Recent Progress, Challenges, and Future Development Needs of Thermally/Energy Efficient Fuel Actuator Pumping Systems for Military Gas Turbine Engine Applications

Thermal management has emerged as one of the primary challenges for modern military gas turbine engines. Fuel actuator pumping systems contribute to the challenge by constantly injecting waste heat into the fuel system. This is due to a fundamental mismatching between an actuation system with a low duty cycle and a pump which is always running. Since the pump is directly coupled to the gearbox, the detriment is twofold: horsepower is always being drawn to drive the pump, and heat is generated. Furthermore, the emergence of variable cycle engines pushes the actuation system in the direction of more effectors and more loads, which drives requirements for high pressure and high flows from the pumping system. Piston pumps have been seen as favorable for the actuation pump application due to their high single stage pressure rise capability. However reducing the number of pumping components alone has not solved the thermal management issue. Variable displacement pumps have been designed to operate over a range of conditions in order to deliver flow more appropriately as demanded by the control system. These pumps allow pressure and flow to be modulated independent of one another and of the pump’s rotational speed. Variable displacement pumps may be considered as a component of a partial-demand actuation pumping system. Even in a partial-demand actuation pumping system, a variable displacement pump will still be coupled to the gearbox and require some minimum flow for lubrication and cooling. On-demand actuation fuel systems deliver only the amount of flow that is being demanded at a given time so that waste heat is minimized. In other words, the duty cycle of the pumping system matches that of the actuation system. The development of an on-demand actuation fuel system will require a new architecture and new components.