Aromatic additive effects on soot formation in a fischer-tropsch diesel (FTD) spray flame via laser spectroscopy

In order to examine the effects of aromatic addition to Fischer-Tropsch Diesel (FTD) fuel on formation and growth processes of PAHs and soot particles in its spray flame, small amount of naphthalene (20 to 13000 ppm) was added to the FTD fuel and the formation and growth processes of PAHs and soot particles in its spray flame were investigated via high-speed laser shadowgraphy, 2-color method and Excitation-Emission Matrix (EEM) technique. The experiments were conducted using an optically accessible constant volume combustion vessel at 1000K and 2.7MPa under EGR-like 15% O₂ condition. The experimental results indicated that naphthalene addition does not affect on ignition delay and heat release rate within the investigated concentration range. The added naphthalene promoted formation and growth of PAHs in the spray flame, advanced soot particle formation in the flame and increased apparent flame temperature measured via 2-color method by up to 100K. The apparent temperature increase is likely due to accelerated soot oxidation in the flame periphery, while the reason for the accelerated oxidation is not clear at this moment. The resulting soot production in the spray flame did not show significant difference due to naphthalene addition, likely because the soot formation promoted by naphthalene addition and the accelerated soot oxidation cancelled out.