LiquidPiston's XTS-210 rotary engine is about the size of a basketball but could replace generator ... [+] engines several times larger.
A Connecticut-based company is on contract with the Army and Air Force to develop rotary engines that could displace the 30,000 small tactical generator sets currently in use and power drones. Industrial Generators
Though formed almost 20 years ago, LiquidPiston has only recently reached the cusp of serving a DoD program of record. The company spun out of the Massachusetts Institute of Technology (MIT), where co-founder Alec Shkolnik was a PhD student in artificial intelligence and robotics.
With his father Nikolay - a Ukrainian-born physicist - he developed a new twist on the classic Wankel rotary engine which has powered automobiles, aircraft and other applications for the last 60 years.
LiquidPiston’s high-efficiency hybrid cycle (HEHC) rotary engines are based on a new architecture and new kind of thermodynamic cycle which lend themselves to compact power generation and powertrain applications where size, weight and power (SWaP) is critical.
“The engine is five to ten times smaller and lighter than other power solutions so we’re finding some good fits within the DoD. Anywhere you go, they love more power and more energy for any application,” Alec Shkolnik affirms.
That has garnered interest and ten contracts - a combination of Small Business Innovation Research (SBIR) and direct development awards - from the Army and Air Force over the last two years adding up to about $20 million. While they cover interest in both mobile power generation and small drone propulsion systems, LiquidPiston is focusing first on small generators for use in the field.
“There’s a push today to distribute mobile [Army] command centers,” Shkolnik observes. “They just make good targets so the Army would ideally like to split them up and if you lose one, you can still maintain functionality.”
But an even more pressing focus for the Army is replacing a generation of gas and diesel-powered small generator sets (gensets) fielded several decades ago.
The Service’s Small Tactical Electrical Power (STEP) program looks to deploy a new generation of gensets offering “increased efficiency, reliability, mobility and maintainability”. A range of sizes and power outputs are up for renewal. LiquidPiston is focused on smaller, low to medium output generators.
“The genset we’re developing could possibly replace the 3 kW to 10 kW generators that are currently fielded. The Army is excited about that because logistically, it’s much simpler to have one product/type to support,” Shkolnik says.
XTS-210 engine core compared to a typical small genset engine, a 25 hp Kohler KDW1003. Not shown on ... [+] the XTS are ancillary systems such as fuel pump, water pump, and oil system.
The rotary engines LiquidPiston has developed are scalable in size from an engine that fits in your palm to end-table sized powerplants that can churn out up to 1,000 horsepower. They share the same basic design which the company refers to as its “X platform”, an architecture with only two moving parts, a rotor and shaft.
That simplicity enhances reliability and maintainability, key STEP attributes. It also allows for competitive power outputs at small size, enabling small vehicle-mounted gensets (potentially on light platforms like the Army’s new Infantry Squad Vehicle) or even man-portable generators which don’t require a truck and/or trailer.
“If a group of two to four people can move a gen set around, it’s really a new capability,” Shkolnik adds.
The X design is capable of two-stroke or four-stroke operation and of accommodating gasoline, kerosene, hydrogen and diesel fuels. This flexibility is highly desired by the Army which is seeking to unify its tactical powerplants to run on a single type of heavy fuel (JP-8/F24), significantly simplifying its logistics challenges.
An $8.3 million contract with Virginia-based engineering firm, Parsons PSN Corporation, based on funding from the Army C5ISR Center will see LiquidPiston integrate its XTS-210 (210cc) rotary engine into a compact 10 kW generator slated to be field-tested by the Army for its Advanced Medium Mobile Power Source (AMMPS) generator requirement. The new genset will be approximately one-quarter the size and weight of the current AMMPS system with similar fuel consumption.
Shkolnik says it fits into a 1.5-foot by 1.5-foot box weighing less than 200 pounds which can be truck mounted and rely on its own eight hours-duration fuel supply or be fed from external tanks.
The qualities above stem from a redesign of the standard Wankel rotary that Shkolnik describes as “turning the Wankel rotary engine inside out.” Rather than employing a triangular rotor inside a peanut shaped housing as in the Wankel, LiquidPiston’s HEHC engine has an epitrochoidal (peanut shaped) rotor spinning inside a tri-lobed (roughly triangular) housing.
This enables it to use a thermal cycle that combines attributes of the classic Atkinson and Otto cycles but estimated to be about 30% more efficient. “Our engine is capable of running a much higher compression ratio [than Wankels],” Shkolnik explains. “We can achieve constant-volume combustion and over-expansion by asymmetrically porting the intake and exhaust.”
The result is competitive power output in a small, high RPM package that overcomes the traditional oil consumption and sealing problems associated with rotaries. The fast-spinning character of the X rotary engine design couples favorably with electric generator motors, allowing them to be smaller as well.
That kind of packaging advantage makes the small rotaries good candidates for powering drones as standalone units or as part of hybrid systems. LiquidPiston has a Phase II SBIR from the Army to develop its Hybrid Electric X-Engine (HEXE) propulsion system for the Service’s Future Tactical Unmanned Aircraft System (FTUAS).
FTUAS will replace the Army’s existing Textron TXT RQ-7 Shadow ISR drone with a new runway-independent VTOL UAV. Shadows are powered by gasoline-fueled Wankel rotaries but the Army wants their replacement to be powered by a JP-8/FT-24-fueled hybrid system capable of longer endurance and quieter operation.
LiquidPiston’s HEXE propulsion system can toggle power between all-electric, engine-only, or a combination of both - on demand - while being able to restart the engine in-air on jet fuel. HEXE has also caught the interest of the Air Force’s AFWERX technology advancement arm which awarded the company a pending $15 million STRATFI (Strategic Financing) contract in June.
The USAF is interested in both airborne and ground power applications in heavy fuel and hybrid formats. LiquidPiston’s immediate goal is to deliver advanced prototype engines and generators to the Army by the end of next year Shkolnik says. And, like any other defense startup, its complimentary goal is to survive until a production contract is realized.
That requires crossing the Valley of Death, the gap between obtaining R&D funding and landing a full-fledged production or service contract. Though LiquidPiston faces the same kind of Valley of Death challenge as its defense startup cohorts, it has had to deal with another issue.
“Everybody in the Army, Navy and Air Force wants more [tactical] power but no one really has ownership of a program that can advance it,” Shkolnik says. Indeed, nowhere among the Services does there appear to be a central acquisition organization/body for tactical power. Instead, military tactical power elements get tied-in with specific programs without the benefit of an overarching view of requirements.
I asked the recently empowered Defense Innovation Unit if it has recognized the lack of a central organization directing the acquisition and sustainment of the ever-expanding need for tactical power across DoD. So far, DIU has not provided an answer. But LiquidPiston’s CEO says his company has worked for years both to educate the services about its capability and the advantages of unifying tactical power efforts.
It has also taken a less-traveled route to secure additional investment. LiquidPiston has been an early adopter of equity crowdfunding. Prior to 2016, investors had to be accredited to fund startups (or even discuss funding with them) but with the advent of regulated crowdfunding, Shkolnik saw an opportunity to raise capital to keep the company on its research and development path.
“That was kind of a game-changer. We’ve done three regulation CF rounds and we hit the legal limit, raising $3 million in those.”
The company has raised almost $30 million in additional funding since 2021 via Regulation A equity offerings to over 10,000 investors. (Regulation A is an exemption from the SEC registration requirements, allowing companies to offer and sell their securities without having to register.)
“That’s been a fantastic way for us [to fund-raise]. We just resonate with a lot of people who get what we do,” Shkolnik enthuses. “They see a picture of an old engine and our engine or see a picture of the inside of our new rotary. They get excited and they invest.”
Strategies like these haven’t been the subject of much discussion in the defense startup space but they could be worth considering. LiquidPiston also plans to leverage opportunities (it holds 84 patents) in the commercial space where batteries cannot offer sufficient power, cost/weight-saving or logistical simplicity - applications including auxiliary power units.
The company’s development of a traditional power system in an age of in-fashion alternative systems demonstrates the continued advantages and appeal of novel engine technology. Shkolnik’s father and co-founder recognized its long-term potential even as he worked on fuel cells, supercapacitors and other technology in the early 2000s.
Alternator Power Generator “Everything he was doing kept coming back to the internal combustion engine as a simple device that could [perform] better.”