Quest for a Reliable Method for Determining Aviation Fuel Thermal Stability: Comparison of Turbulent and Laminar Flow Test Devices

Abstract

Thermal deposition, based on carbon burn off, was evaluated in two turbulent flow and one laminar flow test devices. The two turbulent flow test devices were the Navy Aviation Fuel Thermal Stability Simulator (NAFTSS), developed by Rolls Royce, UK, for the U.S. Navy, and the High Reynolds Number Thermal Stability (HiReTS) bench rig, developed by Shell Global Solutions, UK (formerly Shell Research and Technology Centre). The laminar flow test device was the Tubular Reactor (TR), a bench rig developed by the Naval Air Systems Command Air-4.4.5 (NAVAIR). Three jet fuels were used in the comparison of the NAFTSS and the TR, and six fuels (five jet and one diesel) in the comparison of the HiReTS and the TR. Good correlations were obtained between the laminar flow and the two turbulent flow test devices. A likely explanation of these results is that for the fuels examined, Reynolds number does not appear to be a critical factor in predicting thermal stability. These results are significant for they support the use of laminar flow in devices such as the specification test method, i.e., the JFTOT, ASTM D3241. Furthermore, on the basis of an overall analysis of the results, we postulate that reactant depletion is likely attributable to a difference in fuel temperature (arising from the difference in flow rate (residence time)/test temperature) and not to a difference in flow velocity (laminar vs turbulent flow). We further postulate that fuel temperature is likely the critical and predominant factor in predicting jet fuel thermal stability, as long as attention is paid to the residence time and thermal gradients of the hot section.