This marks the first hybrid application of LPI’s engine technology.

The project team is led by LiquidPiston and also includes HDT Expeditionary Systems (HDT), a leading supplier of expeditionary military equipment including generators sets; and General Atomics (GA), a leading developer of military technology including battery and energy systems.

The CAPS hybrid electric 2kW diesel generator integrates a Lithium-ion Fault Tolerant (LiFT) battery technology developed by GA, which safely increases the CAPS’ power delivery quality, provides a “silent watch” capability, and optimizes the usage and life of the combustion engine. The 2kW CAPS generator, either as a standalone genset or as a hybrid electric power solution, is a capable solution for powering various military as well as non- military applications.

To be demonstrated initially to power the Howitzer M777 Digital Fire Control System, the new CAPS will address the Army’s need to extend mission duration, reduce fuel consumption, and reduce noise and heat signatures in powering digitized towed howitzers.

This marks a shift from research towards a product and a first real commercial application. We also are happy to be working with partners. Developing the technology is one thing, developing the business unfortantely is an almost equal aspect. You can’t develop the technology without developing the business. It’s really hard to start an engine company from scratch. Our model is to work with partners. We bring technology development and innovations. What we find in partners like HFT and General Atomics is the proven capabuility to deliver systems to end users, sales, manufacturing and distribution. We leverage leverage each others’ strengths.

—Dr. Alexander Shkolnik, Founder, CEO LiquidPiston

LiquidPiston develops compact, quiet, fuel-efficient, low-vibration, multi-fuel- capable rotary combustion engines that are scalable from 1hp to more than 1,000hp based on the company’s patented High Efficiency Hybrid thermodynamic Cycle (HEHC) and rotary X engine architecture. (Earlier post.) The company has been looking at a variety of engine architectures to embody HEHC, Shkolnik said, and has patented dozens of types of engines that look different.

HEHC is a patented thermodynamic cycle that combines the advantages of Diesel, Otto and Atkinson thermodynamic cycles. The cycle elements include:

• For maximum efficiency, air is compressed to a high compression ratio, fuel is injected and compression ignited (CI-HEHC). The X Mini utilizes a spark-ignition (SI-HEHC) version of the cycle with a lower compression ratio standard for gasoline engines.

• A dwell near top-dead-center forces combustion to occur at nearly constant-volume conditions.

• Combustion products are over-expanded using a larger expansion volume than compression volume, as in the Atkinson Cycle.

• Cycle-skipping power modulation allows high efficiencies at low power settings while simultaneously cooling the engine’s walls internally and providing partial heat recovery.

• Water may be injected to internally cool the engine. Some of this cooling energy is recuperated, as the water turns to steam, increasing the chamber pressure.

The combination of high compression ratio, true constant volume combustion, expansion into a larger volume than intake, and (optionally) water turning to high pressure steam cumulatively add to the efficiency of the engine. An air-standard analysis predicts an ideal thermodynamic efficiency of 74% at an 18:1 compression ratio.

LiquidPiston previously developed the “X Mini” prototype, a 2.2kW, 70cc SI engine operating LiquidPiston’s HEHC, which was demonstrated in a go-kart. (Earlier post.)

XMv3 engine gas path flows. Green is the intake charge, red is the exhaust, and blue is the cooling flow. The blue outlines represent the outer engine shroud, which separates the “stationary part” and “rotor cooling” flow paths at the orange dashed lines. Shown in red, three triangular openings on each side of the engine allow the passage of rotor cooling air and exhaust flows. Costa et al. (2016) Click to enlarge.

LiquidPiston was also recently awarded a contract by the US Defense Advanced Research Projects Agency (DARPA) to develop an ultra-efficient and compact 30kW diesel rotary X engine that fits in a ten inch box and weighs just 30 pounds, with fuel efficiency better than a heavy duty truck engine. (Earlier post.)

Resources

• Costa, T., Nickerson, M., Littera, D., Martins, J. et al., (2016) “Measurement and Prediction of Heat Transfer Losses on the XMv3 Rotary Engine,” SAE Int. J. Engines 9(4):2368-2380 doi: 10.4271/2016-32-0033.