Experimental and Theoretical Analyses of Deflagrations of Mixtures Involving Hydrogen Enrichment and Helium Dilution Inside a Closed Duct

The aim of the present work is to analyze experimentally and theoretically the deflagrations in a closed duct of mixtures in which natural gas is enriched with hydrogen or diluted with helium. In the first case, hydrogen would increase the flame propagation velocity, while in the second case, helium should make the mixture less reactive. The characterization of these mixtures is carried out with the help of Lewis ( Le ) and Zeldovich ( Ze ) numbers. Therefore, eight mixtures were considered. These mixtures covered a Le interval from 0.60 to 1.36 and a Ze interval from 4.24 to 8.45. Moreover, the mixtures involved species such as natural gas, hydrogen, helium, and air. It was observed that higher dimensionless flame tip velocities were obtained for mixtures with Le below unity. For mixtures with similar Le numbers, it was observed that lower Ze numbers produced higher velocities. A theoretical model available in the literature was applied and compared with the experimental data obtained in the present work for the dimensionless flame speed. It was noticed that the model presented greater discrepancies for mixtures with Le different from unity. The model was also applied to predict the evolution of the dimensionless flame tip position and was compared with published experimental data. Inaccuracies were observed for this comparison. In addition, two possible modifications of the existing theoretical model for determining the evolution of the dimensionless flame tip position are presented and validated in this paper. One of them showed good accuracy.