Monitoring formaldehyde in a shock tube with a fast dual-comb spectrometer operating in the spectral range of 1740–1790 cm–1

Abstract

A dual-frequency-comb spectrometer based on two quantum-cascade lasers is applied to kinetics studies of formaldehyde (HCHO) in a shock tube. Multispectral absorption measurements are carried out in a broad spectral range of 1740–1790 cm–1 at temperatures of 800–1500 K and pressures of 2–3 bar. The formation of HCHO from thermal decomposition of 1,3,5-trioxane (C3H6O3, 0.9% diluted in argon) and the subsequent oxidation of formaldehyde is monitored with a time resolution of 4 µs. The rate coefficient of the decomposition of C3H6O3 (i.e., HCHO formation) is found to be k1 = 6.0 × 1015 exp(− 205.58 kJ mol−1/RT) s–1. For the oxidation studies, mixtures of 0.36% C3H6O3 and 1% O2 in argon are used. The information of all laser lines, along with the consideration of individual signal variance of each line, is utilized for kinetic and spectral analysis. The experimental kinetic profiles of HCHO are compared with simulations based on the mechanisms of Zhou et al. (Combust Flame, 197:423–438, 2018) and Cai and Pitsch (Combust Flame, 162:1623–1637, 2015).

QCL Dual‐Comb Spectroscopy Matures for Applications

“…Combustion diagnostics has different challenges because widely used shock-tube model systems have typical test times of the order of a millisecond, experiments are not exactly repeatable and thermal emission from oxidizing fuel has to be separated from the light used for absorption spectroscopy. Due to these complications, laser-based diagnostics are often used in combustion applications and the added spectral bandwidth at short timescales that dual-comb spectroscopy offers has recently been used to study formation and decomposition time constants [11] and as a means of validating kinetic models [12].…”

Dual-comb soliton rains based on polarization multiplexing in a single-walled carbon nanotube mode-locked Er-doped fiber laser

“…Dual-comb pulses with different repetition rates as one of the multipulse states are widely used in high-precision distance measurement [6] , spectral monitoring [7] , three-dimensional measurement, and coded imaging [8] . The dual-comb light source can be generated in both active and passive ways, such as active mode-locking generation using acousto-optic modulation or electro-optic modulation [9] , or passive mode-locking generation using saturable absorbers (SAs) to generate two sets of optical frequency combs in the same resonator [10] .…”

Mid-infrared virtually imaged phased array spectrometer with optical frequency comb: fast thermometry over large dynamic range

“…The asset of broadband, high spectralresolution spectroscopy is attributed to the wealth of spectroscopic information in a single scan of spectrum, from which temperature, pressure and concentrations of different species may be extracted simultaneously. In recent years, dual-comb spectroscopy has been applied for high-temperature (up to about 2000 K) chemical kinetics studies [11,[21][22][23], while demonstration of VIPA spectrometers mainly focuses on gas composition analysis at around room temperature [24,25]. To fully exploit the advantage of the narrow linewidth nature of the comb teeth, the resolution of the spectrometer needs to be sufficient to resolve at least the tooth interval of the comb [26].…”