Effects of platinum stagnation surface on the lean extinction limits of premixed methane/air flames at moderate surface temperatures

Abstract

A stagnation flow reactor was used to study the effects of platinum on the lean flammability limits of atmospheric pressure premixed methane/air flames at moderate stagnation surface temperatures. Experimental and computational methods were used to quantify the equivalence ratio at the lean extinction limit ( ϕ ext ) and the corresponding stagnation surface temperature ( T s ). A range of flow rates (57–90 cm/s) and corresponding strain rates were considered. The results indicate that the gas-phase methane/air flames are sufficiently strong relative to the heterogeneous chemistry for T s conditions less than 750 K that the platinum does not affect ϕ ext . The computational results are in good agreement with the experimentally observed trends and further indicate that higher reactant flow rates (>139 cm/s) and levels of dilution (>∼10% N 2) are required to weaken the gas-phase flame sufficiently for surface reaction to play a positive role on extending the lean flammability limits.