Investigation of ro‐vibrational spectra of small hydrocarbons at elevated temperatures using infrared degenerate four‐wave mixing

Abstract

The ro-vibrational spectra around 3 μm of four small hydrocarbons (C 2 H 2 , CH 4 , C 2 H 6 and C 2 H 4 ) at 296, 550 and 820 K have been investigated using infrared degenerate four-wave mixing (IR-DFWM). The spectra were recorded in gas flows of nitrogen with small admixtures of the hydrocarbons. A fused silica glass tube surrounded by an electric heating wire was used to heat the gas flows. The recorded IR-DFWM spectra are compared with simulations using the spectral information available in the HITRAN database, in order to identify spectral lines. The measurements demonstrate good signal to noise ratio and good sensitivity even at elevated temperatures. Several weak hot lines were detected that are not included in the current database. This paper demonstrates the potential of IR-DFWM for purposes of investigating spectral lines at elevated temperatures, which is often a challenging task with conventional absorption spectroscopy techniques. The possibility of applying IR-DFWM for combustion diagnostics of small hydrocarbons is discussed from the detection limits of the measurements and the potential water line interference. 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.

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

“…Sahlberg and co‐workers demonstrated nonintrusive, in situ detection of ammonia in hot gas flows with mid‐infrared degenerate four‐wave mixing at 2.3 μm. These results show the potential of IR‐DFWM for detection of NH 3 in combustion environments . Members of the same research group investigated the ro‐vibrational spectra of small hydrocarbons at elevated temperatures using infrared degenerate four‐wave mixing.…”

“…These results show the potential of IR-DFWM for detection of NH 3 in combustion environments. [101] 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.…”

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer

“…At the same time, appearance of additional absorption features indicated by "*" is observed in the spectrum (in red). These absorption features correspond to strongest R QK lines from the ν7 band of ethane (C2H6), along with more weaker lines, which corresponds to the P and R branch of the ν7-band and ν10-band of ethane in this spectral region [51,52]. The HITRAN database only provides nine R QK lines for ethane in this spectral region, which are indicated by "*" and the two weaker lines are indicated by arrows in Figure 4 (a).…”

Mid-Infrared Polarization Spectroscopy Measurements of Species Concentrations and Temperature in a Low-Pressure Flame

“…The HITRAN database line list for C 2 H 6 is not complete in this spectral region, containing only data for the high intensity Q-branches of the ν 7 band. 25 The absorption spectra of C 2 H 6 in this spectral range has been investigated at room temperature 56 and elevated temperatures, 49,51,52 showing the existence of several P- and R-branch transitions between the Q-branches. These transitions can probably account for many of the unidentified lines in the IRPS spectrum in Fig.…”