The blending effect on the sooting tendencies of alternative/conventional jet fuel blends in non-premixed flames

In order to study the blending effect on sooting tendencies for practical alternative/conventional jet fuel blends, the present study has investigated soot formation in non-premixed flames of Jet-A blended with three alternative jet fuels (AJFs), i.e., Hydroprocessed Esters and Fatty Acids from camelina (HEFA-Camelina), Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK), and Alcohol-to-Jet (ATJ). The smoke points of the AJF/Jet-A blends were measured in a wick lamp per ASTM D1322 standard, and their Threshold Sooting Indices were derived. Soot volume fraction profiles of the AJF/Jet-A fuel blends were also measured using the laser-induced incandescence diagnostics in the counterflow non-premixed flames. The effects of AJF blending ratio, strain rate, and reactant concentration on the soot formation were examined. The experimental results show that the Threshold Sooting Indices of the AJF/Jet-A blends exhibit a linear relationship with AJF mole fraction. While the maximum soot volume fractions of fuel blends show a fairly linear relationship with AJF blending ratio, the nonlinearity becomes prominent at high strain rates and low reactant concentrations. Comparing the three AJF/Jet-A fuel blends, the sooting tendencies are ranked as ATJ/Jet-A > FT-SPK/Jet-A > HEFA-Camelina/Jet-A. Correlations of the maximum soot volume fraction with aromatics content, hydrogen content, smoke point, and Threshold Sooting Index were all also examined. It is found that neither aromatics content nor hydrogen content can correlate with the maximum soot volume fraction for all the fuel blends at a given condition; conversely, smoke point shows a nonlinear correlation and Threshold Sooting Index shows an approximately linear correlation with the maximum soot volume fraction for all the fuel blends. It is suggested that the different sooting tendencies of AJF/Jet-A blends are mainly caused by the different sooting propensities of individual AJFs, which are strongly dependent on their distinct paraffinic compositions.