基于傅里叶变换近红外透射光谱的汽车用无水冷却液和制动液掺水检测

Determination of Water Content in Watered Anhydrous Coolant Liquid and Brake Fluid of Automobile Using Fourier Transform Near-Infrared Spectroscopy

冷却液和制动液是车辆工作过程中非常重要的油品,对车辆的正常运行具有非常重要的作用。在冷却液和制动液中掺水是掺假的主要手段之一,掺水后的冷却液和制动液,其有效成分会减少,从而影响了冷却液和制动液本来的功能,对车辆造成危害,从而影响车辆的正常运行。实现对冷却液和制动液含水率的快速准确检测,是保证冷却液和制动液品质的关键。采用傅里叶变换近红外光谱对不同品牌的掺水的汽车无水冷却液和制动液含水率检测进行了研究。分别采集了3个不同品牌无水冷却液和4个不同品牌制动液在掺入不同含水率(0%,5%,10%,15%,20%,25%,30%,35%)下的近红外透射光谱,并基于10067~5442cm^-1范围内的光谱进行了研究。不同含水率的无水冷却液和制动液近红外透射光谱存在差异。单个品牌不同含水率的无水冷却液及制动液的主成分分析(PCA)表明不同含水率样本之间存在差异。采用二阶导数(Second derivative)对单个品牌以及包含有不同品牌的无水冷却液及制动液(不同含水率)的特征波数进行了选择,发现不同品牌之间选择的特征波数相近,且单个品牌与包含不同品牌之间选择的特征波数也相近,而经过特征波数选择后波数减少了至少98.67%。基于单个品牌样本的全谱以及包含有不同品牌样本的全谱和特征波数,分别建立偏最小二乘(PLS)和最小二乘支持向量机(LS-SVM)模型,所有模型的建模集和预测集决定系数均高于0.9,剩余预测偏差(RPD)均高于3,含水率预测模型取得了较好的预测结果。基于全谱的模型预测效果与基于特征波数的模型预测效果相当,表明特征波数选择可用于无水冷却液和制动液中含水率的检测。基于单个品牌样本的模型预测效果与包含不同品牌样本的模型预测效果相近,表明包含品牌差异,建立基于多个品牌的无水冷却液和制动液掺水量的预测模型是可行的。研究结果表明,近红外透射光谱结合化学计量学方法可用于不同品牌汽车无水冷却液和制动液掺水量检测,为研究开发在线检测仪器奠定了基础,也为其他类型的车用液体制品中含水率的检测提供了技术和方法参考。

Coolant liquid and brake fluid are important vehicle oils, and they are of great significance for the normal operation of vehicles. Adding water into the coolant liquid and brake fluid is the common adulteration method for coolant liquid and brake fluid. The active ingredients in adulterated coolant liquid and brake fluid will reduce, and function of coolant liquid and brake fluid will be influenced. This will result in the harm of vehicles, which will influence the normal operation of vehicles. Rapid and accurate detection of water content in coolant liquid and brake fluid is of importance for quality assurance. In this paper, Fourier transform near-infrared spectroscopy was used to determine water content in different brands of watered anhydrous coolant liquid and brake fluid. Three brands of anhydrous coolant liquid, and four brands of brake fluid were used. In addition, samples with water contents of 0%, 5%, 10%, 15%, 20%, 25%, 30% and 35% were prepared. Fourier transform near-infrared transmittance spectra of the samples were acquired, and the spectral range of 10 067~5 442 cm^-1 were used for analysis. There were differences on near-infrared transmittance spectra among samples with different water contents. Based on each brand of anhydrous coolant liquid and brake fluid, principal component analysis(PCA) indicated the obvious differences among samples with different water contents. Besides, second derivative spectra were used to select optimal wavenumbers for each brand of anhydrous coolant liquid and brake fluid, as well as the combination of all brands. The selected optimal wavenumbers were similar among different brands of anhydrous coolant liquid as well as the combination of brands, and the selected optimal wavenumbers were similar among different brands of brake fluid as well as the combination of brands. The number of wavenumbers reduced at least 98.67% after selection. Based on the full spectra and the selected optimal wavenumbers, partial least squares(PLS) and least-squares support vector machine(LS-SVM) were built. All the models obtained quite good performances, with determination of coefficient(R2) over 0.9 and residual prediction deviation(RPD) over 3. These prediction models obtained good performances. The performances of models for single brands were similar to those for the combination of brands, indicating that it was feasible to build calibration models using the combination of brands which would benefit the practical application. The overall results indicated the feasibility of using Fourier transform near-infrared transmittance spectroscopy combined with chemometric methods could be used to determine water adulteration in different brands of anhydrous coolant liquid and brake fluid. The results would help to develop on-line detection systems for water adulteration in different brands of anhydrous coolant liquid and brake fluid, and would provide guidance for detecting water content other fluids for automobile.