Edinburgh Napier University

  The analysis of the Stirling engine has long been hampered by a lack of understanding of the complex relationship between the mechanical dynamics, thermodynamics and fluid dynamics operating within the engine. This thesis outlines the research into Low Temperature Differential Stirling Engines (L TDSE) at Napier University. These engines typically operate at temperatures between 273K and 373K. The pressure profile within the engine varies about atmospheric pressure. As such they are naturally able to exploit heat sources such as process waste heat, solar passive collectors and geothermal hot springs. So far the majority of investigations have been in the field of high temperature engines, with a temperature differential counted in the thousands of Kelvin.
This work presents a third order analysis of the low temperature differential Ringbom - Stirling engine (L TDRSE). This is achieved by identifying the key elements of the engine. The laws of conservation and the ideal gas law are applied to each of these elements. From this a series of equations is written down, describing each element in turn. Simplifying assumptions are used to set boundary and limiting conditions. The equations are encoded to form the prediction program presented in the work. A test engine has been designed and manufactured, which, when equipped with a data logging system designed specifically for the engine, produces data sets for comparison purposes.
It was found that the prediction program indicated many of the unique operating characteristics of the L TDRSE that were confirmed by the data for the test engine. These showed a good correlation between the piston and displacer phase relationship, the discontinuous motion of the displacer and the pressure profiles. Accuracy of the prediction program data was found to be within 30% of the values for test engine data.