激光等离子体助燃温度和活性粒子浓度的原位诊断研究

Laser plasma assisted combustion (LPAC) is a novel combustion enhancement technique characterized with many potential benefits such as easier control of the reaction position, less interference on the hydrodynamic field and better electromagnetic compatibility, etc.. However, the detailed mechanism of the LPAC still remains unclear now. The temperature and concentrations of radicals generated during the LPAC process are important parameters to determine the dominant mechanism of the LPAC: thermal or nonthermal. They can also help to optimize the kinetic model and thus fully understand the kinetic process of the LPAC. This project will concentrate on the in situ diagnostics on the temperature and absolute concentrations of several important radicals during the LPAC process, including the hydroxyl radical (OH) on the ground and excited states (OH(A,X)) and nitrogen molecules on the excited states (N2(A,B,C)), by using the absolute spectral response calibrated optical emission spectroscopy and the planar laser induced fluorescence spectroscopy calibrated with a standard flat flame burner. The effects of the equivalence ratio and flow speed of the combustion gas mixture, laser pulse energy and repetition rate on the temperature and radical concentrations and their temporal and spatial evolutions will be investigated and the roles played by corresponding thermal and nonthermal mechanisms will be discussed accordingly. The dominant mechanism of the LPAC will then be determined via the correlation analysis of the temperature, radical concentration and macro performance of the LPAC, thus promoting the kinetic investigations of the LPAC.

激光等离子体助燃是一种新型的增强燃烧技术，具有作用位置方便可调、流场干扰小、电磁兼容性好等优点，但其机理尚不明确。助燃过程的温度和典型活性粒子的浓度对于确定激光等离子体助燃的主导作用机制（热效应或非热效应机制）、完善助燃化学动力学模型进而明确助燃机理具有重要的意义。本项目采用绝对响应度标定的发射光谱技术和基于标准平焰燃烧器标定的平面激光诱导荧光光谱技术，对助燃过程的温度、基态/激发态OH基团（OH（A,X））和激发态氮气分子（N2（A,B,C））的绝对浓度开展原位在线诊断研究，研究混合燃气当量比、流速、激光脉冲能量、重频等参数对助燃过程的温度和活性粒子浓度及其时空演化特性的影响规律，分析对应的热效应和非热效应两种机制在激光等离子体助燃中的作用，通过对助燃过程的温度、活性粒子浓度和宏观助燃特性三者进行关联分析，明确激光等离子体助燃的主导作用机制，从而促进激光等离子体助燃的机理研究。

激光等离子体助燃是一种新型的增强燃烧技术，能够有效解决高速燃烧系统中火焰稳定的难题，具有作用位置方便可调、流场干扰小、电磁兼容性好等优点，但是其作用机制并不明晰。项目采用发射光谱技术和平面激光诱导荧光光谱技术，建立了激光等离子体助燃温度和活性基团浓度的非接触式原位诊断方法，获得了激光等离子体助燃温度和活性粒子浓度的时空演化特性，明确了激光等离子体助燃的主导作用机制是燃烧化学反应占主导地位的非热作用机制，加深了对激光等离子体助燃物理化学过程的理解和认识。发展了激光烧蚀等离子体助燃技术，使助燃用的激光脉冲能量降低一个数量级，推动了激光等离子体助燃技术的工程应用。采用kHz级高重频激光等离子体作用，实现了持续释热的稳定燃烧，拓展了助燃的当量比范围，吹熄极限在当量比0.8-1.2范围内相比无等离子体作用时提高了0.3-3.4倍。基于直连式超燃冲压发动机实验台，克服了超燃冲压发动机燃烧室中湍流耦合、激波干扰等恶劣条件，成功实现了飞行马赫数Ma 4、Ma 5.5、Ma 6超声速条件下乙烯和飞行马赫数Ma 5.5超声速条件下航空煤油的激光等离子体点火和稳定燃烧，为超燃冲压发动机的可靠点火提供了一种新型技术手段。