基于TDLAS的机动车SCR处理系统中逃逸氨检测的研究-生物医学工程专业论文.docxVIP

ABSTRACT As one of the contributors to PM2.5 in the atmosphere, NH3 has great harm to the environment and human health. NH3 emission pollution from diesel vehicle with selective catalytic reduction (SCR) system is getting more and more attention. It is very important to realize fast and high-precision NH3 detection. Tunable Diode Laser Absorption Spectroscopy (TDLAS) has been widely used in the field of environment and atmosphere detection, because it’s a fast online detection tecnology with high seletectivity, sensitivity and high accuracy. In this paper, the relevant research on NH3 detection of the diesel vehicle with selective catalytic reduction (SCR) system is conducted. Based on the the theory of absorption spectroscopy theory and harmonic detection, a in-depth theoretical research on TDLAS detection is presented. Lorentz and Gauss absorption linetype are analyzed, and the harmonic expression of the absorption signal based on Fourier series expansion is derived. The harmonic expression considering the light intensity modulation is also described. The detection system based on Simulink is modeled. The characteristics of the second harmonic changing with the modulation depth under different absorption linetypes are researched. The distortion theory of the second harmonic and the generating mechanism of residual amplitude modulation (RAM) are researched, and some conclusions are given. The NH3 detection system is built, and the main components are described. NH3 absorption peak is selected, and the design of gas absorbtion cell is completed. The experimentation research and optimization of the paramenters of laser controller and lock-in amplifier are conducted. The effects of relevant parameters on second harmonic are analysed, and the proper parameters that are suitable for this sysetem are given. The background signal is analysed, and the weak second harmonic signal submerged in the background signal is extracted and detected, which realizes the detection of