The U.S. Army has awarded LiquidPiston Inc., a developer of advanced rotary internal combustion engines for diesel and jet fuels, a Small Business Innovation Research (SBIR) Phase I grant to develop its X-Engine as a hybrid-electric propulsion platform for UAS.

During a parallel hybrid UAV demonstration using jet fuel, LiquidPiston successfully showcased its X-Engine powered propulsion platform.

LiquidPiston has also announced that it was named one of 12 winners in the U.S. Army xTechSearch 3.0 for its X-Engine configured as a high-efficiency auxiliary power unit (APU). The company says that these new aviation applications of its X-Engine technology demonstrate the versatility of the X-Engine system and its ability to provide compact, fuel-efficient power for manned or unmanned aircraft using military-grade heavy fuels such as JP8.

“This SBIR award and xTechSearch 3.0 innovation competition showcases the Army’s interest in innovative, fuel-efficient power sources to deliver the power needed to support Future Vertical Lift (FVL) Modernization Priorities,” says Alec Shkolnik, CEO and co-founder of LiquidPiston.

“When we reimagined the rotary engine with the X-Engine, we knew it could be used to improve power generation in a number of different ways, given its high power-to-weight, efficiency, and ability to run on heavy fuel including Jet-A / JP8 fuel which the Army wants to use exclusively. The versatility of LiquidPiston’s X-Engine enables the company to provide hybrid-electric power generation in various form factors, which makes it uniquely suited to serve not just FVL, but all 6 of the Army’s modernization priorities.”

A rotary engine that operates on the company’s patented High-Efficiency Hybrid Cycle (HEHC), the X-Engine is described as the “perfect power source” for a hybrid-electric propulsion platform because of its compact size and fuel efficiency, according to LiquidPiston. LiquidPiston notes that UAS with Vertical Take Off and Landing (VTOL) capabilities enable the Army to launch and land UAS on a small area and set up and stow quickly while the X-Engine hybrid-electric power system allows minimization of heavy, low energy density onboard batteries. When configured as a parallel electric hybrid, the X-Engine also provides UAS with the ability to cruise in “quiet mode” using electric-only power, with the ability to restart the engine mid-flight, which enables more efficient fuel usage and stealthier missions. LiquidPiston says that the ability to do this on jet fuel has not previously been demonstrated in other vehicles currently fielded.

LiquidPiston’s development of various APU concepts for Army aircraft and land vehicles further showcase the flexibility of the X-Engine. The company entered into the xTechSearch competition with a high-efficiency aviation APU concept for rotorcraft. The proposed unit is compact, highly-efficient, and can perform the typical on-ground APU functions, as well as functions in-flight to offload the main engines in providing supplementary power for hydraulics, heating and cooling. It also addresses the increasing power demands of the onboard electronics, weapons and other equipment.

In APU applications, the X-Engine approaches the power density and packaging similar to a turbine-based APU, with the efficiency of a Diesel engine. According to LiquidPiston, today’s APU’s are only 5-10 percent efficient, which makes them useful for only short periods on the ground. LiquidPiston says that its APU would offer “substantial gains” in power and efficiency and offload the main engines, allowing a helicopter substantial gains in range, or adding a passenger or other payload capability.

When matured and deployed, the X-Engine will help to provide the increasing power requirements for direct and hybrid electric propulsion for the US Army Future Tactical UAS (FTUAS) and other DoD UAS programs, as well as Auxiliary Power Units (APUs), Supplemental Power Units (SPUs) and Power & Thermal Management Systems (PTMS) for manned rotorcraft and fixed wing aircraft.

“Advanced power generation and alternative fuels are critical for the Army, and we continuously seek new technologies that can materially improve our ability to execute national security missions,” explains Dr. William Cohen, Chief Technology Officer of the U.S. Army Assistant Secretary of the Army (Acquisition, Logistics and Technology) i.e. ASA(ALT).

“Reliable engine technologies that offer a wide range of sustainable applications, from UAVs to auxiliary power units for air and land vehicles, can increase endurance and lessen reliance on contested or extended supply lines. Potential benefits include increased reliability and access to power, increased redundancy within the power distribution network, reduced logistics footprint associated with fuel distribution, and extended operational reach.”