Variation of chemically active and inert flame-suppression effectiveness with stoichiometric mixture fraction

Abstract

The need to find alternative fire suppressants has motivated experiments to determine the mode of action of possible candidates. An opposed-jet burner was used to characterize the effectiveness of one possible alternative, dimethyl methylphosphonate (DMMP). Similar tests were done with an inert compound, argon, for comparison. Flame strength was characterized by the extinction strain rate. Experiments included both oxidizer-side and fuel-side doping of methane-nitrogen versus oxygen-nitrogen flames of various compositions. The stoichiometric mixture fraction (Zst) is varied systematically while holding the undoped extinction strain-rate constant, by changing the amount of diluent in the reactant flows. This moves the flame location with respect to the stagnation plane, affecting the fraction of a particular reactant stream that reaches the flame. Measured effectiveness, of fuel-side and oxidant-side doping versus Zst reflects this change in quantity of dopant reaching the flame. To account for this dependence on quantity, effectiveness was normalized by the amount of dopant calculated to reach the maximum temperature contour of the flame. Argon's normalized effectiveness was found to be independent of Zst, of adiabatic flame temperature, and of whether the oxidizer stream or the fuel stream is doped. DMMP's normalized effectiveness, however, was observed to be significantly greater when introduced in the oxidizer, rather than fuel, stream. It also exhibits a marked dependence on adiabatic flame temperature, with lower values at higher temperatures.