1、The diameter of the cylinder is called the engine bore.Displacement and compression ratio are two frequently used engine specification.Displacement indicates engine size.and compression ratio compares the total cylinder volume to compression chamber volume The term“stoke“is used to describe the move
2、ment of the piston within the cylinder.The operating cycle may require either two or four stroke to complete. Most automobile engines operate on the four stroke cycleThis type of engine is also know as Otto cycle,after the name of its inventor, Nikolaus Otto,who first applied the principle in 1876.I
3、n the 4-stroke engine, four strokes of the piston in the cylinder are required to complete one full operating cycle. Each stroke is named after the action.It performs intake, compression,power, and exhaust in that order, shown in Fig.1-21.Intake strokeThe piston moves downward to the bottom dead cen
4、ter,a vacuum is created in the cylinder.The intake valve opens and air-fuel mixture comes into cylinder .To obtain the maximum filling of the cylinder the intake valve opens about 10 before t.d.c.giving 20overlap. The inlet valve remains open until some 50after b.d.c.to take advantage of mixture.2.C
5、ompression stroke The air-fuel mixture is compressed within the combustion chamber.While the pressure rise to about 1MP, depending on various factors including the compression ratio, throttle opening and engine speed.The spark plug is fired ignite the air-fule mixture prior to the piston being at th
6、e t.d.cNote that both valves are closed.3.Power strokeThe air-fuel mixture expands, which creates the power to force the piston downward.The exhaust valve opens near the bottom of the stroke.4.Exhaust stroke As the piston starts to move upward, the exhaust valve is opened.The piston moving up force
7、the exhaust gases out of the cylinder.The intake valve usually opens just before the exhaust stroke.This 4-stroke cycle is continuously repeated in every as long as the engine remains running.汽缸体的直径成为缸径。排量和压缩比经常用来反应发动机的效率。排量由发动机的尺寸决定，汽缸体的总体积除以压缩室的体积成为压缩比。“冲程”这一个术语是用来描述活塞在汽缸体中的运动的。一个工作循环可以通过两个或者四个冲程来
8、完成大多数的汽车发动机都是四冲程发动机。这种类型的发动机因为这种四冲程循环而出名，然后是以发明者发明者的名字而命名，尼古拉斯奥托在 1876 年第一次运用这种原理。在四冲程发动机中，活塞的四个冲程在气缸中运动来实现完美的运动循环。每一个冲程都是以他们的作用而命名。他们分别按顺序扮演进气、压缩空气、做功和排气。1进气冲程当活塞向下往下止点运动的时候，气缸中就行成了一个真空。这时候进气门打开，空燃混合物进入气缸。为了保证有更多的混合气进入气缸中，进气门在活塞到达上止点之前10打开。所以就有了一个 20的气门重叠角。为了保证能有更多的混合气进入汽缸，当活塞经过下止点 50之前都是一直保持打开的。2.压缩冲程空燃混合物是在燃烧室内被压缩的，而里面的压缩压力上升到大概 1MP，要取决于很多因素，其中包括压缩比、节气门开度和发动机的转速。当活塞到达上止点的时候火花塞就点燃里面的空燃混合气，在这整个过程中所有的气门都是关闭着的。3 做功冲程空燃混合气膨胀产生的力量推动着活塞向下运动，当达到下止点附近的时候排气门打开。4.排气冲程当活塞开始往上运动的时候，排气门打开，活塞往上运动迫使废弃排除汽缸体，进气门通常是在排气冲程结束之前打开。以上这四个冲程就这样连续反复的不断重复，从而使发动机保持运转。
