Estimation of Fuel Economy Improvement in Gasoline Vehicle Using Cylinder Deactivation

energies

Article Estimation of Fuel Economy Improvement in Gasoline Vehicle Using Cylinder Deactivation

Nankyu Lee 1 , Jinil Park 1,*, Jonghwa Lee 1 , Kyoungseok Park 2, Myoungsik Choi 3 and Wongyu Kim 3

1 Department of Mechanical Engineering, Ajou University, Suwon 16499, Gyeonggi, Korea; [email protected] (N.L.); [email protected] (J.L.) 2 Department of Mechanical System Engineering, Kumho National Institute of Technology, Gumi 39177, Gyeongbuk, Korea; [email protected] 3 Hyundai Motor Company, 150, Hyundaiyeonguso-ro, Jangdeok-ri, Namyang-eup, Hwaseong-si 18280, Gyeonggi-do, Korea; [email protected] (M.C.); [email protected] (W.K.) * Correspondence: [email protected]; Tel.: +82-31-219-2337

Received: 8 October 2018; Accepted: 6 November 2018; Published: 8 November 2018

Abstract: Cylinder deactivation is a fuel economy improvement technology that has attracted particular attention recently. The currently produced cylinder deactivation engines utilize fixed-type cylinder deactivation in which only a fixed number of cylinders are deactivated. As fixed-type cylinder deactivation has some shortcomings, variable-type cylinder deactivation with no limit on the number of deactivated cylinders is under research. For variable-type cylinder deactivation, control is more complicated and production cost is higher than fixed-type cylinder deactivation. Therefore, it is necessary to select the cylinder deactivation control method considering both advantages and disadvantages of the two control methods. In this study, a fuel economy prediction simulation model was created using the measurement data of various vehicles with engine displacements of 1.0–5.0 L. The fuel economy improvement of fixed-type cylinder deactivation was compared with that of variable-type cylinder deactivation using the created simulation. As a result of examining the fuel economy improvement of the test vehicle in the FTP-75 driving cycle, the improvement was 2.2–10.0% for fixed-type cylinder deactivation and 2.2–12.8% for variable-type cylinder deactivation. Furthermore, the effect of the engine load on fuel economy improvement under cylinder deactivation and the effect of changes in engine control were examined via a simulation.

Keywords: cylinder deactivation; vehicle modeling; pumping loss; vehicle fuel economy

1. Introduction Fuel economy improvement technologies have been studied actively and applied to vehicles to address problems such as fossil fuel depletion and greenhouse gas regulations [1–5]. Among such technologies, cylinder deactivation has attracted particular attention recently. Cylinder deactivation reduces the pumping loss to increasing load of working cylinders by deactivating some cylinders in the engine under medium load [6–8]. Various studies have been conducted on cylinder deactivation technology. More of them were focused on the cylinder deactivation mechanism [9–11], the noise, vibration, and harshness due to cylinder deactivation operation [12,13], misﬁre detection [14], or air fuel ratio control logic [15]. The fuel economy improvement of cylinder deactivation presented by previous studies was between 6% and 22%, and it signiﬁcantly varied depending on the characteristics and control of the applied vehicle [16–20]. In particular, the fuel economy improvement was much different depending on the cylinder deactivation control method. Depending on the vehicle, the fuel economy improvement differed by more than 10% point [21].

Energies 2018, 11, 3084; doi:10.3390/en11113084 www.mdpi.com/journal/energies Energies 2018, 11, 3084 2 of 12

The cylinder deactivation control method can be largely divided into the fixed type and variable type. The fixed-type cylinder deactivation deactivates only a fixed number of cylinders while the variable-type cylinder deactivation has no limit on the number of deactivated cylinders. For example, 6-cylinder fixed-type cylinder deactivation deactivates only three cylinders [22] and 8-cylinder fixed-type cylinder deactivation deactivates only four cylinders [23,24]. However, 8-cylinder variable-type cylinder deactivation can deactivate 1–7 cylinders depending on the operating conditions to maximize the fuel economy improvement [25]. While variable-type cylinder deactivation technology has a larger fuel economy improvement than the fixed-type method, its control logic is more complicated and the production cost is higher due to the increase in the operating unit. Although studies on the variable-type control method argue that the additional fuel economy improvement of more than 10% point is possible compared to the fixed type, a direct comparison is difficult because the fuel economy improvement value due to the control method is different as each researcher uses different vehicles and control logic. As such, this study aims to quantify the fuel economy improvement by control method under the same conditions. In particular, the focus was given to the fuel economy difference between the fixed-type control and variable-type control. For this, a fuel economy prediction simulation environment was created based on the actual vehicle data. Although fuel economy prediction simulation on cylinder deactivation was performed in previous studies [16,18,26], the control method was limited to the fixed type and studies on predicting fuel economy for the variable-type control are not available. Moreover, as modeling was performed using the engine efficiency data acquired through a static test, the results were somewhat different from the engine efficiency obtained from vehicles and it took a long time to acquire data for simulation. Other than the fuel economy depending on the control method, various influence factors affecting cylinder deactivation were derived and their influences were identified.

2. Modeling of Fuel Economy Prediction Simulation under Cylinder Deactivation In this study, accumulated driving cycle test data for vehicles with various speciﬁcations were used to identify the effect of cylinder deactivation. The primary physical modeling for vehicle performance was performed based on cycle unit cylinder pressure measurement data, and the modeling error was veriﬁed using driving cycle test results.

2.1. Test Vehicle Selection and Driving Cycle Test Data Analysis The test vehicle was selected as a gasoline vehicle which have engine with 3, 4, 6, or 8 cylinders. The engine displacement was determined to be 1.0–5.0 L depending on the number of cylinders. Their speciﬁcations are shown in Table1. Data were acquired by conducting the FTP-75 driving cycle test using the test vehicles. Data for simulation were summarized by analyzing the data acquired from the vehicle test.

Table 1. Speciﬁcations of test vehicles.

Speciﬁcation Vehicle 1 Vehicle 2 Vehicle 3 Vehicle 4 Volume (L) 1.0 2.4 3.3 5.0 ETW (lb) 2250 4000 4750 5000 Number of cylinders 3 4 6 8

The data for modeling was created such that the data between related variables were expressed in graphs by dividing the FTP-75 driving cycle test data into phases, and modes selected for each interval were connected using an interval linear fitting line. Figure1a shows the indicated mean effective pressure (IMEP) and thermal efficiency measured from vehicle testing. The thermal efficiency increased as IMEP increased at low loads. The thermal Energies 2018, 11, x FOR PEER REVIEW 3 of 12

EnergiesFigure2018, 11 1b, 3084 shows the relationship between IMEP and manifold absolute pressure (MAP).3 of 12 Although linear characteristics are generally expected between these two variables, a slight nonlinearity is observed owing to the thermal efficiency and intake air temperature. efﬁciencyFigure remained 1c shows at the a certain MAP leveland pumping at intermediate mean effective loads but pressure decreased (PMEP). as the MAP load wasand increasedpumping further.loss show These almost are linear typical char load-dependentacteristics, as efﬁciencyexpected. characteristics observed from gasoline engines.

50 100

40 80

30 60

20 40 MAP [kPa] MAP 10 Measured data 20 Measured data

Thermal efficiency [%] mode mode 0 0 2 4 6 8 10 2 4 6 8 10 IMEP [bar] IMEP [bar]

(a) (b) 1 Measured data 0.8 mode 0.6

0.4 PMEP [bar] PMEP 0.2

0 20 40 60 80 100 MAP [kPa]

(c)

FigureFigure 1.1. Test datadata analysisanalysis inin phasephase 33 ofof FTP-75; (a)) Modes of thermal efﬁciencyefficiency divideddivided by intervals; ((bb)) ModesModes ofof manifoldmanifold absoluteabsolute pressurepressure (MAP)(MAP) divideddivided byby intervals;intervals; ((cc)) ModesModes ofof pumpingpumping meanmean effectiveeffective pressurepressure (PMEP)(PMEP) divideddivided byby intervals.intervals.

FigureWhen1 theb shows data above the relationship are applied between to each IMEP test ve andhicle, manifold similar absolute overall patterns pressure are (MAP). observed. Although This linearimplies characteristics that similar fuel are generallyeconomy expectedimprovements between can these be obtained two variables, when cylinder a slight nonlinearitydeactivation isis observedapplied under owing the to same the thermal conditions. efficiency and intake air temperature. Figure1c shows the MAP and pumping mean effective pressure (PMEP). MAP and pumping loss show2.2. Development almost linear of Fuel characteristics, Economy Prediction as expected. Simulation When the data above are applied to each test vehicle, similar overall patterns are observed. The following two assumptions were used for the cylinder deactivation simulation in this study. This implies that similar fuel economy improvements can be obtained when cylinder deactivation is The first assumption is that the base engine control is applied regardless of cylinder deactivation applied under the same conditions. operation if the air amount per cylinder is the same. In other words, although the optimal values may 2.2.be different Development during of Fuel cylinder Economy deactivation Prediction operation, Simulation it is inevitable to assume that the differences are not significant because such values cannot be confirmed in the engines. TheThe followingsecond assumption two assumptions is that the were same used vehicle for the speed cylinder and deactivationload are used simulation in the simulation. in this study. This impliesThe that first the assumption same braking is that torque the base andengine enginecontrol speed are is applied applied. regardless Under these of cylinder assumptions, deactivation the net operationindicated ifmean the air effective amount pressure per cylinder (NMEP) is the must same. be In the other same words, before although and after the cylinder optimal deactivation values may beoperation different because during cylinderother loads deactivation are not required operation, exce it ispt inevitable for the pumping to assume loss that in the the differences vehicle to arebe notchanged significant owing because to cylinder such deactivation values cannot when be confirmed cylinder deactivation in the engines. is applied. TheIt is secondnoteworthy assumption that if only is that the thePMEP same can vehicle be reduced speed by and cylinder load aredeactivation used in the operation, simulation. it is Thispossible implies to decrease that the the same IMEP braking by the torque same and amount engine as speedthe reduced are applied. PMEP, Under and the these reduction assumptions, in fuel thecorresponding net indicated to this mean decrease effective can pressure improve (NMEP) the fuel must economy. be the This same is the before basic and concept after cylinderused for deactivationsimulating fuel operation economy. because other loads are not required except for the pumping loss in the vehicle to beSimulation changed owing was performed to cylinder by deactivation cycle, and whenthe cont cylinderrol logic deactivation was created is to applied. determine the number of deactivatedIt is noteworthy cylinders that iffor only which the PMEPNMEP can was be reducedthe same by as cylinder the measured deactivation value operation, and the itfuel is possibleconsumption to decrease was the the lowest. IMEP byFor the the same stability amount of ascylinder the reduced deactivation PMEP, andoperation, the reduction the operating in fuel corresponding to this decrease can improve the fuel economy. This is the basic concept used for simulating fuel economy.

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Simulation was performed by cycle, and the control logic was created to determine the number of Energies 2018, 11, x FOR PEER REVIEW 4 of 12 deactivated cylinders for which NMEP was the same as the measured value and the fuel consumption wasconditions the lowest. were For set theto operate stability at of an cylinder engine deactivationspeed of 1000 operation, rpm or more the and operating a vehicle conditions speed of were 20 km/h set toor operate more. at an engine speed of 1000 rpm or more and a vehicle speed of 20 km/h or more. SimulationSimulation was was performed performed in in the the following following process. process. Figure Figure2 shows 2 shows the calculationthe calculation process process of the of simulationthe simulation in a ﬂowchart.in a flowchart.

FigureFigure 2. 2.Flowchart Flowchartof ofsimulation. simulation.

1.1. ThroughThrough thethe givengiven vehiclevehicle data,data, initialinitial conditionsconditions (the(the numbernumber ofof activatedactivated cylinders,cylinders, fuel,fuel, etc.)etc.) werewere set and and it itwas was determined determined whether whether these these condit conditionsions are the are operating the operating conditions conditions of cylinder of cylinderdeactivation. deactivation.

2.2. UsingUsing thethe datadata ofof IMEPIMEP andand thermalthermal efﬁciencyefficiency (f (f11),), IMEPIMEP andand MAP MAP (f (f22),), andand MAPMAP andand PMEPPMEP (f(f33),), thethe fuel,fuel, MAP, MAP, IMEP, IMEP, PMEP, PMEP, and and NEMP NEMP calculate calculate for thefor giventhe given IMEP IMEP of 1–12 of bars.1–12 Thebars. fuel, The IMEP, fuel, andIMEP, PMEP and are PMEP calculated are calculated again based again on the based total displacementon the total becausedisplacement they are because calculated they based are oncalculated the activated based cylinders. on the activated cylinders. 3.3. CombinationsCombinations (including(including IMEP, IMEP, PMEP, PMEP, MAP, MAP, and fuel)and infuel) which in thewhich measured the measured NMEP is NMEP identical is toidentical the calculated to the calculated NMEP are NMEP chosen. are chosen. 4. In the case cylinder deactivation operation, steps 2–4 are repeated as the number of activated cylinders was increased to the number of total cylinders to determine the number of deactivated cylinders with the lowest fuel consumption. Data, such as the fuel, IMEP, and PMEP, were

Energies 2018, 11, x FOR PEER REVIEW 5 of 12 Energies 2018, 11, 3084 5 of 12 stored. When cylinder deactivation is not in operation, the number of cylinders is determined 4. Inthe the total case cylinder. cylinder deactivationdata such as fuel, operation, IMEP, stepsand PMEP 2–4 are of repeatedthe total ascylinders the number are stored. of activated 5. cylindersAfter steps was increased1–4 are repeated to the number by cycle, of totalthe fuel cylinders amounts to determine by cycle theare numberadded and of deactivated the total fuel cylindersamount with is calculated the lowest when fuel consumption.all driving cycles Data, are such completed. as the fuel, IMEP, and PMEP, were stored. When cylinder deactivation is not in operation, the number of cylinders is determined the total 2.3. Verification of Fuel Economy Prediction Simulation cylinder. data such as fuel, IMEP, and PMEP of the total cylinders are stored. 5. AfterThe stepscompleted 1–4 are fuel repeated economy by prediction cycle, the simulation fuel amounts was verified by cycle comparin are addedg the and IMEP, the PMEP, total fuel MAP, andamount fuel consumption is calculated (i.e., when the all outp drivingutted cyclessimulation are completed. results) with the measured data. The simulation verification of previous studies did not mention much about the precision of simulation. Papers that 2.3.mentioned Verification the of Fuelprecision Economy revealed Prediction that Simulation errors within 5% existed when compared with the measured engineThe completed data in the fuel static economy state [26]. prediction simulation was verified comparing the IMEP, PMEP, MAP, and fuelTable consumption 2 shows (i.e.,the verification the outputted data simulation that summarize results) withthe measured the measured and data. calculated The simulation results of a verificationvehicle 3 ofusing previous the mean studies values did notof the mention entire muchdriving about cycle, the and precision Figure of3 shows simulation. the comparisons Papers that of mentionedthe fuel masses the precision in phase revealed 3. that errors within 5% existed when compared with the measured engine dataTable in 2 the shows static that state the [26 measured]. NMEP is the same as the calculated NMEP (3.3 bar) and that theTable mean2 shows PMEP, the MAP, verification and fuel consumption data that summarize have almost the measuredno error. and calculated results of a vehicle 3Figure using 3 the shows mean the values comparisons of the entire of the driving fuel masses cycle, and by Figurecycle and3 shows reveals the that comparisons the measured of the and fuelcalculated masses in values phase are 3. similar, being 412 and 411 g, respectively, with less than 1% error.

TableTable 2. Comparison 2. Comparison between between measured measured and and calculated calculated data data of vehicle of vehicle 3 in 3 FTP-75. in FTP-75.

MeanMean MeanMean MeanMean NMEP MeanMean MAP MAP AccumulatedAccumulated Fuel Fuel DataData IMEPIMEP [bar] [bar] PMEPPMEP [bar] NMEP[bar] [bar] [kPa][kPa] MassMass Error Error [%] [%] MeasuredMeasured 3.9 3.9 0.6 0.6 3.3 3.3 50.8 50.8 less thanless 1%than 1% CalculatedCalculated 3.9 3.9 0.6 0.6 3.3 3.3 51.6 51.6

0.2 measured 0.15 calculated

0.1

0.05 Fuel mass [g/cyc] mass Fuel

0 2000 2100 2200 2300 2400 TIME [s]

FigureFigure 3. Comparison 3. Comparison between between measured measured and and calculated calculated fuel fu rateel rate of vehicleof vehicle 3 in 3 phasein phase 3 of 3 FTP-75.of FTP-75.

3. TableFuel 2Economy shows that Improvement the measured under NMEP Cylinder is the same Deactivation as the calculated NMEP (3.3 bar) and that the mean PMEP, MAP, and fuel consumption have almost no error. When the completed fuel economy prediction model was applied to fixed-type and variable- Figure3 shows the comparisons of the fuel masses by cycle and reveals that the measured and type cylinder deactivation for each vehicle, the fuel economy improvement was examined and we calculated values are similar, being 412 and 411 g, respectively, with less than 1% error. confirmed the cause of difference in fuel economy improvement between two cylinder deactivation 3. Fuelcontrol Economy methods. Improvement Furthermore, under the Cylindereffects of Deactivationvariables that may occur when the engine load and engine thermal efficiency were changed under cylinder deactivation application were investigated. When the completed fuel economy prediction model was applied to fixed-type and variable-type cylinder3.1. Comparision deactivation of forFuel each Economy vehicle, Improv the fuelement economy by Cylinder improvement Deactivation was Method examined and we confirmed the cause of difference in fuel economy improvement between two cylinder deactivation control methods.In this Furthermore, study, fixed-type the effects and ofvariable-type variables that cyli maynder deactivation occur when thefuel engineeconomy load simulations and engine were thermalperformed efficiency for werethe test changed vehicles, under and cylinder the fuel deactivation economy improvement application were depending investigated. on the cylinder deactivation method were compared using the obtained IMEP, PMEP, MAP, and fuel.

Energies 2018, 11, 3084 6 of 12

3.1. Comparision of Fuel Economy Improvement by Cylinder Deactivation Method In this study, ﬁxed-type and variable-type cylinder deactivation fuel economy simulations were performed for the test vehicles, and the fuel economy improvement depending on the cylinder deactivation method were compared using the obtained IMEP, PMEP, MAP, and fuel. Table3 summarizes the fuel economy improvement simulation results under cylinder deactivation application for each vehicle. The mean NMEP values are different because the engine displacement and equivalent test weight (ETW) are different. Furthermore, the fuel economy improvement ranges from 2.2% to 12.9%; it was lowest for vehicle 1 and highest for vehicle 4.

Table 3. Summary of fuel economy improvement under cylinder deactivation for each vehicle in FTP-75.

Speciﬁcation Vehicle 1 Vehicle 2 Vehicle 3 Vehicle 4 Volume (l) 1.0 2.4 3.3 5.0 Mean NMEP (bar) 4.5 3.1 3.3 2.2 Fixed 2.2 6.3 5.2 10.0 Fuel economy improvement (%) Variable 2.2 6.8 6.6 12.9

A comparison of the fuel economy improvement between variable-type cylinder deactivation and ﬁxed-type cylinder deactivation revealed that the fuel economy improvement was larger as the number of cylinders and displacement increased and the effect was smaller as the engine size decreased. The fuel economy improvement of variable-type cylinder deactivation increased for engines with larger displacement because the number of cylinders to be controlled increased. Although the predicted fuel economy improvement was compared, as shown in Table3, instantaneous simulation data were used to examine the fuel economy improvement under cylinder deactivation application in more detail. Instantaneous data were examined using the data for vehicle 3. Table4 summarizes the mean engine performance data of the driving cycle. Figure4 show the instantaneous data in phase 3.

Table 4. Summary of mean engine performance data under cylinder deactivation in FTP-75.

Mean IMEP Mean PMEP Mean Mean MAP Fuel Economy [bar] [bar] NMEP [bar] [kPa] Improvement [%] Base engine 3.90 0.6 3.31 51.6 - Cylinder Deactivation Fixed 3.70 0.39 3.31 61.5 5.2 Engine Variable 3.66 0.35 3.31 65.3 6.6

In Table4, the NMEP values are the same but the IMEP, PMEP, and MAP values are different. As the cylinder deactivation engine is a technology for decreasing the pumping loss by increasing the load of activated cylinders, it has higher mean MAP than the base engines and the fuel economy improvement occurs due to the decrease in the average PMEP. As for the cylinder deactivation control methods, variable-type cylinder deactivation can control the number of cylinders more easily than fixed-type cylinder deactivation. Variable-type cylinder deactivation exhibited 1.4% higher fuel economy improvement than fixed-type cylinder deactivation because the average MAP increased and the average PMEP decreased. Figure4a shows the instantaneous MAP values of the base engine and cylinder deactivation engine. The black line represents the base engine, the blue line the fixed-type cylinder deactivation engine, and the red line the variable-type cylinder deactivation engine. Both cylinder deactivation engines exhibited higher MAP than the base engine, and the parts without cylinder deactivation operation operated in the same way as the base engine. Under the operation of variable-type cylinder deactivation, the MAP increased to favorable 80–90 kPa due to cylinder deactivation operation. In the case of fixed-type cylinder deactivation, however, the region with an excellent fuel economy Energies 2018, 11, 3084 7 of 12 improvement could be exceeded depending on the load because the number of deactivated cylinders was limited. Energies 2018, 11, x FOR PEER REVIEW 7 of 12 Figure4b shows comparisons of the PMEP values. Under cylinder deactivation operation, the PMEPit decreased becomes only lower slightly compared in the high-load to that ofregion the basewhere engine. the PMEP For difference fixed-type was cylinder small. For deactivation, fixed- the pumpingtype cylinder loss reductiondeactivation, decreased the instantaneous compared fuel to amount variable-type was high cylinder compared deactivation to variable-type due to the samecylinder reason asdeactivation the MAP. because of many areas with high PMEP.

100 1 Base 80 0.8 Fixed Variable 60 0.6

40 0.4 MAP [kPa] MAP Base [bar] PMEP 20 Fixed 0.2 Variable 0 0 2000 2100 2200 2300 2400 2000 2100 2200 2300 2400 TIME [s] TIME [s] (a) (b)

0.15 Base Fixed 0.1 Variable

0.05 Fuel mass [g/cyc]

0 2000 2100 2200 2300 2400 TIME [s] (c)

FigureFigure 4. Comparison 4. Comparison of resultsof results MAP MAP between betweenbase base engineengine and and cylinder cylinder deactivation deactivation engine engine in phase in phase 3 of FTP-75;3 of FTP-75; (a) MAP; (a) MAP; (b) ( PMEP;b) PMEP; (c) (c fuel) fuel mass. mass.

FigureIn4 cprevious shows thepapers, comparisons the fuel economy of the instantaneousimprovement of fuel cylinder masses. deactivation The fuel presented mass decreased by significantlyprevious in studies the low-load was between region where6% and the 22%, PMEP and wasthe reducedfuel economy significantly improvement in Figure by 4cylinderb; however, deactivation control method differed by more than 10%. However, it significantly varied depending it decreased only slightly in the high-load region where the PMEP difference was small. For fixed-type on the condition and control of the applied vehicle. This study confirmed the fuel economy cylinder deactivation, the instantaneous fuel amount was high compared to variable-type cylinder improvement by cylinder deactivation under the same conditions and control. When the cylinder deactivationdeactivation because was applied of many to areasthe test with vehicle, high it PMEP.was confirmed that the fuel efficiency improvement of In2.2–12.9%. previous Depending papers, the on fuel the economyengine displacement, improvement the offuel cylinder economy deactivation improvement presented was changed by previous by studiesup was to 10.7%. between Depending 6% and on 22%, the cylinder and the deactivati fuel economyon control improvement method, the by fuel cylinder economy deactivation improvement control methodwas differed changed by up more to 2.9%. than 10%. However, it significantly varied depending on the condition and controlThe of fuel the economy applied improvement vehicle. This of study cylinder confirmed deactivation the varied fuel economy depending improvement on the engine byas well cylinder deactivationas vehicle under specifications. the same As conditions the fuel economy and control. improvements When shown the cylinder in Table deactivation 3 resulted from was applying applied to the testall vehicle,the aforementioned it was confirmed variables, that they the differed fuel efficiency depending improvement on the vehicle. of 2.2–12.9%. Depending on the Under cylinder deactivation application, the influence of the aforementioned variables must be engine displacement, the fuel economy improvement was changed by up to 10.7%. Depending on the examined because they may change the fuel economy improvement. Therefore, a simulation was cylinder deactivation control method, the fuel economy improvement was changed by up to 2.9%. performed to examine the influence of changes in engine load and thermal efficiency at high load on Thefuel fueleconomy economy improvement, improvement which ofmay cylinder occur owing deactivation to the use varied of the dependingcylinder deactivation on the engine engine. as well as vehicle specifications. As the fuel economy improvements shown in Table3 resulted from applying all the3.2. aforementioned Fuel Economy Improvement variables, under they Cylinder differed Deactivation depending According on the vehicle. to Engine Load Change UnderAfter cylinder this section, deactivation fuel economy application, prediction the influence was performed of the aforementionedonly for variable-type variables cylinder must be examineddeactivation, because which they mayexhibited change a larger the fuel fuel economy economy improvement. improvement Therefore,than fixed-type a simulation cylinder was performeddeactivation. to examine The target the influence vehicle was of vehicle changes 3. in engine load and thermal efficiency at high load on fuel economyWhen improvement, a cylinder deactivation which may engine occur is used owing in a vehicle, to the usethe change of the cylinderin driving deactivation resistance is small engine. because the vehicle exterior is the same but the vehicle weight changes with the engine replacement. 3.2. FuelIf the Economy vehicle Improvementweight changes, under the Cylinderengine load Deactivation changes; thus, According the fuel to Engineeconomy Load improvement Change also changes. Furthermore, the fuel economy improvement will change owing to engine load changes After this section, fuel economy prediction was performed only for variable-type cylinder caused by other external factors. deactivation, which exhibited a larger fuel economy improvement than fixed-type cylinder deactivation. The target vehicle was vehicle 3.

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A simulation was performed to examine the fuel economy improvement under 10% increase and 10% decrease in vehicle weight. In addition, the tendency of fuel economy improvement according to engine load changes was identified. EnergiesTable2018 ,511 shows, 3084 comparisons of the engine mean NMEP values and fuel economy improvements8 of 12 according to vehicle weight change. As the vehicle weight increased, the engine load increased and the fuel economy improvement decreased. When a cylinder deactivation engine is used in a vehicle, the change in driving resistance is small Table 6 shows the tendency of fuel economy improvement according to engine load change. As because the vehicle exterior is the same but the vehicle weight changes with the engine replacement. shown by the results in Table 5, the fuel economy improvement decreased as the engine load increased. If the vehicle weight changes, the engine load changes; thus, the fuel economy improvement also Figure 5 explain these results. changes. Furthermore, the fuel economy improvement will change owing to engine load changes Figure 5a shows the PMEP according to the NMEP. The dotted and solid lines represent the base caused by other external factors. engine and cylinder deactivation engine, respectively. In the low-load region, the difference in the A simulation was performed to examine the fuel economy improvement under 10% increase and PMEP was large because the number of deactivated cylinders was large. However, as the engine load 10% decrease in vehicle weight. In addition, the tendency of fuel economy improvement according to increased, the number of deactivated cylinders decreased, resulting in no difference in the PMEP engine load changes was identiﬁed. from the NMEP of ~7 bar. From 7 bar, the engine operated similarly as the base engine because the Table5 shows comparisons of the engine mean NMEP values and fuel economy improvements cylinder deactivation application afforded no advantage. according to vehicle weight change. As the vehicle weight increased, the engine load increased and Figure 5b shows the engine efficiency according to the NMEP. The difference between the solid the fuel economy improvement decreased. line, which represents the efficiency of the cylinder deactivation engine, and the dotted line, which represents the efficiency of the base engine, is the fuel improvement that can be obtained owing to Table 5. Summary of fuel economy improvement by weight change in FTP-75. cylinder deactivation operation according to the load. The fuel improvement occurs owing to the aforementioned difference in the PMEP and in the thermalVehicle efficiency Weight [ETWof the 4750]activated cylinders caused by cylinder deactivation operation; this can be confirmed10% Decrease from Figure Base 5a. 10% Increase Mean NMEP (bar) 3.2 3.3 3.4 TableFuel economy5. Summary improvement of fuel economy [%] improvement7.0 by weight 6.6 change in 6.3 FTP-75.

Vehicle Weight [ETW 4750] Table6 shows the tendency of fuel economy10% improvement Decrease Base according 10% to Increase engine load change. As shown by the resultsMean in NMEP Table5 (bar), the fuel economy 3.2 improvement 3.3 decreased 3.4 as the engine load increased. FigureFuel5 explaineconomy these improvement results. [%] 7.0 6.6 6.3

TableTable 6. Summary of fuel economy improvement by mean NMEP in FTP-75.

MeanMean NMEP Decrease Decrease BaseBase MeanMean NMEP NMEP Increase Increase MeanMean NMEP NMEP (bar) (bar) 2.8 2.8 3.3 3.3 3.8 3.8 FuelFuel economy economy improvement improvement [%] 9.1 9.1 6.6 6.6 4.6 4.6

20 Efficiency [%] 10 Base Deactivation 0 1 2 3 4 5 6 7 8 9 10 NMEP [bar] (a) (b)

Figure 5. ComparisonComparison of of results results between between base base engine engine and and cylinder cylinder deactivation deactivation engine; engine; (a) PEMP; (a) PEMP; (b) engine(b) engine efficiency. efﬁciency.

Therefore,Figure5a shows when the the PMEP mean accordingengine load to increases, the NMEP. the The reduction dotted and in pumping solid lines loss represent under thecylinder base deactivationengine and cylinder operation deactivation decreases engine,because respectively.the engine operates In the low-load under higher region, loads the difference than the in base the engine;PMEP was thus, large the becausefuel economy the number improvement of deactivated is decreased. cylinders was large. However, as the engine load increased, the number of deactivated cylinders decreased, resulting in no difference in the PMEP from the NMEP of ~7 bar. From 7 bar, the engine operated similarly as the base engine because the cylinder deactivation application afforded no advantage. Figure5b shows the engine efficiency according to the NMEP. The difference between the solid line, which represents the efficiency of the cylinder deactivation engine, and the dotted line, which represents the efficiency of the base engine, is the fuel improvement that can be obtained owing to cylinder deactivation operation according to the load. The fuel improvement occurs owing to the Energies 2018, 11, x FOR PEER REVIEW 9 of 12

3.3. Fuel Economy Improvement under Cylinder Deactivation According to Engine Thermal Efficiency Change at High Load A simulation was performed to examine the fuel economy improvement under the assumption that all control is the same as that of the base engine under cylinder deactivation application. However, as each vehicle has a specific output, and drivability, its thermal efficiency may change at Energies 2018, 11, 3084 9 of 12 high load. Therefore, the effect of engine thermal efficiency on fuel economy improvement was examined through a simulation. aforementionedThe thermal difference efficiency in curves the PMEP actually and obtained in the thermal from the efficiency data of ofvarious the activated vehicles cylinders were used, caused and bya total cylinder of three deactivation curves were operation; chosen as this shown can be in confirmed Figure 6. Case from 1 Figure is the5 a.thermal efficiency curve from phaseTherefore, 3 of vehicle when 4, theand meanCase engine2 is the load thermal increases, efficiency the reduction curve from in pumpingphase 3 of loss vehicle under 3. cylinder Case 3 deactivationpresent data operationobtained from decreases the vehi becausecle with the the engine best operatesthermal efficien under highercy curve loads among than the the test base vehicles. engine; thus,The cause the fuel of the economy difference improvement between the is decreased.thermal efficiency curves of Case 1 and Case 2 is not ignition retard due to the suppression of knock because the coolant temperature of both vehicles operates 3.3.similarly. Fuel Economy However, Improvement it is expected under that Cylinder the efficiency Deactivation is reduced According by the to Engine calibration Thermal for Efficiencythe ride comfort Change at High Load because vehicle 4 emphasizes the ride comfortable rather than the fuel consumption as compared with Avehicle simulation 3. was performed to examine the fuel economy improvement under the assumption that allThe control IMEP is value the same for asthe that highest of the thermal base engine efficiency under was cylinder 6, 8, deactivation and 10 bar application.for cases 1, However,2, and 3, asrespectively; each vehicle this has can a specificbe considered output, the and maximum drivability, operating its thermal region efficiency of the activated may change cylinders at high under load. Therefore,cylinder deactivation the effect of operation. engine thermal efficiency on fuel economy improvement was examined through a simulation.Figure 6b shows the number of activated cylinders according to the NMEP under cylinder deactivationThe thermal operation. efficiency The curvesNMEP actuallyof the cylinder obtained deactivation from the data termination of various point vehicles increased were in used, the andorder a of total Cases of three 3, 2, curvesand 1. The were IMEP chosen values as shown for the in highest Figure 6thermal. Case 1 efficien is the thermalcy show efficiency the same curveorder, fromindicating phase that 3 of vehiclethe cylinder 4, and deactivation Case 2 is the region thermal in efficiencycreases when curve the from region phase with 3 of vehicleexcellent 3. engine Case 3 presentthermal dataefficiency obtained operates from theat high vehicle load. with the best thermal efficiency curve among the test vehicles. The causeTable of7 thesummarizes difference betweenthe fuel the economy thermal efficiencyimprovement curves in ofthe Case three 1 and cases Case under 2 is not cylinder ignition retarddeactivation due to operation. the suppression As the ofoperating knock becauseregion of the cylinder coolant deactivation temperature increases, of both vehicles the mean operates PMEP similarly.decreased However,and the mean it is MAP expected increased that the because efficiency the acti is reducedvated cylinders by the calibration operated at for high the load. ride The comfort fuel becauseeconomy vehicle improvement 4 emphasizes was thein ridethe order comfortable of cases rather 3, 2, than and the 1; fuel the consumption operating region as compared of cylinder with vehicledeactivation 3. showed the same order.

Case 1 2 Case 2

No. of activation cylinder activation of No. Case 3 0 1 2 3 4 5 6 7 8 9 10 NMEP [bar] (a) (b)

Figure 6. Comparison of data between cases; ( a) thermal efficiency; efﬁciency; (b) number of activated cylinders in cases 1, 2, and 3 andand NMEP.NMEP.

The IMEP value forTable the 7. highest Fuel economy thermal improvement efficiency in was FTP-75 6, 8, of and each 10 case. bar for cases 1, 2, and 3, respectively; this can be considered the maximum operating region of the activated cylinders under Case 1 Case 2 Case 3 cylinder deactivation operation. Mean MAP (kPa) 62.7 66.5 70.1 Figure6b shows the number of activated cylinders according to the NMEP under cylinder Mean PMEP (bar) 0.37 0.33 0.30 deactivation operation. The NMEP of the cylinder deactivation termination point increased in the Fuel economy improvement (%) 6.1 7.2 8.4 order of Cases 3, 2, and 1. The IMEP values for the highest thermal efficiency show the same order, indicating that the cylinder deactivation region increases when the region with excellent engine thermal The fuel economy improvement showed a difference of 0.6% from the value shown for vehicle 3 efficiency operates at high load. in Table 3. This is because the thermal efficiency curve obtained from each phase was applied when Table7 summarizes the fuel economy improvement in the three cases under cylinder deactivation the fuel economy improvement in vehicle 3 was examined, although the thermal efficiency for each operation. As the operating region of cylinder deactivation increases, the mean PMEP decreased and the mean MAP increased because the activated cylinders operated at high load. The fuel economy improvement was in the order of cases 3, 2, and 1; the operating region of cylinder deactivation showed the same order. The fuel economy improvement showed a difference of 0.6% from the value shown for vehicle 3 in Table3. This is because the thermal efficiency curve obtained from each phase was applied when the fuel economy improvement in vehicle 3 was examined, although the thermal efficiency for each case Energies 2018, 11, 3084 10 of 12 was applied throughout the entire driving cycle intervals to examine the fuel economy improvement according to the difference in thermal efficiency.

Table 7. Fuel economy improvement in FTP-75 of each case.

Case 1 Case 2 Case 3 Mean MAP (kPa) 62.7 66.5 70.1 Mean PMEP (bar) 0.37 0.33 0.30 Fuel economy improvement (%) 6.1 7.2 8.4

In summary, Case 1 exhibited the lowest thermal efficiency while Case 3 exhibited the highest thermal efficiency from the thermal efficiency curves alone, indicating that the test vehicles had some differences in thermal efficiency. Such differences are caused by vehicle temperature control or vehicle drivability, and thus they may occur depending on the vehicle calibration. As the fuel economy improvement of 2.3% may occur depending on the thermal efficiency, calibration for using the high-load region with low pumping loss is required for the development of a cylinder deactivation vehicle. In addition, more precise vehicle thermal management and knock control are required for using the high-load region.

4. Conclusions In this study, simulation capable of fixed-type and variable-type cylinder deactivation control was created using the measured vehicle data, and the results were verified through a comparison with the measured data. Using the completed simulation, the expected fuel economy improvement of fixed-type and variable-type cylinder deactivation were compared for each vehicle, and the influences of variables that may occur depending on the vehicle application and the causes were investigated.

1. The fuel economy improvement under cylinder deactivation was 2.2–12.9% depending on the vehicle. The fuel economy improvement differed depending on the engine displacement, engine load, and engine control. 2. The fuel economy improvement was 2.2–10.0% for fixed-type cylinder deactivation and 2.2–12.9% for variable-type cylinder deactivation. The difference in the fuel economy improvement between variable-type cylinder deactivation and fixed-type cylinder deactivation was large for vehicles with large displacement and many cylinders. This is because the control of variable-type cylinder deactivation is easier and the pumping loss reduction is larger when there are more cylinders. 3. When the engine load changed owing to the change in vehicle weight or driving resistance, the fuel economy improvement with cylinder deactivation changed from 6.6% to 4.6–9.1%. Such differences occurred owing to engine pumping loss reduction caused by the change in the engine operating region. 4. When the engine thermal efficiency changed according to the displacement per cylinder or engine control characteristics, the fuel economy improvement with cylinder deactivation changed from 7.2% to 6.1–8.4%. This is because the cylinder deactivation operating region differed depending on the thermal efficiency change.

Author Contributions: The contribution of the authors is summarized as follows: Conceptualization, K.P. and J.L.; software, N.L. and J.P.; data curation, M.C. and W.K.; writing—review and editing, N.L. and J.P. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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