1. M. E. Hofacker, J. Kong, E. J. Barth, “A Lumped-Parameter Dynamic Model of a Thermal Regenerator for Free-Piston Stirling Engines”. 2009 ASME Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power & Motion Control. Accepted for publication June 2009.
  1. E. J. Barth and M. E. Hofacker, “Dynamic Modeling of a Regenerator for the Control-Based Design of Free-Piston Stirling Engines”. NSF CMMI Grantees Conference, June 22-25, 2009, Honolulu, HI. Research director.
  1. J. A. Riofrio, K. Al-Dakkan, M. E. Hofacker, E. J. Barth. “Control-based Design of Free-Piston Stirling Engines,” Proceedings of the 2008 American Control Conference (ACC), pp. 1533-1538, June 11-13, 2008. Seattle, WA.

Control-Based Design of Free-Piston Stirling Engines

In this approach, 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. Initial work indicates that a non-standard control design problem emerges. For the engine to produce power, there must exist at least two complex-conjugate closed-loop poles in the right-half plane. Therefore, the control-based design of free-piston Stirling engines requires seeking instability and instability robustness. Instability in a linear sense implies an engine that produces power, whereby the true nonlinear system will seek a limit cycle.

Stirling engines have unfortunately fallen far short of their historical promises due primarily to low power density – a heavy engine producing small amounts of useable power – particularly at the sub 10kW scale. The free-piston variety of Stirling engine is recognized as possibly holding the key to increasing power density without sacrificing the Stirling engine’s characteristic high efficiency.