Variation of residence time in non-premixed turbulent bluff-body ethylene flames as a function of burner diameter

Abstract

The knowledge of the residence time distribution (RTD) in practical combustion applications, such as gas turbines, is of crucial importance as it has been correlated to soot formation and emission indices. However, the measurement of RTD is challenging in reacting environments. Computational Fluid Dynamics (CFD), on the other hand, offers an easier tool with which to estimate RTD in complex reacting flows. The effect of the bluff-body diameter on the residence time distribution within the recirculation zone, in a turbulent non-premixed ethylene flame stabilized on a bluff-body burner, has been numerically investigated. Models of 2-D axisymmetric bluffbody burners, with three bluff-bodies of different diameter (38, 50, and 64 mm), but identical in other dimensions, have been used in this work. Stochastic tracking model was employed to estimate the particle residence time distribution in the recirculation region. The CFD model was validated using the well-known turbulent bluff-body diffusion flame-HM1 before it was applied to predict similar flames with pure ethylene as fuel. The calculations predict that increasing the bluff-body diameter results in an increase in the recirculation zone length by a factor of two, and a considerably longer residence time in the recirculation zone while keeping jet and co-flow Reynolds numbers the same.