第一章發(fā)動機的工作原理和總體構(gòu)造

第一章發(fā)動機的工作原理和總體構(gòu)造內(nèi)燃機的工作原理與總體構(gòu)造OperationandBasicSystems主要內(nèi)容Contents發(fā)動機的定義及分類Definition&Classifications四沖程發(fā)動機及二沖程發(fā)動機的工作原理Operation發(fā)動機的基本工作系統(tǒng)BasicSystems發(fā)動機的產(chǎn)品名稱和型號編制規(guī)則ProductNamesandTypeEstablishmentRules有關(guān)概念和排量的計算Terminology&Concept1.1IntroductionTheinternalcombustion(IC)engineisaheatenginethatconvertschemicalenergyinafuelintomechanicalenergy,usuallymadeavailableonarotatingoutputshaft.內(nèi)燃機是將熱能（來自于燃料化學(xué)能）轉(zhuǎn)變?yōu)闄C械能的一種熱機。Versussteamenginesandgasturbineenginesareexternalcombustionengines(i.e.，combustiontakesplaceoutsidethemechanicalenginesystem)外燃機

1.1發(fā)動機的定義發(fā)動機將某一種形式的能量轉(zhuǎn)化為機械能的機器。熱機（熱能機械能）外燃機內(nèi)燃機燃氣輪機活塞式往復(fù)活塞式reciprocatingengines旋轉(zhuǎn)活塞式rotaryengines1.2HistoricalBackgroundForcenturies,manwalkedorusedanimalsfortransportation.After

theinventionofmechanicalpropulsionsystems,peopleusedself-

propelledvehicles,whichmoveundertheirownpower.

Majormilestonesinvehicledevelopmentinclude:

ThefirstfairlypracticalenginewasinventedbyJ.J.E.Lenoir(1822-1900)andappearedonthesceneabout1860.1876Ottowasgivencreditwhenhisprototypeenginewasbuiltin1876.1892By1892,RudolfDiesel(1858-1913)hadperfectedhiscompressionignitionen-gineintobasicallythesamedieselengineknowntoday.1.2EarlyHistory2techno-logicaloccurrencesduringlatterhalfofthe1800sstimulatedtheemergenceoftheICEIn1859,thediscoveryofcrudeoilinPennsylvaniaThepneumaticrubbertirefirstmarketedbyJohnB.Dunlopin1888.1912

ElectricstarterinventedbyCharlesF.Kettering.

FirstusedonaCadillac,thestarterwasproduced

byDaytonElectricLaboratoriesCompany

1.2EarlyHistoryThesteamengineworkingprinciple內(nèi)燃機發(fā)展簡史內(nèi)燃機是在蒸汽機的基礎(chǔ)上發(fā)明創(chuàng)制的：1700年，英國人鈕卡姆制成了直立汽缸，密封式活塞、缸內(nèi)噴水冷卻的蒸汽機；后由瓦特改良；1814——1829年，英國人史蒂芬森制成蒸汽機車，建成世界上第一段鐵路；1860年，法國人勒納（lenoir）仿蒸汽機制成世界上第一臺商用煤氣機（?=4%）；內(nèi)燃機發(fā)展簡史內(nèi)燃機是在蒸汽機的基礎(chǔ)上發(fā)明創(chuàng)制的：1876年，德國人奧托制成四沖程火花點火內(nèi)燃機（?=16%）；1883年，英國人司派爾仿奧托四沖程煤氣機創(chuàng)制汽油機；1886年，德國人奔茨制成用汽油機做動力的汽車；1892年，德國人狄塞爾創(chuàng)制柴油機成功，1898年，柴油機作為商品出售，熱效率為29%。1.3EngineOperationFour-StrokeSIEngineCycleIntakeorInductionStrokePowerorExpansionStrokeCompressionStrokeExhaustStroke1.3EngineOperationindicatordiagram1.3EngineOperation1、Piston-EngineConstructionPistonsmoveupanddown(orbackandforth)incylindersReciprocatingmotionischangedtorotarymotionbyconnectingrodandacrankpinonthecrankshaft2、OperationApistonstrokeisthemovementofthepistoninthecylinderfromtoptobottom,orbottomtotopFourpistonstrokes-----------intake,compression,powerandexhaust.Takestworevolutionsofthecrankshaft.Four-stroke-cycleengine1.3EngineOperationFour-StrokeCIEngineCycleIntakeorInductionStrokePowerorExpansionStrokeCompressionStroke1.3EngineOperation四沖程柴油機工作原理（seeanimation）/diesel1.htm1.3EngineOperation四沖程柴油機與汽油機比較同：四個沖程—進氣、壓縮、膨脹和排氣異：燃油，可燃混合氣形成，著火方式汽油易蒸發(fā)，柴油不易揮發(fā)混合氣形成：高壓柴油從噴油器中直接噴入氣缸，形成時間很短（燃燒室形狀，組織進氣渦流）著火方式：自燃溫度約600K（320℃）壓縮比較大。1.3EngineOperationQuestions:Whatmakestheairorair-fuelmixtureenterintothecylinder?Whatmakesthepistonsmoveupanddowninthecylinders?Whatisthepurposeofthevalves？Whatisthepropertimingofthevalves?Howdothecrankshaftandconnectingrodchangethereciprocatingmotionintorotarymotion？1.3EngineOperationAsinglecylinderfour-stroke-cycleenginehasonlyonepowerimpulseforeverytwocrankshaftrevolutions.Thepistondeliverspoweronlyone-fourthofthetime.四個沖程，只有一個行程做功，運轉(zhuǎn)不平穩(wěn)；Foramoreevenflowofthepower,mostautomotiveengineshavefourormorecylinders.Thecylindersfireoneafteranothertoprovideasteadypowerflow.常采用多缸的方式;缸數(shù)曲軸做功間隔12周21周4半周8?周1.3EngineOperation1.3EngineOperationAcarengineusesafour-strokecycle--howcantwostrokesaccomplishthesametasks?想一想，兩沖程發(fā)動機怎么工作？怎樣在活塞的兩個沖程完成一個（進氣、壓縮、膨脹和排氣）完整的循環(huán)？結(jié)構(gòu)特點示功圖1.3EngineOperationYoucanseethattwo-strokeenginesareingeniouslittledevicesthatoverlapoperationsinordertoreducethepartcount.1.3EngineOperationTwo-StrokeSIEnginescheduleSpecialDesignofTwo-StrokeEnginesOnonesideofthepistonisthecombustionchamber,wherethepistoniscompressingtheair/fuelmixtureandcapturingtheenergyreleasedbytheignitionofthefuel.Ontheothersideofthepistonisthecrankcase,wherethepistoniscreatingavacuumtosuckinair/fuelfromthecarburetorthroughthereedvalveandthenpressurizingthecrankcasesothatair/fuelisforcedintothecombustionchamber.Meanwhile,thesidesofthepistonareactinglikevalves,coveringanduncoveringtheintakeandexhaustportsdrilledintothesideofthecylinderwall.1.3EngineOperation兩沖程汽油機在兩個活塞行程內(nèi)完成進氣、壓縮、膨脹和排氣的工作循環(huán)。1、結(jié)構(gòu)三個口：進氣口、排氣口和掃氣口2、工作過程活塞上行：壓縮、進氣、點燃活塞下行：做功、結(jié)束進氣、排氣、掃氣3、總結(jié)由于特殊結(jié)構(gòu)，方使得進氣、壓縮、做功和排氣得以在兩個沖程中完成；有效行程的大小與孔的位置有關(guān)。1.3EngineOperationTwo-StrokeSIEngineCycle1.3EngineOperationTwo-StrokeCIEngineCycle1.3EngineOperationTwo-StrokeoverFourStrokeSIEngineAdvantage優(yōu)點：PowerStrokeeveryrevolution一周有一個做功行程，運轉(zhuǎn)均勻平穩(wěn)；SimpleStructure無專門的換氣機構(gòu)，使用方便。Disadvantage缺點：RemainingofExhaustGases不易將廢氣排除干凈；LessEfficientStroke有效行程小于上下止點間距離；BlowoutofAir-FuelMixture掃氣時有燃油損失。1.3EngineOperationTwo-StrokeCIEngine1、overtwo-strokeSIengine與二沖程汽油機比較，不同之處：exhaustvalves采用排氣門排氣；moreinletports進氣口不止一個，環(huán)布在氣缸周圍，且經(jīng)氣泵加壓；Scavengingwithpureair采用純空氣掃氣，沒有燃油損失；separatecrankcase不用曲軸箱貯存可燃混合氣及空氣。2、工作原理Upwardstroke:scavenge,compression,spray,self-ignition活塞上行沖程：換氣、壓縮、噴油著火；Downwardstroke:expansion,exhaust,intakeandscavenge活塞下行沖程：膨脹做功、排氣換氣。1.3EngineOperation柴油機與汽油機的特點比較柴油機壓縮比大，燃氣膨脹充分，膨脹終了燃氣溫度較低，熱量利用程度較好，比汽油機省燃料。柴油機氣缸壓力較高，機件受力較大，剛度和強度要求較高，與相同功率的汽油機相比，其體積較大，重量也較大