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.柴油機燃油噴射燃油噴射系統的目的是將燃油輸送到發動機缸體內， 同時精確地控制噴射正時、 燃油霧化和其他參數。 噴射系統的主要類型包括泵 - 管 - 嘴、單體泵和共軌。 現代噴射系統可達到很高的噴射壓力，使用的是復雜的電

41、子控制系統。介紹柴油發動機的性能受噴射系統設計的影響很大。實際上， 柴油發動機的先進性直接體現在高級噴射系統的設計上。噴射系統的主要目的是將燃油輸送給柴油發動機的缸體。怎樣輸送燃油才能使發動機的性能、排放和噪音等特性，不象點燃式發動機， 柴油噴射系統可在很高的噴射壓力下輸送燃油。這意味著系統零部件的設計和材料應當選擇能抵抗高壓力，同時能提高發動機可靠性指標。為滿足系統功效， 需要較高的生產精度和較小的公差。除了昂貴的材料和生產成本，柴油發動機噴射系統以具有更復雜的控制要求為特征。所有的這些特點組成系統，其成本可占到發動機總成本的30%。下面將回顧基本的柴油噴射系統和與它相關的附件，以及其他各種

42、類型的噴射系統，還有他們如何測量和輸送燃油給柴油機的缸體的。這些系統的機械功能的重點在于混合物的形成。各種不同的噴射正時和測量策略將被介紹。許多專用術語用于描述零部件和燃油噴射系統的運行。下面是所選得更為普及的一些術語。噴嘴是指噴嘴殼體和針的裝配體，他與發動機的燃燒室相接觸。如P型、 M型和 S型噴嘴之累的術語是指噴嘴參數的標準尺寸，如ISO標準規范。噴嘴支撐或噴射器殼體是指安放噴嘴的部件。在傳統的噴射系統中，這個部件主要用于安放噴嘴和預加載荷的噴嘴針閥彈簧。在共軌系統中， 它包含主要的功能部件：伺服液壓電路和液壓激勵（電磁或壓電）。噴射器通常是指噴嘴支撐和噴嘴的組合體。噴射率是燃油出噴嘴的質

43、量流量，典型地顯示在時間坐標上。噴射的開始和結束是指柴油從噴嘴出來的開始和結束時刻，經常參照發動機的曲軸轉角。開啟和關閉速率分別指針閥開啟和關閉之間噴射率的梯度。噴射壓力并不是一貫使用在文獻中， 它是指支持共軌系統的液壓系統的平均壓力或傳統系統中噴射過程的最大壓力（峰值壓力）2. 燃油噴射系統的作用如上所述， 燃油噴射系統的主要作用是將燃油輸送進發動機的缸體。作用，兩個特別的目的如下所述：而這是系統的一般1）燃油進缸體的時刻介紹，即噴射正時和它的控制。2）輸送精確的燃油量以滿足功率的需要，即噴射計量和它的控制。然而，它仍然不足以滿足精確測量燃油， 在合適的時刻進行輸送， 從而達到好的燃燒效果。

44、怎樣將燃油混合物，含有吸進的空氣，輸送缸體是主要的。因此，燃油霧化，無論燃油顆粒尺寸多么小以及在缸內如何分散， 是成功的柴油噴射系統主要的設計指標。 然而， 一個合適的霧化、 精確的計量和良好的正時時刻， 可能也不會提供想要的燃燒效率。 另外一個重要的參數就是混合物的質量（燃油和空氣）。然而，霧化好對提高燃燒效率是有利的，還有所吸入的空氣的質量也是高效燃燒的一個指標。為達到這個指標，要有高質量的空氣，這個方面可通過壓入汽缸中的空氣中滲入進來的燃油的混合，并且等分配在發動機汽缸內的燃油。柴油機燃油噴射系統的主要作用如下圖6所示。圖 6柴油燃油噴射系統的功能要完成功能介紹是一個不小的任務， 這需要

45、許多專家集體的經驗， 特別在材料規范、 機械設計、液壓和流體動力，還有燃燒系統等方面。由于柴油發動機的排放存在更多的限制，以及來自消費者對更好性能需求的壓力，對附增噴射系統功能的需要明顯了。事實上， 現代柴油噴射系統必須進行計量任務、正時、霧化和充分的空氣燃油混合。此外，自二十世紀七十年代中期以來，所獲取的經驗顯示進入缸體計量燃油的控制，對于性能、 排放和燃燒過程的噪音特性是非常重要的。燃油噴射控制的一般描述是速率修正。然而， 現代系統不僅僅關于每個曲軸轉角的送油量，而且也涉及了每個燃燒循環的噴射次數。柴油機燃油噴射系統的分類柴油燃油噴射系統可以分為3類，如下所示：泵管嘴單體泵共軌泵管嘴結構和組件將在泵管嘴噴射系統做以討論。圖 7泵管嘴系統原理圖泵管嘴系統原理：泵