Inhibition of hydrogen-air mixtures by using chemical vapor additives

Abstract

Various approaches are being used for the minimization of risk related to hydrogen hazards. The present study highlights the suppression of hydrogen-air explosion using additives (bromoethane and bromopropane) through experimental and theoretical methods. The experiments were carried out with different equivalence ratios (Ф = 0.5–2) and additive contents (3–15%) at 298 K and 1 bar initial conditions. The results indicate the influence of additives on the maximum pressure-rise, minimum ignition energy and burning velocity. Theoretical study was conducted using CHEMKIN and determined the sensitivity analysis, species profile and reaction path analysis. After the explosion, pressure increases at lower additive fractions for fuel-lean and stoichiometric mixtures and decreases at higher additive contents. In fuel-rich mixtures, pressure rapidly decreases with the increasing additive contents. In the presence of additives, the relative pressure-rise rate decreases, while the time to maximum pressure-rise and ignition energy increase are irrespective of Ф. Moreover, the maximum declination of burning velocity reflects at Φ = 2 and 3% of either additive reduces the burning rate almost by half. The sensitivity coefficient decreases for the flame-promoting reactions and increases for the flame-inhibiting reactions. In such reactions, the inhibiting radicals capture the free radicals and cease the flame propagation, resulting in flame suppression. The reactions R788 (C2H5Br + OH = C2H4Br + H2O) and R834 (C3H7Br + OH = C3H6Br + H2O) have a negative reaction sensitivity coefficient that reflects the effect of suppression. The enhancement of the mole fraction of hydrogen bromide (HBr) with additive content signifies flame suppression. The effect of additives on the explosion characteristics indicates that bromopropane is more effective than bromoethane in minimizing hydrogen hazards.