Some aspects of ignition by localized sources, and of cylindrical and spherical flames

Abstract

The time dependent conservation equations govering flame propagation in clinidrical and pherical systems have been set up and solved by finite difference methods for the case of a 60% hydrogen-air flame. By this means it is possible (a) numerically to follow the sequence of events following an “ignition” at the axis of a cylinder or the center of a sphere, or (b) to investigate the effect of flame curvature on burning velocity and other flame properties. It was found that the minimum ignition energy depended on the form in which the energy was supplied. For a constant total energy, ignition was facilitated by increasing the proportion supplied as H atoms rather than as thermal energy. The velocities of movement of the freely propagating flames from the ignitions were found to be slightly different from thosed of the inward propagating, cylindrical and spherical stationary flames. The velocities of the latter were independent of the flame diameter. The effect of curvature on the flame properties is shown to be an effect on reaction rate distribution, which also leads to differences in H atom concentrating profiles. Unlike the situation in planar flames, the detailed structure of freely propagating curved flames may not be the same as that of the corresponding stationary flames, and this may lead to the apparent differences in burning velocity.