Influence of electrode geometry and spacing on the critical energy for direct initiation of spherical gaseous detonations

Abstract

The paper reports experimental results on the critical energies for direct initiation of spherical detonations using electrical sparks under various electrode geometries and spacings. The results indicate that for large spacings the detailed electrode configurations have no influence on initiation energy. The critical energy per unit length reaches a minimum asymptotic value corresponding to the value found previously for cylindrical detonations. For electrode spacing less than the characteristic explosion length, the electrode geometry has an effect on the initiation energy. The flanged and the pointed needle electrodes form the lower and upper bounds, respectively, for the critical energy for various electrode configurations. For the case of the flanged electrode, significant increase in the critical energy occurs only when the spacing is less than the transverse wave spacing for the mixture itself. For small spacings the critical energy for pointed electrodes corresponds to the value for laser sparks obtained previously, indicating the approach to spherical symmetry. The results indicate that the effects of the electrode geometry are essentially those corresponding to the severity of gasdynamic expansion generated. The gasdynamic effects fall between the cylindrical and spherical symmetries.