Using flammable gas characteristics to evaluate spontaneous flame instability in gas explosions

Predicting the behavior of flame propagation is necessary to assess the precise risk of gas explosions. However, due to the two types of spontaneous instability, diffusive-thermal instability and Darrieus-Landau (DL) instability, no one can fully explain the mechanism and what affects the instabilities. To investigate these instabilities, especially DL instability, propane, methane, and acetylene were used to restrain the effect of diffusive-thermal instability. As a result, propane-air and methane-air mixtures showed that experiments with lower Lewis numbers reached higher dimensionless flame velocities more quickly. In contrast, acetylene-air mixtures showed that experiments with higher Lewis numbers and higher expansion ratios were disturbed from the earlier phase. From these results, we concluded that lower Lewis numbers led to diffusive-thermal instability, which was then enhanced by DL instability in propane-air and methane-air mixtures, despite higher burning velocities. In contrast, acetylene-air mixtures are strongly affected by DL instability and the expansion ratio.