Non‐intrusive, in situ detection of ammonia in hot gas flows with mid‐infrared degenerate four‐wave mixing at 2.3 µm

Abstract

We demonstrate non-intrusive, in situ detection of ammonia (NH 3 ) in reactive hot gas flows at atmospheric pressure using midinfrared degenerate four-wave mixing (IR-DFWM). IR-DFWM excitation scans were performed in the v 2 + v 3 and v 1 + v 2 vibrational bands of NH 3 around 2.3 μm for gas flow temperatures of 296, 550 and 820 K. Simulations based on spectroscopic parameters from the HITRAN database have been compared with the measurements in order to identify the spectral lines, and an absorption spectrum at 296 K has also been measured to compare with the IR-DFWM spectra. The signal-to-noise ratio of the IR-DFWM measurement was found to be higher than that of the absorption measurement. Some spectral lines in the measured IR-DFWM and absorption spectra had no matching lines in the HITRAN simulation. The detection limit of NH 3 diluted in N 2 with IR-DFWM in this spectral range was estimated at 296, 550 and 820 K to be 1.36, 4.87 and 7.06 × 10 16 molecules/cm 3 . The dependence of the NH 3 IR-DFWM signal on the quenching properties of the buffer gas flow was investigated by comparing the signals for gas flows of N 2 , Ar and CO 2 with small admixtures of NH 3 . It was found that the signal dependence on buffer gas was large at room temperature but decreased at elevated temperatures. These results show the potential of IR-DFWM for detection of NH 3 in combustion environments.

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Members of the same research group investigated the ro‐vibrational spectra of small hydrocarbons at elevated temperatures using infrared degenerate four‐wave mixing. Because of the non‐linear nature of the DFWM technique, it provides much higher contrast for strong lines of small molecules over backgrounds of high‐density weak lines, which commonly exist in hot gas flows of thermochemical reactions . Visser used resonant four‐wave mixing to unravel the electronic structure of transition metal dimers.…”

“…Because of the non-linear nature of the DFWM technique, it provides much higher contrast for strong lines of small molecules over backgrounds of high-density weak lines, which commonly exist in hot gas flows of thermochemical reactions. [102] Visser used resonant four-wave mixing to unravel the electronic structure of transition metal dimers. A new laser vaporization source for the production of transition metal dimers and clusters was constructed, and the new design aims for a high number density and maximum possible shot-to-shot stability.…”

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

“…However, these sampling-based techniques introduce unknown measurement uncertainties due to the high hygroscopicity and reactivity of NH 3 , and the intrusive processes hinder the possibility of reliable in situ measurements, especially in combustion environments. To have nonintrusive measurements of NH 3 in hot gas environments, several optical diagnostics have been developed, such as broadband UV absorption spectroscopy, 19À21 laser-induced photofragmentation fluorescence (LIPF), 22 femtosecond laser-induced plasma spectroscopy, 23 two-photon laser-induced fluorescence, 24À27 degenerate four-wave mixing, 28,29 and infrared absorption spectroscopy. 30À32 Compared with the other techniques, UV absorption spectroscopy has some advantages.…”

Ammonia Measurements with Femtosecond Two-Photon Laser-Induced Fluorescence in Premixed NH3/Air Flames

“…The latter, however, are laser-based techniques that do not possess the drawbacks mentioned above. Laser-based techniques include Raman scattering, absorption spectroscopy , [or tunable diode laser absorption spectroscopy (TDLAS) , ], nonlinear optical techniques, − and fluorescence-based techniques. − Among them, Raman scattering has a relatively simple experimental system, but its signal is weak and susceptible to interference . Absorption spectroscopy, which has a high sensitivity (e.g., 1 ppm), can achieve quantitative measurements but can only obtain line-of-sight information.…”