【作者】 孙亦鹏；

【导师】 周怀春； 娄春；

【作者基本信息】 华中科技大学 ， 热能工程， 2011， 博士

【摘要】 随着全球能源危机的日益严重和人们对环境问题的逐渐重视,化石燃料的燃烧效率的提高和燃烧污染物排放的减少成为各国学者研究的热点,而温度作为确定物质状态和反映燃烧反应过程的重要状态参数之一,其准确测量对于完善燃烧理论和了解燃烧过程都具有重大指导意义。火焰温度和辐射特性参数如黑度、吸收系数、散射系数和烟黑浓度等是耦合在一起的,因此实现温度和辐射特性参数的同时准确测量反演成为一种十分有效的方式,但同时也增加了问题解决的难度。通过对火焰的多光谱测量能够提供大量的包含了火焰温度和辐射特性信息的光谱强度,研究人员不但可以采用对多光谱数据进行直接处理分析来计算火焰边界的温度和辐射特性参数,而且可以采用基于辐射逆问题的计算方法从光谱强度信息中计算反演出火焰内部的温度和辐射特性参数分布。本文在这两个方面进行了模拟和试验研究,主要的研究内容如下：在基于火焰的多光谱辐射信息的直接处理方面提出了一种简单的基于介质边界光谱强度信息的温度和黑度分布检测方法,并在此基础上以一维灰性平行平板和二维灰性轴对称系统为研究对象,结合DRESOR法分析了多种工况下介质内不同温度和吸收、散射系数分布对边界温度和黑度随波长变化分布的影响,结果表明：即使对于内部为灰性介质的系统来说,边界辐射仍然有可能为非灰体特性,检测的温度也可能随波长变化,因此目前很多基于灰体假设的温度测量方法的有效性需要进一步的验证,特别是利用较大波长范围内多波长能量信息的多波长法。利用经过黑体炉标定的200～11 00nm波长范围的可见光光谱仪检测火焰的边界辐射强度分布,然后采用本文提出的方法计算火焰边界的温度和黑度随波长分布,并根据黑度随波长分布确定介质符合灰体条件的波长范围。针对凝固汽油火焰、赤磷火焰、和420t／h的电站锅炉煤粉火焰开展试验研究,结果表明：凝固汽油的火焰辐射在波长550到900nm范围内可以看作是灰体辐射；煤粉火焰则在500到1000nm范围的辐射强度分布符合灰体条件；而赤磷火焰在本文采用的光谱仪的测量范围(200-1100nm)内不能看作是灰体辐射。在基于辐射逆问题从火焰多光谱强度信息中重建火焰内部温度和辐射参数方面,针对吸收、发射、无散射轴对称含烟黑火焰,采用SPSO算法对温度和烟黑浓度的同时重建进行了模拟研究,其中考虑了烟黑的自吸收项。研究中对影响重建的方法自身参数如温度和烟黑浓度的搜索范围、温度和烟黑浓度的进化速度、微粒群的规模以及测量选用的波长、测量误差和光学厚度等对重建结果的影响进行了分析,同时与文献中广泛采用的Abel逆变换和Tikhonov正则化算法进行了对比。结果表明即使仅采用几个波长的辐射强度信息,SPSO算法在重建火焰温度和烟黑浓度分布时具有很高的精度和鲁棒性,特别是在较大光学厚度,如在10倍光学厚度下时SPSO算法的重建误差要远远小于Abel逆变换算法和Tikhonov正则化算法。利用SPSO算法开展了从可见光光谱仪检测的实验室层流轴对称扩散火焰的辐射强度分布中重建火焰不同高度温度和烟黑浓度分布的试验研究,而且分析了光纤进光孔径对检测强度分布的影响,结果表明：选用较小的光纤进光孔径能提高检测强度分布的空间分辨率,本文选用0.5mm的光纤进光孔径。利用可见光波长范围的辐射强度分布重建结果来看,温度沿火焰径向方向从火焰中心到边缘呈逐渐增大的趋势；烟黑浓度分布沿火焰径向方向呈波峰分布,而且随着高度增大,峰值逐渐向火焰中心靠近。与文献重建结果的对比表明在火焰高度与文献中存在一定差异的前提下,火焰整体的温度和烟黑浓度分布趋势与文献中是一致的,而且最大的烟黑浓度水平也很接近。更多还原

【Abstract】 With the growing global energy crisis and increasing emphasis on environment issues, the combustion efficiency improvement and combustion emission reduction of fossil fuel become an important research content. While flame temperature is one of the important parameters to determine physical status and reflect the process of combustion, its accurate measurement is of great significance for developing combustion theory and understanding combustion process. The flame temperature is coupled with radiation parameters such as emissivity, absorption coefficient, scattering coefficient and soot volume fraction, so the reconstruction of temperature and radiation parameters become an effective method, but also increase the difficulty. The multispectral measurement of flame can provide plenty of radiation intensity with flame temperature and radiation information. The researchers not only can calculate temperature and radiation parameters directly from spectral intensity information, but also reconstruct the distributions of temperature and radiation parameters based on the calculation method for radiation inversion problem. In this paper, the simulation and experimental researches about the two problems were carried on. The detailed description is as below.A simple method to determine the distribution of temperature and emissivity with wavelength and judge the gray property based on the media boundary multi-spectral radiation intensity has been demonstrated. For the gray, one-dimensional plane-parallel medium and two-dimensional axisymmetric medium, the effects of different distribution of temperature, absorption and scattering coefficients in the medium to distribution of boundary temperature and emissivity with wavelength were analyzed using the proposal method and DRESOR method. The results showed that:the boundary radiation may still display non-gray body property and the temperature may change with wavelength even for gray medium, so the validity of temperature measurement methods based on the gray body assumption should be further validated, especially for multi-wavelength temperature measurement method based on spectral intensity in a large wavelength range.A calibrated spectrometer system was used for the data acquisition of the radiation intensity profile of a flame over a range of wavelengths (200～1100 nm). The wavelength range that meets the gray body assumption, in which the emissivity can be assumed as a constant, can be determined from the emissivity profile obtained by the proposal method. Then the temperature and emissivity of the flame and their relative mean square deviations were calculated within that range. Experiments were conducted on solidified gasoline, red phosphorus flames, ethylene diffusion flame and pulverized coal-fired flames in a commercial 420 t/h boiler furnace. The results show that the radiation of the gasoline flame can be assumed as a gray body in the range between 550 and 900 nm, for the coal-fired flame the range is between 500 and 1000 nm; while the radiation of the red phosphorus flame and ethylene diffusion flame cannot be assumed as a gray body within the measurement wavelength range. The temperature and emissivity calculation results of coal-fired flames are found to be in reasonable agreement with results using other methods from the literature.A simulation investigation for simultaneous reconstruction of distributions of temperature and soot volume fraction from multi-wavelength emission in an axisymmetric sooting flame using the stochastic particle swarm optimizer (SPSO) algorithm is presented. The self-absorption of the flame is considered. The selection of parameters of the SPSO algorithm and detection wavelengths is analyzed. The effects of measurement errors and optical thickness of the flame on the accuracy of the reconstruction are investigated. A comparison between SPSO algorithm and the other literatures mentioned methods, such as Abel inversion algorithm and Tikhonov regularization method, has been made. It proved that the SPSO algorithm is robust and can obtain accurate distributions of temperature and soot volume fraction from line-of-sight intensities in only several wavelengths, especially in the flame with large optical thickness, while other methods, such as Abel inversion and Tikhonov regularization method, neglecting self-attenuation of the flame will take more errors than the SPSO algorithm.Experimental study of simultaneous reconstruction of distribution of temperature and soot volume fraction at different height of the flame from emission intensity spectra using SPSO algorithm is presented. Measurements are carried out on an axisymmetric, laboratory grate, ethylene/air diffusion flame using the visible spectroscopy. The influence of fiber aperture to the detection intensity distribution is also analyzed. The results show that:the usage of smaller optical fiber aperture can improve the spatial resolution of detection intensity distribution, and the aperture of 0.5 mm is selected. For the visible emission intensity the temperature gradually increases from the center to the edge of the flame along the radial direction, the soot volume fraction shows peak distribution along the radial direction and the peak gradually close to the flame center with the height increases. Comparison of reconstruction results with the literature shows that under the premise of the certain difference of the flame height with that of literatures, the overall distributions of flame temperature and soot volume fraction are consistent with those of the literatures and the maximum of soot volume fraction is very close.更多还原