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Abstract Coflow diffusion flames are a canonical laboratory-scale flame configuration, which is routinely employed in fundamental combustion studies on flame stabilization, chemical kinetics, and pollutants’ emissions. In particular, pressurized coflow flames are used to study the effect of pressure on soot formation. In this work, we explore the opportunity to scale sooting coflow flames at constant Reynolds and Grashof numbers as pressure increases. This is achieved by decreasing the bulk velocity and the diameter of the fuel nozzle with increasing pressure. Despite some minor departures from the ideal scaling due to the effect of radiative heat losses from soot, the coflow flames are shown to be self-similar to a very good approximation. By keeping the Reynolds and Grashof numbers constant, one obtains a set of pressurized flames, which have self-similar nondimensional flow fields. Self-similarity is observed experimentally via direct photography and documented thoroughly by direct numerical simulation of steady axisymmetric coflow flames of methane and air at pressures from 1 to 12 atm. Although the study does not include data on soot yields, the implications for soot formation are explored with emphasis on the field of scalar dissipation rate and on the residence time, temperature, and mixture fraction experienced by a parcel of fluid moving along the centerline and along a streamline on the flame’s wing. We explain how the proposed approach to scaling pressurized flames facilitates the analysis of the effect of pressure on soot formation. [ABSTRACT FROM AUTHOR]

The formation, growth, and oxidation of soot are studied in a set of laminar coflow diffusion flames at pressures ranging from 1 to 8 atm. The modeling approach combines detailed finite rate chemical kinetics mechanisms that model the formation of Polycyclic Aromatic Hydrocarbon (PAH) species up to pyrene, and a bivariate method of moments that describes soot particles and aggregates by their volume and surface area. The spatial distribution of soot observed experimentally and that predicted numerically are in good qualitative agreement with the peak soot volume fraction located at the flame tip and soot appearing on the flame wings and closer to the nozzle as pressure increases. A detailed analysis of the effect of hydrodynamics and mixing on soot formation is presented. We show that the scalar dissipation rate is lower for the higher pressure flames, promoting the formation of PAH species and soot. Thus, the observed increase in soot volume fraction across flames with increasing pressure is not due solely to mixture density and kinetics effects, rather is affected by hydrodynamics and mixing processes also. Similarly, our results indicate that the decrease in the scalar dissipation rate contribute to changing the location where soot forms in the flame, with soot formation occurring closer to the nozzle and outward on the flame’s wings as pressure increases. Radiative heat losses are found to lower the flame temperature, inducing a reduction of the PAH species and associated rates of soot formation. However, heat losses are responsible for a slightly longer flame, which allows for more soot. The overall effect is a modest variation of soot volume fraction if radiation is included. [ABSTRACT FROM AUTHOR]