As a mechanical engineer with my specialty in aerospace and fluid flow, I have helped to design and develop many various jet engines and jet engine control systems, including the GE engine in the F-35 Joint Strike Fighter also known to GE as the F135 engine.
I worked on the FMU (Fuel Metering Unit), the ABC (Afterburner Control), and the CAM (Core Actuation Module).
I worked with a team of about 6 other design engineers tasked specifically with developing/inventing a package of 3 fuel system controls for the F135 engine (GE’s engine in the F-35 Joint Strike Fighter). The three controls are each comprised of a system of electro-hydraulic-servo valves, shuttle valves, relief and recirculation valves, temperature control valves, and flow dividers.
There is an amazing amount of engineering that goes into the design of one of these components, on any given day I would be calculating flow and theoretical pressure drops in these components, I would be sitting with a drafter and designing the shapes and profiles or the components, both inside and out for size, flow, and weight optimization, which is a delicate balance.
I would be running FEA and CFD on the components looking at maximum stress conditions, yielding, and the structural strength of these components. That includes the strength under minimum machining tolerances, min or max possible temperature, maximum vibration, and at max pressure conditions. On any other given days I could be working with tolerances and stack-ups and drawing reviews and cost analysis on the components.
Generally, on a high-level view, this is how the main engine fuel pump and the boost pump, as well as an electrical computer signal from the aircraft’s computer (the FADEC, Full Authority Digital Electronic Control), and they output the exact amount of fuel flow required at that exact moment.
For the FMU, that fuel flow is to the fuel nozzles in the combustion chamber creating a perfect mixture of air and fuel.
For the ABC, that fuel flow output is to the Afterburner when the pilot, adding approximately 50% more of the engine’s thrust, turns it on.
For the CAM, that supply is to the various actuators and components that rely on fuel pressure for regulation.
The FADEC calculates and outputs the electrical signal to the FMU, the ABC, and the CAM correlating to how much fuel should be supplied based on parameters such as throttle position, altitude, temperatures in several locations, humidity, fan speed, air speed, flight envelope, pilot input, and a few others.
Taken from Motorfest Magazine 2012.
http://destininteractive.com/ISSUES/motorfest2.pdf