Simultaneous single-shot LIF-imaging of OH and UHC in a prevaporized, partially premixed, swirl-stabilized n-heptane flame

The prevaporized partially premixed swirl-stabilized n-heptane flame in an atmospheric pressure combustor is investigated using a tuneable KrF excimer laser. Flashing the flame with a laser sheet tuned to the P₂(8) line of OH (hydroxyl radical) single-shot images of the laser-induced signals are taken simultaneously with two ICCD-cameras aligned to the same measuring volume. One camera detects mainly the laser-induced fluorescence (LIF) from the 3→2 band of the OH plus signals from UHC (unburned hydrocarbons). Only broad-band emission from UHC is imaged onto the other camera. Comparing the two images signals stemming from OH and UHC, respectively, can be distinguished. Pictures taken in various planes along the main flow direction reveal highly turbulent structures in the flame. High fluorescence signals from OH can obviously be found both in filament-like flame fronts lying between fresh combustible mixtures and hot combustion products as well as in broadened reaction regions.