In Situ Measurement of NO, NO2, and H2O in Combustion Gases Based on Near/Mid-Infrared Laser Absorption Spectroscopy

Abstract

In this study, a strategy was developed for in situ, non-intrusive, and quantitative measurement of the oxides of nitrogen (NO and NO2) to describe emission characteristics in gas turbines. The linear calibration-free wavelength modulation spectroscopy (LCF-WMS) approach combined with the temperature profile-fitting strategy was utilized for trace NO and NO2 concentration detection with broad spectral interference from gaseous water (H2O). Transition lines near 1308 nm, 5238 nm, and 6250 nm were selected to investigate the H2O, NO, and NO2 generated from combustion. Experiments were performed under different equivalence ratios in a combustion exhaust tube, which was heated at 450–700 K, with an effective optical length of 1.57 m. Ultra-low NOx emissions were captured by optical measurements under different equivalence ratios. The mole fractions of H2O were in agreement with the theoretical values calculated using Chemkin. Herein, the uncertainty of the TDLAS measurements and the limitation of improving the relative precision are discussed in detail. The proposed strategy proved to be a promising combustion diagnostic technique for the quantitative measurement of low-absorbance trace NO and NO2 with strong H2O interference in real combustion gases.

In Situ All-Fiber Remote Gas Sensing Strategy Based on Anti-Resonant Hollow-Core Fiber and Middle-Hole Eccentric-Core Fiber

“…However, a slight non-linear problem can still be seen at higher concentrations, as shown in Figure 4b. For this problem, the logarithm of the spectrum can be obtained to avoid the non-linear trend under strong absorption conditions [35].…”

“…Photonics 2024, 11, 301 7 of 10 as shown in Figure 4b. For this problem, the logarithm of the spectrum can be obtained to avoid the non-linear trend under strong absorption conditions [35]. In addition, in order to verify the stability of the all-fiber RGS, long-term continuous monitoring is also carried out with 30% CO2.…”

Measurement of Light-Duty Vehicle Exhaust Emissions with Light Absorption Spectrometers

“…Algorithms to minimize disturbances have been developed [45][46][47]. TDLAS has been applied in atmospheric monitoring [48][49][50][51][52], industrial monitoring [53], combustion exhaust [54][55][56][57][58][59] for various gases, and also for NH 3 [60,61]. Other lasers commonly used in instruments are interband cascade lasers (ICLs) and quantum cascade lasers (QCLs) [62].…”

Development of High-Precision NO2 Gas Sensor Based on Non-Dispersive Infrared Technology

“…Jing Li et al presented a new strategy based on the linear calibration-free wavelength modulation spectroscopy method to eliminate the effects of water interference by resolving overlapped harmonic signals. NO 2 gas sensing exhibited ppm-level NO 2 detection with a high H 2 O interference [10]. Optical sensors have always been a remarkable area of research, as they are ideal for complex environments.…”