The Free Piston Stirling Principle as Prime Mover for Alternant Hydraulic Propulsion Systems

The objective of the presented research work is the demonstration of the working principle as energy efficient and environmental friendly, low cost vehicle propulsion system of the free piston Stirling principle coupled with the alternant hydraulic transmission in order to use the alternant displacement of the Stirling principle, also to the hydraulic transmission and convert the alternant movement of the liquid using a free wheel based hydraulic motor. The design methodology considers the advantages of efficiency, noise and low emissions of Stirling principle, that can be further improved by a free piston solution and the advantages of a direct alternant energy transfer to the liquid column that is converted in a free wheel based hydraulic motor. An analytical and 1D multi-domain model is used in order to demonstrate the running principle, performance and parameter influences that allow the simulation of the combined Stirling principle with alternant hydraulic transmission integrated on a vehicle. For the heat transfer and flow simulation of the Stirling prime mover, 3D CFD software is used to simulated the temperature distribution. Experimentally the solution was demonstrated on a test rig and integrated on a ATV type demonstration vehicle equipped with the alternant hydraulic propulsion system. Flow, thermal and mechanical parameters are measured to evaluate overall system performance. The former research work of the authors was focused on the demonstration and performance evaluation of the alternant hydraulic propulsion, being demonstrated its efficiency (up to 95 %), adaptability and low mass qualities. Main advantages of the Stirling principle may be improved by using a proper transmission. Coupling also the transmission based on the same alternant principle is a low cost, simple, efficient way to maintain the advantages of the Stirling energy conversion in the same time with an application of the hydraulic transmission that works also alternant in a more efficient way.