Stability and Emissions of Lean, Turbulent, Premixed Flames with Very Lean Coflow

The potential for improving lean stability and reducing NO x emissions of combustion systems by employing an ultralean, partially premixed fuel injection strategy was examined experimentally. The test cone guration was a coannular combustor cone guration at atmospheric pressure with a simulated natural gas fuel. The core e ow consisted of fuel premixed with air; the coe ow was either fuel premixed with air, sufe ciently lean to be below the e ammability limit, or air only. The e ame was stabilized on axisymmetric, bluff body e ameholders sting-mounted along the centerline of the combustor. Mounting the e ameholder from the inlet end of the combustor resulted in a more stable e ame under lean conditions than was the case for the e ameholder mounted from above the combustor exit. When either e ameholder was located sufe ciently far downstream from the core e ow nozzle tip, an enhancement of lean stability was achieved by increasing the fuel content of the coe ow stream. This change in stability can be accounted for by dee ning an effective equivalence ratio at the e ameholder location that takes into account the presence of coe ow fuel and the core/coe ow mixing. The addition of fuel to the coe ow resulted in up to a factor of 4 lower levels of total NO x compared with the case with fuel in the core e ow only. This decrease in NOx was accompanied by a drop in peak temperature. The total exhaust NO x concentration was comparable for all cone gurations when run close to their corresponding lean limits. These results suggest that changing the distribution of injected fuel can have a benee cial impact on the lean-limit stability and emissions characteristics of turbulent, premixed combustion systems.