本文選題：TDLAS + 氨氣濃度檢測(cè)��； 參考：《天津科技大學(xué)》2017年碩士論文

【摘要】：隨著機(jī)動(dòng)車保有量的不斷增加和人們環(huán)保意識(shí)的增強(qiáng),利用選擇性催化還原系統(tǒng)(Selective Catalytic Reduction, SCR)降低汽車尾氣中NOx排放的方法也得到越來(lái)越多的應(yīng)用,但是由于作為還原劑的尿素水溶液很難被控制到絕對(duì)適量,所以過(guò)量的NH3被排放到空氣中。由于NH3不僅對(duì)人類的健康造成危害,而且是PM2.5持續(xù)走高的主要因素,故導(dǎo)致柴油機(jī)尾氣處理的二次污染�？烧{(diào)諧二極管激光吸收光譜技術(shù)(Tunable Diode Laser Absorption Spectroscopy,TDLAS)憑借其高選擇性、高靈敏度等優(yōu)點(diǎn),對(duì)柴油機(jī)尾氣處理中溢出的少量NH3可以進(jìn)行精準(zhǔn)檢測(cè),故本文以TDLAS作為檢測(cè)NH3的方法。本論文針對(duì)應(yīng)用到的波長(zhǎng)調(diào)制光譜學(xué)理論,利用氣體分子吸收理論分析了氨氣擁有特定吸收譜線的原因,對(duì)光譜譜線的線型、線寬、線強(qiáng)進(jìn)行分析,介紹了 Lambert-Beer定律,運(yùn)用了直接吸收檢測(cè)的掃描波長(zhǎng)法來(lái)獲得準(zhǔn)確的氨氣吸收峰,并對(duì)諧波檢測(cè)進(jìn)行了對(duì)比分析,并選用諧波檢測(cè)中波長(zhǎng)調(diào)制方法去除低頻噪聲,選出二次諧波信號(hào)作為濃度信號(hào)的采集信號(hào)。對(duì)TDLAS氨氣濃度檢測(cè)系統(tǒng)進(jìn)行設(shè)計(jì),在利用HITRAN數(shù)據(jù)庫(kù)分析了氨氣的吸收峰和柴油機(jī)尾氣中H2O、CO2、CO、C2H2、NO、N2O氣體成分的吸收峰位置,最終選擇了 1512.22nm的吸收譜線作為本文的氨氣吸收譜線。對(duì)系統(tǒng)中選用的主要器件的型號(hào)、功能原因進(jìn)行分析,對(duì)LabVIEW數(shù)據(jù)采集程序和MATLAB數(shù)據(jù)預(yù)處理程序進(jìn)行設(shè)計(jì)。對(duì)汽車尾氣前處理系統(tǒng)進(jìn)行了以設(shè)計(jì)濾除顆粒物等雜質(zhì),過(guò)濾芯采用三氧化二鋁與二氧化硅的燒結(jié)材料。實(shí)現(xiàn)了柴油機(jī)TDLAS氨氣濃度檢測(cè)系統(tǒng),對(duì)激光驅(qū)動(dòng)器的輸出溫度和驅(qū)動(dòng)電流的選擇進(jìn)行試驗(yàn)分析,并對(duì)信號(hào)發(fā)生器產(chǎn)生的掃描信號(hào)和調(diào)制信號(hào)的頻率和幅度進(jìn)行實(shí)驗(yàn)計(jì)算,最終選擇掃描信號(hào)幅度為600mV、頻率為5Hz;調(diào)制信號(hào)幅度為150mV,頻率為50KHz;最后計(jì)算了鎖相放大器時(shí)間常數(shù)、靈敏度、相位對(duì)二次諧波的影響并得出結(jié)論,最后實(shí)驗(yàn)分析了 TDLAS氨氣檢測(cè)系統(tǒng)穩(wěn)定性為98%。對(duì)采集到的二次諧波數(shù)據(jù)進(jìn)行實(shí)驗(yàn)預(yù)處理,利用氣體分割器將氣體濃度為10000ppm、600ppm、40ppm的氨氣分別分為10%-100%該濃度的10組氣體,并給出了每種濃度氨氣10組氣體的最小二乘擬合結(jié)果,然后利用500ppm的標(biāo)準(zhǔn)氣體模塊與處理后的待測(cè)數(shù)據(jù)利用最小二乘法算法進(jìn)行擬合,待測(cè)氨氣的檢測(cè)限為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.
【學(xué)位授予單位】：天津科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TP274

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本文編號(hào)：1984996