Game-changing rotary engine muscles a go-kart

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This tiny engine, compared here to an iPhone, outputs almost 3.5 horsepower(Credit: LiquidPiston)

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Imagine an engine that's 30 percent smaller than a traditional piston design of like output, and that runs smoothly, with less noise and vibration. Plus, it burns several types of fuel. That's the LiquidPiston X rotary engine, which was recently demonstrated powering a go-kart.

The LiquidPiston rotary engine is a non-Wankel design that we've featured on Gizmag before. Back in 2014, the company announced the engine's development. Now it's showing the new engine with a novel application to showcase its power-to-weight capabilities.

The LiquidPiston X Mini shown in the video at the bottom of the page has nearly 2 horsepower per pound (3.3 kW per kilogram). It's 30 percent smaller and lighter than the equivalent spark-ignited gasoline engine it replaces, and can be up to 75 percent smaller than a like-output diesel engine.

The LiquidPiston X Mini (right) is roughly 30 percent smaller and lighter than the equivalent four-stroke piston engine it replaces(Credit: LiquidPiston)

Even better, the engine's design means that it has no poppet valves and exhaust is balanced through over-expansion, removing the need for a muffler. The X rotary engine can be as much as 20 percent more fuel efficient than its gasoline counterpart and 50 percent more efficient than an equivalent diesel engine. What's more, the LiquidPiston X can be powered by gasoline, diesel, natural gas, or JP-8 fuel. The design, says the company, is scalable from 1 horsepower to over 1,000.

The X Engine is designed as a unique rotary that has three combustion events per rotor revolution, explaining its high power density and balanced operation. The engine is designed to be made with 2-dimensional manufacturing methods, making it simple to build. This also means that it can be easily modified by enthusiasts – something that LiquidPiston is expecting, having released a developer's kit for the X Mini.

The engine's parts in their entirety, showcasing its simplicity – to the right are the central rotary parts, with the oval-shaped to rotor to the right of the shaft; the holes at bottom allow for air intake while the holes at top allow for exhaust expansion to eliminate the need for a muffler(Credit: LiquidPiston)

One of the secrets in the X Engine's design is the unique rotary cycle. Unlike a Wankel rotary, which uses a triangular center rotor, the X Engine has an oval-shaped rotary which rotates in a cloverleaf-like core. This creates higher compression with better seals and exhaust pressure. It also creates a larger expansion volume than compression volume, similar to the high-efficiency Atkinson Cycle engine used in hybrid vehicles.

The design of the X Engine also allows for cycle skipping for lower-output needs and low-RPM power. In larger versions of the engine, LiquidPiston says, water can be injected into chambers after the exhaust cycle to cool the engine when under high loads.

The engine being used in the video to power the go-kart is a four-stroke 70cc gasoline version that produces about 3.5 horsepower (2.2 kW) at 10,000 rpm. LiquidPiston expects to have the engine producing 5 hp (3.7 kW) soon.

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