Design, Modeling, and Experimental Validation of a Stirling Engine with a Controlled Displacer Piston

Abstract

This work presents the design, first-principles model, and experimental setup of a Stirling pressurizer. The Stirling pressurizer is a Stirling engine with an independently controlled displacer piston. The directly controlled, loose-fit displacer is actuated with a small linear motor and moves the pre-pressurized 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. 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°C – 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. The Stirling pressurizer combined with a power extraction unit is intended to fill the technological gap of a compact, quiet, un-tethered, and high energy density power supply.