Mechanical power production by a dynamic micro heat engine with integrated thermal switch is demonstrated. A microengine operated from a constant heat source of 60 °C is shown to produce 350 µW of mechanical power. Employing an active thermal switch to control heat rejection from the microengine enables power to be increased to 2500 µW. Power consumption by the thermal switch is shown to be minimized by operating the cantilever switch at its resonant frequency. Thermal switch power requirements can be reduced to less than 20 µW for operational speeds up to 100 Hz.

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Progress toward the realization of an external combustion dynamic micro heat engine is documented. First, the development of a thermal switch suitable to control heat transfer to and from the micro heat engine is described. Second, the integration of a thermal switch with an engine is detailed. The thermal switch is shown to be an effective means to control heat transfer into the engine from a continuous heat source and out of the engine to a continuous heat sink. The use of the thermal switch is shown to enable engine cycle speeds up to 100 Hz, engine efficiencies up to 0.095% and power output up to 1.0 mW. The internal irreversibility of the engine is measured to be 23%.

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This work examines the design and operation of a new, small-scale Free Piston Expander (FPE) engine that operates using low temperature waste heat sources to produce useful power output. The FPE is based on a sliding-piston architecture that eliminates challenges associated with MEMS-based rotating systems. A nonlinear lumped-parameter model is derived to study the factors that control the performance of the FPE engine and its unique operating cycle. This basic analysis considers a closed cycle operation of the FPE with low thermal or heat inputs and dimensions on the order of several millimeters. Key system design and operating parameters such as piston mass, external load, and heat input are varied to identify conditions and trends for optimal performance. The model indicated the pressure-volume diagram resembles a constant pressure cycle for a certain set of operating conditions but is also condition dependent. Increased heat inputs to the FPE reduced the engine natural or operating frequency while increasing the power output. Thermal efficiencies of the FPE are shown to be predictably low, on the order of 0.2 % due to the small heat input and operating temperature gradients associated with waste heat. Key design features are identified that reveal FPE efficiency, operating frequency, and output power are dependent on piston mass, external load, input heat-rate, and duration of heat input.