Heat Transfer in an Injector-Scaled Additively Manufactured Fuel Passage

Knowledge of heat transfer in fuel wetted passages is important for informing injector design and life estimates due to the effects of temperature on fuel degradation. Future injectors will be manufactured using additive methods in an effort to reduce production costs and time, while also facilitating more agile design practices. Additive manufacturing (AM) is known to result in increased surface roughness compared to conventional manufacturing techniques, however limited data exist on how this roughness impacts heat transfer, particularly in liquid flows. This paper solves the inverse heat conduction problem for heat transfer coefficient in liquid flows through rough 90 deg channel bends typical of the pilot gallery in a lean direct-injection fuel spray nozzle. Heat transfer distributions across two rough surfaces are compared to an equivalent smooth surface. The two rough surfaces have different morphologies but have the same relative effective sand grain roughness which is matched to a prototype AM fuel injector. The sand grain roughness is predicted from a correlation that has been adapted for the high relative roughness scales characteristic of additively manufactured fuel passages. The effective sand grain roughness estimated from surface measurements of a prototype AM fuel gallery was ∼13% of the passage hydraulic diameter. For the two rough surfaces, the heat transfer enhancement is up to three times the smooth surface value for the straight section preceding the bend and up to four times around the bend. Heat transfer distributions across the two rough surfaces are similar, but the magnitudes differ by ∼17% depending on the surface morphology. This highlights the importance of the heat transfer effectiveness of surface features, which unlike the sand grain roughness is not matched for the two surfaces considered. Adjusting the data for differences in heat transfer effectiveness corrects the average heat transfer for the rough surfaces to within 7%.