Excitation strategy and experimental validation of nitric oxide laser-induced fluorescence diagnostics in high-enthalpy flow

High-enthalpy flow is characterized by low number density and a wide temperature range, which pose significant challenges for nitric oxide laser-induced fluorescence (NO-LIF) measurements. Selecting a suitable excitation wavelength is both important and challenging. To address the lack of systematic excitation wavelength selection for NO-LIF diagnostics in high-enthalpy flow, this paper develops an excitation wavelength selection strategy based on the flow environment and the spectral characteristics of NO molecules. This strategy uses an excitation wavelength quality factor S(λ, T) to evaluate the performance of each rotational line in the γ(0, 0) band at different temperatures, including fluorescence intensity, temperature sensitivity, and absorption attenuation. Moreover, this factor can be feedback-corrected according to experimental results, thereby meeting the requirements of various flow diagnostics. Validation tests were conducted in the high-enthalpy flow of an arc-heated wind tunnel. The results show that the excitation wavelength selected based on this strategy exhibits excellent performance in fluorescence intensity, temperature sensitivity, and absorption attenuation.