Flame acceleration and blast wave of H2–O2–N2–Ar mixtures in unconfined areas

Abstract

In the present study, the flame acceleration and blast wave of H2-air and H2–O2–N2–Ar mixtures in nearly unconfined conditions were investigated conducting laboratory-scale and large-scale experiments. In particular, the effect of the volumetric expansion ratio on the flame acceleration examined, because Darrieus-Landau instability is essentially caused by a volumetric expansion of burned gas at flame front. Results demonstrated that the critical Péclet number Pec for the onset of flame acceleration decreased with the decrease in the equivalence ratio and the increase in the expansion ratio diluted with Ar. The dimensionless burning velocity increased as the flame radius became larger. The acceleration exponent for H2-air and H2–O2–N2–Ar mixtures was evaluated. The saturation of the exponent corresponding to the fractal dimension for only very lean H2-air flame is observed, notwithstanding the value for other mixtures still existed in the transition regime. The blast wave intensity of H2-air and H2–O2–N2–Ar explosion discussed by the acoustic theory. From the analysis, it is clear the blast wave intensity depends on the expansion ratio, laminar burning velocity and flame acceleration.