The goal of the current work is to understand the effects of premixing on soot processes in an iso-octane, axisymmetric, co-flow, laminar flame at atmospheric pressure. The flames investigated are non-premixed and partially-premixed (jet equivalence ratios of 24, 15, 12, 9 and 6). The total carbon flow rate is kept constant to facilitate comparison among the six flames. Laser-induced incandescence and laser extinction are applied to obtain two-dimensional soot volume fraction. The experimental results show that the spatial distribution of soot changes with premixing; the peak soot volume fraction location is in the annular region in the non-premixed flame and transitions to the centerline as the jet equivalence ratio is reduced. Numerical simulations are performed using a detailed iso-octane fuel chemistry and bi-variate soot model. The numerical model captures the changes in the spatial distribution of soot due to premixing, as in the experiment. Similar to the change in the soot distribution, the soot production processes, including nucleation, surface growth, and PAH condensation, show the transition behavior with premixing. The simulation shows that the location of peak PAH dimer concentration shifts from the annular region towards the centerline with premixing. As a result, the location where soot nucleation and PAH condensation rates peak show similar transition as observed in the PAH dimer concentration. Furthermore, PAH dimer concentration decreases due to premixing, leading to a decrease in the soot nucleation and soot growth due to PAH condensation. Additionally, soot growth due to surface reactions decrease with premixing due to the reduction in number of active sites on the soot surface.

The goal of this work is to aid in understanding the effects of fuel molecular structure on the spatial development of polycyclic aromatic hydrocarbons (PAH), or soot precursors, in an axisymmetric, co-flow, laminar flame configuration at atmospheric pressure. Two fuels with varying molecular structure are investigated: iso-octane/ndodecane mixture and m-xylene/n-dodecane mixture. The flames investigated are non-premixed and rich premixed (jet equivalence ratio of 6) flames, and the total carbon flow rate is kept constant to facilitate comparison between fuels. A laser-induced fluorescence technique is used to obtain spatially-resolved PAH in the jet flames. The PAH are identified into two classes: single/two ring aromatics (small) and molecules having three/four rings (large). The experimental results indicate that the level of aromatics for m-xylene/n-dodecane fuel is higher compared to isooctane/n-dodecane fuel. The comparison of PAH in non-premixed and premixed flames show significant differences in the spatial development of PAH along the downstream direction. These results are compared to initial simulation results and a methodology for using the PAH-LIF technique for validating soot models in laminar jet flames is proposed.

The goal of this work is to support the development of surrogate fuel mixtures that replicate the chemistry and flame characteristics of renewable Fischer-Tropsch (FT) fuels. In particular, we focus on capturing soot formation and growth with the use of iso-octane as a surrogate for FT jet fuel. An axisymmetric, co-flow, laminar flame configuration is used to study soot formation for non-premixed and rich-premixed mixtures at atmospheric pressure. A laser extinction technique is used to obtain spatially resolved soot volume fraction results, and thermocouple measurements provide profiles of gas temperatures in both the radial and axial directions. Comparisons of flame temperature measurements from both FT and iso-octane flames indicate that the temperatures are the same in both the axial and radial profiles within the uncertainty of the measurement. The flame temperatures for the non-premixed flame are 50100 degrees Celsius higher throughout the flame than those for the rich-premixed flame. Laser extinction measurements with both fuels show that the soot volume fraction profiles are very similar for FT fuel and iso-octane. Additional analysis shows the impact of premixing air on soot formation and the differences in time-scales of soot formation with and without the presence of oxygen.

Experimental data and model results are presented for the effects of m-xylene on aromatic species and soot in a nitrogen-diluted ethylene flame over a range of pressures from 1 to 5atm. The experimental approach was designed to investigate the effects of m-xylene as a perturbation to a base flame by keeping the amount of carbon added as m-xylene to 5% or less. The experimental results indicate that the maximum soot levels and those of small (1 or 2 rings) and large (3 or more ring) aromatic species are roughly first order with respect to the amount of m-xylene added. A chemical kinetic model was formulated, integrated into a 2-D modeling code, and used to simulate the effects of m-xylene addition and pressure on aromatic species and soot. The modeling results capture the general trends in concentration of soot and small aromatics as m-xylene concentration and pressure are varied. However, the model under-predicts the effect of m-xylene concentration and pressure on soot compared to the experimental results.

Results are presented from a combined experimental and modeling study undertaken to understand the pathways by which the addition of ethanol to fuel-rich ethylene flames causes reductions in PAH and soot. The experimental work was conducted in a flat-flame burner at equivalence ratios of 2.34 and 2.64. Ethanol was added to the ethylene at two levels corresponding to 5 and 10% oxygen by weight in the fuel. Soot was measured by laser-induced incandescence calibrated with light extinction, and aromatic species were measured using laser-induced fluorescence. Modeling was based on a 1-D premixed flame model and kinetic mechanisms available in the literature. The modeling work captures the trends in aromatic species with changes in equivalence ratio and oxygen concentration in the fuel. However, the soot predictions do not match the increases observed at the higher equivalence ratio. Analysis of the modeling results for the lower equivalence ratio shows that the addition of ethanol to the ethylene reduces the aromatic species mainly by reducing the amount of carbon that is available to form precursor species.