Initiation of electrically augmented flames

Abstract

A study has been made of the voltage required to initiate an electrically augmented propane-air flame between a copper anode and a pointed graphite or tungsten cathode. The voltage was applied as a ramp input of less than 30 V S−1. The initiation voltage, which varied between 1200 and 2000 V, was measured at propane concentrations of 3·2 to 6·3% and electrode gaps of 0·4 to 1·8 cm, with total gas throughputs of between 525 and 1400 cm3 S−1.The minimum initiation voltage occurred at the stoichiometric propane-air ratio, that is at the highest flame temperature, and decreased with increasing gas velocity. The use of a propane-oxygen-argon mixture of equivalent composition to a propane-air mixture resulted in a 40% reduction of the breakdown potential. The voltage reduction with argon rather than nitrogen as the diluent gas is attributed to the lower heat capacity and breakdown potential of argon, relative to nitrogen. High-speed photographs of the initiation and the discharge path are presented which showed that the discharge initiated from the cathode and developed in approximately 2 ms to a discharge of 6-10 A.