Vehicle Exhaust Detection Method Based on Portable FTIR
QU Li-guo1,2,3, LIU Jian-guo1, XU Liang1*, XU Han-yang1, JIN Ling1, DENG Ya-song1,2, SHEN Xian-chun1, SHU Sheng-quan1,2
1. Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
2. University of Science and Technology of China, Hefei 230026, China
3. School of Physics and Electronic Information, Anhui Normal University, Wuhu 241002, China
Abstract：With the improvement of vehicle emission standards, The relevant VOC standards changed from total hydrocarbon detection to non-methane hydrocarbon (NMHC) detection. With the increase of oxygen-containing fuels, non-methane organic gas (NMOG) measurement was increased. The vehicle exhaust detection method based on portable FTIR is proposed aiming at the problems such as single component analysis, limited accuracy and complex VOC detection process of domestic automobile exhaust analyzer. The structure of the FTIR optical system is optimized based on a corner cube to meet the requirements of anti-vibration. The scanning speed of the moving mirror is improved to meet the requirements of a portable and fast FTIR spectrometer. The output band range of the FTIR infrared light source is 2～20 μm, with a resolution of 0.5 cm-1, a scanning speed of 1 Hz, and a gas pool optical range of 10 m. Stirling detector is used, with spectral responses ranging from 600 to 6 000 cm-1. Typical HC compounds such as CH4, C2H2, C2H4, C2H6, C3H6, n-C5H12, i-C5H12, C7H8, HCHO, C2H5OH, CH3CHO are selected as alternatives to VOC gases. The test bands of vehicle exhaust composition determined by the standard spectrum are 900～1 100 and 2 700～3 100 cm-1, covering all the gas absorption bands to be measured. Based on the AVL bench test, NEDC and WLTC working condition experimental test are carried out. The test vehicle is Toyota VIOS, and the test oil product was No. 92 State 5. The portable FTIR adopts an extraction method for tail gas measurement. The original exhaust sample is from a porous probe installed in the extension part of the exhaust pipe. The front end is equipped with a sample gas sampling device, which mainly includes particulate filtration and moisture removal to prevent pollution of the FTIR optical system. The experiment shows that FTIR can effectively and rapidly measure CO, CH4, NO and main HC compounds in automobile exhaust. When the gas concentration is lower than the FTIR detection limit of mole fraction 0.5 μmol·mol-1, noise signals will be introduced and the reliability will be reduced. It can be seen from the analysis that the average concentration of output gas is downgraded in descending order: CO, C2H4, CH4, NO, i-C5H12, C2H6, C7H8, n-C5H12, C2H5OH, CH3CHO. It can be seen from the three cycles of NEDC working conditions that each gas emission presents a consistent and regular change. The time series comparison of SEMTECH-DS and FTIR measurement data for CO shows a good consistency of laws. However, due to the difference in measurement technology and sampling dilution system of FTIR and SEMTECH-DS, the concentration difference between them is large. Compared with the traditional exhaust detection technology, the portable FTIR measurement system has a good response to the transient events, and can measure the multi-component concentration in real time to obtain the instantaneous emission data of motor vehicles, which can meet the requirements of the new regulation test and also provide reliable data support for the later emission characteristic analysis and simulation of motor vehicles on the actual road.
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