The instability of laminar methane/hydrogen/air flames: Correlation between small and large-scale explosions

Darrieus–Landau (D-L) instability can cause significant acceleration in freely expanding spherical flames, which can lead to accidental large-scale gas explosions. To evaluate the potential of using high-pressure lab-scale experiments to predict the onset of cellular instabilities in large-scale atmospheric explosions, experimental measurements of the cellular instabilities for hydrogen and methane mixtures are conducted, in laboratory spherical explosions at elevated pressures. These measurements are compared with those from several large-scale atmospheric experiments. Comprehensive correlations of the pressure effect on a critical Karlovitz number, $K_{cl}$, together with those of strain rate Markstein number, $M{a}_{sr}$, are developed for hydrogen/air mixtures. The regime of stability reduces for all mixtures, as $M{a}_{sr}$ becomes negative. Values derived from large-scale experiments closely follow the same correlation of $K_{cl}$ with $M{a}_{sr}$. As a result, the extent of the regime where the laminar explosion flames become unstable can be predicted as a function of $M{a}_{sr}$ and pressure.