Numerical study of the transition between slow reaction and ignition in a cylindrical vessel

Abstract

A numerical study of a transiently (uniformly/non-uniformly) heated cylindrical reactor was performed using a computationally inexpensive one-step model capable of capturing the experimentally observed transition behavior from slow to fast reaction. The methodology used to find the kinetic parameters of the simplified model was described in detail. A parametric study using a control volume (0-D) thermal ignition model provided transition maps due to changes in heating rate, initial pressure and composition. Two-dimensional reactive Navier-Stokes equations were used to examine the fluid mechanics and chemical reaction leading to slow or fast consumption of the mixture. During uniform heating, a dynamic buoyancy flow is induced in which the mixture rises along the walls and turns at the centerline creating two well defined vortical structures. Once significant chemical heat release is generated, the flow reverses. During non-uniform heating, the flow field is composed of two large vortices in the center of the vessel, and two sets of smaller vortices trapped at the top and bottom of the reactor. Depending on the heating rate, and irrespective of the mode of heating, the mixture undergoes either slow oxidation or ignition whereby a flame that propagates from the top of the vessel consumes the mixture.