Piston ring assembly of a new symmetrical multi-stage wobble-plate compressor

Abstract

A new compressor design for a natural gas Home Refueling Appliance (HRA) as an equipment for a slow fill of Natural Gas Vehicle (NGV) usage has been developed. It is known as the Symmetrical Multistage Wobble-plate Compressor. This compressor was designed for a high compression gas that requires oil-free piston ring assembly in the cylinder to minimise contamination in order to maintain the purity of the natural gas. The goals of this research were to develop, design, analyse, and test an oil-free Piston Ring Assembly (PRA) for this new compressor. Through this research, the material selection and process of designing the piston ring assembly and considerations taken for this new compressor were explained. To function as an oil-free piston ring material, Polytetraflouroethelyne (PTFE) and Polyetheretherketone (PEEK) as polymer material was selected. The performances of these materials were evaluated using a laboratory scale reciprocating sliding test. Finite Element Analysis (FEA) was used as an effective tooling to analyse the component design of the piston ring assembly numerically. Symmetrical multi-stage wobble-plate compressor prototype with the proposed piston ring assembly was developed and tested successfully on a test rig which was built for this purpose. The results met the design requirement with 3 bar of suction pressure, 260 bar of discharge pressure (more than the specified discharge pressure of 250 bar), 1 m3/hr of flow-rate, and 1000 rpm of rotational speed. The tests and results presented in this study were preliminary tests by using air as the working fluid to replace the natural gas in compression process. The results of this test in this study showed that the proposed piston ring assembly is able to produce and withstand the extremely high pressure of about 250bar. The real tests processes on natural gas were conducted utilising all the experiences and lesson learnt from that of air.