The Stirling cycle has recently been receiving renewed interest due to some of its key inherent advantages. In particular, the ability to operate with any form of heat source (including external combustion, flue gases, alternative (biomass, solar, geothermal) energy) provides Stirling engines a great flexibility and potential benefits for many applications. However, several aspects of traditional Stirling engine configurations (i.e., the Alpha, Beta, and Gamma), specifically complexity of design, high cost, and relatively low power to size and power to volume ratios, limited their widespread applications to date. This study focuses on an innovative Stirling engine configuration that features a rotary displacer (as opposed to common reciprocating displacers), and aims to utilize a preliminary analytical analysis to gain insights on its operation parameters. Although the analysis involves idealizations, it still provides useful design guidelines as a first step towards optimization.
This study adopts some of the assumptions from the well-known Schmidt analysis, and follows a similar approach for the innovative rotary displacer configuration. As part of this preliminary analysis the optimum phase (lead) angle is determined to be 90°. In addition, the work ratio normalized for the optimum phase angle is presented. Other studied parameters include the internal volume of rotary displacer over the volume of power cylinder, and the volume of “dead spaces” over the volume of power cylinder at various ratios. Although the dead space have negative effects on overall performance and efficiency, they are dictated by the practical design constraints. Lastly, this study considers work output of the engine over a range of heat sink to heat source temperature ratios, and varies the heat sink or heat source temperatures independently. The analysis addresses both low and high temperature differential situations for the purpose of waste heat recovery and power generation, respectively.