.

The DARPA-funded company is hoping the tiny, light engine can be used in range-extender applications, as well as household power tools like lawnmowers and so forth. The range extender idea also parallels Mazda's thinking with the circa-2014 Mazda2 RE Range Extender, which featured a 330-cc single-rotor Wankel that was only used to recharge batteries for the EV. It's too early to tell if LiquidPiston's engine will live up to its promise, and while this video does show it powering a vehicle it's not a terribly impressive demonstration. If the company can overcome some of the inherent weaknesses of the Wankel and produce reliable, power-dense engines at extremely low weight in range-extender applications, it would be very impressive. We'll keep following LiquidPiston and let you know how the X Mini develops.

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