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. The effect of fuel volatility on soot is investigated in two experimental configurations: a jet flame and a model gas turbine combustor. The jet flame experiment provides information about the effects of fuel on the spatial development of aromatics and soot in an axisymmetric, co-flow, laminar flame at atmospheric pressure. 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, operated at 5 atm, an inlet temperature of 560 K, and an inlet global equivalence ratio of 0.9 to 1.8. Two fuels with different boiling points are investigated: n-heptane/n-dodecane mixture and n-hexadecane/n-dodecane mixture. The n-hexadecane has a boiling point of 287° C as compared to 216° C for n-dodecane and 98° C for n-heptane. The jet flames investigated are non-premixed and premixed flames (jet equivalence ratios of 24 and 6) in order to have fuel rich 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 non-premixed and premixed flames. The comparison of aromatics and soot volume fraction in non-premixed 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. In comparing the results from these two burner configurations, we draw conclusions about important processes for soot formation in gas turbine combustors and what can be learned from laboratory-scale flames.