On the dynamics of drifting flame front in a confined chamber with airflow disorder in a methane-air mixture

Abstract

When the flame wave passes through obstacles or facilities in confined spaces, it causes airflow disorder. As the flame wave is immersed in the flow field, it can no longer sustain an ideal spherical shape but presents a constantly developing asymmetric flame wave in the flow. Although the mechanisms governing the ideal explosion process have been explored, not much is known about the complicated mechanism of drifting flame front caused by airflow disorder. The perturbation of axial jet gas is used to simulate the airflow disorder effect, and the reflected flame wave in the final stage of explosion under jet gas is reported. The results show that with the elapsing of time since ignition, the propagation behavior of drifting flame front can be identified by three categories: left-direction-propagation-flame (LPF), right-direction-propagation-flame (RPF) and right-direction-reflected-flame (RRF). The maximum rate of pressure increase is 49.26 MPa/s, compared to 20.45 MPa/s for the case without airflow disorder (φ = 1.08 and the initial pressure is 100 kPa). It is speculated that the LPF leases heat into the mixture, increasing the mixing and mass transmission between the reactant and product and promoting the explosion hazard. In addition, after its head-on collision with the chamber inner wall, the RRF is formed, and its heated flame front greatly accelerates the heat and mass transfer process. The flame speed under quiescent conditions is 3.14 m/s. Under the effect of airflow disorder, the flame speed constantly accelerates to 7.4 m/s, which benefits from the enhanced mixing effect of the jet. Under the inertia effect of flow, the speed of the LPF varies from −10 m/s to −22 m/s, and the RRF fluctuates from 6.47 m/s to 16.08 m/s, both of which are much faster than that with no airflow disorder. Our findings fill the gap in the mechanism of drifting flame front caused by airflow disorder from experimental verification, and the results may provide a new understanding of methane explosion under more realistic conditions.