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

摘要

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 tau(e) of CH4-2O(2) 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 (O-2, CO2 and N-2) 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 P-0 (i.e., 40 and 60 kPa). The dual effects of turbulence and gas dilution on the explosion behavior of CH4-2O(2) mixtures are investigated in detail. The results indicate that by adding O-2 into CH4-2O(2) 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 O-2 injection, turbulence overall enhances the explosion, but the amount of O-2 dilution increases at higher p(J0)/p(0) 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 N-2 jet. Both p(max) and tau(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 N-2 dilution with a longer explosion time tau(e).