Effects of Fuel Properties on Soot Formation in Turbine Combustion

A T-63 combustor rig was used to study the sensitivity of combustor performance to the physical and chemical properties of fuels in order to determine the effectiveness of fuel properties as correlating parameters for soot formation in gas turbine engines. The composition, the distillation curve, and viscosity were of special concern, the first property associated with carbon formation chemistry and the latter two related to the effect of mixing on atomization and vaporization. Six fuels blended from a JP-5 base fuel were used to determine the effects of aromatic content, aromatic types, and end point. Three JP-5's derived from coal, shale oil, and tar sands were used to examine correlation with petroleum-derived fuels. Seven other fuels that were blends of marine diesel, JP-5, and gasoline were used for overall evaluation, but with emphasis on viscosity and distillation curve. Four emulsified fuels containing 5%, 10%, 20%, and 30% water were prepared with one of the above high aromatic JP-5 fuel blends; two more emulsified fuels containing 10% and 20% water were prepared with the shale oil-derived JP-5. The combustor was instrumented for flame radiation, exhaust smoke, and gaseous emissions, all measured at full power. The hydrogen/carbon ratio was the most effective correlating parameter for radiation and smoke; sensitivities to molecular structure appeared to be secondary. Similar to the syncrude fuels, the water/fuel emulsions and methanol/aromatic blends correlated in the same way as petroleum fuels. Higher end points did not affect the correlation, indicating that soot formation was due to gas phase reactions and not liquid phase pyrolysis. The results favor a chemical mechanism for the role of water in reducing soot.