Lubricants in Confined Conditions - NOMAD · PDF fileLubricants in Confined Conditions ......
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Lubricants in Confined Conditions Understanding and controlling the fundamental mechanism underlying lubrication is of great interest for oil and gas companies. Confining hydrocarbons under high shear and pressure conditions gives rise to a number of experimental 1 and theoretical 2 phenomena that are both complex and intriguing. This case study is based on the assumption that atomistic simulations based on molecular dynamics can achieve a deeper insight into such phenomena and enable fundamental understanding of the physical behaviour of lubricants, helped by increasing computational power and novel data-and IT-based methods. The complexity of real lubricants is driven by the multiple roles the oil must play within the engine e.g., protecting metal surfaces, preventing wear, reducing friction, cooling the engine, and dispersing soot and other contaminants. These roles must be carried out under different temperature and pressure conditions and a wide range of additive chemistries is required in order to fulfil them. Bridging the gap between the idealised system approachable by modelling and the real behaviour of complex mixtures in a range of environmental conditions remains therefore a challenge. The present case study is also based on the further assumption that it is precisely in such a situation that information efficiency based on systematic data archiving and collective data re-usage by purpose-developed analytics tools is most warranted. Training a private sector R&D operator to opening her methodology to a data-based approach is also part of the plan, to test our assumptions in real conditions. The KCL group, in collaboration with BP, is working on producing the data and developing post-processing analytic tools for tribological applications connected with their UK-based industrially relevant lubricant research (and more generally, relevant for any industrially- hosted modelling of hydrocarbon-based fluids). In particular, Ms Rachel Fort, a BP employee at their Technology Centre in Pangbourne, UK, will be devoting 50% of her time under the joined supervision of Prof. Alessandro De Vita (NOMAD PI) and Dr Sorin Filip (an Expert Research Technologist for BP Formulated Products Technology, working in BP Pangbourne). Support to fund Ms Fort’s work was independently obtained as an Industrial Fellowship awarded by the Royal Commission for the Exhibition of 1851. Ms Fort is working with Dr Martina Stella (based at KCL), investigating the physical behaviour of hydrocarbon-based lubricants. Their work aims at predicting the lubricant viscosity with particular interest for extreme conditions (i.e. high pressure, high temperature). This implies data generation using the MD program LAMMPS, whose NOMAD parser has been developed in KCL by Dr Adam Fekete, and where a LAMMPS expert, Dr Chris Lorenz, will be involved in planning production calculations. At the time of writing, the viscosity properties of squalane (2,6,10,15,19,23-Hexamethyltetracosane) are being investigated in bulk and confined conditions. Various simulations conditions will be explored, namely including roughness of
Transcript of Lubricants in Confined Conditions - NOMAD · PDF fileLubricants in Confined Conditions ......
LubricantsinConfinedConditions
Understandingandcontrollingthefundamentalmechanismunderlyinglubricationisofgreatinterest foroilandgascompanies.Confininghydrocarbonsunderhighshearandpressureconditions gives rise to a number of experimental1 and theoretical2 phenomena that areboth complex and intriguing. This case study is based on the assumption that atomisticsimulationsbasedonmoleculardynamicscanachieveadeeperinsightintosuchphenomenaand enable fundamental understanding of the physical behaviour of lubricants, helped byincreasingcomputationalpowerandnoveldata-andIT-basedmethods.
Thecomplexityofreallubricantsisdrivenbythemultiplerolestheoilmustplaywithintheengine e.g., protecting metal surfaces, preventing wear, reducing friction, cooling theengine,anddispersingsootandothercontaminants.Theserolesmustbecarriedoutunderdifferent temperatureandpressureconditionsandawide rangeofadditivechemistries isrequiredinordertofulfilthem.Bridgingthegapbetweentheidealisedsystemapproachableby modelling and the real behaviour of complex mixtures in a range of environmentalconditions remains therefore a challenge. The present case study is also based on thefurtherassumptionthatitispreciselyinsuchasituationthatinformationefficiencybasedonsystematicdataarchivingandcollectivedatare-usagebypurpose-developedanalyticstoolsismostwarranted.TrainingaprivatesectorR&Doperatortoopeninghermethodologytoadata-basedapproachisalsopartoftheplan,totestourassumptionsinrealconditions.
TheKCLgroup, incollaborationwithBP, isworkingonproducingthedataanddevelopingpost-processing analytic tools for tribological applications connected with their UK-basedindustrially relevant lubricant research (and more generally, relevant for any industrially-hostedmodellingofhydrocarbon-basedfluids).Inparticular,MsRachelFort,aBPemployeeattheirTechnologyCentre inPangbourne,UK,willbedevoting50%ofhertimeunderthejoined supervision of Prof. Alessandro De Vita (NOMAD PI) and Dr Sorin Filip (an ExpertResearchTechnologistforBPFormulatedProductsTechnology,workinginBPPangbourne).Support to fund Ms Fort’s work was independently obtained as an Industrial FellowshipawardedbytheRoyalCommissionfortheExhibitionof1851.
MsFortisworkingwithDrMartinaStella(basedatKCL),investigatingthephysicalbehaviourofhydrocarbon-based lubricants.Theirworkaimsatpredictingthe lubricantviscositywithparticularinterestforextremeconditions(i.e.highpressure,hightemperature).ThisimpliesdatagenerationusingtheMDprogramLAMMPS,whoseNOMADparserhasbeendevelopedinKCLbyDrAdamFekete,andwhereaLAMMPSexpert,DrChrisLorenz,willbeinvolvedinplanningproductioncalculations.Atthetimeofwriting,theviscositypropertiesofsqualane(2,6,10,15,19,23-Hexamethyltetracosane) are being investigated in bulk and confinedconditions.Various simulationsconditionswillbeexplored,namely including roughnessof
the slabs and presence of modifiers on the surfaces. Figure 1 below shows an examplerepresentationofthetypeofsystemsstudied.
LongMDsimulations,inthethousandatomsizescaleorabove,areverydata-intense.Post-processing is also quite demanding, and data-analysis carried out by industrial R&D usersworkinginisolationcanbechallenging.TheNOMADKCLgroupwilldevelopsupportingtoolsfor the analysis of this data.Namely,DrAdam Fekete andDrMartina Stellawill teamupwithMsFort andmake themselves available to respond to anydata-analysis request.Weexpectsoftwaretoolswillbenecessaryforfacilitatingandspeedinguptheextrapolationoftrends and statistical properties (e.g. macroscopic friction coefficients, shearing velocityprofiles) particularly for classical MD simulations. Predicting the viscosity of mixtures(complex lubricant compositions) on the basis of the results of MD calculation is alsoexpectedtorequiremachinelearningbasedtoolsthat industryR&DuserssuchasMsFortwouldbeunlikelytodevelopontheirown,butcouldeasilyuseafterappropriatetraining.The data produced by this study will be uploaded on the NOMAD repository, and anyresultinganalytictoolwillbealsomadeavailableontheNOMADwebsite.
Fig1.Examplesystemforatomistictribologysimulationofconfinedlubricants.ThesearetwoslabsofFeO2,stericacidassurfacemodifiersanddecaneaslubricant.Both2D(left)andprospective(right)representationsare
shown.
1)R.G.HornandJ.N.Israelachvili,J.Chem.Phys.75,1400(1981).
2)J.P.Gao,W.D.Luedtke,andU.Landman,Phys.Rev.Lett.79,705(1997).
Pz = 0.5 GPa
+U /2
-U /2
z
x
y
decane
stearic acid
iron oxide
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Tribology applications
