基于化学自发光的超声速燃烧三维诊断技术研究

Optimization of heat release distribution is vital for controlling ramjet/scramjet mode, increasing combustion efficiency and engine thrust for scramjet. A new three-dimension diagnostics based on Computed Tomography of Chemiluminescence (3D-CTC) is proposed for conquering the difficulty of measuring heat release distribution. Research can be divided into two parts: one is developing 3D imaging technique which is suitable for scramjet application. Another part is extracting information from chemiluminescence signal. In the first part, the hypothesis of parallel beams will be abandoned. Point Spread Function (PSF) will be deduced. And image fiber bundles will be used to overcome the window limitation of scramjet combustor. Consequently, 3D chemiluminescence reconstruction could be implemented under short distance and blur imaging cases, such as in scramjet combustor. In the second part, interpretation of the relationship between the chemiluminescence-emission intensity and the flow/combustion parameters will be studied. Experiments will be performed to obtain the CH*/C2* ratio curve versus equivalence ratio and/or pressure, and the ratio curve of CH* intensity versus heat release rate. Combining these two part, the distribution of heat release and equivalence ratio can be measured by reconstructing the 3D distribution of both CH* and C2* intensity. The high spatial resolution of 3D-CTC (<2 mm) and its high repetition rate (>1 kHz) will advance scramjet diagnostics and finally benefit the optimization of scramjet combustor.

优化燃烧释热分布是控制超燃/亚燃模态、提高燃烧效率和增加发动机推力的关键。针对释热分布的诊断难题，本项目提出发展一种基于化学自发光的三维定量测量技术(3D-CTC)。主要研究内容包括，(1)发展适于超燃应用的三维火焰成像技术：推导成像点扩散函数，摒弃传统的平行束成像假设，实现对近距离、模糊成像的三维重建。针对超燃的窗口限制，发展基于光纤成像的新型三维成像技术。（2）分析获取超燃参数：深入研究化学自发光辐射强度与燃烧参数间的定量关系，利用标定实验的方法获得不同压力和当量比条件下的CH*/C2*辐射强度比曲线，以及CH*强度与释热率q比率曲线。两部分工作相结合，通过同时重建燃烧室的CH*和C2*三维分布，用辐射强度比推导当量比分布，进而实现三维释热分布定量诊断。3D-CTC技术的高空间分辨率(小于2mm)和高重复频率(大于1kHz)将极大提升超燃诊断能力，为超燃燃烧室优化设计提供新的技术支撑。

优化燃烧释热分布是控制超燃/亚燃模态、提高燃烧效率和增加发动机推力的关键。针对释热分布的诊断难题，本项目发展一种基于化学自发光的三维测量技术(3D-CTC)。.主要研究内容包括，(1)发展适于超燃应用的三维火焰成像技术：研制了3D-CTC系统，它具有成像大立体角，测试系统使用9*1光纤传像束和G透镜，仅使用单台CCD相机。该系统的较大立体角、简易和低成本，使得它非常适于内流燃烧诊断。在重建精度方面，研究了模糊成像对于重建精度的影响，使用荧光球标定模糊函数。在后向计算中，使用了清晰成像，模糊分布和去卷积三种方法，结果表明去卷积方法能够在不牺牲时间特征的情况下，提高重建精度。.（2）利用化学发光分析获取燃烧参数：研究波长和光强修正的辐射标定方法，定量测量了不同当量比下甲烷/空气预混平面火焰中的CH*, OH*, C2* CO2*化学发光强度。结合一维计算程序，评估了OH*,CH*反应机理，结果表明数值计算的发光强度与实验处于同一个量级，综合考虑自吸收和炉体冷却影响，OH*机理能够有效计算其发光强度，而CH*机理则高估了发光强度，表明CH*在高温下的机理常数应予以修正。.该3D-CTC技术具有高空间分辨率(小于2mm)和高重复频率(大于1kHz)，它已被用于诊断甲烷/空气旋流火焰和超燃燃烧室。获得了释热分布的三维特征，在未来应加强化学自发光辐射强度与燃烧参数间的定量关系研究，可以获得燃烧室的当量比分布等信息。