| A combined experimental and numerical study was conducted on the effects of chemically inert particles on the extinction and ignition behavior of strained, atmospheric methane, propane and hydrogen flames, both premixed and non-premixed. Experiments were conducted by seeding particles of various types, sizes and number densities into flames in opposed-jet configuration and observing the extinction conditions. Numerical simulations were conducted by solving the conservation equations of mass, momentum, energy, and species with detailed chemical kinetics, molecular transport, and thermal radiation for both phases, along the centerline of the counterflow. Experimental data was compared with numerical simulations to provide insight into the effects of fuel type, composition, strain rate, heat loss, particle size, type and injection orientation with respect to the flame.; It was found that for the same injected solid mass, larger particles could result in more effective cooling and extinction at certain conditions. This results from the fact that the heat exchange between the two phases is controlled by the synergistic effect of the total contact area, the temperature difference between phases and the particle residence time within the flame. It was observed that the particle size that provides the most effective cooling also depends on equivalence ratio.; The cooling effect of particles was found to be more profound in μg compared to 1-g due to the facts that in μg particles are able to penetrate deeper into the flow and the number density is increased within the flame. Meaningful scaling of phase interactions was found to be impossible due to the complexity of the couplings.; For both premixed and non-premixed configurations, increasing methane content was found to inhibit flame ignition. While premixed ignition by hot particles was found to be similar to ignition triggered by impinging a mixture on heated air or O2, differences were observed for non-premixed systems due to different gas temperature profiles. Finally, it was found that ignition response changes by moving the particle seeding from the fuel to the oxidizer side due to the different thermal properties of air and fuel. |
