Premixed CO/air combustion in a closed duct with inhibition

Syngas is a promising alternative energy carrier with low pollutant emissions. Carbon monoxide is the main component of syngas. Once accidentally exposed to air, CO/air mixture could be easily ignited starting fire or explosion, which has been scarcely investigated. Therefore, experiments were conducted in a closed duct to study the premixed stoichiometric CO/air combustion characteristics with/without CO2 addition. Flame images and overpressure were captured by the high-speed schlieren photography and pressure sensor, respectively. It shows that the inhibitor had remarkable negative effect on flame and pressure dynamics. The competitive effect between flame instabilities and buoyancy on flame deformation was established. The classic tulip flame was more robust when the flame instabilities were strengthened along with attenuated buoyancy effect. When the buoyancy effect was significant with higher inhibitor content, an inclined flame front would form without tulip inversion and then propagate downwards. At specific conditions, tulip structure did occur at early stages when the flame instabilities were dominant, while at later stages, with decreasing flame speed, the buoyancy effect became more prominent leading to an inclined front. The thermal and kinetic effects of CO2 on premixed CO/air combustion were scrutinized for a comprehensive view of inhibiting mechanism.