火焰化学发光三维重建方法的研究

发布时间：2019-01-05 08:54

【摘要】：汽油机缸内的湍流运动和工质的不均匀分布使得缸内火焰在三维空间上呈现出复杂的形态,影响火焰的发展及其与未燃混合气之间的相互作用。因此,研究缸内火焰的三维空间特征对研究三维湍流燃烧区域内的传质传热和化学反应动力学间的强耦合机制有着重要意义。目前,相关研究的一个重要难题是传统燃烧诊断技术的二维测量结果与湍流燃烧三维特性不匹配。为了解决该问题,本文采用火焰化学发光三维重建技术进行燃烧诊断,利用多角度的火焰图像积分数据实现燃烧区域内辐射强度空间分布重建,从而获取火焰三维特征信息。针对拍摄相机的光电转换过程、几何成像模型和火焰辐射强度空间分布函数分别进行简化,进而推导出简化的火焰成像模型,从数学角度上描述了燃烧区域内辐射强度空间分布与拍摄照片像素值间的关系,建立了以辐射强度为变量的病态矩阵,将火焰化学发光三维重建转化为该病态矩阵的求解问题。模型系数利用外凸多边形的几何特性与准蒙特卡洛算法进行计算。本文采用了代数重建法求解该病态矩阵。基于简化的火焰成像模型,在MATLAB环境下搭建了虚拟火焰重建计算平台,用于模拟火焰化学发光三维重建过程,研究基本重建参数对重建结果的影响规律。本文参考汽油机混合燃烧模式下的火焰特征构建了一系列虚拟火焰,并利用构建的虚拟火焰在虚拟火焰重建计算平台上研究了拍摄角度数量与拍摄图像分辨率对重建精度的影响规律,分析了重建火焰误差分布特征,优化了代数重建法迭代收敛判据。搭建了美克灯火焰多角度图像拍摄系统,并基于简化的火焰成像模型,在MATLAB环境下建立了美克灯火焰重建计算平台。基于该平台,依据多角度的美克灯火焰图像数据成功实现了燃烧区域内CH*空间分布重建。重建结果揭示了美克灯火焰前锋面三维空间结构特征,证明了该技术用于复杂湍流火焰重建的有效性和潜力。
[Abstract]:The turbulent motion in the cylinder of gasoline engine and the uneven distribution of the working fluid make the flame in the cylinder take on complex shape in three dimensional space, which affects the development of the flame and the interaction between the flame and the unburned mixture. Therefore, it is of great significance to study the strong coupling mechanism between mass transfer, heat transfer and chemical reaction kinetics in the three-dimensional turbulent combustion region. At present, an important problem in the related research is that the two-dimensional measurement results of conventional combustion diagnosis techniques do not match the three-dimensional characteristics of turbulent combustion. In order to solve this problem, the flame chemiluminescence three-dimensional reconstruction technique is used to diagnose combustion, and multi-angle flame image integral data are used to reconstruct the spatial distribution of radiation intensity in the combustion region, and the three-dimensional characteristic information of the flame is obtained. The geometric imaging model and the spatial distribution function of flame radiation intensity are simplified respectively in view of the photoelectric conversion process of the camera, and then the simplified flame imaging model is deduced. The relationship between the spatial distribution of radiation intensity in the combustion region and the pixel value of the photograph is described from a mathematical point of view. A ill-conditioned matrix with radiation intensity as a variable is established, and the three-dimensional reconstruction of flame chemiluminescence is transformed into the solution of the ill-conditioned matrix. The model coefficients are calculated by using the geometric properties of the convex polygon and the quasi-Monte Carlo algorithm. In this paper, algebraic reconstruction method is used to solve the ill-conditioned matrix. Based on the simplified flame imaging model, a virtual flame reconstruction computing platform was built in MATLAB environment, which was used to simulate the three-dimensional reconstruction process of flame chemiluminescence, and the influence of basic reconstruction parameters on the reconstruction results was studied. In this paper, a series of virtual flames are constructed according to the flame characteristics of gasoline engine in mixed combustion mode. The influence of shooting angle number and image resolution on reconstruction accuracy is studied on the virtual flame reconstruction computing platform, and the error distribution characteristics of reconstruction flame are analyzed. The iterative convergence criterion of algebraic reconstruction method is optimized. Based on the simplified flame imaging model, a multi-angle image capturing system of Mick lamp flame was built in MATLAB environment. Based on this platform, the CH* spatial distribution reconstruction in the combustion region is successfully realized based on the multi-angle Mick lamp flame image data. The reconstruction results reveal the three-dimensional spatial structure of the front surface of the Mick lamp flame, and prove the effectiveness and potential of this technique in the complex turbulent flame reconstruction.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK411

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