We present a comparative study of the onset and propagation dynamics of the fingering phenomenon in uniform porous media with a radial configuration. With the help of the Finite Element Method (FEM)-based 2D simulations and image processing techniques, we investigate finger morphology, growth rate, interfacial length, finger length and the number of fingers which are affected due to inertial forces and convective acceleration in a two-phase porous media flow. We considered a modified Darcy’s law with inertial force coupled with convective acceleration and investigate their impact on interfacial instability with different velocity-viscosity combinations. Interestingly, the consequences of inertial corrections become significant with changes in viscosity at high Reynolds numbers. Due to the intrinsic bifurcation nature of inertial forces in the radial flow geometry, finger morphology is changed mostly at high viscosity ratios. We find that the effects of inertia and convective acceleration are markedly significant at relatively high Reynolds numbers while the interfacial length and the number of fingers—which are important parameters for Enhanced Oil Recovery (EOR)—are most affected by the neglecting of these forces. Moreover, at high Reynolds numbers, the rate of growth of fingering instabilities and the fractal number tend to deviate from that for Darcy’s law.

We present a numerical study of viscous fingering occurring during the displacement of a high viscosity fluid by low viscosity fluid in a circular Hele-Shaw cell. This study assumes that the fluids are miscible and considers the effects of inertial forces on fingering morphology, mixing, and displacement efficiency. This study shows that inertia has stabilizing effects on the fingering instability and improves the displacement efficiency at a high log-mobility-viscosity ratio between displacing and displaced fluids. Under certain conditions, inertia slightly reduces the finger-split phenomenon and the mixing between the two fluids.

Five recently developed chemical kinetics mechanisms for ammonia oxidation are analysed and compared, in the context of homogeneous adiabatic autoignition. The analysis focuses on the ignition delay and is based on the explosive mode that is shown to drive the process. Using algorithmic tools based on the Computational Singular Perturbation algorithm, the reactions responsible for the generation of the explosive mode are identified, along with the variables (species mass fractions and temperature) that associate the most to this mode. Comparison of these sets of reactions and variables, obtained for each mechanism, allows to correlate the differences in the predictive outcomes from the mechanisms with specific reactions. The major differences identified, which lead to different ignition delay times, relate to (i) the relative duration of chemical and thermal runaways (a sizeable chemical runaway develops only in some mechanisms) and (ii) the dominant chemistry during the chemical runaway (chemistry involving species with two nitrogen atoms is active only in some mechanisms). The major similarities identified refer to the thermal runaway and in particular to (i) the chemical activity, which is supported mainly by OH-producing reactions and by reactions producing their reactants and (ii) the thermal activity, which is dominated by strongly exothermic OH-consuming reactions.