一种基于近红外光谱技术的柴油在线软测量方法研究

为解决柴油凝点难以实时在线检测的问题，提出一种应用近红外(NIR)光谱分析技术的软测量方法。首先，利用光谱分析仪对柴油样品在750～1 550 nm光谱区的信息进行采集，并用多项式卷积对NIR光谱数据进行光谱平滑、基线校正和标准归一化；再由主元分析(PCA)提取NIR光谱数据集特征，降低输入维数，提高了各维特征的敏感性；最后, 通过SVR算法建立凝点的软测量模型。150个柴油样品作为实验材料，其中100个作为校正(训练)样本，其余作为测试样本。经过PCA分析之后，401维的原始NIR吸收光谱数据集被降到了6维。为了验证检测方法的效率，用四种不同的软测量模型(BP，SVR，PCA+BP和PCA+SVR)对测试样品进行估计。实验结果表明：(1)用PCA进行特征提取的软测量模型普遍优于直接作用在光谱波长域的模型；(2)SVR模型的测量效果明显优于BP网络模型，其测试误差只有后者的一半；(3)所提软测量方法的检测值与用冷凝法测量的标准化学值之间的均方误差小于4.2。研究说明了本方法可用于对柴油产品凝点的快速测量。

Online Soft Sensing Method for Freezing Point of Diesel Fuel Based on NIR Spectrometry

To solve the problems of real-time online measurement for the freezing point of diesel fuel products, a soft sensing method by near-infrared (NIR) spectrometry was proposed. Firstly, the information of diesel fuel samples in the spectral region of 750-1 550 nm was extracted by spectrum analyzer, and the polynomial convolution algorithm was also applied in spectrogram smoothness, baseline correction and standardization. Principal component analysis (PCA) was then used to extract the features of NIR spectrum data sets, which not only reduced the number of input dimension, but increased their sensitivity to output. Finally the soft sensing model for freezing point was built using SVR algorithm. One hundred fifty diesel fuel samples were used as experimental materials, 100 of which were used as training (calibrating) samples and the others as testing samples. Four hundred and one dimensional original NIR absorption spectrum data sets, through PCA, were reduced to 6 dimensions. To investigate the measuring effect, the freezing points of the testing samples were estimated by four different soft sensing models, BP, SVR, PCA BP and PCA SVR. Experimental results show that (1)the soft sensing models using PCA to extract features are generally better than those used directly in spectrum wavelength domain; (2)SVR based model outperforms its main competitors-BP model in the limited training data, the error of which is only half of the latter; (3)The MSE between the estimated values by the presented method and the standard chemical values of freezing point by condensing method are less than 4.2. The research suggests that the proposed method can be used in fast measurement of the freezing point of diesel fuel products by NIRS.