OCR Text |
Show identical mech ani sm as in Fig. 1. In both cases NO reduction is achieved by the introduction of an agent into a fuel lean environment at 9000 C. These results have some similarities with those reported by Johnson et al. 30 Johnson finds significant NO reduction can occur during staging, tne eTficiency of which is temperature dependent. This is attributed to the presence of HCN in the rich gas, which converts to amine species during staging and subsequently reacts with NO. In the present experiment the reduced nitrogen is artifically introduced prior to the leanout point. The i n flu e n ceo f the fin a 1 s to i chi 0 me try iss how n i n Fig. 6. In th e s e tests the first zone stoichiometry was 0.9 and 0.99, and the burnout air was an 02/N2 mixture. The mixture composition was adjusted to provide the varying final oxygen levels shown on the figure while holding the total molar flow rate constant. The solid symbols represent exhaust NO values under staged conditions without agent addition. The open symbols show the exhaust NO with an ammon ium sulfate solution spray. The reduction is favored by low excess air at either first zone stoichiometry. DATA INTERPRETATION The detailed kinetic model was used to generalize the results to other con d i t ion san d to i de n t i f y the con t roll i n g me c han isms. The mode 1 1 i n e 0 f Fig. 1 is for anmonia injection. This fuel-lean reduction chemistry is well understood 24 and is dominated by the following reactions: NH3 + OH = NH2 + H2O (50) NH2 + NO = N2 + H2O (54 ) NH2 + NO = NNH + OH ( 53) NNH + M = N2 + H + M (45) H + 02 = OH + 0 ( 1) o + H2O = OH + OH ( 9) NH2 + 0, 0 = = NO (Global A) (Global A rep re sents Reactions 51, 52, 56, and subsequent reactions leading to NO.) The optimum temperature for NO removal is defined by the balance between the chain branching of Reactions 1, 9, and 45, and chain termination due to recombination reactions and the combined effect of Reactions 50 and 54. At lower temperatures the recombination reactions become relatively favored, preventing the development of a self sustaining reaction. At higher temperatures, the abundance of chain carriers causes Global A to compete with Reactions 53 and 54 for NH2. When the reducing agent is added under fuel rich conditions a very different environment exists at the burnout point. Figure 7 shows detailed measurements obtained at the exit of the rich zone under the conditions of Fig. 5. These were obtained to characterize the environment under which the reduction reaction occurs. The CO increases from 1500 ppm at SRI = 0.99 to 2.25 percent at 0.90. This increase in CO represents over an order of magnitude change in the amount of fuel available for reaction at the burnout point. The N concentration in the rich zone decreases with increasingly 1 3 |