fuel injection and egr systems control in … fuel injection and egr systems control in a common...

03A2034

FUEL INJECTION AND EGR SYSTEMS CONTROLIN A COMMON RAIL DIESEL ENGINE

M. Capobianco, M. Montini, G. Zamboni - Department of Thermal Machines, EnergySystems and Transportation (DIMSET) – ICE Laboratory – University of Genoa – Italy

Abstract

A wide experimental investigation was performed on the engine test bench at the InternalCombustion Engines Laboratory of the Department of Thermal Machines, Energy Systems andTransportation of the University of Genoa in order to study the influence of fuel injection system(FIS) and exhaust gas recirculation (EGR) control on operating parameters and exhaust emissionsof an automotive Direct Injection (DI) Diesel engine fitted with a Common Rail FIS, a waste-gatedturbocharger and an uncooled EGR system. Referring to engine part load operating conditions,related to the European driving cycle, different control variables were taken into account: pilot-maininjections dwell angle, pilot injection energising time, fuel pressure and EGR rate. The mainexperimental results are presented and discussed in the paper, focusing on the influence of controlvariables both on fuel consumption, pollutants and smoke emission and on other engine operatingquantities.

Nomenclature

Notation

bmep brake mean effective pressurebsfc brake specific fuel consumptionf mass fractionm specific mass emissionn rotational speedp pressuret temperatureAFR air-fuel ratioFSN Filter Smoke NumberECU electronic control unitEGR exhaust gas recirculationET injector energising timeTDC Top Dead Centreθ crank angle

Subscript

main main injectionpilot pilot injectionrail fuel railE engine exhaust, turbine inletEGR exhaust gas recirculationI engine intakeMAX maximumNOx nitrogen oxides

Giorgio

Casella di testo

4th International Conference on "Control and Diagnostics in Automotive Applications", CDAUTO03, ATA, Sestri Levante, 6/2003

S sootTC turbocharger

1 – Introduction

The Direct Injection (DI) Diesel engine is gaining an increasing share of the European passengercar market, due to its low fuel consumption (and related CO2 emission) and to the advantages ofelectronically controlled Fuel Injection System (FIS) based on the common rail technology, whichallows to improve torque and drivability and to reduce engine noise.

Automotive DI Diesel engines are usually fitted with turbochargers and Exhaust GasRecirculation (EGR) systems: engine management has therefore to take into account therequirements of all the components involved in order to fully exploit their potential and to complywith the different requirements in terms of performance, fuel consumption and pollutant emissions.To get this goal, a deep knowledge of FIS, turbocharger and EGR system behaviour and of therelated interactions is necessary and on-engine experimental investigations can be very useful toachieve a better understanding of the whole system.

A dedicated study was performed on the engine test bench at the Internal CombustionEngines (ICE) Laboratory of the Department of Thermal Machines, Energy Systems andTransportation of the University of Genoa on an automotive DI Diesel engine fitted with a commonrail FIS, a waste-gated turbocharger and an uncooled EGR system. In the paper, the results ofexperimental tests aimed at the investigation of the effects of FIS and EGR systems control onengine operating quantities considering part load working conditions are presented and discussed,with particular reference to fuel consumption, pollutants and smoke emissions. Moreover, theinteractions between the involved systems are outlined, showing the reciprocal influence whenapplying different regulating strategies to the considered control parameters.

The analysis of experimental results confirmed that an integrated control of FIS and EGRsystems could be useful in order to comply with by-law exhaust emissions limits. However, afurther development of other engine components (such as turbocharger, aftertreatment, etc) and afull exploitation of the possibilities offered by the management of the whole engine system, withparticular reference to multiple injection strategies [1, 2, 3] will be necessary to meet futureemission standards (EURO 4).

2 – Engine Test Facility and Control System

The experimental activity was developed on an in-line 4 cylinders automotive DI Diesel engine,with a displacement of about 1.9 litre, fitted with a Common Rail injection system, an exhaustturbocharger with a waste-gated turbine, an intercooler and an uncooled EGR system.Measurements were performed through a dedicated test bench [4, 5], equipped with an eddycurrent dynamometer, exhaust gas analysers for carbon monoxide and dioxide, unburnthydrocarbons and nitrogen oxides, a variable sample smoke meter and an automatic dataacquisition and processing system, based on several instruments (multichannel scanner, highspeed A/D converter, digital storage oscilloscope, counter, etc) connected on an IEEE bus andcontrolled by a personal computer through a GPIB interface.

In each experimental point, the main engine operating parameters (i.e. engine rotationalspeed, brake torque and power, air and fuel mass flow rate, volumetric concentrations of exhaustpollutants, smoke, EGR rate, waste-gate valve opening degree, etc) were measured. Dataacquisition and post processing were carried out through dedicated virtual instruments developedin LabVIEW® environment.

The engine is controlled by an open electronic control unit (ECU) fitted with an EPROMemulator module (ETK 3.1 by ETAS®), in order to set engine operating parameters in real time.The ETK module is connected through a ETAS® MAC2F interface to a dedicated PC, in which aspecific software (VS100 by ETAS®) allows to edit all the curves and maps stored in the ECU, thusenabling proper changes of the available engine operating variables.

The maps taken into consideration within this experimental activity are related to the controlof the fuel rail pressure, the main injection advance, the pilot-main injections dwell angle, the pilot

energising time and the EGR set point. Generally, the selected levels of control variables areobtained through simple modifications of related maps, while EGR rate control is more complex:the air mass flow sensor fitted in the intake circuit measures the actual intake air providing thisvalue to the ECU, which compares it with the intake air set point level: on the basis of thecalculated difference, the duty-cycle of an electro-pneumatic valve is properly modified, thuschanging the EGR valve opening degree. In order to verify the actuated EGR rate (fEGR, defined asthe mass flow of recirculated gas divided by the total mass flow), the ratio between intake andexhaust carbon dioxide concentrations is calculated; if necessary, the intake air set point is thenmodified until the correct EGR rate is obtained.

3 – Investigation Programme

The application of electronics to Diesel engine management has rapidly increased the number ofavailable control variables, since through the use of an open control unit it is possible to changethe level of engine operating parameters in a quite simple way. Among the items that the enginemanagement through an open ECU involves, three different aspects can be quoted: first of all, thechoice of the engine subsystems and of the relevant control variables for the scheduling of aninvestigation programme must be carefully performed, taking into account the objectives of thestudy and the engine operating conditions. The second aspect is related to engine optimisation, forwhich is now unavoidable to apply proper design of experiments techniques and statisticalprocedures [6, 7], in order to consider all the control parameters and bonds, to give reasonablepriorities to the different objectives through proper weights, to reduce the experimental work bymeans of models and so on. Finally, it is also more and more difficult to understand the enginebehaviour and to evaluate the influence of the different parameters on engine performance, fuelconsumption and emissions.

Starting from the above considerations, the investigation programme presented in the paperwas scheduled in order to comply with the following goals:• deepening of the knowledge about the effects of fuel injection and exhaust gas recirculation

systems control on engine outputs (with particular reference to fuel consumption and exhaustemissions) and about the interactions between these systems;

• enlarging the wide experimental database available at DIMSET ICE Laboratory on automotiveDiesel engines, previously focused on EGR and turbocharger control [4, 5, 7, 8];

• creating an information background to plan further on-engine tests applying more complex fuelinjection schemes (pilot or pre, main and post injections);

• applying and validating a proposed optimisation procedure [7] to reduce the number ofmeasurements when extending tests to other engine operating conditions.

To fulfil the previous requirements, a typical part load condition, related to on-vehicle engineoperation when performing the ECE15 + EUDC driving cycle [9], was selected (tab.1); pilotinjection parameters (energising time ETpilot and pilot-main injections dwell angle θpilot), fuel railpressure prail and EGR rate fEGR were selected as control variables. Different levels wereconsidered for each parameter, taking into account also the ECU baseline calibration (tab.1).

Tab.1 – Experimental operating condition and baseline calibration values

Engine rotational speed (n) 2000 rpm

Brake mean effective pressure (bmep) 2.0 bar

Fuel rail pressure (prail) 535 bar

Main injection advance (θmain) 4.5 deg BTDC

Pilot-main injection dwell angle (θpilot) 24.5 deg

Pilot injection energising time (ETpilot) 140 µs

EGR rate (fEGR) 27.0%

In order to simplify the tests and the results analysis, the investigation programme wasdivided in two steps: the first was focused on pilot injection and EGR control, considering a set of4x4 values of ETpilot and θpilot (tab.2) for three fEGR levels, while keeping prail and θmain constant attheir reference values (tab.1).

Tab.2 – Selected levels of pilot injection parameters and EGR rate

fEGR = 0, 15 and 30%

ETpilot [µs] θpilot [deg]

140 18 24.5 30 35.5

170 18 24.5 30 35.5

210 18 24.5 30 35.5

250 18 24.5 30 35.5

In the second phase of the investigation (tab.3), the effect of the fuel rail pressure controlwas analysed, considering four prail levels. In this case, only pilot-main injections dwell angle wasvaried, while ETpilot was kept constant at its reference value (tab.1).

Tab.3 – Selected levels of fuel rail pressure, pilot-main injections dwell angle and EGR rate

fEGR = 0, 15 and 30%

prail [bar] θpilot [deg]

400 18 24.5 30

535 18 24.5 30 35.5

670 18 24.5 30

800 24.5 30 35.5

In the following section the main results of the study are presented and discussed,according to the same scheme adopted for the tests.

4 – Analysis of Results

4.1 – Effect of Pilot Injection and EGR Control

The first step of the investigation was focused on the influence of pilot injection and EGR control onengine operating parameters and emissions (tab.2): experimental results referred to brake specificfuel consumption (bsfc), engine pumping pressure gradient (expressed through the pressuredifference pE–pI), turbocharger rotational speed (nTC) and air-fuel ratio (AFR) are presented in fig.1as a function of pilot-main dwell angle for different levels of pilot energising time and EGR rate;smoke and specific emissions of NOx, CO and HC are reported in fig.2.

A general consideration has to be pointed out introducing this analysis: bsfc variationswhen controlling FIS and EGR system variables are always limited to a few percent, thus requiringa further experimental validation of the observed trends, while changes in exhaust emissions levelsare probably higher than measurements errors or uncertainties due to shifts from control set-points, therefore outlining a more indicative behaviour.

At constant ETpilot and fEGR, an increase of pilot-main dwell angle generally leads to higherbsfc, especially for EGR rate equal to zero or 15 per cent, while trends related to other parameters(among which those presented, i.e., pE–pI, fig.1b, nTC, fig.1c, and air-fuel ratio, fig.1d) don’t show asignificant influence of θpilot, since they are quite constant or with slight variations. As regards the

turbocharger, it should be noted that the waste-gate valve was always fully closed in theconsidered operating conditions.

Fig.1 – Effect of control variables θpilot, ETpilot and fEGR on engine parameters

Fig.2 – Effect of control variables θpilot, ETpilot and fEGR on engine exhaust emissions

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The behaviour of bsfc is probably related to changes of the combustion process whencontrolling pilot injection characteristics, which causes variations of in-cylinder pressure and heatrelease.

As reported in [10] with reference to measurements on an automotive DI Diesel engine in asimilar operating condition, a lower θpilot value results in a higher value of pressure, due to areduction of the ignition delay for the main injection, with the maximum of heat release approachingTDC position. This result is confirmed by higher NOx emissions (fig.2a), especially for longer pilotinjection energising time, while the values of CO (fig.2c) and HC (fig.2d) emissions seems to provea good combustion development for the lowest pilot-main dwell angle level. A further qualitativeconfirmation is related to the observed decrease in combustion noise for θpilot = 18 degrees. On thecontrary, an increase of θpilot causes a shift of heat release after TDC [10] and a consequentreduction of maximum cylinder pressure and NOx emission (except for fEGR = 0 and ETpilot = 140µs); the little decrease of smoke (fig.2b) is perhaps related to this shift, since it probably results in abetter condition for soot oxidation.

ETpilot control while keeping constant θpilot and fEGR, doesn’t lead to a clear behaviour asregards fuel consumption, while its influence on other engine parameters is negligible. On the otherhand, significant variations of exhaust emissions were found, generally leading to an increase athigher ETpilot levels; the only exception is apparent for NOx specific emission (fig.2a) when θpilot isover 30 degrees (24.5 for fEGR = 0). In this case, different phenomena are involved (ignition delayand heat release for pilot and main injection, combustion duration, etc) with a more complexdevelopment of combustion: perhaps, the oxygen availability is locally reduced when increasingETpilot, thus leading to the observed trends.

The activation of EGR has significant effects on the whole engine behaviour, since it resultsin a decrease of all the presented parameters: lower nTC and AFR (fig.1b and 1c, respectively) arerelated to the reduction in intake air, which also justifies lower intake and exhaust pressure, withthe second one reducing more rapidly; this is probably due to the higher intake charge and exhausttemperatures, which partly compensate for the lower turbine inlet enthalpy [4, 5]. As aconsequence, pumping pressure gradient decreases when fEGR grows, with a benefit in bsfc(fig.1a).

EGR influence on NOx and exhaust smoke shows the expected trends (fig.2a and 2b,respectively), related to the lower oxygen availability and the lower local combustion temperaturecaused by the higher thermal capacity of the intake charge when recirculating part of the exhaustgases [11, 12]. On the contrary, CO and HC emissions trends (fig.2c and 2d, respectively), aresomewhat unexpected, since the reduction of in-cylinder oxygen concentration should result inhigher values; anyway, their decrease may be related to the above mentioned changes incombustion pattern which leads also to the observed better fuel consumption.

As regards the interactions between EGR and pilot injection control, the following pointscan be highlighted: the reduction in NOx emission (fig.2a) when increasing θpilot is less significantfor the highest EGR rate, while the intersection of NOx curves for different ETpilot and a fixed fEGRlevel, shifts to higher θpilot values when EGR rate increases; this may be related to a reducedignition delay of the fuel quantity introduced in the pilot injection, due to higher intake temperature.Finally, it is evident from fig.2b that the increase in exhaust smoke levels for different ETpilot isamplified by EGR: this is not related to air-fuel ratio (fig.1d), since it is not influenced by ETpilot forthe same EGR rate, but probably to a more complex development of combustion when pilotinjection is applied, with variable extension of the phases when soot is generated and oxidised.

An attempt to summarise the previous results, for example to select proper values of theconsidered control variables according to a specific objective, is shown in figs.3 and 4; the first isrelated to the trends of fuel consumption and NOx emissions (figs.3a and 3b) and to the trade-offbetween soot (mS, evaluated on the basis of measured smoke levels through an empiricalcorrelation) and NOx emissions (figs.3c and 3d), considering a value of pilot injection energisingtime (140 and 250 µs) for each graph, while each curve is related to a different level of pilot-maindwell angle; EGR rate increases from right to left.

As previously outlined, there is no a clear trend for bsfc: for ETpilot = 140 µs, the lowestvalues are obtained for the minimum dwell between pilot and main injection (fig.3a), while it is notpossible to identify a similar curve for ETpilot = 250 µs (fig.3b).

Fig.3 – Trade-off between bsfc, NOx and soot specific emissions (θpilot as a parameter, two levelsof ETpilot)

Fig.4 – Trade-off between bsfc, NOx and soot specific emissions (ETpilot as a parameter, two levelsof θpilot)

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An easier analysis is possible for soot and NOx emissions trade-off, since the best curve isobtained for the maximum pilot-main dwell angle, while higher values are obtained when θpilot

decreases, for both the considered energising times; however, for ETpilot = 140 µs trends are muchcloser, with a smoother slope and with lower values, especially for mS.

Results reported in fig.4 show a different choice of parameters: graphs of bsfc – NOx trendsand mS – mNOx trade-off are related to two values of pilot-main dwell angle (θpilot = 18 deg, figs.4aand 4c, and 30 deg, figs.4b and 4d) for all the considered levels of ETpilot, always with EGR rateincreasing from right to left.

While confirming once again the complex behaviour of fuel consumption, the best curvesfor soot and NOx emissions trade-off are generally obtained for the lowest value of pilot energisingtime; for θpilot = 30 deg trends are almost superimposed, with a smoother slope and with lowervalues especially for mS.

4.2 – Effect of Fuel Rail Pressure and EGR Control

The second phase of the investigation programme was related to the study of the influence of fuelrail pressure and exhaust gas recirculation control on engine performance and emissions, fordifferent values of pilot-main dwell angle (tab.3).

In fig.5 the effects of prail on brake specific fuel consumption, turbine inlet temperature tE,CO and NOx specific emissions are presented as a function of θpilot, for fEGR = 0.

For the minimum pilot-main dwell angle, an increase in prail corresponds to lower bsfc andhigher mNOx values, since a better fuel atomisation probably leads to an increase in mass burningvelocity during the first part of combustion and to a reduction of the total burning angle [9, 13]: as aconsequence, the fuel is burned when the instantaneous cylinder volume is smaller and a higherpressure is achieved, strongly influencing the observed trends related to fuel consumption (fig.5a)and NOx emission (fig.5d) and probably resulting in a lower exhaust temperature (fig.5b).

Fig.5 – Effect of control variables prail and θpilot on engine parameters and exhaust emissions

When θpilot increases over 30 degrees, the influence of prail on bsfc is opposite to the onepreviously outlined, while again growing levels of mNOx can be observed; furthermore, a rapid

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growth of CO emissions is achieved. In these conditions different aspects are involved, the main ofwhich can be summarised as follows:• the increase in prail is related to a better spray atomisation, a faster heat release and a reduced

combustion duration;• another consequence of higher prail is the higher combustion noise, resulting from a qualitative

observation, related to a different heat release law;• since ETpilot is constant, for higher fuel rail pressure the pilot injected quantity grows

significantly;• in order to obtain the requested effect of the pilot injection (i.e., a decrease of main injection

ignition delay and a lower peak in heat release) pilot-main dwell angles have to be properlyselected; as outlined by other authors [10, 14], when θpilot increases, it is possible to reach acondition in which there is no ignition of the pilot injected quantity, since its delay is soextended that fuel-air mixture is too lean to burn; in this case, main injection ignition delay and,consequently, maximum heat release increases;

• according to different pilot and main injection ignition delay values, combustion approaches orgoes away from TDC; it seems difficult that burning of the main injection may occur beforeTDC, even if this event cannot be completely excluded.

As regards worst bsfc and NOx emission for high levels of θpilot and prail, it must be probablyconsidered that a great quantity of fuel is delivered during the pilot injection without igniting, thusaffecting fuel consumption, and then resulting in higher maximum in-cylinder pressure and heatrelease, due to an extended main injection ignition delay. The combustion duration and shift arerelated to the significant variations of exhaust temperature shown in fig.5b, which probably lead tothe increase in emissions of carbon monoxide, since a reduced time is available for its completeoxidation.

Further aspect are involved when activating exhaust gas recirculation [11, 12], but trendsreported in fig.5 are generally confirmed: for a more detailed analysis, experimental values of maininjection energising time (ETmain), turbocharger rotational speed, air-fuel ratio and engine pumpingpressure gradient are reported in fig.6 as a function of pilot-main dwell angle for different levels offuel rail pressure and EGR rate, while fig.7 is related to bsfc, NOx, smoke and HC emissions.

Fig.6 – Effect of control variables prail, θpilot, and fEGR on engine parameters

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As regards prail influence at constant θpilot and EGR rate, ETmain shows the expected trends,reducing when prail grows, while it is apparent that slightly lower turbocharger speed (fig.6b) andair-fuel ratio (fig.6c) are obtained when increasing prail (especially without EGR), probably due to areduction of the available energy at the turbine inlet related to the decrease of exhaust temperature(fig.5b): pE–pI gradient is quite not affected by prail control. EGR and θpilot effects on engineoperating parameters confirm the analysis of the first part (see 4.1).

Finally, fig.7 proves that, for the developed tests, EGR has generally a positive influence onbsfc (fig.7a) and HC emissions (fig.7d) for each considered fuel rail pressure value, NOx emissionis affected by fEGR and prail as previously discussed (fig.2a and 5d, respectively), while, as regardssmoke (fig.7c), increasing prail allows to reduce it significantly, even for the highest EGR rate, dueto the better fuel atomisation.

Fig.7 – Effect of control variables prail, θpilot, and fEGR on engine bsfc and exhaust emissions

Fig.8 – Trade-off between bsfc, NOx and soot specific emissions

In fig.8, the trade-off between fuel consumption, soot and NOx emissions are presented,with each curve related to different levels of fuel rail pressure and pilot-main dwell angle, while

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EGR rate increases from right to left. The first graph shows that EGR considerably decreases NOxemissions without affecting, in this case, fuel consumption, while at constant EGR rate, increasingfuel rail pressure causes a worst bsfc and higher mNOx. The positive effects of increasing prail areclear from soot – NOx trade off, where, in spite of an increase in mNOx, mS values are considerablylower. As expected, an increase of EGR rate causes higher soot emissions, more evident for lowerfuel rail pressure levels.

5 – Conclusions

The wide experimental investigation described in the paper, developed on the engine test bench atthe Internal Combustion Engines Laboratory of the Department of Thermal Machines, EnergySystems and Transportation of the University of Genoa referring to a DI Diesel engine fitted with aCommon Rail fuel injection system, outlined some interesting hints on the influence of pilotinjection, fuel rail pressure and EGR control on fuel consumption and exhaust emissions. In a fixedengine working condition, related to the ECE15 + EUDC driving cycle, a great number ofexperimental points were considered in a two-steps study, applying different levels of pilot-maininjections dwell angle, pilot injection energising time, fuel rail pressure and EGR rate.As regards the first phase, the main conclusions about the influence of the pilot injection andexhaust gas recirculation control on engine operating parameters can be summarised as follows:• the increase of pilot-main dwell angle, at constant level of other control parameters (i.e., EGR

rate and pilot energising time) leads to higher specific fuel consumption and lower NOx specificemission, probably due to an extended pilot ignition delay causing a shift of heat release afterTDC and consequently a reduction of maximum cylinder pressure and temperature;

• these behaviours are confirmed when increasing pilot injection energising time, since theinjected quantity during the pilot injection is greater;

• when activating exhaust gas recirculation, the expected reduction of NOx emission and theincrease of exhaust smoke emissions are achieved, while, at the same time, the enginepumping pressure gradient decreases, with benefits on bsfc; at higher EGR rates, also lowervalues of HC and CO were measured, probably due to a positive influence of EGR oncombustion behaviour in the considered working conditions.

With reference to the second phase of the investigation, the following considerations weredeveloped with reference to the interaction between pilot-main injections dwell angle, fuel railpressure and EGR rate:• the influence of fuel rail pressure control at different levels of pilot-main injections dwell angle is

very complex, since its increase leads to an improvement of bsfc for lower θpilot, while fuelconsumption and NOx emission grows for higher values of both control variables. These trendsare probably related to different counteracting effects (extended main and pilot injectionsignition delay, faster heat release, combustion shift within the expansion stroke, etc), which arefurther complicated by EGR activation;

• as expected, exhaust smoke emissions values are significantly lower when increasing fuel railpressure, due to a better spray atomisation;

• for higher EGR rate, similar trends are highlighted, with slight advantages in bsfc and littleincrease in smoke emissions.

The study confirmed that an integrated control of FIS and EGR systems can be a very powerfultool in order to improve engine behaviour and performance. However, the development of suitablecontrol strategies requires a careful selection of objectives, control variables and operating limits,for which it is now unavoidable to find a strong support in design of experiments techniques andstatistical procedures. A further development of this investigation will therefore be the application ofoptimisation procedures to more complex scheme of fuel injection strategies (pilot or pre, main andpost injections), always taking into account exhaust gas recirculation and turbocharging systemscontrol.

ACKNOWLEDGEMENTS

This work was developed within the project “Development of new methodologies for the definition

of strategies for management, control and diagnostic of intake and exhaust system of automotiveI.C.Engines”, with the financial support of the MIUR (PRIN, year 2001).

References

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[4] Capobianco M., Gambarotta A., Zamboni G., Experimental Characterisation of Turbochargingand EGR Systems in an Automotive Diesel Engine, 3rd International Seminar on Application ofPowertrain and Fuel Technologies to Meet Emissions Standards for the 21st Century, paperC517/027/96, Institution of Mechanical Engineers, London, 1996.

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[8] Capobianco M., Gambarotta. A., Silvestri P., Zamboni G., Turbocharger and EGR ControlStrategies in an Automotive DI Diesel Engine, 2nd International Conference on “Control andDiagnostics in Automotive Applications”, CDAUTO98, Genova, 1998.

[9] Borrione S. M., Capobianco M., Zamboni G., On the Control of the Turbocharging System in aCommon Rail DI Diesel Engine, 3rd International Conference on “Control and Diagnostics inAutomotive Applications”, CDAUTO03, paper 01A3036, ATA, Sestri Levante, 2001.

[10] Carlucci P., Ficarella A., Laforgia D., Effects of Pilot Injection Parameters on Combustion forCommon Rail Diesel Engines, The SAE 2003 World Congress, Detroit, USA, 2003.

[11] Plee S. L., Ahmad T., Myers J. P., Flame Temperature Correlation for the Effects of ExhaustGas Recirculation on Diesel Particulate and NOx Emissions, SAE paper 811195, 1981.

[12] Ladommatos N., Abdelhalim S. M., Zhao H., The Effects of Carbon Dioxide in EGR on DieselEngine Emissions, 3rd International Seminar on Application of Powertrain and FuelTechnologies to Meet Emissions Standards for the 21st Century, paper C517/028/96,Institution of Mechanical Engineers, Londra, 1996.

[13] Badami M., Nuccio P., Trucco G., Influence of Injection Pressure on the Performance of a DIDiesel Engine with a Common Rail Fuel Injections System, SAE paper 1999-01-0193, 1999.

[14] Tennison P.J., Reitz R., An Experimental Investigation of the Effects of Common-Rail InjectionSystem Parameters on Emissions and Performance in a High-Speed Direct-Injection DieselEngine, ASME Journal of Engineering for Gas Turbines and Power, Vol.123, pages 167 – 174,January 2001.

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