Chronology and topography of sparks at minimum energy for ignition

Abstract

Microsecond exposure schlieren observations of ignition kernels and developing flames are reported for a set of minimum energy conditions holding for electrostatic spark ignition of 8·5 percent methane-air mixtures at 0·1 atmosphere initial pressure. Time of appearance of a flame and the extent of influence of the shock wave generated by the electric discharge were determined experimentally. A time of appearance investigation has also been reported by Lintin and Wooding; their mixtures ere at one atmosphere initial pressure. Comparison of the two results then gives an estimate of the effect of pressure upon time of appearance. This investigation indicates that the time of appearance of the flame varies inversely with initial pressure and also indicates that only a small portion of the original stored energy is caused to be dissipated outside the ignition kernel as a consequence of the shrok wave.