GB571525A - Improvements in and relating to multi-cylinder two-stroke cycle internal combustion engines - Google Patents

Abstract

571,525. Two-stroke engines. ARMSTRONG WHITWORTH & CO. (ENGINEERS), Ltd., SIR W. G., MANSFIELD, W. P., and WHITE, J. Feb. 1, 1944, No. 1865. [Class 7 (ii)] A multi-cylinder twostroke internal-combustion engine has an excess charge passed into each cylinder in charging or supercharging, whereby a predetermined quantity passes into the exhaust passage and manifold branch of the cylinder, and the number of cylinders, crank spacing and exhaust and inlet periods are so arranged that each cylinder exhausts towards the end of the charging period of the preceding cylinder in the firing order and the exhaust action is utilized to supercharge said preceding cylinder by returning into said cylinder part of the excess fresh charge which has passed through the cylinder into the exhaust passage. A fourcylinder engine, Fig. 1, has an exhaust manifold a leading through a duct c to a turbine g driving a blower h. The excess charge between the exhaust orifices and the manifold is greater than that to be returned into the cylinder as a supercharge. The exhaust wave from one cylinder occurs while the exhaust orifices of the preceding cylinder are still open and is propagated through the.fresh charge to return it to said cylinder. Increased supercharging effect may be obtained by using the reflection action of the exhaust wave from a closed end of the manifold. For this purpose a rotary disc valve b may be located at the end of the manifold, said valve being opened to allow discharge of gases when the supercharging action is complete. Before this valve opens, the pressure in duct c should be substantially atmospheric. After the valve opening, when the pressure wave has moved beyond the valve for a distance equal to its length, the pressure distribution will cause a zone of low pressure in the manifold a against which the scavenging and charging of the following cylinder may take place. With a four-cylinder engine, the cylinders exhaust at 90 degrees relative to each other and the exhaust periods slightly exceed 90 degrees. The disc valve may be arranged as shown in Fig. 4, and may consist of a watercooled disc d mounted in a casing c and has orifices f to provide the required open periods. In some cases, more than one manifold may be controlled by the same disc valve, and any number of disc valves may be used. Alternatively, the disc valve, or valves, may be in planes parallel to the crank-shaft axis as shown in Fig. 11. Fig. 12 shows a timing diagram for a six-cylinder engine indicated in Fig. 11. For operation without supercharging, the exhaust gases may byepass the disc valves or a synchro-mesh gear may be used to hold the valve stationary in the fully-open position and ensure correct timing when rotation is restarted. The exhaust overlap necessary for supercharging should be from 5 to 15 degrees depending mainly upon engine speed. A number of typical timings for four- and threecylinder engines are given in the Specification. For efficient operation of the turbine g, the duct c should be half the length of the exhaust pressure wave forming a zone of high pressure gas trapped between the turbine and the valve b. The calculations of exhaust duct length are based on a mean wave velocity of 400 to 550 metres per second. To permit continued scavenging and charging to atmospheric pressure, an auxiliary orifice to atmosphere may be opened when the valve b closes. This orifice may be arranged at i in Fig. 6, and is controlled by a flange d<1> on the valve disc d. The turbine g is designed to pass gas at such a rate that in normal conditions the duct pressure falls to atmospheric pressure before the arrival of the next pressure wave. An additional valve l, Fig. 1, may be provided to control the rate of flow to the turbine. In some cases a progressive reflection action may be obtained by a gradual decrease in the duct area. The turbine may return power to the crank-shaft or may drive another machine.