Ignition of lean methane-air mixtures by high pressure glow and ARC discharges

Glow and arc discharges have been used to study the spark-ignition of lean quiescent methane-air mixtures at room temperature and a pressure of p =2 bar. The regions of stable long-duration sparks with aluminum, cadmium, copper, platinum and tungsten electrodes as well as the fall voltages and voltage gradients of the positive column have been determined. For both discharge modes the minimum ignition energies and the corresponding quenching distance have been obtained for Cu electrodes at equivalence ratios of 0.59, 0.67 and 0.77. Minimum ignition energies for various electrode materials have been measured at the quenching distance and an equivalence ratio of =0.67. The experimental results indicate that the energy dissipated in the anode and cathode fall is completely lost to the electrodes, whereas the energy of the positive column determines the flame initiation process. These findings are substantiated by spark-flashlight schlieren photographs of the incipient spark and flame kernel.