“Virtual” smoke point determination of alternative aviation kerosenes by threshold sooting index (TSI) methods

One benefit attributable to blending of alternative jet fuels into conventional petroderived kerosenes is reduced sooting tendency relative to the conventional unblended kerosenes. This benefit is largely due to the lower aromatics content of the alternative fuels/blends, and it is desirable with respect to sooting tendency limits embedded in aviation turbine fuel specifications (e.g., ASTM D1655 and D7566). However, the relatively high smoke points of many alternative jet fuels are not directly measurable by the prevailing ASTM D1322 smoke point (SP) method and its international variants. This frustrates characterization of these alternative fuels and prediction of their blending properties. The present work addresses an extrapolative “virtual” smoke point (VSP) technique for determination of smoke points compatible with the ASTM D1322 standard. Importantly, this compatibility removes the significant ambiguity historically associated with measurements of non-standard smoke points, herein categorically designated SP*. The VSP approach invokes the linear-by-mole blending functional basis of the Threshold Sooting Index (TSI), which has been empirically demonstrated in the literature for both defined molecular species and complex hydrocarbon fluids. If the average molecular weights (MWs) of the blending component fuels are known, then the VSPs of low-sooting tendency fuels can be forecast using D1322 SP measurements. This is demonstrated here for iso-octane and ndodecane as illustrative pure-component test fuels, as well as the full boiling range POSF 7720, a camelina sativa-derived hydrotreated jet fuel (HRJ). In part, the approach is facilitated by the ability to easily determine the average molecular weight of a fuel using a method recently developed by this laboratory.