High-temperature measurements of methane and acetylene using quantum cascade laser absorption near 8 μm

M.B. Sajid, T. Javed, A. Farooq
Journal of Quantitative Spectroscopy and Radiative Transfer, Issue 155, 66-74, (2015)


Methane, Acetylene, Quantum-cascade laser, Differential absorption, Shock tube


​The mid-infrared wavelength region near 8 μm contains absorption bands of several molecules such as water vapor, hydrogen peroxide, nitrous oxide, methane and acetylene. A new laser absorption sensor based on the ν4 band of methane and the ν45 band of acetylene is reported for interference-free, time-resolved measurements under combustion-relevant conditions. A detailed line-selection procedure was used to identify optimum transitions. Methane and acetylene were measured at the line centers of Q12 (1303.5 cm−1) and P23 (1275.5 cm−1) transitions, respectively. High-temperature absorption cross sections of methane and acetylene were measured at peaks (on-line) and valleys (off-line) of the selected absorption transitions. The differential absorption strategy was employed to eliminate interference absorption from large hydrocarbons. Experiments were performed behind reflected shock waves over a temperature range of 1200–2200 K, between pressures of 1–4 atm. The diagnostics were then applied to measure the respective species time-history profiles during the shock-heated pyrolysis of n-pentane.




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