CAREER: Progression from soot to nanocrystalline carbon in elevated temperature flames

碳烟的形成仍然是影响燃烧性能、公众健康和环境的关键因素。由于燃用煤油的火箭、富氧燃料燃烧系统和其他新兴燃烧过程的突出，对极热火焰中碳烟形成的特征的需求日益增加。科学目标是阐明火焰中碳烟的形成比传统研究更热。一种互补的实验和计算建模方法将被用来分离这种烟尘形成区域特有的基本现象。迫在眉睫的航天货运和旅游企业需要烟尘模型来进行火箭推进器设计和颗粒物排放预测。在由煤油和其他碳氢化合物推进剂提供动力的火箭飞行过程中，会形成纳米晶碳。更全面地考虑绩效和未知的环境影响(如公共健康、气候等)是通过研究高温下煤烟的形成来促进的。高温氧燃料燃烧、预热空气系统和富气处理也是新兴燃烧技术比传统燃烧更热的例子。在社会影响方面，将通过与麦克奈尔项目和布里奇斯社区学院项目的合作，加强对研究生和学术生涯更具包容性的参与的迫切需求。还将开发热流体理论和应用的虚拟教学模块，以增加当地高中生的参与。量化竞争的烟尘形成过程仍然是一个挑战。导致气相碳烟前体的富燃料火焰化学模型在常规燃烧温度下差别很大，目前还没有关于高温火焰的研究。同样的道理也适用于烟尘纳米结构中的气溶胶动力学和演化。中心假设是，为了准确捕捉高温下的碳烟行为，需要量化可逆的碳烟前体反应、降低碰撞效率、极端粒子石墨化，或许还需要电离过程。在拟议的活动结束时，PI将具有：(1)系统地测量具有良好特性的层流和湍流实验室火焰中的单个多环芳烃分布和碳烟颗粒尺寸分布；(2)表征在高温火焰中形成的颗粒的碳纳米结构和形态的演变；(3)评估电离过程在这一体系中对碳烟形成的作用；(4)将新的实验观察纳入更高温度碳烟形成的新模型；(5)展示了控制从碳烟向新发现的纳米晶碳结构转变的独特的高温过程。拟议的项目意义重大，因为全面的实验和建模方法将促进烟尘形成理论的自我一致发展，以造福于传统和更高温的方案。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Soot formation remains a crucial factor in combustion performance, public health and the environment. There is a rising need to characterize soot formation in extremely hot flames due to prominence of kerosene-fueled rockets, oxy-fuel combustion systems and other emerging combustion processes. The scientific objective is to shed light on soot formation in flames hotter than traditionally studied. A complementary experimental and computational modeling approach will be used to isolate fundamental phenomena unique to this soot formation regime. Imminent space cargo and tourism enterprises require soot models for rocket thruster design and particulate emissions predictions. Nanocrystalline carbon forms during rocket flight powered by kerosene and other hydrocarbon propellants. A more thorough consideration of performance and unknown environmental impacts (i.e. public health, climate, etc.) is facilitated by studying soot formation at elevated temperature. High temperature oxyfuel combustion, preheated air systems and enriched air processing are also examples of emerging combustion technologies operating hotter than conventional combustion. In terms of societal impact, the urgent need for more inclusive participation in graduate school and academic careers will be enhanced through collaboration with the McNair program and Bridges Community College program. Virtual teaching modules for thermofluids theory and applications will also be developed to increase participation of local high-school students.Quantification of competing soot formation processes remains a challenge. Fuel-rich flame chemistry models leading to gas-phase soot precursors vary widely for conventional combustion temperatures and no studies for elevated temperature flames exist. The same can be said for the underlying aerosol dynamics and evolution in soot nanostructure. The central hypothesis is that quantification of reversible soot precursor reactions, reduction in collision efficiency, extreme particle graphitization and, perhaps, ionization processes are required to accurately capture soot behavior at elevated temperatures. At the conclusion of the proposed activities the PI will have: (i) systematically measured individual PAH profiles and soot particle size distributions in well-characterized laminar and turbulent laboratory flames; (ii) characterized evolution in carbon nanostructure and morphology for particles formed in elevated temperature flames; (iii) assessed the role of ionization processes on soot formation in this regime; (iv) incorporated new experimental observations into new models for higher temperature soot formation; (v) demonstrated unique higher-temperature processes governing the transition from soot to newly discovered nanocrystalline carbon structure. The proposed project is significant because self-consistent development of soot formation theory will be facilitated by the comprehensive experimental and modeling approach for the benefit of conventional and higher-temperature regimes.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.