Experimental Analysis of Calculation of Fuel Consumption Rate by On-Road Mileage in a 2.0 L Gasoline-Fueled Passenger Vehicle

applied sciences

Article Experimental Analysis of Calculation of Fuel Consumption Rate by On-Road Mileage in a 2.0 L Gasoline-Fueled Passenger Vehicle

Jaehyuk Lim 1, Yumin Lee 2, Kiho Kim 1 and Jinwook Lee 2,*

1 Korea Petroleum Quality & Distribution Authority, Chungcheongbuk-do 28115, Korea; [email protected] (J.L.); [email protected] (K.K.) 2 School of Mechanical Engineering, Soongsil University, Seoul 06978, Korea; [email protected] (Y.L.) * Correspondence: [email protected]; Tel.: +82-2-820-0929

Received: 7 October 2018; Accepted: 7 November 2018; Published: 26 November 2018

Abstract: The five-driving test mode is vehicle driving cycles made by the Environment Protection Association (EPA) in the United States of America (U.S.A.) to fully reflect actual driving environments. Recently, fuel consumption value calculated from the adjusted fuel consumption formula has been more effective in reducing the difference from that experienced in real-world driving conditions, than the official fuel efficiency equation used in the past that only considered the driving environment included in FTP and HWFET cycles. There are many factors that bring about divergence between official fuel consumption and that experienced by drivers, such as driving pattern behavior, accumulated mileage, driving environment, and traffic conditions. In this study, we focused on the factor of causing change of fuel efficiency value, calculated according to how many environmental conditions that appear on the real-road are considered, in producing the fuel consumption formula, and that of the vehicle’s accumulated mileage in a 2.0 L gasoline-fueled vehicle. So, the goals of this research are divided into four major areas to investigate divergence in fuel efficiency obtained from different equations, and what factors and how much CO2 and CO emissions that are closely correlated to fuel efficiency change, depending on the cumulative mileage of the vehicle. First, the fuel consumption value calculated from the non-adjusted formula, was compared with that calculated from the corrected fuel consumption formula. Also, how much CO2 concentration levels change as measured during each of the three driving cycles was analyzed as the vehicle ages. In addition, since the US06 driving cycle is divided into city mode and highway mode, how much CO2 and CO production levels change as the engine ages during acceleration periods in each mode was investigated. Finally, the empirical formula was constructed using fuel economy values obtained when the test vehicle reached 6500 km, 15,000 km, and 30,000 km cumulative mileage, to predict how much fuel consumption of city and highway would worsen, when mileage of the vehicle is increased further. When cumulative mileage values set in this study were reached, experiments were performed by placing the vehicle on a chassis dynamometer, in compliance with the carbon balance method. A key result of this study is that fuel economy is affected by various fuel consumption formula, as well as by aging of the engine. In particular, with aging aspects, the effect of an aging engine on fuel efficiency is insignificant, depending on the load and driving situation.

Keywords: 5-cycle test; fuel consumption equation; fuel economy; vehicle driving range

1. Introduction One of the most important criteria for judging performance of a passenger vehicle is fuel economy. Although revision and supplementation have been provided yearly to reﬂect the actual situation of

Appl. Sci. 2018, 8, 2390; doi:10.3390/app8122390 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 2390 2 of 19 the fuel economy system, a suitable solution has not been suggested for the problem that divergence exists between real world fuel efficiency and certified fuel economy [1]. So, there are currently continuing struggles to identify ways to bridge the gap, between certified fuel consumption and fuel economy in real world driving. In particular, combined fuel efficiency has been introduced that reflects the fuel efficiency of the highway mode (HWFET mode), as well as the conventional urban mode, by introducing a new fuel economy system for passenger vehicles in 2012. Recently, a 5-cycle correction formula has been applied globally, as a way to produce certified fuel consumption, to consider the effect of various operating conditions on fuel economy [2]. In a vehicle-specific 5-cycle fuel efficiency, used to derive a 5-cycle correction formula, and which known to assist in approximating real world fuel economy, real-world driving conditions have been well accounted for in fuel consumption. This can be achieved by considering the effects of driving environments shown in US06, SC03, and cold FTP driving cycles, invisible in the FTP-75 and HWFET cycles, on fuel consumption. Each of these newly introduced regulatory driving cycles are characterized by the presence of frequent acceleration and deceleration regions, driving a vehicle with an air conditioner on, and driving a vehicle in a cold environment [3]. So, fuel consumption calculated from the process contributes to bridging divergence between real world and laboratory fuel consumption. Lee et al. revealed that the characteristics demonstrated in additional driving cycles, US06, SC03, and cold FTP, have a major effect on lowering fuel consumption. Also, it was found that the presence of frequent acceleration and deceleration regions are the heaviest factors undermining fuel consumption [4]. Lim et al. presented the results of a vehicle powered by different fuel, mostly affected by characteristics of each additional three driving cycles, in terms of deterioration of fuel consumption. In low-temperature environmental condition mode and air conditioner mode, the hybrid vehicle was most affected, and in rapid acceleration and deceleration mode, the vehicle fueled by gasoline was most affected, in terms of deterioration of fuel efficiency [5]. The study of the Environment Protection Association (EPA) delves into SC03 and Cold FTP drive cycles, from the perspective of fuel economy. Like that of the SC03 test, excess fuel use due to operating the air conditioner varies in inverse proportion to vehicle speed. For the cold FTP driving cycle, how quickly the engine reaches the warmed-up state is the critical factor in determining fuel efficiency [6]. Lee et al. tested average emission rates of all measured gaseous pollutants (CO, NOx, and THC, as well as CO2) for HWFET testing, and compared these with those for all other testing. For US06 testing, CO and THC emission rates were significantly higher than those of other testing. For CO2, average emission rate of SC03 testing was the highest, followed by those of FTP, UDDS, US06, and HWFET. The authors believe that different measured emission rates for different testing and pollutants were due to different characteristics of test driving schedules [7]. Massimo, et al. presented a tailored model for the assessment of environmental benefits achievable by “light-weighting” in the automotive field. The work is composed of two main sections: simulation and environmental modelling. Simulation modelling performs an in-depth calculation of weight-induced FC whose outcome is the FRV evaluated for a wide range of Diesel Turbocharged (DT) vehicle case studies. Environmental modelling converts fuel saving to impact reduction basing on the FRVs obtained by simulations [8]. Michiel, et al. compares the benefits of two parallel drivetrain configurations with an Integrated Starter Generator (ISG): one with the ISG connected directly to the engine, and one with the ISG connected to the drivetrain, after the clutch. Both configurations include Start-Stop operation, but only the latter one can turn off the engine during propulsion. The effect on fuel economy is analyzed by simulations using optimization over a given driving cycle [9]. Zhang, et al. measured on-road emissions for 60 LDPVs in three of China’s cities and calculated their fuel consumption and CO2 (carbon dioxide) emissions. We further evaluated the impacts of Appl.Appl. Sci.Sci.2018 2018,,8 8,, 2390 x FOR PEER REVIEW 3 ofof 1919

Zhang, et al. measured on-road emissions for 60 LDPVs in three of China’s cities and calculated variationstheir fuel consumption in area-averaged and speedCO2 (carbon on relative dioxide) fuel emissions. consumption We offurther gasoline evaluated LDPVs the for impacts the UAB of (urbanvariations area in of Beijing)area-averaged [10] speed on relative fuel consumption of gasoline LDPVs for the UAB (urbanLike area the of above Beijing) method, [10] it is possible to reduce divergence between official fuel consumption and real-worldLike the above fuel consumptionmethod, it is calculatedpossible to throughreduce divergence such a fuel between consumption official correction fuel consumption formula, butand 10~15% real-world difference fuel consumption exists between calculated the fuel throug economyh such experienced a fuel consumption by a driver, correction and certified formula, fuel but consumption.10~15% difference The reasons exists forbetween this difference the fuel inecon fuelomy economy experienced are as followsby a driver, [8]. and certified fuel consumption. The reasons for this difference in fuel economy are as follows [8]. • Many external factors, such as driving conditions, accumulated mileage, traffic conditions, • temperature,Many external weather factors, conditions, such as driving etc., affect conditions, fuel economy. accumulated Also, rapidmileage, acceleration/braking, traffic conditions, high-speedtemperature, driving, weather excessive conditions, use of etc., air conditioners, affect fuel economy. unnecessary Also, loading rapid of acceleration/braking, cargo, excessive use ofhigh-speed electrical equipment,driving, excessive and four-wheel use of air drive, conditioners, all contribute unnecessary to fuel efficiency. loading of cargo, excessive • Maintenanceuse of electrical status equipment, of the and vehicle, four-wheel fuel drive, quality, all contribute and condition to fuel ofefficiency. the car also affect • drivingMaintenance conditions. status of the vehicle, fuel quality, and condition of the car also affect driving conditions. Among factors that cause the difference between fuel consumption that is experienced by a driver Among factors that cause the difference between fuel consumption that is experienced by a driver and certified fuel economy, the study focused on factors of accumulated mileage of the vehicle, as well and certified fuel economy, the study focused on factors of accumulated mileage of the vehicle, as as different unadjusted and adjusted fuel consumption formula. Moreover, since little attention has well as different unadjusted and adjusted fuel consumption formula. Moreover, since little attention been paid to relationship between vehicle’s operating condition and aging engine, we investigated the has been paid to relationship between vehicle’s operating condition and aging engine, we change of CO2 around the selected accumulative mileage: 0 km, 6500 km, 15,000 km, and 30,000 km investigated the change of CO2 around the selected accumulative mileage: 0 km, 6500 km, 15,000 km, during the FTP-75, HWFET, and US06 driving cycle. Also, the detailed factors that contribute to and 30,000 km during the FTP-75, HWFET, and US06 driving cycle. Also, the detailed factors that aggravating fuel consumption as the engine has aged was additionally investigated in US06 drive contribute to aggravating fuel consumption as the engine has aged was additionally investigated in cycles. Finally, based on the empirical formulae developed by the results of the vehicle-specific 5-cycle US06 drive cycles. Finally, based on the empirical formulae developed by the results of the vehicle- fuel economy values measured at 6500 km, 15,000 km, and 30,000 km mileage, the aggregation of specific 5-cycle fuel economy values measured at 6500 km, 15,000 km, and 30,000 km mileage, the fuel efficiency results was estimated within 100,000 km mileage. Figure1 shows the difference of fuel aggregation of fuel efficiency results was estimated within 100,000 km mileage. Figure 1 shows the efficiency values according to the weight of vehicle. Among these cars, a Sonata with intermediate difference of fuel efficiency values according to the weight of vehicle. Among these cars, a Sonata weight and fuel efficiency was selected as the experimental vehicle in this study. with intermediate weight and fuel efficiency was selected as the experimental vehicle in this study.

Kia Morning

Hyunda Avante

Hyundai Sonata 12.3

Kia all new K7 10

Chevrolet Trax 8

Hyundai Tuscon Feul consumption [km/L] 6

Hyundai Santafe 4

0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Curb weight [kg]

Figure 1. Correlation between fuel efﬁciency and vehicle curb weight of ICEV(internal combustion Figure 1. Correlation between fuel efficiency and vehicle curb weight of ICEV(internal combustion engine vehicle) on sale in the Republic of Korea. engine vehicle) on sale in the Republic of Korea. Appl. Sci. 2018, 8, 2390 4 of 19

2. Experiment Description

2.1. Vehicle Specification and Test Description In this study, the experiment was performed with a 2.0 L gasoline powered-vehicle (Hyundai Co., Asan Plant, Korea), which is combusted by premixed air-fuel mixture. The test vehicle came equipped with a 16-valve four-cylinder engine. A multipoint fuel injection system is applied to the vehicle, implemented in such a way that the fuel is injected into the intake stroke just upstream of each cylinder’s intake valve. The cylinder valve was operated with continuous variable valve timing-technology (CVVT), which improves fuel efficiency by changing the cam valve profile depending on operating conditions and operating strategies, instead of opening and closing intake and exhaust valves with a fixed-cam profile [8]. Table1 shows the remainder of the detailed specification of the vehicle engine.

Table 1. Speciﬁcation of the test vehicle used in this study.

Item Unit Speciﬁcation Bore × stroke mm 88 × 90 Displacement cc 1999 Engine Valves per cylinder - 4 (2 intake and 2 exhaust) Compression ration - 16 Engine type - l4 Overall length mm 4855 Overall width mm 1865 Vehicle Overall height mm 1475 Wheel base mm 2805 Vacant weight kg 1460

Figure2 shows a chain diagram of a chassis dynamometer and an exhaust gas analyzer that can measure exhaust gas and the fuel efﬁciency of a vehicle. The chassis dynamometer simulates running resistance and inertia resistance corresponding to running speed and acceleration of an automobile. The chassis dynamometer that was used in this test is an AC dynamometer of AVL. It is composed of inertia weight, power absorption unit, and controller. Table2 shows details of the speciﬁcations of the test vehicle used in this study. The vehicle was operated on the chassis dynamometer along driving modes, and real-time exhaust gas and vehicle data were obtained for a prescribed speed trace of each driving cycle. Vehicle emissions measurements were made with CVS tunnels and exhaust gas analyzer (MEXA-7 series). The result of the vehicle emissions was analyzed by inspecting the trapped bag containing exhaust gases. Test modes that were used in this study were the FTP, HWFET, and US06 driving cycles, and experiments were performed under the following conditions. The test of these driving cycles was performed in the test room maintained at constant temperature of 25 ± 1 ◦C and constant relative humidity of 50 ± 5%. The FTP-75 mode was tested by soaking the test vehicle for more than 12 h under test temperature conditions, and the HWFET and US06 modes were tested in the preconditioning mode, which serves to warm up the engine to maintain the vehicle at a constant temperature. Appl. Sci. 2018, 8, 2390 5 of 19 Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 19

Figure 2. SchematicsSchematics of of the the gasoline vehicle emission measurement system.

Table 2. Speciﬁcations of the chassis dynamometer. Table 2. Specifications of the chassis dynamometer.

ItemItem Specification Specification RollRoll type type & diameter & diameter Roll Roll type type & & diameter diameter SingleSingle Roll Roll (48 (48 inch inch MIM MIM type) type) SimulatedSimulated vehicle vehicle weight weight 454~5400 kg kg Electric motor absorber type AC IGBT Electric motorMax. absorber speed type 200 AC km/h IGBT RegistrationMax. of speed actual speed value ±0.01% 200 km/h km/h RegistrationRegistration ofof actualactual tractive speed forcevalue value ±0.1%± 𝟎. F.S. 𝟎𝟏% (5870km/h N) RegistrationMeasurement of actual of tractive driving force distance value ±0.1% Encoder F.S.( type5870 N) Max. flow rate of cooling fan 63,000 CFM Measurement of driving distance Encoder type Max. flow rate of cooling fan 63,000 CFM 2.2. Three Regulatory Driving Cycles 2.2. ThreeThe threeRegulatory regulatory Driving driving Cycles cycles, FTP-75, HWFET, and US06, which were established by the EPAThe (Environment three regulatory Protection driving Agency), cycles, were FTP-75, selected HWFET, for measuringand US06, vehiclewhich were emissions. established These by three the EPAdriving (Environment cycle modes Protection show various Agen situationscy), were that selected can occur for measuring on real roads. vehicle emissions. These three drivingThe cycle FTP-75 modes cycle show is shown various in situations Figure3a. that The can cycles occur are on introduced real roads. to simulate the urban way. CharacteristicsThe FTP-75 of cycle cycles is areshown described in Figure with 3a. distance The cycl traveled,es are introduced 17.77 km, duration to simulate 1874 the s, andurban average way. Characteristicsspeed 34.1 km/h. of Ascycles seen are in described Figure3a, thewith FTP distance mode cantraveled, be separated 17.77 km, into duration three regions 1874 s, with and different average speedoperating 34.1 conditions.km/h. As seen The in first Figure phase 3a, in the the FTP range mode from can 0~505 be separated s is called into the three cold regions start phase. with Sincedifferent the operatingengine does conditions. not start untilThe first the phase FTP cycle in the begins, range itfrom is relatively 0~505 s is colder called than the cold in other start phases. phase. Since The cold the enginestart phase does is not followed start until by a the second FTP phase,cycle begins, called theit is transient relatively phase, colder that than plays in other the role phases. of warming The cold up startthe engine. phase is In followed the third by phase, a second called phase, the hot called start the phase, transient the vehicle phase, is that driven plays along the therole same of warming trace as upthe the first engine. phase region.In the third phase, called the hot start phase, the vehicle is driven along the same trace as the first phase region. The HWFET cycle is shown in Figure 3b. The driving cycle is developed for simulating a mixture of interstate highway and rural driving. The cycle is tested using a warmed-up engine, and distinguished from other driving cycles with regard to making no-stop during the test. Details of the cycle’s characteristics are described with duration of 765 s, total distance of 16.45 km, and average speed of 77.7 km/h. The US06 profile is shown in the Figure 3c. The driving cycle can be distinguished from other cycles in terms of the presence of frequent acceleration and deceleration regions. Characteristics of the cycle are a total distance of 12.8 km, average speed of 77.9 km/h, maximum speed of 129.2 km/h, and duration of 596 s. In addition, the US06 drive cycle can be divided into two regions, city, and highway mode. Appl. Sci. 2018, 8, 2390 6 of 19 Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 19

100 Cold start phase Transient phase Hot start phase 0-505 s 506-1370 s 1371-1875 s

40 Speed [km/h]

0 0 125 250 375 500 625 750 875 1000 1125 1250 1375 1500 1625 1750 1875 Time [s]

(a)

120

100

Speed [km/h] 40

0 0 60 120 180 240 300 360 420 480 540 600 660 720 780 Time [s]

(b)

140 City mode Highway mode City mode 0-130 s 131-495 s 496-596 120

100

60 Speed [km/h] 40

0 0 50 100 150 200 250 300 350 400 450 500 550 600 Time [s]

(c)

FigureFigure 3. Three regulatoryregulatory driving driving cycles cycles established established by theby Environmentthe Environment Protection Protection Association Association (EPA). (EPA).(a) FTP-75 (a) FTP-75 driving driving cycle, (cycle,b) highway (b) highway mode mode (HWFET) (HWFET) driving driving cycle, cycle, and (c and) US06 (c) US06 driving driving cycle. cycle.

The HWFET cycle is shown in Figure3b. The driving cycle is developed for simulating a mixture of interstate highway and rural driving. The cycle is tested using a warmed-up engine, and distinguished from other driving cycles with regard to making no-stop during the test. Details of

Appl. Sci. 2018, 8, 2390 7 of 19 the cycle’s characteristics are described with duration of 765 s, total distance of 16.45 km, and average speed of 77.7 km/h. The US06 proﬁle is shown in the Figure3c. The driving cycle can be distinguished from other cycles in terms of the presence of frequent acceleration and deceleration regions. Characteristics of the cycle are a total distance of 12.8 km, average speed of 77.9 km/h, maximum speed of 129.2 km/h, and duration of 596 s. In addition, the US06 drive cycle can be divided into two regions, city, and highway mode.

2.3. 4-Equations for Calculation of the Unadjusted and Adjusted Fuel Consumption Figure4 demonstrates the flow chart of fuel consumption equations. This flow chart indicates how each of fuel consumption equations are related with each other. Table3 shows the one unadjusted and three adjusted fuel consumption equations. Equation (A) which calculates the unadjusted fuel consumption is divided into two processes. The first step is to obtain each emission concentration of HC, CO, and CO2, through Equation (a) required for mass of emission discharged during a specific stage of one cycle. Next, the concentrations of each emission calculated through Equation (a) and characteristics of fuel are substituted into Equation (b). Then, unadjusted fuel consumption for LPG can be produced for each 5-driving cycles. The reason why the equation is called an unadjusted fuel efficiency formula is that no adjustment factors are applied. Also, it should be noted that Equation (b) is only applied to vehicles that are fueled by LPG. The first Equation (B), of three adjusted fuel consumption equations had been used until 2007. The Equation B for fuel consumption of city and highway mode demand for fuel efficiency were obtained from Equation A measured during the FTP and HWFET driving cycle. Then, each of its values was multiplied by the adjustment factor, 0.9 and 0.75, to produce adjusted fuel consumption of city and highway modes. Next, the second equation, Equation (C), was developed to approximate real world fuel consumption by implying fuel economy results obtained from Equation (A) measured during 5-cycle tests, characterized with various external atmospheric conditions and driving environments. Fuel efficiency results that were measured during US06, SC03, and cold FTP driving cycles calculated from Equation A were put into the Equation (C) for each city and highway mode, making it possible to consider each characteristic that the three driving cycles contain. Each of the three cycles, US06, SC03, and cold FTP, are characterized by the presence of frequent acceleration and deceleration regions, driving a car with the air conditioning system operating, and the condition of cold atmosphere temperature. Fuel efficiency value of city and highway modes obtained from Equation (C) measured with diverse vehicles, regardless of the types of fuel used in the vehicles, can be used for making linear interpolations for city and highway modes. Then, slopes and intercepts that were obtained from linear interpolations are used for making D fuel consumption equations of city and highway modes. So, each fuel consumption value for these two modes accounting for various driving environments can be conveniently obtained without going through the complex process shown in Equation (C). These three correction formulas (B–D) can be used, regardless of fuel used. However, since fuel consumptions are measured in compliance with the carbon balance method that emitted gases comprised of carbon element are used for estimating fuel economy measured with the vehicle placed on the chassis dynamometer and driving along the driving cycles, it is limited in perfectly reflecting conditions shown on the real-road on fuel consumption that are calculated from adjusted fuel consumption equations. Appl. Sci. 2018, 8, 2390 8 of 19 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 19

Each phase

ACi=1/𝑋 (𝑋,𝑋,𝑋,….)

BCi=1/𝑌 (𝑌,𝑌,𝑌,….)

AHi=1/𝑋 (𝑋,𝑋,𝑋,….)

Bci=1/𝑌 (𝑌,𝑌,𝑌,….)

FigureFigure 4. Flow 4. Flow chart chart of fuel of fuel consumption consumption equations. equations.

Appl. Sci. 2018, 8, 2390 9 of 19

Table 3. One unadjusted and three adjusted fuel consumption equations.

Case Equations for Fuel Consumption

(a) Total exhaust gas concentration for HC, CO and CO2 measured during the FTP cycle. Ywm = 0.43×Yct +Ys÷Dct +Ds + 0.57×[Yht+Ys÷Dht+Ds] (b) Fuel efﬁciency for the vehicle powered by LPG. 4 Fuel Efﬁciency = 3179×10 ×CWF×SG [(CWF×HC+0.429×CO+0.273×CO2)]×[(0.6×SG×NHV)+12,722]

Ywm = (CO, CO2, NOx, HC, CH4, and NMHC) Weighted exhaust gas mass(g/km, g/mile) Yct = mass of emission at the initial stage of cold start test (g/test phase) A Yht = mass of exhaust gas (g/test phase) at the initial stage of the hot start test Ys = mass of exhaust gas (g/test phase) at the stabilization stage of cold start test Dct = driving distances (km, mile) at the initial stage of the cold start test. HC, CO, and CO2 (g/km) = the exhaust gas concentration obtained from the above equation. CWF = the ratio of carbon content in the fuel. SG(g/mL) = the fuel density. NHV(J/g) = calorific power. (a) City mode F.E = FTP_75 F.E × 0.9 (b) Highway mode F.E = HWFET F.E × 0.75 B FTP_75 F.E: the fuel efficieny for FTP-75 cycle HWFET F.E: the fuel efficiency for HWFET cycle 1 (a) City mode F.E = 0.905 × ( (Start FC+Running FC) ) ((0.76×StartFuel75)+(0.24×StartFuel20)) Start FC=0.330×( 4.1 ) Running FC 0.48 0.41 0.11 0.5 0.5 1 0.61 0.39 =(0.82∗( + + ))+(0.18×( + ))+0.133×1.083×( −( + )) Bag2FE75 Bag3FE75 US06FE Bag2FE20 Bag3FE20 SC03FE Bag3FE75 Bag2FE75 C StartFuel75 = (3.6/Bag1_FE75) − (3.6/Bag3_FE75) StartFuel20 = (3.6/Bag1_FE20) − (3.6/Bag3_FE20) 1 (b) Highway mode F.E = 0.905 × ( (Start FC+Running FC) ) ((0.76×StartFuel75)+(0.24×StartFuel20)) Start FC=0.330×( 60 ) Running FC = 1.007×( 0.79 + 0.21 )+0.133×0.377×(( 1 )−( 0.61 + 0.39 )) US06FE HWFET SC03FE Bag3FE75 Bag2FE75 (a) City mode F.E (b) Highway mode F.E D 1 1 = 1.1886 = 1.3425 0.007639+ FTP_75 F.E 0.004425+ HWFET F.E Appl. Sci. 2018, 8, 2390 10 of 19

3. Results and Discussion

3.1. Comparision between Fuel Consumption Resullts Obtained From A, B, C and D Equations Figure5 shows fuel consumption results that were obtained for city and highway mode using the A, B, C, and D equations. Mileage of the vehicle used to measure fuel efficiency was 6500 km. Since the certified fuel consumption was labeled at the vehicle’s mileage 6500 ± 1000 km, mileage was selected. Figure5 shows the difference between the fuel efficiency value and the ones obtained from formulas B,

C,Appl. and Sci. D. 2018, 8, x FOR PEER REVIEW 10 of 19

14 A B C D 13.09 10% 22.4% 22.2%

12 11.78

10.16 10.18 10

6 Fuel[km/L] efficency

(a)

22 20.55 A B C D 20 22% 30.3% 32%

16.03 16 14.33 13.96 14

Fuel [km/L] efficency 8

0 (b)

Figure 5. Comparison of fuel efﬁciency calculated from Equation A, B, C, and D. (a) City mode (b) Highway mode. Figure 5. Comparison of fuel efficiency calculated from Equation A, B, C, and D. (a) City mode (b) Highway mode. Appl. Sci. 2018, 8, 2390 11 of 19

As seen in Figure5a, when the fuel efficiency value obtained from formula A is compared with that obtained from formula B, C, or D, the difference is approximately 10%, 22.4%, or 22.2%, respectively. It can be observed that the gap between fuel efficiency derived from the C and D equations when considering US06, SC03, and cold FTP fuel economy results, that helps to reflect various driving environments, and that obtained from Equation A when considering only one driving characteristic of the FTP-75 driving cycle, indicates a major difference. This observation suggests that fuel economy differs significantly, depending on how many driving situations are considered in producing fuel consumption. However, the fuel efficiency value calculated from Equation B differs somewhat from results from the Equation C and D, which calculate fuel efficiency value in consideration of various driving environments. So, it is thought to be inadequate to calculate corrected fuel efficiency value when considering the environment appearing on the actual driving road by simply multiplying by 0.9 constant value. Figure5b shows the difference between highway fuel consumption values obtained from A, B, C, and D equations. This shows comparable trends to those shown in fuel consumption results of the urban way mode. Because same fuel consumption results obtained from SC 03, US 06, and cold FTP are also applied to adjusted highway fuel economy equations, C and D, this result is not unexpected. In the Equation B for highway mode, even the 0.75, a lower value than that of the city correction factor, 0.9, is multiplied by unadjusted fuel consumption for highway cycle, but the marked difference was represented in fuel consumption, when compared with results that were obtained from Equation C and D.

3.2. Comparison between CO2 Emissions in FTP75, HWFET, and US06 Drive Cycles According to 0, 6500, 15,000 and 30,000 km Mileage

Figure6 shows average CO 2 concentration that was obtained from the test vehicle according to each mileage during FTP-75 cycle tests. The experiment was repeated twice, and the arithmetic mean of CO2 results calculated to reduce the effect on the change in CO2 emissions caused by the driving behavior. CO2 levels show differences by 3.24%, 3.77%, and 2.36% at 0 km, 15,000 km, and 30,000 km mileage, when compared with that at 6500 km mileage. In the case of the vehicle at 0 km mileage, CO2 emission was emitted slightly higher than that at the 6500 km mileage. Since taming of the vehicle at the initial driving of the vehicle usually results in poor fuel economy, it is assumed that CO2 concentrations at 0 km mileage were measured higher. While CO2 emission levels increased higher as compared with the result at 6500 km mileage as the engine ages, CO2 concentration levels at 30,000 km mileage were revealed to decrease when compared with that measured at 15,000 km mileage. This observation suggests increase in CO2 levels is driven by aging of the vehicle engine, as well as driving characteristics of the driver seem to have significant influence on increasing or decreasing CO2 emission even though the same vehicle travels along the same driving cycle. Also, it was shown that there is slight difference in total CO2 production when compared between 15,000 km and 30,000 km cumulative mileage. Since the total amount of CO2 emissions that are generated over the same driving cycle can be considered to be an indicator of fuel efficiency, there is assumed to be almost no variance in fuel consumption until at least 30,000 km after 15,000 km mileage over the FTP cycle. However, because all experiments in this study were conducted using a chassis dynamometer, a vehicle, and instruments for measuring exhaust gas, it was difficult to precisely identify why such results were reached without detailed modeling tools. Appl. Sci. 2018, 8, x FOR PEER REVIEW 11 of 19

3.2. Comparison between CO2 Emissions in FTP75, HWFET, and US06 Drive Cycles According to 0, 6500, 15,000 and 30,000 km Mileage

Figure 6 shows average CO2 concentration that was obtained from the test vehicle according to each mileage during FTP-75 cycle tests. The experiment was repeated twice, and the arithmetic mean of CO2 results calculated to reduce the effect on the change in CO2 emissions caused by the driving behavior. CO2 levels show differences by 3.24%, 3.77%, and 2.36% at 0 km, 15,000 km, and 30,000 km mileage, when compared with that at 6500 km mileage. In the case of the vehicle at 0 km mileage, CO2 emission was emitted slightly higher than that at the 6500 km mileage. Since taming of the vehicle at the initial driving of the vehicle usually results in poor fuel economy, it is assumed that CO2 concentrations at 0 km mileage were measured higher. While CO2 emission levels increased higher as compared with the result at 6500 km mileage as the engine ages, CO2 concentration levels at 30,000 km mileage were revealed to decrease when compared with that measured at 15,000 km mileage. This observation suggests increase in CO2 levels is driven by aging of the vehicle engine, as well as driving characteristics of the driver seem to have significant influence on increasing or decreasing CO2 emission even though the same vehicle travels along the same driving cycle. Also, it was shown that there is slight difference in total CO2 production when compared between 15,000 km and 30,000 km cumulative mileage. Since the total amount of CO2 emissions that are generated over the same driving cycle can be considered to be an indicator of fuel efficiency, there is assumed to be almost no variance in fuel consumption until at least 30,000 km after 15,000 km mileage over the FTP cycle. However, because all experiments in this study were conducted using a chassis dynamometer, a vehicle, and instruments for measuring exhaust gas, it was difficult to precisely identify why such Appl.results Sci. 2018 were, 8, 2390reached without detailed modeling tools. 12 of 19

6 6 3.77% 12.56×10 3.24% 12.62×10 12.45×106 2.36% 12.16×106 1200000112×106

1000000110×106

80000018×106 [mg/L] 2

CO 60000016×106

40000014×106

20000012×106

0 1 0 6500 15,000 30,000 Mileage [km]

Figure 6. Total CO2 emissions measured during the FTP-75 driving cycle according to each mileage. Figure 6. Total CO2 emissions measured during the FTP-75 driving cycle according to each mileage.

Figure7 shows the results of average CO 2 concentration levels that were measured during the HWFET driving cycle according to each mileage. Results of CO2 concentration are also the arithmetic average of two measurements to reduce the amount of change in emissions due to the behavior of the driver. For the HWFET driving cycle, the variance in average CO2 production with each vehicle’s cumulative mileage value reveals a similar tendency to those confirmed in results that are shown in the FTP-75 driving cycle. When compared with CO2 concentration levels that were measured at 6500 km mileage, these were 3.7% higher at 0 km mileage, and 3.4% and 4.0% higher at 15,000 km and 30,000 km mileages, respectively. The reason why amounts of CO2 gas emitted at 0km mileage were higher compared with the result at 6500 km mileage is thought to be the same effect as that found with the FTP testing result. CO2 concentration levels reveal slight difference by 0.6% when comparing results that were measured at 15,000 km and 30,000 km mileage, that means at least between 15,000 km and 30,000 km mileage, like the case of FTP-75 driving cycle, there was negligible change in fuel efficiency in the HWFET driving cycle. However, as mentioned above, there are limitations in investigating why such results are reached, without detailed modeling tools. Figure8 shows the results of total CO 2 concentration levels measured during US06 driving cycle according to each mileage. Experiments were also conducted twice to evaluate arithmetic mean of total CO2 concentration levels to reduce the effect of driving behavior on CO2 emission. As seen in the US06 cycle test, increases in CO2 levels were also detected at 0 km, 15,000 km, and 30,000 km mileage, revealing the difference by 3.31%, 4.23%, and 6.35%, in comparison with the results measured at 6500 km mileage. Trend of increase in CO2 production levels was definitely revealed as vehicle-mileage accumulates after the 6500 km mileage, that cannot be observed in other driving cycles. Since the US06 cycle is characterized by frequent presence of acceleration and deceleration regions, which brings the combustion chamber to the situation wherein frequent load is applied on the engine, some of the relatively large amounts of heat energy generated due to aggressive driving behavior appears more Appl. Sci. 2018, 8, x FOR PEER REVIEW 12 of 19

8.0E+06 8×106 6 7.31×106 7.29×10 3.7% 7.27×106 3.4% 4.4% 7.03×106 7.0E+06 7×106

6.0E+06 6×106

5.0E+06 5×106

[mg/L] 4.0E+066

2 4×10 CO

3.0E+063×106

2.0E+06 2×106

1.0E+06 1×106

Appl. Sci. 2018, 8, x FOR PEER REVIEW 13 of 19 0.0E+000 behavior appears more0 likely to be dissipated6500 through the15 aging,000 cylinder wall.30,000 So, the result of Mileage [km] undermining fuel efficiency, equivalent to increase in CO2 production according to increased mileage, is clearly shown. Figure 7. Total CO2 emissions measured during the HWFET driving cycle according to each mileage. Figure 7. Total CO2 emissions measured during the HWFET driving cycle according to each mileage. 101.0E+07×106 6 Figure 8 shows the results of total CO2 concentration levels measured× 6 during 9.55US06×10 driving6.35% cycle 9.28×106 3.31% 9.36 10 4.23% according to each mileage. Experiments were8.98× also106 conducted twice to evaluate arithmetic mean of 9.0E+069×106 total CO2 concentration levels to reduce the effect of driving behavior on CO2 emission. As seen in the US06 cycle test, increases in CO2 levels were also detected at 0 km, 15,000 km, and 30,000 km mileage, revealing8.0E+068×106 the difference by 3.31%, 4.23%, and 6.35%, in comparison with the results measured at 6500 km mileage. Trend of increase in CO2 production levels was definitely revealed as vehicle-mileage7.0E+067×106 accumulates after the 6500 km mileage, that cannot be observed in other driving cycles. Since the US06 cycle is characterized by frequent presence of acceleration and deceleration

regions, which6.0E+066×10 6brings the combustion chamber to the situation wherein frequent load is applied on the engine, some of the relatively large amounts of heat energy generated due to aggressive driving

6 [mg/L] 5.0E+065×10 2 CO

4.0E+064×106

3.0E+063×106

2.0E+062×106

1.0E+0611××101066

0.0E+000 0 6500 15,000 30,000 Mileage [km]

Figure 8. Total CO2 emissions measured during the US06 driving cycle according to each mileage. Figure 8. Total CO2 emissions measured during the US06 driving cycle according to each mileage.

3.3. Detailed Analysis of the US06 Cycle

Since both city and highway mode characteristics and the increase in CO2 concentration levels as the vehicle’s cumulative mileage increases were clearly demonstrated in the US06 driving cycle, CO2 and CO productions discharged from the driving cycle are closely investigated by separating city and highway modes of US06 cycles into several regions, wherein the vehicle is operated with acceleration and deceleration in the city mode, and only with acceleration in the highway mode. Figure 9 shows the velocity profile of the city mode in the US06 driving cycle. The speed profile is largely divided into three regions in terms of the relative magnitude of load applied to the engine. The regions of A, B, and C correspond to the areas wherein middle, high, and low load are applied to the engine, respectively. As mentioned previously, since the measurement of CO2 concentration levels made during one driving cycle is largely affected by driving behavior, specifically through instantaneous speed, all comparisons of changes in CO2 and CO due to aging of the engine were made from test data that revealed the most similar velocity profile in the time domain corresponding to rapid acceleration and deceleration regions among test data tested according to cumulative mileage of each vehicle. Appl. Sci. 2018, 8, 2390 14 of 19

3.3. Detailed Analysis of the US06 Cycle

Since both city and highway mode characteristics and the increase in CO2 concentration levels as the vehicle’s cumulative mileage increases were clearly demonstrated in the US06 driving cycle, CO2 and CO productions discharged from the driving cycle are closely investigated by separating city and highway modes of US06 cycles into several regions, wherein the vehicle is operated with acceleration and deceleration in the city mode, and only with acceleration in the highway mode. Figure9 shows the velocity profile of the city mode in the US06 driving cycle. The speed profile is largely divided into three regions in terms of the relative magnitude of load applied to the engine. The regions of A, B, and C correspond to the areas wherein middle, high, and low load are applied to the engine, respectively. As mentioned previously, since the measurement of CO2 concentration levels made during one driving cycle is largely affected by driving behavior, specifically through instantaneous speed, all comparisons of changes in CO2 and CO due to aging of the engine were made from test data that revealed the most similar velocity profile in the time domain corresponding to rapid acceleration and deceleration regions among test data tested according to cumulative mileage of Appl. Sci. 2018, 8, x FOR PEER REVIEW 14 of 19 each vehicle.

140 US06 city drive cylce B(a) B(b) 120 trace 0-130 s

100 A(a) 80

Speed [km/h] 40

0 0 102030405060708090100110120130 Time [s]

(a)

120 US06 city drive cylce trace 496-596 s A(b) 100

80 C 60

Speed [km/h] 40

0 495 515 535 555 575 595 Time [s]

(b)

FigureFigure 9. 9. VelocityVelocity profile proﬁle for city mode corresponding to the US06 driving cycles.cycles. (a) (a) trace 0-130 0–130 s s (b) (b) tracetrace 496-596 496–596 s s

FigureFigure 10 represents thethe concentrationconcentration of of CO CO22and and CO CO measured measured during during the the A, A, B B and and C C regions regions in inthe the city city mode mode of the of US06the US06 driving driving cycle. cycle. In the In (a) the part (a) of part the A of region the A corresponding region corresponding to the beginning to the beginningof the cycle, of thethe tendencycycle, the of tendency increase of in increase CO2 and in CO CO productions2 and CO productions was conﬁrmed was asconfirmed the cumulative as the cumulativemileage of themileage vehicle of increases. the vehicle In contrast, increases. in the In ﬁnal contrast, part of in the the US06 final cycle part corresponding of the US06 to thecycle (b) correspondingpart of the A region to the wherein (b) part comparableof the A region load wherei is requiredn comparable as in the (a)load part is ofrequired A region, as in there the is(a) nearly part of A region, there is nearly no variation in CO2 production with each mileage. Since exhaust gas measurement starts in the US06 driving cycle after the engine has stopped for 70 s at the end of the preconditioned process, the (a) region is thought to be colder than the (b) region. Also, it is assumed that the cylinder wall is worn out to some degree due to aging of the engine, so that the lower the ambient temperature inside the cylinder of the engine, the greater the heat transfer loss in the aging engine. In the B region, the CO2 and CO emissions are analyzed by dividing the B region into two sections according to whether the load of the engine is taken at a stop, or at high rpm. In the B region, it can be observed that, as the cumulative mileage of the vehicle increases, the amount of CO2 emissions also increases. In addition, when the overall growth rate of CO2 according to the increase of the cumulative running distance of the vehicle is examined, it can be observed that as cumulative mileage of the vehicle increases, rate of increase of CO2 emission becomes larger as the load of the engine gets heavier. Because the larger the load, the more heat energy is generated, it is estimated that heat loss is proportional to amount of heat energy generated in the worn cylinder wall. Interestingly, when the load is applied to the engine at high rpm in the (b) part of the B region, growth rates of CO2 and CO emissions were higher, in comparison to when applied to an engine with stationary state in the (a) part of the B region. It is assumed that the rapidly incoming fresh charge may play a role in increasing the heat transfer rate on the worn cylinder wall, which makes it difficult for the wall to be maintained in steady state at a high temperature. So, the aging engine at high rpm Appl. Sci. 2018, 8, 2390 15 of 19

no variation in CO2 production with each mileage. Since exhaust gas measurement starts in the US06 driving cycle after the engine has stopped for 70 s at the end of the preconditioned process, the (a) region is thought to be colder than the (b) region. Also, it is assumed that the cylinder wall is worn out to some degree due to aging of the engine, so that the lower the ambient temperature inside the cylinder of the engine, the greater the heat transfer loss in the aging engine. In the B region, the CO2 and CO emissions are analyzed by dividing the B region into two sections according to whether the load of the engine is taken at a stop, or at high rpm. In the B region, it can be observed that, as the cumulative mileage of the vehicle increases, the amount of CO2 emissions also increases. In addition, when the overall growth rate of CO2 according to the increase of the cumulative running distance of the vehicle is examined, it can be observed that as cumulative mileage of the vehicle increases, rate of increase of CO2 emission becomes larger as the load of the engine gets heavier. Because the larger the load, the more heat energy is generated, it is estimated that heat loss is proportional to amount of heat energy generated in the worn cylinder wall. Interestingly, when the load is applied to the engine at high rpm in the (b) part of the B region, growth rates of CO2 and CO emissions were higher, in comparison to when applied to an engine with stationary state in the (a) part of the B region. It is assumed that the rapidly incoming fresh charge may play a role in increasing the heat transfer rateAppl. on Sci. the 2018 worn, 8, x FOR cylinder PEER REVIEW wall, which makes it difficult for the wall to be maintained in steady15 of state 19 at a high temperature. So, the aging engine at high rpm is faced with more difficulty in achieving completeis faced with combustion more difficulty as the load in achieving gets higher complete to accelerate, combustion which as leads the load to the gets production higher to ofaccelerate, more CO emissions,which leads an to indicator the production of incomplete of more combustion. CO emission Ins, thean Cindicator region, of wherein incomplete the vehicle combustion. is required In the to repetitivelyC region, wherein accelerate the andvehicle decelerate is required while to arepeti similarlytively low accelerate load is appliedand decelerate on the enginewhile a moresimilarly than low load is applied on the engine more than four times, CO2 emissions are revealed to vary, four times, CO2 emissions are revealed to vary, irrespective of the vehicle’s cumulative mileage at each irrespective of the vehicle’s cumulative mileage at each acceleration and deceleration region. This acceleration and deceleration region. This observation suggests that when the engine is applied at low observation suggests that when the engine is applied at low load, the effect of aging engine on fuel load, the effect of aging engine on fuel efficiency is negligible. Figure 11 shows the velocity profile efficiency is negligible. Figure 11 shows the velocity profile of the highway mode in the US06 driving of the highway mode in the US06 driving cycle. In the highway mode, the acceleration regions are cycle. In the highway mode, the acceleration regions are only considered to confirm the effect of aging only considered to confirm the effect of aging engine on CO2 and CO productions. As indicated in engine on CO2 and CO productions. As indicated in Figure 10, the acceleration regions are marked Figure 10, the acceleration regions are marked with A, B, and C letters. with A, B, and C letters.

14×103 8×105

7×105 12×103

6×105 10×103

5×105 8×103 4×105 6×103 3×105 4×103 2×105

2×103 1×105

0 0

FigureFigure 10. 10.Total Total amount amount of of CO CO22 andand COCO emittedemitted during acceleration acceleration and and deceleration deceleration regions regions in in the the city mode of the US06 driving cycle.city mode of the US06 driving cycle. Appl. Sci. 2018, 8, x FOR PEER REVIEW 15 of 19

is faced with more difficulty in achieving complete combustion as the load gets higher to accelerate, which leads to the production of more CO emissions, an indicator of incomplete combustion. In the C region, wherein the vehicle is required to repetitively accelerate and decelerate while a similarly low load is applied on the engine more than four times, CO2 emissions are revealed to vary, irrespective of the vehicle’s cumulative mileage at each acceleration and deceleration region. This observation suggests that when the engine is applied at low load, the effect of aging engine on fuel efficiency is negligible. Figure 11 shows the velocity profile of the highway mode in the US06 driving cycle. In the highway mode, the acceleration regions are only considered to confirm the effect of aging engine on CO2 and CO productions. As indicated in Figure 10, the acceleration regions are marked with A, B, and C letters.

7×105 12×103 12×103

6×105 10×103

5×105 8×103 4×105 6×103 3×105

3 1 4×10 2×105

2×103 1×105

0 0

Appl. Sci.Figure2018, 10.8, 2390 Total amount of CO2 and CO emitted during acceleration and deceleration regions in the16 of 19 city mode of the US06 driving cycle.

Figure 11. Velocity proﬁle for highway mode corresponding to US06 driving cycles.

Figure 12 represents concentration of CO2 and CO measured during the A, B, and C regions in the highway mode of the US06 driving cycle. In the A regions, even though the vehicle was preconditioned to some extent, which makes the engine warmed up, an increase in CO2 emissions was observed as the vehicle’s cumulative mileage mounts. For the same reason as the cause of the result shown in the (a) part of the B region in the city mode, this result can also be interpreted that, regardless of engine temperature, fuel economy deteriorates in the aging engine when the engine is subjected to relatively high load. In the remaining B and C regions of highway mode with similar operating condition as in the (b) part of the B region in city mode, CO2 and CO emissions increase as the cumulative driving distance of the vehicle mounts, for the same reason as that shown in the (b) part of the B region. When considering the results of CO2 and CO emissions measured during acceleration regions in the city and highway modes, the results show that temperature of the engine, whether the load is applied on the engine at high rpm or stationary state and how much load is applied to the engine are the factors affecting aggravation of fuel efﬁciency due to increased vehicle’s cumulative mileage. In addition, as a result of examining growth rate of CO2 as the engine ages in the urban and highway areas of the US06 driving cycle, it was conﬁrmed that the rate of increase of CO2 emissions was the highest when acceleration was performed while the vehicle was running. Based on these results, it is estimated that the aged engine has the greatest adverse impact on fuel economy when the vehicle is loaded at high speed. Appl. Sci. 2018, 8, x FOR PEER REVIEW 16 of 19

Figure 11. Velocity profile for highway mode corresponding to US06 driving cycles.

Figure 12 represents concentration of CO2 and CO measured during the A, B, and C regions in the highway mode of the US06 driving cycle. In the A regions, even though the vehicle was preconditioned to some extent, which makes the engine warmed up, an increase in CO2 emissions was observed as the vehicle’s cumulative mileage mounts. For the same reason as the cause of the result shown in the (a) part of the B region in the city mode, this result can also be interpreted that, regardless of engine temperature, fuel economy deteriorates in the aging engine when the engine is subjected to relatively high load. In the remaining B and C regions of highway mode with similar operating condition as in the (b) part of the B region in city mode, CO2 and CO emissions increase as the cumulative driving distance of the vehicle mounts, for the same reason as that shown in the (b) part of the B region. When considering the results of CO2 and CO emissions measured during acceleration regions in the city and highway modes, the results show that temperature of the engine, whether the load is applied on the engine at high rpm or stationary state and how much load is applied to the engine are the factors affecting aggravation of fuel efficiency due to increased vehicle’s cumulative mileage. In addition, as a result of examining growth rate of CO2 as the engine ages in the urban and highway areas of the US06 driving cycle, it was confirmed that the rate of increase of CO2 emissions was the highest when acceleration was performed while the vehicle was running. Based onAppl. these Sci. results,2018, 8, 2390 it is estimated that the aged engine has the greatest adverse impact on fuel economy17 of 19 when the vehicle is loaded at high speed.

1.5E+06 A BC1.6E+04 14×105 L : 6500 KM 1.38×106 1.4E+06 1.34×106 M : 15000 KM 141.4E+04×103 4 12×105 R: 30000 KM 1.39×104 1.39×10 1.2E+06 1.24×106 121.2E+04×103 1.1E+0610×105 9.88×103 101.0E+04×103 9.0E+05 9.14×103 8.86×103 8×105 8.21×105 3 [mg/L] 7.5E+05 7.93×105 88.0E+03×10 2 5 5 × 5 6.42×10 5 7.43 10 6.19×10

× CO [mg/L]

CO 6 10 6.0E+05 5.55×105 66.0E+03×103 6.34×103 5.65×103 4.5E+054×105 44.0E+03×103

3.0E+05 3 2×105 3.52×10 22.0E+03×103 1.5E+05 776.78 0 0 0.0E+00 0.0E+00 L M R L M R L M R

FigureFigure 12. 12. TotalTotal amount amount of of CO CO2 and2 and CO CO discharged discharged during during accelera accelerationtion regions regions in inthe the highway highway mode mode ofof the the US06 US06 driving driving cycle. cycle.

3.4.3.4. Estimation Estimation of ofFuel Fuel Efficiency Efficiency within within 100 100,000,000 km km Mileage Mileage Based Based on on These These Test Test Results Results FigureFigure 13 13 represents represents the the trendlines trendlines of of fuel fuel efficie efficiencyncy with with respect respect to to each each mileage mileage of ofthe the vehicle. vehicle. TrendlinesTrendlines for for city city and and highway highway modes modes were were develop developeded based based on on fuel fuel efficiency efficiency results results of of the the test test vehiclevehicle with with 6500 6500 km, km, 15,000 15,000 km, km, and and 30,000 30,000 km km cumu cumulativelative mileage, mileage, as as calculated calculated from from Equation Equation C. C. As previously indicated in the results of total CO emissions measured during the 5-cycles, rate of As previously indicated in the results of total CO2 2emissions measured during the 5-cycles, rate of change of CO emission with respect to mileage exceeding 15,000 km was only significant for the US06 change of CO2 2emission with respect to mileage exceeding 15,000 km was only significant for the US06cycle, cycle, while while those those for thefor otherthe other cycles cycles reveal reveal very very slight slight change. change. So, fuelSo, fuel efficiency efficiency of the of the vehicle vehicle with with15,000 15,000 km mileagekm mileage measured measured through through the A the formula A form inula the in rest the of rest the drivingof the driving cycles (FTP-75,cycles (FTP-75, HWFET, HWFET,SC03, COLD SC03, FTP)COLD is takenFTP) is as taken a fixed as constanta fixed constant in the Equation in the Equation C, while C, the while fuel the efficiency fuel efficiency for the US06for thedriving US06 cycledriving of citycycle or of highway city or highway mode is assignedmode is assigned to the Equation to the Equation C as trendline C as trendline equations equations developed developedusing fuel using efficiency fuel efficiency measured measured from the from vehicle the withvehicle 6500 with km, 6500 15,000 km, km, 15,000 and km, 30,000 and km30,000 mileage. km mileage.Although Although the equation the equation cannot conveycannot accurateconvey accu fuelrate consumption, fuel consumption, it can be usedit can as be an used indicator as an to estimate how much fuel economy of the A vehicle exceeding 15,000 km cumulative mileage would diverge from that measured at 6500 and 15,000 km mileage. As observed in the Figure 13, it can be confirmed that there is slight difference in results between fuel efficiency obtained by the empirical formula, and those that were obtained by Equation C at the 6500 km and 15,000 km mileage. Through the empirical formula, approximately 6.7% difference between the fuel consumption at 6500 km mileage calculated from Equation C, and that produced from the empirical formula at 100,000 km mileage for city mode, is shown, while 11.5% difference was confirmed in fuel efficiency for the highway mode. Even though the absolute values of fuel consumption at 100,000 km mileage are invalid, it can be ascertained that when the vehicle is driven at the specific type of driving in the highway mode of US06 driving cycle wherein the engine is taking load at high rpm, fuel efficiency would deteriorate severely. This result is consistent with what was revealed in the above section. Appl. Sci. 2018, 8, x FOR PEER REVIEW 17 of 19 indicator to estimate how much fuel economy of the A vehicle exceeding 15,000 km cumulative Appl. Sci. 2018, 8, 2390 18 of 19 mileage would diverge from that measured at 6500 and 15,000 km mileage.

14 13.97 13.31 12 11.5%

10 10.18 9.81 6.7% 8

6 Empirical equation for City mode

Fuel efficiency [km/L] [km/L] efficiency Fuel Empirical equation for Hihghway mode 4 6500 km, 5-Cycle F.E for Hihgway mode 6500 km, 5-Cycle F.E for City mode 2 15000 km, 5-Cycle F.E for City mode 15000 km, 5-Cycle F.E for Hihgway mode 0 6500 15,000 23,500 32,000 40,500 49,000 57,500 66,000 74,500 83,000 91,500 100,000 Mileage [km]

Figure 13. Forecast of fuel consumption for city and highway mode of A vehicle with the cumulative Figureincrease 13. in Forecast vehicle of mileage. fuel consumption for city and highway mode of A vehicle with the cumulative increase in vehicle mileage. 4. Conclusions AsIn observed this study, in the Figure difference 13, it between can be confirmed unadjusted that and there adjusted is slight fuel difference consumption in results results between was fuel efficiency obtained by the empirical formula, and those that were obtained by Equation C at the confirmed, and how CO2 emission varies with the aging engine under the test of three regulatory 6500 km and 15,000 km mileage. Through the empirical formula, approximately 6.7% difference driving cycles, FTP-75, HWFET, and US06, was investigated. CO2 and CO measured during the betweenUS06 driving the fuel cycles consumption was closely at investigated 6500 km mileage to discern calculated what factorsfrom Equation have adverse C, and effect that on produced an aging fromengine the in empirical terms of formula fuel efficiency. at 100,000 Also, km fuel mileage efficiency for city was mode, predicted is shown, using empiricalwhile 11.5% formulas difference that waswere confirmed developed in by fuel fuel efficiency consumption for the results highway obtained mode. at 6500 Even km, though 15,000 the km, absolute and 30,000 values km mileage.of fuel consumptionConclusions fromat 100,000 this study km mileage can be summarized,are invalid, it ascan follows: be ascertained that when the vehicle is driven at the specific type of driving in the highway mode of US06 driving cycle wherein the engine is taking load(1) atThere high isrpm, some fuel difference efficiency inwould fuel consumptiondeteriorate severely. for city This and result highway is consistent modes betweenwith what values was revealedcalculated in the above from Equationsection. A considering only one driving environment, FTP-75 mode, and results in Equation C and D that help to derive fuel economy when considering various driving 4. Conenvironments,clusions including fuel consumption measured in several cycles that were established by the EPA. Conversely, it appears that the Equation B adjusted fuel consumption developed In this study, the difference between unadjusted and adjusted fuel consumption results was from the EPA cannot consider various driving environments that affect fuel economy. confirmed, and how CO2 emission varies with the aging engine under the test of three regulatory (2) When the amount of CO2 exhaust gas was measured according to mileage of the vehicle in driving cycles, FTP-75, HWFET, and US06, was investigated. CO2 and CO measured during the US06 drivingthree cycles drive was cycles closely used investigated in this study, to discern it increased what factors in the have entire adverse cycles effect as the on engine an aging ages engine after in terms6500 of kmfuel of efficiency. cumulative Also, mileage fuel efficiency of the vehicle. was predicted In particular, using the empirical greatest formulas growth rate that of were CO2 developedemissions by fuel was consumption revealed in theresults US06 obtained cycles, amongat 6500 thosekm, 15,000 cycles km, with and the 30,000 aging ofkm the mileage. engine. ConclusionsIn contrast, from the this remaining study can two be summarized, cycles revealed as an follows: increase rate of CO2 emission less than the US06 cycle after 6500 km, and a similar amount of CO2 exhaust gas was emitted between 15,000 km (1) Thereand 30,000 is some km. difference in fuel consumption for city and highway modes between values calculated from Equation A considering only one driving environment, FTP-75 mode, and (3) Factors affecting CO2 and CO exhaust gas as the vehicle’s cumulative mileage increases are resuanalyzedlts in Equation in the US06 C and driving D that cycles, help to which derive include fuel economy urban andwhen highway considering modes. various In the driving region environments, including fuel consumption measured in several cycles that were established by wherein low load is applied on the engine, CO2 and CO are discharged, irrespective of aging of thethe EPA. engine. Conversely, In the region, it appears wherein that middle the Equati loadon is takenB adjusted on the fuel engine, consumption fuel consumption developed is worsefrom thewith EPA the cannot aging consider engine, depending various driving on the en engine’svironments temperature. that affect In fuel addition, economy. it can be observed (2) Whenthat when the amount the vehicle of CO accelerates2 exhaust gas while was moving, measured it is according more easily to facedmileage with of thethe atmospherevehicle in three that drivecomplete cycles combustion used in this is study, difficult it increased to achieve in in the comparison entire cycles with as when the engine the engine ages after in a stationary 6500 km ofstate cumulative is applied mileage on the of load. the Finally,vehicle. inIn the particular, regions whereinthe greatest high growth load is rate applied of CO on2 theemissions engine, was revealed in the US06 cycles, among those cycles with the aging of the engine. In contrast, unlike for the middle load case, CO2 emissions increase as the engine ages, regardless of the temperature at which the engine is operated. Appl. Sci. 2018, 8, 2390 19 of 19

(4) How much fuel economy of the test vehicle would deteriorate in the city and highway modes of the US06 driving cycle within the 100,000 km cumulative mileage of the vehicle was predicted. Even though the fuel consumption value calculated by the empirical formula cannot be completely relied on, it may help to identify the tendency of fuel economy value. The fuel consumption values that were obtained from the empirical formula are well consistent with the above results.

Author Contributions: Y.L. and J.L. (Jinwook Lee) conceived and designed the data analysis, analyzed the data, and wrote the paper; J.L. (Jaehyuk Lim) and K.K. performed the experiment and produced the experimental data; J.L. (Jinwook Lee) supervised and advised on all parts of this paper. Funding: This work was supported from the R&D project of MOTIE (Ministry of Trade, Industry and Energy) in Republic of Korea. Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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