SGER: Green Energy via Control-Based Design of Free-Piston Stirling Engines

Vanderbilt University, Nashville TN

Investigators

Abstract

The research objective of this work is to apply linear and nonlinear dynamical systems and control design tools to formulate a systematic design methodology for free-piston Stirling engines, which have been traditionally designed from a purely thermodynamic point of view. Historically, the design of Stirling engines has progressed from its original purely kinematic arrangement, where the motion of the displacer and the piston are kinematically constrained, toward a purely dynamic arrangement ? such engines are called ?free-piston? Stirling engines. Unfortunately, this shift toward a dynamic engine has not seen a commensurate development in the tools needed to realize their design. In this research, free-piston Stirling engines are recast and reinterpreted from a dynamic systems and controls perspective by viewing the interacting dynamic system elements in the context of designing a feedback loop. The design methodology is twofold: 1) apply linear control design tools to design parameter groups of the system as feedback gains, and 2) apply nonlinear dynamical systems analysis tools to verify and refine the design with regard to the full nonlinear system. The broader impacts of this research will be both intellectual and societal. On an intellectual level, the proposed dynamic design methodology is applicable to power production from dynamically dominant devices more general than free-piston Stirling-based designs, and has the potential to form the basis and framework for the design of all such ?dynamic? engines. On a societal level, as the availability of the world?s traditional fossil fuels continues to decline, the development of a viable alternative engine capable of transitioning society toward renewable, environmentally friendly fuels and energy sources becomes a paramount call to such research. Given the need only for a heat source, Stirling engines offer the advantage over conventional internal combustion engines of utilizing non-refined and/or non-petroleum-based energy sources such as: biomass, solar, geothermal, and other ?green? sources of heat.