Abstract Effects of CO2 on soot formation during ethylene pyrolysis were investigated in a laminar flow reactor with the addition of various amounts of CO2 (0–99.5% in mole fraction). Based on a quantitative dilution sampling technique and a scanning mobility particle sizer, soot particle size distributions and the associated global properties, including soot volume fraction, number density, and soot induction delay time, were examined. Results show that while addition of a small amount of the CO2 (0 - 10%) tends to promote soot formation as the total number and volume of soot particles increase and the soot induction delay time decreases, its further increase, from 10% to 99.5%, leads to an obvious reduction of the soot nucleation and mass growth rates. Subsequent kinetic modeling of the gas-phase chemistry showed that with increasing CO2 concentration, the corresponding concentrations of the soot precursors, namely benzene and pyrene, first increase and then decrease, which is consistent with the observed trend in soot formation. Further sensitivity and reaction path analyses of benzene formation indicate that CO2 addition produces more hydroxyl radicals, such that while the presence of a small amount of hydroxyl radicals increases the propargyl concentration and thereby promotes the formation of soot precursors, excessive hydroxyl radicals lead to more oxidation and hence inhibit soot formation.

中文翻译：

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CO2 对乙烯热解过程中碳烟形成的影响

摘要 在层流反应器中研究了 CO2 对乙烯热解过程中碳烟形成的影响，并添加了不同量的 CO2（摩尔分数为 0-99.5%）。基于定量稀释采样技术和扫描迁移率粒度仪，检查了烟尘粒度分布和相关的全局属性，包括烟尘体积分数、数密度和烟尘诱导延迟时间。结果表明，虽然随着烟灰颗粒总数和体积的增加以及烟灰诱导延迟时间的减少，添加少量 CO2 (0 - 10%) 倾向于促进烟灰形成，但其进一步增加，从 10% 到 99.5 %，导致烟灰成核和质量增长率的明显降低。随后的气相化学动力学模型表明，随着 CO2 浓度的增加，相应的烟灰前体浓度，即苯和芘，先增加然后减少，这与观察到的烟灰形成趋势一致。苯形成的进一步敏感性和反应路径分析表明，CO2的加入会产生更多的羟基自由基，因此少量羟基自由基的存在会增加炔丙基浓度，从而促进烟尘前体的形成，过量的羟基自由基会导致更多的氧化从而抑制烟灰形成。