A comparative study of chlorine and bromine species addition on the explosion limits of hydrogen-oxygen mixtures

In this work, we investigate the effects of chlorine (Cl) and bromine (Br) containing species additions on the pressure-temperature explosion limits of hydrogen-oxygen (H₂-O₂) mixtures computationally. It is shown that, with the addition of HCl, Cl₂, HBr and Br₂, the explosion limit evolves from being a non-monotonic Z-shaped curve to monotonic or maintains its non-monotonic response depending on the different types of additives. Specifically, with the addition of HCl to the mixtures, the limit always maintains the non-monotonic structure, while with the addition of around 18% of Cl₂, it loses its Z-shaped structure. Compared with HCl and Cl₂, more sensitive responses were found for HBr and Br₂. With the addition of around 1% of HBr and 0.7% of Br₂ to the H₂-O₂ mixtures, the limit's non-monotonic feature disappears rapidly, and becomes a monotonic curve. Further detailed kinetics analysis explains that after the addition of the halogen species, the radical competitions are different at the low- (P = 1.0 × 10² Pa), intermediate- (P = 1.0 × 10⁴ Pa) and high- (P = 1.0 × 10⁶ Pa) pressures respectively, resulting in the change of the dominant reactions. These findings enhance the understanding of Cl and Br containing species sensitization for the explosion limits of the H₂-O₂ mixtures and help to understand the kinetic interaction between the H₂-O₂ system and halogen.