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Show The low flow rate, stoichiometric mixture allowed the reaction zone to propagate upstream through the second-stage burner core. This process was monitored visually through the quartz burner walls. As the flame traveled down into the first-stage burner core, the fuel and air flow rates were gradually increased until the desired first-stage equivalence ratio and flow rate was achieved. If a single-stage experiment was to be performed, the start-up sequence was complete. For two-stage experiments, the burner was allowed to reach steady-state operation in the first stage before the second-stage reactants were introduced. Burner operating conditions were chosen to allow comparison of emissions from a single-stage versus a two-stage burner at comparable energy release rates and overall equivalence ratios. Single-stage burner emissions were obtained using the two-stage burner apparatus with no additional fuel or air added to the second stage. For the two-stage experiments, both lean/rich and rich/lean staging configurations were investigated. The fuel and air flow rate in the first stage were calculated from, · air = V1 · tot Y1 1 + ( Pair) ( 4>1 ) Ptuel AFst Y· fuel = y. air ( Pair) (~) 1 1 P tuel AFst (1) (2) where the stoichiometric fuel air ratio is 17.2 for a methane air mixture and the density ratio of air to methane is 1.805. In Equations 1-4, the equivalence ratio (~) is defined as the stoichiometric air/fuel ratio divided by the actual air/fuel ratio. Thus, equivalence ratios less than one represent lean operating conditions while equivalence ratios greater than one represent rich operating conditions. The second stage air flow rate was derived as a function of the ' overall equivalence ratio, the first- and second-stage equivalence ratios (~1 and ~2)' and the first-stage air flow rate, -6- |