Jet Fuel Oxidation and Deposition

Abstract

The chemistry leading to homogeneous deposit formation when Jet A fuel is heated between 170–300°C was investigated by characterizing both the deposits and changes in the fuel after deposit formation. The maximum amount of deposits that form from static Jet A fuel heated at 200°C with a continuous airflow is ∼5 wt. % indicating the presence of a finite concentration of easily oxidizable species that lead to the deposits. The deposits were characterized using CPMAS NMR, FTIR, elemental analysis, GCIR and chemical derivatization. They are highly aromatic, enriched in oxygen, nitrogen and sulfur relative to the fuel, and contain carboxylic acids and ketone functional groups. The role of nitrogen and sulfur containing compounds is also discussed. Gel permeation chromatography (GPC) of derivatized heated fuel shows a substantial growth in molecular weight. We find hydrocarbons equivalent to C-70 oxidation compounds in fuel heated in an air environment. In Jet A fuel, whose deposit formation capacity is not exhausted, the latter can continue to react at room temperature to form deposits. This is a concern especially for recirculating applications since it implies that once the fuel has been heated, deposits can precipitate in the holding tanks even when the fuel is cool.