激光能量密度对激光诱导炽光技术测试碳烟粒径的影响

Impact of laser fluence on test of soot particle size by laser induced incandescence

激光诱导炽光(Laser Induced Incandescence,LII)技术,由于其具有高的时间和空间分辨率,被认为是一种适合于测试碳烟浓度的技术,也可以用来测试碳烟主小球粒径。在LII测试过程中,不同激光能量密度对测试精度影响很大,高激光能量密度具有较高的信噪比,但是对于碳烟粒径测试,为了避免升华,应尽量使用低的激光能量密度。具体在利用激光诱导炽光技术推断碳烟粒径的实验中所用的低能量密度为何值,需要结合理论模型分析和实验进行确定。首先基于LII测试过程的数学模型进行了理论分析,然后在乙烯层流扩散火焰的相同位置上,测试得到了不同激光能量密度下的碳烟主小球粒径,分析确定了测试所需的最佳激光能量密度。为进一步测试碳烟的主小球粒径奠定了基础。

Laser Induced Incandescence （LII） is considered a very effective method for soot volume fraction measurement and can also be used to measure primary soot particle diameter with high spatial and temporal resolution. The laser fluence can potentially have a significant influence on the measured results. A high laser fluence in general results in a higher signal-to-noise ratio. But for soot particle size measurement, lower laser fluences should be used in order to avoid soot sublimation. To determine the optimal values of laser energy during the experiment, a combined approach of theoretical analysis and experiment was required. A mathematical model was established and analyzed ftrstly, then the primary particle size was measured using different laser fluences in the same position of a coflow ethylene/air laminar diffusion flame. Lastly, the optimal laser fluence was determined in the flame conditions investigated. This article laid the foundation for further investigations of the primary soot particle size measurement using low-fluence LII.