ABSTRACT

The impact on the use of carbon dioxide (CO₂) as a diluent in the fuel and oxidizer streams on the formation and evolution of precursor nanoparticles and soot in axisymmetric ethylene laminar coflow diffusion flames is experimentally explored using optical diagnostics in this paper. The optical diagnostics employed are based on temporally and spectrally resolved point measurements of laser-induced fluorescence, elastic scattering, and laser-induced incandescence. The measurements provide insight to indicative structure and concentration of precursor nanoparticles, and enable the determination of volume fraction and mean diameter of soot. Previous studies have indicated that the use of CO₂ as a diluent compared to nitrogen can reduce soot formation through both chemical and thermal effects. However, the effect of CO₂ addition on precursor nanoparticles’ concentrations and structure is not well understood, hence exploring the impact of CO₂ on precursor nanoparticles is one of the primary aims of this study. Flames with CO₂ as a diluent in the jet only, coflow only, and both streams are identified and investigated. For the flames studied with respect to the replacement of N₂ with CO₂: i), the soot volume fraction and mean soot diameter is reduced, and ii) precursor nanoparticles concentration is reduced, and the structural transformation is delayed.

摘要

本文使用光学诊断技术对轴对称乙烯层流共流扩散火焰中使用二氧化碳 (CO _{2 ) 作为燃料和氧化剂流中的稀释剂对前体纳米颗粒和烟灰的形成和演化的影响进行了实验探索。}所采用的光学诊断基于对激光诱导荧光、弹性散射和激光诱导白炽的时间和光谱分辨点测量。测量提供了对前体纳米颗粒的指示性结构和浓度的洞察，并能够确定烟灰的体积分数和平均直径。以前的研究表明，使用 CO ₂与氮气相比，作为稀释剂可以通过化学和热效应减少烟灰的形成。然而，CO ₂添加对前体纳米粒子浓度和结构的影响尚不清楚，因此探索CO ₂对前体纳米粒子的影响是本研究的主要目的之一。以 CO ₂作为稀释剂的火焰仅在射流中，仅在共流中，并且两种流都被识别和研究。对于关于用CO _{2代替N 2}所研究的火焰：i)降低了烟灰体积分数和平均烟灰直径，并且ii)降低了前体纳米颗粒浓度，并且延迟了结构转变。