Anatoli Mokhov

CO behavior in laminar boundary layer of combustion product flow

Abstract Results are reported from the experimental investigation and numerical simulation of the laminar boundary layer formed on the flat plate in flowing combustion products of propane in air. During the experiments such parameters as the temperature of the plate surface and the composition of the oncoming flow (due to a change of the fuel to air equivalence ratio φ) have been varied. In addition, when performing numerical simulations, the catalytic properties of the surface have been changed. The comparison of the measured profiles of velocity, temperature, OH and CO concentrations with the results of the calculation based on the chemically reacting boundary layer model has revealed that the model adequately described both distributions of parameters in the boundary layer and their dependence on the boundary conditions and parameters of the free stream flow.

NO formation in the burnout region of a partially premixed methane-air flame with upstream heat loss

Abstract Measurements of temperature and NO concentration in laminar, partially premixed methane–air flames stabilized on a ceramic burner in coflow are reported. The NO concentration and temperature were determined by laser-induced fluorescence (LIF) and coherent anti-Stokes Raman scattering (CARS), respectively. Upstream heat loss to the burner was varied by changing the exit velocity of the fuel–air mixture at a constant equivalence ratio of 1.3; this alters the structure of the flame from an axisymmetric Bunsen-type to a strongly stabilized flat flame. To facilitate analysis of the results, a method is derived for separating the effects of dilution from those of chemical reaction based on the relation between the measured temperature and the local mixture fraction, including the effects of upstream heat loss. Using this method, the amount of NO formed during burnout of the hot, fuel-rich combustion products can be ascertained. In the Bunsen-type flame, it is seen that ∼40 ppm of NO are produced in this burnout region, at temperatures between ∼2100 K and ∼1900 K, probably via the Zeldovich mechanism. Reducing the exit velocity to 12 cm/s reduces the flame temperature substantially, and effectively eliminates this contribution. At velocities of 12 and 8 cm/s, ∼10 ppm of NO are formed in the burnout region, even though the gas temperatures are too low for “Zeldovich” NO to be significant. Although the mechanism responsible for these observations is as yet unclear, the results are consistent with the idea that the low temperatures in the fuel-rich gases caused by upstream heat loss retard the conversion of HCN (formed via the Fenimore mechanism) to NO, with this “residual” HCN then being converted to NO during burnout.

Angle-Dependent Light Scattering Study of Silica Aggregate Growth in 1-D Methane/Air Flames with Hexamethyldisiloxane Admixture : Effects of Siloxane Concentration, Flame Temperature, and Equivalence Ratio

ABSTRACT Silica aggregate formation was studied in 1D premixed methane/hexamethyldisiloxane/air flames by angle-dependent light scattering measurements for various siloxane concentrations, flame temperatures, and equivalence ratios, using Guinier analysis to interpret the experimental data. A sublinear dependence of the aggregate radii of gyration of generated silica particles on residence time, and non-monotonic dependence on flame temperature with a maximum around 2000 K have been observed, with radii of gyration in the range of 10 to 120 nm. Furthermore, a lean flame environment appears to foster aggregate growth compared to rich and stoichiometric flames, in which growth is very similar. When fixing the initial conditions at the residence time corresponding to the first measurement point, a simple model describing particle evolution as a result of collisional growth and sintering predicts well the functional dependence of the growth of particle radii.