基于光谱诊断的烃类火焰碳烟形成机理研究综述

The Mechanism of Hydrocarbon Flame Soot Formation in Spectral Diagnosis:A Review

碳烟主要是烃类燃料不完全燃烧生成的产物,其对人类健康、空气质量以及燃烧装置的使用寿命都会产生有害影响。碳烟生成是一个复杂的物理化学过程,控制碳烟排放,需要克服碳烟生成和燃烧过程中物理和化学演化的巨大差异,这些差异表现为对碳烟纳观结构和表面官能团随碳烟氧化活性反应变化的深入探索研究。近些年,研究人员对碳烟的生成机理开展了系列研究,对碳烟生成各个物理化学反应阶段有了一定认识。结合光谱诊断技术可深入了解燃烧系统碳烟形成过程,确定碳烟颗粒分子组成、精细结构、浓度分布等特征,也可从碳烟结构变化、黑体辐射强度等方面详细了解碳烟形成过程。该文旨在阐述光谱诊断技术对烃类火焰碳烟表征的研究进展和发展趋势,探讨LIBS,LII和LIF等作为诊断工具在包含背景辐射的火焰中检测碳烟生成过程产生辐射强度准确性等问题。主要介绍了烃类火焰碳烟的形成机理(从前驱体产生、生长到颗粒生成、凝聚,最后进行颗粒氧化)。总结了探测碳烟性质光谱诊断方法的应用以及光谱诊断技术对燃烧过程中碳烟表征的研究现状,包括对碳烟体积分数、温度和基于图像处理的碳烟结构表征,反应碳烟前驱体(多环芳烃)、反应气氛、温度等对碳烟颗粒物生成的影响。最后,对光谱诊断方法在碳烟中的应用进行展望。未来光谱诊断方法将会呈现对碳烟生成化学反应机理进行更细致准确的研究、降低不均匀碳烟对火焰图像造成影响、优化光谱诊断测量方法对火焰中多种气体组分及生成碳烟浓度进行同时采集和实时在线监测等发展趋势。光谱诊断方法和图像分析在均相燃烧火焰碳烟中的分析将为推动清洁燃烧和为非均相流动领域研究提供思路并具有重要的科学指导意义。

As the main by-product of incomplete combustion of hydrocarbon fuel,soot not only has a detrimental effect on the combustion equipment but also harms air quality and human health.The formation of soot is a complex physical and chemical process.It is necessary to decrease the striking differences between the physical evolution and the chemical process of soot generation and combustion.In the past few decades,some scholars have investigated the mechanism of soot generation by spectral diagnostic technology and have had the understanding of soot formation in different generation stages to some extent.By using spectral diagnosis technology,the process of soot generation in the combustion system could be researched more comprehensively,and the molecular composition,fine structure,concentration distribution and other characteristics of soot could also be determined.More importantly,the process could be explained from the changes of soot structure and blackbody radiation intensity in detail.The aim of this study,on the one hand,is to illustrate the research process and developing trend of hydrocarbon flame soot by using spectral diagnosis technology.On the other hand,it is to discuss the problems like the accuracy of the radiation intensity generated during the process of soot generation in flames containing background radiation by the diagnostic tools,LIBS,LII and LIF included.Additionally,the formation mechanism of hydrocarbon flame soot(from precursor generation and growth to particle generation and aggregation,and finally,particle oxidation)is introduced in detail.Meanwhile,it summarized the application of spectral diagnostic methods to detect the properties of soot and the research status of spectral diagnostic techniques on the characterization of soot during combustion,including the volume fraction,reaction temperature and structure characterization of soot based on image processing,and the influence of polycyclic aromatic hydrocarbons,reaction atmosphere and temperature on the formation of soot particles was explored as well.Finally,the future application of spectral diagnostic methods in soot is forecasted.Spectroscopy diagnosis will present a more detailed and accurate study of the chemical reaction mechanism of soot formation in the future.The impact of uneven soot on flame images needs to be reduced,and the development trend of optimizing spectral diagnostic measurement methods to collect and monitor the concentration of multiple gas components in flame simultaneously and the generated soot in real-time.The analysis of spectral diagnostic and image analysis in homogeneous combustion flame soot will provide directions and have crucial scientific significance for promoting clean combustion and heterogeneous flow research.