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The influence of pressure and environment on urban polyethylene (PE) gas pipeline makes structural deterioration and leaking to the pipeline and pipeline easy. This paper proposes an analysis method for optimizing Variational Mode Decomposition (VMD) algorithm. Firstly, the optimal bandwidth is obtained by using the adaptive weighted frequency band entropy (AFBE), and the optimal quadratic penalty factor is obtained by curve fitting. Then, the AFBE is used as the fitness function, and the optimal decomposition level is obtained by the optimized beetle whisker search algorithm. Experimental results show that the signal-to-noise ratio (SNR) is improved by 12.74% on average. [ABSTRACT FROM AUTHOR]

In order to reduce the power of methane explosion in natural gas pipelines and effectively improve the explosion suppression efficiency of a single explosion suppressant, we carry out the explosion suppression of HFC‐227ea/carbon dioxide mixed gas as well as mixed gas/ultrafine water mist through a self‐built methane explosion suppression experimental platform. Based on the changes in parameters such as explosion overpressure, flame propagation velocity, and flame propagation structure, the coupling mechanism of methane explosion suppression between mixed gases and between mixed gases and ultrafine water mist is revealed, which provides scientific support for promoting the development of methane explosion suppression technology. The experimental results show that when the mixed gas HFC‐227ea/carbon dioxide and ultrafine water mist synergistically suppresses methane explosion, the addition of the mixed gas can effectively improve the suppression effect of ultrafine water mist on methane explosion. [ABSTRACT FROM AUTHOR]

In order to explore the influence of the side duct position and venting position on the premixed combustion and explosion characteristics of methane/air, a premixed combustion and explosion experiment of methane/air and a simulation of an explosion of the same size were carried out in a tube with an internal size of 2000 mm × 110 mm × 110 mm. The results showed that the side duct could change the flame structure and accelerate the flame inside the tube. The maximum increase ratio of the flame propagation speed was 106.1%. The side duct had a certain venting effect on the explosion pressure. For different position cases, when the venting film was placed over the bottom section, the maximum overpressure first decreased and then increased. When the venting film was placed over the middle section and the top section, the maximum overpressure first increased and then decreased, and the change trend of the top section was stronger. Turbulence mostly occurred inside the side duct when the venting film of the side duct ruptured. There is no linear relationship between the maximum flame propagation velocity within the tube and the maximum turbulent kinetic energy inside the side duct. The two had a relationship that could be fitted to the Gauss function; the correlation coefficient R2 was 0.836, and the minimum value was at (4767.72, 17.918), suggesting that the side duct had the best venting effect on the flame inside the duct at this maximum turbulent kinetic energy. The analysis results of the influence of the location of the vent on the maximum flame propagation velocity inside the tube are helpful for optimizing the layout design of the underground space, reducing the combustion efficiency, and ensuring the safety of the process. [ABSTRACT FROM AUTHOR]