柴油机燃油喷射毕业论文外文翻译

1、Diesel Fuel InjectionThe purpose of the fuel injection system is to deliver fuel into the enginecylinders,whilepreciselycontrollingthe injectiontiming,fuelatomization,otherparameters.The main types of injectionsystems includepump-line-nozzle,injector, and common rail. Modern injection systems reach

2、very high injectionpressures, and utilize sophisticated electronic control methods.andunit1.IntroductionThe performance of diesel engines is heavily influenced by their injectionsystemdesign.In fact,themost notableadvances achieved indieselenginesresulteddirectlyfromsuperiorfuelinjectionsystemdesign

3、s.Whilethe main purpose of thesystem is to deliver fuel to the cylinders of a diesel engine, it is how that fuelis deliveredthatmakes the differenceinengineperformance,emissions,and noisecharacteristics.Unlikeitsspark-ignitedenginecounterpart,thedieselinjectionsystemdeliversfuelunderextremelyhighinj

4、ectionpressures.Thisaspect impliesthat the system component designs and materials should be selected to withstandhigherstresses,while stillperformingforextendeddurationsmatching theenginesdurability targets. Greater manufacturing precision and tight tolerances are alsorequiredforthesystem efficientf

5、unction.In additiontoexpensivematerialsandmanufacturing costs, diesel injection systems are characterized by more intricatecontrolrequirements.Allthesefeaturesadd up toa systemwhose costmay representas much as 30% of the total cost of the engine.This and thefollowingpapers willreviewthe basicdieself

6、uelinjectionsystemand its components, thevarious types of injection systems, and how they meter anddeliverfuel intothecylindersof a dieselengine.The mechanicalfunctionofthesesystems will be described with emphasis on their mixture formation role. Variousinjection timing and metering schemes will be

7、described.Many specialized terms are used to describe the components and the operationof fuel injection systems. The following are definitions of selected, more commonterms .Nozzle refers to the part of the nozzle body/needle assembly which interfaceswith the combustion chamber of the engine. Terms

8、like P-Type, M-Type, or S-Typenozzle refer to standardized dimensions of nozzle parameters, as per ISOspecifications.Nozzle holder or injector body refers to the part the nozzle is mounted on. Inconventional injection systems this part mainly served the nozzle mounting andnozzleneedlespring preloadi

9、ngpurpose.In commonrailsystem,itcontainsthemainfunctional parts: the servo-hydraulic circuit and the hydraulic actuator (electromagnetic or piezoelectric).Injector commonly refers to the nozzle holder and nozzle assembly.Rate of injection is the mass flow of fuel out of the nozzle, typically shown o

10、ver a time axis. Start of injection and end of injection refer to the start and end of flow from the nozzle, often referred to with reference to the engine crank angle.Opening rate and closing rate refers to the gradients in the rate of injection during needle nozzle opening and closing, respectivel

11、y.Injection pressure is not used consistently in the literature. It may refer to the mean pressure in the hydraulic system for common rail systems, or to the maximum pressure during an injection (peak injection pressure) in conventional systems.2.Purposes of Fuel Injection SystemAs stated above, the

12、 main purpose of the fuel injection system is to deliver fuel into the cylinders of an engine. While this may be the general purpose of thesystem, two specific objectives of a fundamental importance may be described by the following functions:（ 1）Timelyintroductionofthefuelintothe cylinder,thatis,in

13、jectiontimingand its control.（ 2）Deliveryofan accurateamount of fueltomeet power requirement,thatis,injection metering and its control.To deliver an accurately metered amount of fuel at the proper time to achievegood combustion.Howwellthisdeliveredfuelmixeswiththeinductedairisof majorimportance.Ther

14、efore, fuel atomization, i.e., how small the fuelparticle size isand howdisperseditisinthecylinder,shouldbe a primarydesignobjectivefora successfuldiesel fuel injection system. Yet, even a properly atomized, accurately metered,and well timed fuel delivery may not provide the desired combustion effic

15、iency.Anotherimportantparameterin thisrespectisthequalityofthe mixture(fuelandair). Whilegood atomizationgoes a longway towardimprovingcombustionefficiency,how wellthe availableairisused is alsoan indicatorofhighcombustionefficiency.To achievethisobjective,betterairutilizationmust be achieved.Thispa

16、rametercan be accomplished through a combination of fuel penetration into the dense airthat is compressed in the cylinder, and equally dividing the total fuel among thecylinders of an engine. The primary purposes of the diesel fuel injection system are graphically represented in Figure 6.Figure 6 Fu

17、nctions of Diesel Fuel Injection SystemTo accomplishthedescribedfunctionsisno smalltask,and todo it effectivelyrequires the collective experience of many experts specialized in the disciplinesofmaterials,mechanicaldesign,hydraulicsandfluiddynamics,aswellascombustion systems. As more limits were impo

18、sed on emissions from diesel engines,andpressureswerefeltfromcustomersforbetterperformance,theneedforadditionalfuelinjectionsystem functionsbecame apparent.Indeedthe modern dieselinjection system mustperform the tasks of metering, timing, and atomizing as wellas contributetogood airand fuelmixing.In

19、addition,experiencegainedsincethemid- 1970shas shown thatschedulingofthemeteredfuel intothecylinderisveryimportanttotheperformance,emissions,and noise characteristicsofthe combustionprocess.A generaltermdescribingtheschedulingof injectedfuelisrateshaping .Yet,modern systemsarenotonlyconcernedwithhow

20、 much fuelisdeliveredper crankangle degree, but also with the number of injections per combustion cycle.3.Types of Diesel Fuel Injection SystemsDiesel fuel injection systems can be classified into three categories, as follows:(1)Pump-Line-Nozzle(2)Unit Injector(3)Common RailP-L-N configurations and

21、components are discussed inPump-Line-Nozzle Injection SystemFigure 7. Pump-Line-Nozzle System PrinciplePump-Line-Nozzle System Principle Pump-line-nozzle (P-L-N) is a fuel systemusingcentralinjectionpump drivenoffthe enginegeartrain,Figure7.The injectionpump feeds separate injection nozzles located

22、in the cylinder head above eachcylinder. Lineswhich must be of exactly equal lengthlink the pump with thenozzles. In the case of the in-line pump, the central pump incorporates a numberof separate plunger/barrelpumping elements (such as that shown in Figure 7),eachservingone injector.Each nozzle inc

23、orporatesa needlevalveand the orificeswhichprovide fuel atomization.The P-L-N fuel system used to be the most common type of diesel injection,dominatingmost dieselengineapplications.In additiontothein-linepump design,where each injector is fed by a separate pumping element, several otherconfiguratio

24、ns that have been developed, including the distributor/rotary pump.Bothtypesofpump systems and theircomponents arediscussedin more detailin thePump-Line-Nozzle Injection System paper.More details are available in Common Rail Fuel Injection .The total common rail system includes a low pressure supply

25、 pump that draws fuelfrom the tank and feeds it to the high pressure pump. High pressure fuel deliveredintotherailmay bringalong pressurepulsations,thereforethevolume ofthecommonrail should be designed to dampen those pulsations. These pulsations result fromthe delivery characteristics of the multi-

26、plungers radial fuel pump. Driving thepump atengine speed increasesfuelpumping capacityand improvesthepotentialforhigh injection pressure. Control of fuel metering and injection timing is similarto thatinthein-linepump and unitinjectorsystems.In spiteoftheavailabilityof these desirable features in c

27、ommon rail systems, it needs to be emphasized thatsuch systems could not attain their potential without the help from electroniccontrols.In fact, electronicswere introducedinalltypesoffuelinjectionsystemsto expand their capabilities and improve their performance.For each of the above injection syste

28、m categories there are a number ofsub-categories that will be detailed in the following papers. However, there aresome generalized comments that can be made at this stage to further clarify howquickly these three very general categories can branch out into many unique anddistinct designs. For instan

29、ce, pump-line-nozzle systems include in-line,distributor (rotary), as well as unit pumps. Not only could we differentiate themas such, but we can also separate between them on the basis of whether they aremechanically- or electronically-controlled. Similarly, unit injectors can bemechanically- or el

30、ectronically-controlled. Unit injector systems can also bedesigned to deliver extremely high injection pressures, in which case they mayfeature mechanical intensifiers in the form of plungers having two differentdiameters. They may also be actuated by brute force imparted to the top of theinjector b

31、y a large cam such as the Cummins pressure-time controlled (PT) system.The common rail category enjoys a similar variety of design details.The evolution of the diesel injection systems from the oldmechanically-controlledP-L-Ndesignsto themodern electronically-controlledunitinjectorand accumulatordes

32、igns,drivenin generalby the need of achievingtighterinjection control and lower emissions, follows one distinct trend: increased injection pressures. In fact, this trend continued through the last century. Forheavy- duty applications,itacceleratedin the 1970s to meet the demand forcleaner,as well as

33、 more fuel efficient engines. Eventually the high speed, passenger car market adopted the same philosophy, and even though it started a decade after the heavy-duty applications, both light-duty and heavy-duty applications have now similar injection pressures.4.Electronic Control in Fuel InjectionOve

34、rviewThe need tomeet emissionregulationswas one ofthemost important ifnot themost important reasonformodernizingthe dieselfuelinjectionsystem.Customerdemand for better engine response and driveability also played a major role inadvancing the fuel systemsstate-of-the-art.Dieselenginedesignersand buil

35、derswere not just satisfied with its superior fuel economy, but sought to continue toimproveittomaintain itsleadoveritscompetition.Not onlywas thegoaltoimproveitsfueleconomy standing,buttoachievethisobjectivewhilealsomeeting thetoughemissionregulationsthatwere imposedinthe1980s and 1990s,as wellas e

36、arlyin the 21 Century.As already mentioned, some of the early gains in the evolution of the moderndieselinjectionsystemwere realizedthroughincreasinginjectionpressures.However, engine designers felt their hands were tied and were unable to make othergains untiltheywere abletointroduceelectroniccontr

37、olintotheinjectionsystem.Introducing this technology made other advances easier to achieve. It was easiertocustomizetorqueoutputsfromthe same base enginetomeet thedemands ofseveralapplicationsintheheavy-dutymarket.Itwas also easyto includemany valueaddedfeatures such as limiting maximum road speed f

38、or fleets where fuel consumption isdirectly related to driving habits. For the first time injected fuel quantity wastrimmedaccording tofueltemperatureforconsistentpower outputregardlessoffueltemperature,withincertainlimits.Electronicsbroughtalongthepromiseofreducedcost through simplifying many of th

39、e functions otherwise provided by cumbersomemechanical devices, and allowed the implementation of full-authority parametercontrolstrategies.For instance,a drive-by-wiresystemallowed the implementationof low- or no-smoke strategies versus systems where the injection was solidlyconnectedto theaccelera

40、torpedal.Inadditiontosmoke-freestrategies,electroniccontrols facilitated flexibility in injection timing and metering control, andreduced cycle-to-cycle, and cylinder-to-cylinder variability.柴油机燃油喷射燃油喷射系统的目的是将燃油输送到发动机缸体内， 同时精确地控制喷射正时、 燃油雾化和其他参数。 喷射系统的主要类型包括泵 - 管 - 嘴、单体泵和共轨。 现代喷射系统可达到很高的喷射压力，使用的是复杂的电

41、子控制系统。介绍柴油发动机的性能受喷射系统设计的影响很大。实际上， 柴油发动机的先进性直接体现在高级喷射系统的设计上。喷射系统的主要目的是将燃油输送给柴油发动机的缸体。怎样输送燃油才能使发动机的性能、排放和噪音等特性，不象点燃式发动机， 柴油喷射系统可在很高的喷射压力下输送燃油。这意味着系统零部件的设计和材料应当选择能抵抗高压力，同时能提高发动机可靠性指标。为满足系统功效， 需要较高的生产精度和较小的公差。除了昂贵的材料和生产成本，柴油发动机喷射系统以具有更复杂的控制要求为特征。所有的这些特点组成系统，其成本可占到发动机总成本的30%。下面将回顾基本的柴油喷射系统和与它相关的附件，以及其他各种

42、类型的喷射系统，还有他们如何测量和输送燃油给柴油机的缸体的。这些系统的机械功能的重点在于混合物的形成。各种不同的喷射正时和测量策略将被介绍。许多专用术语用于描述零部件和燃油喷射系统的运行。下面是所选得更为普及的一些术语。喷嘴是指喷嘴壳体和针的装配体，他与发动机的燃烧室相接触。如P型、 M型和 S型喷嘴之累的术语是指喷嘴参数的标准尺寸，如ISO标准规范。喷嘴支撑或喷射器壳体是指安放喷嘴的部件。在传统的喷射系统中，这个部件主要用于安放喷嘴和预加载荷的喷嘴针阀弹簧。在共轨系统中， 它包含主要的功能部件：伺服液压电路和液压激励（电磁或压电）。喷射器通常是指喷嘴支撑和喷嘴的组合体。喷射率是燃油出喷嘴的质

43、量流量，典型地显示在时间坐标上。喷射的开始和结束是指柴油从喷嘴出来的开始和结束时刻，经常参照发动机的曲轴转角。开启和关闭速率分别指针阀开启和关闭之间喷射率的梯度。喷射压力并不是一贯使用在文献中， 它是指支持共轨系统的液压系统的平均压力或传统系统中喷射过程的最大压力（峰值压力）2. 燃油喷射系统的作用如上所述， 燃油喷射系统的主要作用是将燃油输送进发动机的缸体。作用，两个特别的目的如下所述：而这是系统的一般1）燃油进缸体的时刻介绍，即喷射正时和它的控制。2）输送精确的燃油量以满足功率的需要，即喷射计量和它的控制。然而，它仍然不足以满足精确测量燃油， 在合适的时刻进行输送， 从而达到好的燃烧效果。

44、怎样将燃油混合物，含有吸进的空气，输送缸体是主要的。因此，燃油雾化，无论燃油颗粒尺寸多么小以及在缸内如何分散， 是成功的柴油喷射系统主要的设计指标。 然而， 一个合适的雾化、 精确的计量和良好的正时时刻， 可能也不会提供想要的燃烧效率。 另外一个重要的参数就是混合物的质量（燃油和空气）。然而，雾化好对提高燃烧效率是有利的，还有所吸入的空气的质量也是高效燃烧的一个指标。为达到这个指标，要有高质量的空气，这个方面可通过压入汽缸中的空气中渗入进来的燃油的混合，并且等分配在发动机汽缸内的燃油。柴油机燃油喷射系统的主要作用如下图6所示。图 6柴油燃油喷射系统的功能要完成功能介绍是一个不小的任务， 这需要

45、许多专家集体的经验， 特别在材料规范、 机械设计、液压和流体动力，还有燃烧系统等方面。由于柴油发动机的排放存在更多的限制，以及来自消费者对更好性能需求的压力，对附增喷射系统功能的需要明显了。事实上， 现代柴油喷射系统必须进行计量任务、正时、雾化和充分的空气燃油混合。此外，自二十世纪七十年代中期以来，所获取的经验显示进入缸体计量燃油的控制，对于性能、 排放和燃烧过程的噪音特性是非常重要的。燃油喷射控制的一般描述是速率修正。然而， 现代系统不仅仅关于每个曲轴转角的送油量，而且也涉及了每个燃烧循环的喷射次数。柴油机燃油喷射系统的分类柴油燃油喷射系统可以分为3类，如下所示：泵管嘴单体泵共轨泵管嘴结构和组件将在泵管嘴喷射系统做以讨论。图 7泵管嘴系统原理图泵管嘴系统原理：泵