The origin and nature of “prompt” nitric oxide in flames

✍ Scribed by A.N. Hayhurst; I.M. Vince

• Publisher: Elsevier Science
• Year: 1983
• Tongue: English
• Weight: 829 KB
• Volume: 50
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(83)90047-0

✦ Synopsis

Measurements are presented of the quantity of "prompt" NO formed by the addition of small amounts of various hydrocarbons to a wide range of well-defined premixed laminar flames of H 2, 0 2. and N 2. The effect of the following variables has been determined: residence time, N 2 concentration, hydrocarbon additive concentration, flame temperature, stoicheiometry, and identity of the hydrocarbon. The amount of prompt NO produced in most flames is found to be proportional to the concentration of N 2 and also to the total number of carbon atoms present, i.e., "'prompt" NO formation is proportional to the concentration of added hydrocarbon. Also, a molecule ofC2H 2 results in twice as much prompt NO as a molecule of CH 4, etc. This fact, coupled with the observed insensitivity of the yield of prompt NO to both temperature and stoicbeiometry (within limits) fumisbes a simple rule for predicting the quantity of prompt NO in many flames. Complications do occur, e.g.. in very fuel-rich flames, where evidently hydrocarbons can attack NO, as well as produce it.

The observations are consistent with either CH or CH 2 radicals attacking N 2 in or close to the reaction zone in CH + N-, -.-'-HCN + N or CH 2 + N 2 --* HCN + NH. In either case. HCN, NH, and N atoms are all oxidized to NO. The production of CH or CH 2 appears to be by a complete breakup of the hydrocarbon to CHi (i = 0---4) species before oxidation occurs in the reaction zone. The likelihood is that this fragmentation to CHi occurs by pyrolysis of hydrocarbon molecules and attack by H atoms in the preheating region of these flames. The observed quantities of prompt NO are consistent with the known rate of CH originally attacking N 2.