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Engineers, Part D: Journal of AutomobileProceedings of the Institution of Mechanical

http://pid.sagepub.com/content/199/2/113The online version of this article can be found at:

DOI: 10.1243/PIME_PROC_1985_199_148_01

1985 199: 113Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile EngineeringG L Bird

The Ford 2.5 Litre Direct Injection Naturally Aspirated Diesel Engine

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113

The Ford 2.5 litre direct injectionnaturally aspirated diesel engineG L Bird, CEng, MIMechEFord Motor Company Limited, Basildon, Essex

The advantages of a high-speed direct injection diesel over an indirect injection engine are well established. In the last decade manyszudies have been presented which suggest that most of he technical issues preventing operation at high speed have been overcome. Thenew Ford 2.5 litre engine introduces a fir st generation of production high-speed direct injection engines. Based on controlled high swirlair management, combined with high ra tes offuel injection, the engine produces 52 kW at 4000 rlmin. Initial installation of the 2.5 litrehigh-speed direct injection engine is in the Ford Transit range of vehicles where 25 per cent fuel economy improvements over itspredecessor, the York 2.36 litre indirect injection engine, have been achieved.Designed to meet the demands of modern vehicle application, the engine includes many features to improve reliabi lity and durability .This paper describes the engine systems and components of the engine, together with the key aspects of the performance developmentwith specijic reference to the actions employed to control noise.

1 INTRODUCTIONThe new Ford 2.5 litre high-speed direct injection(HSDI)ngine is the result of several years of intensivedesign and development activity. Based on the conceptsof controlled swirl air flow . manag emen t an d high-'pressure short period fuel injection, the engine incorpo-rates an intake port initially developed by AV List (l),of Austria.Designed to meet the demands of the medium vansegment of the com me rcial vehicle ma rket, th e engine isfitted to the Ford Transit range of vehicles. It is alsoavailable for industrial and marine applications.The new engine replaces the Ford York 2.36 litreindirect injection (IDI) engine first introduced in 1972and offers increased power and speed, improved fueleconomy and major improvements in durability. Anall new production facility has been installed at Dagen-ham with many manufacturing and process improve-ments to enable production capacity to be increasedfrom 80000 to 113OOO units p.a. The prime objective ofthe new engine is to capitalize on the well establishedfuel efficient direct injection combustion system at arated power of 52 kW at 4OOO r/min (BSAU 141a). Thisselection of power and speed enables the transmissionsto be optimized to achieve an in-vehicle fuel consum p-tion improvement of up to 25 per cent. After prolongedstudies of service da ta g athere d on the Y ork I D1 engine,objectives to increase the durability by 50 per cent andthe service period s by 30 per cent were set. Although thenew engine retains the same layout as its predecessor,every component has been redesigned to meet the newdemands.The decision to proceed with the development of ahigh-speed direct injection engine was taken aftercareful examination of the alternative systems availableand demonstrated by laboratory engines. The AV Listsystem was selected because it is inherently simple andwith the exception of the fuel injection equipment doesThis paper was presented at an Ordinary Meeting held in Birmingham on 5February 1985. The MS was received on 21 February 1984 and was acceptedforpublication on 27 December 1984.

not require any new unproven engine components.However, it was still necessary to p rove that labora torytheory could become a mass production reality. Toprove this and strengthen confidence, three sub studieswere undertaken. Each of these studies used York ID12.36 litre base engine componen ts with the exception ofthe pistons, cylinder head an d fuel injection equipment,i.e. those com ponents necessary to convert the en gine toa d irect injection system.1.1 Study I: casting and machining consistencyBeing aware that small variations in inlet port dimen-sions could greatly affect engine performance, it wasnecessary to define the limits within which the newengine would be manufactured. To establish a measureof this effect, twenty cylinder heads were cast andmachined t o cover the extrem es of production tolerance.Analysis of the results concluded that the variationswithin practical production tolerancing were small andwell within acceptable limits, equating to f 2 . 3 per centbrake specific fuel con sum ption (b.s.f.c.) an d k6.5Har-tridge smoke units (HSU) at 3600 r/min. At 4OOO r/min,the new engine's objective rated speed, the variation wasslightly greater and represented a development task ofair management to be tackled in the full prototypeprogramme.

of inlet ports

1.2 Study 11: factorial analysisBy using a factorial grid approach it is possible toanalyse the effects that extremes of tolerance of thecomponents, key to the combustion process, may haveon overall engine performance. Two cylinder headsfrom the consistency exercise (Section 1.1)were selectedto provide mean (ranked ninth) and worst (rankedeighteenth) air flow properties, but still within theplanned design tolerances. These were assessed againstthe extremes of tolerance of the following:(a) piston bowl volume;(b) piston bump clearance;

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114 G L BIRD

/'Cylinder head effect- thranked*---x 18th ranked0 J* 20700

300

Full load b.s.f.c.2251 1 I 1 I I I 1800 1200 1600 2000 2400 2800 3200 3600Engine speedr h i n

Fig. 1 Factorial analysis: performance comparison of twocylinder heads(c) injector protrusion;(d) injection timing.

From the analysis it was possible to conclude that thetolerances chosen for the variables listed above matchedthe design objectives, but the variation in performanceresulting from the cylinder head were more critical, asshown in Fig. 1, a factor which was to prove significantin later development. In recognition of the contributionthat the inlet port makes to the overall performance, thedecision to check every cylinder head for swirl and flowin production was made.

1.3 Study 111: production line consistencyFinally it was necessary to assess the consistency ofperformance of the engine under production conditions.This was achieved by building a production batch ofone hundred 2.36 litre DI engines within the toleranceestablished by the first two studies and comparing theirperformance with a similar sample of York ID1 engines.The results, which are shown in Table 1, are very

Fig. 2 General arrangement: front viewinteresting and clearly demonstrated that the DI engineis less variable than the ID1 when compared in a largeproduction sample.The combined analysis of these three studies providedthe confidence and additional knowledge needed and arecommendation to proceed with HSDI engine prog-ramme was given approval in October 1980.This paper describes the engine component designand reviews the development of the high-speed com-bustion system, particularly the feature development ofthe fuel injection system, to meet the demands of com-bustion throughout an extended speed range.

2 COMPONENT DESIGN2.1 General arrangementThe general arrangement of the engine is shown in Figs.2 and 3. Although the layout of the engine is similar tothe 2.36 litre York IDI, with an inclined bore centre-lineand the camshaft located high in the engine block, everycomponent has been redesigned and developed to meetthe objectives of the new engine.

Table 1 Production consistency: comparison of DI and ID1 performancefactors at 2.36 litre capacity, sample size 100 engines.Engin e Specific fuel - eanCond ition Power Smok e Temperature consumption gain

speed Load ha s t h S t Least Least DI


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2.5 LITRE DIRECT INJECTION NATURALLY ASPIRATED DIESEL ENGINE 115retain the basic dimensions of the new cylinder block sothat it could be used as a service part for the outgoingYork ID1 engine. To this end, the cylinder bore centres,head bolt pattern and the main bearing locations andsizes are retained.The new block has been designed to include noiseattenuation features which are described later. Attentionhas also been paid to other aspects of design to improveoil pump location at the front of the block, the provi-sion for a spin-on oil filter pad and the deepening of thecylinder head bolt thread locations to facilitiate the useof 'torque to yield' hardware. A further feature is theprovision of a flywheel pegging location which is accu-rately set in production and provides a permanenttiming point for top dead centre (TDC) and enginetiming for service repairs.

Fig. 3 General arrangement :side viewThe engine is slightly over-square with a bore of 93.67mm and stroke of 90.54 mm and has a total capacity of2496 cm3.The five bearing crankshaft drives the over-head valve train and fuel injection equipment via atoothed timing belt. Detailed system descriptions follow.

2.2 Cylinder beadThe cylinder head is a key component of the HSDIengine and is manufactured in cast iron. The inlet andexhaust ports are positioned to give a cross flowarrangement, with particular attention being paid to theaccuracy of the port locations during casting and theinitial machining stages. The helical intake port is theresult of careful development, which is dealt with laterin detail. The final design incorporates the improve-ments of four phases of development and includes criti-cal dimensions for manufacturing control as well asrefined contours for optimized air flow and motion.The exhaust port follows conventional practice, withminimal restriction to gas flow. Heat flux in a HSDIengine is less severe than in an ID1 engine, and thedetailed design of the casting enables the valve seats tobe induction hardened after final machining, therebyavoiding the need for valve seat inserts. The valve seatdiameters, together with the profile of the intake tractadjacent to the seat, have been carefully developed toimprove air flow at 4000 r/min. The inlet seat angle isset at 30" and the exhaust at 45".The injector is locatedat 23" to the vertical, slightly off-centreof the piston.In production every cylinder head is subjected to aswirl and flow check on the intake ports. This ensuresthat the swirl ratio is held within specification andenables a degree of selection of cylinder heads for per-formance conformity.2.3 Cylinder blockIn setting the objectives of the new engine only onemajor constraint was applied. This was the need to(Q IMechE 1985

2.4 CrankshaftBasic dimensions of the crankshaft are the same as theYork ID1 with the exception of the crank throw whichis increased by 2.48 mm to 90.54 mm providing theincreased stroke of the 2.5 litre engine. A high qualitynodular iron, in which the silicon and total carbon arecontrolled within tight limits, is specified. This enablesthe main bearings and and crankpins to be inductionhardened and all journals are fillet rolled for increasedfatigue strength. The rear journal carries the flywheelvia eight bolt fixing and the journal also provides ahardened surface for the oil seal. A high frequencyinduction hardening process is employed for this toprevent cracking through to the flywheel bolt threads.At the front of the crankshaft a hardened steel geardrives the oil pump. The primary drive sprocket, whichdrives the valve train, is integral with the torsionalvibration damper.2.5 Valve trainThe valve train is a conventional OHV design with thechilled iron camshaft mounted on the exhaust side ofthe engine in five bearings. The valve timing has beenoptimized to suit the combustion process and with aninlet period of 232" and the exhaust 244" the valveoverlap is 26".A chilled cast iron tappet is specified to ensure longlife and avoid cam/tappet spalling. A short push rodtransfers the cam lift to a ball and socket rocker adjus-ter. Particular attention has been paid to rocker shaftretention to ensure overspeed protection up to 5400r/min. The rocker arms are bushed, to improve dura-bility, and the valve pad is induction hardened by amedium frequency process after profile grinding.Rotation of the vertically mounted valves is providedby multi-groove collets. The inlet valve stem is phos-phate coated and the exhaust is chrome finished and oilcontrol is by a positive polyacrylic seal. A single coilspring, common to both inlet and exhaust valves anddesigned to specifically meet the overspeed objectives, isseated on a hardened steel washer in the cylinder headto eliminate fretting.2.6 Primary driveIn 1972 the York ID1 engine was introduced with aprimary drive system driven by a fabric faced/glass fibre

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Fig. 4 Primary drive layou t: 2.5 litre DI compared to YorkID1tension member toothed belt and as such was a fore-runner of this type of drive for diesel engines. Previousexperience with this system made it first choice for the2.5 litre DI diesel. The instantaneous torques imposedby the HSDI fuel injection pump are approximatelythree times that of the ID1 engine which, combined withthe speed increase to 4000 r/min, required an improvedbelt layout; Fig. 4 compares the two arrangements. Thenumber of teeth engaged on the crankshaft gear hasbeen increased by four and the belt wrap angle on thefuel injection pump pulley increased to 180". Thisrearrangement has resulted in the mean tooth load atthe rated engine condition being reduced by 6 per centwhen compared to the ID1 engine, and although themaximum instantaneous tooth loading is 85 per centhigher than the IDI, this represents only 7 per cent ofthe ultimate tooth shear strength. The Pirelli RH belt isretained to provide the drive. Although lightweightpress steel pulleys were developed to drive the camshaftand fuel injection pump during the prototype prog-ramme, production process problems have delayed theirintroduction, and cast iron pulleys have been retainedfor initial production.

2.7 Piston and connecting rodConventional expansion controlled pistons are specifiedfrom two supply sources, Hepworth and Grandage, andMahle. Although they operate under slightly differingprinciples both provide the close controlled tolerancessought to minimize noise in the hot and cold modes. Athree ring pack, common to both piston types, islocated above the gudgeon pin. The top ring, carried ina cast iron insert is a parallel chrome faced SG cast ironspecification. The second ring is taper faced, in standardgrey iron. The oil control ring is a conventional twinnarrow land iron ring, chrome plated and activated by a1.19 N expansion spring.Proc I ns tn M cc h E n p Vol 199 No D2

To protect the top ring from combustion gas spillageand improve piston stability at TDC, the piston pinisoffset 0.5 mm to the anti-thrust side in preference toseeking small noise reduction by offsetting to th e thrustside, a benefit hard to substantiate with a close con-trolled autothermatic piston design.A conventional toroidial combustion bowl is set ofl-centre 5.3 mm forward and 1.5 mm toward the exhaustvalve. The bowl aspect ratio is 2.74 and dimensioned togive a 19.1 compression ratio. Minimum clearance valvecutouts are included in the piston crown.The forged connecting rod is manufactured in vana-dium air hardened steel, which provides additionalstrength to meet the higher loads of the DI engine,without increasing weight or basic dimensions. It has asecondary use as a service part for the York ID1 engine.Piston crown to head face dimension (bump clearance)is controlled to a maximum 0.9 mm. By using fourgrades of con-rod lengths and five grades of piston com-pression heights (pin centre to crown), the pistons androds are individually selected to suit a measured crank-shaft and block assembly. As a further assembly control,four grades of piston skirt diameter enable minimumpiston to bore clearances to be achieved.

2.8 Cooling systemTo maintain the engine in the best balanced thermalcondition and effect fast warm-up for vehicle heaterconsiderations, a controlled flow bypass system hasbeen developed. Situated at the front of the cylinderhead a complex housing incorporates a double actingthermostat and also an aperture for the wax elementunit which provides, by a cable linkage to the fuel injec-tion pump, a fast idle control when the engine is cold.Balanced thermal distribution within the engine ismaintained by optimizing coolant flow between cylinderblock and head by graduated coolant holes in thegasket. The system circulation is provided by a conven-tional impeller and involute housing water pump. Awell proven cassette type seal is used in conjunctionwith a heavy duty ball and roller bearing. Improve-ments in manufacturing and assembly of the waterpump have been introduced to ensure correct locationand loadings of the seal and each pump is cycled andair tested prior to assembly to the engine.

2.8 Covers and sealin gField and service studies of the York ID1 engine indi-cated that oil leakage is a constant source of concern,therefore the new engine set prime objectives to improveboth the rotary and the cover sealing.A significant change to the cylinder headblocksealing is the introduction of torque to yield bolt tight-ening. In production a multi-spindle machine isemployed and a controlled thickness gasket obviates theneed for retorquing in service.To improve the rocker cover sealing, the number offasteners has been increased from six to nine andimprovements have been made to the cover gasket railto give greater rigidity and flatness. A cork-based gasketcompletes the seal.

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2.5 LITRE DIRECT INJECTION NATURALLY ASPIRATED DIESEL ENGINE 117The oil pan sealing faces have been subject to radicalchange. The pan rail of the cylinder block has beenstiffened and the swaged flange of the oil pan has beenredesigned to provide a flat gasket face. External rein-forcing strips improve clamping and the joint is com-pleted by a controlled swell gasket. In production amulti-spindle tool ensures uniform clamping. Oil filtersealing is improved by the inclusion of a spin-on unitlocated horizontally on the right hand side of the block.It is in the area of rotary seals that the biggestimprovement has been realized where poly-tetrafluoroethylene (PTFE) seals, carried in simple steelcarriers, are fitted to the crankshaft front and rear andthe camshaft cover housings. Test experience withPTFE seals in the early prototype stage of the prog-ramme showed them to be vastly superior to conven-tional lip seals with the result that the new seals wereintroduced in production on the York ID1 engine in1982, with exceptional success. To protect the sealingsurface and aid assembly, each seal is supplied with a

purpose designed plastic mandrel, which is pushed asideduring the final assembly operation.3 PERFORMANCE DEVELOPMENT

The initial studies conducted on 2.36 litre DI engineshad established a good base of information to enablethe full development of the 2.5 litre engine to proceed.The performance of a HSDI diesel engine is dependenton bringing together the two main components of com-bustion, air and fuel, in the appropriate quantities andcondition, i.e. volume and swirl for the air and volume,pressure and timing for the fuel. Add to this the otherdemands of hot and cold operation, driveability andnoise (both sound level and subjective opinion) and theequation becomes extremely complex.The development of all systems progressed in parallelthrough three phases and hence the normal practice ofcross-check, balance, and recheck prevailed throughout.For ease of presentation the contributing system devel-opments are discussed under the following headings:(a) air management;(b) fuel injection equipment;(c) cold start/cold running;(d) noise;(e) summary of achievements.

4 AIR MANAGEMENTThe combustion process depends very heavily on themotion and flow of the air into the cylinder throughoutan extended speed range, and the conflicting values offlow and swirl have to be balanced against legal smokelimited performances. Many components have an effecton this total air management and each has to be opti-mized throughout the speed range if the total system isto work satisfactorily. The key components are :4.1 Intake portIn developing the 2.5 litre HSDI engine, the inlet portwent through four stages of development. At each stage,air flow and swirl were monitored using a Tippelman (2)flow rig. The envelopes of performance of the port typesQ IMechE 1985

I I I I I60 65 70 75 80Airflowft3/min

Fig. 5 Anemometer air flow nlet port comparison

used are shown in Fig. 5, and although all aspects ofengine performance as measured on the dynamometerwere considered in great detail at each stage, the deci-sion to change was based on the following synopsis.Type 1 proved to be marginal on smoke at highspeed, while Type 2 with less swirl but improved flowgave outside limits smoke at low speed. Type 3 provid-ed an interim improvement leading finally to the devel-opment of Type 4. This port provides the finelybalanced requirement of optimized performance againstlegal smoke objectives throughout the speed range. Thecritical areas of the port design are the profile directlybehind the valve seat and the area in the throat justprior the vortex shown in Fig. 6.4.2 Valve seat sizeEarly engines were built with inlet valve seat diametersof 42 mm. The need to minimize the dead volume in themachined area of the valve seats combined with theflow studies suggested that an increase in valve seatdiameter to 43 mm would be beneficial. However, thiswas not fully supported by engine test and a period ofindecision followed when engines with 42 mm and 43mm valve seat diameters were compared.The development of the intake port (Type 4), part ofwhich was the finalization of the throat detail, showedthat the smaller valve gave more consistent smoke per-formance throughout the speed range than the largervalve which places the air closer to the cylinder wallwhen the valve is fully open. The closer proximity

wFig. 6 Helical inlet port general dimensions

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Fig. 7 The intake manifold has been designed as an extension of the inlet portcaused disturbance to the generated swirl in the cylin-der. For this reason the smaller valve was finallychosen.4.3 Intake manifoldAn important component of the air management is theintake manifold, and several designs were consideredbefore it was finalized. Some consultant agencies recom-mend ram manifold designs for successful high-speed DIcombustion, but these were not an option because ofvehicle installation constraints. The early designs con-centrated on confirming that some form of independenttracking to the intake port provided a performancebenefit. The final manifold is the evolution of threedesigns and a computer study (Fig. 7) by the WolfsonUnit at Cambridge University whose program was usedto optimize tract diameters, minimize dead volumes andreduce surface areas for lower noise emission. Otheraspects taken into account in this design are the needsof minimum length high-pressure fuel pipes and theoptimum location for the -20C cold start fast flamedevice and, of course, low material and casting costs.4.4 Exhaust port and manifoldThe exhaust port and manifolding are less critical to theHSDI performance and a conventional exhaust port hasbeen designed to provide a 20 per cent increase in areathrough the port tract above the seat area. Detailedchanges to the valve guide boss, the throat and seatangles, further improved flow performance by 15 percent over the York ID1 port.

5 FUEL INJECI'ION EQUIPMENTA fundamental decision for the new engine was the sel-ection of fuel injection equipment (FIE). The laboratoryProc Instn Mcch Engrs Vo l 199 No D2

engines and the production viability study engines hadused conventional in-line plunger pumps with high ratecams. These met the needs of the early studies butwould they meet the demands of an automotive enginein production and service? The in-line multi-elementpump has greater potential in terms of pressure andperiod control, but is far less adaptable in terms ofinjection timing, fuel delivery and governor control. Onthe other hand, the capability of the then existing rotaryequipment to pump the higher pressures needed forHSDI combustion and remain durable were far fromproven.The decision to use rotary was finally based on thegreater need for FIE flexibility rather than the possibleneed for mechanical strength which, in the end, cangenerally be achieved, albeit with some cost increase. Aconscious decision was therefore made to develop inparallel the Bosch VE and the Lucas CAV DPS pump.This decision together with the persistence and dedica-tion of the performance engineers to keep the develop-ment of both types of equipment alive, no matter whatsetbacks occurred, has enabled the HSDI to go intoproduction meeting all of the project objectives.It was important that the initial specification list forthe fuel injection system was both comprehensive anddefinitive to ensure that programme cost estimates andperformance objectives could be achieved. In support ofthis requirement, the following listing was prepared andsubmitted to the fuel injection vendors.5.1 Fuel injection pumpThe fuel injection pump (FIP) was to be a self-containedfully automatic unit with functions and features u iz :Featurespeed

RequirementFull load operation7004000 /min(Q IMcchE 1985



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2.S LITRE DIRECT INJECTION NATURALLY ASPIRATED DIESEL ENGINE 119FeatureOverspeedGoverning

Stop controlPumping pressureDelivery periodAutomatic speed advanceLight load adv ance/retardDynamic timing settingAutomatic fuel controlPreset fuel settingAutomatic excess fuelCold-fast idleCold start advance

Requirement5400 r/min constantTwo-speed: runou t15 per cent maximum atrated speedkey offAutomatic solenoid,

U p t o 750 bar24 maximum at 4000 r/minFrom idle to maximumpowerFo r o ptimum specific fuelconsumption and smokeConsistent with pegtiming production+50 per cent of maximumfuel requirementTo meet developed torquecurveAt all temperatures withbelow idle speed cut-outOperated by coolant temp-erature sensed controlAutomatic matched to fastidle cut o utAll settings tamper proofed System to be developed tosuit manufacturingfacilityfuel pressureDurability B10; OOO hours maximum

Injectors To achieve the best installation conditionand provide a cost benefit, a barstock 21/17 mm injec-tor body is specified in preference to 21 mm forging.The advantage this type of injector includes axial topentry for the high-pressure pipes and improvements tothe water passage design in the most constricted area ofthe cylinder head. Nozzle specification was left openpending development.Filtration Single element 5 pm unit with minimumleak paths and improved serviceability.Cold Start Basic system to achieve down to -10Cstarting in under ten seconds from key on. For tem-peratures down to -2OC, with the addition of a mani-fold heater, starting to be completed within twentyseconds from key on.The development of fuel injection equipment to give abalanced performance for all the objectives of a modernautomotive engine is difficult when working withknown technology. When new boundaries have to beexplored it seemed, at times, totally impossible, espe-cially when objectives of power, smoke and cold startdirectly oppose the requirements of noise which in thedirect injection engine is a fundamental problem at allspeeds. However the final product vindicates the beliefthat with a little determination most things are possible.To meet the durability objective both the Bosch VEand the CAV DPS pumps were uprated by designchanges to the drive system, but testing found weak-nesses which were resolved by improvements inmaterials and component manufacture. Durability hasbeen finally established by extensive rig, dynamometerand vehicle testing and a total in excess of 200000hours running has been completed. Early performancework centered on demonstrating that power and smokeobjectives could be met with fixed fuelling by raising

injection pressures and shortening the injection periods.As understanding of the combustion process increasedthe FIE specification developed accordingly. However,it was the need to meet acceptable in-vehicle subjectivenoise that prompted the deepest research.The base engine sound level noise objective of 98dBA (SAE) had been met by component design changes,described later in this paper. These enabled vehicledrive by legal noise limits to be achieved with appro-priate vehicle package treatments. The outstandingobjective was an acceptable vehicle interior subjectivenoise level for the driver and passengers. In this situ-ation the only way of reducing the offending dieselcrackle of the HSDI engine is to reduce the rate ofcylinder pressure rise by retarding the injection timingto the borders of smoke limitation, and then resolve thesubsequent side-effects of efficiency loss, cold start capa-bility and vehicle driveability.The final design level of the fuel injection pump is theresult of extensive development to balance these con-flicting demands and although the mechanisms in thetwo FIP designs are different in concept, by the natureof the basic principle of their operation, the functionalrequirements are the same. In describing the systemswhich have been developed specifically for the 2.5 litreDI engine, this is best done by considering the key func-tions as follows:(a) fuelling;(b) timing: full and part load;(c) governing;(d) cold start and fast idle.

5.2 Fuel controlThe original engine performance requirement was formaximum torque to occur at 2200 r/min. To achievethis, the fuel curve shown in Fig. 8 was specified.Retardation of the injection timing in the mid-speedrange to reduce subjective noise, resulted in excessivesmoke which could not be overcome by air manage-ment improvement. Revision to the torque curve andhence the fuel curve was therefore the only alternativeand the maximum torque speed of 2700 r/min wasagreed. Even so, this still left a task because the fueldelivery could not be controlled to the new shape withthe existing fuel setting devices. Consequently newcontrol mechanisms incorporating two and three-stagesetting operations have been developed. On theCAV-DPS a dual spring rate torque trimmer is1

I --- Original objective max. torque 2200 r/min25i R&CXXI noise specification- max. torque2700 r/minI I I I 1 I 1 1loo0 2000 3000 4oooEngine speedr/minFig. 8 Comparison of pre an d low noise fuel curves

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im G L BIRDemployed, while on the Bosch VE the hydraulic torquecontrol employs an adjustable piston with compoundangle.These devices enable the fuel curves to be preset bythe FIE vendors to tight limits necessary for statisticalcontrol of fuelling throughout the speed range andhence the engine performance as measured on pro-duction test beds.5.3 Fuel injection timing: full and part loadThe initial specification included automatic advancesystems which provided a linear advance through theoperating speed range. In order to reduce the subjectivenoise in the acceleration mode, while retaining theobjective rated power and also ensuring optimum coldstarting times, a three-stage full load timing advanceschedule has been developed. Figure 9 shows the fullload advance curves before and after low noise develop-ment. In production when all tolerances of pump andengine are taken into account, the timing schedules arewithin &2" crank at 3 sigma limits.To ensure that the change from part load to full loadduring acceleration does not induce a pronouncedchange in combustion crackle, constant beginning ofinjection (CBI) through the load spectrum is desirable.However, under cold conditions and light load theretarded timing does not support complete combustionand some light load advance has been included. Thefinal injection timing schedule gives a satisfactory sub-jective interior noise in all driving modes while stillachieving power, smoke and fuel consumption targets.Having established satisfactory hot running condi-tions, it was necessary to re-establish the cold start andcold running operation which had deteriorated as aresult of the retardation.

//\ /\ /'./

Full load advance ho cold advanceJ --- ull load advance,low noise0 -.-.- Cold running advanceI I I I I I I

1000 1500 2000 2500 3000 3500 4OOOEngine speedr h i nFig. 9 Nominal uel load 'start of injection' timing curves

Roc Instn Mech Engrs Vol 199 NoD2

At coolant temperatures below +3O"C the timingadvance schedules are automatically switched to coldoperation. This advances the timing by up to 10" crankangle and holds it in this mode until the engine reachesnormal operating temperatures. This cold modeadvance schedule (Fig. 9) overcomes poor driveability,prevents the production of white smoke and increasesthe capability to accelerate the engine under extremecold temperature conditions. The time-scale involveddepends upon the prevailing ambient but should not bemore than ten minutes, the time taken to raise thecoolant temperature from -20C to +4O"C undertown driving conditions.Known as the CIA (cold idle advance) on the LucasCAV DPS pump the function is mechanical/hydraulicand controlled via the same wax element feature whichactivates the fast idle device. The KSB (cold startadvance) on the Bosch VE is a hydraulic device con-trolled by an independent electrically heated waxelement fitted directly to the advance switch regulatingvalve. An electric circuit provides a signal indicatingblock temperature.Even with a cold advance system it is necessary, whenoperating in very cold temperature on low load drivecycles, to supplement the combustion with heated airand a thermostatically controlled air heating system hasbeen added to the engine, with the Bosch fuel injectionequipment. Taking air from a collector box mounted onthe exhaust manifold a temperature rise of 20C isachievable at ambients down to - 5C.5.4 Speed governingBoth fuel injection specifications employ two-speed gov-erningswhich provide a very flexible control in thevehicle. The full load run-out is set between 8 and 12per cent which gives a good driving feel in the vehicle.Some difficulty was experienced with driveability atlow engine speeds at very light load; this was due to thesmall amounts of fuel needed by the engine at low load/low speed, causing pressure reflections in the pumpresulting in governor instability. This was overcome byequalizing the pressure fluctuations and correspondingmatching governor control in the idle and low-speedregions.

6 COLD STARTThe early demonstration engines gave encouraging per-formance when assessed for cold starting at - 0C and-20C. At - 0C starting was easily achieved with theaddition of excess fuel. The use of a single fast flameunit placed strategically in the inlet manifold demon-strated that this additional heat source provided suffi-cient temperature rise to effect good starting at -20Cand below, thereby obviating the need to specify in-cylinder glowplugs. This, of course, simplifies the cylin-der head and the combustion chamber and contributesa significant cost saving over conventional ID1 systems.Early development centred on establishing optimumlevels of excess fuel and when start of injection timingwas retarded to improve the subject noise quality, themechanics of the systems were modified to retain theseoptimum settings and the start advance systems wereadded to ensure complete combustion and avoid theproduction of white smoke during the warm-up period.

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2.5 LITRE DIRECT INJECTION NATURALLY ASPIRATED DIESEL ENGINE 121A major objective for the lower -20C specificationwas to reduce the delay period associated with manifoldflame heaters. This was achieved by developing a newheater unit which incorporates a solenoid valve in placeof the traditionally used bi-metal strip.The new unit has been developed in conjunction withBeru and is known as 'fast flame start'. The unit iscontrolled by a temperature sender unit and operates attemperatures below -1o"C, with a warning light forthe driver to indicate flame assistance is needed. A rapidflame is achieved by subjecting the heating coil to asurge voltage for five seconds then the fuel is released toprovide the flame. Engine cranking is commenced whenthe indicator light goes out, which is approximately fiveseconds after key-on. Starting is achieved within fifteenseconds depending on prevailing ambient temperatures.

7 ENGINE NOISE7.1 Base engine noiseOne major disadvantage of the DI engine versus ID1engine is the base engine noise. In broad terms, enginefor engine of equivalent capacity, power and speed, theDI engine will be 1.5 dBA noisier than the IDI. Add tothis a 1.5 dBA increase for a 400 r/min speed increaseand it is apparent that the new engine set an immediatetask of 3.0 dBA reduction if existing York ID1 baseengine noise levels are to be realized.Using experience gained from the York engine it waspossible to identify three major sources of noise whichrequired attention. The first task was to redesign thecylinder block structure to minimize noise transmissionand since the design of the new block was basically tothe same dimensions as the established production unitthere existed a bank of information from which to feed.Using this, and undertaking a programme of vibrationstudies in the 500-3000Hz frequency range on a blockand head assembly, enabled comparison with resultsobtained from finite element studies (3). After modalcorrection and allowing for material thickness varia-tions results correlated to within 10 per cent. With thisplatform established it was possible to rearrange thestructure in the computer model to increase the struc-tural stiffness in the areas of maximum noise transmis-sion. As a result the oil pan rail was stiffened and twolongitudinal webs were placed strategically on the lefthand side of the outer surface. In all 23 kg of materialwere repositioned from non-critical to more beneficialareas. The effect of these changes is a reduction of 1dBA of noise emanating from the block.Specifying an expansion controlled piston is also amain contributor to the base engine noise reduction andconsiderable development work was directed to achieveminimum running clearance of the profile turned pistonskirt and minimum clearances down to 15 pm areachieved. In base engine noise terms it is assessed that0.75 dBA reduction can be attributed to the pistondesigns adopted.Finally attention turned to the front of the enginewhich was identified as a major source of noise emis-sion. Test work identified that noise was being radiatedfrom the crankshaft and the ancillary drive pulley. Inconsequence a new integral torsional vibration damperwhich includes both the primary drive sprocket and theQ IMechE 1985

ancillary pulleys has been designed. A further reductionwas achieved by blanking off the fixing bolt aperturewith a simple neoprene plug which creates a flat surfaceat the front of the pulley. The overall effect is to reducetotal engine noise by 1-13 dBA while at the front of theengine the noise is reduced by 34dBA.

7.2 Subjective noiseIt was always known that the noise characteristic of theHSDI engine would be different to the ID1 engine it wasreplacing. At programme approval this was recognizedas a concern but considered acceptable. However, afterseveral full prototype appraisals at the mid-programmepoint, it was established that improvements to in-vehicle noise would be required before the engine wouldbe acceptable in a competitive market.The condition could not be overcome by mechanicalchanges or cost effective palliative treatments to thevehicle installation. The problem had to be tackled byattention to the combustion process, and in particularthe development of a more retarded fuel injection. Thiswas not possible immediately since the engine wassmoke limited in the upper speed range. The firstrequirement therefore, was to get more air availableabove 3500 r/min without loss of swirl; this wasachieved by the intake port modification describedearlier.The new port gave the flexibility of manoeuvrerequired and by moving the maximum torque speedslightly up the speed range, fuel at the bottom was con-trolled to ensure that smoke would not be a problem.It was possible to adjust the injection timing curve tothe most retarded smoke limited condition for eachpoint of the speed range. This resulted in the develop-ment of the full and light load advance curves discussedearlier. The resulting specifications give a very accept-able in-vehicle subjective noise level.

8 PROGRAMME AND PERFORMANCE SUMMARYExcluding the pre-programme viability studies thedevelopment programme was completed in two majorstages of engine builds covering 128 units. All individualengine systems were developed by specific work prog-rammes designed to over-test and expose design weak-nesses; once these had been satisfied complete enginesets were built for final durability prove-out. In all, over110000 hours of dynamometer test and 700 OO km ofvehicle operation were accumulated on prototypeengines. Further extensive testing was carried out by themanufacturers of the proprietary parts specified bothduring prototype and early production stages to ensurethat the individual components met the engineering spe-cification.

Two lengthy periods of cold climate vehicle testing inFinland were used to verify cold start, cold running andheater performance. The Scandanavian climate is alsovery good for assessing subjective interior noise, andteams of engineers took part in drive appraisals, toverify the final level of engine performance.Production of the 2.5 litre HSDI commenced at theDagenham engine plant, in February 1984, after a six-month period of extensive pre-production validation

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G L BIRD22r

50-

40-

20-10-

310290

1 2 5 070 21%230

1000 2000 3000 4OOOr/minFig. 10 BSAU 141a full load power curve

testing involving over 200 engines. The validation prog-ramme, which covered every aspect of performance andreliability testing, provided the statistical prove-out ofthe engineering designs.The engine is certified at 52 kW at 4OOO r/min andFig. 10 gives the BS AU14la performance curves. Thebest specific output of 237 gm kWh occurs at 2000r/min, but a better indication of the fuel economy isshown in Fig. 11 which gives the total fuel consumptiondata in map form.

I II I I I rI I500 2000 2500 3000 3500 4OOO 4500

Engine speedr/min

Fig. 11 Fuel consumption map

In-vehicle fuel economy has been optimized by select-ing new ratios for the four-speed transmission and theintroduction of an overdrive option. Using these, with anew 3.9 :1 rear axle ratio in a Transit 120 van, gave fuelconsumptions of 7.8 and 7.6 1/100 km (36.2 and 37.2mile/gal) when driven through the ECE 15 urban cycleand 90 km/h steady speed test.Engine starting is good at all temperatures and canbe executed by just turning the ignition key. At - 0Cstarting is achieved within ten seconds, while at - 0"C,with the time controlled fast flame aid, is extendedslightly to twenty seconds, an improvement of 15-20seconds over ID1 engines with inchamber glowplugs.Finally, a word about gaseous emissions.The engine meets the current European legal require-ment as specified by EEC 15/04 with typical results astabled below.InertiaGlaSS RAR CO(g/m) HC +NO, (g/m)

1810 kg 3.91 9.4 15.6Legal limit - 93.0 25.0If more stringent requirements are specified in futureyears, the HSDI engine is capable of meeting the chal-lenge especially in the higher inertia weight categorieswhere exhaust gas recirculation (EGR) will be a require-ment for all diesels to meet the stringent NO, levels.Recognizing that EGR tends to increase particulates,this is generally more problematical in indirect injectionengines.

9 CONCLUSIONAs the world's first volume production high-speed directinjection engine, the Ford 2.5 litre engine has demon-strated that the fuel efficient diesel still has great poten-tial as an automotive power unit.ACKNOWLEDGEMENT

The author acknowledges the contributions made by allthe engineering groups within Ford Motor Companywho made this project possible, and in particular thededication and support of Messrs W. edwell and D.Neil.Acknowledgement is also due to consultants A. V.List and the fuel injection equipment manufacturersLucas CAV and Robert Bosch, and the engineeringstaffs involved throughout the programme, for theirsupport and perseverance.

REFERENCESCartel l ien, W. and Scbukoff, H. Direct injection as a combustionsystem for light duty diesel. FISITA Congress, 1978.Tippelmaan, G. A new method of investigation of swirl ports. SA EPaper No. 770404, 1977.Johnsoa, R. W. A computer-aided engineering approach to thereduction of light duty diesel engine noise. Diesel enginesfor pass-enger cars a d ight duty vehicles, IMechE Conference, 1982, C123/82, pp 119-124.

Proc Instn Mcch Engrs Vo l 199 No D2 Q IMechE 1985


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