STABILITY AND EMISSIONS OF LEAN, TURBULENT, PREMIXED FLAMES WITH VERYLEAN COFLOW

The potential for improving lean stability and reducing NOx emissions of combustion systems by employing an ultralean, partially premixed fu el injection strategy was examined experimentally, The test configurat ion was a coannular combustor configuration at atmospheric pressure wi th a simulated natural gas fuel. The core flow consisted of fuel premi xed with air; the coflow was either fuel premixed with air, sufficient ly lean to be below the flammability limit, or air only, The flame was stabilized on axisymmetric, bluff body flameholders sting-mounted alo ng the centerline of the combustor, Mounting the flameholder from the inlet end of the combustor resulted in a more stable flame under lean conditions than was the case for the flameholder mounted from above th e combustor exit, When either flameholder was located sufficiently far downstream from the core flow nozzle tip, an enhancement of lean stab ility was achieved by increasing the fuel content of the coflow stream , This change in stability can be accounted for by defining an effecti ve equivalence ratio at the flameholder location that takes into accou nt the presence of coflow fuel and the core/coflow mixing, The additio n of fuel to the coflow resulted in up to a factor of 4 lower levels o f total NOx compared with the case with fuel in the core flow only Thi s decrease in NOx was accompanied by a drop in peak temperature, The t otal exhaust NOx concentration was comparable for all configurations w hen fun close to their corresponding lean limits, These results sugges t that changing the distribution of injected fuel can have a beneficia l impact on the lean-limit stability and emissions characteristics of turbulent, premixed combustion systems.