Rizzo (1997) reported that Kolin experimented with 16 LTD Stirling engines, over a period of 12 years. Kolin presented a model that worked on a temperature difference between the hot and cold ends of the displacer cylinder which was as low as 15 C. Iwamoto et al. (1997) compared the performance of a LTD Stirling engine with a high-temperature differential Stirling engine. They concluded that the LTD Stirling engine efficiency at its rated speed was approximately 50% of the Carnot efficiency. However, the compression ratio of their LTD Stirling engine was approximately equal to that of a conventional Stirling engine. Its performance, therefore, seemed to be the performance of a common Stirling engine operating at a low operating temperature.