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We have developed a novel device to supply hydraulic power for anaerobic mobile robotic systems. This power source demonstrates the possibility of operation in oxygen-free environments, such as underwater or in space. Unlike the internal combustion engine, the design produces power on demand, eliminating idling when there is no load on the system. This monopropellant-powered free piston hydraulic pump (FPHP) was designed as a human scale (1.0-3.0 kW) power source, and produces only steam and oxygen as its byproducts. The FPHP utilizes high concentration hydrogen peroxide as the monopropellant energy source, which decomposes into hot gas when exposed to a catalyst. Energy is extracted from the hydrogen peroxide and transferred directly to hydraulic fluid by expanding the hot decomposition gas in an integrated piston/cylinder arrangement. Based on a specific power and specific energy analysis using a Ragone plot, the performance of the FPHP potentially exceeds that of a battery-based hydraulic power source for short operation times. Note to Practitioners-This project was motivated by the need for a simple free piston engine that is capable of producing hydraulic power. A free piston engine has no crankshaft or rotating motion, only a piston assembly that is constrained to move in a linear fashion within a bore. The energy of the free piston can be harnessed by pressurizing a working fluid or generating electrical power. Instead of relying on the combustion of gasoline or diesel fuel to move the free piston, which involves problems with fuel/air mixing and ignition timing, we created a device that is powered by the catalytic decomposition of a monopropellant. This concept overcomes the problems with a combustion powered free piston engine and also affords operation in environments with no atmosphere, such as underwater or in space. The device we constructed is an integrated free piston engine and hydraulic pump with very few moving parts. This monopropellant free piston engine could be adapted for use with any source of pressurized gas (preferably one with a high specific energy) and could be scaled to varying power outputs. The largest hurdle to overcome before realizing reliable operation of the free piston hydraulic pump (FPHP) is ensuring that the catalyst effectively decomposes the monopropellant.
Raade et al. (Tue,) studied this question.