Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments

Abstract

Ammonia (NH3) is regarded as an important nitrogen oxides (NOx) precursor and also as an effective reductant for NOx removal in energy utilization through combustion, and it has recently become an attractive non-carbon alternative fuel. To have a better understanding of thermochemical properties of NH3, accurate in situ detection of NH3 in high temperature environments is desirable. Ultraviolet (UV) absorption spectroscopy is a feasible technique. To achieve quantitative measurements, spectrally resolved UV absorption cross-sections of NH3 in hot gas environments at different temperatures from 295 K to 590 K were experimentally measured for the first time. Based on the experimental results, vibrational constants of NH3 were determined and used for the calculation of the absorption cross-section of NH3 at high temperatures above 590 K using the PGOPHER software. The investigated UV spectra covered the range of wavelengths from 190 nm to 230 nm, where spectral structures of the [Formula: see text] transition of NH3 in the umbrella bending mode, v2, were recognized. The absorption cross-section was found to decrease at higher temperatures. For example, the absorption cross-section peak of the (6, 0) vibrational band of NH3 decreases from ∼2 × 10−17 to ∼0.5 × 10−17 cm2/molecule with the increase of temperature from 295 K to 1570 K. Using the obtained absorption cross-section, in situ nonintrusive quantification of NH3 in different hot gas environments was achieved with a detection limit varying from below 10 parts per million (ppm) to around 200 ppm as temperature increased from 295 K to 1570 K. The quantitative measurement was applied to an experimental investigation of NH3 combustion process. The concentrations of NH3 and nitric oxide (NO) in the post flame zone of NH3–methane (CH4)–air premixed flames at different equivalence ratios were measured.

Sensitive Detection of OCS Using Thermal Conversion Combined with Spectral Reconstruction Filtering Differential Optical Absorption Spectroscopy

“…This includes a plot of the distribution between the two straight lines after reconstruction and a formulaic derivation of the slope-concentration relation. C = k normalm k normals × C s The interference caused by gas mixtures is similar to that caused by noise, which can be eliminated by fitting, and in order to verify the effect of interference elimination, experiments on the detection of gas mixtures were carried out. NH 3 and NO are common gases found in the environment and in exhaled breath. , To validate the anti-interference capability of this measurement method, NH 3 and NO were used as interfering gases. The gas mixtures, calculation results, and relative biases are presented in Table .…”

“…NH 3 and NO are common gases found in the environment and in exhaled breath. 46,47 To validate the anti-interference capability of this measurement method, NH 3 and NO were used as interfering gases. The gas mixtures, calculation results, and relative biases are presented in Table 1.…”

Measurement of the absorption cross-sections of sulfur compounds in the 180–270 nm region considering nonlinear effects

“…Wu et al 20 investigated the temperature effect of the ACS of SO 2 and found that its amplitude increased by an order of magnitude when the temperature increased from 200 K to 400 K. Dua et al 21 established functions of the ACS with temperature and pressure by fitting spectra onto parameterized curves, and found that the ACS of acetone at a wavelength of 193 nm increased with increasing pressure and temperature. However, when Weng et al 18 studied the ACS of NH 3 at 295–590 K, they observed that the ACS decreased with increasing temperature. The effect of temperature on the ACS was investigated by Jin et al 22 through recording the changes in SO 2 absorption spectra, and it was also found that the pattern of changes in the ACS at various bands was inconsistent.…”

“…10 In this law, the absorption cross-section (ACS) is an important optico-physical parameter, and an effective cross-section can accurately invert the concentration of the substance. [15][16][17][18] This parameter can usually be calculated using the energy level transition theory formula or obtained through experimental measurements (Lambert-Beer law). Due to the availability of spectral line parameters for various substances in infrared spectroscopy, the ACS can be directly computed from the energy level transition theory.…”