基于调制辐射消光法的高背压火焰中碳烟含量与温度场同时测量

Soot stems from the uncompleted fuel combustion inside the aeronautical engines、internal-combustion engines and so forth is a major reason of haze pollution. More lights are deserved to shed into the soot formation mechanisms under elevated pressures, however, the accurate soot volume fraction and temperature information stand the heart of the soot formation research. At present, simultaneous soot volume fraction and temperature measurement under high-pressure circumstance such as in combustion chamber of engines is still a technical difficulty. Based on the fact that soot is a strong absorber and emitter of light and the RDG-FA theory, one high-pressure adopted laser diagnostic technique that allows detection of soot volume fraction and temperature fields in the flame simultaneously is proposed in this project. Some critical scientific issues will be mainly addressed in project research, which covers aligning of high pressure induced signal beam steering, scattering light modification for soot volume fraction measurement and elimination of the temperature dependence on the soot refractive index and signal self-absorption. To clarify these scientific problems, the novel optical system、the calculation of soot scattering and novel deconvolution algorithms are respectively conducted. As the anticipated results, an optical technique used in high pressure for simultaneous soot volume fraction and temperature measurement is provided, which offers the opportunities to gain thorough insights into the soot formation mechanisms under elevated pressure and development of the novel high efficiency and clean engine combustion system.

航空发动机、内燃机等动力装置中因燃料的未完全燃烧而产生的碳烟排放是雾霾形成的主要原因之一。发动机中碳烟生成都在高压下进行，而高压下碳烟生成机理尚不清楚，高压火焰中准确的碳烟含量和温度信息是厘清碳烟生成机理和提高碳烟模型精度的关键。本项目拟根据碳烟辐射和消光以及其颗粒散射的 RDG-FA 原理, 开发一种适合于高背压火焰中同时诊断碳烟含量和温度分布的激光诊断技术。通过优化的光路设计、引入碳烟散射计算和发展新的反卷积算法，着重分别解决高压引起的激光和信号偏向、碳烟散射对碳烟含量测量准确性的影响、碳烟光学性质(折射率)和信号自身吸收对碳烟温度测量准确性的影响等关键科学问题。通过本项目研究,可望建立一种高压下同时准确测量碳烟含量和温度的诊断方法, 为探明高压下碳烟生成机理和开发新型清洁高效发动机燃烧系统提供有效的碳烟测试手段和工具。

高压下可靠的碳烟光学诊断技术是厘清各类发动机内碳烟生成机理的必由之路。本项目从理论和实验两方面，研究了双色测温中两波长组合的选择和碳烟自吸收对于温度测量精度的影响。基于此，将双色调制吸收辐射法中的两波长发展为645nm和785nm，并通过标准火焰测量，验证了测试方法的碳烟体积分数和温度测量的准确性。其次，通过该测试方法，展开了部分预混火焰中，氧比例对于层流扩散火焰中碳烟生成特性的定量研究，并发现随着燃料管中氧比例从0%增大至32%，存在两个火焰碳烟生成转捩，并通过实验的碳烟体积分数和温度结果分析，发现初始碳烟相对氧化速率和停留时间是碳烟生成转捩的重要因素。最后，项目研究了反卷积过程中比如，矩阵病态分布，引起的碳烟体积分数和温度的误差，创新地运用多层神经网络的方法，将火焰自身辐射作为输入参数，得到与传统光学诊断方法精度一致的碳烟参数，一方面提高了后续实验数据处理的速度，另一方面为重复性实验节省了实验成本。综上所述，项目开发的诊断方法为高压下厘清碳烟生成机理奠定了重要实验基础，为开发新型清洁高效发动机燃烧系统提供有效的碳烟测试手段和工具。除此之外，采用的波长优化的方法和神经网络预测模型，同样适用于双色-激光诱导炽光技术，因此具有较高的学术理论价值和实际应用价值。