Patent GB-914443-A (GB)
Title: Improvements in or relating to internal combustion free piston engines
IPC: F02B71/02
Filed: 1961-04-18
Abstract: 914,443. Free-piston engines; starting; fuel injection. WELLS, A. A. April 18, 1961, No. 14006/61. Classes 7(2), 7(3) and 7(5) [Also in Group XXVIII] A free-piston engine having a compression ignition working cycle, comprises a free-piston assembly and a liquid-filled cushion chamber for driving the piston assembly from its outer position to its inner position, the cushion chamber being filled with liquid fuel during operation of the engine, the engine further comprising fuel injection means for injecting fuel from the cushion chamber into the combustion chamber. In the operation of the device, an atomized jet of liquid fuel at high pressure is injected into the upper part of the cylinder 1 and the combustion chamber 20, when the power piston 15 is near the top of its compression stroke, from a nozzle 21 at the centre of the power piston crown. The fuel for injection is led from the cushion chamber 11 through a bore in the cushion piston 19. However, the fuel pressure is at its lowest in the cushion chamber 11 when injection is required and so it is necessary to introduce an appropriate phase delay for the injection pressure in comparison with the cushion pressure. In this embodiment of the invention the delay is introduced through the fuel metering chamber 14. The parts 13, 14 and 19 are shown to a larger scale in the cross-sectional view of Fig. 2. The axial fuel duct 22 in the cushion piston 19 is interrupted near the middle of its length, the two inner ends of the duct portions communicating through transverse bores 23 and 24 with small annular peripheral ports 25 and 26 at appropriate positions along the length on the outer wall of the piston. During the movement of the piston 13, the port 26 momentarily coincides with a port 27 in the metering chamber 14, and at a later moment, the port 25 momentarily coincides with a port 28 in the chamber 14. The ports 27 and 28 communicate with passages 29 and 30 in the chamber 14. When the ports 26 and 27 coincide the cushion chamber 11 is at high pressure and the metering chamber 14 is charged with a suitable quantity of fuel under pressure which is then trapped as the ports are moved out of register. At a later stage when the power piston 15 is almost at the top of its compression stroke the upper ports coincide and the fuel trapped in the metering chamber 14 is discharged at high pressure to the injection nozzle 21. The latter is preferably of the spring-loaded type, or of a characteristic similar to that of the spring- loaded type, so that the discharge rate increases rapidly above a certain pressure, whereby appreciable changes in fuel charge may be made through proportionally smaller changes in mean pressure in the cushion chamber 11. As the fuel supply line is freely connected to the cushion chamber 11, it experiences a fluctuating pressure from the cushion chamber, and the fluctuations may be made to work a fuel pump of the volumetric displacement type at a control station where the fuel tank is located. The pump used in the embodiment which is being described is shown in section in Fig. 3. For starting the action of drawing back the piston assembly is performed by forcing fuel into the cushion chamber by means of an ancillary starter pump, for instance of the single stroke force pump type. As the pressure is increased the spring 52 will be compressed by an amount equivalent to the load difference arising from the slightly larger diameter of the starter piston 51 and the diameter of the cushion piston 19. At a certain point in the withdrawal of the piston assembly 15, 17 and 19, the outer sleeve of the sphincter catch 53 will engage with the flat end of the starter cylinder 50 and will commence to move axially relative to the inner sleeve 54. A little later the balls will register again with the annular groove in the outer sleeve, and they will be forced radially outwards to release the two plungers 19 and 51, which will then separate. The starter plunger 51, having returned already substantially to its extreme position, will remain there in response to the positive cushion chamber mean pressure, while the cushion piston 19 will be caused to commence a working stroke of the piston assembly 15, 17 and 19.. The fuel pump may be driven electrically at starting. When the engine has started the fuel pump driving motor may act as an electrical generator. In a modification the end of the fuel pipe adjacent the fuel tank is enlarged in diameter and is provided with a close fitting plunger which is movable from an external control and which contains a non-return valve permitting only passage of fuel from the tank to the fuel pipe. The fuel pipe is made to be of such a length that the fuel within it partially resonates in tune with pressure fluctuations in the cushion chamber. A modified fuel injection arrangement is described. The generator may be mounted to move axially.