LiquidPiston, an innovator of compact and efficient engine technology and hybrid power systems, intends to commercialize the XTS-210, a 25-horsepower, two-stroke, supercharged, liquid-cooled, 210cc rotary engine. The XTS-210 is heavy-fuel compatible (diesel, Jet A, JP-8, kerosene) and multi-fuel capable (gasoline, propane, hydrogen). Compared to current piston diesel engines, the XTS-210 design reduces size and weight by nearly 80%, while maintaining comparable power output.

XTS-210 engine core (left) compared to 25 hp Kohler KDW1003 (right).

This announcement builds upon a $9-million development contract from the US Army to develop a prototype core engine based on the XTS-210 design for military applications. (Earlier post.)

Representing the latest generation of LiquidPiston’s X-Engine platform architecture, the XTS-210 engine addresses the fuel efficiency, lubrication, and fuel type limitations of the traditional Wankel rotary engine.

The X-Engine is inherently simple in design, with just two primary moving parts: a rotor and shaft. The 25-horsepower XTS-210 adds up to one bar of boost through supercharging and operates as a two-stroke, producing six combustion events per revolution of the rotor, to deliver smooth power from a lightweight package, roughly the size of a basketball.

The XTS-210 uniquely addresses four major market requirements:

• 5x the power-to-weight (specific power) and power-to-volume (power density), and up to 3x the torque-to-weight (specific torque) compared with piston diesel engines of similar power;

• Ultra-portable and configurable for operation in both engine-only and hybrid-electric modes. Capable of running up to 7,000 RPM, which matches well with small and lightweight electrical machines, enabling increased mobility for power generation and hybrid applications;

• Liquid-cooled and capable of either Spark-Ignition (SI) or Compression-Ignition (CI). Designed for military-grade robustness from its inception; and

• Multi-fuel capability, with initial testing focuses on JP-8/Jet-A fuels for defense and aerospace applications.

The XTS-210 model will meet demanding commercial and military heavy-fuel 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-horsepower power class today that are suitable for aerospace and mobile military applications, where size and weight parameters are especially critical.

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.

—Dr Alec Shkolnik, co-founder and CEO of LiquidPiston

LiquidPiston is targeting delivery of an XTS-210 prototype to the US Army in 2024. 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 five to 40 horsepower.

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. This brings the company’s Department of Defense contracts total to over $30 million.