Dual-comb spectroscopy for high-temperature reaction kinetics

In the current study, a quantum-cascade-laser-based dual-comb spectrometer (DCS) was used to paint a detailed picture of a 1.0 ms high-temperature reaction between propyne and oxygen. The DCS interfaced with a shock tube to provide pre-ignition conditions of 1225 K, 2.8 atm, and 2% p-C₃H₄/18% O₂/Ar. The spectrometer consisted of two free-running, non-stabilized frequency combs each emitting at 179 wavelengths between 1174 and 1233 cm⁻¹. A free spectral range, $f_r$, of 9.86 GHz and a difference in comb spacing, $\Delta f_r$, of 5 MHz, enabled a theoretical time resolution of 0.2 µs but the data was time-integrated to 4 µs to improve SNR. The accuracy of the spectrometer was monitored using a suite of independent laser diagnostics and good agreement observed. Key challenges remain in the fitting of available high-temperature spectroscopic models to the observed spectra of a post-ignition environment. (paper)