Big engines like the 707-horsepower monster Dodge put in the Challenger Hellcat or Volvo's little four-cylinder that makes 425 ponies get all the attention these days. But there are millions of tiny engines doing tiny things (think garden trimmers, leaf blowers, that sort of thing) that we never give much thought to. But just as there are engineers pondering how to make big engines more powerful, so too are there engineers pondering how to make tiny engines more powerful.

Some of those engineers work at the engine development firm LiquidPiston, which has created a 70cc pistonless rotary engine that it expects to produce five horsepower at an astounding 15,000 RPM—in a package 30 percent smaller than a similar piston engines. Now, five horsepower doesn't sound like a lot, but it's more than adequate for the applications such an engine might be used in. And further refinement of the prototype could, of course, bring more power.

What's more interesting is how those five ponies are produced.

LiquidPiston calls the new engine the X Mini. It can run on diesel fuel or spark-fired gasoline like the engine in your car. Because so many potential applications are in the lawn care and landscaping biz, the current design runs on a mix of gasoline and oil for lubrication.

The engine is similar to the Wankel engine Mazda used for years in the RX-series sports car. It has just two moving parts: a rotor and a shaft to transfer power from the engine. Minimal moving parts means the engine is smaller, lighter, more reliable and quieter than a conventional piston-fired engine. It's also smoother, which, if you've ever used a weed whacker or leaf blower, you'll consider a big plus.

So what's a pistonless rotary engine, you ask? In a conventional four-stroke reciprocating piston engine, the piston moves within a cylinder. Air and fuel are drawn in with a downstroke and compressed in an upstroke. The mixture is detonated as the piston reaches the top of the cylinder; the explosion forces the piston down, creating power. Exhaust gasses are expelled on the following upstroke, and the process begins anew.

A Wankel pistonless rotary engine has a rotor that looks like a rounded triangle, a shape called an epitrochoid. It rotates in an eccentric orbit within an oval chamber; each rotation results in three power "strokes." The big advantage of a pistonless rotary engine is its high power to weight ratio, reduced weight, and simplicity. LiquidPiston riffed on the Wankel design and uses an oval rotor that spins within an epitrochoid chamber. The company claims its design—one of 60 it says it has patented—improves upon the Wankel to create a more durable engine.

GIF: WIRED, Source: LiquidPiston

The engine, which is 95 percent aluminum, uses a pair of counterbalancers to minimize vibration. LiquidPiston claims it is two orders of magnitude smoother than a conventional engine. Such an engine could see use in everything from scooters to drones, but LiquidPiston is focusing on the lawn and garden market—even if it has no plans to actually build engines.

"We're not looking to manufacture engines," says company president Alexander Shkolnik. Instead, the company plans to continue developing the engine and work with a manufacturing partner to tailor it to a particular application, perhaps a chain saw or leaf blower. Shkolnik presented a paper on the new engine this week at the SAE/JSAE 2014 Small Engine Technology Conference & Exhibition in Italy. Next year, the company plans a contest to solicit ideas for how the engine might best be used.

"A lot of the major risks have been addressed," Shkolnik says. "Now it's all about optimization and calibration."