Design and Control of a Free-Liquid-Piston Engine Compressor for Compact Robot Power

Abstract

This paper presents the design and control of a free-liquid-piston engine compressor (FLPEC). The FLPEC produces low temperature, high-pressure air for use as a high energy density power supply for untethered, compact robots. Internal combustion with a propane-air mixture in the engine combustion chamber drives a high inertance, low mass liquid piston, which compresses air into an onboard reservoir. A real time logical controller is implemented in Matlab to regulate the timings of the air and fuel injection, spark, and exhaust valve and to compensate for misfires. Experimental pressure data is overlaid with the logical state of the injectors, spark plug, and exhaust valve to demonstrate the efficacy of the controller to account for cycle-to-cycle pressure variations in the combustion chamber.