A Completely New Type of Actuator -or- This Ain't Your Grandfather's Internal Combustion Engine

Abstract A completely new type of actuator – one that is proposed for use in a variety of environments from sea to land to air to space – has been designed, patented, built, and tested. The actuator is loosely based on the principle of the internal combustion engine, except that it is a completely closed system, only requiring electrical input, and the working fuel is water. This paper outlines the theory behind the electrolysis- and ignition-based cycle upon which the actuator operates and describes the performance capability test apparatus and results for the actuator. A mechanism application that harnessed the unit’s power to twist a scaled rotor blade is also highlighted. Introduction Traditional electro-chemical actuators use electrolysis to produce hydrogen and oxygen to generate pressure that can be used for mechanical work. These actuators can create substantial forces over large strokes but are inefficient and relatively slow. The Aerospace Corporation developed an actuator in which the hydrogen and oxygen are produced electrochemically and then ignited when actuation is desired. The process takes place in a closed volume so the water produced during combustion is contained and used again. The actuator essentially acts as a power amplifier that converts a low electrical power into stored chemical energy. The stored chemical energy can then be rapidly released (~10 ms) to produce high mechanical power in the actuator. The advantage of this device is the extremely high energy density that can be safely stored, then delivered instantaneously. It is essentially a power amplifier – a low level of power can be input over an extended period of time, then quickly reclaimed, on the order of single-digit milliseconds. The time duration of the actuation pressure pulse can be controlled from tens of microseconds to tens of milliseconds by adding variable quantities of inert “buffer” gas, which slows down the thermal activity during combustion. In the design space of energy density vs. speed of operation, this actuator lies outside the current state-of-the-art envelope, as shown in Figure 1.