High enthalpy source dedicated to quantitative infrared emission spectroscopy of gas flows at elevated temperatures

Abstract

The High Enthalpy Source (HES) is a novel high temperature source developed to measure infrared line-by-line integrated absorption cross sections of flowing gases up to 2000 K. The HES relies on a porous graphite furnace designed to uniformly heat a constant flow of gas. The flow compensates thermal dissociation by renewing continuously the gas sample and eliminating dissociation products. The flowing characteristics have been investigated using computational fluid dynamics simulation confirming good temperature uniformity. The HES has been coupled to a high-resolution Fourier transform spectrometer to record emission spectra of methane at temperatures ranging between 700 and 1400 K. A radiative model has been developed to extract absolute line intensities from the recorded spectra.

An Accurate, Extensive, and Practical Line List of Methane for the HITEMP Database

“…The difficulty of extending assignments is strongly exacerbated at higher temperatures. For this reason, a number of high-temperature laboratory measurements have been made of CH 4 in both emission (Nassar & Bernath 2003;Thiévin et al 2008;Hargreaves et al 2012;Amyay et al 2018a,b;Georges et al 2019) and absorption (Alrefae et al 2014;Hargreaves et al 2015;Ghysels et al 2018;Wong et al 2019).…”

“…Nevertheless, the RNT2017 line lists available via the last update of the TheoReTS database has previously been validated against hightemperature experimental observations particularly in the frame of the e-PYTHEAS project (Coustenis et al 2017)) aimed at astrophysical exoplanetary applications. This included DAS laser absorption spectroscopy experiments at 1000 K in the the region near 6000 cm −1 by the Grenoble University group (Ghysels et al 2018) and emission spectroscopy experiments at ∼1300 K near 3000cm −1 by the Rennes University group (Amyay et al 2018a,b;Georges et al 2019). Comparisons with FTS measurement at Norfolk University over a larger spectral range (5600-9000 cm −1 ) were reported as an absorption cross-section atlas at eight temperatures from 300 K to 1000 K (Wong et al 2019).…”

Measurement and assignment of double-resonance transitions to the 8900–9100- cm−1 levels of methane

“…However, the lack of experimental high-temperature spectra prevents validation of the accuracy of the theoretical predictions at temperatures above 1000 K [12,13]. Heating the sample to reach these temperatures under controlled conditions is an experimental challenge, because methane decomposes to graphite and hydrogen on warm surfaces, and the gas-phase spectra are congested and difficult to assign [13][14][15].…”

Non-LTE spectroscopy of the tetradecad region of methane recorded in a hypersonic flow

“…Detailed description of the SMAUG experimental setup can be found in previous publications [45,46]. Briefly, the gas mixture consisting of a carrier gas (argon) and the IR active molecule (methane in the present study) were preheated up to 850 ± 100 K in the high enthalpy source (HES) [47] before being expanded through a specially designed contoured Laval nozzle [48] into a low pressures chamber evacuated by a group of roots pumps. By properly adjusting stagnation and discharge pressure, the Laval nozzle produces a remarkably collimated hypersonic flow, which, combined with a low translational temperature, results in both reduced convective and thermal Doppler broadenings.…”