Engineering Application of Oxygen Laser-Induced Fluorescence Temperature Measurements in Aerodynamic Flows

Oxygen laser-induced fluorescence was studied experimentally to quantify significant error and uncertainty sources and to evaluate the technique feasibility for gas temperature measurements in the 1-6-atm, 300-500-K regime. The dominant uncertainty source is quantum noise. For low-speed flows, the dominant error source is nonlinear process errors originating from oxygen ion fluorescence and saturation. For flows where the pressure is unknown or variable, collisional quenching may introduce an additional error up to 3 K/atm. For high-speed flows above 300 K, the dominant error source is the slow vibrational relaxation time of oxygen molecules. The optimum experimental conditions are determined by budgeting the allowable temperature inaccuracy to various uncertainty and error sources. In general, the nonlinear process errors limit the laser fluence that may be used, and the quantum noise determines the minimum number of laser shots per measurement.