Investigation of Nitric Oxide Kinetics in Diffusion Flames with Laser-Induced Fluorescence Spectroscopy and Detailed Modeling

密歇根大学、帝国理工学院(伦敦)和桑迪亚国家实验室(利弗莫尔)参与的这个联合项目的目标是提高对一氧化氮(NO)从有利于扩散和燃料丰富的火焰的快速(Fenimore)途径形成的理解和预测能力。对快速反应机理的关键化学物种进行了测量，并与详细动力学模型的结果进行了比较。利用基于激光的非侵入性诊断技术，测量了稳定扩散火焰中NO、CH自由基和氧原子的温度和浓度。所研究的火焰是稳定在筑路式逆流燃烧器上的甲烷/空气扩散火焰。物种测量是用纳秒和皮秒激光诱导荧光(LIF)进行的。用相干反斯托克斯拉曼光谱(CARS)测量温度，通过解析皮秒激光诱导荧光信号的时间衰减直接测量猝灭。使用瑞利散射(CH，O原子)或通过测量已知量的掺杂剂(NO)进行校准。调整火焰应变率(空气和燃料流量)以提供不同的反应条件，并将一氧化氮添加到燃料中以测量与碳氢化合物反应(再燃)对NO的破坏。减少污染物排放，特别是氮氧化物，是汽车发动机、燃气轮机和家用加热炉等能源转换设备设计中的一个关键问题。根据火焰条件的不同，一氧化氮的形成可以通过两种不同的机制进行：热(Zeldovich)机制或迅速(Fenimore)机制。在燃料贫乏的预混系统中占主导地位的热机制被很好地描述出来。然而，人们对这种快速反应机制知之甚少。

The objective of this joint project involving the University of Michigan, Imperial College (London), and Sandia National Laboratory (Livermore) is to improve understanding and predictive capability of nitric oxide (NO) formation from the prompt (Fenimore) pathway favored in diffusion and fuel-rich flames. Chemical species critical to the prompt mechanism are measured and compared to the results from detailed kinetic models. Temperature and concentrations of NO, CH radical, and oxygen atoms are measured in a stable diffusion flame using nonintrusive laser-based diagnostics. The flame studied is a methane/air diffusion flame stabilized on a Tsuji-type counterflow burner. Species measurements are made with nanosecond and picosecond laser-induced fluorescence (LIF). Temperatures are measured with coherent anti-Stokes Raman spectroscopy (CARS) and quenching is measured directly by resolving the temporal decay of the picosecond LIF signal. Calibration is performed using Rayleigh scattering (CH, O-atom) or by measuring known amounts of dopant (NO). Flame strain rates (air and fuel flows) are adjusted to provide various reaction conditions, and nitric oxide is added to the fuel to measure destruction of NO by reaction with hydrocarbons (reburn).Reduction of pollutant emissions, especially nitrogen oxides, is a key issue in the design of energy conversion devices including automobile engines, gas turbines, and home heating furnaces. Depending on flame conditions, formation of nitric oxide can proceed by two different mechanisms: the thermal (Zeldovich) mechanism or the prompt (Fenimore) mechanism. The thermal mechanism, which dominates in fuel-lean, premixed systems, is fairly well characterized. However, the prompt mechanism is poorly understood.