Innovative High-Temperature Aircraft Engine Fuel Nozzle Design

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Abstract
The objective of the Innovative High-Temperature Aircraft Engine Fuel Nozzle Program was to design and evaluate a nozzle capable of operating at a combustor inlet air temperature of 1600°F (1144 K) and a fuel temperature of 350°F (450 K). The nozzle was designed to meet the same performance requirements and fit within the size envelope of a current production F404 dual orifice fuel nozzle. The design approach was to use improved thermal protection and fuel passage geometry in combination with fuel passage surface treatment to minimize coking at these extreme fuel and air temperatures. Heat transfer models of several fuel injector concepts were used to optimize the thermal protection, while a series of sample tube coking tests were run to evaluate the effect of surface finish, coatings, and tube material on the coking rate. Based on heat transfer analysis, additional air gaps, reduced fuel passage flow area, and ceramic tip components reduced local fuel wetted wall temperatures by more than 200°F (110 K) when compared to a current production F404 fuel nozzle. Sample tube coking test results showed the importance of surface finish on the fuel coking rate. Therefore, a 1 μin. (0.025 μm) roughness was specified for all fuel passage surfaces. A novel flow divider valve in the tip was also employed to reduce weight, allow room for additional thermal protection, and provide back pressure to reduce the risk of fuel vaporization. Phase II of this program will evaluate the fuel nozzle with a series of contaminated fuel and coking tests.

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