LiquidPiston to commercialize compact rotary engine

04 April 2023

LiquidPiston, a Bloomfield, Conn., developer of compact engine technology and hybrid power systems, has announced its intent to commercialize its XTS-210 rotary engine. The XTS0-210 is a supercharged, liquid-cooled engine with a displacement of 210 cc and an output of 25 hp at 6500 rpm.

LiquidPiston XTS-210 rotary engine Liquid Piston said it will commercialize its compact XTS-210 rotary engine. (Photo: Liquid Piston)

Compared to current reciprocating diesel engines, Liquid Piston said the XTS-210 design reduces size and weight by nearly 80%, while maintaining comparable power output. It is targeted toward commercial and military applications, including mobile electric power generation, primary or hybrid-electric propulsive power for vertical take-off and landing aircraft (VTOL) and small unmanned aircraft systems (sUAS), as well as auxiliary power units for land, air and marine vehicles.

“There are essentially no diesel engines in the 25 hp power class today that are suitable for aerospace and mobile military applications, where size and weight parameters are especially critical,” said Dr. Alec Shkolnik, co-founder and CEO of LiquidPiston. “The reduced weight, size, and heavy- or multi-fuel capability of the XTS-210 delivers significant end-system capability and utility benefits, especially for the military to reduce supply chain and logistical burdens in an era where ‘power on the move’ is increasingly important.

“Following nearly two decades of breakthrough thermodynamics research with various types of rotary diesel engines, we are excited to converge on this latest generation as our first X-Engine model that we plan to bring to market.”

Representing the latest generation of the X-Engine platform architecture, LiquidPiston said the XTS-210 engine addresses the fuel efficiency, lubrication and fuel type limitations of the traditional Wankel rotary engine. Roughly the size of a basketball, the engine has two primary moving parts – a rotor and shaft – and operates on a two-stroke cycle, either spark ignited or compression ignition.

The trochoidal rotor is within a three-lobed housing with a stationary combustion chamber that produces six combustion events per revolution of the rotor. This, Liquid Piston said, enables a higher compression ratio with direct fuel injection, leading to better efficiency and optimized fuel air mixing. Stationary apex seals are used to reduce blowby and offer direct lubrication, improving efficiency, emissions and durability, the company said.

Liquid Piston said the XTS-210 is available in engine-only and hybrid-electric versions and it is multifuel capable, though initial testing has focused on JP-8/Jet-A fuels. Dry weight of the engine is approximately 46.7 lb., with dimensions of 8.7 in. x 10.6 in. x 10.7 in. (221 x 270 x 272 mm).

This latest announcement builds upon a $9 million development contract from the U.S. Army to develop a prototype “core engine” based on the XTS-210 design for military applications. The company has previously prototyped several variants of rotary X-Engines, demonstrating significant versatility in engine architecture, including naturally aspirated four-stroke versions ranging from 5 to 40 hp.

LiquidPiston is targeting delivery of an XTS-210 prototype to the U.S. Army in 2024. The company aims to partner with the military for low-volume applications and with other manufacturers for commecial applications. 

In addition to the recent $9 million award to contribute to the development of the XTS-210, LiquidPiston has also received a $1.7 million Army contract to power a hybrid-electric VTOL UAV demonstrator. The company said its Dept. of Defense contracts total more than $30 million.

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