Patent GB-793239-A (GB)
Title: Improvements in or relating to pulse jet engines
Inventor: THARRATT CHARLES EDWARD
IPC: F02K7/067
Filed: 1954-04-28
Abstract: 793,239. Generating combustion products under pressure. SAUNDERS-ROE, Ltd. July 27, 1955 [April 28, 1954], No. 12366/54. Class 51 (1). [Also in Group XXVI] A pulse jet engine with aerodynamic valving comprises a substantially cylindrical tube 10, Fig. 6, constituting the combustion chamber of the engine and open at its rear end but closed at its front end apart from a permanently open annular port 17 communicating by rearwardly branching annular neck 15 with an annular rearwardly facing air intake 12 surrounding the tube, the cross-sectional area of the air intake, the cross-sectional area of the neck throughout its length and the cross-sectional area of the port being substantially equal and the ratios of the cross-sectional areas of the port and of the tube and of the lengths of the tube and of the neck being such that the engine will operate continuously with a unidirectional but periodically reversing. gas flow throughout the system. It is explained in the Specification that this construction functions as a modified Helmholtz resonator and theoretically the dimensions should be related so that where Li is the total length of the neck and air intake, Ai is the cross-sectional area of the neck, L is the length of tube 10 and A is its crosssectional area. In practice, due to damping, this does not give the correct value of Li, which must be found by experiment, the ratio Ai/A  being chosen to suit the combustion requirements. Referring to Fig. 7, fuel supply and return pipes 18, 19 support a fuel injector 20 which discharges fuel against a baffle plate 21 ; this baffle plate causes the formation of a circular disc of atomized fuel which is entrained by the entering air and blown through an annular port 22 into the combustion chamber. Ignition takes place to the rear of the port 22 and an ignition plug (not shown) is provided at this point for use when starting the engine on compressed air delivered through a pipe 30. As shown in Fig. 6, a cowl 28 may be fitted to the forward end of the engine and a sheathing 14 may be provided round the tube 10 ; alternatively the tube 10 may be shaped to the form 14, and its rear end may be flared at 13. If desired, perforations may be provided in the transverse plate 16 to allow a quantity of hot gas to pass into the interior of the cowl for de-icing purposes. In the modification shown in Fig. 8, the fuel injector 20 discharges fuel rearwardly against a baffle plate 121 supported on a plate 26. In the arrangement shown in Fig. 9 the injector 20 discharges fuel against a baffle plate 121 and the atomized fuel passes to the combustion chamber through a circular port 22 of the same cross-sectional area as the annular port 17. The engine may be used for propulsion, and individual small engines may be fitted to the tips of the blades of a helicopter ; the engine may also be used as a heater in an aircraft or for de-icing purposes in which case the rear end of the inner tube may be bent to extend transversely to the axis of the engine and divert hot gases along the leading edge of a wing or into contact with any other surface to be de-iced.