The imaging experiment of Methylidyne (CH) radical generated from methane combustion on a swirl burner was carried out using Planar Laser Induced Fluorescence technology (PLIF), and the C-X (0,0) band was selected as the excitation method. The laser wavelength and laser energy have a significant impact on the signal strength and signal-to-noise ratio of CH radical, and the imaging quality of CH reached the best with the laser wavelength and energy are of 314.415 nm and 0.3 mJ. The fluorescence signal of CH radical from swirling flame mainly distributed on the outside of the image and exists in a narrow area. As the of equivalence ratio of methane combustion increased, the signal of CH radical gradually strengthened, and the flame profile of chemiluminescence gradually evolved from "V" type to "M" type, and the number of vortices formed by CH radical from PLIF imaging gradually increased.
A single-laser-shot N2 Q-branch Coherent Anti-Stokes Raman Scattering (CARS) is used to measure the instantaneous temperature of supersonic combustion in kerosene/air flame with Mach 2.6. The Unstable-resonator spatially enhanced detection (USED) phase matching is used to reduce turbulence effects and to improve the CARS signal intensity. An USED CARS measurement system, which has a high spatial solution of ~100μm in diameter, and a CARS spectrum calculating and fitting program CARSCF are developed. The CARS signal in supersonic combustion is measured and then used to calculate temperature, the results show that, during kerosene/Air ignited in Mach 2.6, the CARS signal first rise rapidly then fall sharply and finally rise slowly, while the temperature increase sharply and then decrease slowly and the average temperature is 1970 ± 144K with 6.5% of repeatability.
Planar laser induced fluorescence (PLIF) is a powerful tool to visualize the flame structure, especially for the turbulent flame. In this paper, we employ OH-PLIF technique to analyze the structure of a supersonic ethylene jet flame on a turbulent burner. This burner consists of a central jet and hot coflow. The Mach numbers of the jet vary from 1.0 to 1.6, corresponding to Reynolds numbers ranging from 40893 to 65455. The flame structures are imaged by OH-PLIF measurement. The measurement results reveal that the OH concentrations decrease with the increase of jet velocity or decrease of the O2 fraction. And the extinction and re-ignition of flame take place when the jet velocity is high or the O2 fraction is small. These measurement results help to understand the interaction between flame and highly turbulent flow.
Due to non-interruption of laser intensity and dye content, two-colour Laser Induced Fluorescence (LIF) ratio thermometry approach is widely used in the studies of fluid. Ratio of temperature sensitive dye Photo Luminescence (PL) intensity at two wave bands with different temperature sensitivity can efficiently remove interruption of laser intensity and dye content in time and space. To achieve high temperature sensitivity and Signal to Noise Ratio (SNR) in these technique, selection of two wave bands’ peak wavelengths and band widths should be carefully considered. In this work, influences of peak wavelengths, band widths and SNR to temperature sensitivity of this two-colour LIF ratio thermometry approach are discussed. Temperature property of a traditional temperature sensitive dye (rhodamine B) aqueous solution is studied in a wide temperature range from -10°C to 90°C by spectroscopic method. A non-linear fitting method based on Arrhenius equation is present to accurate describe rhodamine B PL intensity decay along with increasing of temperature, achieving significant improved fitting accuracy compared with traditional linear fitting model. Based on this non-linear fitting method, influences of filters’ center wavelengths and band widths to temperature sensitivity are analyzed. These results give very important information of filter’s selection to ensure sufficient temperature sensitivity and SNR in two-colour LIF ratio thermometry approach.
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