Simulation of an oil-pumping ring seal for a Stirling engine

Potentially, the Stirling engine is a more efficient, less polluting replacement for the internal combus tion engine in automobiles, trucks, and buses. However, a critical design problem for this engine is the seal between the working fluid and the lubricat ing fluid. The current approach to solving this problem is to use rolling diaphragm seals to perfect ly separate the working fluid (hydrogen under high pressure) from the lubricating fluid (oil at atmo spheric pressure). The large pressure difference across these rolling diaphragm seals leads to fatigue and failure. This paper reports an investigation of the use of a pumping ring to maintain an oil reservoir on the low-pressure side of the seal. The operation of a pumping ring is simulated, taking into account the axially symmetric unsteady flow in the fluid domain coupled with the elastic distortion of the solid ring. The computer program for solving the mathematical model uses finite differences in the fluid domain and finite-element methods in the solid (pumping ring) domain. The validity of the simulation was checked by comparing its results with analytical solutions for limiting cases. We used the model to investigate the effects of changing various parameters of the ring, such as its geometry, material, rod size and speed, O-ring loca tion, crown spring, and interference fit. Our findings are reported.