《内燃机理论与构造》结构、工作原理.ppt

第一章、内燃机的工作原理和总体构造,一般构造（见图和模型。）,Engine(发动机),内燃机的基本名词定义及分类,一、基本名词术语；（见图）1、活塞止点与冲程2、气缸容积3、气缸工作容积：Vh=/4 d2 S x 10 64、燃烧室容积：Vc5、气缸总容积：Va=Vh+Vc6、内燃机排量；VH=/4 i d2 S x 10 6（i-气缸数）7、压缩比：=Va/Vc=1+VH/Vc汽油机为：79，柴油机为1822,二、分类（往复活塞式内燃机）,1.按所用燃料分：柴油机、汽油机、煤气机2.按工作循环的冲程数分：（四、二冲程）3.按气缸数及排列方式分：单缸、多缸；直列立式；直列卧式；V型；对置式。4.按冷却方式分：水冷、风冷5.按进气方式分：自然吸入式、增压式6.按点火方式分：压燃、火花点燃,Engine(发动机),四冲程内燃机工作原理,一、四冲程内燃机工作原理：（吸、压、爆、排。）第一冲程进气冲程：活塞由上止点下止点，进气门开、排气门关。第二冲程压缩冲程：活塞由下止点上止点，进气门关、排气门关。第三冲程作功冲程（燃烧膨胀冲程）：活塞由上止点下止点，进气门关、排气门关。第四冲程排气冲程：活塞由下止点上止点，进气门关、排气门开。,二、四冲程柴油机工作原理（结合示功图、工作过程示意图）,第一冲程进气冲程：在起点r压力Pr=1.051.15巴略大于大气压Po，终点a压力Pa=0.80.9巴略小于大气压Po，温度Ta=300340K第二冲程压缩冲程：在终点c压力Pc=3050巴，温度Tc=750950K（自燃温度约600K）。在C点为燃油喷入开始。第三冲程作功冲程（燃烧膨胀冲程）：在起点z气缸内压力Pz=6090巴，温度Tz=18002200K，在终点b气缸内压力下降Pb=3巴，温度Tb=10001200K。第四冲程排气冲程：由br压力几乎不变，Tr=700900Kpr=1.051.2巴。,三、四冲程汽油机工作原理（结合示功图、工作过程示意图）,第一冲程进气冲程：在起点r压力Pr=1.051.2巴略大于大气压Po，终点a压力Pa=0.750.9巴略小于大气压Po，温度Ta=370400K第二冲程压缩冲程：在终点c压力Pc=814巴，温度Tc=600700K在C点为火花塞开始点火。第三冲程作功冲程（燃烧膨胀冲程）：在起点z气缸内压力Pz=3050巴，温度Tz=22002700K，在终点b气缸内压力下降Pb=4巴，温度Tb=12001500K。第四冲程排气冲程：由br压力几乎不变，Tr=8001100KPr=1.051.2巴。,四、柴油机与汽油机比较：,1、压缩比大，膨胀充分，热利用程度较好节省燃料。柴油价低，经济性好。2、柴油机坚固，耐用。3、无点火系统，故障少。4、柴油机气缸内压力高，机件刚度和强度要求高，结构尺寸大。5、柴油机的喷油泵和喷油器精度高，制造成本高。6、柴油机运转时噪声较大。7、柴油机为压燃，较难启动。因此柴油机多用于农业林业工程、机车、船舶等，汽油机结构轻巧、制造方便、容易启动常用于轿车、轻型载重汽车及小型动力等。,五、增压式内燃机工作原理：带增压器,1、目的：增加每循环空气量2、效果：功率增大30%以上3、工作原理,六、示功图比较,四冲程内燃机工作循环特征参数比较,特征点,二冲程内燃机工作原理,一、二冲程柴油机工作原理,二、二冲程汽油机工作原理,二冲程内燃机示功图,多缸内燃机的工作顺序,由平稳性和结构决定，对三缸以上直列四冲程内燃机用下式计算：=720/i i 为气缸数四缸排列：1342或1243六缸排列：153624及142635,内燃机总体构造,见模型及课件,内燃机车总体内燃机车构成,The Inline Engine,We all know the engine is the heart of the automobile.What is the core of the engine?Yes,its the cylinder.Most cars have more than one cylinder(four,six and eight cylinders are common).In a multi-cylinder engine,the cylinders usually are arranged in one of three ways:inline,V or flat.,In an inline engine,the cylinders are arranged in a line in a single bank.The inline arrangement is the simplest and most common one and has many advantages.First,the engine has a good stability and more power.Second,the structures of the cylinder block and the crankshaft are very simple and they share only one cylinder head.The cost to manufacture and install is less.,Because of these advantages,BMW and also many American car manufactures like to use the inline cylinder engine.This kind of engine is widely used in the cars made in home.,1-2 Basic Terms of Engine 发动机基本术语,TDC=top dead center,top center,outer dead center 上止点 BDC=bottom dead center,bottom center,inner dead center 下止点 S=piston stroke,piston travel 活塞行程 Sk=piston clearance from TDC 活塞离上止点距离 r=crank radius 曲柄半径=crank angle,crankshaft angle 曲柄角 Vh=swept volume of a cylinder或piston displacement或cylinder swept volume 气缸工作体积，每缸排量 VC=combustion volume或 combustion chamber(space)volume 或cylinder compression volume 燃烧室容积 VC+Vh=cylinder total volume 气缸总容积（VC+Vh）/VC=compression ratio 压缩比,Main Terms,There are many terms in describing the operations of an automobile engine.Lets see some basic terms.Stroke refers to piston movement.A stroke occurs when the piston moves from one extreme position to the other extreme position inside the engine cylinder.The highest position that the piston reaches inside the cylinder is called TDC(top dead center).Similarly,the lowest position that the piston reaches inside the cylinder is called BDC(bottom dead center).So we can also say a stroke is piston movement from TDC to BDC or vice versa.,During the induction stroke,the volume of air/fuel mixture to fill a single cylinder is swept by the piston;this volume is called the swept volume.During the compression stoke,the swept volume is compressed into a small space above the piston.And at this time,the piston reaches the top of the cylinder.The space is called as the clearance volume.The clearance volume and the swept volume determine the compression ratio.Generally，a high compression ratio is good for performance and efficiency.,1-3 Four-Stroke Engine 四冲程发动机,A-intake stroke或suction stroke 进气行程 The intake valve is open while the exhaust valve is close.进气门开启而排气门关闭。IV=intake valve 进气门EV=exhaust valve 排气门,B-compression stroke,compression travel 压缩行程 Both the intake and exhaust valves are close.进气门和排气门均关闭。,C-power stroke,combustion,working stroke,firing stroke,expansion stroke 膨胀（作功）行程 Both the intake and exhaust valves are close.进气门和排气门均关闭。,D-exhaust stroke 排气行程 The intake valve is close while the exhaust valve is open.进气门开启而排气门关闭。,内燃机性能指标,一、内燃机指示指标1、指示功Wi 2、平均指示压力Pi 3、指示功率Ni 4、指示耗油率gi,二、内燃机有效指标1、有效功率Ne 2、机械效率e 3、输出转矩Me 4、耗油率、转速n,