Quantitative OH concentration measurement using OH(2,0) band bi-directional LIF method for high-pressure and high-temperature symmetrical flames

Abstract

Combustion measurements using laser diagnostics are vital for experimentally revealing both qualitative and quantitative flame characteristics. This paper focuses on the application of the quantitative OH laser-induced fluorescence (OH-LIF) method for high-pressure and high-temperature flames. Under high-pressure conditions, the intense OH chemiluminescence drastically decreases the signal to noise ratio (S/N). However, OH(2,0) band excitation is an alternative method to the typical OH(0,0) or OH(1,0) band excitation LIF under high-pressures. OH(2,0) band LIF sufficiently maintains the S/N under high-pressure because the OH fluorescence can be detected away from the peak OH chemiluminescence wavelength. In addition, the bi-directional LIF method is known as a quantitative OH concentration measurement that can ignore the quenching factor. Therefore, this study proposed a quantitative OH concentration measurement by combining the OH(2,0) band LIF and bidirectional LIF methods for high-pressure and high-temperature flames. First, an H2/air premixed flame created by a McKenna burner under atmospheric pressure was used to validate the quantitative OH(2,0) band bidirectional LIF method. Furthermore, a CH4/O2/N2 oxygen-enriched premixed flame created by a multi-hole calibration burner was used to verify the method under high-pressure (~0.5 MPa) and high temperature (~2900 K) conditions. A comparison of the experimental and numerical results revealed that the calculated OH concentrations were within the experimental uncertainty for the McKenna burner configuration. The experimental OH concentration results under high-pressure conditions deviated approximately 10%-20%, but they were also in good correlation with the calculation. In addition, the qualitative correlations with equivalence ratio and pressure variation were also acceptable. Although further consideration of the method is desirable for high-pressure turbulent flames, the results in this study showed that the OH(2,0) band bi-directional LIF method is feasible for measuring OH concentration in high-pressure and high-temperature flames.

OH(2,0) PLIF Measurement of the Flame Base in High-pressure H₂/O₂ Jet Diffusion Flame up to 5.0 MPa

“…Optical diagnostic methods are important tools for understanding combustion phenomena. While OH-planar laserinduced fluorescence (OH-PLIF) measurements are a laser diagnostic technique widely used to visualize flame structures 1) and quantify physical quantities, 2,3) there are few studies on their use under high-temperature and high-pressure extreme conditions, such as those generated during rocket engine combustion. Under rocket engine combustion condi-tions, the signal-to-noise ratio (S=N) is significantly reduced owing to a combination of excitation line broadening, increased quenching, interference of flame chemiluminescence, and scattered light.…”