10. Combustion and Reacting Flows

Flammability limits in oxyfuel combustion systems are critical for safe and efficient operation, particularly when considering the addition of water as a diluent. This study investigates the role of water dilution on the flammability limit of oxyfuel flames in counterflow diffusion flame. This flammability is calculated by using OpenFoam through chemical mechanisms obtained from the literature. The flammability is calculated for various input conditions to find the maximum amount of water that can be added to the oxidant prior to extinction of flame. The cooling effect of water evaporation during combustion is mimicked for these simulations. The sensitivity analysis was performed using the fuel mass flux rate, equivalence ratio, fuel composition, pressure and inlet temperature as the input variables. We found that at a critical concentration of water, the amount of heat generated by pyrolysis and reaction is not enough to sustain the flame, thus leading to extinction. Moreover, results show linear dependence of the flammability limit with the flame strain rate. The inlet temperature does not appear to have a significant impact on the maximum water concentration that can be tolerated by the flame. At higher pressure, a larger amount of water can be tolerated in the oxidant prior to the extinction of flame. Using a reference configuration, the maximum water mole fraction that can be allowed in the oxidant is 0.75. This work is an initial step to bridge one of the gaps in the fundamental understanding of oxyfuel combustion of syngas. Yet, results indicate significant shifts in flammability limits with increasing water content, illustrating the complex interplay between dilution effects and combustion kinetics. Understanding these limits is essential for optimizing oxyfuel processes, enhancing safety protocols, and advancing sustainable combustion technologies.