Suburban Propane Partners taking 39% stake in DME producer Oberon Fuels; rDME/propane blends
European Parliament votes to phase out conformity factor for new car emissions under real driving conditions by Sep 2022

LiquidPiston receives SBIR grant to develop X-Engine as hybrid-electric platform for UAVs

LiquidPiston, Inc., a developer of advanced rotary internal combustion engines for diesel and jet fuels (earlier post), received a Small Business Innovation Research (SBIR) Phase I grant from the US Army for the development of its X-Engine as a hybrid-electric propulsion platform for UAVs. The company showcased its X-Engine powered propulsion platform in a successful parallel hybrid UAV demonstration using jet fuel.


The company was also named one of 12 winners in the US Army xTechSearch 3.0—a prize competition to award and to accelerate innovative technology solutions that can help solve key Army challenges—for its X-Engine configured as a high-efficiency auxiliary power unit (APU).

These new aviation applications of LiquidPiston’s 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.

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.

—Alec Shkolnik, CEO and co-founder of LiquidPiston

X Mini vs iPhone 6

X Mini vs iPhone 6

The X-Engine, a rotary engine that operates on the company’s patented High-Efficiency Hybrid Cycle (HEHC), is suited for a hybrid-electric propulsion platform because of its compact size and fuel efficiency. UAVs with Vertical Take Off and Landing (VTOL) capabilities enable the Army to launch and land UAVs 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.


LiquidPiston’s HEHC is a patented thermodynamic cycle that combines the advantages of Diesel, Otto and Atkinson thermodynamic cycles, resulting in up to 30% improved efficiency.

The X-Engine, configured as a parallel electric hybrid, also provides UAVs with the ability to cruise in “quiet mode” using electric-only power, with the ability to restart the engine mid-flight, enabling more efficient fuel usage and stealthier missions. The ability to do this on jet fuel has not previously been demonstrated in other vehicles currently fielded.

Wankel vs X Engine 1

The flexibility of the X-Engine can further be seen with the company’s development of various APU concepts for Army aircraft and land vehicles. 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 but also functions in-flight to offload the main engines in providing supplementary power for hydraulics, heating and cooling, and addresses the increasing power demands of the onboard electronics, weapons and other equipment.

X Mini_Side

X Mini

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. Today’s APU’s are only 5-10% efficient, making them useful for only short periods on the ground. The LiquidPiston 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.

The X-Engine, when matured and deployed, 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. 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.

—Dr. William Cohen, Chief Technology Officer of the US Army Assistant Secretary of the Army (Acquisition, Logistics and Technology)



Does anyone know what is going on with this company.
It seems to be puttering along, with about 19 employees for more than a decade, going from funding to funding.
It makes incredible claims, but we don't see the sales.
It has been going long enough to get the engines working so that is no excuse.


They have to have an application, now they found it.


This design looks familiar to me. In 2005 I received a patent for a rotary engine with a rotating elliptical piston and rotary valves. The advantages of that design were the elimination of all the disadvantages that the Wankel engine posed. None of the car MFRCs worldwide showed interest at that time. After five years of wasting time and money on the patent rights, I released the patent around 2010. What a coincidence!


Patents need to be defended if they are to be worth much.

The comments to this entry are closed.