Radical recombinations in acetylene-air flames

Abstract

In this paper an analysis is given of the behaviour of excess radical concentrations, H, OH and O as a function of height above the reaction zone in premixed acetylene-air flames at 2–200° to 2400°K and 1 atmosphere pressure. The intensity was measured of the Li resonance line which is related to the H concentration through the lithium-water equilibrium. The OH concentration was measured by absorption of the (0,0) band of OH at 3064 Å. The H, OH and O concentrations are related to one another by rapid, binary exchange reactions with stable flame molecules. A rather elaborate but complete mathematical expression is derived, which takes into account (i) the four recombination reactions H+H, H+OH, O+O and CO+O, and the reverse reactions; (ii) the variation of stable molecule concentrations due to radical recombination; (iii) the effect of varying temperature on the flame equilibria. The experimental results were found to be consistent with theory. By making use of some additional literature data it appeared that the decay of excess radicals in our flames is mainly governed by H+OH and (to a less extent) CO+O recombination. The binary rate constant jor the first reaction, which was found in this investigation to equal (1·3±0·4)×10−13cm3sec−1, agrees with literature data obtained in hydrogen flames. As a side result of this investigation the dissociation energy of LiOH was found to be 110±5 kcal/mol which narrows the uncertainty in this quantity when combined with two other values reported in the literature.