Influence of carbon black nanoparticles on the front flame velocity of methane/air explosions

This work aims to study the influence of low concentrations of carbon black nanoparticles in gas mixtures on the front flame velocity. Due to their low settling velocity, nanoparticles offer the opportunity to study the hybrid mixture explosion at low turbulence levels of dispersion. They can also be used as particles to model the presence of soot. The flame velocity of carbon black nanoparticles/methane/air mixtures was measured in a vertical 1 m long tube with a square crosssection connected to a gas mixing system. Dust clouds are generated by a pulse of methane/air mixture at 5 barg from the bottom of the tube, where the mixture is also ignited. A high-speed video camera is used to record the flame propagation. An estimation of the laminar burning velocity is obtained using the method proposed by Andrews and Bradley. Although this method may not be precise for laminar flame velocity estimations, it offers a first approximation for hybrid systems explosions. The influence of the initial turbulence was also studied by varying the ignition delay. The influence of low concentrations of carbon black nanoparticles on the front flame velocity has been appreciated by comparing the results obtained for gaseous mixtures explosions at different turbulence levels. The burning velocity of gaseous mixture seems to increase when the initial turbulence of the system is augmented. However, when the initial turbulence is significant, the front flame velocity seems to decrease, suggesting that the flame kernel can be strongly destabilized by turbulent vortices. Moreover, it appears that the flame burning velocity can slightly decrease when carbon black nanoparticles concentration is increased. The unstretched burning velocity is decreased by 43% when 20 mg of carbon black nanoparticles are added to the system. This trend could be explained by the enhancement of the heat radiation transfer of the system. The results are then compared to the explosions trends in a 20 L spherical vessel.