Effect of Aromatics on the Thermal-Oxidative Stability of Synthetic Paraffinic Kerosene

The effect of aromatic type and concentration on the thermal-oxidative stability characteristics of a synthetic paraffinic kerosene (SPK) aviation fuel was performed using batch and flow reactor systems, in combination with detailed chemical fuel analyses. An improved understanding of the impact of aromatic addition will assist in optimizing beneficial operational characteristics of the SPK feedstocks and the development of fully synthetic jet fuels. A primary goal of this study was to elucidate the controlling reaction chemistry and identify the cause for differing stability characteristics for varying types of aromatics. Studies were performed using a SPK comprised primarily of mildly branched iso- and n-paraffins as the base feedstock; limited studies were performed using a highly branched SPK. Commercially available aromatic solvents were used to represent petroleum-derived jet fuel and potential synthetic aromatic blending streams. These solvents were composed of mono- and diaromatic compounds of varying average molecular weight and size. The resulting thermal-oxidative stability characteristics were highly sensitive to the blend composition, with both increasing aromatic size and concentration, resulting in a higher deposition propensity upon stressing. It was determined that oxidation and molecular growth of the aromatic compounds are the probable primary pathways of surface deposit formation for these blends. Larger aromatic compounds (e.g., diaromatic) require fewer successive growth steps to produce insoluble deposit precursors, resulting in significantly higher deposition propensity than lower molecular weight (e.g., monoaromatic) species. Limited testing showed that the impact of aromatic type on deposition is consistent for different SPK compositions, but the deposit magnitude may be affected.