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Show rich conditions. This represents a response to the fuel rich environment that is independent of the agent. Total unburned hydrocarbons (THC) were measured by a flame ionization detector, and were found to be negligible throughout the stoichiometries of interest. Finally, HCN was also measured, but the values were insignificant. Thus, the apparent role of the rich zone is to supply CO and agent to the burnout point. Fi gure 8 shows a predi cted ti me resolved profi le of the major species for ammonium sulfate addition at SRI = 0.99, SR2 = 1.02 (identical conditions as those of Figure 5). Upstream of the agent injection point the composition has relaxed to equilibrium and the NO concentrations are frozen. At the agent injection point a rapid increase in NH3 is the response from the decomposition of the ammonium sulfate. Most of the NO reduction chemistry occurs immediately downstream of the air staging point. The high rate exhibited by the overall reaction implies that in the experiment the bulk of the NO reduction is accomplished within the mixing zone at the staging point. Note that at an -NINO ratio of 1.5 the model predicts a substantial amount of ammonia bypass. Other modeling has suggested that -NINO ratios near unity will yield high NO reductions with much lower ammonia emissions. Figure 2 illustrates that the presence of the agent at the staging point can yield very high NO reductions. The model suggests that the inherent limitations on lean reduction are overcome for the following reasons. At the staging point CO, 02, and ammonia all co-exist. The CO initiates a chain branching sequence that consists of the following reactions: co + OH = C02 + H H + 02 = OH + 0 o + H20 = OH + OH (26 ) ( 1) (9 ) This sequence provides the OH needed to activate Reaction 50. The weak temperature dependence of Reactions 53 and 54 present no barrier to the subsequent consumption of NO by NH2. The effectiveness of the NO reduction is limited at lower temperatures by the failure of the CO to react. This is in contrast to the results of Fig. 1 in which the low temperature limit was defined by the failure of the ammonia to react. The data of Figs. 5 and 6 show that the amount of NO reduction depends on both the rich zone and lean zone stoichiometry. The kinetic modeling suggests that thi s occurs for related reasons. The principal role of the rich zone is to provide CO for reaction at the burnout point. At the optimum stoichiometry, SR = 0.99, the CO concentration in the rich zone is shown from Fig. 7 to be about 1500 ppm. Upon introduction of the burnout air the CO oxi dation sequence provides only a small excess of OH. The small excess OH is almost completely consumed by Reaction 50. Both the low NH2 concentration and the low OH concentration cause Global Reaction A to proceed at a much lower rate than Reactions 53 and 54. Thus, no effective competition for NO reduction exi sts. At SR = 0.9, the CO concentration at the end of the rich zone is 2.25 percent. This much higher CO value promotes higher radical concentrations (particularly hydrogen atom) during air addition, which causes Global Reaction A to become a competitive sink for NH2. Thus, NO destruction is reduced under these conditions. 1 6 |