发动机原理English.docx
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发动机原理English.docx
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发动机原理English
第一章发动机性能及其参数
[1]三种理想循环
1)ottocycle:
2)diedelcycle:
3)dualcycle;(theefficiencyliesbetween~)
isentropiccompression;additionofheat;isentropicexpansion;rejectionofheat;
[2]评价理论循环的参数
Cyclefuelconversionefficiencyt和MeaneffectivepressurePt
t:
Thecyclefuelconversionefficiencytisusedtoevaluatethecycleeconomy,whichisdefinedas:
(ηtincreaseswiththeincreasingofcompressionratioε,pressureratioλ,isentropicexponentKanddecreaseswiththeincreasingofexpansionratioρ.)
Pt:
Ptiscycleworkdonebyunitcylindervolume.Itisusedtoevaluatethepowercapabilityofacylinder:
(Ptincreaseswithincreasingofpa、、、、kandt.)
[3]realcycle实际循环
1、intake(induct)stroke2、compressionstroke
3、power(combustion)stroke4、exhauststroke
[4]Whichlossesexistedinrealcyclecomparedwithidealcycle?
explaineverylossandtheformingreason.(实际循环与理想循环相比,存在的损失及其形成原因。
)
1)Heattransfer.Heattransferfromunburnedmixturetothecylinderwalls.Thepressureattheendofcombustionintherealcyclewillbelower.
2)Finitecombustiontime.Finitetimerequiredtoburnthecharge.Thepeakpressureintheengineisbelowtheidealcyclepeakpressurevalue.
3)Incompletebustionofthecylinderchargeisincomplete;theexhaustgasescontaincombustiblespecies.
4)Exhaustblowdownloss.Thegaspressureattheendofexpansionstrokeisreduced.
5)Creviceeffectsandleakage.Theseeffectsreducethecylinderpressure.
6)Pumpingloss.Theworkisusedtoovercometheresistanceininletandexhaustpassages.
[5]enginesindicatedparametersa(发动机指示指标及作用?
和类容)
1>概念及作用:
.Indicatedparameters:
Theparametersarecalculatedonbasisoftheworkdonebyworkingfluidtopistons.itiswidelyusedtoevaluatetheconversionefficiencyofheatintopowerpercycleandiswidelyusedinengineresearchfield.
2>内容
1、IndicatedworkpercycleWi(循环指示功)
2、Indicatedmeaneffectivepressure(imep)Pmi(平均指示压力)
3、IndicatedpowerPi(指示功率)
Pi(kw)=[Pmi(Mpa)*Vs(L)*n(r/min)*i]/[30*tao](i为汽缸数,tao为冲程数)
4、Indicatedefficiencyηi(指示热效率)
5、Indicatedspecificfuelconsumptionbi(指示油耗率)
指示热效率与指示油耗率的关系
[6]enginebrakeparameters(何谓发动机有效指标及作用)
1>概念:
Enginebrakeparametersarebasedonenginecrankshaftoutputwork.Itisusedtoevaluateeconomicanddynamicperformanceofanengine。
2>内容:
1.BraketorqueTtqandpowerPe(有效转矩和有效功率)
2.BrakeworkWeandbrakemeaneffectivepressurePme(有效功和平均压力)
We=Wi-WmWi---指示功;Wm---机械损失功
3.Brake(thermal)efficiencyηe(有效热效率)
4.Brakespecificfuelconsumption(bsfc)be(有效油耗率)
热效率有油耗率的关系
5.EnginespecificpowerPL(升功率)
[7]enginemechanicalefficiency(机械效率)
定义:
Theratioofthebrake(oruseful)powerdeliveredbytheenginetotheindicatedpoweriscalledthemechanicalefficiencyηm:
.
影响因素:
Thefactsthatinfluenceitare:
thepeakcombustionpressuresincylinder,enginespeedorpistonmeanspeed,engineloads,thecharacteristicoflubricationandtemperatureofcoolingwater,andtheconditionsofengineruns.
第二章发动机的换气
[1]gasexchangeprocessesoffour-strokeengine.(四冲程发动机换气过程)
Thegasexchangeprocessofanengineconsistsofthedurationfromopeningtheexhaustvalvetoclosingtheinletvalve.itcanbadividedintofourphases
1.blowdown自由排气2.displacement强制排气
3.inductionprocess进气行程4.valveoverlapandscavenging气门重叠与扫气
[2]volumecoefficientv充量系数(容积效率)重点
定义:
Volumeefficiencyisameasureoftheeffectivenessoftheinductionandexhaustprocesswhichisdefinedasthemassoffreshmixturewhichpassesintothecylinderinonesuctionstroke,dividedbythemassofthismixturewhichwouldfillthepistondisplacementatinletdensity.
.
提高充量系数Inaqualitativeanalysis,volumetricefficiencyȠvincreaseswith:
1)increasingmixturepressureattheendofintakestrokepa;(影响最大)
2)suitablevalveparametersξandφ;3)increasingcompressionratioɛ;
4)decreasingmixturetemperatureattheendofintakestrokeTa;
5)reducingresidualcoefficientγ.必考内容(可能是大题)
[3]effectofoperatingconditionsanddesignonvolumetricefficiency
1.InletMatchindex进气马赫数
定义:
Theratioofthetypicalvelocitytotheinletsonicvelocity,u/α,iscalledtheinletMachindex.Whenitexceeds0.55,volumetricefficiencydropsgreatly.
2.Effectofintakesystemfriction进气摩擦力
3.Effectofinhaledchargeheating受热程度
4.Effectofspeedandvalvetiming速度与气门正时
5.Effectofintakerunnerlength进气管的长度
第四章燃烧与化学
[1]physicalandchemicalpropertiesofpetrolanddieselfuels?
汽油及柴油的重要理化指标
Characteristicofpetrolorgasline.汽油
1)Antiknockperformance抗爆性
定义:
Itisusedtoresiststhetendencytoproducedetonationandthisproperty.
表示:
Theoctanenumber(辛烷值)ofafuelisameasureofitsanti-knockperformance.2)Volatility挥发性
标号markthenumber:
actanenumber
Characteristicofdieselfuel.柴油
1)cetanenumber十六烷值
thisindicateshowreadilythefuelself-ignites.(自燃性)
2)volatility挥发性3)viscosity粘度
标号markthenumber:
solidifyingtemperature(凝点)
[2]somealternativefuels.代用燃料。
Alcohol醇类Methanol甲醇Ethanol乙醇Hydrogen氢气
Naturalgas天然气Compressednaturalgas(CNG)压缩天然气
Liquefiedpetroleumgas(LPG)液化石油气
本节重点
[3]Pleaseexplainthedefinitionofaccessaircoefficient,air-fuelratio.
试述过量空气系数、空燃比的定义。
空燃比:
Air-fuelratio(AFR)istheratiobetweenthemassofairandthemassofduelinthefuel-airmixatanygivenmoment.
.
Accessaircoefficientλistherelativeair/fuelratio.
Itequalstotheratiooftheactualair/fuelratio(AFR)tothestoichiometric/[stɔɪkɪ'metrɪk]/(化学计量的,理想匹配的)ratio.
.
第五章柴油机的燃烧
[1]WhatarethefactsthatsatisfactoryoperationofCIenginedependson?
Howtoevaluateanidealcombustionsystem?
柴油机理想工作的决定因素,如何评价?
决定因素:
Dependsonpropercontroloftheairmotionandfuelinjection.
评价:
Thisidealcombustionsystemshouldhaveahighoutput(bemp压力),highefficiency,rapidcombustion,acleanexhaustandbesilent.
[2]HowtorealizefuelinjectioninCIengine?
Whichdemandsarethereinthecourseoffuelsprayandatomization?
柴油机如何实现燃油喷射?
燃油雾化有哪些要求?
Neartheendofthecompressionstroke,liquidfuelisinjectedatveryhighvelocity(速度)asoneormorejetsthroughsmallnozzles(喷嘴)ininjector(喷射器)tip(尖端),atomizes(雾化)intosmalldrops(滴)intothecombustionchamber.
Therearetwodemands(雾化要求):
Thedistribution(分布)offuelspray(喷雾器)trajectory(轨道)throughoutthecombustionchamber.Atomization(雾化)oftheliquidfuelintoalargenumberofsmalldrops.Theyarenecessarytocreatealargesurfaceareaacrosswhichliquidfuelcanevaporate(蒸发).
[3]AnalyzefourstagesofCIenginecombustionprocesses.分析柴油机燃烧过程的四个阶段。
(本章重点)
(i)Ignitiondelay,AB.滞燃期(开始喷油到离开理论压缩曲线)
(ii)Rapidoruncontrolledcombustion,BC.速燃期(到最高压力点)
(iii)Controlledcombustion,CD.缓燃期(最高压力点到最高温度点)
(iv)Finalcombustion,DE.后燃期(直至燃料耗尽)
[4]definitionofdelayperiodofCIenginecombustion?
Whichfactsinfluenceit?
柴油机燃烧过程滞燃期定义是什么?
滞燃期的影响因素有哪些?
(一定得背下)
定义:
thedelayperiodiscountedfromthestartofinjectiontothepointwherethep-φcompressioncurvedepartsfromaircompression(ornoignition)curve.
影响:
Theeffectsoffactorsondelayperiod:
1)Fuelproperties(属性)2)Intaketemperature3)Compressionratio
4)Enginespeed5)Typesofcombustionchamber6)Injectoradvance
[5]EnginesofIndirectinjection(IDI)chambers非直喷式anddirectinjection(IDI)chambers直喷式柴油机
第六章汽油机的燃烧
[1]Brieflyexplainthecompositionofelectricpetrolinjectionsystemandmainfunctionsofeachpart.简述电控汽油喷射系统的组成和各部分的主要功用。
组成:
Theelectricpetrolinjectionsystemcanbedividedintothreeparts:
airinductionsystem,fueldeliverysystem,andtheelectroniccontrolsystem
功用:
1)Airinductionsystem:
Whenthethrottlevalveisopened,airflowsthroughtheaircleaner,throughtheairflowmeter,pastthethrottlevalve,andthroughawelltunedintakemanifoldrunnertotheintakevalve.
2)Fueldeliverysystem:
Fuelisdeliveredfromtanktotheinjectorbymeansofanelectricfuelpump.Fuelismaintainedataconstantpressurebymeansofafuelpressureregulator.Andanyfuelwhichisnotdeliveredtotheintakemanifoldbytheinjectorisreturnedtothetankthroughafuelreturnpipe.
3)Electroniccontrolsystem:
TheECUdeterminespreciselyhowmuchfuelneedstobedeliveredbytheinjectorbymonitoringtheenginesensors.TheECUturnstheinjectorsonforapreciseamountoftime,referredtoasinjectionpulsewidthorinjectionduration,todelivertheproperair-fuelratiototheengine.
[2]maincharacteristicsofeverystagesofSIenginenormalcombustionprocesses汽油机正常燃烧的三个阶段
1.Delayperiod.(点火延迟期)
2.Secondstage.(速燃期)
3.Thefinalstage.(后燃期)
[3]thefactorswhichaffectingnormalcombustioninSIengineare(影响正常燃烧):
1.inductionpressure2.enginespeed3.ignitiontime
4.mixturestrengthpressionratio
[4]WhatisthedefinitionofdelayperiodofSIenginecombustionprocess?
Whichfactsinfluenceit?
汽油机燃烧过程滞燃期的定义?
汽油机滞燃期的影响因素?
定义:
DelayperiodofSIengineisthefirststageinwhichgrowthanddevelopmentofaselfpropagatingnucleusofflametakesplace.
影响因素:
Thedurationofdelayperioddependsonthefollowingfacts:
1)Fuel.2)Mixtureratio.3)Initial(初始的)temperatureandpressure.4)Turbulence.
[5]describetheinfluentfactsofflamepropagationspeedinSIengine.试述汽油机火焰传播速度的影响因素。
1)turbulence(湍流)2)fuel/airratio3)temperatureandpressure
4)compressionratio5)enginespeed.
[6]Whatissurfaceignition?
何谓汽油表面点火?
定义:
Surfaceignitionisignitionofthefuel/airmixturebyahotspotonthecombustionchamberwalls(名词解释题).
[7]Whatisthegasolineengineknock?
Whatisthemechanismofknock?
Whichfactsinfluenceit?
Howtoavoidithappeninengine?
什么叫汽油机爆燃?
爆燃的机理是什么?
有哪些影响因素?
如何避免发动机出现爆燃?
定义:
Knockisthe
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