Underground » General
The aim of this project was to develop a proof-of-concept Stirling Engine and heat cell for use in the mining industry, primarily for underground applications. In particular, the Stirling engine, being an external combustion engine, offers the potential to operate on stored heat in low-oxygen or inert underground atmospheres. This makes it attractive for rescue vehicles, which are required to operate in such environments.
A prototype Stirling engine with power output in the 15kW range was constructed and tested. Experimental measurements showed that this output was not achieved. While the basic thermodynamic principles of the design were valid, achieved output was well below the required value, due largely to the following issues:
Heat source: Because of budgetary constraints it was not possible to use the molten salt bath-type of heat source for which the heat exchanger was designed. Instead a gas burner was used which did not transfer sufficient heat into the engine.
Working gas pressure: The heat to mechanical energy conversion process efficiency depends strongly on the pressure of the working gas. Because of a problem with seal design the pressure for the test was only 7% of the design value.
Seals: It is apparent that the perennial problem of seal design in Stirling engines was not solved in this implementation. Gas pressure could not be maintained, and even with the modest pressure used, friction, mainly caused by the seals produced unacceptable losses. These losses would be exacerbated if the working gas pressure was raised.
The conclusion is that, because of the lack of commercial Stirling cycle-based products and the difficulty experienced in this project in overcoming the problem of high temperature seal implementation to produce a working prototype, the short term potential of the Stirling engine for mine rescue applications is limited.