Experimental observation of the quenching distance of flames propagating in a closed duct at different velocities and with different Lewis and Zeldovich numbers

Abstract

Investigation of the quenching distance is important for the design of flame arresters. The quenching process is related to the coupled effects of heat and mass transfer in reactive flows. The aim of this work is to experimentally determine the quenching distance of flames propagating in a closed duct. The mixtures involve natural gas, hydrogen, helium and air to obtain Lewis and Zeldovich numbers from 0.6 to 1.36 and from 4.24 to 8.45, respectively. In addition, obstacles were placed inside the duct to evaluate the effect of flame propagation velocity on the quenching distance via the Peclet number. The quenching distance was measured as the distance between two horizontal plates that does not allow the flame to continue propagating. The results show that mixtures with Lewis numbers less than one and low values of Zeldovich have the smallest quenching distances. Conversely, mixtures with Lewis numbers greater than one or high Zeldovich values have higher quenching distances. When mass diffusion dominates over heat diffusion, the flame temperature is higher. In addition, the negative exponential dependence of the heat release is controlled by the Zeldovich number. This explains the experimental results. In the experiments where the flame velocity was increased by obstacles, the mixtures with high Zeldovich number increased their quenching distance, whereas the opposite was observed for mixtures with low Zeldovich. The Peclet numbers determined show that advection dominates over heat diffusion. The critical Peclet numbers calculated on the basis of laminar flame velocity were always less than 35.