The effects of pre-ignition turbulence by gas jets on the explosion behavior of methane-oxygen mixtures

Most of the previous studies investigating explosion characteristics of combustible mixtures were performed at quiescent state. However, in realistic accidental explosion scenarios, the ignition of the combustible mixture usually occurs under a turbulent environment. In this study, we examine the maximum explosion pressure p_max and explosion time τ_e of CH₄-2O₂ mixtures under the pre-ignition turbulence condition in a spherical closed chamber at a room temperature of 298 K. Turbulence is generated using fluidic jet of three different gases (O₂, CO₂ and N₂) and its intensity is controlled by changing the initial pressure of the gas jet p_J0 (i.e., 200 and 500 kPa) and the explosion chamber pressure p₀ (i.e., 40 and 60 kPa). The dual effects of turbulence and gas dilution on the explosion behavior of CH₄-2O₂ mixtures are investigated in detail. The results indicate that by adding O₂ into CH₄-2O₂ mixture at quiescent condition, p_max increases but the rate of overpressure rise is reduced. By introducing turbulence through gas jets into the combustible mixture, the explosion behavior is affected by both the turbulence and gas dilution. With O₂ injection, turbulence overall enhances the explosion, but the amount of O₂ dilution increases at higher p_J0/p₀ and longer jet duration time (t_J0), rendering the mixture to tend toward fuel-lean side and slow down the explosion rate. The present results also demonstrate that the turbulence effect of CO₂ is more profound than that of N₂ jet. Both p_max and τ_e are enhanced by CO₂ jet turbulence when t_J0 is relative short (t_J0 < 400 ms). However, for longer t_J0, the dominance of CO₂ dilution becomes more noticeably than N₂ dilution with a longer explosion time τ_e.