基于TDLAS的柴油机SCR氨污染检测系统研究

发布时间：2018-06-06 04:07

本文选题：TDLAS + 氨气浓度检测　；参考：《天津科技大学》2017年硕士论文

【摘要】：随着机动车保有量的不断增加和人们环保意识的增强,利用选择性催化还原系统(Selective Catalytic Reduction, SCR)降低汽车尾气中NOx排放的方法也得到越来越多的应用,但是由于作为还原剂的尿素水溶液很难被控制到绝对适量,所以过量的NH3被排放到空气中。由于NH3不仅对人类的健康造成危害,而且是PM2.5持续走高的主要因素,故导致柴油机尾气处理的二次污染。可调谐二极管激光吸收光谱技术(Tunable Diode Laser Absorption Spectroscopy,TDLAS)凭借其高选择性、高灵敏度等优点,对柴油机尾气处理中溢出的少量NH3可以进行精准检测,故本文以TDLAS作为检测NH3的方法。本论文针对应用到的波长调制光谱学理论,利用气体分子吸收理论分析了氨气拥有特定吸收谱线的原因,对光谱谱线的线型、线宽、线强进行分析,介绍了 Lambert-Beer定律,运用了直接吸收检测的扫描波长法来获得准确的氨气吸收峰,并对谐波检测进行了对比分析,并选用谐波检测中波长调制方法去除低频噪声,选出二次谐波信号作为浓度信号的采集信号。对TDLAS氨气浓度检测系统进行设计,在利用HITRAN数据库分析了氨气的吸收峰和柴油机尾气中H2O、CO2、CO、C2H2、NO、N2O气体成分的吸收峰位置,最终选择了 1512.22nm的吸收谱线作为本文的氨气吸收谱线。对系统中选用的主要器件的型号、功能原因进行分析,对LabVIEW数据采集程序和MATLAB数据预处理程序进行设计。对汽车尾气前处理系统进行了以设计滤除颗粒物等杂质,过滤芯采用三氧化二铝与二氧化硅的烧结材料。实现了柴油机TDLAS氨气浓度检测系统,对激光驱动器的输出温度和驱动电流的选择进行试验分析,并对信号发生器产生的扫描信号和调制信号的频率和幅度进行实验计算,最终选择扫描信号幅度为600mV、频率为5Hz;调制信号幅度为150mV,频率为50KHz;最后计算了锁相放大器时间常数、灵敏度、相位对二次谐波的影响并得出结论,最后实验分析了 TDLAS氨气检测系统稳定性为98%。对采集到的二次谐波数据进行实验预处理,利用气体分割器将气体浓度为10000ppm、600ppm、40ppm的氨气分别分为10%-100%该浓度的10组气体,并给出了每种浓度氨气10组气体的最小二乘拟合结果,然后利用500ppm的标准气体模块与处理后的待测数据利用最小二乘法算法进行拟合,待测氨气的检测限为2.4ppm。
[Abstract]:With the increasing of vehicle ownership and people's awareness of environmental protection, the method of reducing NOx emission from automobile exhaust by selective catalytic reduction system (Catalytic Reduction, SCR) has been applied more and more widely. However, because the urea solution as a reducing agent is difficult to be controlled to an absolute appropriate amount, excessive NH3 is discharged into the air. NH3 is not only harmful to human health, but also the main factor of PM2.5 rising continuously, which leads to secondary pollution of diesel engine exhaust gas treatment. Tunable Diode Laser Absorption Spectroscopy-TDLASA can accurately detect a small amount of NH3 overflow in diesel engine exhaust treatment by virtue of its high selectivity and high sensitivity. Therefore, TDLAS is used as a method to detect NH3 in this paper. Based on the theory of wavelength modulation spectroscopy applied in this paper, the reason why ammonia has a specific absorption line is analyzed by using the gas molecular absorption theory. The line shape, line width and line strength of the spectrum line are analyzed, and the Lambert-Beer law is introduced. The scanning wavelength method of direct absorption detection is used to obtain the exact absorption peak of ammonia gas, and the harmonic detection is compared and analyzed, and the method of wavelength modulation in harmonic detection is used to remove the low frequency noise. The second harmonic signal is selected as the sampling signal of the concentration signal. The TDLAS ammonia concentration detection system was designed. The position of the absorption peak of ammonia and the absorption peak of CO _ 2H _ 2C _ 2H _ 2C _ 2H _ 2N _ 2O in diesel engine exhaust gas were analyzed by using HITRAN database. Finally, the absorption spectrum line of 1512.22nm was chosen as the absorption spectrum line of ammonia gas in this paper. This paper analyzes the models and functional reasons of the main devices selected in the system, and designs the LabVIEW data acquisition program and the MATLAB data preprocessing program. The pre-treatment system of automobile tail gas was designed to filter the impurity such as particulates, and the filter core was sintered with aluminum trioxide and silica. The TDLAS ammonia concentration detection system of diesel engine is realized. The selection of output temperature and driving current of laser driver is tested and analyzed, and the frequency and amplitude of scanning signal and modulation signal produced by signal generator are calculated experimentally. Finally, the scanning signal amplitude is 600mV, the frequency is 5Hz, the modulation signal amplitude is 150mV and the frequency is 50kHz. Finally, the influence of the time constant, sensitivity and phase of the phase-locked amplifier on the second harmonic is calculated and concluded. Finally, the stability of TDLAS ammonia detection system is analyzed. The collected second harmonic data were pretreated experimentally. The ammonia gas with a concentration of 10 000 ppm-1, 600 ppm or 40 ppm was divided into 10 groups of 10 groups of gases with a concentration of 10 to 100% by using a gas splitter. The least square fitting results of 10 groups of gases with each concentration of ammonia were given. Then the standard gas module of 500ppm is used to fit the measured data, and the detection limit of ammonia gas is 2.4 ppm.
【学位授予单位】：天津科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP274

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