Research On Nitrogen Monoxide Detection Method Based On Tunable Diode Laser Absorption Spectroscopy

The tunable diode laser absorption spectroscopy(TDLAS) technique is used primarily in gas detection of the greenhouse gases in the atmospheric environment and the trace gases in the field of industrial by scanning the absorption spectrum of the measured gas because of its characteristics of high monochromaticity and narrow linewidth. The NO takes up most of the nitrogen oxides emitted by marine diesel engine, although it is no apparent harm to human to inhale low concentrations of NO, the environment and human health still be damaged seriously because of that but it is very easy to be NO2 which is a gas with strong toxicity. So it is very necessary to develop a device for the real-time monitoring of the emission gas of Marine diesel.To achieve this function of a single fiber optical tweezers, the main work was carried out as follows:In this article, a new type of nitrogen monoxide detection method based on tunable diode laser absorption spectroscopy is researched and it is supposed to be used in the real-time monitoring of the emission gas of Marine diesel. To achieve this function of nitrogen monoxide detection, the main work was carried out as follows:First,depending on the molecular spectroscopy theory,it is easily to analyze the spectral line intensity, spectral lines and absorption coefficient of the absorption line of the gas. At the same time ,the computational method of the partition function of the NO under high temperatures is researched.Second, we do the detailed analysis about the influence of various parameters of the mathematical model on the absorption coefficient. Thus, the influence of working temperature and pressure on the experimental result is determined,and in order to achieve the better real-time monitoring effects of the experimental system,the necessary correction is introduced.Then,we present a method to calculate the temperature and pressure of the detected gas by scanning the voigt linetype which is convenient to the application of the TDLAS system because of that is needless to monitor the temperature and pressure of the system.Furthermore, a practical TDLAS experimental system is set up. In this system, the NO absorption spectrum with proper working wavelengths is determined by analyzing HIRAN molecular spectroscopy database. We measure the NO with different concentration by the methods of direct absorption and the harmonic detection. After analysis and processing the experimental data, it is clear that the simulated and testing results have good consistencies.