Experimental study on liquid piston Stirling engine combined with self-rectifying turbine

A liquid piston Stirling engine is an external combustion engine that uses air and water under atmospheric pressure as its working fluids. Resulting from its uncomplicated design and the capacity to operate under relatively low temperature differentials of less than 100 °C, it has attracted considerable attention in recent years. This paper presents the fundamental characteristics of the liquid piston engine combined with a self-rectifying turbine for the advancement of thermal generators. When the turbine is installed in the water region rather than in the air region, it exhibits unidirectional rotation with a rotational speed directly proportional to the velocity amplitude of the reciprocating axial flow. Additionally, the acoustic impedance within the duct section containing the turbine is determined, demonstrating that the real part of impedance rises with increasing axial velocity, indicating a loss mechanism similar to the minor loss. Furthermore, the installation of the turbine results in a breakdown of symmetry in the engine oscillation mode. To maintain symmetry and improve system design, future developments must consider the installation of a turbine in each unit. These findings can pave the way to the design of liquid piston Stirling engines and their applications in thermal energy conversion.