Design, Modeling, and Experimental Validation of a Stirling Pressurizer With a Controlled Displacer Piston

This paper presents the design, first-principles model, and experimental setup of a Stirling pressurizer. A Stirling pressurizer is defined as the portion of a Stirling engine or device with a displacer piston and is responsible for generating large-pressure oscillations. Unlike conventional Stirling devices, the power piston can be separated by directly and independently controlling the motion of the displacer piston in the pressurizer. The directly controlled loose-fit displacer is actuated with a small linear motor and moves the prepressurized working fluid (helium) between the hot and cold side of the sealed engine section, therefore inducing a pressure change. The position of the displacer is the only control input to the first-principles model of the pressurizer, and the output of the model is the dynamic pressure inside the device. The first-principles model is validated with experimental results for different controlled displacer piston motion profiles. Modeled and experimentally measured pressures are compared for average pressures ranging from 10–20 bar, and heater head temperatures ranging from 250–500 °C. The first-principles model is intended for: 1) the design and sizing of the pressurizer and power piston/power extraction, 2) specification of a displacer piston motion profile to optimize the efficiency and/or power output, and 3) the general design of Stirling devices, beyond the design of the experimental prototype investigated here, through the use of a lumped parameter model with well defined and measurable parameters.