Jet fuel oxidation on conventionally and additively manufactured metallic tubes

In the aviation industry, jet fuel is a propellant as well as a coolant. At elevated temperatures, the jet fuel experiences significant thermal stresses, which leads to the oxidation of hydrocarbons when exposed to the heat exchanger walls. As a result, undesirable insoluble carbon deposits on the internal heat exchanger walls impede the effectiveness of the heat exchanger and the aircraft fuel circulatory system, compromising aircraft safety and performance. Here, we study the jet fuel fouling behavior on additively manufactured tubes created using stainless steel, aluminum alloy, titanium, and Inconel, during autoxidation at elevated temperatures. Additively manufactured materials are tested due to their numerous potential benefits for the aerospace industry, which include design flexibility for the creation of complex and optimized parts that enhance performance and aerodynamics. Experiments were conducted using a fuel-fouling open loop system based on the Jet Fuel Thermal Oxidation Test (JFTOT). Scanning electron microscopy and characterization of the internal surface of the tubes showed that the jet fuel reacts differently with different metals and alloys. Comparisons were made with traditionally manufactured materials and benchmarked with the performance of bare copper tubes. We show that additively manufactured tubes were more prone to fuel fouling due to the larger inherent roughness associated with the additive manufacturing process. We show that applying a thin layer of commercially available Silcolloy 2000 coating onto the internal surface minimizes jet fuel degradation significantly. Our work helps to enable the application of additive manufacturing for aircraft thermal management component manufacture by alleviating concerns related to fuel blockage and performance deterioration stemming from surface deposition.