Two-dimensional flow effects on soot formation in laminar premixed flames

Abstract

Experimental measurements on axisymmetric laminar premixed flames have been used extensively for chemical and soot model validation. Numerical simulations of these flames always rely on the assumption of one-dimensionality. However, the presumed one-dimensionality has not been justified in general, and may not be valid under all circumstances. In the current work, two-dimensional flow effects are investigated in four representative ethylene/air laminar premixed flames, which have been selected as validation targets for the International Sooting Flame workshop. These flames cover all typical experimental arrangements, namely stabilizing plate, steel plate with centered hole, and enclosed chamber. To assess the assumption of one-dimensionality, detailed numerical simulations with finite-rate chemistry are performed with the exact experimental set-ups. It is shown that flow entrainment and acceleration are significant for all four flames. Further, it is found that the flame centerlines cannot be approximated as one-dimensional, since the mass flow rates vary substantially along the centerlines. As a consequence, non-negligible differences are found between the soot profiles predicted in two-dimensional simulations and in simulations where one-dimensionality is assumed. Using data extracted from the two-dimensional simulations, a modified one-dimensional model is derived on the flame centerline to include two-dimensional effects. Results from the modified one-dimensional model are compared against detailed, two-dimensional simulation results and experimental measurements.