Measure of Friction losses on Common Rail Engine

Seoul 2000 FISITA World Automotive CongressJune 12-15, 2000, Seoul, KoreaF2000A057<strong>Measure</strong> <strong>of</strong> <strong>Friction</strong> <strong>losses</strong> on Common Rail EnginePHILIPPE JOLY 1) * STÉPHANE LAFOND 2) * NICOLAS CROTTÉ 3)1),3) SAEM - D2T Z.A. de Trappes-Elancourt 11 Rue Denis Papin 78190 Trappes, France2) BSF - D2T Z.A. de Trappes-Elancourt 11 Rue Denis Papin 78190 Trappes, FrancePast years, the decreasing <strong>of</strong> friction <strong>losses</strong> has been an essential factor in fuel consumption improvement <strong>of</strong> internalcombustion engines and would be the key to reach the targets <strong>of</strong> lower CO 2 requirements in the beginning 2010’s.Nevertheless, improvements are going to be always lower and tests have to be more precise and decrease torquemeasurement error.A solution consists in using a test bench equipped with an eddy current dyno for the positive torque phases coupled with amiddle power electrical machine driving the engine.The torque measurement is realised by the balance mounting <strong>of</strong> both Eddy curent dyno and electrical machine. Thismeasurement is permanently doubled by a torquemeter installed on the transmission shaft coupled with the crankshaft. Thisprocess allows to obtain the exactitude <strong>of</strong> the measured torque value.This solution provides some great precision in friction <strong>losses</strong> measurements on the low torque values and keeps also theability to do any measurements in positive torque values to validate specific consumption disparities between differenttechnological solutions.Realised tests show that such a system is able to measure the influence <strong>of</strong> piston rings or any other part <strong>of</strong> the engine, <strong>of</strong>which evolutions can have low incidences on the friction <strong>losses</strong>.The results analysis shows advantages and drawbacks <strong>of</strong> the two torque measurement systems, and the repeatability androbustness <strong>of</strong> results both concerning friction <strong>losses</strong>.Keywords: Common rail, <strong>Friction</strong> <strong>losses</strong>, Diesel enginesINTRODUCTIONIn order to reduce CO 2 emissions, carmakers and supplierswere taken to a point where they have to explore anyimprovement way which could reduce fuel consumption.Even if recent improvements <strong>of</strong> injection systems haveallowed to reduce those emissions, engine friction <strong>losses</strong>decrease is still an unavoidable stage. Though enginepassive <strong>losses</strong> improvements were respectable during thelast decade, the next ones will be less considerable andmore difficult to quantify. As a result measurement meansmust be more and more accurate. To this end, D2T grouphas developed a simple and reliable measurement processwhich allows to evaluate small torque in order to show theeffect <strong>of</strong> engine constitutive parts on passive <strong>losses</strong>.With this study the quality, the repeatability and thereproducibility <strong>of</strong> two friction torque measurement meanscan be compared. Moreover, the use <strong>of</strong> passive <strong>losses</strong>measure methodology allows us to evaluate the influence<strong>of</strong> the constitute parts <strong>of</strong> a common rail series engine onpassive <strong>losses</strong>.MATERIAL DESCRIPTIONPassive <strong>losses</strong> measurement requires a machine whichallows the engine driving without combustion. Thesolution developed for these specific applications isconstituted <strong>of</strong> an eddy current dyno for the positive torquephases coupled with a middle power electrical machine forthe negative torque phases. This allows to divide thebraking and the driving function. The main advantage <strong>of</strong>this configuration is the optimisation <strong>of</strong> the electricalmotor (in order to dispose <strong>of</strong> the necessary power to drivethe internal combustion engine) and a low inertia and highspeeddirect-current motor.As a matter <strong>of</strong> fact, the necessary driving power is lessimportant than the necessary breaking power. So ourapplication is a compromise which allows the use <strong>of</strong> a lowinertia direct-current motor which driving power is 70 kWand the use <strong>of</strong> a 220 kW brake. The accelerations <strong>of</strong> themachine are approximately 2500 rpm/s and importantenough for this application.Tandem bench caracteristics:1

Inertia: 0.35 m 2 kgBraking torque : 610 N.mBraking power : 220 kWDriving torque : 133 N.m (Constant up to 5000rpm)Driving power : 70 kWMaximum speed : 7500 rpmA torquemeter (cramp pattern without ball-bearing) is seton the dumb-bell shaft between the engine and the eddycurrent dyno in order to establish the correlation betweentorque measures.heated with conditioners set up in the engine test bench.Once temperature choice made, a two minutes stabilityperiod is necessary before the acquisition <strong>of</strong> the workingconditions parameters.Past tests showed a significant influence <strong>of</strong> the oil level.To free this parameter, the engine oil quantity is fixed at 4liters and the oil grade is 15W40 whatever the test (Fig.2).6.565.5Oil temperature influence on the Mean friction pressureTemperature difference 25/80Temperature difference 80/110Oil at 298캩Oil at 353캩Oil at 383캩403530525M.F.P. (bar)4.5420Difference (%)153.53102.552R□ ime 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250Engine speed (rpm)0Fig.1Grade oil influence on the Mean <strong>Friction</strong> Pressure54.03.53.0<strong>Friction</strong> <strong>losses</strong> measurement requires engine fluid heaterfor oil or engine cooling fluid. The system designed forthis application is made <strong>of</strong> heating resistors set inpressurised tanks. The resistors <strong>of</strong> the oil circuit areequipped with temperature probe set on the superficialfaces in order to avoid any risks <strong>of</strong> oil destruction. Anengine fluids external circulation is unavoidable in order totest the engine without these elements. This function isperformed by circulation pumps equipped with frequencyvariator which can be short-circuited if the engine partsmust be used. The heat exchangers <strong>of</strong> oil and enginecooling liquids are set in the bench. Both temperatures andcooling fluid flow rate can be controlled.Oil and cooling fluid caracteristics :Heating power <strong>of</strong> cooling fluid circuit : 24 kWHeating power <strong>of</strong> oil circuit : 12 kWMaximum oil temperature : 418 KMaximum cooling fluid temperature : 398 KMaximum oil pressure : 6 barTESTING METHODOLOGYBecause <strong>of</strong> the bond between passive <strong>losses</strong> and oilviscosity, engine temperature conditioning is a crucialpoint for the validity measure before any acquisition (Fig1).In order to free this influence, the temperature <strong>of</strong> bothengine cooling system liquids and oil is controlled andM.F.P. (bar)43210800 1000 1500 2000 2500 3000 3500 4000 4500Engine speed (rpm)Fig.2Gain: 10W40 / 15W40Working condition parameters are computer recorded inthe test bench during 20 seconds and then averaged. Testbench operators can evaluate the validity <strong>of</strong> their measurewith torque or engine speed stability criterions.For each working condition, 3 measures is taken by theoperating system and the test bench acquisition system.With stability criterions, these measures are statisticallyprocessed in order to determine the best point.For a determined engine configuration, passive <strong>losses</strong> arealways measured in terms <strong>of</strong> engine speed from high speedto idling speed in order to hold the thermal conditions inan easier way.Before any new test, the bench operator checks the zerotorque in order to detect a possible drift <strong>of</strong> the sensor orthe measurement channel.Calibration is checked daily with calibration arm andsprung masses for the brake and the machine and with anelectrical system for the torquemeter set on the dumb-bellshaft.15W4010W402.52.01.51.00.50.0-0.5-1.0-1.5-2.0-2.5-3.0-3.5-4.0-4.5-5.0gain (%)2

MEASUREMENT QUALITY.The torque measurement incertitude is known (+/- 0.25N.m for the balanced machine and +/- 0.2 N.m for thetorquemeter) for both methods. Repeatability dubiousnesswas determined in order to evaluate their capability tomeasure passive <strong>losses</strong>.Comparaison des incertitudes de r□ □□abilit□ □ entre le montage en balance et la mesure au couplem□ reIncertitude de r□ □abilit□□95% du montage en balance : +/- 0.31 N.mIncertitude de r□ □abilit□□95% du montage avec couplem□ re : +/- 0.25 N.mSigma montage avec couple-□Sigma montage en balance0-0.10.1Repeatability <strong>of</strong> measurement means and testsThis dubiousness is statistically determined by calculation<strong>of</strong> differences between two passives <strong>losses</strong> curvesestablished with the same engine configuration (6 differentconfigurations were tested) (Fig.3).-0.5-0.4-0.3-0.2Montage en balanceCouple-m□ re0.20.30.40.5Fig.4Torque (N.m)25Repeatability <strong>of</strong> torque measurmentDiff□ ence(N.m)0.30Reproducibility <strong>of</strong> measurement means and tests0.20200.10150.0010-0.105-0.200-0.30800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400Engine speed (tr/min)Essai 1 Essai 1 Essai 6 Essai 6 Ecart 1 Ecart 6The reproducibility <strong>of</strong> a test is determined with differentengines supposed equivalent except the dispersion <strong>of</strong>engine parts machining , tightening torque and thicknessseals.During our tests, this method has not been employed.Nevertheless, to reinforce the credibility <strong>of</strong> our measures,we compare the friction <strong>losses</strong> <strong>of</strong> engines before and aftertheir analyze. The figure 5 shows the results and thecalculated dubiousness.Fig.380Reproducibility <strong>of</strong> torque measurment0.4Let A be a sample :A = ( a , a2,... a i,... a )Let a' be the mean value1 nTorque (N;m)70605040Reproducibility at 95 % : 0.4 N.m0.30.20.10-0.1-0.2Difference (N.m)30-0.3a'=n∑ a ii=1Let σ be the standard deviation :σ =n∑i=1( a'−ai)n −1So the dubiousness repeatability at 95% is +/- 2 σ.The figure 4 shows the distribution <strong>of</strong> the differencesbetween the measures. We can determine that thedubiousness <strong>of</strong> the balanced machine is +/-0.43 Nm andthe torquemeter is +/-0.3 Nm.220500 1000 1500 2000 2500 3000 3500 4000 4500Engine Speed (tr/min)Begin analyse End analyse DifferenceFig.5In consideration <strong>of</strong> our repeatability results with the twomeasurement means, we have chosen the torquemeter. Itsmost positive aspect is that the measure is absolutelyindependent <strong>of</strong> the possible mechanical problems <strong>of</strong> themachine or the brake.RESULTS AND DISCUSSIONThe engine tested and which results are presented is a 2liters Common Rail engine. These results are compared-0.43

with another direct injection engine equipped with amechanical injection pump, and an indirect injectionengine.4.54<strong>Friction</strong> <strong>losses</strong> comparaisonIDI Complete versionHDI Complete versionThe wearing period was established with a 15 hours cycle<strong>of</strong> different engine speed and load. This cycle wasrepeated until the stability <strong>of</strong> fuel consumption and friction<strong>losses</strong>. This engine was considered stabilized after 100hours.The stage by stage cutting up <strong>of</strong> the Common Rail engineshows the influence <strong>of</strong> the different constitutive parts. Thefriction <strong>losses</strong> repartition is the following:• The moving parts represent 20 % <strong>of</strong> the global friction<strong>losses</strong> and 0.5 % for crankshaft.• The cylinder head, the pumping and the timingrepresent 50 %• The intake and exhaust <strong>losses</strong> represent 20 % and18 % because <strong>of</strong> the turbocharger and the exhaustaerodynamic <strong>losses</strong>• Balance is due to accessories.To be more precise, the tests show that the friction torquegenerated by the top ring can grow up to 2N.m and that itis responsible for 3% <strong>of</strong> the global friction <strong>losses</strong>.Comparison between direct injection, commonrail and indirect diesel engineBecause <strong>of</strong> the accessories and engine parameterdifferences, the comparison between these 3 diesel enginetechnologies is not easy. Nethertheless tests show thatsome implicit rules can be drawn from results.All the results go to prove the importance <strong>of</strong> the <strong>losses</strong> <strong>of</strong>charge generated by swirl formation in a direct injectiondiesel engine (Fig. 6). Intake <strong>losses</strong> <strong>of</strong> charge grow up to20% less at 4000 rpm for an indirect injection engine thanfor a direct one. Even if the difference between the 2 directinjection engine is not huge, one can suppose that higherinjection pressure could decrease the swirl requirements.That could be why the Common Rail pumping <strong>losses</strong> areless important than the DI ones. But this result should beproved by other experiments, especially with a swirlmeasurement in these cylinder heads.As far as the moving parts are concerned, differencesmeasured cannot show any hierarchy between CommonRail and DI engines. Yet the friction <strong>losses</strong> due to themoving parts are less important for a direct injectionengine than for an indirect one.The working principle <strong>of</strong> a direct injection engine inducesthermal stresses that have drawn piston, rod, andcrankshaft to be heavier. As a result, their friction <strong>losses</strong>should be more important. Despite the indirect injectionengine generation is older than the direct one, so one canthink than technological progress have taken the level <strong>of</strong>this trend.M.F.P. (bar)3.532.521.510.50CONCLUSION1500 Engine speed (rpm)4000Fig. 6DI Complete verisonIDI pumping+intake+exhaustHDI pumping+intake+exhaustDI pumping+intake+exhaustIDI cranckshaftHDI cranckshaftDI cranckshaftIDI piston+rod+ringsHDI piston+rod+ringsDI piston+rod+ringsThe study driven on this engine has given data consideringthe choices and the testing means limits. The differencesmeasured during the stage by stage cutting up are sensitiveenough so that experiment planning is not necessary tocompare an engine to similar ones. Nevertheless, if the aim<strong>of</strong> the study is to evaluate mechanical <strong>losses</strong>, which aresmaller than the incertitude <strong>of</strong> repeatability orreproducibility, an experiment planning is unavoidable.Yet other ways can be explored such as amplification <strong>of</strong>phenomenon. For example, in order to compare thefriction <strong>losses</strong> generated by different top ring geometry, itis possible to increase the engine speed <strong>of</strong> the test or to usea special piston equipped with several similar top rings. Acomplementary solution could be the use <strong>of</strong> a torquemeterwhich sensibility is compatible with the measure.Oil and fuel consumption reduction and the correlationwith friction loss simulations will need furtherinvestigations in top ring geometry. To this end, this kind<strong>of</strong> testing bench is appropriated to keep abreast <strong>of</strong> thatdomain.REFERENCES[1] Heywood.J.B – 930p 1988a Mc Graw-Hill – NewYork. Internal combustion enginefundamentals[2] Young Cheng – SAE technical paper 982686 - The online estimation <strong>of</strong> the power performance and mechanical<strong>losses</strong> <strong>of</strong> engines.4