An Investigation of Extinguishment by Thermal Agents Using Detailed Chemical Modeling of Opposed Jet Diffusion Flames

Abstract

Detailed chemical kinetic modeling of methane planar opposed-jet laminar diffusion flames burning in air mixed with a variety of thermal agents is used to characterize their effects on maximum flame temperature and extinction behavior. The identification of a well-defined limit temperature allows extinguishing concentrations for buoyancy-dominated methane flames to be predicted. Predicted extinguishing volume fractions are shown to be in good agreement with experimental results for opposed flow methane flames. It is further demonstrated that the calculations provide reliable estimates of relative thermal agent extinguishing effectiveness for both methane coflow flames and liquid-fueled heptane flames burning in a surrounding coflow, even though the required volume fractions of a given agent can differ substantially from those predicted for the opposed flow methane flames. This is the case despite the fact that the extinction mechanisms for the opposed-flow (global flame extinction due to flame cooling) and coflow (blow off of an edge flame stabilized in the local flow field by a reaction kernel) flames are believed to be different. The results of the calculations demonstrate the dependence of extinguishment mechanism on the local flow fields at the flame and the need for thermal agents to lower the temperature of the flame zone to a well defined limit temperature.