An American company has developed an innovative type of rotary piston engine, and it boasts extremely light weight and could be perfect for a range of applications.

The engine is a small capacity 250cc prototype, and unlike a conventional (if you can call them that) rotary engine, this unit features conrods. It’s only a single-cylinder design, although the reciprocating motion of the piston is transferred to the crank via dual conrods. Explaining the engineering behind the engine in more detail, Avadi describes the engine as a “single-cylinder with a self-centering rotating piston connected to a pair of counter-rotating, self-balancing connecting rods. The connecting rods’ scissor-like action efficiently translates the piston’s vertical stroke into rotational movement without a traditional crankshaft-based powertrain, placing minimal side pressure on the cylinder wall—meaning less friction, heat and wear.”

As piston motion occurs, the two rods move in a scissor-like fashion and each rod is independently connected to a pinion gear at the bottom-end and those two gears rotate on a fixed ring gear attached to the crankcase. The ring gear is the only primary mechanical component that does not rotate. The piston, the cylinder, and the connecting rods all rotate. Those two connecting rods and their corresponding pinion gears reside in what Avadi calls a ‘halfshaft’, which is essentially the housing where up-and-down piston motion is translated to rotational motion. It’s fixed to the output shaft that extends from the back of the engine and is connected to the final drive component being powered.

Innovative internals aside, quite possibly the biggest bonus of the engine’s design comes from its compact dimensions and very light weight. The entire engine tips the scales at just 10.7kg and even in the early stages of prototype production it’s making 15bhp at 3,700rpm and 22.3lb ft at 3,500rpm. It’s this low weight and compact design that makes the Avadi an interesting prospect in the power sports, ATV and motorcycle sectors. It’s also nice to see that, despite an ongoing (and in some cases forced) march towards electrification, there are still some people innovating in the internal combustion engine sector.