A New Optical Analysis System for Online Measurement of NO Temperature and Concentration in Combustion Processes

In the combustion process, the nitric oxide (NO) concentration and temperature are considered to be highly related to the combustion efficiency. Currently, ultraviolet differential absorption optical spectroscopy (UV-DOAS) has become an ideal method for NO analysis due to its strong absorption characteristics in the UV spectral regime. However, since temperature and concentration have similar effects and complex correspondences on intensity, it is a challenge to achieve dual-indicator sensing of NO at this time. In this paper, we first report a system based on UV-DOAS that allows simultaneous detection of NO temperature and concentration. Specifically, NO temperature was acquired by spectral blueshift, and then, concentration could be calculated based on Gaussian spectral reconstruction combined with the dual parametric surface. First, the mechanism of the temperature-induced blueshift for the NO spectrum was explained based on the energy level distribution theory. On this basis, the relationship between blueshift and temperature has been established based on multipeak spectral autocorrelation algorithm. Second, we introduced a Gaussian spectral reconstruction method based on the mapping domain transformation to improve the data quality. Then, the dual parametric surface about NO temperature and concentration was constructed using the reconstructed optical parameter. After the temperature has been acquired using the blueshift, the NO concentration can also be calculated. The test results indicated that the mean relative error for NO temperature and concentration detection was 1.86 and 2.55% in the ranges 295.15-773.15 K and 0-50 ppm, respectively. Meanwhile, this system exhibited excellent long-term stability with a detection limit of 22.5 ppb∗m.