Simulation of combustion in porous media using the lattice boltzmann method

Abstract

Increasing combustion efficiency saves huge amounts of fuel, decreases combustion pollution, and conserves the living environment. Among all the ways that are proposed for increasing combustion efficiency, utilizing porous media in the combustion zone is one of the best. High developing inner surface and turbulence structure of the gas flow through porous media make combustion totally different form that of free flame combustion. Due to the complexity of the porous structure and high temperature value of the combustion product, installing experimental devices to investigate the effects of the porous media on fluid behaviour in the combustion zone is difficult and expensive. In this situation numerical methods are utilized to investigate the flow behaviour for combustion in the porous media. However, simulation of combustion in the porous media by conventional CFD methods is not straight forward. Many assumptions and modifications are usually considered in conventional CFD methods for simulation of combustion in porous media. These modifications and assumptions are taken into consideration because of the different length and time scales, sharp gradient of variables, and complexity of the physical geometry. The Lattice Boltzmann Method (LBM) based on kinetic theory was recently introduced for simulation of fluid dynamics problems. Beside the other advantages, relatively simple implementation of the LBM in simulation of fluid flow especially for complex geometry systems attracting scientific attention in different fields of engineering. The special features of the LBM method make it suitable for simulation of combustion in porous media especially when the simulation performed in pore scale. Application of LBM in the simulation of combustion in porous media is performed in this study. Since combustion is consist of fluid flow, heat transfer, and chemical reaction, in the present study, step by step approach is adopted to develop a model and simulate the combustion in porous media. First, the LBM simulation of heat transfer and fluid flow in porous media are investigated. The predicted results are found to agree well with the existing data in literature. In this work, porous media is created by scattering solid obstacles inside the flow path and a new model is introduced for simulation of heat transfer in the porous matrix. As expected, distribution of temperature tends to be more uniform and the maximum temperature decreases when porous media is utilized in the combustion zone. Also, effects of the porous structure and its length on the combustion characteristics are investigated.