Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed

Abstract

This study investigates the interaction between a premixed methane-air flame and particles inside a model packed bed. The opacity of the spherical packed beds to visible light poses a major barrier to the implementation of highly resolved optical diagnostics, so that no detailed experimental data were so far available for the validation of numerical simulation. Here, a two-dimensional cylindrical packed bed design is set up, which enables direct line-of-sight optical measurements without loss of spatial resolution over the fluid region between the particles. In this study, the case of cold metallic cylindrical particles (T = 377 K) relevant to start-up of a reactor is investigated using internal particle cooling, which also allows cylinder specific heat transfer rate measurements by differential temperature measurements on the coolant streams. The two dimensional assumption is first verified by measuring the inflow velocity and cylinder temperature profile along the cylinders. Chemiluminescence imaging is then performed using a telecentric lens to observe the position and geometry of the two-dimensional flame front with respect to the surrounding cylinders without loss of resolution. Simultaneously, the cylinder-specific flame to cylinder heat transfer rates and cylinder surface temperature are measured. As the flame is closely surrounded by the three cooled cylinders, intense heat transfer is observed in this region corresponding to 25 ± 2.5% of the flame thermal power. Flames were stabilised at different positions depending on inflow velocity and equivalence ratio, and a direct correlation between flame to cylinder stand-off distance and the heat transfer rate normalised to the flame thermal power was found for both top and side cylinders. Also, sidewall quenching distances to the curved cylinder surfaces were evaluated, and seem to be influenced by the presence of a warm recirculation zone behind the cylinders. This investigation provides fully resolved flame front position and heat transfer rates for a known geometry and cylinder thermal boundary conditions, and provides validation data for numerical simulations of this high flame particle coupling case.