Influence of natural convection on the concentrational limits of ignition of a fuel mixture in a closed vessel

Abstract

This article attempts to calculate the concentrational limits of the ignition of a fuel mixture in a subcritical initial state when the chemical reaction is initiated by a specified heat source. In order to examine the role of convection, a broad range of Damkohler numbers are used which characterize the ratio between the gas-dynamic and chemical time, and the concentrational limits in the field of an external force (gravity) and when g=O are compared. A methane-air mixture is investigated. The motion of a gaseous fuel mixture in a plane vessel of quadratic cross section is described by nonsteady two-dimensional NavierStokes equations, taking account of the consumption of the reagent present in adequate amounts, in a first-order exothermal chemical reaction. The aim of the calculation of the concentration limits is to establish the dependence of the Damkohler number on a parameter which characterizes the initial mixture composition. Improvements are made in a numerical method allowing the process of combustion-source development in a closed vessel to be modeled on the basis of sufficiently complete nonsteady two-dimensional equations of motion of the reacting gas, and allowing the limits of ignition of the fuel mixture with a subcritical initial state to be calculated. Itmore » is shown that convection leads to different concentrational limits in the ignition of a fuel mixture.« less