EXPERIMENTAL AND NUMERICAL-STUDIES ON CHEMICAL INHIBITION OF NONPREMIXED METHANE FLAMES BY CF3BR

An experimental and numerical study is performed to elucidate the mech anisms by which bromotriflouoromethane (CF3Br) extinguishes laminar no npremixed flames. Experiments are conducted on methane flames stabiliz ed in the counterflowing configuration. The fuel and oxidizer streams are diluted with nitrogen and the inhibitor CF3Br is added to one of t he reactant streams. The volumetric flow rate of the reactants and the ir composition at extinction are used to calculate the characteristic strain rate at extinction employing a previously developed theory. The critical conditions of extinction are measured with various amounts o f the inhibitor added to either the fuel or the oxidizer stream. Numer ical calculations are performed using detailed chemistry and applying boundary conditions similar to those in the experiments. The chemical- kinetic mechanism employed in these calculations includes the detailed description of fuel oxidation and inhibition by CF3Br. In general, th e critical conditions of extinction calculated using this detailed che mical-kinetic mechanism are found to agree reasonably well with the me asurements. The influence of preferential diffusion is examined. The a nalysis of the experimental and numerical results show that CF3Br exti nguishes the flame by chemical mechanisms. Also, CF3Pr is shown to be more effective in extinguishing the methane flame when it is added to the oxidizer stream rather than to the fuel stream.