A unique burner consisting of a pressure swirl atomizer, a converging outer shroud, a coaxially assembled converging splitter, and coaxial swirlers at the inlets of the inner and outer circuits is being developed for low-NOx emissions (below 0.5 g/kg-fuel) at the higher inlet air temperatures and better flame stability at the lower inlet air temperatures. Liquid fuel is atomized only into the air flowing in the inner circuit and the resulting mixture jet is injected into the combustion chamber from the exit of the splitter, surrounded by the annular swirling air jet from the outer circuit. Emissions measurements, direct flame imaging, and Mie scattering imaging of the sprays were conducted for inner swirler vane angles of 40 and 50 degrees and a fixed outer swirler vane angle of 45 degrees at inlet air temperatures of 453 to 753 K (a 100-degree step) and atmospheric pressure. A lifted flame was stabilized with the flame front at a distance from the burner exit. Direct flame images were successfully used to correlate the NOx emissions with flame structure. Additionally, local gas sampling was done at 753 K. The measured distributions of equivalence ratio and of chemical species concentrations in the combustion chamber were used to explain the lower NOx emissions for the smaller vane angle.
