柴油机工作原理(双语教学)

1、第二讲 船舶柴油机的工作原理Lesson 2 How Does a Marine Engine Work Review：1.船舶柴油机的基本特征往复式 reciprocating 压缩发火 ignition by compression 内燃机 internal-combustion engine2.船舶柴油机的分类根据工作循环(working cycle)：二冲程 two stroke（what is a stroke?）四冲程 four stroke根据结构特征：筒形活塞式 trunk piston diesel十字头式 Crosshead dieselExhaust valveInlet

2、 valveFuel injectorCylinderPistonPiston ringConnecting rodFour-stroke/trunk piston diesel engineCombustion chamberPiston pincrankshaftNew lesson: The working principle of marine diesel engine vContent:v1.四冲程柴油机工作原理v2.两冲程柴油机工作原理v3.两冲程柴油机的换气形式(scavenge form) 工作循环：柴油机做一次功，或者两次喷油间的工作循环：柴油机做一次功，或者两次喷油间的运

3、转过程叫一个工作循环，它由一些程序固定的运转过程叫一个工作循环，它由一些程序固定的过程组成。过程组成。The process that a engine do a complete work, or process between two fuel injections is called a working cycle, which consists of a fixed sequence of events. 进气进气膨胀膨胀排气排气压缩压缩燃烧燃烧工作循环工作循环This cycle may be achieved（达到，（达到，完成）完成） either in four strokes

4、(冲程、行冲程、行程程) or two.四冲程柴油机：用活塞的四个行程完成一个工作四冲程柴油机：用活塞的四个行程完成一个工作循环的柴油机循环的柴油机二冲程柴油机：用活塞的两个行程完成一个工作二冲程柴油机：用活塞的两个行程完成一个工作循环的柴油机循环的柴油机Four stroke working cyclesuction吸气行程expansion膨胀作功行程Compression压缩行程Exhaust排气行程1.The working principle of four stroke diesel enginesuction吸气行程Compression压缩行程1.1.吸气冲程吸气冲程进气阀上止

5、点前开，下止点后关进气阀上止点前开，下止点后关进气持续角进气持续角220220250250度度CACA。2.2.压缩冲程压缩冲程压缩终点温度压缩终点温度tctc达达600600700700C C 压缩后期喷油器在上止点前一定压缩后期喷油器在上止点前一定角度喷油，上止点附近压缩发火角度喷油，上止点附近压缩发火燃烧，压缩过程持续燃烧，压缩过程持续140140160 160 度度CACA。四冲程柴油机具体工作过程（1）（2） expansion 膨胀作功行程 Exhaust 排气行程3.3.燃烧和膨胀行程燃烧和膨胀行程 p pz:5-8MPa, 10z:5-8MPa, 101515CA after

6、TDC CA after TDC tz:1400 tz:14001800 1800 C， 高温高压燃气推动活塞下行作高温高压燃气推动活塞下行作功，上止点后约功，上止点后约4040CACA燃烧基本完燃烧基本完成成. .4.4.第四行程排气行程第四行程排气行程 排气初期靠内外压差，当活塞排气初期靠内外压差，当活塞由下止点上行时靠活塞推挤作用由下止点上行时靠活塞推挤作用（耗功），排气阀延迟到上止点后（耗功），排气阀延迟到上止点后关。排气持续角关。排气持续角230230260 260 度度CACA（3）（4）pz动画动画气阀正时圆图气阀正时圆图（valve timing diagram ）intake

7、 advance angle intake lag angle exhaust advance angle exhaust lag angle Valve overlap angle:+:Four-stroke cycle and timing diagrams2-Inlet valve closes2-Inlet valve closes1-Inlet valve opens1-Inlet valve opens7 78 85-Exhaust valve opens5-Exhaust valve opens 6-Exhaust value closes6-Exhaust value clos

8、es7-Injection commences7-Injection commences 8-Fuel valve closed8-Fuel valve closed图1-7 四冲程柴油机定时圆图图1-7 四冲程柴油机定时圆图1 12 25 56 6TDCBDC气阀重叠角气阀重叠角(Valve overlap angle) ：在换气上止点附近，进排气阀同在换气上止点附近，进排气阀同时开启所持续的曲轴转角时开启所持续的曲轴转角目的：目的：提高换气效果，实现燃烧提高换气效果，实现燃烧室扫气；降低循环温度。室扫气；降低循环温度。气阀重叠角的大小：气阀重叠角的大小：非增压四冲程机（非增压四冲程机（25

9、50CA） 增压四冲程机（增压四冲程机（80130CA ）summary :1. For a four stroke engine, a recycle takes 2 revolution (720 CA) of crankshaft and 1 revolution of camshaft. The speed ratio of camshaft to crankshaft is 1 to 2. the working cycle is the third one. 总结：四冲程机一个工作循环曲轴转两转（总结：四冲程机一个工作循环曲轴转两转（720 CA），），凸轮轴转一转，凸轮轴与曲轴转

10、速比为凸轮轴转一转，凸轮轴与曲轴转速比为1：2，做功行程为第三，做功行程为第三行程。多缸机其余三行程能量由其他正在作功的气缸供给，单行程。多缸机其余三行程能量由其他正在作功的气缸供给，单缸机由飞轮供给缸机由飞轮供给二、二冲程柴油机工作原理two stroke engine working principle1 1结构特点结构特点曲轴一转完成一个工作循环，故没有单独曲轴一转完成一个工作循环，故没有单独的进气与排气（换气）过程，进、排气几乎的进气与排气（换气）过程，进、排气几乎同时进行。同时进行。If we combine the suction and exhaust operations wi

11、th the compression and expansion strokes, the four-stroke engine will be turned into a two-stroke one2、二冲程机二冲程机扫气、扫气、压缩压缩作功、作功、扫气扫气弯流扫气The two-stroke cycle begins with the piston coming up from the bottom of its stroke, i.e. bottom dead center (BDC), with the air inlet ports or scavenge ports(扫气口扫气口

12、) in the sides of the cylinder being openedAs the piston moves about one fifth of the way up, it closes the inlet ports and the exhaust ports. The air is then compressed as the piston moves up. When the piston reaches the top of its stroke, i.e. the top dead center (TDC), both the pressure and the t

13、emperature of the air rise to very high values. vThe fuel injector injects a fine spray of fuel into the hot air and combustion take place, producing much higher pressure in the gases. The piston is forced(迫使迫使) downward as the high pressure gases expand until it uncovers the exhaust ports. The burn

14、ing gases begin to exhaust and the piston continues down until it opens the inlet ports. Then another cycle begins.In the two-stroke engine, each revolution of the crankshaft(曲轴曲轴) makes one power or working stroke, while in the four-stroke engine, it takes two revolutions to make one power stroke.

15、That is why a two-stroke cycle engine will theoretically（理论上）（理论上） develop twice (two times) the power of a four-stroke engine of the same size.3二冲程机工作循环的表示方法二冲程机工作循环的表示方法1）p-v示功图示功图2 2）定时圆图）定时圆图 无气阀重叠角无气阀重叠角2-Inlet opens2-Inlet opens1-Exhaust opens1-Exhaust opens3-Inlet closes3-Inlet closes4-Exhaust closes4-Exhaust closes5-Injectio