MODELLING OF ALKALINITY CHANGES IN LUBRICATING OILS USED IN MARINE DIESEL ENGINES

Transcription

1 Jurnal f ONES Pwertrain and Transprt, Vl. 16, N MODELLING OF ALALINITY CHANGES IN LUBRICATING OILS USED IN MARINE DIESEL ENGINES Andrzej Mynarczak Gdynia Maritime University Department f Marine Pwer Plant Mrska Street 81-87, Gdynia, Pland tel.: wmks@am.gdynia.pl Abstract As the time is passing, lubricating il in marine engine lubricating il system lses its quality because f il deteriratin prcess. Lubricating il quality influences the wear f triblgical system elements. The ttal base number (TBN) is ne f the mst imprtant il quality prperties. During peratin f diesel engines the TBN decreases as alkaline additives are exhausted mainly thrugh neutralizatin f fuel burning acid prducts. S as t imprve lubricating il prperties an engineer uses sme maintenance methds. One f these methds is refilling prcess. The paper presents theretical researches f ttal base number changes mdelling at varius lubricating il refilling methds. Theretical mdel f il-deteriratin prcess was wrked ut n the basis f mass balance equatin f ttal base number. The methd f slving the prblem, structural mdel f experimental unit, ttal base number change in case f cnstant refilling prcess, calculating example, ttal base number changes in PIELSTIC 12PC2-5V engine il versus parameter d, percentage changes f ttal base number in PIELSTIC 12PC2-5V engine il versus parameter d are presented in the paper. eywrds: transprt, marine diesel engines, ttal base number, refilling prcess 1. Intrductin As the time is passing, lubricating il in marine engine lubricating il system lses its prperties. One f these prperties is the ttal base number (TBN), an index f il alkalinity. During peratin f diesel engines the lubricating il alkalinity decreases as alkaline additives are exhausted mainly thrugh neutralizatin f fuel burning acid prducts. The refilling prcess is ne f used methds applied t imprve lubricating il prperties. The amunt f fresh il added t lubricating il system always balances its cnsumptin, but the way f refilling depends n marine engineer. He can add small prtins f fresh il at shrt intervals r big nes at large intervals. It is always pssible t maintain cnstant amunt f il in lubricating il system by cntinuus refilling. The article aim is t determine the influence f lubricating il-refilling methds n ttal base number changes. The internatinal literature review [1-2, 5, 7, 9] and authr s experience shw that lubricating il alkalinity level cnsiderably influences crrsive wear f triblgical system elements. Fr that reasn scientific researches leading t determine the influence f lubricating il refilling methd n alkalinity level in lubricating il have, accrding t authr s pinin, an imprtant meaning either cgnitive r practical. 2. The methd f slving the prblem Lubricating il prperties changes versus perating time can be examined theretically using its mass balance equatins. In these equatins the tested prperty velcity change is the algebraic sum f inflw and utflw factrs intensity, which determine its temprary value.

2 A. Mynarczak dw dt d i, (1) i where: W - examined lubricating il prperty, d i - intensity f inflw factrs which influence cnsidered lubricating il prperty, i - intensity f utflw factrs which influence cnsidered lubricating il prperty. In case f lubricating il used in trunk pistn marine diesel engines the fllwing phenmena determine the right side f equatin (1): - marine diesel engine internal prcesses which cause decrease r increase f sme lubricating il cmpnents, - lubricating il maintenance (purifying, filtering, refilling), - lubricating il cnsumptin. In accrdance with the abve mentined phenmena, the ttal base number change in lubricating il during peratin can be submitted as mass balance equatin where the fllwing factrs determine cnsidered lubricating il prperty: - neutralizatin f fuel burning and lubricating il xidatin acid prducts, - adsrbing alkalinity additives n hard mechanical impurities and their remving by filtering and purificatin, - burning f alkalinity additives tgether with lubricating il, - refilling prcess. Figure 1 presents a structural mdel f experimental unit (trunk pistn marine diesel engine) which takes int cnsideratin the abve mentined factrs. G, b m d, d m, 1 Q w, m, 2 c Fig.1. Structural mdel f experimental unit: 1- trunk pistn marine diesel engine, 2 - centrifuge, b - velcity f alkalinity additives cnsumptin used n neutralizatin f acid prducts [mg OH/h], c - velcity f alkalinity additives remved by purifying devices [mg OH/h], G - lubricating il cnsumptin per hur [kg/h], - current value f lubricating il ttal base number [mg OH/g], d - ttal base number f added il [mg OH/g], - initial value f lubricating il ttal base number [mg OH/g], m - current mass f lubricating il in engine lubricating il system [kg], m - initial mass f lubricating il in engine lubricating il system [kg], m d - mass f added il per hur [kg/h], Q w - capacity f lubricating il centrifuge [kg/h] Taking int accunt the abve mdel the prcess f ttal base number change can be described by equatin (2): 330

3 Mdelling f Alkalinity Changes in Lubricating Oils Used in Marine Diesel Engines d m md G b c, (2) dt where: t - lubricating il wrking time [h]. Because: m m G md t, (3) then the equatin (2) has the fllwing frm: d [ m G m d t] m d G b c. (4) dt In real marine diesel engines peratin the refilling f lubricating il ges n peridically after the cnsumptin f sme amunt f il wrking in lubricating il system, that is between refillings m d = 0. Then equatin (4) has the fllwing frm: d. (5) dt m G t b c S as t slve equatin (5) the parameters G, b and c shuld be steady in time. Hwever these simplifying assumptins require a cmmentary. In real peratin, the lubricating il cnsumptin G depends n engine technical cnditin, its revlutins and lad. Taking int accunt that particular functinal systems f the engine are verhauled peridically we can assume its mean, cnstant technical cnditin. The velcity f alkalinity additives cnsumptin used n neutralizatin f acid prducts depends n sulphur cntent in fuel, fuel cnsumptin and sulphur cnversin cefficient [8]. The sulphur cnversin cefficient depends n engine design (tw-strke r fur-strke engine) and cylinder temperature [4]. Cnsidered trunk pistn engine is the main prpulsin engine c-perating with cntrllable pitch prpeller. If a given engine is fed by determined fuel and runs with cnstant lad and revlutins it can be assumed that the velcity f alkalinity additives cnsumptin b and lubricating il cnsumptin G are cnstant. The velcity f alkalinity additives remved by purifying devices c, depends n lubricating il centrifuge efficiency characterized by parameter Q w (prduct f lubricating il centrifuge capacity Q w and purifying cefficient ) and ability f these additives t adsrb n slid impurities and centrifuge s elements surfaces. The purifying cefficient is defined by the fllwing frmula: x x, (6) x where: x - mass cncentratin f slid impurities in lubricating il behind the centrifuge [%]. Physically, centrifuge efficiency determines a part f whle lubricating il stream (flwing thrugh the centrifuge) that underges cmplete cleaning. It changes versus perating time and depends n rate f centrifuge cntaminatin (assuming cnstant capacity f centrifuge and intensity f impurities inflw int engine lubricating il system). If prfessinal technical staff ensures required cleanness f lubricating il centrifuge it can be assumed that the parameter Q w is cnstant in time. The ability f alkalinity additives t adsrb n slid impurities and centrifuge s elements surfaces is a prblem still waiting fr slving. Taking int accunt the abve mentined assumptins we have the fllwing slutin f equatin (5): 331

4 A. Mynarczak b c G t ln 1, fr: G m m G 0 t. In real peratin the lubricating il refilling ges n peridically after cnsumptin f sme il in lubricating il system. In that case the changes f ttal base number in lubricating il between fllwing refilling run accrding t mntnusly falling lgarithmic curve presented as equatin (7). The refilling prcess causes the increase f the ttal base number, which depends n the amunt and alkalinity level f added il (fr simplificatin it is assumed that refilling time t d 0). Received in that way characteristic assumes the shape f the s-called saw-shape curve and was presented in Fig. 2. (7) k, n-1 k, n p, n-1 p, n t t t t Fig. 2. Ttal base number change in case f cnstant refilling prcess Fr the practical reasns it is imprtant t determine the average value f ttal base number versus refilling methd, which is defined by parameter d. That parameter determines the amunt f added il related t initial il amunt in lubricating il system. Equatin (8) shws its definitin: G t m d, fr 0 t, (8) m G where: t - time between the fllwing refilling [h]. If, fr simplificatin, we cnsider that (see Fig. 2): - the refilling prcess is cnstant, it means the amunt f added il m d and time between the fllwing refilling t are cnstant, - alkalinity levels after time t = n. t, it means at the end f n perid t are marked: p,n - befre adding the fresh il, k,n - after adding the fresh il. Then n the basis f Fig. 2 and equatins (7) and (8) we can write: b c p n k n ln1 d, (9),, 1 G Hence we btain: d p n d k n,, 1. (10) 332

5 Mdelling f Alkalinity Changes in Lubricating Oils Used in Marine Diesel Engines p n 1 1 d b c, n ln 1 d, (11) d G n 1 1 d 1 d b c k, n ln1 d. (12) d G Analysing equatins (11) and (12) we can ntice that when lubricating il perating time appraches infinity (number f the refilling n) then the expressin 1 d n appraches zer. In that case actual, instantaneus values f lubricating il alkalinity (just befre and after adding the fresh il) stabilise n the fllwing levels: 1 b c p, ln1 d, d G (13) 1 d b c k, ln1 d. (14) d G The average value f lubricating il ttal base number can be presented in the fllwing frm: p, k,. (15) 2 Taking int cnsideratin equatins (13) and (14) we btain: 1 1 b c ln1 d. (16) d 2 G Analysing the equatin (16) we can ntice that the average level f ttal base number depends n applied refilling methd (quantity and frequency f refilling determined by parameter d). We can than assume that there is such a value f parameter d that initial ttal base number change in lubricating il is the smallest, accrding t the frmula:. (17) Cnsidering expressin (16) equatin (17) takes the fllwing frm: 1 1 b c ln1 d 2 d G. (18) Mathematical mdel presented as equatin (18) enables t estimate initial ttal base number change in trunk pistn marine diesel engine lubricating il versus applied refilling methd characterised by parameter d. 3. Calculating example In rder t determine the influence f applied refilling methd n the ttal base number change in lubricating il, accrding t equatin (18), the numerical simulatin fr main prpulsin trunk pistn marine diesel engine PIELSTIC 12PC2-5V was carried ut. The engine was fed with high sulphur fuel (sulphur cntents 2%). Fig. 3 presents the results f the simulatin: 333

6 A. Mynarczak [mg OH/g] ,1 5,11 5,12 5,15 5,21 5,3 5,47 5,7 6,16 7, ,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 d [ - ] Fig. 3. Ttal base number changes in PIELSTIC 12PC2-5V engine il versus parameter d Analysing Fig. 3 we can ntice that the smallest change f lubricating il ttal base number (related t the fresh il) 5.1 mg OH/g was btained fr the methd f the smallest prtins f added il (d = 0.05). Ttal base number f the fresh il was in that case 30 mg OH/g. As a result the average level f alkalinity btained fr 5% refilling was 24.9 mg OH/g. Increase f the parameter d (relative quantity f refilling) causes bigger alkalinity drp which culd enlarge the crrsive wear f engine elements. Therefre, bearing in mind the average level f ttal base number, which shuld be the highest, the methd f the smallest prtins f added fresh il d = d min appears t be the best. Percentage changes f ttal base number in PIELSTIC 12PC2-5V engine lubricating il (related t fresh il ttal base number level) fr varius refilling methds were presented in Fig. 4. [%] , ,03 17,07 17,17 17,37 17,67 18, , d [-] Fig.4. Percentage changes f ttal base number in PIELSTIC 12PC2-5V engine il versus parameter d We can see that in range f parameter d permissible changes, which fr cnsidered engine are restricted by value d max 0.5 [3] the influence f realized refilling methd n alkalinity level is irrelevant. In case f 5% refilling (d = 0.05) 17% drp f ttal base number was btained (related t fresh il alkalinity), whereas fr 50% refilling (d = 0.5) that drp was 17.67%. Therefre, lubricating il alkalinity changes caused by different refilling methds are nt s imprtant frm the pint f view the ability t neutralize the acids. 334

7 Mdelling f Alkalinity Changes in Lubricating Oils Used in Marine Diesel Engines 4. Summary Theretical researches f lubricating ils (used in trunk pistn marine diesel engines) quality changes mdelling and cnsequently achieved ptimum lubricating il maintenance methds can be used in real peratin f marine engines. The mathematical mdels wrked ut during these researches shuld take int accunt pssible wide cllectin f il prperties, changeable wrking cnditins f marine engines and parameters describing lubricating il systems. The mathematical mdel wrked ut in that article allws determining the influence f applied refilling methd n ttal base number change in lubricating il. Bearing in mind the average alkalinity, which shuld be the highest, the methd f the smallest prtins f added il at shrt intervals appears t be the best. The ptimum and simultaneusly real (in marine engines perating cnditins) range f parameter d changes culd be determined as fllws: d pt = d min (0; 0.05 Results f mdelling present ambiguus influence f used refilling methd n lubricating il prperties. The methd f the smallest prtins f added il at shrt intervals advantageusly influences the alkalinity level but disadvantageusly affects mass cncentratin f slid impurities [10]. Mrever, changes f the abve-mentined prperties in permissible (because f engine safety) range f parameter d variatins are irrelevant. It wuld suggest that when chsing the lubricating il refilling methd, thers factrs shuld als be taken int accunt, fr example: the amunt f il in engine lubricating il system, velcity f xidatin prcess r efficiency f purifying devices. References [1] Burtenshaw, R. P., Lilly, L. R. C., Twards wear reductin in engines using residual fuel, Transactins, Vl. 84, Part 12, [2] Cyulin, W., Lemski, J., Effect f perating influences n wearing speed f marine diesel engine elements, II Internatinal Scientifically-Technical Cnference, EXPLO-DIESEL & GAS TURBINE, Gdask - Midzyzdrje - penhaga [3] PIELSTIC 12PC2-5V manual, S.E.M.T. PIELSTIC, [4] Glthan, D. W., Larcmbe, J. G., Smarwanie rednibrtwych silników wyskprnych spalajcych paliwa pzstaciwe, Silniki spalinwe, 4/1973. [5] Glthan, D. W., A review f the causes f cylinder wear in marine diesel engines, Technical Reprts (Transactins), Vl. 90, Series A, Part 3 f 7, [6] Mynarczak, A., Optymalizacja prcesu uytkwania lejów biegwych w silnikach krtwych, Praca dktrska, Akademia Mrska w Gdyni, [7] Paluszkiewicz, B., Abryswska-Tymiska, E., Rszczypaa, B., Prblemy krzyjne w silnikach krtwych zasilanych paliwami pzstaciwymi, Budwnictw krtwe, 5/82. [8] Smlka, R., System bada i kntrli stanu leju smarweg krtwych silników spalinwych, Instytut Mrski, Gdask [9] Wdarski, J.., Pdstawy eksplatacji maszyn, Tarcie i zuycie, Wydawnictw Akademii Mrskiej w Gdyni, [10] Mynarczak, A., Mdelling f mass cncentratin f slid impurities changes in lubricating ils used in trunk pistn marine diesel engines during varius lubricating il refilling methds, Jint Prceedings N. 21,

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