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 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 indieselenginesresulteddirectlyfromsuperiorfuelinjectionsystemdesigns.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,thedieselinjectionsystemdeliversfuelunderextremelyhighinjectionpressures.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 efficientfunction.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 basicdieselfuelinjectionsystemand 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 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 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 preloadingpurpose.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 over 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, respectively.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 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,injectiontimingand 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.Therefore, 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