The Dilemma Between Aluminum and Cast Iron

energies

Article Life-Cycle and Energy Assessment of Automotive Component Manufacturing: The Dilemma Between Aluminum and Cast Iron

Konstantinos Salonitis , Mark Jolly * , Emanuele Pagone and Michail Papanikolaou

Manufacturing Theme, Cranfield University, Cranfield, Bedford, MK43 0AL, UK * Correspondence: m.r.jolly@cranfield.ac.uk; Tel.: +44 (0)1234 758347

Received: 6 June 2019; Accepted: 30 June 2019; Published: 3 July 2019

Abstract: Considering the manufacturing of automotive components, there exists a dilemma around the substitution of traditional cast iron (CI) with lighter metals. Currently, aluminum alloys, being lighter compared to traditional materials, are considered as a more environmentally friendly solution. However, the energy required for the extraction of the primary materials and manufacturing of components is usually not taken into account in this debate. In this study, an extensive literature review was performed to estimate the overall energy required for the manufacturing of an engine cylinder block using (a) cast iron and (b) aluminum alloys. Moreover, data from over 100 automotive companies, ranging from mining companies to consultancy ﬁrms, were collected in order to support the soundness of this investigation. The environmental impact of the manufacturing of engine blocks made of these materials is presented with respect to the energy burden; the “cradle-to-grave approach” was implemented to take into account the energy input of each stage of the component life cycle starting from the resource extraction and reaching to the end-of-life processing stage. Our results indicate that, although aluminum components contribute toward reduced fuel consumption during their use phase, the vehicle distance needed to be covered in order to compensate for the up-front energy consumption related to the primary material production and manufacturing phases is very high. Thus, the substitution of traditional materials with lightweight ones in the automotive industry should be very thoughtfully evaluated.

Keywords: Manufacturing; energy eﬃciency; life-cycle assessment; aluminum; cast iron

1. Introduction Over the years, the material selection for modern car components changed a lot. As a reference, in the 1970s, a design engineer would have to select from four to ﬁve sheet forming grades, whereas today there are more than 50 options [1]. A number of material selection criteria need to be considered including corrosion and wear resistance, crashworthiness, and manufacturability. At the same time, legislation pushes for lighter vehicles, on the basis that lighter cars result in lower fuel consumption. Since 1995 in Europe, the average car CO2 emission requirement dropped from 186 g/km to 161 g/km in 2005, and it is expected to further reduce to 95 g/km in 2021 [2]. For achieving these requirements, automotive manufacturers opt to use aluminum alloys in vehicles as a “lightweight” material. The average usage of aluminum (Al) in a passenger car varies from 12% to 60% depending on the vehicle. With regard to cast Al alloys, these are mostly used for engine blocks, cylinder heads, and wheels, although they are increasingly used for nodes in the chassis structure and can potentially reduce weight by 40%. Substituting with lower-density materials leads to lower tailpipe emissions; however, this does not consider the CO2 footprint of the materials used in the manufacturing of vehicles. The CO2 footprint of

Energies 2019, 12, 2557; doi:10.3390/en12132557 www.mdpi.com/journal/energies Energies 2019, 12, x FOR PEER REVIEW 2 of 23 Energies 2019, 12, 2557 2 of 23 footprint of any material is related to its embodied energy, which is a synonym of the “track record” of a material and the way it is produced. In every production phase, energy is needed for changing any material is related to its embodied energy, which is a synonym of the “track record” of a material the phase, geometry, and properties of the material. This energy is, thus, virtually embodied in the and the way it is produced. In every production phase, energy is needed for changing the phase, material. Ashby et al. [3] presented the embodied energy of producing components for the geometry, and properties of the material. This energy is, thus, virtually embodied in the material. automotive industry and discussed the contribution of each life-cycle phase. According to their Ashby et al. [3] presented the embodied energy of producing components for the automotive industry investigation, the energy involved during the use phase of a vehicle is much larger than that during and discussed the contribution of each life-cycle phase. According to their investigation, the energy the material extraction and manufacturing phase. Similar conclusions were reached by Sorger et al. [4] whoinvolved investigated during the the effects use phase of substituting of a vehicle an is aluminum much larger cylinder than thatblock during with a the newly material developed extraction one andmade manufacturing of cast iron (CI phase.). Their Similar results conclusions showed that were the reached CI engine by Sorgerblock presents et al. [4] some who investigatedsignificant the effects of substituting an aluminum cylinder block with a newly developed one made of cast iron (CI). advantages with respect to cost, energy savings, and CO2 emissions. TheirManufacturing results showed process that efficiency the CI engine can obviously block presents have a great some impact significant on the advantages energy consumption with respect to duringcost, that energy life-cycle savings, phase and of COthe2 vehiemissions.cle. Salonitis and Ball [5] highlighted the importance of energy efficiencyManufacturing for both manufacturing process effi ciency processes can obviously and systems. have One a great of impact the most on the energy energy-consuming consumption manufacturingduring that processes life-cycle is phase casting of (when the vehicle. considering Salonitis all sub and-processes Ball [5] highlightedsuch as melting, the importance holding, of finishing),energy and efficiency a lot of for research both manufacturing is undertaken processes on how andto improve systems. its One energy of the efficiency most energy-consuming [6–10]. The castingmanufacturing process is used processes in the automotive is casting (when sector considering for the manufacturing all sub-processes of a number such asof melting,components holding, bothfinishing), in the powertrain and a lot ofand research in the isbody undertaken in white on (BIW) how. toA improvecouple of its attempts energy e ffiwereciency also [6 reported–10]. The on casting the useprocess of different is used inmaterials the automotive for the casting sector forof automotive the manufacturing components of a number [11,12]. of components both in the powertrainThe objective and of in the the present body ininvestigation white (BIW). is Ato coupleestablish of a attempts methodology were alsofor the reported environmental on the use of impactdiff erentassessment materials of substitution for the casting of material of automotives in thecomponents automotive sector [11,12]. so as to improve the current decision-Themaking objective practices of the in the present automotive investigation sector. The is to discussion establish ais methodologyon whether Al foralloys the are environmental a better optionimpact than assessment cast iron (CI), of substitution when the total of materials energy burden in the automotive is considered sector (and so not as toonly improve the tailpip the currente emissions).decision-making For assessing practices the energy in the required, automotive an extensive sector. The literature discussion review is on was whether undertaken Al alloys, and are a overbetter 100 expertsoption than from cast the iron automotive (CI), when supply the total chain, energy such burden as original is considered equipment (and not manufacturers only the tailpipe (OEMsemissions).), engineFor design assessing consultancy the energy firms, required, foundries, an extensive mining literaturecompanies, review primary was alloy undertaken, producers and, over and100 recycling experts companies, from theautomotive as well as machining, supply chain, heat such treatment as original, and impregnation equipment manufacturers companies, were (OEMs), contacted.engine The design case consultancy study selected firms, wa foundries,s the engine mining block, companies, as it is the single primary heaviest alloy producers,component and in most recycling passengercompanies, cars. as well as machining, heat treatment, and impregnation companies, were contacted. The case study selected was the engine block, as it is the single heaviest component in most passenger cars. 2. Methodology: Assessment Approach 2. Methodology: Assessment Approach Focusing only on the use phase, or only on the manufacturing phase for the assessment of the overall environmentalFocusing only impact on the use of a phase, product or onlydoes on not the allow manufacturing for a full understanding phase for the ofassessment the whole of the picture.overall The environmental “cradle-to-grave” impact approach of a product aims doesto include not allow the energy for a full consumption understanding that of occurs the whole due picture.to resourceThe “cradle-to-grave” extraction and approach processing, aims component to include andthe energy product consumption assembly, that use, occurs and dueend- toof- resourcelife processingextraction of a and vehicle processing, (Figure component1). The evaluation and product of the assembly,overall impacts use, andthat end-of-lifea product processinghas on the of a environmentvehicle (Figure through1). Theall of evaluation these life- ofcycle the stages overall would impacts give that a complete a product picture has on of the the environment lightweighting through shiftall validity. of these life-cycle stages would give a complete picture of the lightweighting shift validity.

Materials & Energy

Extraction and Componenet Material Choice Processing of Raw Vehicle Use Phase Vehicle Disposal Production Materials

Waste

Figure 1. “Cradle-to-grave” approach. Figure 1. “Cradle-to-grave” approach.

For assessing the energy required and the CO2 emissions in each stage of the life cycle, an For assessing the energy required and the CO2 emissions in each stage of the life cycle, an extensive extensive literature review was undertaken. The present study focused on all the processes, from literature review was undertaken. The present study focused on all the processes, from cradle to

Energies 2019,, 12,, x 2557 FOR PEER REVIEW 33 of of 23 23 cradle to grave, in the production of passenger vehicle engine blocks, such as mining, smelting and electrolysis,grave, in the productionmelting, holding, of passenger casting, vehicle fettling, engine heat blocks, treatment, such as mining, machining, smelting impregnation and electrolysis,, and recycling.melting, holding, casting, fettling, heat treatment, machining, impregnation, and recycling.

3.3. Embodied Embodied Energy Energy in in Materials Materials D Dueue to to Primary Primary Production TheThe starting starting point point is is the the calculation calculation of of the the primary primary production production energy energy for for each each type type of of material. material. ForFor the the calculation calculation of of embodied embodied energy, energy, the the methodology methodology proposed proposed by by Brimac Brimacombeombe et et al. al. [13] [13] is is used. used.

3.1. Primary Aluminum Production 3.1. Primary Aluminum Production TheThe production of primary aluminum requires a number of steps. Allwood Allwood and and Cullen Cullen [14] [14] suggestedsuggested that that,, for for primary primary aluminum aluminum,, the energy required is of the order order of 170 170 GJ/ton. GJ/ton. The The literature literature reviewreview indicated indicated that that energy energy ranges ranges from from 50 50 to to100 100 GJ/ton. GJ/ton. Due Due to the to theambiguity ambiguity in these in these figures, ﬁgures, the energythe energy requirements requirements were were calculated calculated theoretically; theoretically; Figure Figure 2 2 shows shows that that,, for for one one ton ton of primary primary aluminum,aluminum, 98 98 GJ GJ of of energy energy is is required. required. In In the the paragraphs paragraphs below, below, the the calculation calculation of ofthese these figures ﬁgures is explained.is explained.

FigureFigure 2 2.. PrimaryPrimary aluminum aluminum production production steps steps with with associated associated energy energy content content for for producing producing one ton ofof material material..

Primary production of aluminum starts with the mining of dry bauxite, which requires 0.17 0.08 GJ/t. Primary production of aluminum starts with the mining of dry bauxite, which requires± 0.17 ± This figure was calculated after reviewing a number of reported energy figures in the literature review 0.08 GJ/t. This figure was calculated after reviewing a number of reported energy figures in the as listed in Table1. literature review as listed in Table 1. Table 1. Bauxite mining energy per ton of bauxite. Table 1. Bauxite mining energy per ton of bauxite. Source Energy (GJ/t) Source Energy (GJ/t) [15] 0.145 [15] 0.145 [16] 0.150 [[16]17] 0.150 0.150 [[17]18] 0.150 0.153 [[18]19] 0.153 0.188 [[19]20] 0.188 0.210 [20] 0.210 Alumina is refined from bauxite through the Bayer process, where the main steps are digestion, clarification,Alumina precipitation,is refined from and bauxite calcination through [21 the]. Bayer Firstly, process, dry bauxite where is the crushed main steps in large are digestion, mills and clarification,blended with precipitation liquor to form, and slurry. calcination Then, lime [21] and. First causticly, dry soda bauxite are added, is crushed mixed, and in large poured mills into and the blendeddigester, with where liquor a solution to form of hotslur causticry. Then soda, lime dissolves and caustic thealumina. soda are Duringadded, themixed digestion,, and poured impurities into thedrop digester, to the bottom where and a solution form a solid of hot waste caustic residue soda called dissolves red mud. the alumina.In order to During separate the the digestion, alumina impuritiesfrom the red drop mud, to thethe mixbottom is moved and form to clarification. a solid waste By residue cooling, called aluminum red mud. hydroxide In order is precipitatedto separate thefrom alumina the caustic from sodathe red and mud, then the washed. mix is moved The last to clarification. step is calcination, By cooling, where aluminum the water hydroxide content inis precipitatedhydroxide is from removed, the caustic and the soda alumina and then white washed. powder The is produced last step [22is ].calcination, The energy where consumption the water in contentthis process in hydroxide varies in a is range removed where, and the calculated the alumina average white is powder 13.2 6.4 is GJ produced/t of alumina [22]. (Table The 2 energy). consumption in this process varies in a range where the calculated average± is 13.2 ± 6.4 GJ/t of alumina (Table 2).

Energies 2019, 12, 2557 4 of 23

Table 2. Alumina reﬁning energy per ton of alumina.

Source Energy (GJ/t) [19] 13.17 [17] 12.52 [23] 10.65 [15] 12.77 [16] 14.20 [18] 17.90 [24] 15.00 [25] 13.80 [23] 10.95 [26] 10.65 [20] 13.82

Red mud is highly alkaline (pH = 13), having great environmental impact; thus, it is very difficult to dispose of. It represents a major problem in the primary aluminum production. Red mud disposal covers vast areas which consequently cannot be built or farmed on, even after red mud is dried after several years. The most common ways to dispose of it is by land storage in the form of lagoons, dry stacking, or dry cake [23]. Two or more tons of red mud is produced for every ton of aluminum. The key process for producing Al is electrolysis. Alumina is dissolved in a molten cryolite to decrease the melting point of alumina. The process, known as the Hall–Heroult process after the inventors, passes an electric current through the molten alumina to dissociate it into aluminum and oxygen. The oxygen reacts with the carbon anode to produce CO2, whilst molten aluminum remains and is tapped off periodically into teapot ladles [22]. In terms of process consumables, carbon anodes are used. A mix of calcined petroleum coke, recycled anodes butts, and coal are baked at 1150 ◦C to produce anodes, consuming 3.1 GJ per ton of anode. Depending on the anode use, the produced Al can be differentiated. The two main technologies are prebake (anodes are baked in ovens and then consumed in the electrolysis cells) and Soderberg (anodes are baked directly in the electrolysis cell) [23]. Furthermore, the carbon anode is totally consumed in Soderberg technologies, while, in prebake technologies, 80% is consumed and the other 20% is used again in the anode production process. In Europe, most of the electrolysis facilities use prebake technology with the exception of two Soderberg smelters placed in Spain. By calculating the average from the range of energy consumptions required for electrolysis, the process consumes approximately 54.4 4.5 GJ/t of produced Al (Table3). ± Also, if 80% of the total amount of carbon anode is converted into carbon dioxide, an extra energy of 14 GJ/t aluminum is added to the process [26], ending up with a total energy consumption of 68 GJ/t aluminum in the electrolysis process.

Table 3. Electrolysis energy per ton of aluminum.

Sources Energy (GJ/t) [27] 56 [24] 52 [28] 66 [21] 54 [29] 53 [16] 55 [20] 47 [23] (95% prebaked and 5% Soderberg) 53.6 [23] (89% prebaked and 11% Soderberg) 55.0 [24] 50 [18] 55 [26] 56 Energies 2019, 12, 2557 5 of 23

Energies 2019, 12, x FOR PEER REVIEW 5 of 23 Afterward, the molten aluminum is poured into molds to solidify in different shapes, which are Afterward, the molten aluminum is poured into molds to solidify in different shapes, which are shipped as ingots. In some cases, liquid aluminum is transported in insulated ladles by road depending shipped as ingots. In some cases, liquid aluminum is transported in insulated ladles by road on the proximity of the foundry [18]. The average energy consumption for ingot casting from the depending on the proximity of the foundry [18]. The average energy consumption for ingot casting range collected from the literature review is 1.81 0.17 GJ per ton of aluminum (Table4). Finally, from the range collected from the literature review± is 1.81 ± 0.17 GJ per ton of aluminum (Table 4). by adding up all the energy consumed in all the different processes, the production of one ton of Finally, by adding up all the energy consumed in all the different processes, the production of one primary aluminum requires 98 GJ. ton of primary aluminum requires 98 GJ. Table 4. Cast ingot energy per ton of aluminum. Table 4. Cast ingot energy per ton of aluminum. Sources Energy (GJ/t) Sources Energy (GJ/t) [26] 2.00 [26] 2.00 [18] 1.77 [20[18]] 1.77 1.67 [20] 1.67 3.2. Pig Iron Production 3.2. Pig Iron Production Similarly, for primary iron/steel, the energy required for the production of pig iron, according to Similarly, for primary iron/steel, the energy required for the production of pig iron, according the literature review, ranges from 20 to 40 GJ/ton. Revisiting the process and calculating the energy per to the literature review, ranges from 20 to 40 GJ/ton. Revisiting the process and calculating the energy phases theoretically indicated that the energy content of one ton of primary iron is 17 GJ (Figure3). per phases theoretically indicated that the energy content of one ton of primary iron is 17 GJ (Figure In the paragraphs below, the calculation of these figures is explained. 3). In the paragraphs below, the calculation of these figures is explained.

FigureFigure 3 3.. PrimaryPrimary iron iron production production steps steps with associated with associated energy energycontent for content producing for producing one ton of material one ton. of material. According to Moll et al. [30], the main raw material in pig iron production is iron ore, consuming an averageAccording energy to Mollof 0.44 et al.± 0.2 [30 GJ/t], the of mainiron ore raw mined material (Table in pig 5). ironFine productioniron ores are is converted iron ore, consuming into lump anores average before energycharging of 0.44into the0.2 blast GJ/t furnace, of iron ore in mineda process (Table known5). Fine as iron iron ore ores agglomeration. are converted into There lump are ± orestwo before different charging processes into ofthe agglomeration blast furnace, in which a process are used known in as industry: iron ore sintering agglomeration. and pelletizing. There are twoSintering diﬀerent plants processes are usually of agglomerationlocated near the which blast arefurnace used site in, industry:while pelletizing sintering plants and are pelletizing. situated Sinteringnear the mines plants [31] are. usuallyFrom the located range of near data the collected, blast furnace the aver site,age while energy pelletizing required plants for this are process situated is near1.59 ± the 0.36 mines GJ/t [of31 iron]. From agglomerate the range (Table of data 6). collected, the average energy required for this process is 1.59 0.36 GJ/t of iron agglomerate (Table6). ± Table 5. Iron ore mining and concentration energy per ton of iron ore. Table 5. Iron ore mining and concentration energy per ton of iron ore. Sources Energy (GJ/t) Sources[32] Energy0.153 (GJ /t) [32[33]] 0.142 0.153 [33[30]] 0.177 0.142 [30[27]] 0.956 0.177 [27[34]] 0.750 0.956 [34] 0.750

Energies 2019, 12, 2557 6 of 23

Table 6. Iron ore agglomeration per ton of iron ore agglomerated.

Sources Energy (GJ/t) [35] 1.70 [33] 1.50 [27] 1.37 [36] 1.60 [30] (pelletizing) 1.33 [30] (sintering) 1.55 [37] (pelletizing) 0.82 [37] (sintering) 1.54 [38] (sintering) 2.25 [34] (sintering) 1.75 [31] (pelletizing) 2.10 [31] (sintering) 1.60

Coal is converted at high temperatures to produce coke, which will provide permeability, heat, and gases which are required to reduce and melt the iron ore, pellets, and sinter [39]. The energy consumed to produce one ton of coke is approximately 3.98 1.1 GJ (Table7). In some countries like ± Brazil, charcoal is commonly used in the production of pig iron instead of coke.

Table 7. Coke manufacturing energy per ton of coke.

Sources Speciﬁc Country Energy (GJ/t) [27] 2.19 [40] 3.70 Germany 2003 3.70 [34] Japan 2002 3.50 China 2004 4.20 [35] 4.30 [37] 4.45 [22] 3.59 [36] 5.80 [38] 2.40 [31] 6.00

Finally, limestone is added in order to remove the impurities [33]. Similar to iron ore, limestone also has to be extracted from the earth, in a process that consumes close to 0.9 0.5 GJ per ton (Table8). ± Table 8. Energy consumption per ton of limestone.

Sources Energy (GJ/t) [41] 0.964 [27] 0.848

The iron ore (lump, sinter, and/or pellets), along with additives such as limestone and reducing agents (coke), is put into the blast furnace in order to smelt. Then, a hot air blast is injected into the blast furnace. The limestone is melted to remove the sulfur and other impurities, originating a residue known as slag. This process, known as smelting, is the most energy-consuming in the production of pig iron, accounting for 13 GJ (Table9) of the total 17.4 GJ per ton of pig iron. Energies 2019, 12, x FOR PEER REVIEW 7 of 23

Table 9. Energy consumption per ton of limestone.

Sources Specifics Energy (GJ/t) [22] 16.90

Energies 2019, 12, 2557 [38] 13.6–16.2 7 of 23 [42] Blast furnace 12.3 [40] Blast furnace 10.4 [27]Table 9. EnergyRaw iron consumption manufacturing per ton of limestone.12.8 Sources[31] Blast Speciﬁcs furnace Energy13–14.1 (GJ /t) [43] Blast furnace 12.7–18.6 [22] 16.90 [38[44]] 13.6–16.212.0 [42[34]] blast Blast furnace furnace 10.4 12.3 [40[45]] Blast furnace 12.2 10.4 [27[36]] Rawblast iron manufacturingfurnace 10.4 12.8 [31[37]] Blast furnace 13.63 13–14.1 [43] Blast furnace 12.7–18.6 [44] 12.0 3.3. Outcome [34] blast furnace 10.4 [45] 12.2 In Figure 4, the various stages and their energy consumption for the production of one ton of [36] blast furnace 10.4 pig iron and primary aluminum[37] are shown. The difference in the total 13.63 energy consumed to produce one ton of primary aluminum when compared to the production of the same amount of pig iron sums up to roughly 80 GJ. 3.3. Outcome Furthermore, red mud is a by-product of the primary aluminum production at a rate of two tons per tonIn Figure of aluminum4, the various (120 million stages andtons theirper year) energy and, consumption at this moment, for the there production are no solutions of one ton for of it. pig On ironthe other and primary hand, the aluminum slag from are the shown. smelting The process diﬀerence is easily in the recycled total energy into consumedroad and cement to produce making. one tonFinally, of primary the electrolysis aluminum of when alumina compared consumes to the four production times more of theenergy same than amount the whole of pig production iron sums up of topig roughly iron. 80 GJ.

FigureFigure 4.4. EnergyEnergy consumptionconsumption forfor thethe productionproduction ofof pigpig ironiron andand primaryprimary aluminum.aluminum.

4. CaseFurthermore, Study: Engine red mud Block is a by-product of the primary aluminum production at a rate of two tons per ton of aluminum (120 million tons per year) and, at this moment, there are no solutions for it. On theThe other heaviest hand, single the slag component from the in smelting a passenger process vehicle is easily is the recycled cylinder into block. road Over and the cement last 10 making. years, Finally,the most the significant electrolysis transformation of alumina consumes in engines four was times the capacity more energy to provide than more the whole power production with a lower of pigdisplacement. iron. This is a result of one of the most significant engine trends: downsizing. Comparing 2001 with 2013, engine power increased 20% while engine displacement decreased by 10% [46]. 4.Furthermore Case Study:, the Engine top-selling Block vehicle models worldwide follow this trend. According to Reference [46], the engineThe heaviest displacem singleent component of the most in asold passenger vehicles vehicle is between is the cylinder0.8 and block.2.0 L, Overexcept the for last the 10 United years, the most significant transformation in engines was the capacity to provide more power with a lower displacement. This is a result of one of the most significant engine trends: downsizing. Comparing 2001 with 2013, engine power increased 20% while engine displacement decreased by 10% [46]. Furthermore, the top-selling vehicle models worldwide follow this trend. According to Reference [46], the engine EnergiesEnergies 2019 2019, ,12 12, ,x x FOR FOR PEER PEER REVIEW REVIEW 88 of of 23 23 Energies 2019, 12, 2557 8 of 23 StatesStates ofof AmericaAmerica ((USAUSA)) andand Canada,Canada, wherewhere enginesengines withwith moremore powerpower andand displacementdisplacement areare highlyhighly valued. displacementvalued.Energies 2019 of, 12 the, x FOR most PEER sold REVIEW vehicles is between 0.8 and 2.0 L, except for the United States of8 Americaof 23 The four-cylinder blocks were selected as a case study in the present study, as they represent (USA)The and four Canada,-cylinder where blocks engines were with selected more as power a case and study displacement in the present are highly study, valued. as they represent approximatelyapproximatelyStates of America 71%71% ofof ( USA thethe total)total and blocksCanada,blocks manufacturedmanufactured where engines worldwidewithworldwide more power [47][47]. .and ForFor displacement thethe reasonsreasons mentionedarementioned highly inin Thevalued. four-cylinder blocks were selected as a case study in the present study, as they represent thethe previous previous paragraph, paragraph, the the present present investigation investigation focuses focuses on on in in--lineline four four--cylindercylinder 1.6 1.6--LL engine engine blocks blocks. . approximatelyThe four 71%-cylinder of the blocks total blocks were selected manufactured as a case worldwidestudy in the [present47]. For study, the reasons as they mentionedrepresent in TheseThese can can be be found found in in both both diesel diesel and and petrol petrol versions versions and and in in both both CI CI and and Al Al--alloyalloy materials. materials. Al Al--alloyalloy the previousapproximately paragraph, 71% of the the present total blocks investigation manufactured focuses worldwide on in-line [47] four-cylinder. For the reasons 1.6-L mentioned engine blocks.in engine blocks are lighter than CI engine blocks as illustrated in Figure 5. However, due to the fact Theseenginethe can blocks previous be found are paragraph, lighter in both than the diesel presentCI andengine investigation petrol blocks versions as focuses illustrated and on in in both- linein Figure CIfour and-cylinder 5. Al-alloy However, 1.6-L materials. engine due blocks to Al-alloythe. fact that CI is stronger than Al alloys, Al-alloy engine blocks need thicker walls between cylinder bores, enginethat CIThese blocksis stronger can are be found lighter than in Al than both alloys, CIdiesel engine Al and-alloy blockspetrol engine versions as illustrated blocks and needin inboth Figurethicker CI and5. walls However,Al-alloy between materials. due tocyli theAlnder-alloy fact bores that , making them longer. As a result, the volume of CI required is considerably less, being in the region CImaking is strongerengine them blocks thanlonger. are Al alloys,lighterAs a result, Al-alloythan CI the engine engine volume blocks blocks of CIas need requiredillustrated thicker is in considerably wallsFigure between 5. However, less, cylinder being due to bores, in the the fact making region of 55% of that of the equivalent Al-alloy block, and CI engines are considerably more compact. As themof 55%that longer. of CI that is As stronger of a the result, equivalent than the Al volume alloys, Al -Alalloy of-alloy CI block required engine, and blocks is CI considerably engines need thicker are less, considerablywalls being between in the morecyli regionnder compact. bores of 55%, As of illustratedmaking in themFigure longer. 5, the As weight a result, different the volumeials between of CI required the petrol is considerably and diesel less, engines being madein the ofregion Al alloy thatillustrated of the equivalentin Figure 5, Al-alloy the weight block, different and CIials engines between are the considerably petrol and more diesel compact. engines made As illustrated of Al alloy in and CIof are 55% 9 andof that 11 of kg the, respectively. equivalent Al However,-alloy block more, and compact CI engines engines are considerably lead to an more even compact. smaller weightAs Figureand CI5 are, the 9 weightand 11 dikgff, respectively.erentials between However, the petrol more and compact diesel engines engines lead made to ofan Aleven alloy smaller and CI weight are 9 differenceillustrated in the in Figure fully assembled5, the weight engine, different asials a between result the of smallerpetrol and ancillary diesel engines components. made of Al Thus, alloy our anddifference 11 kg, respectively. in the fully assembled However, more engine, compact as a result engines of leadsmaller to an ancillary even smaller components. weight diThus,fference our calculationscalculationsand CI areare are 9 based basedand 11 on onkg an ,an respectively. on on--thethe--roadroad However, weight weight moredifferential differential compact for for engines the the engine engine lead to of ofan 7 7even kg kg and andsmaller 9 9 kg kg weight for for petrol petrol in thedifference fully assembled in the fully engine, assembled as a result engine, of as smaller a result ancillary of smaller components. ancillary components. Thus, our Thus, calculations our andand diesel diesel, ,respectively respectively, ,which which was was substantiated substantiated by by a a number number of of design design consultancy consultancy firms firms and and OEMs. OEMs. are basedcalculations on an on-the-roadare based on an weight on-the di-roadfferential weight for differential the engine for the of 7engine kg and of 97 kg and for 9 petrol kg forand petrol diesel, respectively,and diesel which, respectively was substantiated, which was substantiated by a number by of a number design consultancyof design consultancy firms and firms OEMs. and OEMs.

FigureFigureFigureFigure 5 5.5. .Weight Weight 5. Weight difference didifferenceﬀ erencedifference betweenbetween between castcast cast iron ironiron iron and andand and aluminum aluminum-alloyaluminum--alloy-alloyalloy engine engine engine blocks blocksblocks according according accordingaccording to the to to fuelthe thethe fuel fuelfuel consumedconsumedconsumedconsumed by byby the thethe by vehicle vehiclevehiclethe vehicle for forfor for1.6 1.6-L1.6 -1.6-LL -engines engines.Lengines engines. . .

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CORE SAND GREEN SAND CORE SAND GREEN SAND CORE SAND CORE ANGDR EEN SAND MOLD PIG IRON SCRAP CORE AND CORMEA KAINGD MMOOLLDD PIPGIG IR IROONN SCSRCRAAPP MMAAKKININGG

MELTING HOLDING CASTING FETTLING MACHINING

MMEELLTTININGG HHOOLLDDININGG CCAASSTTININGG FFEETTTLLININGG MMAACCHHININININGG Figure 6. Process flow for cast iron (CI) engine block manufacturing . Figure 6. Process flow for cast iron (CI) engine block manufacturing. FigureFigure 6.6. Process ﬂowflow for castcast ironiron (CI)(CI) engineengine blockblock manufacturing.manufacturing. MELTING HOLDING CASTING FETTLING MACHINING

MMEELLTTININGG HHOOLLDDININGG CCAASSTTININGG FFEETTTTLLININGG MMAACCHHININININGG INGOT CORE SAND CORE AND LINERS MOLD HEAT HEAT MAKING TREATMENT TREATMENT INGOT CCOORREE GS RSAEANENDND SAND CORE AND LILNINEERRSS INGOT CORE AND HEAT HEAT MMOOLLDD HEAT HEAT MAKING TTRREEAATTMMEENNTT TTRREEAATTMMEENNTT Figure 7. Process flowMAK INforG Al-alloy engine block manufacturing. GGRREEENN S SAANNDD 4.1. CI Engine BlocksFigureFigureFigure 7 7.7. .Process Process flow ﬂowflow for forfor Al Al-alloyAl--alloyalloy engine engineengine block blockblock manufacturing manufacturing.manufacturing. . Producing engine blocks from cast iron requires casting to a near net shape and machining to 4.1. CI Engine Blocks 4.1.4.1. CI CIthe E Engine ngineexact Blocks dimensions.Blocks For collecting the required data (material use and energy consumption), three Producing engine blocks from cast iron requires casting to a near net shape and machining to the ProducingProducing engineengine blocksblocks fromfrom castcast ironiron requiresrequires castingcasting toto aa nearnear netnet shapeshape andand machiningmachining toto exact dimensions. For collecting the required data (material use and energy consumption), three casting thethe exactexact dimensions.dimensions. ForFor collectingcollecting the the requiredrequired datadata (material(material useuse andand energyenergy consumption),consumption), threethree

Energies 2019, 12, 2557 9 of 23 Energies 2019, 12, x FOR PEER REVIEW 9 of 23

foundries were visited. Thesecasting three found foundriesries were are visited. responsible These for three the foundries production are of responsible more than 60%for the of production of more than the world’s cast-iron engine60% blocks. of the world’s cast-iron engine blocks.

4.1.1. Melting Stage 4.1.1. Melting Stage The casting temperatures for CI and Al vary around 1500 C and 730 C, respectively. This normally The casting temperatures for◦ CI and Al◦ vary around 1500 °C and 730 °C , respectively. This occurs in a melting furnace which can differ from foundry to foundry and/or for different metals. normally occurs in a melting furnace which can differ from foundry to foundry and/or for different Normally, two types of furnaces are used: cupola and induction. By a number of foundries, it was metals. Normally, two types of furnaces are used: cupola and induction. By a number of foundries, verified that they only use cupola furnaces to produce CI engine blocks. Cupola furnaces use coke as it was verified that they only use cupola furnaces to produce CI engine blocks. Cupola furnaces use an energy source, and their thermal efficiency ranges between 20 and 30%. The main inputs in these coke as an energy source, and their thermal efficiency ranges between 20 and 30%. The main inputs furnaces are pig iron (4.8%), ferrosilicon 75% Si (4%), and steel and/or CI scrap (91.2%). Unrecoverable in these furnaces are pig iron (4.8%), ferrosilicon 75% Si (4%), and steel and/or CI scrap (91.2%). metal losses, mainly due to oxidation, are reported by foundries, to an average of 2%. In total, three CI Unrecoverable metal losses, mainly due to oxidation, are reported by foundries, to an average of 2%. foundries were audited, and the energy per ton of liquid metal was measured to be 3.9 0.1 GJ In total, three CI foundries were audited, and the energy per ton of± liquid metal was measured to be (Figure8). 3.9 ± 0.1 GJ (Figure 8).

4.5 4.5 4.0 4.0 4.0 3.6 4.0 3.5 3.5

3.0 3.0 ) )

2.5 ) 2.5 metal 2.0 metal 2.0 1.5 1.5 1.0 1.0 0.3

0.5 0.5 0.1 Normalised Normalised Melting Energy (GJ/t of Energies 2019, 12, x FOR PEER REVIEW 9 of 23 Normalised Melting Energy (GJ/t of 0.0 0.0 casting foundries were visited. These three foundries are responsibleCI - F1 for the CIproduction - F2 ofCI more - F4 than CI - F1 CI - F2 60% of the world’s cast-iron engine blocks. Figure 8. Melting energy per ton of liquid metal in three different cast-iron foundries. Figure 8. Melting energy per ton of liquid 4.1.1. Melting Stage Figure 9. Holding energy per ton of liquid 4.1.2. Holding Stage metal in three different cast-iron metal in two different cast-iron foundries. The casting temperatures for CI and Al vary aroundfoundries 1500. °C and 730 °C , respectively. This normally occurs in a meltingAfter furnace melting, which to keepcan differ the metalfrom foundry at casting to foundry temperature and/or and for different with a consistent composition, it is metals. Normally, twotransferred types of andfurnaces kept are in theused: holding cupola furnaceand induction. as a bu Byffer a duenumber to di offferent foundries, production rates. The energy per it was verified that tonthey of only liquid use metalcupola wasfurnaces measured to produce to be CI 0.2 engine0.1 blocks GJ in. two Cupola foundries furnaces (Figure use 9). The holding furnaces 4.1.2. Holding Stage± coke as an energy source,in both and foundries their thermal were efficiency electricity ranges powered. between One 20 and of 30%. the biggest The main factors inputs in the energy consumption After melting, to keep the metal at casting temperature and with a consistent composition, it is in these furnaces areduring pig iron the holding(4.8%), ferrosilicon process is 75%the holding Si (4%), time. and steel This and/or changes CI from scrap foundry (91.2%). to foundry according to the Unrecoverable metal losses, mainly due to oxidation,transferred are reported and kept by foundries, in the holding to an average furnace of as 2%. a buffer due to different production rates. The energy production rate, casting method, and of course the type of metal. In the holding process, the foundries In total, three CI foundries were audited, and theper energy ton of per liquid ton of metalliquid metalwas measured was measured to be to be0.2 ± 0.1 GJ in two foundries (Figure 9). The holding reported an unrecoverable metal loss of 2%. 3.9 ± 0.1 GJ (Figure 8). furnaces in both foundries were electricity powered. One of the biggest factors in the energy consumption during the holding process is the holding time. This changes from foundry to foundry 4.5 4.5 4.0 4.0 according to the production rate, casting method, and of course the type of metal. In the holding 4.0 3.6 process, the4.0 foundries reported an unrecoverable metal loss of 2%. 3.5 3.5

3.0 4.1.3. Core3.0- and Mold-Making Stage ) )

2.5 ) 2.5 metal 2.0 In enginemetal 2.0 block castings, cores are used to form the complex internal geometry of the block. 1.5 Cores are1.5 made from silica sand using the cold box method, where a binder system is used to cure 1.0 the sand 1.0and resin to form the core. The design of the core varies depending on the material to be 0.3

0.5 casted, and0.5, for CI engine0.1 blocks, the reported core weight is 42.6 ± 4 kg (Figure 10a). The process of

Normalised Normalised Melting Energy (GJ/t of Normalised Normalised Melting Energy (GJ/t of 0.0 core-making0.0 also consumes a significant amount of energy, as the cores are normally coated and CI - F1 CI - F2 CI - F4 baked before use. CIThree - F1 foundriesCI reported - F2 average energy needed for core-making to be 0.97 ± 0.3 GJ per ton of core sand (Figure 10b). In addition to the cores, a sand mold is used to form the outer Figure 8. Melting energy per Figureton of liquid 9. Holding energy per ton of liquid metal in two diﬀerent cast-iron foundries. limits ofFigure the casting. 9. Holding It is energy also usedper ton to of support liquid the core package, which together form the core package metal in three different cast-iron system. Themetal weight in two different of the sandcast-iron mold, foundries according. to one of the foundries, is approximately 180 kg. For foundries.

4.1.2. Holding Stage After melting, to keep the metal at casting temperature and with a consistent composition, it is transferred and kept in the holding furnace as a buffer due to different production rates. The energy per ton of liquid metal was measured to be 0.2 ± 0.1 GJ in two foundries (Figure 9). The holding furnaces in both foundries were electricity powered. One of the biggest factors in the energy consumption during the holding process is the holding time. This changes from foundry to foundry according to the production rate, casting method, and of course the type of metal. In the holding process, the foundries reported an unrecoverable metal loss of 2%.

4.1.3. Core- and Mold-Making Stage In engine block castings, cores are used to form the complex internal geometry of the block. Cores are made from silica sand using the cold box method, where a binder system is used to cure the sand and resin to form the core. The design of the core varies depending on the material to be casted, and, for CI engine blocks, the reported core weight is 42.6 ± 4 kg (Figure 10a). The process of core-making also consumes a significant amount of energy, as the cores are normally coated and baked before use. Three foundries reported average energy needed for core-making to be 0.97 ± 0.3 GJ per ton of core sand (Figure 10b). In addition to the cores, a sand mold is used to form the outer limits of the casting. It is also used to support the core package, which together form the core package system. The weight of the sand mold, according to one of the foundries, is approximately 180 kg. For

Energies 2019, 12, 2557 10 of 23

4.1.3. Core- and Mold-Making Stage In engine block castings, cores are used to form the complex internal geometry of the block. Cores are made from silica sand using the cold box method, where a binder system is used to cure the sand and resin to form the core. The design of the core varies depending on the material to be casted, and, for CI engine blocks, the reported core weight is 42.6 4 kg (Figure 10a). The process of ± core-making also consumes a signiﬁcant amount of energy, as the cores are normally coated and baked before use. Three foundries reported average energy needed for core-making to be 0.97 0.3 GJ per ± ton of core sand (Figure 10b). In addition to the cores, a sand mold is used to form the outer limits of the casting. It is also used to support the core package, which together form the core package system. The weightEnergies 2019 of the, 12, x sand FOR PEER mold, REVIEW according to one of the foundries, is approximately 180 kg.10 of For 23 the formation of the mold, machining is used that is reported to consume 0.16 0.2 GJ (Figure 10c) per ton the formation of the mold, machining is used that is reported to consume± 0.16 ± 0.2 GJ (Figure 10c) of green sand. per ton of green sand.

70 1.6 1.5 0.2 0.18 58 0.18 60 1.4 0.16 1.2 0.14 50 0.14 39 1 0.9 40 0.12 31 0.8 0.1 30 0.6 0.5 0.08 0.06

Core weight Core weight (kg) 20

0.4 (GJ/t (GJ/t of Core Sand)

Normalised Normalised Mould Making 0.04 10 Energy (GJ/t of Green Sand) 0.2 0.02 0 Normalised Core Making Energy 0 0 CI - F1 CI - F2 CI - F4 CI - F1 CI - F2 CI - F4 CI - F1 CI - F2 (a) (b) (c)

FigureFigure 10. Mold- 10: M andold- and core-making: core-making: (a )(a core) core weight, weight, ( (bb)) core-makingcore-making energy, energy, and and (c () cmold) mold-making-making energy energy..

4.1.4. Casting4.1.4. Casting Stage Stage For theFor casting the casting of CI of intoCI into engine engine blocks, blocks, all all visited visited foundriesfoundries reported reported that that only only gravity gravity sand sand castingcasting is used, is used, using using green green sand sand molds molds and and a a core core package. package. In In gravity gravity sand sand casting, casting, liquid liquid metal metal is is pouredpoured into a into cavity a cavity that isthat formed is formed by aby monolithic a monolithic sand sand mold, mold, as as explained explained previously.previously. The The pouring pouring of the metalof the can metal be fullycan be automated, fully automated, semi-automated, semi-automated or completely, or completely manual. manual. Flow Flow rates rates of of the the metal metal may vary frommay vary the beginningfrom the beginning to the end to the of aend casting of a casting campaign campaign as the as pouringthe pouring ladle ladle empties. empties. Metal Metal ﬂow flow velocities should be adequate to avoid turbulence and achieve a good-quality casting. Sand velocities should be adequate to avoid turbulence and achieve a good-quality casting. Sand castings castings have a low cooling rate because of the sand insulating mass surrounding the casting. have a low cooling rate because of the sand insulating mass surrounding the casting. 4.1.5. Fettling Stage 4.1.5. Fettling Stage Following the casting process and the removal of the solid block from the sand mold, it has to Followingbe roughlythe machined casting to process remove andsecondary the removal cavities, of risers, the solidrunners block, and from gates the(also sand known mold, as fettling). it has to be roughlyThis machined excess material to remove is usually secondary re-melted. cavities, The mold risers, yield runners, reported andfrom gates all three (also foundries known was as fettling).75 ± This excess1% (Figure material 11a). isThe usually energy re-melted. consumed Theduring mold the proces yield reporteds varies significantly from all three per foundry, foundries and was the75 ± 1% (Figurereported 11 a).values The range energy from consumed 0.1 to 1.4 GJ during per ton the of processliquid metal varies (Figure signiﬁcantly 11b). per foundry, and the reported values range from 0.1 to 1.4 GJ per ton of liquid metal (Figure 11b). 90% 1.6 77% 75% 76% 1.4 4.1.6. Machining80% Stage 1.4 70% 1.2 60% Castings are produced volumetrically larger than required.1.0 Surfaces such as cylinder bores, 50% deck faces, crankshaft bores, etc. are casted with an excess0.8 material of 2–3 mm that allows later 40% metal) 0.6 dimensional corrections.30% A large number of holes must be drilled for oil circulation,0.4 bolts, etc. The main machining operations process (%) 20% in an engine block are cubing, boring,0.4 drilling, and threading. Machining 0.1

Mould Mould Yield vs casting 10% 0.2 Normalised Normalised Fettlinf Energy performance and, consequently, machining energy consumption Consumption (GJ/t of liquid may vary according to the machining 0% 0.0 parameters used. TheCI - F1 energyCI can- F2 be signiﬁcantlyCI - F4 reduced byCI arranging - F1 CI - for F2 castingCI - F4 feeders to be

(a) (b)

Figure 11. Fettling process: (a) mold yield in different casting processes; (b) fettling energy consumption.

4.1.6. Machining Stage Castings are produced volumetrically larger than required. Surfaces such as cylinder bores, deck faces, crankshaft bores, etc. are casted with an excess material of 2–3 mm that allows later dimensional corrections. A large number of holes must be drilled for oil circulation, bolts, etc. The main machining

Energies 2019, 12, x FOR PEER REVIEW 10 of 23

the formation of the mold, machining is used that is reported to consume 0.16 ± 0.2 GJ (Figure 10c) per ton of green sand.

70 1.6 1.5 0.2 0.18 58 0.18 60 1.4 0.16 1.2 0.14 50 0.14 39 1 0.9 40 0.12 31 0.8 0.1 30 0.6 0.5 0.08 0.06

Core weight Core weight (kg) 20

0.4 (GJ/t (GJ/t of Core Sand)

Normalised Normalised Mould Making 0.04 10 Energy (GJ/t of Green Sand) 0.2 0.02 0 Normalised Core Making Energy 0 0 CI - F1 CI - F2 CI - F4 CI - F1 CI - F2 CI - F4 CI - F1 CI - F2 (a) (b) (c)

Figure 10: Mold- and core-making: (a) core weight, (b) core-making energy, and (c) mold-making energy.

4.1.4. Casting Stage For the casting of CI into engine blocks, all visited foundries reported that only gravity sand casting is used, using green sand molds and a core package. In gravity sand casting, liquid metal is poured into a cavity that is formed by a monolithic sand mold, as explained previously. The pouring of the metal can be fully automated, semi-automated, or completely manual. Flow rates of the metal Energies 2019, 12, 2557 11 of 23 may vary from the beginning to the end of a casting campaign as the pouring ladle empties. Metal flow velocities should be adequate to avoid turbulence and achieve a good-quality casting. Sand locatedcastings on areas have which a low arecooling to be rate machined. because of Thethe sand approach insulating used mass to quantify surrounding the the energy casting. requirements during machining is based on an analytical model provided by MAG Manufacturing Technology [48]. 4.1.5. Fettling Stage The model used is based on real machining energy measurements and has the capability to aggregate all the ancillaryFollowing energy the casting requirements process and (air, the coolant removal supply, of the etc.)solid intoblock each from operation.the sand mold, Cycle it has times to for each operationbe roughly were machined obtained to remove from secondary machining cavities, outsourcing risers, runners houses, and for twogates in-line (also known four-cylinder as fettling). blocks. This excess material is usually re-melted. The mold yield reported from all three foundries was 75 ± The total energy consumption calculated for machining one cast-iron block is 61 MJ, i.e., 1.6 GJ/ton of 1% (Figure 11a). The energy consumed during the process varies significantly per foundry, and the cast-ironreported block. values Usually, range 10 from kg of0.1 material to 1.4 GJ isper removed, ton of liquid which metal represents (Figure 11b 20%). of the block.

90% 1.6 77% 75% 76% 1.4 80% 1.4 Energies 201970%, 12, x FOR PEER REVIEW 1.2 11 of 23 60% 1.0 50% operations in an engine block are cubing, boring, drilling0.8, and threading. Machining performance 40% and, consequently, machining energy consumption may varymetal) 0.6 according to the machining parameters 30% 0.4 used. The process (%) 20% energy can be significantly reduced by arranging0.4 for casting feeders to be located on areas 0.1

which Mould Yield vs casting are10% to be machined. The approach used to quantify the0.2 energy requirements during machining Normalised Normalised Fettlinf Energy is based on0% an analytical model provided by MAG Manufacturing Consumption (GJ/t of liquid 0.0 Technology [48]. The model used is based on real machiningCI - F1 energyCI - F2 measurementsCI - F4 and has the capabilityCI - F1 to aggregateCI - F2 allCI the - F4 ancillary energy requirements (air, coolant supply, etc.) into each operation. Cycle times for each operation (a) (b) were obtained from machining outsourcing houses for two in-line four-cylinder blocks. The total FigureenergyFigure 11.consumptionFettling 11. Fettling process: calculatedprocess: (a )(a mold) moldfor machining yield yield in in didifferentff erentone cast casting -iron processes; processes; block is ( b61) ( bfettling MJ,) fettling i.e. energy, 1.6 energy GJ/ton consumption consumption. of cast. -iron block. Usually, 10 kg of material is removed, which represents 20% of the block. 4.1.7.4.1.6. Ancillary Machining Processes Stage 4.1.7. Ancillary Processes MiscellaneousCastings are energy produced is related volumetrically to the facility larger operationthan required. and Surfaces other ancillary such as cylinder processes bores, like deck heating, lighting,face etc.sMiscellaneous, crankshaft The energies bore energys, included etc. are is relatedcasted in each with to foundry the an excess facility for material operation the miscellaneous of 2 and–3 mm other that processes ancillaryallows later vary processes dimensional widely. like In the heating, lighting, etc. The energies included in each foundry for the miscellaneous processes vary case ofcorrections. the three A CI large foundries, number the of holes reported must energybe drilled ranged for oil circulation, from 0.1 to bolts 3.8 GJ, etc. per The ton main of machining good casting. widely. In the case of the three CI foundries, the reported energy ranged from 0.1 to 3.8 GJ per ton of 4.1.8.good Inspection casting.Stage Quality4.1.8. Inspection inspection Stage is undertaken throughout the casting process. Foundries aim to minimize their internal rejectionQuality inspection rate to increase is undertaken their e ffithroughciencyout by the applying casting process. strict internal Foundries inspection aim to minimi standardsze in ordertheir to not internal ship rejection and transport rate to increase bad product. their efficiency CI foundries by applying reported strict aninternal average inspection of 3% standards internal scrap and 0.5%in order external to not ship scrap. and Internal transport scraped bad product. CI blocks CI foundries are re-melted reported directly. an average of 3% internal scrap and 0.5% external scrap. Internal scraped CI blocks are re-melted directly. 4.1.9. Material Recycling 4.1.9. Material Recycling In all foundries, material is recycled. The furnace charge that foundries are using for engine block manufacturingIn all foundries, comes from material two di isff recycled.erent sources—external The furnace charge recycling that foundries (new scrap, are using old scrap,for engine turnings, and dross)block manufacturing and in-house comes recycling from (Figure two different 12). According sources— toexternal foundry recycling practices, (new the scrap, ratio old between scrap, the turnings, and dross) and in-house recycling (Figure 12). According to foundry practices, the ratio two differs. The dominant production route for steel made from scrap is electric arc furnace, while the between the two differs. The dominant production route for steel made from scrap is electric arc energy needed is equal to on average 7 GJ/ton (Table 10). The most common route for primary steel furnace, while the energy needed is equal to on average 7 GJ/ton (Table 10). The most common route productionfor primary is basic steel oxygen production furnace is basic that oxygen converts furnace pig iron that into converts steel. pig The iron energy into steel. for this The step energy on for average is equalthis to step 0.8 GJon /ton. average Together is equal with to pig0.8 iron GJ/ton. production Together energy, with pig a full iron steelmaking production processenergy, ais full equal to 18.2 GJsteelmaking per ton. process is equal to 18.2 GJ per ton.

Figure 12. Material flow diagram of the recycling. Figure 12. Material ﬂow diagram of the recycling.

Energies 2019, 12, 2557 12 of 23

Table 10. Energy for steel recycling with electric arc furnace. Energies 2019, 12, x FOR PEER REVIEW 12 of 23 Source Energy (GJ/t) TableWorld 10. Energy Steel Associationfor steel recycling (2015) with electric 5.3–8.7 arc furnace. Source[49 ] 6–15Energy (GJ/t) [50] 8.1–9.0 World Steel Association[13] (2015) 10 5.3–8.7 [49][22 ] 5.5 6–15 [50][43 ] 5.3 8.1–9.0 [13][44 ] 5.5 10 [22] 5.5 Because the history of the scrap that[43] is used as a furnace charge is5.3 not known [13], it is necessary to consider all the stages that the material[44] might go through, from initial5.5 manufacture to final disposal. Based on the number of product cycles, the embodied energy in the material can be estimated by Because the history of the scrap that is used as a furnace charge is not known [13], it is necessary calculation.to consider The all total the stages energy that content the material for the might chosen go through, number from of cycles initial can manufacture be calculated to final as disposal. follows [13]: Based on the number of product cycles, the embodied" energy# in the material can be estimated by (1 r) calculation. The total energy contenX t= forX thepr chosenXre number− of+ cyclesXre. can be calculated as follows [13]: (1) − (1 rn) (−1 − 푟) 푋 = (푋푝푟 − 푋푟푒) [ ] + 푋푟푒. (1) According to Equation (2), the energy burden for( multiple1 − 푟푛) recycling, where the material is recycled indefinitely,According can be obtained to Equation by (2), calculating the energy the burden following for multiple [13]: recycling, where the material is recycled indefinitely, can be obtained by calculating the following [13]: X = Xpr r Xpr Xre , (2) 푋 = 푋푝푟−− 푟(푋푝푟−− 푋푟푒), (2) wherewhereXpr stands푋푝푟 stands for energyfor energy for for manufacturing manufacturing one ton ton of of material material via via the theprimary primary route, route, 푋푟푒 isX there is the energyenergy for manufacturing for manufacturing one tonone ofton material of material via the via recyclingthe recycling route, route,r is the푟 is overall the overall recycling recycling efficiency overefficiency one life cycle over (oner = lifeRR cycleY), RR (푟is= the푅푅 ∙ scrap푌), 푅푅 recovery is the scrap rate recovery (%), and rateY stands (%), and for 푌 the stands efficiency for the of the · recyclingefficiency process of the (%). recycling Figure process 13 represents (%). Figure the embodied13 represents energy the embodied for steel energy scrap afterfor steel recycling. scrap after For the recycling. For the electric arc furnace (EAF) route and steel scrap processing, the average overall electric arc furnace (EAF) route and steel scrap processing, the average overall recycling efficiency (r) recycling efficiency (푟) includes the furnace yield and the efficiency of recovering the steel at the end- includes the furnace yield and the efficiency of recovering the steel at the end-of-life (r = 0.89) [13]. of-life (푟 = 0.89) [13].

FigureFigure 13. Steel13. Steel scrap scrap embodied embodied energy energy ((XX == 8.2) for for electric electric arc arc furnace furnace (EAF (EAF)) recycling recycling route route..

However,However, the the above above analysis analysis considersconsiders only only the the once once-through-through product product system. system. To undergo To undergo a full a full energyenergy analysis, analysis, the the influence inﬂuence of recycling of recycling and reusing and reusing material material in the casting in the process casting should process also be should considered [14]. As a result, the multiple life-cycle method needs to be adopted. The residue metal also be considered [14]. As a result, the multiple life-cycle method needs to be adopted. The residue that can be again re-melted comes from fettling (in the form of runners and feeders), rarely machining metal that can be again re-melted comes from fettling (in the form of runners and feeders), rarely (swarf), and internal inspection. Apart from metal, other process materials like core sand and green machiningsand can (swarf), also be and recycled internal (via inspection.thermomechanical Apart or from thermal metal, sand other reclamation) process materials or reused like[51]. core The sand and greenembodied sand energies can also for be cast recycled-iron, core (via sand thermomechanical after reclamation or and thermal green sandsand are reclamation) illustrated orin Figure reused [51]. The embodied14a,b,c respect energiesively. for cast-iron, core sand after reclamation and green sand are illustrated in Figure 14a,b,c respectively. The alloying and treatment materials need to be considered as well. For CI, ferrosilicon is added to enhance the grain structure and metallurgy of the ﬁnished component. The energy content to produce one ton of ferrosilicon master alloy is just over 30 GJ. However, the addition rate into the iron is such that this contributes 1.6 GJ/ton of CI engine blocks.

Energies 2019, 12, x FOR PEER REVIEW 13 of 23

Energies 2019, 12, 2557 13 of 23

Figure 15 shows the Sankey diagram representation of the energy and materials ﬂows. Using this, the largest areas of energy input, recycling loops, and material losses are shown. Energies 2019, 12, x FOR PEER REVIEW 13 of 23

(a) (b)

(a) (b) (c)

Figure 14. (a) Energy embodied in metal collected from the production stage and re-melted in-house in the cast-iron foundries (assumed 2% of the embodied energy for pig iron addition), (b) energy embodied in core sand after reclamation process, and (c) energy embodied in green sand for its multiple reuse.

The alloying and treatment materials need to be considered as well. For CI, ferrosilicon is added to enhance the grain structure and metallurgy of(c ) the finished component. The energy content to produce one ton of ferrosilicon master alloy is just over 30 GJ. However, the addition rate into the Figure 14. (a) Energy embodied in metal collected from the production stage and re-melted in-house Figureiron is 14.such(a that) Energy this contributes embodied in 1.6 metal GJ/ton collected of CI engine from the blocks. production stage and re-melted in-house in in the cast-iron foundries (assumed 2% of the embodied energy for pig iron addition), (b) energy the cast-ironFigure foundries15 shows (assumedthe Sankey 2% diagram of the embodied representation energy of for the pig energy iron addition), and materials (b) energy flows. embodied Using embodied in core sand after reclamation process, and (c) energy embodied in green sand for its inthis, core the sand largest after areas reclamation of energy process, input, recycling and (c) energy loops embodied, and material in green losses sand are forshown. its multiple reuse. multiple reuse.

The alloying and treatment materials need to be considered as well. For CI, ferrosilicon is added to enhance the grain structure and metallurgy of the finished component. The energy content to produce one ton of ferrosilicon master alloy is just over 30 GJ. However, the addition rate into the iron is such that this contributes 1.6 GJ/ton of CI engine blocks. Figure 15 shows the Sankey diagram representation of the energy and materials flows. Using this, the largest areas of energy input, recycling loops, and material losses are shown.

Figure 15. Energy and material ﬂow in CI sand casting, showing that 1000 kg of good castings require

the melting of 1739 kg of CI and 32.57 GJ.

4.2. Al-Alloy Engine Blocks Figure7 shows the process ﬂow for Al-alloy engine block manufacturing. Compared to CI engine blocks, the process is slightly more complicated, as there is need for the use of liners as explained later on, as well as heat treatment of the cast components. Furthermore, the casting processes to

Energies 2019, 12, 2557 14 of 23

Energies 2019, 12, x FOR PEER REVIEW 14 of 23 be used vary from company to company.Figure 15. Energy Three and dimaterialfferent flow casting in CI sand processescasting, showing can that be 1000 identified kg of good castings that require are widely used for the manufacturing,the melting namely of 1739 high-pressurekg of CI and 32.57 G dieJ. casting (HPDC), low-pressure die casting (LPDC), and low-pressure sand casting (LPSC; also known as the Cosworth process). Overall, 4.2. Al-Alloy Engine Blocks 70% of aluminum-alloy engine blocks are casted by HPDC, while the other 30% are casted through a Figure 7 shows the process flow for Al-alloy engine block manufacturing. Compared to CI combination of the other methods [23]. engine blocks, the process is slightly more complicated, as there is need for the use of liners as The LPDC process consistsexplained of a dosing later furnaceon, as well which as heat is pressurized,treatment of the forcing cast components. liquid aluminum Furthermore, to the casting enter the mold from the bottom.processes The mold to be consistsused vary of from steel company dies combined to company. with Three internal different sand casting cores. processes can be The repeatable rising and fallingidentified of the that metal are widely through used the for delivery the manufacturing, tube may namely introduce high-pressure oxide layersdie casting (HPDC), low-pressure die casting (LPDC), and low-pressure sand casting (LPSC; also known as the Cosworth which eventually are delivered to the casting. LPDC is used for medium to long series of casting process). Overall, 70% of aluminum-alloy engine blocks are casted by HPDC, while the other 30% are runs, where better mechanicalcasted properties through are a combination required whenof the other compared methods to [23] HPDC.. In HPDC, the alloy is inserted into a cold chamber andThe a LPDC hydraulic process pistonconsists squeezesof a dosing thefurnace metal which into is pressurized a steel die, forcing mold liquid at aluminum extremely high speed (up to 80to m enter/s) andthe mold pressure from the (3500 bottom. tons). The mold No sandconsists cores of steel can dies withstand combined with the internal high sand cores. The repeatable rising and falling of the metal through the delivery tube may introduce oxide layers pressure; thus, the HPDC block designs are limited to open-deck blocks. which eventually are delivered to the casting. LPDC is used for medium to long series of casting runs, Similar to cast-iron greenwhere sand casting,better mechanical aluminum properties gravity are required sand casting when compar also usesed to coreHPDC. packages. In HPDC, the alloy is In the LPSC (Cosworth process),inserted the metal into a is cold usually chamber pumped and a hydraulic into the piston sand squeezes mold from the metal the bottom into a steel by die mold at an electrical pump. The differenceextremely from high LPDC speed is (up that to 80 the m/s) metal and pressure in the pump (3500 tons). never No dropssand cores back can to withstand the the high pressure; thus, the HPDC block designs are limited to open-deck blocks. level of the metal and, consequently, the level of oxide generated is potentially lower than in a gravity Similar to cast-iron green sand casting, aluminum gravity sand casting also uses core packages. system [52]. Data were collectedIn the from LPSC a number(Cosworth of process), foundries the metal that is employ usually pumped such processes. into the sand mold from the bottom by an electrical pump. The difference from LPDC is that the metal in the pump never drops back to the 4.2.1. Melting and Holding level of the metal and, consequently, the level of oxide generated is potentially lower than in a gravity system [52]. Data were collected from a number of foundries that employ such processes. In Al-alloy engine block foundries, tower furnaces are most commonly used [6]. The unrecoverable metal losses are of the same order4.2.1. ofMelting magnitude and Holding as CI. The foundries contacted reported an average energy consumption of 6.5 3 GJIn per Al ton-alloy of engineliquid block metal foundries, (Figure 16 tower). With furnaces regard are to most the commonly holding of used [6]. The ± the liquid metal, the holding timeunrecoverable varies between metal losses foundries. are of the In same HPDC order and of LPDC, magnitude the as holding CI. The time foundries is contacted around four hours, while for LPSCreported it is an 13 average hours energy because consumption of the additional of 6.5 ± 3 GJtime per ton required of liquid metal for refining (Figure 16). of With regard to the holding of the liquid metal, the holding time varies between foundries. In HPDC and LPDC, the metal. The foundry using thethe Cosworthholding time process is around used four holdinghours, while as afor refining LPSC it is step 13 hours to allow because unwanted of the additional time trace elements to settle out of therequired liquid for Al refining alloy of and the oxidesmetal. The to foundry float to using the surface.the Cosworth Figure process 17 usedshows holding the as a refining holding energy in GJ per ton ofstep liquid to allow metal. unwanted trace elements to settle out of the liquid Al alloy and oxides to float to the surface. Figure 17 shows the holding energy in GJ per ton of liquid metal.

12 7 6.5 9.8 10 6 5 8 6.1 4 6 3 2.5

liquid liquid metal) 3.7 4

liquid liquid metal) 2 1.5

2 1 Normalised Normalised Melting Energy (GJ/t of

0 0 Normalised Normalised Holding Energy (GJ/t of HPDC LPDC LPSC HPDC LPDC LPSC

Figure 16. Melting energyFigure per 16. ton Melting of liquid energy metal per ton in of threeliquid diﬀerent AlFigure foundries. 17. Holding energy per ton of liquid metal in three different Al foundries. metal in three different Al foundries. 4.2.2. Core- and Mold-Making The material and the process used for the core- and mold-making depend on the type of the casting process to be used. In LPSC foundries, cores are made from silica sand using the cold box method, where a binder system is used to cure the sand and resin to form the core. In HPDC, sand cores are not used due to the high-pressure injection of the metal which would destroy the cores. The core weight also varies for the diﬀerent metals. The cores in cast iron sand casting are much heavier than in aluminum LPDC. This is because it includes the whole core package (cores + core shells). The energy required for making cores and the mold is quite similar with cast-iron sand casting (CISC), with the exception of when dies are used. Energies 2019, 12, x FOR PEER REVIEW 14 of 23

Figure 15. Energy and material flow in CI sand casting, showing that 1000 kg of good castings require the melting of 1739 kg of CI and 32.57 GJ.

4.2. Al-Alloy Engine Blocks Figure 7 shows the process flow for Al-alloy engine block manufacturing. Compared to CI engine blocks, the process is slightly more complicated, as there is need for the use of liners as explained later on, as well as heat treatment of the cast components. Furthermore, the casting processes to be used vary from company to company. Three different casting processes can be identified that are widely used for the manufacturing, namely high-pressure die casting (HPDC), low-pressure die casting (LPDC), and low-pressure sand casting (LPSC; also known as the Cosworth process). Overall, 70% of aluminum-alloy engine blocks are casted by HPDC, while the other 30% are casted through a combination of the other methods [23]. The LPDC process consists of a dosing furnace which is pressurized, forcing liquid aluminum to enter the mold from the bottom. The mold consists of steel dies combined with internal sand cores. The repeatable rising and falling of the metal through the delivery tube may introduce oxide layers which eventually are delivered to the casting. LPDC is used for medium to long series of casting runs, where better mechanical properties are required when compared to HPDC. In HPDC, the alloy is inserted into a cold chamber and a hydraulic piston squeezes the metal into a steel die mold at extremely high speed (up to 80 m/s) and pressure (3500 tons). No sand cores can withstand the high pressure; thus, the HPDC block designs are limited to open-deck blocks. Similar to cast-iron green sand casting, aluminum gravity sand casting also uses core packages. In the LPSC (Cosworth process), the metal is usually pumped into the sand mold from the bottom by an electrical pump. The difference from LPDC is that the metal in the pump never drops back to the level of the metal and, consequently, the level of oxide generated is potentially lower than in a gravity system [52]. Data were collected from a number of foundries that employ such processes.

4.2.1. Melting and Holding In Al-alloy engine block foundries, tower furnaces are most commonly used [6]. The unrecoverable metal losses are of the same order of magnitude as CI. The foundries contacted reported an average energy consumption of 6.5 ± 3 GJ per ton of liquid metal (Figure 16). With regard to the holding of the liquid metal, the holding time varies between foundries. In HPDC and LPDC, the holding time is around four hours, while for LPSC it is 13 hours because of the additional time required for refining of the metal. The foundry using the Cosworth process used holding as a refining Energies 2019, 12, 2557 15 of 23 step to allow unwanted trace elements to settle out of the liquid Al alloy and oxides to float to the surface. Figure 17 shows the holding energy in GJ per ton of liquid metal.

12 7 6.5 9.8 10 6 5 8 6.1 4 6 3 2.5

liquid liquid metal) 3.7 4

liquid liquid metal) 2 1.5

2 1 Normalised Normalised Melting Energy (GJ/t of

0 0 Normalised Normalised Holding Energy (GJ/t of HPDC LPDC LPSC HPDC LPDC LPSC

Figure 16. Melting energy perFigure ton of 17.liquidHolding energyFigure per 17.ton Holding of liquid energy metal per ton in of threeliquid different Al foundries. metal in three different Al foundries. metal in three different Al foundries. 4.2.3. Casting The four different casting processes were presented already. As per CI, the energy consumed during the casting process is negligible with the exception of HPDC. In HPDC, automatic spray-up for lubrication and robotic casting removal after solidification also consume a lot of energy. The dies are usually monolithic and contain cooling and heating channels. Due to these extra energies in HPDC, a casting energy is accounted for in this casting method only (1.2 GJ per ton of casting). HPDC parts are near net shape, and less fettling and machining operations are required. Due to the nature of metal filling, HPDC castings are often non-heat-treatable but might go through a stress-relieving thermal cycle.

4.2.4. Fettling Once the cast engine block is removed from the sand mold or the die, fettling is required as per the CI process as well. In the case of Al-alloy engine blocks, the reported mold yield is lower compared to CI and is approximately 65 2%. The material removed from fettling aluminum-alloy ± engine blocks can be re-melted directly in the foundry or sold to an external recycling company to be transformed again into aluminum alloys. The second case relates to aluminum LPDC and, therefore, the calculations in this study, for LPSC, are based on outside recycling. The energy consumed during the fettling process was reported in all three foundries to be 0.6 GJ per ton of liquid metal.

4.2.5. Heat Treatment A key difference in the CI process flow is the need for heat treatment. Al–Si alloys used to produce Al-alloy engine blocks usually require T6 and T7 heat treatments which are used to improve both mechanical and wear properties [53]. Foundries also reported that T5 is the most common heat treatment process used in HPDC. The average energy consumption per casting can be calculated when temperature and holding times are known. Considering a treatment efficiency of 100%, the average energy consumption for heat treatments T6 and T7 can be calculated to be 3.2 GJ/ton of finished casting. For T5, the average energy consumption is calculated to be 1.0 GJ/t. For the case of engine block casting, 20% heat treatment efficiency is required; thus, the values considered were scaled accordingly.

4.2.6. Impregnation Casting introduces porosities during the solidiﬁcation of the liquid metal. Turbulent metal ﬂow, gas entrapment, and metal shrinkage are the main factors that introduce voids in the casting. Porosity is more pronounced in aluminum-alloy castings because of its higher volumetric shrinkage and hydrogen content. The three main forms of porosity are full enclosed, blind, and through porosity. Such porosity could result in leaking under pressure, and would, thus, require the block to be scrapped. an impregnation process that introduces a polymer sealant in the pores and cracks of castings is used for Energies 2019, 12, 2557 16 of 23

Energies 2019, 12, x FOR PEER REVIEW 16 of 23 this reason. The most commonly used impregnation process is the vacuum dry process. The castings are stashedAround into 90% a basketof the energy and inserted in an impregnation in a series of chambers cycle is co untilnsumed a full heating impregnation up the cyclewater is at achieved. around 90 °CAround, and the 90% remaining of the energy 10% isin used an impregnationfor circulation cycle pumps, is consumed vacuum pumps, heating rotational up the water mechanisms at around, 90and◦C, other and ancillary the remaining systems. 10% The is used energy for circulationinvolved in pumps, the process vacuum was pumps, ascertained rotational to be mechanisms, around 7.2 andMJ/engine other block. ancillary systems. The energy involved in the process was ascertained to be around 7.2 MJ/engine block. 4.2.7. Machining 4.2.7. Machining Using the MAG analytical model [48], the total energy consumption for machining is 51 MJ, of whichUsing 13 MJ the is for MAG the analyticalinitial machining model [of48 the], the cylinder total energy liners. consumption for machining is 51 MJ, of which 13 MJ is for the initial machining of the cylinder liners. 4.2.8. Liner Casting 4.2.8. Liner Casting For the aluminum-alloy in-line four-cylinder blocks, for all casting processes, cast-iron cylinder linersFor are the cast aluminum-alloy in the block. The in-line wear four-cylinderand mechanical blocks, properties for all of casting hypoeutectic processes, alloy cast-iron sliding cylindersurfaces linersare not are adequate cast in theto withstand block. The the wear friction and mechanical of the moving properties piston in of the hypoeutectic cylinder bore. alloy Cast sliding-in CI surfaces liners are notused adequate for the tribological to withstand system the friction “cylinder of the–piston moving–piston piston ring”. in the The cylinder liners bore.are centrifugally Cast-in CI liners cast areand used the induction for the tribological pre-heated system prior “cylinder–piston–piston to casting at around 375 ring”. °C to The achieve liners arebetter centrifugally bonding with cast andthe theliquid induction Al, ending pre-heated up with prior a total to energy casting of at 188 around MJ/engine 375 ◦C block. to achieve For the better fettling bonding of the with solid the casting liquid Al,system, ending the up yield with ratio a total is approximately energy of 188MJ 67%/engine with block.a total Forenergy the fettlingconsumption of the solidof 0.6 casting GJ per system, ton of theliquid yield metal. ratio is approximately 67% with a total energy consumption of 0.6 GJ per ton of liquid metal.

4.2.9. Material Recycling As with with the the CI CI foundries, foundries, Al Al foundries foundries charg chargee their their furnaces furnaces with with recycled recycled material material as well. as well. The Theprocess process is quite is quite similar similar;; however however,, Figure Figure 12 needs 12 needsto be updated to be updated in order in to order include to includesecondary secondary smelter smelterand the andproduction the production of ingots. of Figure ingots. 18 Figure illustrates 18 illustrates the common the common processes processes for the formaterial the material flow of ﬂow the ofrecycling the recycling model model for the for case the of case Al alloys. of Al alloys.

Secondary Ingot Raw material smelter* production*

In-house Furnace charge recycling

New scrap Manufacturing Use phase

End of life

Old scrap Recycling

*Aluminium only New scrap - fabrication or process scrap Old scrap - post consumer scrap Figure 18.18. Material flow ﬂow diagram of the recycling recycling..

Al-alloyAl-alloy engine blocks are usually made from secondary ingot. The alloy used is A383 or A380 for LPDC and HPDC,HPDC, and A319 for LPSC. The process of recycling Al scrap to form the alloys is by reﬁning,refining, a process that uses a combination of rotary and reverberatory furnaces [[54]54].. The recycled Al can have similar properties to primary Al. However, However, in a course course of multiple multiple recycling, more and more alloying elements are introduced into the metal cycle. Se Secondarycondary alloys have relatively high levels of impurities, especiallyespecially iron,iron, whichwhich is is detrimental detrimental to to many many properties. properties. The The multiple multiple life-cycle life-cycle method method is, thus,is, thus used, used (as (as in thein the CI CI recycling) recycling) for for calculating calculating an an average average energy energy consumption. consumption. FiguresFigures 19–21 present thethe SankeySankey diagramsdiagrams forfor thethe LPSC,LPSC, LPDC,LPDC, andand HPDCHPDC cases,cases, respectively.respectively.

Energies 2019, 12, 2557 17 of 23 Energies 2019, 12, x FOR PEER REVIEW 17 of 23 Energies 2019, 12, x FOR PEER REVIEW 17 of 23

FigureFigure 19. 19Energy. Energy and and materialmaterial ﬂowflow in low-pressurelow-pressure sand sand casting casting (LPSC (LPSC),), showing showing that that 1000 1000 kg kgof of Figure 19. Energy and material flow in low-pressure sand casting (LPSC), showing that 1000 kg of goodgood castings castings require require the the melting melting ofof 21232123 kgkg of Al and 181.06 181.06 GJ GJ.. good castings require the melting of 2123 kg of Al and 181.06 GJ.

Figure 20. Energy and material flow in low-pressure die casting (LPDC), showing that 1000 kg of FigureFigure 20. 20Energy. Energy and and material material ﬂow flow in in low-pressure low-pressure die die casting casting (LPDC), (LPDC showing), showing that that 1000 1000 kg kg of goodof good castings require the melting of 2067 kg of Al and 115.28 GJ. castingsgood castings require require the melting the melting of 2067 of kg 2067 of Alkg andof Al 115.28 and 115.28 GJ. GJ.

Energies 2019, 12, 2557 18 of 23

Energies 2019, 12, x FOR PEER REVIEW 18 of 23

Figure 21.21. Energy and material ﬂowflow in high-pressurehigh-pressure sandsand castingcasting (HPDC),(HPDC), showing that 1000 kg ofof good castings require the melting of 2040 kg of Al and 98.09 GJ. good castings require the melting of 2040 kg of Al and 98.09 GJ. Figure 21. Energy and material flow in high-pressure sand casting (HPDC), showing that 1000 kg of 5. The Answer to the Dilemma between Al Alloys and CI 5. The Answergood to castings the Dilemma require the melting between of 2040 Al kg Alloys of Al and and 98.09 CIGJ. Figure 22 shows the energy breakdown in each material source and indicates that ingot and Figure5. The 22 Answershows tothe the energyDilemma breakdown between Al Alloys in each and CImaterial source and indicates that ingot and external scrapscrap representrepresent thethe highest highest embodied embodied energy energy of o thef the charge charge and and feedstock feedstock for for Al-alloy Al-alloy and and CI Figure 22 shows the energy breakdown in each material source and indicates that ingot and engine blocks. Figure 23 demonstrates the process energy breakdown for each casting. It is obvious that CI engineexternal blocks. scrap Figure represent 23 demonstrates the highest embodied the process energy energy of the charge breakdown and feedstock for each for Al casting.-alloy and It is obvious thethat CI the engine CI CI engine engine block blocks. requires block Figure requires considerably23 demonstrates considerably lessthe process energy. energy less The energy.breakdown excess energy The for each excess spent casting. energy for It is the obvious manufacturing spent for the ofmanufacturing Al-alloythat engine the of CI A blocks enginel-alloy should block engine requires be blocks compensated considerably should be for less compensated by energy. the fact The that excess for the by energy vehiclethe fact spent is that lighter for the and,vehicle thus, is consumeslighter andmanufacturing less, thus energy, consu of during mesAl-alloy less its engine use.energy blocks during should its be use. compensated for by the fact that the vehicle is lighter and, thus, consumes less energy during its use.

Figure 22. Embodied material energy per ton of engine blocks. Figure 22. Embodied material energy per ton of engine blocks.

Figure 22. Embodied material energy per ton of engine blocks.

Energies 2019, 12, 2557 19 of 23

Energies 2019, 12, x FOR PEER REVIEW 19 of 23

Figure 23. Process energy per ton of engine blocks. Figure 23. Process energy per ton of engine blocks. Figures 22 and 23 provide information about the embodied and process energy per ton of engine Figuresblock. 22 However, and 23 provide it is equally information significant about to represent the embodied the data above and using process a single energy block per as ton a of engine block. However,functional it unit. is equally The values signiﬁcant of process, to embodied represent, and the total data energy above, which using is equal a single to theblock sum of as the a functional unit. Theembodied values of and process, process energy, embodied, required and for totalthe production energy, whichof each single is equal engine to theblock sum via the of four the embodied manufacturing processes, are listed in Table 11. and process energy, required for the production of each single engine block via the four manufacturing processes, areTable listed 11. Total in Table energy 11 per. engine block. HPDC—high-pressure die casting; LPDC—low-pressure die casting; LPSC—low-pressure sand casting; CISC—cast-iron sand casting.

Table 11. Total energy per engine block.HPDC HPDC—high-pressure LPDC die casting;LPSC LPDC—low-pressureCISC die casting; LPSC—low-pressure sandDiesel casting; Petrol CISC—cast-iron Diesel Petrol sand Diesel casting. Petrol Diesel Petrol Process energy (GJ/t) 25.8 25.8 36.78 36.78 59.12 59.12 13.11 13.11 Embodied energy (GJ/t) HPDC72.37 72.37 78.63LPDC 78.63 114 114 LPSC 19.46 19.46 CISC Weight of single block (kg) 27 18 27 18 27 18 38 27 Diesel Petrol Diesel Petrol Diesel Petrol Diesel Petrol Process energy (GJ/block) 0.64 0.41 0.91 0.58 1.46 0.93 0.5 0.35 ProcessEmbodied energy (GJenergy/t) (GJ/block)25.8 1.79 25.81.14 36.781.94 1.24 36.78 2.81 59.121.79 59.120.74 0.53 13.11 13.11 EmbodiedTotal energy energy (GJ (GJ/block)/t) 72.372.43 72.371.54 78.632.85 1.81 78.63 4.28 1142.72 1141.24 0.88 19.46 19.46 Weight of single block (kg) 27 18 27 18 27 18 38 27 Process energyThe embodied (GJ/block) energy due0.64 to manufacturing 0.41 0.91and use is 0.58illustrated 1.46in Figure 24 0.93 (shown for 0.5 the 0.35 Embodiedcase energyof diesel (GJ engines/block); similar1.79 results were 1.14 attained 1.94 for petrol 1.24 engines). 2.81 The starting 1.79 values 0.74 of the 0.53 Totalembodied energy (GJ energy/block) correspond2.43 to the total 1.54 energy of 2.85the manufacturing 1.81 process 4.28 (Table 2.72 11). It is evident 1.24 0.88 that the vehicle would have to be driven more in order for the lightweighting to yield benefits. This is due to the much higher embodied energy of Al alloys compared with CI as a result of the huge The embodiedenergy content energy during due both to the manufacturing electrolysis and and bauxite use is conversion illustrated stages in Figure of the production 24 (shown of for the case of diesel engines;aluminum. similar results were attained for petrol engines). The starting values of the embodied energy correspond to the total energy of the manufacturing process (Table 11). It is evident that the vehicle would have to be driven more in order for the lightweighting to yield benefits. This is due to the much higher embodied energy of Al alloys compared with CI as a result of the huge energy content during both the electrolysis and bauxite conversion stages of the production of aluminum. The distance needed to be covered by a vehicle in order to compensate for the additional energy due the manufacturing and primary production of the engine block is estimated using the break-even distance (BED) according to ∆PEB 4 BED = 10 , (3) · δFs E f ∆M · · where ∆PEB (MJ) is the difference in the process energy burden between the manufacturing process with the lowest total energy (CISC) and the rest of the processes, δFs is the fuel savings, E f is the energy content of the fuel, and ∆M is the engine block weight differential (Table 12). The values of the break-even distance for the two types of engine blocks (diesel and petrol) and the various manufacturing processes under examination are summarized in Table 13. Energies 2019, 12, 2557 20 of 23 Energies 2019, 12, x FOR PEER REVIEW 20 of 23

12,000

)

10,000

(

8,000

g n 6,000

c 4,000 CISC

o f LPDC

a 2,000 LPS

m HPDC 0 0 50 100 150 200 250 300 350 400 450 Distance (x1000 km)

FigureFigure 24 24.. Break-evenBreak-even distancedistance for for paying paying back back the the lightweight lightweight material material (for a (for diesel a dieselautomotive automotive vehicle vehicleof 1200 of kg 1200 with kg an with average an average consumption consumption of 7l,100 of km). 7l,100 km).

Table 12. Parameters for the break-even distance (BED) calculation. Table 12. Parameters for the break-even distance (BED) calculation.

DieselDiesel Petrol Petrol δF L 퐿 0.2 0.25 훿s퐹100( km 100 kg ) 0.2 0.25 푠 100 × km × 100 kg E MJ 38.6 34.2 f L 푀퐽 ∆M(퐸kg)( ) 938.6 34.2 7 푓 퐿 ∆푀(푘푔) 9 7 Table 13. BED (km) vs. CISC for various types of engine blocks and manufacturing processes. The distance needed to be covered by a vehicleDiesel in order to Petrol compensate for the additional energy due the manufacturing and primary production of the engine block is estimated using the break-even HPDC 170,889 110,611 distance (퐵퐸퐷) according to LPDC 232,141 155,809 LPSC 369,221∆푃퐸퐵 256,960 퐵퐸퐷 = ∙ 104, (3) (훿퐹푠 ∙ 퐸푓 ∙ ∆푀) 6. Conclusions where ∆푃퐸퐵 (푀퐽) is the difference in the process energy burden between the manufacturing process with theCurrently, lowest thetotal legislation energy (CISC) around and the the automotive rest of the industry processes, is focused 훿퐹푠 is onthe the fuel reduction savings, of 퐸푓 tailpipe is the energyemissions content of vehicles of the fuel and, and does ∆푀 not is the consider engine the block production weight differential phase of (Table automotive 12). The components. values of theAutomotive break-even companies distance are for compelled the two types to pursue of engine a lightweighting blocks (diesel and and engine-downsizing petrol) and the various design manufacturingstrategy to comply processes with theunder steadily examination more stringent are summari targetszed in in emission Table 13. standards. The objective of this investigation was to perform a thorough life-cycle analysis of an automotive component (engine block) madeTable of13 two. BED di (km)fferent vs. materials,CISC for various CI and types Al alloy, of engine in order blocks to and review manufacturing the potential processes energy. savings of lightweighting. Diesel Petrol The “cradle-to-grave” approach was adopted to calculate the overall energy requirements, HPDC 170,889 110,611 including the energies for the production of the raw materials, while acknowledging the embodied LPDC 232,141 155,809 energy from the initial manufacture up to the final disposal. Our results indicate that the energy LPSC 369,221 256,960 required for the primary production and manufacture of CI engine blocks is much lower compared to the Al-alloy engine case. On the other hand, Al-alloy blocks are more lightweight and contribute to the 6. Conclusions increase in fuel savings during the use phase of the particular component. CurrentlyIn order to, the evaluate legislation the around effects ofthe lightweighting automotive industry on the is overall focused energy on the consumptionreduction of tailpipe during emissionsthe component’s of vehicles life cycle, and does the weighted not consider average the break-even production distance phase of (required automotive to compensate components. for Automotivethe extra energy companies consumption are compelled in Al-alloy to pursue engine a blocks) lightweighting was estimated and engine and- founddownsizing to be arounddesign strategy175,000 km.to comply The breakeven with the steadi distancely more fluctuated stringent between targets 175,000 in emission and 370,000standards. km The for aobjective diesel and of thisbetween investigation 115,000km wa ands to perform 260,000 km a thorough for a petrol life engine-cycle analysis block. The of conclusionan automotive drawn component is that, compared (engine block)to an average made of passenger two different vehicle materials, life of 200,000 CI and km, Al for alloy, the LPDC in order and to LPSC review processes, the potential the vehicle energy will savings of lightweighting.

Energies 2019, 12, 2557 21 of 23

never recover the extra energy in the Al-alloy engine blocks while being on the road. Therefore, the substitution of materials, traditionally used in the automotive industry, with lighter ones should be very carefully considered.

Author Contributions: Conceptualization, M.J. and K.S.; methodology, M.J. and K.S.; validation, E.P. and M.P.; formal analysis, all; investigation, all; writing—original draft preparation, K.S.; writing—review and editing, M.P.; visualization, E.P.; supervision, M.J. and K.S. Funding: This research was partially funded by the UK EPSRC projects “Small Is Beautiful” and “Energy Resilient Manufacturing 2: Small Is Beautiful Phase 2 (SIB2)” for funding this work under grants EP/M013863/1 and EP/P012272/1, respectively. Acknowledgments: The authors would like to acknowledge the UK EPSRC projects “Small Is Beautiful” and “Energy Resilient Manufacturing 2: Small Is Beautiful Phase 2 (SIB2)”. Earlier versions of this manuscript were presented at the 38th International Vienna Motor Symposium, Vienna, Austria in 2017 [11] and the TMS Annual Meeting and Exhibition in 2018 [12]. Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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