Under-expanded jet and diffusion characteristics for small-hole leakage of hydrogen-blended natural gas in high-pressure pipelines

Abstract

Hydrogen blending in natural gas pipelines is an economical method of hydrogen transportation, but it can increase explosion risks from leakages. Current leakage models struggle to capture under-expanded jet structures near leakage holes due to limited computational resources and cannot accurately describe explosion hazardous distances of subsequent diffusion. A two-stage model for simulating the leakage of hydrogen-blended natural gas (HBNG) pipelines is introduced, comprising jet and diffusion models. The source strength determined in the jet model serves as the inlet boundary condition for the subsequent diffusion model. The results show that considering the under-expanded jet structure can more accurately reflect the pressure fluctuation changes near the leakage hole, particularly at the location of the Mach disc, xm. The pressure at the 10xm section of the jet region stabilizes at atmospheric pressure and utilizing this value as the inlet boundary for the diffusion model prevents supersonic and oscillatory regions. Subsequently, the impact of pipeline operating pressure, leakage hole diameter, and hydrogen blending ratio (HBR) on the far-field diffusion characteristics is analyzed. Notably, the leakage hole diameter has a more pronounced effect on the explosion hazardous distance compared to other factors. This research provides insights for the prevention and management of HBNG leakage accidents.