M. A. Endo Kokubun

Bio: M. A. Endo Kokubun is an academic researcher from University of Bergen. The author has contributed to research in topics: Porous medium & Combustion. The author has an hindex of 3, co-authored 5 publications receiving 19 citations. Previous affiliations of M. A. Endo Kokubun include Instituto Nacional de Matemática Pura e Aplicada.

A pore-scale study of transport of inertial particles by water in porous media

Abstract: We study the transport of inertial particles in water flow in porous media. Our interest lies in understanding the accumulation of particles including the possibility of clogging. We propose that accumulation can be a result of hydrodynamic effects: the tortuous paths of the porous medium generate regions of dominating strain, which favour the accumulation of particles. Numerical simulations show that essentially two accumulation regimes are identified: for low and for high flow velocities. When particles accumulate at the entrance of a pore throat (high-velocity region), a clog is formed. This significantly modifies the flow, as the partial blockage of the pore causes a local redistribution of pressure, which diverts the upstream water flow into neighbouring pores. Moreover, we show that accumulation in high velocity regions occurs in heterogeneous media, but not in homogeneous media, where we refer to homogeneity with respect to the distribution of the pore throat diameters.

Stabilization and extinction of diffusion flames in an inert porous medium

Abstract: Diffusion flames established in inert porous media have been reported to present temperatures lower than a comparable gaseous mixture. Therefore, the study of the flame structure, temperature and extinction limits of confined diffusion flames is of importance. In the present work we discuss extinction conditions for such flames. Using an asymptotic model that accounts for the excess/deficient enthalpy at the reaction region, we study the multiscale problem and analyze the effects of the heat exchange between gas and solid phases on the flame structure. When the heat removed from the flame by the solid matrix is large, the flame can extinguish because the lowering in the flame temperature leads to increasingly large leakage of reactants through the flame sheet. We show that this occurs when the porosity or the mass injection rate is small enough. The extinction limit associated with a small value of the mass injection rate adds to the kinetic extinction limit (which is associated with a large value of the mass injection rate) to characterize a dual-extinction-point behavior for this problem. When the porosity of the medium reaches a minimum critical value, these two distinct extinction points collapse, such that for porosities lower than the critical porosity no flame can be established inside the porous chamber. Then, it is possible to construct a flammability map for the confined diffusion flame, where the critical porosity defines an absolute flammability limit.

Multicomponent effects in liquid–gas filtration combustion

Abstract: This paper develops the theory of liquid–gas filtration combustion, when an oxidizer (air) is injected into porous rock containing two-component liquid fuel. We found a qualitatively new combustion mechanism controlled by the successive vaporization and condensation of the liquid phase sustained by the reaction. Motivated by the problem of recovery of light oil by air injection, as an enhanced oil recovery method, we consider a liquid composed of light and medium pseudo-components. The light part is allowed to oxidize and vaporize, while the medium part is non-volatile and only oxidizes. The liquid mobility depends strongly on its composition, with a small viscosity (high mobility) of the purely light component and a high viscosity for the purely medium (immobile) component. We show that the combined vaporization and condensation in the combustion wave leads to accumulation of the light component in the upstream part of the wave, considerably increasing mobility and, therefore, playing a crucial role in the mechanism of the combustion process. We describe physical implications of this effect, as well as its importance for applications. The results are confirmed by numerical simulations.

Combustion in miscible displacement for high-pressure air injection

Abstract: This paper describes miscible displacement upon air injection in a porous medium saturated with oil corresponding to conditions of high-pressure air injection (HPAI). We assume that injection fluids and produced fluids are fully miscible with the oil at the prevailing high pressure. We use three pseudo-components, viz., oxygen, oil, and an inert component, which includes nitrogen, carbon dioxide, etc. To model the fingering instabilities, we follow a similar procedure as proposed by Koval (SPE J. 3(02):145–154, 1963) and include the reaction between oxygen and oil in the Koval model. The equations are solved numerically, using a finite element software package (COMSOL). The results show that a combustion wave is formed. We study the performance at low and high viscosities and show that the reaction improves the speed and degree of recovery at later times.

Singularity of a Combustion Wave Profile: A Clue to the MultiComponent Theory for Liquid-Gas Filtration

Abstract: We study a nonlinear wave for a system of balance laws in one space dimension, which describes combustion for two-phase (gas and liquid) flow in a porous medium. The problem is formulated for a general $N$-component liquid for modeling the strong multicomponent effects reported recently for an application to light oil recovery by air injection. Despite the immense complexity of the model, the problem allows an analytic solution. The clue to this solution is a special form of a folding singularity, which occurs at an internal point of the wave profile. Analysis of this singularity provides a missing determining relation for wave parameters. This result is not only interesting for the application under consideration but also motivates a deeper mathematical study of such singularities for general systems of balance laws.

Insight into particle detachment in clogging of porous media; a pore scale study using lattice Boltzmann method

Abstract: Particle deposition in porous media alters hydraulic properties including porosity and permeability. The extent of these alterations depends on both porous media structure and its geometrical and topological properties. In the present study, a Lattice Boltzmann modeling is developed and used to systematically simulate particle clogging and to explore the evolution of hydraulic properties using realistic pore structures obtained from x-ray tomography. A total of six different porous media are studied where three domains have different porosities and grain sizes, but the same pore connectivities, to explore the geometrical effects, and three domains have the same porosity but different grain arrangements and pore connectivities to study the effect of porous media topology. The results have shown the impact of the underlying pore-scale mechanisms resulting in porous media clogging and how they are affected by the initial porosity and topology of the media. Moreover, simulation has been utilized to develop porosity-permeability relations, covering the initial sample permeability all the way to complete clogging of the media where permeability vanishes. To provide more generic relations, the obtained coefficients of the porosity-permeability formulations are correlated to each porous media geometrical and topological properties.

Effect of particle rolling resistance on drained and undrained behaviour of silty sand

Abstract: This paper explores the effect of particle rolling resistance on the mechanical behaviour of silty sand under various shearing conditions. The elastic–plastic spring–dashpot rolling resistance model was employed, and drained and undrained triaxial tests were conducted on silty sand with various fines contents and rolling resistance. It was found that the rolling resistance of fines contents had a strong impact on the critical state, peak state, phase transformation state as well as zero-dilatancy state of silty sands. Moreover, depending on the correlation between rolling resistance of coarse and fine particles, fines can positively or negatively contribute to the overall structure of silty sand. Increasing the rolling resistance of fines enhances the liquefaction resistance of silty sands. Thus, the presence of fines of high rolling resistance in the sand can result in a marked decrease in collapsibility or liquefaction susceptibility compared with the presence of fines of lower rolling resistance.

Combustion characteristics of blast furnace gas in porous media burner

Abstract: This paper studied the combustion of blast furnace gas in a porous media burner. A numerical model method was established to analyze the combustion characteristics of blast furnace gas and solved by using the finite volume method. The temperature distribution, the position of the ignition, the flame structure, the recirculation zone and the concentration of the fuel were analyzed in the furnace. It was found that as increase of the distance between the porous body and the burner inlet, the temperature of the gas and the flame length increased and then decreased. When the porous media was located at 0.14 m in the burner, the peak temperature of the smoke gas was 1598 K at 0.36 m and the flame length was up to 0.41 m. With the porous media away from the burner nozzle, the ignition position was first away from the nozzle and then stabilize. The heat recirculation area increased and then stabilized. The position of the ignition was stable at 0.11 m. The flame length and flame radiation surface were wider and the oxygen concentration was the lowest at the exit, only 0.0043, when porous media was at 0.14 m.

Experimental investigation on propagation characteristics of n-heptane/air combustion wave in foamed porous media

Abstract: Although porous media combustion is suitable for micro/meso-scale power systems, the accurate flame dynamics in porous media have not been revealed, which are critical for understanding the flame stabilization mechanism. In this work, the propagation characteristics of combustion wave in the porous media are investigated. In the experiments, a clear blue flame front is observed and the instantaneous flame speed is determined. The flames in porous media both exhibit characteristics of pulsating propagation at different heating powers and pore densities. The average speed of the laminar submerged flame is much lower than that of the free flame, ranging from 0.20 mm/s to 0.97 mm/s, which is mainly caused by the wall quenching effect. The preheating temperature has a significant effect on flame propagation. Furthermore, as the pore density increases from 10 ppi to 30 ppi, the maximum speed of the flame decreases, while the average speed increases and then decreases. The average flame speed is comprehensively influenced by wall quenching and heat recirculation effects.

Experimental and numerical studies on the effect of packed bed length on CO and NOx emissions in a plane-parallel porous combustor

Abstract: Gas diffusion combustion in a plane-parallel packed bed filled with 2.5 mm alumina pellets is experimentally and numerically investigated. Special attention is focused on the influence of bed length (h) on the CO and NOx emissions for different excess air ratios ( α ) and gas mixture velocities (ug,in). It is found that h has significant influence on NOx emission when h 120 mm. Increase in h always leads to an linear increases in CO emission over the bed length range from 40 mm to 200 mm regardless of α and ug,in. For the lowest α (1.88), good performance regarding CO emission is observed, CO emission increases from 2 ppm to 49 ppm when h increases from 40 mm to 200 mm. Moreover, wide high temperature zone of the external combustor walls indicates that it is feasible to develop radiative burner based on diffusion filtration combustion.