Research On Measurements Of Air Mixing Ratio Using Acetone Planar Laser Induced Fluorescence

In the operation of engine, the mixing ratio of fuel and air distribution determines the performance of the engine ignition, flame stability, and harmful exhaust emissions, which play a key role in the engine design. Generally, the engine combustion is diffusion combustion. Therefore, we measure, in this paper, the quantitative distribution characteristics of mixing ratio in diffusion stream flow field used high-precision optical diagnostic technique—tracer PLIF technique. We got quantitative mixing ratio distribution under static and dynamic environment.Comparing and analyzing some commonly used tracer particles, such as formaldehyde, toluene, NO, and acetone. Besides, according to the experimental requirements of tracer particles used in PLIF, we choose acetone as an ideal tracer in the measurement of gas flow mixing ratio. And through the known fluorescence intensity expression of acetone PLIF, we analyze the relevant factors affecting the fluorescence intensity. By simplifying the fluorescence intensity expression, we propose a experimental program to measure the quantitative mixing ratio of gas flow. To meet the requirements of the experimental program, we designed a temperature-controlled acetone injection system and achieved a quantitative ratio of the mole fraction of acetone.Quantitative measurements of gas flow mixing ratio is based on calibration experiment of acetone mole fraction. In order to obtain high SNR images, we measured the fluorescence lifetime of acetone and determined the delay between the various components and gate width. The lifetime is 6ns. Then, by experiment, we know that the fluorescence intensity of acetone is linear to the laser energy. It is the most suitable for measuring the flow field when the laser energy is 1m J. Finally, using flat flame burner in the calibration experiment of the mole fraction of acetone, we obtained a function about fluorescence intensity and mole fraction of acetone.Based on the calibration experiment, we measure quantitatively the mixing ratio in the diffusion flow field. In coaxial burner, when the annular jet velocity is zero, the mixing ratio is affected by the diffusion of the central jet alone. And with the increase of the central jet velocity, airflow mixing weakened. When there is exists annular jet velocity, the mixing ratio is affected by not only the diffusion, but also the disturbances between the jets. And when the annular jet velocity is small, the mixing ratio is less affected. Increasing the annular velocity, the disturbance of the jets will be enhanced, which leads to the increase of airflow mixing.