GB762179A - Improvements in or relating to fuel supply systems for ram-jet engines - Google Patents

Abstract

762,179. Jet propulsion plant. BRISTOL AEROPLANE CO., Ltd. May 26, 1954 [May 29, 1953], No. 15083/53. Class 110 (3). [Also in Group XXIX] A fuel supply system for a ram-jet engine comprises a fuel pump in driven connection with a fluid, pressure motor, the pump being arranged to supply liquid fuel to the combustion zone of the engine through flow-control means including at least one variable area orifice for controlling the flow of fuel in approximately direct proportion to the. pressure of fuel passing to the flow-control means, and pressure control means for controlling the pressure of fuel passing to the flow-control means in substantially direct proportion to a control pressure which, during operation of the engine, is a measure of the mass flow of combustion air through the engine. Referring to Fig. 1, liquid fuel is delivered by a centrifugal pump 11 driven by an air turbine wheet 12 through pressure control means 13 to spray injectors 14. The pressure control means 13 comprises a balanced valve member 20 cooperating with a port 80 and operated by two diaphragms 22, 23 of different areas. The fuel at reduced pressure enters the chamber 24 bounded by the diaphragm 23 and the same pressure is transmitted through holes 25 to the chamber 26 where it acts on one side of the diaphragm 22. A chamber 27 on the other side of diaphragm 23 is connected-by a passage 28 to an air flow duct having a ram air inlet 30 directed upstream in the airflow through the engine. Downstream of the passage 28 the duct is provided with two restrictions 32, 33, the latter being fitted with a needle 34 whereby its throat area may be adjusted. From between these two restrictions a passage 35 leads to a chamber 36 on the side of diaphragm 22 remote from valve 20. The arrangement is designed to operate with a super-critical pressure drop across the second restriction 33, and under these conditions the pressure in chamber 36 is a constant proportion of the pressure upstream of the first restriction; thus the fuel pressure is proportional to the pressure measured by the inlet 30. The flow of fuel to the combustion zone is made proportional to the fuel pressure by spray injectors 14 which have a variable area discharge orifice, the area of which is controlled by a spring-loaded pintle valve. The supply of air to the turbine wheel 12 may be controlled by a throttle valve 41 operated by a piston 42 subjected on either side to the pressure of the fuel on the upstream and downstream sides of the valve 20. In an alternative arrangement, Fig. 4 (not shown), the throttle valve 41 is replaced by a spill valve which is similarly controlled. The needle 34 may be controlled by a Mach number responsive device, Fig. 5, comprising a diaphragm AL connected by a rigid member to a smaller diaphragm AS, the diaphragms being enclosed in a casing which is thus divided into three chambers 103, 104, 105. In chamber 105 is a valve comprising valve member 106 connected to the diaphragms and control ports 108, 109 on each side of the valve member. A high pressure passage 110 supplies ram air to a venturi 112 designed to be choked in operation and connected to chamber 103. Chamber 105 is connected to passage 110 and the middle chamber 104 is connected to a static head port 117. A throttle valve 114 is in the form of a piston, movable to the right (closing direction) by pressure fluid in a chamber 118 and to the left by pressure in chamber 119, and carries the needle 34. The arrangement shown in Fig. 2 differs from that in Fig. 1 principally in that the fuel supply pressure is controlled by regulating the speed of the air turbine 12. A spill valve 50 in the working fluid duct is operated by a diaphragm 51 subjected to the pressure of air in a chamber 52 to which air is admitted through a ram air inlet 53 containing a restrictor 54 and discharged through a port 81. The area of the port is controlled by a valve 55 operated by a pressure control device 56 similar to the pressure control device 13 of Fig. 1. The pump delivers fuel to the discharge orifices 64 through a metering device comprising an inner chamber 70 receiving the fuel and containing a piston 71 held against fuel pressure by a spring. The area of orifices 73 in the wall of the chamber is adjusted by movement of the piston 71, and the orifices are so shaped that the pressure-flow characteristic is substantially linear.