Investigation of High-Pressure Ignition Phenomena of CO2-Diluted Syngas in Shock Tubes

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Abstract With the rise in popularity of syngas comes the need to better understand the chemistry and combustion phenomena that occur during its use in applications such as the Allam-Fetvedt cycle that utilizes supercritical-CO2 (sCO2) as a working fluid. Several recent studies have shown significant model discrepancies in ignition delay time (IDT) data of syngas diluted in CO2 from shock-tube facilities. However, undesirable inhomogeneous ignition may occur at high pressures behind reflected shock waves in a shock tube. Understanding these undesirable events and when they arise during CO2-diluted syngas combustion is crucial to produce data for chemical mechanism refinement. To allow for imaging studies of these ignition and combustion events, a new addition has been made to the High-Pressure Shock Tube facility at the TEES Turbomachinery Laboratory at Texas A&M University. This paper presents the findings from that facility during the ignition and combustion of CO2-diluted syngas from reflected-shock ignition experiments. Pressures from 12 to 43 atm were studied in a 0.05 H2 + 0.05 O2 + 0.05 CO + 0.85 CO2 blend. Results from high-speed OH* imaging through the endwall showed evidence of homogeneous ignition and combustion within a central core region, but with a clear delineation between the central core and a concentric band adjacent to the sidewall, likely due to reflected-shock bifurcation. Follow-on imaging experiments are suggested before a complete understanding of syngas-CO2 ignition at high pressures in shock tubes is obtained.