1、- a a - - COMMON RAILAND ADVANCED FUEL INJECTION SYSTEMS Philip J. G. Dingle and Ming-Chia D. LaiDieselCommon Rail and Advanced Fuel Injection Systems Philip J.G. Dingle Ming-Chia D. Lai “lnternational Warrendale, PAAll rights reserved. No part of this publicationmaybe reproduced, stored in a retrie
2、val system, or transmitted, inanyform orby anymeans, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission ofSAE. For permission and licensing requests, contact: SAE Permissions 400Commonwealth Drive Warrendale, PA 15096-0001 USA E-mail: permissionssae.o
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4、6-1615 ISBN 0-7680-1257-0 Library ofCongress Control Number. 2005927223 Copyright 2005 SAE International Positions and opinions expressed in thisbook are entirely those of the authors and donot necessarily represent those ofthe organizations towhich the authors are affiliated orSAE. The authors are
5、solely responsible for the content of thisbook. SAE Order No. T-117 Printed in the United States of America.OtherSAE titles of interest: The Diesel Engine By Daniel J. Holt (Order No. PT-109) Diesel Engine Reference Book By Bernard Challen and Rodica Baranescu (Order No. R-183) Practical Diesel-Engi
6、ne Combustion Analysis By Bertrand D. Hsu (Order No. R-327) Diesel Particulate Emissions Landmark Research 1994-2001 ByJohn H. Johnson (Order No. PT-86) Diesel Nitrogen Oxide Emissions Landmark Research 1995-2001 ByJohn H. Johnson (Order No. PT-89) Formore information or to order abook, contactSAE a
7、t 400Commonwealth Drive, Warrendale,PA 15096-0001; phone (724) 776-4970; fax (724) 776-0790; e-mail CustomerServicesae.org; website http:/store.sae.org.Contents Preface .7 Executive Summary .9 ChapterOne History and Background 15 ChapterTwo Injector Nozzle and Spray Technologies and Their Impact on
8、Emissions .25 ChapterThree Common Rail Fuel Injection Equipment 43 Chapter Four Hydraulic Electronic Unit Injectors 75 Chapter Five Unit Injectors and UnitPumps .81 Chapter Six CurrentApplication Issues 91 Chapter Seven Future Outlookand Technology Trends .99 References 127 Acronyms and Definitions
9、133 About the Authors 137 5Preface It is a strange dichotomy, but true, that while in the heavy-duty sector NorthAmerican manufacturers arguably lead theworld with their diesel truckengine technology, to the extent that the engines are emulated and sold across the globe, in the dieselpassenger car s
10、ectorNorthAmerica lags behind the world. Tosome extent, this is due to anunhappy experience with passenger car diesel engines in the early 1980s, but there are also several socioeconomic reasons for this situation. As a result, NorthAmerica today is a strongbastion ofspark ignition (SI)hegemony, a s
11、ituation thatmight easily be expected to continue well into the future. However, the times are chang- ing. ProposedCO2 reduction legislation ostensibly favors the diesel engine, and the forward-thinking product planners can see that a gasoline/dieselmix in the fleetcan open anew niche andbring flexi
12、bility to the Corporate Aver- age FuelEconomy (CAFE) calculations. Elsewhere in the world, diesel engine penetration into the light-duty vehicle markethas advanced rapidly over the pasttwenty years and particularly over the last five years. In large measure, this recent growth spurt is due to the av
13、ailability of the so-called“common rail“ fuel injection system, which has almost single-handedly transformed the diesel engine, making it seriously competitive with the gasoline engine as a private vehicle powerplant. Now, a number of factors are converging thatimprove the prospect for the availabil
14、- ity of diesel engines in the NorthAmerican light-duty market, not the least ofwhich is the market shifttoward sport utility vehicles (SUVs), forwhich diesel engine characteristics are most admirably suited. These characteristics include fueleconomy, invincible low-speed torque, and all-around good
15、 driv- ability enabled inpartby sophisticated engine subsystems such as the fuel injection system and variable geometry turbochargers (VGTs). 7However, ifpassenger car diesels are to return toNorthAmerica inany volume, either through the import ofenginesproduced elsewhere or particu- larly in the ca
16、se ofnew engines designed and assembled locally, it is neces- sary to get all aspects of the process right this time. No onewants a repeat of the dismal experience ofthe early 1980s. Many factors are different this time. There is a greater understanding of dieselcombustionnowwithin the global diesel
17、 community, extensive experience with light-duty engines is available from Europe, and precision inmanufacture has improved. However,by the same token, the performance and emissions challengeshave intensified, too. Some thingshave notchanged. The engineers inproduct developmentand manufacturingwho w
18、illbe charged with specifying, optimizing, and pro- ducing these engines will perforcebe steeped in the lore and language of SI engines andmaynotbe attuned to the subtlebut important differences with the compression ignition (CI) engine. If thatwerenot the case, therewould beno need for thisbook. He
19、re, then, in fairly general terms, is a resource that addresses the important aspects relating to the diesel fuel injection system, explaininghowwehave arrivedwherewe are,what systems are available today, providing pointers for what aspects are importantandwhat aspects are not, and finally looking a
20、t the current state ofdevelopmentand projecting the likely technologypath for the future. There isno doubt that dieseldevelopment requires a slightly different mindset, and thisbookshould help in establishing that. Thebook isnotaimed exclusively at either the light-duty orheavy-duty sector, but itpo
21、ints out where those sectors diverge in their solutions to thecommonproblems. 8Executive Summary n the 110-year history of the diesel engine and its associated fuel system, therehavebeen threewatershed periods inwhich technological progress was particularly rapid. The firstandmost spectacular occurr
22、ed in the 1920s,when “air-blast“ injection gaveway to “solid“ injection. A less spectac- ular revolution took place 35 years later in the mid-1950s and into the 1960s when the rotary distributorpump came onto the market. Finally, the intro- duction of themodem electronically controlledcommon rail in
23、jection system in the late 1990s has significantly changed the outlook for the diesel engine. In each case, technological advancesmade to the injection systemopened hugenew market opportunities that previouslyhad notbeen accessible. In the case of solid injection, itbrought the diesel engine into th
24、e automotive truck market. Rotary distributorpumpsopened the light-duty automotive market for indirect injection (IDI) diesels, andcommon rail has enabled the emissions-controlled direct injection (DI) diesel engine tobe successful in sev- eralmarket sectors. Most visible of these is the light-duty
25、automotive market, particularly in Western Europe, where diesel penetration is currently atan aggregate average of44% and is still climbing. But the impact ofcommon rail technology also canbe felt at the otherend of the spectrum. Modem cruise ships allnowhavecommon rail injection systems, so that th
26、eymay avoid the visiblesmoke emissions thatwere anunwelcome attribute overmuch of the propeller-load curve with the previous traditional fuel injectionequipment (FIE). Essentially, common railhas established anewbenchmark for diesel injection systems thatmost traditional systems are not able to assa
27、il, and as a result, they are fallingby the wayside. In-line and rotarypump-line-nozzle (PLN) systems are in rapid decline, and only the unit injector family is in a position to compete. Althoughnot anew concept,common rail, which gets itsname from the high-pressure accumulator typically runningdown
28、 one side of the cylinderhead and feeding all injectors from thiscommon source, has logically moved most of the fundamental system functions close to the point of injec- tion. TraditionalPLN systems controlled fuel metering, injection timing, and 9pressure generation at thepump, with only the inject
29、or being responsible for atomization. On the otherhand,common rail integrates fuel metering, injec- tion timing, and fuel dispersion all within the injector, which imparts ahuge advantage in precision of control relative to previous systems. Moreover, with thepump freed of these responsibilities, it
30、 isnow able tomodulate the system pressure as ameans of controlling overall injection rate, which again is a valuable feature notpreviously available. Drivers for the ready acceptance of thenew electronically controlledcommon rail systems are largely emissions related. On onehand, legislated reduc-
31、tions in tailpipe emissions demanded continuous FIE improvements with respect to parameters such as injection pressure, injection rate flexibility, and control precision, whichhad tobemet if current diesel engine familieswere to remain in production. On another front, thecommon rail systemhasbeen fo
32、und tobe ideal for the light-duty DI automotive engine as noted above, where its sophistication of control over the combustion process has effectively made this engine the equal and insome respects superior to the previously hegemonic spark ignition (SI) engine. In turn, the popularity of the light-
33、duty DI diesel is due in part to the desire for economical mobility in an era of rising motor fuel taxation and a desire to limitCO2 greenhouse gas emissions. In comparison to the gasoline engine, the light-duty dieselshows to advan- tage in the areas of specific fuel consumption, low-speed torque,
34、and fun-to- drive factor. While improvements arebeingmade continuously to the diesel engine,OEMs are still obliged to focus on nitrogen oxide (NOx) and particu- late matter (PM) emissions, cold startingand associated idle noise, and initial powertrain cost. In all of these, the FIE plays a decisive
35、role. Indeed, the FIE is and always hasbeenkey to the diesel combustion process, and although exhaust aftertreatment is under intensive development, the usual decision is to exploit the FIE capabilities to their fullest extent. The cost-to-benefit ratio almost always favors minimizing engine-out emi
36、ssions in the first instance rather than expecting aftertreatment to cleanup a polluting engine thathas less capable FIE. Additionally, FIE sophistication usuallybrings side benefits such as reduced noise, vibration, and harshness (NVH) forwhich the con- sumer is prepared to pay, whereas exhaust aft
37、ertreatment providesfew consumer-perceived benefits and a likely fuelconsumption penalty. 10The technical challenges associated with continuous emissions improvement in all classes of engine, as well as attainment ofpowertrain costand refine- ment goals, drive the solutions, whichmayvaryfrom onemark
38、et sector to another. At present, common railhasmade onlymodest inroads into the heavy-duty truckmarketwhere the unit injector isnow the dominant fuel system. There are multiple reasons for this situation, covered in the appropri- ate chapter here. However, a reason that willbecome increasingly impo
39、rtant in the future is that the unit injector offers unique and compelling benefits of itsown that are not yetmatchedby currentcommon rail systems. These include significantly higher injection pressure capability, always beneficial where high levels of diluent are involved, and in the latest two-val
40、ve elec- tronic unit injector (EUI) a capability for multiple injections with shot-to- shot pressure and rate control. Nevertheless, looking to the future, it canbe assumed thatbothcommon railand unit injectors will strive to converge on the “ideal“ fuel injection system specification, and in so doi
41、ng, they will each appropriate the superior features ofthe other system. The presentparadigm, however, viewscommon rail as offering greater refinementand unit injec- tor as offering higher specificpower ratingsby virtue of the higher-pressure capability-hence, the dominance ofcommon rail in light-du
42、ty applications and EUI inheavy-duty applications, withhydraulic electronic unit injection (HEUI) systems making a strongshowing inmedium-duty applications. Fuel injection technology roadmapsprovide a pointer for the development direction of diesel engines as a whole, becausemany ofthe advancesmade
43、to the engine aredependenton FIE technologies. Generation-by-generation increases inpeak injection pressure capabilityhavebeen drivenby thedemand forhigher specificpower outputs andlowerPMemissions for a givenpower level. Pilot injection capabilityhasbeen an ideal for decades,butonlynow withcommon r
44、ailhas itworked wellenough that itcanbe fully exploited for reduction ofnoiseandNOx. To a significant extent, control ofcombustion heat releasehasbeenenabledby multiple injection capabilities that, in effect, “digitize“ the injection rate profile. Advances inmanufacturing precisionand software contr
45、ol algorithms, both in the manufacturing plantand in the engine control unit (ECU), have greatlyimproved unit-to-unit consistency and refine- ment. All ofthese featuresandmanymore tocome are changing thepercep- tion of diesel engines fromonewith negative connotations to one thathas a rapidly growing
46、 acceptance and often preference in ownership. 11The positive features of diesel engines for automotive applications notwith- standing, many open questions remain tobe answered aswe look to the future. Diesel enginescompare unfavorably to SI engines on the basis of initial cost, and this situation w
47、illbe aggravatedby the significant costs of exhaust aftertreatment. Moreover, the active nature of the aftertreatment regeneration requires regular dosingwith a reductant, frequently the fuel itself, which detracts from the overall vehicle fuel economy. These factors affect the market appeal of the
48、diesel engine, leaving the dooropen for SI engine improvements thatcouldbe decisive inmarket share retention. How- ever, in the struggle formarket share, technological improvements appear set to continue at a rate at least as rapid as in the recent past, with piezoelectric control actuators and vari
49、able orifice nozzles being examples of FIE progress that will enablenew low-emissions combustion opportunities. While these technologies would appear to add to the initial system cost, they willbe per- ceived as highly cost effective if they enablehomogeneous charge compres- sion ignition (HCCI), mixed-mode, or other low-temperature combustion strategies thatminimize the exhaust gas aftertreatment requirements. Other opportunities for cost reduction willcome from intensive efforts atsystem integration by, for instance, exploiting the significant synergiesbetween the fuel system and engin
