This paper describes stereo-PIV, OH-PLIF and fuel-PLIE (planar laser induced emission) measurements in a pressurized, liquid fueled, swirl combustor. Data were obtained at globally fuel lean conditions, combustor pressures of 2–5 bar, and an inlet air temperature of 450 K. The experiments were performed to characterize the flowfield, heat release and fuel spray distribution. Several challenges are associated with OH-PLIF in pressurized, liquid fuel systems at sustained high repetition rates. For example, in addition to the significantly lower pulse energies of high repetition rate systems relative to low repetition rate ones, the ultraviolet laser used to excite OH also causes the fuel to emit, with the brighter liquid fuel signal overlapping the OH fluorescence spectrum. To overcome these challenges, two intensified high-speed cameras were used to maximize signal separation during data collection and perform signal subtraction in post-processing. The first camera used narrow band spectral filtering, and the intensifier was gated to miss much of the slower decaying fuel signal. As a result, it satisfactorily captures the OH fluorescence along with some of the stronger fuel fluorescence signal. The second camera detected primarily fuel emission with the intensifier gate delayed to capture the tail of the longer-lived fuel phosphorescence, and a long-pass spectral filter capturing all the fuel emission. This paper presents illustrative results showing the instantaneous flow field, flame position as indicated by OH-PLIF, and spray distribution from the fuel PLIE. Multiple flame topologies are observed — specifically, flames stabilized in the outer shear layer occur for all the cases studied, but inner shear layer stabilized flames are also seen in the higher pressure cases.
Confocal Raman imaging of optical waveguides in LiNbO3 fabricated by ultrafast high-repetition rate laser-writing