Patent GB-564682-A (GB)
Title: Improvements in or relating to the starting of internal-combustion-operated motive-gas generators of the free-piston-type
IPC: F02B75/10
Filed: 1943-08-13
Abstract: 564,682. Internal-combustion -motivegas plant. PESCARA, R. P. Aug. 13, 1943, No. 13188. Convention date, Aug. 13, 1942. [Class 7 (i)] An internal -combustion-operated motive-gas generator of the free-piston type has means for charging the motor cylinder with air above atmospheric pressure before accelerating the free piston assembly on its instroke to start the gas generator. In one form, Fig. 1, which shows one of a number of generators connected to a manifold 1, a motor cylinder 2 is associated with a compressor cylinder 4 having a double-acting compressor piston 5 connected to the motor piston. A pneumatic cushion 7 comprising a cylinder 8 ensures the instroke of the piston assembly 3, 5 and receives compressed air for accelerating the assembly on its instroke for starting, the said air being admitted to a chamber 9a connected to cylinder 8 by a port 9b. The compressor cylinder is supplied from the atmosphere by valves 4a and delivers through valves 4b to a receiver 10 having parts connected by a pipe 11. Casing 10 is connected to the motor cylinder by inlet ports 2a, and exhaust ports 2b lead to the manifold via a valve 16. Starting air is stored in a reservoir 14 and passes through a line 15 past a non-return valve 9c to the chamber 9a, a valve 21 being closed by a spring 22a acting on piston 21a. By a valve 15b the chamber 22 can be opened to the atmosphere, whereupon piston 21a falls and valve 21 opens to cause acceleration of the free piston assembly. At starting the compressed air also acts through a line 24a on a piston 23a to position an abutment 23 so as to move the piston assembly to a suitable starting position, the abutment being subsequently withdrawn by a spring 23b. The gas generator is isolated when necessary by the valve 16, the piston 16a of which may be subjected to the pressure in reservoir 14 by means of a line 16c. The valve 16 is held open during running by the pressure in chamber 9a acting through a line 16e. According to the invention, the casing 10 which forms the receiver for charging and scavenging air for the motor cylinder is connected to reservoir 14 by a pipe 17 regulated by a throttle-valve 17a. A line 18 leads to the cylinder from the casing 10 for the purpose of moving the assembly outwards to the starting position if the piston 3 is above ports 2a. Where some generators of a set are already running a pipe 35 communicating with the air receivers 10 of all the gas generators may provide the means for putting under pressure the air receiver and the motor cylinder of the generator to be started. Since the delivery pressure, which is substantially the pressure to which the receiver 10 and motor cylinder 2 are charged before starting, is variable, the energy to be supplied by the cushion cylinder is also variable. The starting energy is preferably adjusted automatically under the control of the delivery pressure. For this purpose a needle valve 25a is carried by a piston having one side subjected to the starting pressure by a line 26a and the other to the delivery pressure through a line 26b. The volume of air in the cushion is varied by a cylinder 27, the piston in which is moved by a screw actuated by a rack 31 whose position is responsive to the pressure in the receiver 10. Another manner of varying the starting energy is to throttle the air during its expansion by a valve 32 controlled by a piston 32a subjected to the pressure in receiver 10. In some cases either one or a combination of two of the means for varying starting energy shown in Fig. 1 may be used. In a modification, the necessary variations of starting energy may be reduced by varying the quantity of air to be compressed during the starting stroke by the provision of decompression ports controlled by means responsive to the desired delivery pressure. Thus, in Fig. 4, the compressor cylinder 51a has inlet valves associated with pistons 52a which may be subjected to the pressure in an air reservoir by a pipe 53 or valve 58. This line is further controlled by a valve 54 having a piston 54b moved in one direction by a spring 54d and in the other by the delivery pressure pm. The number of open decompressing valves, and hence the degree of decompression, depends on the position of the valve 54. The transfer to normal compression is preferably effected progressively. For this purpose escape of air from the cylinders 52a may be effected through a needle valve 55b controlled partly by the pressure in cylinders 52b and partly by the cushion pressure. In an installation including a number of generators, an idle generator may be started by gas extracted from the cushion of an active gas generator. In Fig. 5, the chamber 38a serves as a compressor cylinder for air supply to the motor and the chamber 38b serves as a cushion. The chamber 38a has an inlet valve 39 and delivery valve 40 communicating with the receiver 41 having ports 41a leading to the motor cylinder. The fuel injection device is operated by a rod 37c mounted on the compressor piston 37b. Each air receiver is connected to a common pipe 48. The quantity of air in the cushion is controlled as described in Specification 556,454. A controller A has a valve 50 actuated by a piston 50c and controlling oppositely opening valves 50a, 50b. The piston has its opposite faces exposed respectively to the cushion pressure and delivery pressure and is biassed by a spring 50d. In order to start one generator from another already in operation, the idle compressor piston is locked by a device 45 in the starting position. To fill the cushion 38b, a second common pipe 49 is connected to the cushion of each generator by a pipe 38f and in the starting position a valve 37f is open to allow the cushion to be filled. When the starting pressure is attained in cushion 38b a valve 38e is shut, the piston 37b unlocked by a valve 47b. After the first instroke the valve 38d is opened to permit the controller A to regulate the gas content of the cushion 38b. Another modified means for filling the cushion with starting gas is also described.