Cavity-enhanced absorption sensor for carbon monoxide in a rapid compression machine |
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| Affiliation: | 1. Department of Energy and Power Engineering, Tsinghua University, 100084 Beijing, PR China;2. IVG, Institute for Combustion and Gas Dynamics – Reactive Fluids, University of Duisburg-Essen, 47057 Duisburg, Germany;1. Physico-Chemical Fundamentals of Combustion, RWTH Aachen University, Schinkelstraße 8, D-52062 Aachen, Germany;2. Institute of Technical Thermodynamics, RWTH Aachen University, Schinkelstraße 8, D-52062 Aachen, Germany;1. King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Physical Sciences and Engineering Division, Thuwal 23955-6900, Saudi Arabia;2. Molecular Science and Nano-Materials Lab, Institute for Computational Science and Technology, SBI Building, Quang Trung Software City, Tan Chanh Hiep Ward, District 12, Ho Chi Minh City, Viet Nam;3. University of Science, 227 Nguyen Van Cu, Ward 4, District 5, Ho Chi Minh City, Vietnam;4. Vietnam National University – HCMC, Quarter 6, Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam;5. Institute of Chemistry, University of Miskolc, Egyetemváros A/2, H-3515 Miskolc, Hungary;6. School of Chemical and Environmental Engineering, International University, Quarter 6, Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam |
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| Abstract: | A sensor based on cavity-enhanced absorption spectroscopy (CEAS) was implemented for the first time in a rapid compression machine (RCM) for carbon monoxide concentration measurements. The sensor consisted of a pulsed quantum cascade laser (QCL) coupled to a low-finesse cavity in the RCM using an off-axis alignment. The QCL was tuned near 4.89 µm to probe the P(23) ro-vibrational line of CO. The pulsed mode operation resulted in rapid frequency down-chirp (6.52 cm−1/µs) within the pulse as well as a high time resolution (10 µs). The combination of rapid frequency down-chirp and off-axis cavity alignment enabled a near complete suppression of the cavity coupling noise. A CEAS gain factor of 133 was demonstrated in experiments, resulting in a much lower noise-equivalent detection limit than a single-pass arrangement. The sensor thus presents many opportunities for measuring CO formation at low temperatures and for studying kinetics using dilute reactive environments; one such application is demonstrated in this work using dilute n-heptane/air mixtures in the RCM. The formation of CO during first-stage ignition of n-heptane was measured over 802–899 K at a nominal pressure of 10 bar. These conditions correspond to the NTC region of n-heptane and such results provide useful metrics to test and compare the predictions of low-temperature heat release by different kinetic models. |
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