GB935942A - Improvements in fuel systems for aircraft gas turbine engines - Google Patents

Abstract

935,942. Gas turbine plant. DOWTY FUEL SYSTEMS Ltd. April 14, 1960 [Jan. 15, 1959; April 13, 1959], Nos. 1544/59 and 12469/59. Class 110 (3). [Also in Group XXIX] An acceleration fuel flow control for a gas turbine engine comprises apparatus arranged to control fuel flow to the engine during acceleration in accordance with two linear relations between non-dimensional engine speed N/#T 1 or an expression uniquely related to it under maximum acceleration conditions and non-dimensional engine fuel flow Q/P 1 #T 1 or an expression uniquely related to it under maximum acceleration conditions, one of the linear relations being operative in the low engine speed range and the other being operative in the upper engine speed range to control fuel flow in such a manner as to maintain approximately the non-linear relation between non-dimensional engine speed and non- dimensional fuel flow for maximum engine acceleration. In the embodiments described, the ratio compressor outlet pressure P 2 to compressor inlet pressure P 1 is used for non-dimensional engine speed and the ratio of 'fuel flow rate Q to the product of P 1 and the square root of the compressor inlet temperature T 1 for non-dimensional fuel flow. Two valves 8, 9 are provided controlling the flow of fuel from an inlet 2 to an outlet 3, leading to the burners through throttle passages 14, 15. Fuel is supplied to chambers 43, 44 and 25, 26 at either end of the valves respectively and the position of the valves is determined by levers 49, 34 controlling the escape of fuel from these chambers through nozzles 47, 48, 32, 33 respectively. The lever 34 is pivoted at 35 and pressures P 1 , P 2 act on the lever through bellows 36, 37 opposed by evacuated bellows. The bellows 37 acts through a second lever 38 whose fulcrum may be adjusted by a rod 39. A spring 41 is provided between the valve 9 and the lever 34 such that movement of the lever due to changes in P 1 , P 2 varies the pressures in chambers 25, 26 causing movement of the valve 9 to vary the throttle opening 15 and the spring 41 acts as a feedback determining the final position of the valve 9. The valve 8 is controlled in a similar manner through lever 49 pivoted at 51 and feedback spring 56, but in this case the pressures P 1 , P 2 in bellows 52, 53 act in opposition on the lever. The pressures in the lines 2, 3 are fed through conduits 16, 17 to pads 18, 19 which act on a lever 21 which is also subject to the compressor inlet temperature T 1 acting through bellows 24. The lever 21 controls a servo vent 22 in known manner, e.g. by means of a by-pass valve, to control the flow delivery from the fuel pump to maintain a pressure drop in the passages 2, 3 determined by bellows 24 and spring 23. In operation, the valve 8 closes the throttle 14 during the lower non-dimensional speed range and adjustment of the valve 9 provides the first linear relation. At a predetermined speed, the valve 8 opens and both valves 8, 9 then control the flow to provide the second linear relation. In a modification, a single valve member is provided instead of the two valves 8, 9 in which the position of the valve is determined by two servo vents, the first providing control of the first linear relation and the second controlling the valve for the second linear relation.