Inhibition of premixed carbon monoxide-hydrogen-oxygen-nitrogen flames by iron pentacarbonyl

This paper presents measurements of the burning velocity of premixed CO-H-2 -O-2-N, flames with and without the inhibitor Fe(CO)(5) over a range of ini tial H-2 and O-2 mole fractions. A numerical model is used to simulate the flame inhibition using a gas-phase chemical mechanism. For the uninhibited flames, predictions of burning velocity are excellent and for the inhibited flames, the qualitative agreement is good. The agreement depends strongly on the rate of the CO + OH <-> CO2 + H reaction and the rates of several ke y iron reactions in catalytic H- and O-atom scavenging cycles. Most of the chemical inhibition occurs through a catalytic cycle that converts O atoms into O-2 molecules. This O-atom cycle is not important in methane flames. T he H-atom cycle that causes most of the radical scavenging in the methane f lames is also active in CO-H-2 flames, but is of secondary importance. To v ary the role of the H- and O-atom radical pools, the experiments and calcul ations are performed over a range of oxygen and hydrogen mole fraction. The degree of inhibition is shown to be related to the fraction of the net H- and O-atom destruction through the iron species catalytic cycles. The O-ato m cycle saturates at a relatively low inhibitor mole fraction (similar to 1 00 ppm), whereas the H-atom cycle saturates at a much higher inhibitor mole fraction (similar to 400 ppm). The calculations reinforce the previously s uggested idea that catalytic cycle saturation effects may limit the achieva ble degree of chemical inhibition. Published by Elsevier Science Inc.