Beschreibung:
A fuel-rich, methane–oxygen, premixed flame at atmospheric pressure was doped with 0.2 mol% of OCS. More than 40 different sulphurous cations were observed in the mass range < 100 u by sampling the flame into a flame-ion mass spectrometer. Ion concentration profiles along the flame axis are presented, together with mass spectra at fixed points in the flame. In the reaction zone, primary sulphur ions CHxS+ (x = 1, 3, 5) undergo extensive ion–molecule reactions (association and condensation) with CH4/CH3, C2H2, and OCS to form a considerable variety of secondary sulphurous cations. Just downstream of the reaction zone, the ion chemistry is somewhat different; it appears to be dominated by reactions of primary sulphur ions including HxS+ (x = 0–3) with C2H2 present as an intermediate. A few ions (HxS+, OS+, S2+) persist throughout the burnt gas region in equilibrium with the natural flame ions CHO+ and H3O+. These sulphurous cation signals show the evolution of the sulphur chemistry, both ionic and neutral, through the flame reaction zone into the burnt gas downstream where H2S, not SO2, is the major product in fuel-rich combustion.