Investigation of fragmentation during soot oxidation

烟灰氧化过程中碎片的研究

• 批准号: 1133480
• 负责人: Kerry Kelly
• 金额: $ 27.65万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1133480&HistoricalAwards=false
• 关键词: Investigation; fragmentation; during; soot; oxidation

1133480LightySoot formation and oxidation are important because of soot's adverse health effects, role in climate forcing, and importance to ambient air quality and visibility. The adverse health effects of soot have been reported by numerous researchers. Soot has been implicated in climate forcing; however, its actual contribution is still somewhat uncertain. Manufacturers of air pollution control equipment, i.e. diesel particulate filters, are also interested in understanding the rates and mechanisms of soot oxidation at lower temperatures.Previous work has identified the fragmentation of soot particles under various combustion conditions, including high soot burnout (70% carbon burned) and low burnout, close to the burner (about 10% carbon burned) in a high temperature, flame environment. In addition, recent modeling has identified the importance of fragmentation in predicting the particle size distribution and other soot properties. However, little experimental data exist for fully understanding the conditions under which fragmentation potentially occurs and the mechanisms. Others have suggested that oxygen diffuses into the particles which allows for internal burning, breaking apart the soot agglomerate. The proposed work has the following three objectives:Objective 1. Identify the conditions, i.e. temperatures, equivalence ratios, radical pool, etc. where fragmentation occurs for ethylene flames at both low burnout and high burnout;Objective 2. Determine the mechanisms of fragmentation, such as oxygen diffusion in breaking of bridges and soot particle break down; Objective 3. Perform tests on surrogate liquid fuels to determine the applicability of the mechanisms identified in Objective 2 to these fuels and the role of aromatic versus aliphatic components.The experiments will be conducted in a two-stage, premixed burner system which can be used for both gaseous and liquid fuels. In this system the first burner generates soot, while the second burner is used to oxidize the soot under various temperatures and equivalence ratios. A Scanning Mobility Particle Sizer (SMPS), with a size range of 3-100 nm, will be used to determine particle size distributions as a function of height above burner. When needed, long-differential mobility analyzer measurements can extend the range to 660 nm. Gas-phase concentrations of key components (i.e. O2, H2, CO, CO2) and temperature profiles will be taken. Objective 1 will use ethylene to gather the data and develop mechanisms, while Objective 3 will explore liquid fuels. Utilizing TEM and HR-TEM and particle size distribution data, we will explore in Objective 2 the oxidation of "bridge" material between particles via oxygen diffusion and also increases in particle porosity which can lead to particle fragmentation. The intellectual merit of the study is in understanding the mechanisms of soot fragmentation during oxidation and the conditions under which it is likely to occur. The novelty of the work is exploring the phenomenon under the two scenarios: high and low soot burnout. Furthermore, soot oxidation has not been studied in depth, and recent advances in particle measurements can add to the existing knowledge. The data can be used to modify oxidation mechanisms which, when used in simulations, will more accurately predict the structure, size distribution and mean properties of soot as it oxidizes. In addition, this project will begin to address the role of different fuel constituents in fragmentation. The broader impacts are realized when industry can apply these fundamentals to their systems to reduce soot emissions, important to protect human health and to better understand/mitigate climate forcing. On the other hand, for industries producing carbon black, these data will add to the existing knowledge base of soot formation/oxidation.

LightySoot的形成和氧化很重要，因为煤烟对健康有不良影响，在气候强迫中的作用，以及对环境空气质量和能见度的重要性。许多研究人员已经报道了煤烟对健康的不利影响。烟尘与气候强迫有牵连；然而，它的实际贡献仍有些不确定。空气污染控制设备的制造商，即柴油微粒过滤器，也有兴趣了解碳烟在较低温度下的氧化速率和机理。以前的工作已经确定了在各种燃烧条件下碳烟颗粒的碎裂，包括在高温火焰环境中靠近燃烧器的高碳烟燃尽(70%碳燃烧)和低燃尽(约10%碳燃烧)。此外，最近的模型已经确认了碎裂在预测颗粒尺寸分布和其他碳烟特性方面的重要性。然而，几乎没有实验数据来充分了解可能发生碎裂的条件和机制。其他人认为，氧气扩散到颗粒中，允许内部燃烧，分解煤烟凝聚体。拟议的工作有以下三个目标：目标1.确定乙烯火焰在低燃尽和高燃尽时发生破碎的条件，即温度、当量比、自由基池等；目标2.确定破碎的机制，如桥断裂中的氧气扩散和烟尘颗粒的分解；目标3.对替代液体燃料进行测试，以确定目标2中确定的机制对这些燃料的适用性以及芳香族和脂肪族组分的作用。实验将在两级预混合燃烧器系统中进行，该系统既可用于气体燃料，也可用于液体燃料。在该系统中，第一个燃烧器产生碳烟，而第二个燃烧器用于在不同的温度和当量比下氧化碳烟。扫描流动粒度仪(SMPS)的尺寸范围为3-100 nm，将被用来确定粒度分布作为燃烧器上方高度的函数。当需要时，长差分迁移率分析仪测量可以将范围扩展到660 nm。将采集关键成分(即O2、H2、CO、CO2)的气相浓度和温度分布。目标1将使用乙烯收集数据并开发机制，而目标3将探索液体燃料。利用透射电子显微镜和高分辨透射电子显微镜以及粒度分布数据，我们将在目标2中探索氧扩散在颗粒之间的“桥梁”材料的氧化，以及可能导致颗粒破碎的颗粒孔隙率的增加。这项研究的学术价值在于理解了氧化过程中煤烟碎裂的机制和可能发生的条件。这项工作的新奇之处在于探索了两种情景下的现象：高煤烟烧毁和低煤烟烧毁。此外，煤烟氧化还没有得到深入的研究，最近在颗粒测量方面的进展可以增加现有的知识。这些数据可以用来修改氧化机制，当用于模拟时，将更准确地预测碳烟在氧化时的结构、尺寸分布和平均性质。此外，该项目将开始处理不同燃料成分在碎裂中的作用。当工业能够将这些基本原理应用于其系统以减少烟尘排放时，就会实现更广泛的影响，这对保护人类健康和更好地了解/缓解气候强迫很重要。另一方面，对于生产炭黑的行业来说，这些数据将增加现有的烟尘形成/氧化知识库。