Quantitative Measurements of Temperature and Species in Counterflow Flames Near Extinction

精确的温度测量对于提高我们对火焰结构和火焰中污染物形成的理解和建模至关重要。层流和湍流火焰的现代计算模型都包含了化学反应动力学和传输过程的详细模型。化学反应的速率尤其能表现出强烈的温度依赖性。因此，准确和有效的测量火焰温度的方法对于火焰结构和污染物形成的数值计算与实验的严格比较至关重要。相干反斯托克斯拉曼散射（CARS）光谱被广泛认为是最精确的火焰温度测量技术，但很难准确评估该方法的绝对温度精度，主要是因为缺乏其他有效的方法来测量超过2000 K的温度。在这项工作中，使用激光诊断方法CARS光谱对温度测量的准确性进行了严格的理论分析。此外，将开发一种新型的CARS实验系统，以消除导致CARS温度测量不确定度增加的一些因素。该项目的目标是证明温度测量精度优于1%，这将使计算火焰模型的重要方面得到严格的评估。使用先进的高光谱分辨率扫描CARS系统，将在近绝热的henken燃烧器火焰和非预混逆流火焰中测量温度。这些测量是由我们小组最近获得的高功率，单频模式，可调谐钛：蓝宝石连续波激光系统实现的。对于N2和H2等物质，CARS激光束的光谱宽度大约比拉曼谱线的光谱宽度小一个数量级。因此，我们将能够解析CARS谱线，最大限度地减少线宽不确定性的影响。从理论上研究了振动-旋转相互作用（Herman-Wallis效应）和振动非调和性对N2和H2 CARS光谱温度提取精度的影响。高光谱分辨率CARS温度测量的准确性将在近绝热的Hencken燃烧器火焰中得到验证。经过验证的CARS温度测量将在层流、逆流、非预混碳氢化合物/空气火焰中进行，重点是对接近熄灭的火焰结构进行测量。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。

Accurate measurements of temperature are critical for improving our understanding and modeling of flame structure and pollutant formation in flames. Modern computational models of both laminar and turbulent flames incorporate detailed models of chemical reaction kinetics and transport processes. The rates of chemical reactions in particular can exhibit strong temperature dependence. Consequently, accurate and validated methods for measuring flame temperatures are critical for rigorous comparison of numerical calculations of flame structure and pollutant formation with experiment. Coherent anti-Stokes Raman scattering (CARS) spectroscopy is widely considered to be the most accurate temperature measurement technique for flames but it is difficult to assess accurately the absolute temperature accuracy of the method, mostly because of the lack of other validated methods for measuring temperatures in excess of 2000 K. In this work a rigorous theoretical analysis of the accuracy of temperature measurements using the laser diagnostic method CARS spectroscopy will be performed. In addition, a new type of CARS experimental system will be developed to eliminate some factors which cause increased uncertainty in CARS temperature measurements. The goal of the project is to demonstrate temperature measurement accuracies of better than one per cent, which will enable rigorous evaluation of important aspects of computational flame models. Temperatures will be measured in both near-adiabatic Hencken burner flames and in non-premixed counterflow flames using an advanced high-spectral-resolution scanning CARS system. These measurements are enabled by the recent acquisition by our group of a high-power, single-frequency-mode, tunable titanium:sapphire continuous-wave laser system. The spectral width of the CARS laser beams will be approximately an order of magnitude less than the spectral width of the Raman lines for species such as N2 and H2. Consequently, we will be able to resolve the CARS spectral lines, minimizing the effects of the uncertainties their linewidths. The impact of the vibration-rotation interactions (the Herman-Wallis effect) and the effect of vibrational anharmonicity on the accuracy of temperatures extracted from N2 and H2 CARS spectra will be theoretically investigated. The accuracy of the high-spectral-resolution CARS temperature measurements will be validated in near-adiabatic Hencken burner flames. The validated CARS temperature measurements will then be performed in laminar, counterflow, non-premixed hydrocarbon/air flames, emphasizing measurements of flame structure near extinction.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.