Premixed jet flame behavior in a hot vitiated crossflow of lean combustion products

Improvement in NO_x emissions from gas turbine combustors requires development of safe and reliable lean-premixed combustion systems. In this paper, the flame stabilization behavior of a premixed ethylene–air jet injected normal to a hot vitiated crossflow (JICF) of lean combustion products was studied experimentally. The equivalence ratio of the premixed jet was varied from lean to rich conditions. Measurements of the flame were conducted using high-speed chemiluminescence imaging and simultaneous particle image velocimetry (PIV), hydroxyl (OH) and formaldehyde (CH₂O) planar laser-induced fluorescence (PLIF). From the PLIF measurements, pixel-by-pixel multiplication of OH and CH₂O fluorescence signals was conducted to estimate the heat release zone of the JICF flame front. The unsteady windward flame exhibited both attached and lifted flame behavior, while the leeward flame branch remained consistently attached to the jet exit. When the windward flame was lifted, chemiluminescence imaging showed that both flame propagation and auto-ignition kernel formation contributed to flame anchoring. From the PLIF imaging, formaldehyde signal was observed upstream of the lifted windward flame base, suggesting pre-ignition behavior due to mixing between the jet reactants and the hot crossflow. The windward flame base was always in the jet shear layer and the trailing flame remained in the shear layer under lean conditions but traversed the shear layer into the bulk jet flow for stoichiometric and rich conditions. Alignment between 2D dilatation and heat release was seen to vary depending on the location of the flame relative to the shear layer. Two-dimensional dilatation and heat release location aligned best when the flame resided away from the shear layer, where jet and crossflow mixing and out-of-plane motion are minimal.