The explosion region becomes smaller under flow conditions: the ignition of ethene-air mixtures with a hot surface

The occurrence of explosions in ethene-oxygen-nitrogen mixtures was studied as a function of the gas velocity and of the temperature of the electrically heated wire that served as the ignition source. Experiments were done with ethene in excess, at pressures of 10 and 20 bar, with a catalytic and a noncatalytic wire, with the gas flowing in an upward and a downward direction, and with the wire fixed horizontally and vertically. No influence of catalytic activity could be observed, because of soot deposition. In three distinct operating regimes different phenomena were observed: negligible reaction, local reaction, and explosion. The negligible reaction region occurred at wire temperatures below a critical value which only depended on the contact time of the gas with the wire. It reached a constant value of 670 C at long contact times. At higher temperature either a local reaction around the wire or an explosion occurred. The critical oxygen concentration which separates the local reaction and explosion regimes depended on the gas velocity in the vicinity of the wire.