GB671379A - Improvements in or relating to fuel systems for gas-turbine aircraft engines - Google Patents

Abstract

671,379. Gas turbine plant. R O L L S - ROYCE, Ltd. April 27, 1950 [March 23, 1949] No. 7977/49. Class 110(iii) [Also in Group XXIX] In a fuel system for gas-turbine engines of the kind in which a fuel pressure difference is controlled by means responsive to an " atmospheric condition," pressure sensitive means responsive to an operating condition of or associated with the engine and dependent at least in part on the fuel supply to the engine, are arranged to apply a load to the means responsive to the "atmospheric condition" so as to modify the control exercised thereby and so prevent the value of the operating condition falling below a predetermined value. The pressure sensitive means may be influenced differentially by two operating conditions. The term "atmospheric condition" includes ambient atmospheric pressure or temperature or both and also includes these conditions as modified by the flight of the aircraft. The invention prevents "negative speed creep" with altitude at low power settings and "positive speed creep" at high power settings. As shown in Fig. 1, the pressure difference between the fuel outlet 11b and the fuel inlet 11a of a variable delivery swash-plate pump 16 is regulated by an evacuated capsule 36 'exposed through a conduit 34 to compressor air intake or nacelle pressure. The angularity of the swash-plate 19 is regulated by a servo-piston 21 under the control of a " half-ball " valve 27 carried on a lever 28. The lever 28 is fulcrumed in a diaphragm 29 and is normally loaded by the capsule 36, by a spring 35, and by a diaphragm or piston 37 subject to the fuel pressure difference to be regulated. One side of the piston 37 is connected to the pump inlet through a pipe 33 and ports 41 whilst the other side is subject to the pressure in the fuel delivery line 12 on the inlet side of a throttle 13 operated by a power control lever (not shown). The additional load on the capsule 36 is exercised by a tappet 49 the head 49a of which is constantly urged against a spring-loaded diaphragm 42, constituting the aforesaid pressure sensitive means, by a spring 48. As shown, the upper side of the diaphragm 42 is subject through a pipe 45 to the same atmospheric condition as the capsule 36, whilst the underside of the diaphragm is subject to the burner fuel pressure through a pipe 46 opening on the upstream side of a shut-off cock which is normally fully open and does not occasion any appreciable pressure loss. Alternatively, the underside of the diaphragm 42 may be exposed to the delivery pressure of the engine compressor. In a further arrangement, the underside of the diaphragm 42 is exposed to the burner fuel pressure and the upper side to the delivery pressure of the engine compressor. Where the engine compressor also supplies a pressurized aircraft cabin, the pressure sensitive means may be responsive to cabin pressure and the predetermined minimum value to be maintained by such means may correspond to the minimum cabin pressure desired. In a modification, the diaphragm or piston 37 is subject to the pressure difference on the opposite sides of a spring- loaded throttle valve in the fuel delivery line 12. This valve is shaped so that the pressure drop across it is proportional to the flow through it. Specification 577,016, [Group XXIX], is referred to.