2018 Jason GHG benefit of lightweight.pdf
Contents lists available at ScienceDirectTransportation Research Part Djournal homepage gas emission benefits of vehicle lightweighting MonteCarlo probabalistic analysis of the multi material lightweightvehicle gliderJason M. Luka, Hyung Chul Kimb, Robert D. De Kleineb, Timothy J. Wallingtonb,Heather L. MacLeana,⁎aDepartment of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario M5S 1A4, CanadabMaterials HEV, 100, and BEV, 74.The extent to which life cycle GHG emissions are reduced depends on the powertrain, whichaffects fuel cycle GHG emissions. Lightweighting an ICEV results in greater base case GHGemissions mitigation 10t CO2eq. than lightweighting a more efficient HEV 6 t CO2eq.. BEVlightweighting can result in higher or lower GHG mitigation than gasoline vehicles, dependinglargely on the source of electricity.1. IntroductionLightweight materials are increasingly being used Davis et al., 2014 to improve vehicle fuel economy and reduce fuel cycleproduction and use greenhouse gas GHG emissions. However, the production of lightweight materials is often more GHG-in-tensive than the production of conventional materials, which leads to higher vehicle cycle production emissions. Therefore, asKirchain et al. 2017 explain, the full life cycle needs to be considered to assess the GHG emission benefits of vehicle lightweighting.Kim and Wallington 2013 conducted a literature review of the life cycle GHG mitigation potential of lightweighting internalcombustion engine vehicles ICEVs. They found examples in the literature reporting that lightweighting can increase or decrease lifecycle GHG emissions. The divergence in results reflects the wide range of assumptions used in the analyses, including the lightweightmaterial used and its material substitution ratio mass of lightweight material required to replace a unit mass of conventionalmaterial.https//doi.org/10.1016/j.trd.2018.02.006⁎Corresponding author.E-mail address heatherl.macleanutoronto.ca H.L. MacLean.Transportation Research Part D 62 2018 1–10Available online 13 February 20181361-9209/ © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license http//creativecommons.org/licenses/BY-NC-ND/4.0/.TBushi et al. 2015 analyzed the Multi Material Lightweight Vehicle MMLV, which is a real world concept vehicle whosedevelopment was funded by the US Department of Energy Sarkar, 2014. Ford Motor Company and Magna International designedthe MMLV to be similar to the Ford Fusion, but 25 lighter through the use of aluminum and other lightweight materials instead ofsteel and iron, along with design changes in components Sarkar, 2014. Bushi et al. 2015 found little sensitivity of life cycle GHGemissions to assumptions regarding material recycling allocation , material transportation, plastics and tire disposal ,end-of-life scrap rate, and energy intensity of metal stamping. However, Bushi et al. 2015 found the GHG emission mitigationpotential for the MMLV relative to the Ford Fusion Ford Motor Company, 2016 to be highly sensitive to lifetime driving distanceand the fuel savings associated with lightweighting. Fuel savings depend on the powertrain type Pagerit et al., 2006; Reynolds andKandlikar, 2007; Brooker et al., 2013; Carlson et al., 2013; An and Santini, 2004; Wohlecker et al., 2007; Wilhelm et al., 2012.Several studies have analyzed the life cycle GHG mitigation potential of lightweighting alternative powertrain vehicles. Kim andWallington 2016 and Lewis et al. 2014b analyzed how potential fuel savings from lightweighting differ by powertrain type. Thisincluded differences between ICEV and hybrid electric vehicle HEV internal combustion engine size, which affect the degree towhich they can be downsized to provide further fuel savings without sacrificing acceleration perance. Similarly, Muttana andSardar 2013 highlighted the benefits of adjusting the battery size in battery electric vehicles BEVs to maintain driving range,which reduces mass and provides further fuel savings. Schuh et al. 2013 and Egede et al. 2015 analyzed the impact of drivingconditions on the potential fuel savings of alternative powertrain vehicles. Lewis et al. 2014a illustrated how the substitution ofgasoline with ethanol changes the GHG benefits of potential fuel savings. Similarly, Faβbender et al. 2012 and Lewis et al. 2012analyzed how the GHG-intensity of electricity fuel savings can vary widely. Colette et al. 2016 examined the GHG intensity ofelectricity and found it to have a substantial impact on the GHG-intensity of aluminum production.There are publicly available models that can be used to examine the impact of vehicle lightweighting on life cycle GHG emissions.Argonne National Laboratory s GREET Greenhouse gasses, Regulated Emissions, and Energy use in Transportation life cycle modelArgonne National Laboratory, 2016 includes default vehicle specifications for conventional steel-intensive and lightweightcarbon fiber-intensive vehicles with different powertrains detailed in Kelly et al., 2015. However, comparisons of these hy-pothetical vehicles are limited by inconsistencies in their specifications detailed in Luk et al., 2017. There are also models com-missioned by WorldAutoSteel 2011 and European Aluminum Ricardo, 2015 that are designed to compare steel and aluminumvehicles. These industry models produce conflicting results due to differing assumptions regarding the use of aluminum seeSupplementary Material.In our prior work, Luk et al., 2017 we replaced the default vehicle specifications in GREET Argonne National Laboratory, 2016with those based on the real world Ford Fusion and MMLV gliders vehicles without powertrains or batteries to provide a consistentand realistic basis for our analysis. Unlike Lewis et al. 2014b; we modelled the use of these gliders with different powertrains, Luket al., 2017 which impact life cycle GHG emissions Kim and Wallington, 2016; Lewis et al., 2014b, 2014a; Argonne NationalLaboratory, 2016; WorldAutoSteel, 2011; Ricardo, 2015. The effect of BEV battery downsizing examined by Muttana and Sardar,2013 on life cycle GHG emissions was found to be as substantial as the impact of HEV internal combustion engine downsizingexamined by Kim and Wallington, 2016Luk et al., 2017. However, our previous study Luk et al., 2017 did not analyze many ofthe other variables examined in the literature.These studies have made significant contributions to the literature, but no study has comprehensively examined the manyvariables that impact the ability for lightweighting to reduce life cycle GHG emissions. Therefore, this study builds upon our previouswork Luk et al., 2017 by conducting a Monte Carlo analysis to systematically examine the variables affecting the life cycle GHGemissions impact of vehicle lightweighting. We examined the life cycle GHG emissions of vehicles with either the Ford FusionFord Motor Company, 2016 steel-intensive glider or the MMLV glider to provide a realistic and consistent basis for the analysis.The use of each of these gliders in combination with ICEV, HEV and BEV powertrains was modelled. Incremental vehicle cycle andlife cycle GHG emissions from lightweighting were estimated by comparing results for conventional and lightweight versions ofvehicles with each powertrain. A sensitivity analysis of incremental results was conducted by examining the effect of changes to thue of individual assumptions applicable to US model year 2015 vehicles where possible. A Monte Carlo analysis was conducted onthe incremental results by computing results based on combinations of the different assumptions examined in the sensitivity analysis.Results are compared with those from literature/models.2. sWe uate the life cycle GHG emissions of a set of US conventional steel-intensive and lightweight multi-material vehicleswith alternative powertrains. The reference vehicle is a US model year 2015 Ford Fusion Ford Motor Company, 2016 with a 2.5 L,130kW 175 hp ICEV powertrain and 0–97km/h acceleration time of 8.8s Zal, 2013. The steel-intensive Ford Fusion Ford MotorCompany, 2016 glider was also modelled with HEV and BEV powertrains with similar 0–97km/h acceleration times. Powertraincomponents were sized using the ology developed by MacKenzie and Heywood 2012. Lightweight counterparts for each ofthese vehicles were modelled with the MMLV glider. The fuel consumption of each vehicle was estimated using equations developedby Kim and Wallington 2016. Key specifications of the base case vehicles are presented in Table 1. The sensitivity and Monte Carloanalyses also include other vehicle specifications based on modifications of the parameters discussed below.Base case vehicle cycle and life cycle GHG emissions were estimated by replacing the default GREET Argonne NationalLaboratory, 2016 model vehicle specifications with those of the vehicles described above, which avoids the concerns regardingdefault vehicle specifications detailed in Luk et al. 2017. Incremental vehicle cycle and life cycle GHG emissions were calculated bysubtracting the results for conventional vehicles from those of the lightweight vehicles with the same powertrain type. The sensitivityJ.M. Luk et al. Transportation Research Part D 62 2018 1–102analysis of these incremental results was conducted by developing a spreadsheet model that is able to both reproduce the base caseresults estimated in GREET Argonne National Laboratory, 2016 and analyze the effect of changes to the value of individualparameters based on data applicable to US model year 2015 vehicles where available. As discussed below, these parameters wereselected based onfindings in the literature. Crystal Ball Oracle, 2015 was used to conduct a Monte Carlo analysis on the incrementalresults using 10,000 Hassenzahl, 2004; Maverick, 2015different combinations of the parameters from the sensitivity analysis toestimate the probability of different results. Incremental life cycle GHG emissions results and underlying variables were comparedwith those of models commissioned by WorldAutoSteel 2011 and European Aluminum Ricardo, 2015, which analyze the use ofaluminum-intensive vehicles. Base case vehicle specifications, material breakdowns and comparisons with industry models arepresented in the Supplementary Material.2.1. Vehicle cycle variablesVehicle cycle GHG emissions include those from vehicle production, maintenance, and disposal. Vehicle production GHGemissions are a function of the mass of each of the materials used and its GHG-intensity see Fig. 1. The mass and materialbreakdowns of the conventional and lightweight gliders used in this study are shown in Fig. 1a. Steel, cast aluminum and wroughtaluminum comprise the majority of each glider. The GHG intensities of the production of parts with these materials are shown in theSupplementary Material. The energy intensities were varied by modifying the recycled material contents of steel and aluminum. TheGHG intensities of the electricity used for steel production and aluminum smelting were each examined. These and other parametersanalyzed are detailed in Table 2.Each of the gliders was modelled in combination with the three powertrains, with the mass and material breakdowns for eachshown in Fig. 1b. The masses of the internal combustion engine system 1.2kg/kW and transmission 89kg were estimated basedon the Ford Fusion reference vehicle Ford Motor Company, 2016. The masses of the electric motor and electronics controller22kg0.8kg/kW were estimated based on FASTsim FASTSim, 2012. The material breakdowns of these components are fromGREET Argonne National Laboratory, 2016. Internal combustion engines are utilized in the ICEV and HEV, while electric motors areutilized in the HEV and BEV. The sizes of these propulsion components and battery within the HEV are based on the power outputratios of components in the Ford Fusion Hybrid 105kW internal combustion engine, 88kW electric motor, 35kW high voltagebattery Ford Motor Company, 2016.Conventional vehicle powertrain peak power output was varied to provide a range of different 0–97km/h acceleration perfor-mance. Lightweight vehicle peak power output was either assumed the same as that of the non-lightweighted vehicle, reduced toincrease fuel savings and maintain acceleration perance, or reduced to a lesser degree to provide both fuel savings and improvedperance. The powertrain parameters were varied using the findings of Kim and Wallington 2016 regarding the impact offriction losses associated with powertrain component sizing on the ability for lightweighting to reduce life cycle GHG emissions.Different transmissions within the powertrains were also examined because of their impact on powertrain efficiency, as noted byPagerit et al. 2006, and acceleration perance, as determined by MacKenzie and Heywood 2012.Equations by MacKenzie and Heywood 2012 were used to calculate 0–97km/h acceleration time. The equations are based on aregression analysis of over 1500 US vehicles and are a function of vehicle curb mass, peak power output, gasoline engine dis-placement volume, powertrain type, transmission type, and technological improvements over time. The parameter that representstechnological improvements over time −0.16 was calibrated to reflect the perance of the Ford Fusion reference vehicle FordMotor Company, 2016.The HEVs and BEVs in this study were modelled with the different battery chemistries from GREET Argonne National Laboratory,2016 shown in Fig. 1c and d. The use of different battery chemistries impacts vehicle material composition and vehicle mass. TheHEV and BEV batteries were scaled based on acceleration discussed above and driving range requirements, respectively. The drivingrange of the conventional BEV, and the degree to which if any the battery in the lightweight BEV is downsized to increase fuelsavings and maintain driving range were varied. BEV driving range was estimated using fuel consumption equations by Kim andWallington 2016. Battery parameters were varied because battery downsizing has been reported by Muttana and Sardar 2013 toimpact the relative life cycle GHG emissions of aluminum and steel vehicles.Table 1Base case vehicle specifications data or values calculated as described in text.ICEV HEV BEVConventional Lightweight Conventional Lightweight Conventional LightweightEngine Power kW 130 107 103 86Motor Power kW 93 74 192 155HEV Battery Power kW 37 29BEV Battery Energy kWh 126 108Fuel Consumption L/100km 8.4 7.0 6.0 5.1 3.9 3.4Curb Weight kg 1556 1233 1661 1320 2450 1997Note ICEVinternal combustion engine vehicle, HEVhybrid electric vehicle, BEVbattery electric vehicle.J.M. Luk et al. Transportation Research Part D