Abstract

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 pmax and explosion time τe 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 pJ0 (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, pmax 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 pJ0/p0 and longer jet duration time (tJ0), 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 pmax and τe are enhanced by CO2 jet turbulence when tJ0 is relative short (tJ0 < 400 ms). However, for longer tJ0, the dominance of CO2 dilution becomes more noticeably than N2 dilution with a longer explosion time τe.