A nanosecond pulsed dielectric barrier discharge (ns-DBD) setup is built to preliminarily analyze effect of different discharge repetition (600Hz ~ 1800Hz) and voltage (6.0kV ~ 10.4kV) on CH4-air diffusion flame. Emission spectral is used to understand temperature and relative change of components’ concentrations in diffusion flame, such as O radical (777nm band), OH radical (308nm band). Plasma induced consumption process of repetitive pulsed nanosecond discharges on O radical has been directly observed at 900Hz discharge repetition. Based on time resolved emission spectral, significant changes of OH radical distribution at early discharge stage can be observed, which can be due to air-discharge plasma, and rapidly recover in microsecond scale due to rapidly consumption of generated OH radical. Besides, great differences in reaction time scale of OH radical (half-value period of OH radical consumption ~81.8μs) and O atom (half-value period of O atom consumption ~3.6min) is observed, corresponding to different chemical reaction mechanism of O atom and OH radical. A model based on rate equation is built to describe generation and consumption process of O atom and OH radical, which can also well predict voltage behavior of 777nm band at steady state (6.0kV ~ 10.4kV).
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.
Cavity structure is used to increase the Interferometric Rayleigh scattering signal intensity. By using ZEMAX method, we simulate a special cavity mode comprising two spherical reflectors with different size, including the focal length and the diameter. The simulations suggest that the parallel beam can reflect repeatedly in the resonant cavity and concentrate on the focus. Besides, the reflection times and the ray width can reach about 50 and 2.1 cm after some feasible solutions.
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