Single-pulse laser-induced predissociative fluorescence imaging of OH in swirling methane jet flames

Two-dimensional (2D) single-pulse laser-induced predissociative fluorescence (LIPF) imaging of OH coupled with thermocouple temperature measurement is used to study the flame structure and identify the NOx formation mechanism in swirling methane jet flames operated with three different fuel-air momentum flux ratios. In the upstream of the swirling flame, three major reaction zones are observed from the measured OH images. In addition, two characteristic combustion modes, the fuel jet-dominated flame and the strongly recirculating flame, are also identified from the OH visualization. The measured high OH intensity (superequilibrium OH) and low temperature (less than 1100 K) are identified to be the major sources of prompt NO formation in swirling methane jet flames.