Development of Double Gear Fuel Pump for Heat Management Improvement

A unique double gear fuel pump system with operation mode switching capability for aircraft engines was developed to solve the heat management problem of current high efficiency turbofan engines and improve specific fuel consumption (SFC). Mode switching from parallel operations to series operations was found to reduce the discharge flow and pump work to nearly half. This resulted in the reduction of the rise in fuel temperature due to the fuel recirculation at the high altitude low Mach number flight condition. Air cooled oil cooler (ACOC) is usually required for sufficient oil cooling at descent or approach flight conditions. Since fuel consumption at those conditions is not very high, most of the gear pump discharge fuel flow proportional to the engine speed is returned to the fuel pump inlet resulting in significant heating. The ACOC that provides additional cooling capability degrades SFC due not only to the increased weight but also to the wasted fan discharge air. By reducing fuel temperature rise at the pump at those flight conditions, the necessity of ACOC may be eliminated. Further, it is shown that a reduction by half of the double gear pump weight can be achieved by increasing pump speed twice without incurring a durability penalty. Extensive tests showed sufficient steady state pump performance, switching characteristics, and durability.