GB884509A - Fuel supply system for ram jet engine - Google Patents

Abstract

884,509. Ram jets. HOBSON Ltd., H. M. Sept. 9, 1957 [Sept. 18, 1956], No. 28547/56. Class 110 (3). [Also in Group XXIX] A fuel supply system for a ram jet engine having linear-flow pilot and main burners comprises an air-driven fuel pump, a first control device for controlling the fuel output of the pump so as to maintain stoichiometric combustion at one or more pilot burners at all times and also stoichiometric combustion at the main burners up to a limit prescribed by predetermined temperature and aerodynamic conditions, and a second control device operative on attainment of either of said conditions to reduce the fuel supply to the main burners. Thus the second control device may operate to prevent overheating of the body of the ram jet and to prevent the shock wave from moving beyond the entrance to the air intake, whereas the pilot burners are always alight to re-ignite the main burners should the main fuel supply be reduced to the point of flame extinction. The air at pressure Pc adjacent the air intake is compressed to a pressure P 3 by an air flow control element situated within the intake and the fuel pump is driven so that the pressure drop across the linear fuel spray nozzles is maintained directly proportional to Pc. As shown in Fig. 1 the fuel pump 1 driven by air through an intake 8 supplies fuel to the main and pilot burners through outlets 2 and 3 respectively. The entrance to intake 8 is controlled by a slidable valve 6 secured to a diaphragm 7, the diaphragm being acted upon on its left-hand side by fuel pressure tapped off by a conduit 18. To ensure stoichiometric combustion the valve 6 is controlled by a device 12 having a pair of diaphragms 13, 14 acted upon by pressures as shown, KPc being a fraction of Pc and Pp being the pilot fuel pressure. Diaphragms 13, 14 control a rocking arm 16 controlling an orifice 17 of a conduit 20 whereby an increase in Pc or P3 or a decrease in Pp will open orifice 17 to cause a pressure drop across restriction 19 as the fuel flows back to the tank 21 so that the diaphragm 7 moves to the left to open valve 6. The main fuel supply at pressure Pm is additionally controlled by a valve 25 which is normally open, the valve 25 being controlled by a device 24 having a pair of diaphragms 124 acted upon by pressures as shown. Spillage of the shock wave at the air intake and overheating of the ram jet causes opening of one or both of a pair of valves 32, 33 whereby the right-hand side of the right-hand diaphragm 124 is exposed to ambient pressure Po thus causing opening of orifice 30. This action causes an increase in the pressure drop across an orifice 31 in diaphragm 28 whereby the valve 25 closes. In a modification (Fig. 2, not shown) in which the valve 32 is omitted, the right-hand side of the right diaphragm 124 is exposed to a pressure derived from a pick-up tube fitted to the outside of the engine cowl, a small hole being provided in the cowl forwardly of the tube so that the pressure in the tube is effected by movement of the shock wave past the hole.