Comparison of laser-induced and planar laser-induced fluorescence measurements of nitric oxide in a high-pressure, swirl-stabilized, spray flame

We report spatially resolved linear laser-induced fluorescence (LIF) and planar laser-induced fluorescence (PLIF) measurements of nitric oxide (NO) in a pre-heated, high-pressure (4.27 atm), lean direct-injection (LDI) spray flame. The feasibility of using PLIF in lieu of LIF is assessed with respect to measuring NO concentrations in high-pressure LDI spray flames. NO is excited via the resonant Q2(26.5) transition of the γ(0,0) band while a non-resonant wavelength is employed to subtract background interferences. LIF detection is performed in a 2-nm region centered on the γ(0,1) band. PLIF detection is performed in a 68-nm window that captures fluorescence from several vibrational bands. An in situ NO doping scheme for fluorescence calibration is successfully employed to quantify the LIF signals. However, a similar calibration scheme for the reduction of PLIF images to quantitative field measurements is plagued by the laser-excited background. Excitation scans and calibration comparisons have been performed to assess the background contribution for PLIF detection. Quantitative radial NO profiles measured by LIF are presented and analyzed so as to correct the PLIF measurements to within the accuracy bars of the LIF measurements via a single-point scaling of the PLIF image.