Two-dimensional numerical simulation of the transition between slow reaction and ignition
2015
会议
Ninth Joint US Sections Meeting of the Combustion Institute
Thermal ignition of flammable gaseous mixtures from a hot surface is a major concern for a wide range of industrial activities. When homogeneous hydrocarbon fuel/oxidizer mixtures are heated in a closed vessel from ambient temperature to values near their autoignition temperature these mixtures undergo either a slow reaction or an ignition, when heat transfer to the surroundings is accounted for. Experiments and 0-D simulations using detailed chemical mechanisms have shown that this behavior is a function of the heating rate, initial composition, and pressure. The present study develops a one- step reaction model suited to capture the transition from slow to fast reaction that is appropriate for the wide range of conditions typically encountered in realistic industrial applications. A vertical cross- section of a cylindrical reactor is modeled to gain insight into the sequence of events leading to a slow reaction or an ignition. The heating of the reactor’s wall induces a very dynamic buoyancy driven flow in which the mixture rises along the walls and separates at the centerline creating two well defined vortical structures. Chemical heat release starts at the top of the vessel (where the mixture is hottest), and the flow reverses: the gas then rises along the centerline, separates and descends along the walls. Depending on the heating rate, the mixture undergoes slow oxidation or ignition whereby a flame that emanates from the separation point fully consumes the mixture.
