Dwell Mechanism for Increasing Free-Piston Stirling Engine Specific Power and Efficiency

Proposed is a displacement dwell mechanism for increasing Stirling engine power output and efficiency. The dwell mechanism allows for deviations from a sinusoidal displacement profile found in crank-driven Stirling engines. Longer dwell allows slightly more time for heat transfer to occur in both the hot- and cold-side heat exchangers. Preliminary simulations using freely available Stirling engine simulation code by Israel Urieli indicates that even a modest increase in dwell time increases power output and efficiency. Increasing the power output and efficiency of a Stirling engine by way of a simple mechanical device represents the ?low hanging fruit? compared to complex and expensive regenerator/heat exchanger optimization and development.

The NASA applications for a Stirling power conversion system having higher efficiency and higher power density are long duration missions far from the sun, and missions in hostile environments and other cases where photovoltaic systems cannot meet the power generation requirements.

One potential commercial application for a more efficient and lighter weight Stirling power conversion system is large scale renewable power generation using solar thermal energy input. Another potential application is residential and small commercial CHP (combined heat and power) systems using a range of energy sources from geothermal to solar to biofuels and other renewable hydrocarbon fuel sources, as well as non-renewable energy sources such as natural gas. Stirling CHP power systems can also be used directly or with a modified design to meet the needs of the military for portable power generation units. Other potential applications include power for electric vehicles and electric power for marine applications, including underwater power generation for which the higher efficiency of our system has substantial benefit.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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