lesson 9　STARTING SYSTEM 轮机英语课件.ppt

LESSON 9 TEXT STARTING SYSTEM 第9课 起动系统 Diesel engines are started by supplying compressed air into the cylinders in the appropriate sequence for the required direction. A supply of compressed air is stored in air reservoirs or bottles or receivers at pressures about 30 or 40 bar ready for immediate use. Some times compressed air pressure is dropped to a lower value by means of a reducing valve(减压阀) for other uses. The receivers are charged by compressors. The design of starting air systems, including the number and capacity of compressors and receivers, the provision （规定）of features and drainage facilities are the subject of stringent(严格) requirements by Classification Societies(船级社). Up to 12 starts are possible with the stored quantity of compressed air. The starting air system usually has interlocks to prevent starting if any thing is not in order. The compressed air is supplied by a large bore pipe to a remote operating non-return or automatic valve and then to the cylinder air start valves(气缸起动阀). The opening of each cylinder air start valves will admit compressed air into the corresponding cylinder. The automatic valve and the cylinder start valves are controlled by a pilot air system. Each cylinder start valve will be opened immediately after the top dead centre(TDC) position has been passed and closed just before the exhaust ports are due to open according to the direction of rotation required. Thus, when compressed air from the main supply is supplied to the starting system of an engine at rest it enters those cylinders in which the pistons are in a position corresponding to some part of the power stroke, the resulting pressure on the pistons causes the engine to rotate. When a sufficiently high speed, say about 20 r/min, has been achieved the air supply is cut off and fuel is injected causing the cylinders to fire and continue to run in the normal way. The pilot air is drawn from the large pipe and passes to a pilot air control valve which