The Stirling engine is a type of heat engine known as its high efficiency. It is applied in solar thermal power, cogeneration, space nuclear power, and other fields. Although there are many different types of Stirling engines, their airflow paths are always linear. This article designs two types of Stirling engines with loop airflow path: the O-type engines without regenerator and the 8-type engines with regenerator. The modeling and simulation of the O-type engines show its extremely excellent performance compared with the conventional Stirling engine. Because the regenerator is the main loss and power limitation in Stirling engines, O-type engines do not have this limitation. At the same time, its design without regenerator makes it more practical and has greater potential in terms of power. The 8-type engines use its unique 8-type airflow path to allow gas to enter the regenerator in advance, eliminating the almost useless four heat exchanges, resulting in higher thermal efficiency and better robustness.

18pages, 16figures