STRUCTURE RELIABILITY ANALYSIS OF A NEW FREE PISTON EXPANDER

asme-orc2015 Tracking Number 72

ABSTRACT A new free piston expander coupled with liner generator (FPE-LG) was proposed, which can be used as a thermo-electric conversion device for organic Rankine cycle (ORC). Compared to other expanders, the free piston expander (FPE) is more suitable for engine exhaust waste heat recovery owing to variable compress ratio and compact-simple structure [1]. A novel inlet/outlet control mechanism was designed for FPE and a FPE-LG prototype was manufactured [2]. In this paper, mechanical structure simulation about valve control mechanism (VCM) of the FPE was carried out, which has a significant impact on the FPE performance. Based on elastic mechanics theory and finite element method, more precise simulation results about stress distribution of the VCM was obtained through transient structural module in Ansys14.5. Subsequently, the FPE was experimentally validated in the air test rig before it is connected into whole ORC system. The results show that the maximal stress is 1.2e6 Pa between sliding block and cam disc in design condition which can be eliminated through heat treatment. The stress on the valve reaches 5.8e8 Pa that exceeded its allowable stress when the FPE worked at input frequent 6Hz. FPE prototype with VCM can realize the suction, expansion and discharge processes properly in the air test rig. The FPE can work stably in a relatively wide range of servo motor input frequency from1Hz~4Hz.The theoretical basis for mechanism performance optimization can provide a good reference value for next generation FPE and further validation of the FPE-LG in the ORC system will be conducted in the near future.