| OCR Text |
Show NO can also be formed by the prompt-NO route involving the sequence: CH + N2 ~ HCN + N (viii) followed by reaction (vi) and the oxidation of HCN subsequently leading to NO and N2, the latter predominating under lean reaction conditions. If the reaction rate is controlled by reaction (viii) then the rate of formation of prompt-NO, [NO]Pr' is given by (2) where Co = 2 in very lean flames since both the HCN and N can form NO. In s to i ch i omet ri c and ri ch mi xtures the values can be between 1 and 2. If [CH] is formed under these lean conditions by the steps ( (ix), (x), (xi) ) and if 0, OH and H are in partial equilibrium via the reactions or equivalent reactions (xii) and (xiii) then it can be shown that d[NO]Pr Coka kg klO kll kl3 3 / 4 ---Q dt kl23/2 [H20] 3/2 (3) There are a number of uncertainties. Firstly whether partial, radical equilibrium is maintained, secondly the conversion efficiency of HeN to NO which varies with stoichiometry and indeed with [02]' and thirdly the uncertainty about the value of ka. For instance, there are considerable doubts about ka and recent estimates include ka = 4.4 x 1012 (-11060/T) cm3 mol-1 S-1 [6], ka = 6. 1 x 1011 exp(-7000/T) [7], and ks = 1.2 X 1012 exp(- 6844/T) [8]. At a temperature of 1300 K, typical of the present work, this 4 |
