In this paper, the basic principles of differential optical absorption spectroscopy (DOAS) technology are studied in depth, and the architecture of a motor vehicle exhaust gas detection system is built. The simultaneous detection of nitrogen oxides (NOx) and hydrocarbons (HC), the main components of motor vehicle exhaust based on Ultraviolet spectroscopy was achieved. NOx (NO) and HC (1,3-butadiene) in the exhaust of motor vehicles as the object of study. The DOAS detection system is used to obtain the spectral data, calculate the differential absorption spectrum of the gas, invert the concentration of the gas to be measured using the least squares method, and reduce the error of the measured gas concentration value using the nonlinear compensation method. The results show that the accuracy and stability of the testing system is good, and the relative error of the measurement results is within ±10% of the latest national metrology specifications.
Based on the absorption mechanism of infrared spectrum of ethanol gas, a detection system is designed to detect the concentration of ethanol gas quickly and accurately. Based on the Beer-Lambert law and the absorption rate of ethanol gas in the near-infrared region, the infrared diode with the center wavelength of 1300 nm is selected as the light source, and then the cascaded air chamber is designed, and the light source driving circuit and detecting circuit are designed and made. The results show that the system is simple in structure, stable in performance. The measurement error is within 5.3%, which meets the current demand of ethanol concentration detection in the liquor industry.
In order to monitor the emissions of HC and NOx in vehicle exhaust timely, a real-time monitoring system for vehicle exhaust based on ultraviolet differential optical absorption spectroscopy(DOAS) technology is designed. First, the UV spectrum data are collected by PIC microcontroller and FreeRtos real-time operating system. Then the gas concentration is obtained through the least squares method on Industrial Personal Computer(IPC). Finally, the stability and accuracy of the system are tested.
Wavelength modulation technology (WMS) is widely used in exhaust telemetry system now, but frequency modulation
technology (FMS) is rarely used for the highest working frequency limitation of phase-locked amplifier. Based on FMS
and tunable diode laser absorption spectroscopy (TDLAS), a real-time detection system for CO and CO2 of automobile
exhaust is designed by embedded system, Industrial Personal Computer(IPC) and a phase-sensitive detection circuit with
radio frequency(RF) mixer as the core. It can be shown that the system works stably,and can detect CO and CO2 timely
and accurately by experimental data.
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