Milton Linevsky

REDUCTION OF PAH AND SOOT IN PREMIXED ETHYLENE-AIR FLAMES BY ADDITION OF DIMETHYL ETHER

ABSTRACT Results are presented from a combined experimental and modeling study undertaken to understand the pathways by which the addition of dimethyl ether (DME) 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. DME 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 1D, premixed flame model and kinetic mechanisms described 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 DME to the ethylene reduces the aromatic species by increasing the concentration of oxidizing radicals, OH and O, and by reducing the amount of carbon that is available to form precursor species.

Simulating the Sooting Propensity of JP-8 with Surrogate Fuels from Hydrocarbon Fluids

Surrogate fuel mixtures were formulated using hydrocarbon fluids to investigate the ability of different surrogate formulations to match the sooting characteristics of a specific jet fuel (JP-8 POSF 5699). Three different surrogates were studied: two binary mixtures and a ternary mixture. The first surrogate matched the threshold soot index and average molecular weight of the JP-8; the second matched the threshold soot index and hydrogen-to-carbon; and the third matched the threshold soot index, hydrogen-to-carbon, and derived cetane number. For the second and third surrogates, average molecular weight was within 10% of the estimated average molecular weight of the target JP-8. Soot distributions of JP-8 and its surrogates were compared in wick-fed coflow diffusion flames, and net soot production was compared in a model gas turbine combustor. Line-of-sight and local soot volume fraction measurements were obtained using laser extinction on the wick burner for flames at their smoke point. Line-of-sight soot...

Effects of Fuel Molecular Weight on Emissions in a Jet Flame and a Model Gas Turbine Combustor

The objective of this study is to understand the effects of fuel volatility on soot emissions. This effect is investigated in two experimental configurations: a jet flame and a model gas turbine combustor. The jet flame provides information about the effects of fuel on the spatial development of aromatics and soot in an axisymmetric, co-flow, laminar flame. The data from the model gas turbine combustor illustrate the effect of fuel volatility on net soot production under conditions similar to an actual engine at cruise. Two fuels with different boiling points are investigated: n-heptane/n-dodecane mixture and n-hexadecane/ n-dodecane mixture. The jet flames are nonpremixed and rich premixed flames in order to have fuel conditions similar to those in the primary zone of an aircraft engine combustor. The results from the jet flames indicate that the peak soot volume fraction produced in the n-hexadecane fuel is slightly higher as compared to the n-heptane fuel for both nonpremixed and premixed flames. Comparison of aromatics and soot volume fraction in nonpremixed and premixed flames shows significant differences in the spatial development of aromatics and soot along the downstream direction. The results from the model combustor indicate that, within experiment uncertainty, the net soot production is similar in both n-heptane and n-hexadecane fuel mixtures. Finally, we draw conclusions about important processes for soot formation in gas turbine combustor and what can be learned from laboratory-scale flames. [DOI: 10.1115/1.4037928]

Evaluation of Soot Models in Computing Jet Flames formed with n-Dodecane and iso-Octane

Calculations for steady, laminar non-premixed, partially premixed and premixed flames established with n-dodecane, iso-octane and a blend of n-dodecane and iso-octane are performed for understanding the fuel effects on flame characteristics. Gas phase chemistry is described with the SERDP-2014 mechanism that consists of 522 species and 6398 reactions. Calculations have predicted the flame shapes and heights reasonably well. Calculations have also a predicted decrease in soot when the fuel was diluted with nitrogen and/or premixed with air. However, when iso-octane was added to n-dodecane in a nonpremixed, partially premixed or premixed flame, calculations predicted only small changes to the flame structure. Detailed comparisons of flame structures along the centerline for pure fuels and a blended fuel are made. Consumption of fuel components and formation of intermediate fuel fragments and polycyclic aromatic hydrocarbon (PAH) species are investigated for understanding the growth of soot in these flames. Detailed comparisons of the flame structures revealed that non-premixed flames are most sensitive to the type of fuel (iso-octane or n-dodecane). However, when these two fuels are blended, flame characteristics seemed to be dominated by those of n-dodecane. Differences in flame characteristics diminished with premixing of fuel with air. A premixed flame showed very little sensitivity to the fuel type, whether it is iso-octane or n-dodecane.