GB737340A - Improvements in and relating to turbo-charged two-stroke cycle internal combustion engines - Google Patents

Abstract

737,340. Scavenging and supercharging twostroke engines; passages and ports. AKTIESELSKABET BURMEISTER & WAIN'S MASKIN-OG SKIBSBYGGERI. June 25, 1953 [June 4, 1953], No. 17704/53. Class 7(2). In a turbocharged two-stroke engine of the type in which the necessary scavenging and charging air or a major portion thereof is supplied under normal operating conditions by one or more turbine-driven blowers 17 actuated by the engine exhaust gas, which latter is supplied direct to all or part of the turbine guide apparatus, the exhaust valve, such as a ring of piston-controlled ports 13, is opened before and closed later than the inlet valve, for example the ring of piston-controlled ports 12, and that the passage area of the guide apparatus and the time area i.e. the product of the average effective port area during operation of the valve and the total time of operation, of the exhaust valve after closure of the inlet valve are such that during normal operation the blower maintains air in a scavenging air receiver 11 at a higher pressure than the charging pressure desired in the cylinder 2 upon closure of the exhaust valve, the exhaust from the cylinder after closure of the inlet valve reducing the scavenging pressure in the cylinder to the desired charging pressure. The main piston 3 is connected to the crank 5 by a connecting rod 7 and piston rod 8 whilst the top piston 4 is attached to a pair of eccentrics 6, one on either side of the crank 5, through eccentric straps 9 and tie rods 10. The cylinder 2 opens into the receiver 11 which is common to all the engine cylinders or divided into sections for groups of cylinders ; the piston 3 controls the scavenging ports 12 and piston 4 co-operates with one or more rings of exhaust ports 13. The exhaust pipe may consist of a central and two side branches for each group of three cylinders or two separate branches each of which is bifurcated where there are four cylinders in each group. The blower 17 supplies air through a pipe 19 and an intercooler 20 to the scavenging pipe 21. The ports 12 are open for 35 degrees (crank angle) on each side of B.D.C. whilst the exhaust ports 13 are open for 65 degrees on each side of T.D.C., the exhaust-valve controlmeans having an advance of 6-10 degrees in relation to the main crank ; the exhaust ports open 37 degrees before the inlet ports and close 23 degrees after the latter. Three engine cylinders operating with a 120 degrees phase displacement may be connected to the same guide apparatus so that the exhaust pressure will begin to rise due to the commencement of exhaust in one cylinder before the exhaust ports of the previous cylinder have closed thereby terminating the after exhaust period of the latter cylinder ; under such circumstances the angle of advance between T.D.C. and B.D.C. may be reduced so that the engine is more suitable for reverse operation. The invention may be applied to engines which have other means for supplying scavenging and charging air either in the event of failure of the turboblowers or as a permanent supplement. An increase in the energy content of the exhaust gases may be obtained by burning fuel therein or by additionally driving the blower from an electric motor. The passage area of the guide apparatus and the time areas of both valves are so chosen that at normal speed a full or less than full stroke volume of air flows into the cylinder.