M D. Rumminger

Numerical study of the inhibition of premixed and diffusion flames by iron pentacarbonyl

Iron pentacarbonyl (Fe(CO){sub 5}) is an extremely efficient flame inhibitor, yet its inhibition mechanism has not been described. The flame-inhibition mechanism at Fe(CO){sub 5} in premixed and counterflow diffusion flames of methane, oxygen, and nitrogen is investigated. A gas-phase inhibition mechanism involving catalytic removal of H atoms by iron-containing species is presented. For premixed flames, numerical predictions of burning velocity are compared with experimental measurements at three equivalence ratios (0.9, 1.0, and 1.1) and three oxidizer compositions (0.20, 0.21, and 0.24 oxygen mole fraction in nitrogen). For counterflow diffusion flames, numerical predictions of extinction strain rate are compared with experimental results for addition of inhibitor to the air and fuel stream. The numerical predictions agree reasonably well with experimental measurements at low inhibitor mole fraction, but at higher Fe(CO){sub 5} mole fractions the simulations overpredict inhibition. The overprediction is suggested to be due to condensation of iron-containing compounds since calculated supersaturation is suggested to be due to condensation of iron-containing compounds since calculated supersaturation ratios for Fe and FeO are significantly higher than unity in some regions of the flames. The results lead to the conclusion that inhibition occurs primarily by homogeneous gas-phase chemistry.

Flame Inhibition by Ferrocene and Blends of Inert and Catalytic Agents

The production of the fire suppressant CF3Br has been banned, and finding a replacement with all of its desirable properties is proving difficult. Iron pentacarbonyl has been found to be up to several orders of magnitude more effective than CF3Br, but it is flammable and highly toxic. Ferrocene [Fe(C5H5)2], which is much less toxic and flammable than Fe(CO)5, can also be used to introduce iron into a flame. We present the first experimental data and numerical modeling for flame inhibition by ferrocene and find it to behave similarly to Fe(CO)5. A ferrocene mole fraction of 200 ppm reduced the burning velocity of slightly preheated premixed methane/air flames by a factor of two, and the effectiveness dropped off sharply at higher mole fractions. For air with a higher oxygen mole fraction, the burning velocity reduction was less. We also present experimental data and modeling for flames with ferrocene blended with CO2 or CF3H. The combination of the thermally acting agent CO2 with ferrocene mitigated the loss of effectiveness experienced by ferrocene alone at higher mole fractions. An agent consisting of 1.5% ferrocene in 98.5% CO2 performed as effectively as CF3Br in achieving a 50% reduction in burning velocity. Likewise, four times less CO2 was required to achieve the 50% reduction if 0.35% ferrocene was added to the CO2. In contrast, addition of 0.35% ferrocene to the hydrofluorocarbon CF3H reduced the CF3H required to achieve the 50% reduction in burning velocity by only about 25%. Thermodynamic equilibrium calculations predict that the formation of iron/fluoride compounds can reduce the concentrations of the iron-species oxide and hydroxide intermediates which are believed to be responsible for the catalytic radical recombination cycles.

The role of particles in the inhibition of counterflow diffusion flames by iron pentacarbonyl

Abstract Laser light scattering and thermophoretic sampling have been used to investigate particle formation in counterflow diffusion flames inhibited by iron pentacarbonyl Fe(CO) 5 . Three CH 4 -O 2 -N 2 reactant mixtures are investigated, with Fe(CO) 5 added to the fuel or the oxidizer stream in each. Flame calculations that incorporate only gas-phase chemistry are used to assist in interpretation of the experimental results. In flames with the inhibitor added on the flame side of the stagnation plane, the region of particle formation overlaps with the region of high H-atom concentration, and particle formation may interfere with the inhibition chemistry. When the inhibitor is added on the non-flame side of the stagnation plane, significant condensation of metal or metal oxide particles is found, and implies that particles prevent active inhibiting species from reaching the region of high radical concentration. As the inhibitor loading increases, the maximum scattering cross section increases sharply, and the difference between the measured and predicted inhibition effect widens, suggesting that particle formation is the cause of the deviation. Laser-based particle size measurements and thermophoretic sampling in low strain rate flames show that the particles have diameters between 10 nm and 30 nm. Thermophoresis affects the nanoparticle distribution in the flames, in some cases causing particles to cross the stagnation plane. The scattering magnitude in the counterflow diffusion flames appears to be strongly dependent on the residence time, and relatively independent of the peak flame temperature.

The role of particles in the inhibition of premixed flames by iron pentacarbonyl

An MRI-use magnetic field generator structured such that there is no loss of magnetic field uniformity, temperature fluctuation is reduced and thermal efficiency enhanced, and the temperature of the permanent magnets can be controlled to high precision. With this invention, temperature control heaters are embedded in the base yokes of magnetic path formation members, and as a result of this structure, when the temperature control heaters are heated by a temperature regulator according to the temperature detected by a temperature sensor, the permanent magnets disposed in the vicinity of the base yokes are heated efficiently, so control follow-up is excellent. Furthermore, because the temperature control heaters are embedded inside the base yokes, and the heat generated by the heaters is conducted through the base yokes and reaches the permanent magnets directly, the heat is not diffused to the outside and lost, affording extremely efficient thermal control.

Premixed carbon monoxide–nitrous oxide–hydrogen flames: measured and calculated burning velocities with and without Fe(CO)5‡

Abstract The burning velocity of premixed carbon monoxide–nitrous oxide flames (background water levels of 5 to 15 ppm) has been determined experimentally for a range of fuel–oxidizer equivalence ratio φ from 0.6 to 3.0, with added nitrogen up to a mole fraction of X N 2 = 0.25, and with hydrogen added up to X H 2 = 0.005. Numerical modeling of the flames based on a recently developed kinetic mechanism predicts the burning velocity reasonably well, and indicates that the direct reaction of CO with N 2 O is the most important reaction for CO and N 2 O consumption for values of X H 2 ≤ 0.0014. The calculations show that a background H 2 level of 10 ppm increases the burning velocity by only about 1% compared to the bone-dry case. Addition of iron pentacarbonyl, Fe(CO) 5 , a powerful flame inhibitor in hydrocarbon–air flames, increases the burning velocity of the CO–N 2 O flames significantly. The promotion is believed to be due to the iron-catalyzed gas-phase reaction of N 2 O with CO, via N 2 O + M = N 2 + MO and CO + MO = CO 2 + M, where M is Fe, FeO, or FeOH.

TEMPERATURE REGIONS OF OPTIMAL CHEMICAL INHIBITION OF PREMIXED FLAMES

Chemically active fire suppressants may, due to their properties or the means by which they are added to flames, have strong inhibition effects in particular locations in a flame. To study the spatial effects of chemically active inhibitors, numerical experiments are conducted in which the rates of reactions of model inhibitors are varied in spatial regions defined by temperature. The influence of three types of spatial regions are investigated, those with the inhibitor (1) active only within a narrow temperature band (offon-off), (2) active below a cutoff temperature (on-off), and (3) active above a cutoff temperature (off-on). The effect of several localized chemical perturbations on the burning velocity are studied, including the

Numerical Modeling Of Counterflow Diffusion Flames Inhibited By Iron Pentacarbonyl

This paper presents the first detailed numerical study of the extinction of methane-air counterflow diffusion flames by the super-effective agent iron pentacarbonyl. Calculations using a gas-phase chemical mechanism reproduce the magnitude of inhibition for small amounts of inhibitor in the air, but overpredict the inhibition effect for larger amounts of inhibitor. Reaction pathway and reaction flux analyses show that a catalytic cycle involving FeO, Fe(OH),, and FeOH is primarily responsible for catalytic recombination of H atoms which produces the inhibition, and that a new cycle involving Fe(OH), FeOOH and Fe(OH), has a minor role. Reaction flux calculations demonstrate that the fractional flux of H and 0 atoms through the iron reactions increases as inhibitor concentration increases, but eventually the fractional fluxes level off. Saturation of the catalytic cycles can partially explain the diminishing effect of the inhibitor at high inhibitor loading shown in both the calculated and experimental results. Flame structure calculations are used to determine the reasons for stronger inhibition for air-side addition of the inhibitor than for fuel-side. Simulations using a idealized inhibitor confirm the important role of transport in inhibition of counterflow diffusion flames.