Structural modification and parameter optimization of the piston rod sealing system in a Stirling engine

Abstract

To address the issues of inherent stress concentration in the O-ring and excessive deformation of the thin-walled C-ring in a Stirling engine's conventional cap-type piston rod seal, a novel sealing configuration incorporating a toothed slip ring is proposed to improve structural adaptability. A two-dimensional axisymmetric finite element model was developed to analyse the stress distribution and wear behaviour of the proposed seal under reciprocating motion, and its performance was compared with the original cap-type seal. The results show that under steady-state operation, the maximum von Mises stress in the toothed slip ring was reduced by approximately 45.9% and 54.6% during the forward and return strokes, respectively, and that in the O-ring was reduced by approximately 11.6% and 10.5%, significantly improving the overall stress state of the sealing assembly. Subsequently, distinguishing this work from conventional single-parameter studies, a coupled regression-based design approach was employed to optimise the O-ring compression ratio, the cross-sectional width of the toothed slip ring, and the interference fit. The optimisation results indicate that with an O-ring compression ratio of 15%, a toothed slip-ring width of 0.754 mm, and an interference fit of 0.03 mm, the wear rate at the sealing interface is minimised. Compared to the initial design, this optimal configuration achieves reductions in wear rate of approximately 21.7% in the forward stroke and 8.9% in the return stroke. These findings provide insights and practical guidelines for designing high-performance piston rod seals, minimizing friction-induced damping, and enhancing the service life and dynamic stability of Stirling engines.