Effect of Selective Diffusion on Quenching Distances of Flammable Gases

Abstract

Quenching distances have been measured between parallel electrode flang es (Fig.1) for methane through heptane (Fig.2), diethyl ether, ethylene oxide (Fig.3), and carbon monoxide (Fig.4). For each of these gases, the value of equivalence ratioΦ_d, has been de termined which corresponds to the minimum quenching distance (Table 1). It has been found that the value of Φ_d is smaller than the equivalence ratioΦ₁, which gives the smallest value of the minimum ignition energy of the gas (Table 2 and Fig.5), the ratio being approximately 1.55, and that the value is about the same as or a little larger than the equ ivalence ratioΦ_xwhich corresponds to the mean concentration of the flammable range of the gas (Tab le 2and Fig.5), where the ratio is 0.95. These findings can be explained in terms of the flame size used in measuring each of these quantities. However, the latter correlation becomes faulse if the corresponding fuel can sustain cool flame or other unusual burning (Fig.5), because the flammability limit (in particular the upper limit) is affected by these phenomena (Table 3) while the value of Φ_d, does not seem to be. If the quenching distances and the flammability limits are measured for downward propagation flames, effect of selective diffusion on their values may become small (Table 4).