INNOVATIVE HIGH-TEMPERATURE AIRCRAFT ENGINE FUEL NOZZLE DESIGN

The objective of the Innovative High-Temperature Aircraft Engine Fuel Nozzle Program was to design and evaluate a nozzle capable of operatin g at a combustor inlet air temperature of 1600-degrees-F (1144 K) and a fuel temperature of 350-degrees-F (450 K). The nozzle was designed t o meet the same performance requirements and fit within the size envel ope of a current production F404 dual orifice fuel nozzle. The design approach was to use improved thermal protection and fuel passage geome try in combination with fuel passage surface treatment to minimize cok ing at these extreme fuel and air temperatures. Heat transfer models o f several fuel injector concepts were used to optimize the thermal pro tection, while a series of sample tube coking tests were run to evalua te the effect of surface finish, coatings, and tube material on the co king rate. Based on heat transfer analysis, additional air gaps, reduc ed fuel passage flow area, and ceramic tip components reduced local fu el wetted wall temperatures by more than 200-degrees-F (110 K) when co mpared to a current production F404 fuel nozzle. Sample tube coking te st results showed the importance of surface finish on the fuel coking rate. Therefore, a 1 mum. (0.025 mum) 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 protectio n, and provide back pressure to reduce the risk of fuel vaporization. Phase II of this program will evaluate the fuel nozzle with a series o f contaminated fuel and coking tests.