A numerical investigation on combustion characteristics in a thermally orthotropic narrow channel with hydrocarbon fuels

Abstract

A novel approach of using thermally orthotropic wall materials to enhance stabilization of premixed methane/air and propane/air flames in a narrow channel between two parallel plates is numerically demonstrated. The streamwise and spanwise wall thermal conductivities kxx and kyy are respectively adjusted from 2 to 128 W/m⋅K by a step of eight times, to investigate the influence of directional heat transfer in solid walls on the combustor’s performance in terms of the flame stability limits and heat loss resistance. Results show that the lower velocity limit (LVL) is nearly insensitive to the wall thermal conductivities while the upper velocity limit (UVL), on the contrast, can be significantly affected. The thermally orthotropic combustor with a higher level of kxx but lower level of kyy, is observed to show a unique kind of wall temperature profile in the pre-flame region, which leads to a larger extent of preheatings to the unburnt mixture and less heat losses to the ambient, and consequently an elevated flame propagation speed. The resistance to external heat losses can be enhanced by decreasing the heat conductivity in either the streamwise or spanwise direction. However, since the latter has exhibited much more noticeable effects, and in order to avoid sacrificing the flame stability limit, the thermally orthotropic combustor thereby takes the superiority in overall performance.