Measurement Techniques for High-Pressure, Liquid-Fueled Combustors with High Soot Loading

The primary objective of this Phase-I research effort is to build an ultraviolet (UV) hyperspectral sensor at ~310 nm to perform spatially resolved temperature and OH concentration measurements based on multi-line laser-induced fluorescence (LIF) of OH molecule in reacting flows. The proof-of-the-concept demonstration measurements will be performed in an atmospheric-pressure, near-adiabatic H2-air Hencken burner for various equivalence ratios. The potential of two different concepts of generating UV light using hyperspectral sources will be evaluated. These are: (1) generating UV light by sum-frequency mixing of 5W 532 nm light with a high-power hyperspectral source at ~763 nm in a nonlinear crystal and (2) development of an UV hyperspectral source based on native ultraviolet gain, e.g., using quadrupled Nd:YVO4-pumped Ce3+:LiCaAlF6 or Ce3+:LiLuF4 crystals which can provide broadband gain in the 280-333 nm range. High-bandwidth LIF measurements based on continuous-wave (CW) lasers is limited by the low power output of typical distributed feedback (DFB) diode-lasers used for their construction. Hyperspectral sources will allow generating high-power CW laser-light at the desired frequency, i.e., either at ~763 nm or ~310 nm. This feasibility study will pave the way for designing the optimum UV source for implementation in a high-pressure test-rig at WPAFB during the Phase-II research effort.