Study of Pollutant Formation and Its Control in the Non-Uniform Combustion

本研究旨在澄清高湍流流场中不均匀燃烧过程，以控制燃烧过程中污染物的形成。本文的研究内容总结如下：1。通过对湍流涡流的瞬时LLS（激光片法）图像的观测，研究了射流扩散火焰中的湍流。结果表明：大涡主要集中在方位角截面上，燃料与空气的混合主要通过喷射流在涡环发展过程中界面层的拉伸进行。此外，利用涡度输运方程讨论了斜压效应在高密度梯度区附近诱导涡的能力。粒子图像测速（PIV）是一种测量湍流中速度矢量的方法，它基于两幅图像在小时间间隔内的二维互相关系数。使用模拟图像评估了P…More IV在可能误差下的准确性。射流和射流火焰的测量结果表明，剪切层非定常运动产生的涡环促进了混合，而反应区波动运动由于温度的升高而层叠化，导致火焰下游烟灰层的形态复杂。基于详细的化学动力学研究了两段燃烧过程中氮氧化物的产生和破坏。通过对富甲烷-空气燃料燃烧气体稀释过程的分析表明，由于强湍流引起的快速混合导致NOx的大量减少，并且如果在稀释引起放热之前随着体积膨胀而温度降低，则可以进一步减少NOx。此外，还讨论了在不同压力和温度条件下生成NOx的反应路径，并通过对各NO生成速率的积分给出了各元素反应的贡献。少

This study aims at the clarification of the non-uniform combustion process in highly-turbulent flowfields for controlling pollutant formation during combustion. The contents of the prsent study are summarized as follows :1.Turbulence in jet diffusion flames was investigated based on observations of instantaneous LLS (laser-light sheet method) images of turbulent eddies. Results show that only larger eddies can be seen mainly on the azimuthal cross-section, and that mixing between fuel and air mainly proceeds by stretching of the interfacial layr during development of vortex rings due to an ejecting flow. Furthermore, the capability of inducing vortices near the zone of a higher density gradient due to baroclinic effect was discussed using a vorticity-transport equation.2.Particle image velocimetry (PIV) for measuring velocity vectors in a turbulent flow was developed based on a two dimensional cross-correlation coefficient between two images with a small time interval. An accuracy of P … More IV was assessed at probable errors using the simulated images. The measured results in jets and jet flames reveal that vortex rings produced associated with the unsteady motion in the shear layr promote the mixing, whereas in the reacting region fluctuating motions are laminarized due to an increase in temperature, causing the complicated pattern of soot layrs in the downstream of flame.3.Production and destruction of nitrogen oxides in the two-stage combustion was investigated based on a detailed chemical kinetics. From the analysis of dilution processes of methane-air fuel-rich burnt gas, it is shown that fast mixing due to strong turbulence causes a considerable NOx reduction, and that a further reduction can be achieved if the temperature decreases with the volume expansion prior to the heat-release due to the dilution. In addition, reaction paths into NOx formation were discussed in the conditions of different presure and air-temperature, and contributions of individual elementary reactions were given by the integration of each NO formation rate. Less