Potassium and sulfur interactions in hydrocarbon flames : an application to the CFFF secondary combustor

Potassium concentration and OH concentration measurements were made in the post flame gases of methane/oxygen/nitrogen flames seeded with potassium. Sulfur was added to some of the flames. These concentration measurements were used to investigate the finite rate chemistry of potassium and sulfur at high temperature. A new potassium oxidation mechanism has been developed herein based on this data for flames with no added sulfur. This mechanism is a modification and extension of the model discussed by Slack, et al [20] and Hynes, et al [18]. Potassium 'catalytically' consumes flame radical, like OH, primarily through two termolecular reactions: K + O₂2 + M ⇔ KO₂ + M (1) K + OH + M ⇔ KOH + M (2) and a handful of bimolecular reactions, most importantly KO₂ + O ⇔ KO + O₂ (6) KOH + H ⇔ K + H₂O (16) KO + H₂O ⇔ KOH + OH (17). The catalytic cycle includes the channel K ⇒ KOH ⇒ K via reactions (2) and (16) and the alternate path; K ⇒ KO₂ KO ⇒ KOH ⇒ K via reactions (1), (6), (17), and (16). The latter path is particularly important in fuel-lean flames. In flames with added sulfur, it was found that the post flame chemistry was still governed by reactions (1), (2), (6), (16) and (17). However, reactions of the flame radicals with sulfur compounds H + SO₂ + M ⇔ HOSO + M (34) H + HOSO ⇔ H₂ + SO₂ (36) OH + HOSO ⇔ H₂O + SO₂ (37) perturbed the potassium species in the post flame. Reactions between potassium and sulfur species are required to explain the concentration data in the fuel-rich flames investigated. The reactions K + SO₂ + M ⇔ KSO₂ + M (48) KSO₂ + OH ⇔ KOH + SO_{2,/sub> (53) Are analogs of reactions (34) and (37). These reactions open an alternate channel between K and KOH through KSO2 in fuel-rich flames. The potassium/sulfur reaction mechanism develop herein was applied in a simple model the MHD combustion system and adequately explained the ignition behavior in question.}