Revolutionary engine maker Liquid Piston seeks commercialization partners after landing $2.5 million DARPA funding for 40HP engine that will be 30 lbs instead of conventional 2700 lbs for diesel

LiquidPiston says it is currently in negotiations with potential partners to bring its small engines to market. Shkolnik also said the engines could be used as range-extenders for mass market electric vehicles.

“The engine would produce less CO2 than plugging the car into the U.S. power grid,” Shkolnik said.

In the future, the company believes it can build larger engines that compete with those currently in cars and trucks, military aircraft and large boats, targeting a market it estimates is worth $460 billion.

LiquidPiston is looking to raise $5 million to 7 million in a Series A round of investment in early 2017, according to the pitch deck. The company currently has 16 patents granted for its technology and 13 employees, though Shkolnik said he’s looking to expand with the infusion of cash from DARPA.

DARPA awarded LiquidPiston Inc. $2.5 million to continue development of a new, patented, high-efficiency, lighter-weight rotary engine. LiquidPiston, a developer of advanced combustion engine technology, received the award for the first phase of a program to realize the full capability of its patented high-efficiency hybrid cycle (HEHC) engine. This is the second award DARPA has made to LiquidPiston in the past 18 months, following an earlier test program for a different LiquidPiston rotary engine prototype, which achieved promising results.

LiquidPiston will be developing its X4 test rig: a prototype 30 kW diesel X-engine, with targeted brake specific fuel consumption (BSFC) of 186 g/kWh (better fuel efficiency than heavy duty truck engines, and twice the fuel economy of a gasoline engine over a typical drive cycle). The X4 is designed for extremely high specific power, with an objective of 1.5 hp/lb, making it up to ten times (10x) more powerful than a standard diesel engine with the same weight.

A standard 35 HP diesel engine (left) next to LiquidPiston’s proof of principle 40HP diesel engine (right)

The X Engine has few parts and three combustion events per rotor revolution, resulting in tremendous power density.

LiquidPiston’s 4-stroke HEHC-cycle engines are designed to be:

Lightweight and Compact

High power density – up to 2 HP/Lb (3.3 kW/kg)
30% smaller and lighter for spark-ignition (SI) gasoline engines
Up to 75% smaller and lighter for compression-ignition (CI) diesel engines


No poppet valves
Exhaust turbulence minimized by over-expansion; no muffler required


Only two primary moving parts, optimally balanced, resulting in near-zero vibration


20% decrease in fuel consumption possible for SI gasoline engines
50% decrease in fuel consumption possible for CI diesel engines

Multi-Fuel Capable

Diesel, gasoline, natural gas, JP-8


From 1 HP to over 1000 HP

“Our goal is to create a reliable X4 test rig that will support optimization of the X-engine architecture and the HEHC cycle. Combined, the cycle and architecture offer a compression-ignition, diesel-fueled rotary-engine power solution that is a fraction the size and weight of a comparable piston engine, while offering the advantages of greater fuel efficiency, quieter operation and reduced vibration,” says Alexander Shkolnik, CEO and Founder of LiquidPiston.

“Today, a typical 30 kW military diesel generator weighs 2,700 lbs. Such a generator can be used to power a mobile command center, for example. Soldiers would benefit as the X4 prototype would enable an ultra-portable diesel generator that produces electricity in a package one-tenth the size and weight, and operates with greater efficiency,” explains Shkolnik. “We seek to help reduce the military’s logistical and carbon footprint. Our design would also give greater range and capability to drones or other vehicles. The same technology would benefit civilian consumers as well – lighter, quieter more efficient generators or auxiliary power units for homes, boats or vehicles, as well as range-extended electric vehicles.”

LiquidPiston recently installed its 70cc X-mini rotary engine prototype into a go-kart demonstrator, replacing a 40 lb, 6 hp gasoline piston engine with the 4 lb, 3-5 hp 70cc X-mini engine.

LiquidPiston develops compact, quiet, fuel-efficient, low-vibration, multi-fuel-capable combustion engines that are scalable from 1 hp to over 1,000 hp, based on the company’s patented High Efficiency Hybrid Cycle and rotary X engine architecture