Dynamic Model-Based Design, Validation, and Characterization of a Compact, High-Inertance Free Liquid Piston Engine Compressor

Abstract

Pneumatically actuated robotic systems are attractive alternatives to traditional electromechanical systems (i.e., batteries and DC motors) due to the inherent power density advantage of pneumatic actuators. This assumes that a power source is available to provide the pneumatic supply at a sufficient energy density to compete with batteries. To this end, a high-inertance free liquid piston compressor (HIFLPC) was developed as a portable, efficient, compact power supply for pneumatically actuated systems. Given that free piston engine performance is highly dependent on the dynamic characteristics of the piston, this work presents the idea of incorporating a liquid piston whose geometry can be manipulated to achieve the desired piston dynamics while maintaining the compactness and light weight necessary for applications in the power output range of 100W. An inertance-based dynamic model of the liquid piston is developed and validated experimentally. The piston model is incorporated into a complete system dynamic model of a proposed high inertance free liquid piston compressor (HIFLPC.) Critical model parameters for individual components and subsystems of a proposed HIFLPC prototype are experimentally characterized. The design and fabrication of an experimental prototype of the device is detailed. Efficiency, power output, and other operational characteristics of the prototype are assessed. A validation of the dynamic model developed for the HIFLPC is conducted, and model-based studies are performed to investigate the influence on system performance by varying liquid piston dynamics.