Patent GB-572191-A (GB)
Title: Improvements in and relating to two-stroke cycle internal combustion engines
IPC: F02B37/02
Filed: 1944-02-01
Abstract: 572,191. Two-stroke engines. ARMSTRONG WHITWORTH & CO. (ENGINEERS), Ltd., SIR W. G., MANSFIELD, W. P., and WHITE, J. Feb. 1, 1944, No. 1863. [Class 7 (ii)] [Also in Group XXVI] In a two-stroke internal-combustion engine, the exhaust gases are used to drive a gas turbine a and the duct b between the engine, and the turbine is arranged so that after each exhaust event the pressure in the duct comprises a high-pressure zone adjacent to the outer end, and a low-pressure zone adjacent the inner end, valve means f being provided which opens to permit said pressure distribution and then closes to separate the two zones. The turbine may drive a compressor c charging the engine, or in some cases the turbine may return power to the crank-shaft or may drive an auxiliary machine. The total quantity of fresh charge passed into cylinders should exceed the cylinder volume by about 0.15 to 0.6 of the cylinder volume at N.T.P. The extent of the high-pressure zone following an exhaust action, depends on the exhaust area and the rate of discharge and is arranged to give the required length to the high-pressure zone. The estimate of the length of the said zone is based on a mean velocity of the outward and return waves of the order of 450/600 metres per second. The timing of the valve # is such that it is fully opened when the front of the pressure wave reaches it, and substantially closed when the return action reaches it. The closure normally occurs after the opening of the inlet orifices. In some cases an auxiliary orifice leading to the atmosphere may be provided so that when the main valve closes to trap the high.-pressure gases, the auxiliary orifice is open to permit scavenging at atmospheric pressure. A self-induction effect may be utilized to obtain further lowering of the pressure at the cylinder end of the exhaust duct. The position of the valve # is such that the length of duct b between the valve and the turbine is substantially half the length of the pressure wave. For operating the engine without supercharging, means may be provided for byepassing the gases round the valve f. In one form of valve, Figs. 3 and 4, a disc g rotates at three times engine speed for a threecylinder engine, and is located in a watercooled housing i, the ports h extending round half the disc. The manifold k and exhaust duct b extend from opposite faces of the disc. Cooling is assisted by the provision of air holes i<2>, the air being directed by vanes g<1> on the disc into a pipe b<1>. In a modification, Fig. 6, the disc has a flange m provided with orifices and arranged to control outlet to atmosphere through a pipe b<2>. In some cases the disc valve, or valves, may be mounted with their planes parallel to the crank-shaft axis, and the peripheries of the separate disc valves may be formed as gears to convey the drive along the train of valves. Fig. 8 shows an arrangement of two valves each controlling two cylinders of a four-cylinder engine. In this form, the valves are driven at three times engine speed and only one of the three openings given by the valves is required, the extra openings occurring while the cylinder valves are closed as shown by the timing diagram of Fig. 11. The valves are driven through bevel gear from an auxiliary shaft of the engine. Other arrangements of disc valves are also described. Where more than one exhaust duct is used, these may be connected separately to the turbine, or to different sections of the turbine nozzle ring. Additional valve means p, Fig. 1, may provide further control of the exhaust gas flow to the turbine. In another modification, Fig. 12, fresh charge is supplied at two different pressures, viz. a relatively low pressure q through the ports s for charging and high pressure r to separate adjacent ports t for supercharging.' The supercharge may be controlled by a rotary valve u in addition to the normal piston control. Alternatively both high- and low-pressure charging may be supplied through the normal inlet orifices, and be controlled by valves in the inlet duct. Where two charge pressures are required, these may be obtained from a two-stage compressor driven by the turbine. An adjustable distributer valve may be provided between the first and second stages; thus, in Fig. 16 the ducts v and w lead from the low- and high-pressure stages, the charge flowing along pipe v passing through an adjustable distributing valve x, and duct z leading to the high-pressure stage. A rotary valve y controls low-pressure and high-pressure supplies to the cylinder ports through ducts y' and y<2> respectively.