No abstract

Low-pressure, lean, laminar, premixed hydrogen/oxygen/argon flames seeded with iron pentacarbonyl (35−170 ppm Fe(CO)5) were modeled with detailed chemistry and the results were compared to laser-induced fluorescence imaging measurements of iron atom concentration and gas-phase temperature. The model includes recent rate coefficients for the decomposition of iron pentacarbonyl and thermodynamic data. The simulated iron concentrations correspond well with the measurements with only minor discrepancies in the rise of the iron profiles at low Fe(CO)5 concentrations. In addition, it was shown that the mechanism is able to predict the effect of Fe(CO)5 on the flame speed also for lean conditions, where the model was not established yet. The major iron species, aside from atomic iron, in this flame are predicted to be FeOH and Fe(OH)2 with some FeO2 early in the flame. The observed increased flame temperatures in the presence of Fe(CO)5 are attributed to catalytic hydrogen recombination.

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Ferrocene-doped low-pressure, laminar, premixed propene/oxygen/argon flames of different stoichiometries were investigated experimentally using laser induced fluorescence (LIF) and the results were compared with numerical simulations. The influence of ferrocene on the flame temperature proved to be minimal both in the measurement and in the simulation. The measured flame temperatures were 100–250 K below the adiabatic flame temperature, as expected. However, the modeled flame temperatures were around 450 K below the measurements. It is assumed that the reason for this lies in the incorrect modeling of the flame speed since systematic errors in the LIF measurements should be small, as discussed in the paper. Iron atom concentrations were also measured using LIF. The results show the influence of the stoichiometry on the iron atom concentration, which is also reproduced by the model. The majority of the added iron was observed to exist as atomic iron in the flame. As more oxygen becomes available in leaner flames, iron will tend to form more FeO so that the iron atom concentration decreases with decreasing equivalence ratio.

Abstract:The thermochemistry of iron in flames has been investigated theoretically using the Cantera software package. The focus was placed on the iron intermediates as well as the conditions under which condensed phases of iron or ironspecies could be expected in a flame. For this purpose, equilibrium calculations were carried out for iron seeded hydrogen/oxygen/argon and propene/oxygen/argon gas mixtures at combustion relevant conditions. Varying stoichiometries over a wide range of temperatures and pressures were investigated. The results allow a prognosis which gas phase iron species may be expected in measurable concentrations at given flame conditions, and also whether condensed phases of iron or iron species are likely. Also, the effect of sampling probes on the gas mixture composition due to flame cooling is discussed.