Quantitative imaging of OH concentrations in a swirling methane jet flame via single-pulse laser-induced predissociative fluorescence

Yei-Chin Chao; Der-Chyun Wu; Tsarng-Sheng Cheng

doi:10.1117/12.337486

22 January 1999 Quantitative imaging of OH concentrations in a swirling methane jet flame via single-pulse laser-induced predissociative fluorescence

Yei-Chin Chao, Der-Chyun Wu, Tsarng-Sheng Cheng

Author Affiliations +

Proceedings Volume 3535, Advanced Sensors and Monitors for Process Industries and the Environment; (1999) https://doi.org/10.1117/12.337486
Event: Photonics East (ISAM, VVDC, IEMB), 1998, Boston, MA, United States

Abstract

A quantitative imaging method using 2D single-pulse laser- induced predissociative fluorescence (LIPF) of OH concentrations is developed to study the flame structure in a swirling methane jet flame. A narrowband tunable KrF excimer laser is used to excite the P₂(8) rotational line of the A²(Sigma) implied by (Chi) ²(Pi) (3,0) transition at (lambda) equals 248.46 nm. Though this transition produces a relatively weak signal, LIPF is much less sensitive to collisional quenching in atmospheric flames and suitable for generating quantitative data. OH concentration data are obtained by careful calibration against the flat flame burner data of known fuel-air equivalence ratio and temperature using identical optical setup. In this experiment, the OH fluorescence signal is imaged onto an intensified CCD camera. Since the distribution of OH concentration has good correspondence with the flame, the measured 2D imaging of OH indicates the instantaneous shape of the reaction zone. In the present experiment, the flame structure is first identified from the flame visualization. In the upstream of the swirling flame, combustion is found to take place in two regions; the recirculation vortex inside the recirculation bubble and the thin layer between and the thin layer between the recirculation zone and the ambient air. Higher intensity of OH is found early in recirculation zone. It is superequilibrium OH, because its intensity is higher than that from the recirculated burnt gas and the measured temperature is low. The measured OH concentrations have a direct influence on flame stabilization and NOx pollutant formation.

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Yei-Chin Chao, Der-Chyun Wu, and Tsarng-Sheng Cheng "Quantitative imaging of OH concentrations in a swirling methane jet flame via single-pulse laser-induced predissociative fluorescence", Proc. SPIE 3535, Advanced Sensors and Monitors for Process Industries and the Environment, (22 January 1999); https://doi.org/10.1117/12.337486

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KEYWORDS

Combustion

Luminescence

Temperature metrology

Methane

Calibration

Nitrous oxide

Laser induced fluorescence

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