Soot inception in highly controlled counterflow flames at pressures up to 4MPa

燃烧过程中排放的煤烟是一个困扰世界数百年的问题，其对健康和气候的影响直到最近几十年才得到充分认识。烟尘的形成一直是燃烧研究中的一个棘手的挑战，因为很难遵循从燃料到烟尘核的关键生长过程步骤。为了了解烟灰的化学途径，有必要对火焰中的气体进行取样，以便进行化学分析。然而，将探针插入火焰会产生扰动，并且需要了解其对结果分析的影响。大多数燃烧应用，如发动机，发生在高压下，现代燃烧涡轮在2.5-4.0 MPa的压力范围内工作。了解火焰中烟灰形成的挑战在高压下变得更加复杂，因为火焰总是变得更薄，对探针的扰动更敏感。该研究项目旨在通过创建可控的实验室火焰环境，并使用独特的技术来量化烟尘核（即小分子碳化合物）的生长，了解高压火焰中烟尘形成的化学过程。这些研究将影响我们对烟灰过程的基本理解，对实际发动机的设计、减少燃烧的环境足迹以及对空气质量、公共健康和气候的有益影响产生潜在影响。在本研究项目中，火焰结构和从母体分子到大烟尘前体，最终到碳质烟尘纳米颗粒的演变，将被确定为压力和峰值温度变化的函数。在测量气体种类和温度的基础上，采用双色热分析法、激光光散射法和激光诱导白炽灯法测量煤烟的体积分数、尺寸和色散指数，色散指数与煤烟年龄和碳氢比间接相关。扩散火焰和丰富的部分预混火焰都将被研究。关键的创新包括：即使在非常薄的高压火焰中也能以良好的空间分辨率确定物种剖面；通过与麻省理工学院的合作，对烟灰的关键组成部分进行量化，即6环大小的芳香前体，远远超出了与微探针采样结合使用的分析化学仪器的典型范围；以及对被检测火焰的前所未有的控制水平，包括恒定和/或精确缩放时间-温度历史的条件。通过与德国亚琛大学（University of Aachen）和意大利米兰大学（University of Milan）的研究人员合作，通过详细的化学动力学机制对火焰进行建模，补充了实验计划，以便在本研究项目产生的实验数据库的基础上改进化学机制和烟灰模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The emission of soot from combustion processes is a problem that has been plaguing the world for centuries, with repercussions on health and climate that have been fully appreciated only in recent decades. The formation of soot remains a thorny challenge in combustion research because of difficulties in following the critical growth process steps from fuel to soot nuclei. To understand the chemical pathway to soot, it is necessary to sample the gases in a flame in order to conduct chemical analyses. However, inserting a probe into the flame creates a perturbation, and its impact on the resulting analyses needs to be understood. The majority of combustion applications, such as in engines, occur at high pressures, with modern combustion turbines operating in the 2.5-4.0 MPa pressure range. The challenges of understanding soot formation in flames are compounded at high pressures, because the flames become invariably thinner and more sensitive to probe perturbations. This research project aims to understand the chemistry of soot formation in flames at high pressures, by creating controlled laboratory flame environments and using a unique technique to quantify the growth of soot nuclei (i.e., small molecule carbon compounds). These studies will impact our fundamental understanding of the soot process, with potential consequences on the design of practical engines, the reduction of the environmental footprint of combustion, and beneficial effects on air quality, public health and climate. In this research project, the flame structure and the evolution from parent molecule to large soot precursors, and eventually carbonaceous soot nanoparticles, will be determined as a function of changes in pressure and peak temperature. Gaseous species and temperature measurements will be complemented by soot measurements by two-color pyrometry, laser light-scattering and laser induced incandescence for the determination of soot volume fraction, size and dispersion index, the latter being indirectly related to soot age and carbon-hydrogen ratio. Both diffusion flames and rich partially premixed flames will be examined. Key novelties include: the determination of species profiles with good spatial resolution even in very thin high-pressure flames; the quantification, through a collaboration with MIT, of key building blocks of soot, namely, aromatic precursors up to 6-ring in size, well beyond the typical range of analytical chemistry instrumentation used in conjunction with microprobe sampling; and an unprecedented level of control of the examined flames, encompassing conditions of constant and/or accurately scaled time-temperature history. The experimental program is supplemented by modeling of the flames with detailed chemical kinetic mechanisms through collaborations with researchers at the University of Aachen (Germany) and the University of Milan (Italy) for the refinement of chemistry mechanisms and soot models on the basis of the experimental database produced from this research project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.