Fuel mobility dynamics and their influence on applied smouldering systems

• A previously developed smouldering model was equipped with multiphase flow equations. • The dynamics of organic liquid fuel mobility were quantified. • A condition with more fuel in the reaction zone leads to more robust smouldering. • Sensitivity analyses of fuel and porous media characteristics were performed. • Energy analysis determined the system's robustness in different conditions. Many recent environmentally beneficial applications of smouldering treat hazardous organic liquid fuels in inert porous media. In these applications, organic liquid mobilization can affect the treatment process, and the dynamics are poorly understood. Organic liquid mobilization is therefore a key knowledge gap that hinders the optimization of applied smouldering. This is especially the case in large scales where mobilization appears to be more significant. Liquid mobilization inside a porous medium cannot be easily measured directly, therefore numerical modelling is essential to understand the fundamental processes and to clarify the effects and dynamics of the fuel mobilization on the smouldering reaction. Contrasting numerical models with experimental temperature measurements have revealed many aspects of smouldering that cannot be measured. In this study, a previously developed 1D smouldering model was equipped with multiphase flow equations and compared against laboratory column experiments. The combination of model and experiments has served to quantify the dynamics of organic liquid fuel mobility by simulating high (i.e., non-mobile) and low (i.e., mobile) viscous fuels. The findings from this study shed light on the complicated interplay between multiphase flow, heat and mass transfer, and smoulder chemistry common to many applied smouldering systems. Numerical results confirmed that increasing the viscosity results in fuel remaining in the reaction zone and led to an increase in the peak temperature and smouldering front velocities. Lower viscosity fuels mobilized away from the reaction zone, thereby accumulating fuel in the pre-heating zone of the reactor. The fundamental understanding generated from this research will improve the design, implementation, and optimization of smouldering-based technologies for environmentally beneficial applications worldwide.