Nei Wei, Ye Qing-hao, Xu Zhen-yu, Zhang Guang-le, Xia Hui-hui, Kan Rui-feng
Guang Pu Xue Yu Guang Pu Fen Xi. 2017 Mar;37(3):816-21.
In the field of the absorption spectrum, especially for direct tunable diode laser absorption spectroscopy (dTDLAS) technology, the integrated area of the absorption spectrum is needed to be measured accurately for calculating the temperature and the component concentration of the flow field. Doing single optical path absorption spectroscopic measurement in the non-uniform flow field, spectral lineshape broadening is varied with the flow changes, in previous research reports, researchers mainly use single Voigt or Lorentz profile to fit absorbance curve or use directly integral to obtain the integrated area of the absorption spectrum. There are some shortcomings in these methods, resulting in certain error between the fitting result and the actual area, which is not conducive to the accurate measurement of flow field parameters. Firstly, the error is analyzed theoretically, and then, we adopt the simulation method to obtain the error size of the method. Finally, we proposed the Voigt wings fitting absorbance method to reduce the fitting error. The operation of Voigt wings fitting method is to Select the wings of the spectral line, and then use Voigt profile fitting, The difference between the two wings was used the numerical integral method to calculate area, the integrated area is sum of Voigt profile fitting area and numerical integral area. We have used water vapor as the target gas, with eight absorption lines which have different low-level states energy from HITRAN 2012 database being selected-, building two kinds of non-uniform flow field model base on the flat flame furnace, and through the method of segmentation to equivalent processing the no uniformity of flow field. Using Voigt profile fitting method, numerical integral method and Voigt profile wings fitting method to obtain the integral area of models, the error size is obtained by comparing with the theoretical value. As the result of contrast, the fitting error of Voigt profile fitting method is large and related to the different absorption line, the error of numerical integral method is biggest but it is nothing to do with absorption line, the fitting error of Voigt profile wings fitting method is least and stable. By force of contrast, we determined the appropriate method to obtain integral area in the different non-uniform flow field, which is beneficial to obtain accurate integrated area and flow field parameters.
在吸收光谱领域，特别是对于直接可调谐二极管激光吸收光谱（dTDLAS）技术，为了计算流场的温度和组分浓度，需要精确测量吸收光谱的积分面积。在非均匀流场中进行单光路吸收光谱测量时，谱线形状展宽会随流动变化而改变，在以往的研究报道中，研究人员主要使用单一的沃伊特（Voigt）或洛伦兹（Lorentz）线型来拟合吸光度曲线，或者直接使用积分来获得吸收光谱的积分面积。这些方法存在一些缺点，导致拟合结果与实际面积之间存在一定误差，不利于流场参数的精确测量。首先从理论上分析误差，然后采用模拟方法得到该方法的误差大小。最后，提出了沃伊特线型翼拟合吸光度方法以减小拟合误差。沃伊特线型翼拟合方法的操作是选取谱线的翼部，然后用沃伊特线型进行拟合，利用两翼部的差异通过数值积分法计算面积，积分面积为沃伊特线型拟合面积与数值积分面积之和。我们以水蒸气作为目标气体，从HITRAN 2012数据库中选取了八条具有不同低能级态能量的吸收线，基于平焰炉建立了两种非均匀流场模型，并通过分段方法对等流场的不均匀性进行处理。使用沃伊特线型拟合方法、数值积分法和沃伊特线型翼拟合方法获得模型的积分面积，通过与理论值比较得到误差大小。对比结果表明，沃伊特线型拟合方法的拟合误差较大且与不同吸收线有关，数值积分法的误差最大但与吸收线无关，沃伊特线型翼拟合方法的拟合误差最小且稳定。通过对比，确定了在不同非均匀流场中获取积分面积的合适方法,这有利于获得准确的积分面积和流场参数。
