Molecular beam sampling of H 2CO and NO in one-atmosphere methane-air flames

Abstract

A one-atmosphere premixed methane-air flame was studied using a molecular-beam mass-spectrometer sampling system. For equivalence ratios of 0.8, 1.0 and 1.1, the signal intensity at m e = 30 was measured along the burner centerline from the flame holder ( z = 0) to z = 100 mm. Two distinct reaction regions were found: a primary reaction zone, which occupied approximately the first 4 mm, and a secondary reaction zone, which occupied the rest of the sampling distance. A distinctive peak corresponding to the formation and consumption of H 2CO defined the primary reaction zone. Nitric oxide was formed in the secondary reaction zone. The measured rate of formation of NO is compared with theoretical predictions based on a modified Zeldovich mechanism. The data discount the formation of “prompt” NO.