Intrinsic Cellular Instabilities of Hydrogen Laminar Outwardly Propagating Spherical Flames

In this study, the influences of pressure, temperature and equivalence ratio on the onset of cellular instabilities in premixed hydrogen/air laminar flames were studied using a constant volume fan-stirred combustion vessel. The onset of instability is marked by the critical stretch rate, at which the flame speed rapidly deviates from its prior response to stretch. It is noted that the critical Peclet number, Pecl, increases with increasing both equivalence ratio and temperature, indicating a more stable flame. Whilst, Pecl decreases with increasing the initial pressure due to the associated decrease in the flame speed Markstein number, Mab with increasing pressure. Empirical correlations of Pecl and Kcl, as a function of Mab, pressure, temperature, and equivalence ratio are developed and presented. Such correlations can be employed to estimate the severity of large-scale atmospheric hydrogen flames.