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.
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).
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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