Premixed combustion of methane–air mixture stabilized over porous medium: A 2D numerical study

Abstract

The advancing development of small portable devices and miniaturization of electronic components such as smartphones, laptops, Global Positioning Systems (GPS), Unmanned Aerial Vehicles (UAVs) and sensors have led to an increasing demand for small scale power generators, such as the Ultra Micro Gas Turbine (UMGT). This study focuses on the two dimensional numerical investigation of premixed methane–air flames stabilized over a porous medium in a cylindrical combustion chamber which is a fundamental part of an UMGT. A reduced skeletal mechanism of methane combustion including 17 species and 73 reactions was employed for the simulations. The main objective of the present work is to investigate the effect of important parameters such as incoming mixture mass flow rate, equivalence ratio, reactants’ initial temperature, thermal conductivity and porosity of flame holder on the combustion process. Results show that combustion can be considerably affected by the flame holder, especially because under certain conditions it could lead to considerable heat losses and eventually flame quenching. Generally when the burning velocity is much higher than the incoming flow velocity, the flame lays on the surface of the porous medium and heat is lost through the flame holder causing a decrease in the flame temperature. On the other hand, when the flame is slightly lifted from the flame holder, heat is dispersed to the outer wall and through axial conduction the porous medium is heated up, allowing the mixture to increase its temperature before combustion. Finally the effect of the thermal conductivity and porosity of the porous medium are analysed, showing that the more insulating the flame holder is, the less heat losses occur.