哈工程轮机英语--lesson 13.ppt

LESSON 13 MARINE MEDIUM SPEED(300—1000r/min) DIESEL ENGINE Ⅱ Prof. Song Zhou;New Words and Expressions in Text; accuracy 精度 circular 圆形的 tighten 上紧 assist 援助，帮助 expel 驱逐，驱赶 thermal 热的 recondition 修理，使复原 frequent 频繁的 accomplish 完成 rocket 摇，臀杆 tappet 挺杆，凸子，顶头 prop 支撑，维持 allowance 允许，裕量 appropriate 适当的;Pistons The piston is a pot shaped(筒状) component. The crown is fairly thick with the cylindrical parts tapering to a thinner section. ;The combustion chamber is enclosed between the cylinder head and the piston and the most of it is contained in the top of the piston. ;For this purpose the top surface of the piston crown may be bowl shaped or toroidal(环形的) shaped. ;The rim of the piston may contain cut-out portions(避让坑) to accommodate the valves when they open. ;Bowl/Toroidal shape;The cooling of the piston is carried out by circulating lubricating oil across the underside of the crown and inside the ring belt or through specially shaped passages. ;The simplest means is by splash(飞溅) or spray(喷射) on the underside of the piston crown. ;A more complex design involves a chamber specially constructed for the oil to circulate through.;In some designs this chamber takes the form of a coil cast into the material of the piston and conducting the heat away from the piston ring region. ;In another design the chamber is open and constructed so that the oil splashes about violently. ;;This design is termed the ‘cocktailshaker(震荡式)’; the motion of the oil providing extremely good heat transfer. ;The pistons of high output(power) engines are often made in two pieces bolted together to form precisely shaped cooling chambe