Control of confined nonpremixed flames using a microjet

Industrial burners, such as those used in materials processing furnaces, require precise control over the flame length, shape, and other physical flame attributes. The feasibility of hydrodynamic control of confined nonpremixed flames was studied by injecting air through a high-momentum microjet. A novel strategy for the control of flame shape and luminosity was demonstrated based on a high-momentum coaxial microjet injected along the center of a confined nonpremixed flame burning in a coflowing oxidizer stream. The introduction of the microjet shortened a nonpremixed flame and reduced the amplitude of the buoyancy-induced flickering. For a microjet-assisted flame, the flame length was more sensitive to the fuel flowrate than for laminar or turbulent nonpremixed flames. This provided greater flexibility for the dynamic control of their flame lengths. Measurements of NO x and CO emissions showed that the method is robust. Effective flame control without an emissions penalty was possible over a large range of microjet velocities that significantly alter the flame shape. Since the influence of the microjet is primarily of a hydrodynamic nature, inert microjet fluids could be used. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).