Additive influence on ignition of stoichiometric ethylene-air mixture by break sparks

The minimum ignition currents for the stoichiometric ethylene-air mixture diluted with various amounts of argon, nitrogen or carbon dioxide were measured at various initial pressures within 20 and 120 kPa by using break sparks produced between Cd and W electrodes. The baric coefficients of ignition currents were determined from the correlation of minimum ignition currents with the total initial pressure. Compared to the previously reported ignition energies of initiation by high voltage inductive-capacitive sparks, the ignition energies of initiation by break sparks are systematically higher, due to important energy losses appearing at the contact between electrodes. From the minimum ignition currents of ethylene-air-additive mixtures, the maximum experimental safe gaps (MESG) were calculated using an empirical phenomenological correlation reported in literature. The measured minimum ignition currents, as well as the derived ignition energies and maximum experimental safe gaps are discussed in connection with the amount and nature of inert additive of ethylene-air mixtures.