The Radially Stratified Flame Core Burner a Low-NOx Burner of Novel Type

Results of an investigation to establish the design principles of a 10w-NOx burner of novel design are discussed. The admixing of the combustion air to the fuel is staged by radial stratification in the flame due to the combination of swirling burner air flow and a strong positive radial density gradient. Fuel/air mixing is suppressed close to the burner but is promoted further downstream where vortex breakdown results in the development of a toroidal recirculation zone in the central region of the flame. A flexible experimental burner capable of varying the radial distributions of the combustion air flow and the swirl velocity has been designed and constructed. Computer modeling of the flow, temperature and stable species concentration distributions in natural gas-air turbulent flames guided parametric and detailed experimental studies which were carried out in the 1.2mx1.2mx4.Sm test section of the MIT Combustion Research Facility. Results of experiments showed that by the optimization of the flow in the radially stratified flame core (RSFC) burner, emission levels of 70ppm NOx and 56ppm CO can be obtained with natural gas fuel flames. Further reductions to below 15ppm NOx were obtained when flue gas recirculation and steam injection were added to the aerodynamically optimized natural gas flames.