Viscosity, by definition, is an oil’s resistance to flow and shear under the forces of gravity.
Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane – at an unit velocity – when maintaining an unit distance apart in the fluid. The dynamic viscosity units are cP = 1 mPa·s. Measured according to ASTM D 2983.
Kinematic viscosity is the ratio of – absolute (or dynamic) viscosity to density – a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density. In the SI-system the theoretical unit of kinematic viscosity is m2/s – or the commonly used Stoke (St) where: 1 St (Stokes) = 10-4 m2/s = 1 cm2/s
Describes the behavior of the fluid at low temperatures, and is determined on a device that simulates the start in cold conditions (CCS -Cold Cranking Simulator for simulation of starting chilled parts). It is described in standard methods: DIN 51377 and ASTM D 2602.
Increase in the oil viscosity value may be due to:
– increased amounts of soot in oil
– oxidation and polymerization of certain hydrocarbons present in the oil.
Decreasing in the viscosity value can be due to the contamination with the fuel and degradation of the improver.
Viscosity index (VI) is an arbitrary measure for the change of viscosity with variations in temperature. The lower the VI, the greater the change of viscosity of the oil with temperature and vice versa. It is used to characterize viscosity changes with relation to temperature in lubricating oil. This is described in standard methods: ISO 2909; ASTM D 2270; JUS B.H8.024. The viscosity index change in a motor oil sample appears as a result of viscosity changes at 40oC and 100oC. The decreasing occurs due to degradation of the viscous index impruver. If a high quality improver is used when engine oil is produced, degradation does not occur during operation and the oil will retain the initial values of viscosity and viscosity index for a long time. If this is the case of an unknown oil sample, this characteristic can tell us whether it is a multigrade or monograde oil.
ZDensity is defined as mass divided by volume at given temperature. For the European Union that temperature is 15oC and 60oF (14.56oC) in the Anglo-Saxon literature . Density of oil and his derivates are determined by standard methods: ISO 3675; ASTM 1298; DIN 51757; JUS B.H8.015.
Relative density, or specific gravity is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water.
In the US oil industry, API degrees are obtained as a relative density value mesured at 60oF. According to this form: API = (141.5 / density to 60oF) – 131.5. API degrees are determined by the ASTM D 287 method.
The flash point of a volatile material is the lowest temperature at which vapours of the material will ignite, when given an ignition source. Measured according to ISO 2592; ASTM D 92; IP 36; DIN 51376. Checking the flash point indicates whether fuel is present in the oil. The presence of fuel leads to a drop in the flash point, and lead as to informations regarding exessive wear of piston-cylinder assembly and improperly installed fuel injection system.
Predstavlja temperaturu (OC) pri kojoj se u ohlađenom fluidu (mazivu) jave prvi kristali parafina. Do tada bistro ulje, počinje da se muti. Određuje se po metodi ISO 3016 i DIN 51597; JUS B.H8.034.
Predstavlja onu temperaturu (OC) na kojoj se pri hlađenju fluida pod određenim uslovima ispitivanja može još uvek uočiti tečenje. Temperatura na kojoj se, u datom kratkom vremenskom intervalu, više ne uočava tečenje je tačka stinjavanja. Kod parafinskih ulja tečenje sprečavaju kristali parafina. Tačke tečenja i stinjavanja se određuju metodama: ISO 3016; ASTM D 97; DIN 51597; JUS B.H8.034.
Predstavlja količinu fluida koja ispari u propisanom vremenu i na propisanoj temperaturi. Određuje se po metodama: ASTM D 943; DIN 51581 (Noack Test).
Predstavlja mjeru kiselosti fluida. Određuje se istim metodama kao neutralizacioni broj u mgKOH/g uzorka. Titracija se ne završava pri istoj pH vrijednosti pa je za isti uzorak ova vrijednost obično manja.
Ukupan kiselinski broj TAN (Total acid number) je veličina koja nam pokazuje da li je u ulju usljed oksidacije došlo do stvaranja kiselih produkata sagorijevanja. Ovaj broj se tokom rada povećava, a najveća dozvoljena vrijednost je 5 ili kada se približi vrijednosti TBN-a.
Predstavlja mjeru alkalnosti nastale od svih materija u fluidu koje pokazuju bazne reakcije. Izražava se u mgKOH/g uzorka. Određuje se metodama: ISO 3771; ASTM D 2896 i 664; IP 276 i 177; DIN EN 55.
TBN (Total Base Number) obezbjeđuje zaštitu motora od uticaja različitih korozivnih produkata sagorijevanja kao i produkata oksidacije i nitratacije. Za ocjenu stepena istrošenosti ulja vrijednost TBN-a ne smije pasti ispod 50% vrijednosti svježeg ulja. Ukoliko nemamo nov uzorak i ne znamo početnu vrijednost ovaj broj se poredi s TAN-om i ukoliko su im vrijednosti približne ulje se mora zamijeniti. Nagli pad ovog broja može da bude posledica korištenja goriva lošeg kvaliteta (sa velikim procentom sumpora).
Predstavlja mjeru sadržaja jedinjenja metala i drugih neorganskih komponenata u ulju. Uzorak se sagorijeva po standardnom postupku i mjeri sadržaj pepela po metodama: ISO 3987; ASTM D 874; DIN 51768 i 51450. Ako se vrši samo sagorijevanje onda je to oksidni pepeo. Kada se on tretira sumpornom kiselinom dobije se sulfatni pepeo. Sulfatni pepeo obično daje predstavu o sadržaju aditiva (na bazi metala Ca, Mg, Zn, Ba i dr.) u fluidu. Metode: oksidi DIN EN 7; sulfati DIN 51575; gvožđe DIN 51397; Ba, Ca, Zn po metodi DIN 51391; mangan DIN 51431; hlor DIN 51577; fosfor ASTM D 1091; olovo ASTM D 810; Sn, Si, Al po ASTM D 811.
Sadržaj vodu u fluidima se mjeri po metodam DIN 51777 u ppm (dijelova na milion) ili mg/kg. Do pojave vode u ulju može doći usljed:
– kondenzacije u toku rada motora (često vožnja u gradskim uslovima, kratke relacije na kojim motor ne postigne radnu temperaturu),
– curenje iz sistema za hlađenje zbog oštećenih zaptivki, pukotine u bloku motora ili zbog nedovoljno pritegnute glave motora.
Prema podacima dostupnim u literaturi dozvoljena količina vode u ulju je do 0,2 %.
Ovom analizom se određuje prisustvo metala u ulju. Čestice metala u ulju su jako abrazivne i njihovo prisustvo povećava habanje, a dovodi i do ubrzanja procesa oksidacije ulja. U toku laboratorijskog ispitivanja vrši se određivanje količine Fe (željeza), Cr (hroma), Cu (bakra), Al (aluminijuma), Pb (olova), Sn (kalaja). Metali koji ukazuju na potrošenost aditiva su: Zn (cink), Ca (kalcijum), Ba (barijum), Mg (magnezijum). Ukoliko se u ulju pojavi veća količina Na (natrijum), K (kalijum) ili B (bor) možemo sumnjati na prodor rashladne tečnosti, jer se ovi elementi nalaze u rashladnoj tečnosti. Povećan sadržaj Si (silicijum) ili Ca (kalcijum), koji potiču iz vazduha (prašina) ukazuje na neispravnost filtera za vazduh.
Organski spojevi, koji su sastavni dio maziva, pri povišenim temperaturama i pritiscima, a uz prisustvo kiseonika iz vazduha oksidiraju pri čemu nastaju spojevi kao što su: ketoni, aldehidi, esteri i kiseline. Nastale organske kiseline se neutrališu aditivima koji su sastavni dio motornog ulja, pri čemu se ti aditivi troše. Stvaranje kiselih produkata doprinosi zgušnjavanju ulja (povećanje viskoziteta) kao i koroziji metalnih dijelova. Utvrđivanje stepena oksidacije vrši se primjenom FT-IR spektrofotometrije.
Kada se organski spojevi izlažu dejstvu povišenih temperatura i pritisaka u prisustvu azota i kisika, kao što je to slučaj kod motora, dolazi do stvaranja azotnih oksida kao što su: NO, NO2 i N2O4. S kondenzovanom vodom stvaraju azotnu kiselinu ili se vežu za druge organske spojeve koji doprinose zgušnjavanju i stvaranju lakova na metalnim površinama. Visok nivo nitratacije može ukazivati na nepravilno podešen odnos gorivo / vazduh.
Produkti nastali oksidacijom sumpora prisutnog u gorivu pri čemu se stvaraju sumporni oksidi SO2 i SO3 koji u reakciji s vodom stvaraju sumpornu kiselinu. Ovi produkti doprinose stvaranju taloga i lakova, a izazivaju i koroziju metalnih dijelova.
Povećana količina čađi u ulju može biti posljedica lošeg sagorijevanja goriva. Kod EGR (Exhaust Gas Recirculation) motora jedan dio gasova s izduvne grane se vraća u motor čime se u proces sagorijevanja uvodi određena količina čađi i smanje temperatura sagorijevanja u motoru, što doprinosi nastajanju čađi. Zato je kod analize ulja iz ovih motora pojava većih količina čađi donekle i očekivana. Kod svih drugih motora ona ukazuje na probleme u radu (nepotpuno sagorijevanje).
Američki naftni institut je najveće američko udruženje proizvođača nafte i prirodnog plina. Predstavlja oko 625 korporacija uključenih u proizvodnju, preradu , distribuciju i ostale djelatnosti vezane za naftnu industriju.
Predstavlja udruženje evropskih proizvođača vozila, koje je 1991. godine naslijedilo prijašnji CCMC (Comite des Constructeurs d`Automobiles du Marche Commun) i preuzelo CCMC specifikacije. Prve ACEA specifikacije za motorna ulja izdate su krajem 1995. God pod oznakom ACEA European Oil Sequences 1996.
| Viscosity | Viscosity, by definition, is an oil’s resistance to flow and shear under the forces of gravity. |
| Dynamic (Absolute) Viscosity | Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane – at an unit velocity – when maintaining an unit distance apart in the fluid. The dynamic viscosity units are cP = 1 mPa·s. Measured according to ASTM D 2983. |
| Kinematic Viscosity | Kinematic viscosity is the ratio of – absolute (or dynamic) viscosity to density – a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density. In the SI-system the theoretical unit of kinematic viscosity is m2/s – or the commonly used Stoke (St) where: 1 St (Stokes) = 10-4 m2/s = 1 cm2/s |
| Apparent Viscosity | Describes the behavior of the fluid at low temperatures, and is determined on a device that simulates the start in cold conditions (CCS -Cold Cranking Simulator for simulation of starting chilled parts). It is described in standard methods: DIN 51377 and ASTM D 2602.
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| Viscosity Index | Viscosity index (VI) is an arbitrary measure for the change of viscosity with variations in temperature. The lower the VI, the greater the change of viscosity of the oil with temperature and vice versa. It is used to characterize viscosity changes with relation to temperature in lubricating oil. This is described in standard methods: ISO 2909; ASTM D 2270; JUS B.H8.024. The viscosity index change in a motor oil sample appears as a result of viscosity changes at 40oC and 100oC. The decreasing occurs due to degradation of the viscous index impruver. If a high quality improver is used when engine oil is produced, degradation does not occur during operation and the oil will retain the initial values of viscosity and viscosity index for a long time. If this is the case of an unknown oil sample, this characteristic can tell us whether it is a multigrade or monograde oil. |
| Density | ZDensity is defined as mass divided by volume at given temperature. For the European Union that temperature is 15oC and 60oF (14.56oC) in the Anglo-Saxon literature . Density of oil and his derivates are determined by standard methods: ISO 3675; ASTM 1298; DIN 51757; JUS B.H8.015. |
| Relative Density | Relative density, or specific gravity is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. In the US oil industry, API degrees are obtained as a relative density value mesured at 60oF. According to this form: API = (141.5 / density to 60oF) – 131.5. API degrees are determined by the ASTM D 287 method. |
| Flash Point | The flash point of a volatile material is the lowest temperature at which vapours of the material will ignite, when given an ignition source. Measured according to ISO 2592; ASTM D 92; IP 36; DIN 51376. Checking the flash point indicates whether fuel is present in the oil. The presence of fuel leads to a drop in the flash point, and lead as to informations regarding exessive wear of piston-cylinder assembly and improperly installed fuel injection system. |
| Cloud Point | Predstavlja temperaturu (oC) pri kojoj se u ohlađenom fluidu (mazivu) jave prvi kristali parafina. Do tada bistro ulje, počinje da se muti. Određuje se po metodi ISO 3016 i DIN 51597; JUS B.H8.034 |
| Pour Point | The pour point of a liquid is the temperature below which the liquid loses its flow characteristics. This is described in standard methods: ISO 3016; ASTM D 97; DIN 51597; JUS B.H8.034 |
| Volatility | The NOACK Volatility Test, described in standard methods: ASTM D 943; DIN 51581, determines the evaporation loss of lubricants in high-temperature service. The more motor oils vaporize, the thicker and heavier they become, contributing to poor circulation, reduced fuel economy and increased oi consumption, wear and emissions. |
| Total Acid Number – TAN | The total acid number (TAN) is a measurement of acidity that is determined by the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil. The total acid number TAN (total acid number) is the characteristic that tells us about presence of acidic combustion products due to oxidation of oil.
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| Total Base Number – TBN | TBN is a measure of (alkaline) additives in the oil. Higher TBN oils are able to neutralize a greater amount of acidic materials, which results in improved protection against corrosive reactions and longer oil life.
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| Ash Content | Ash content is defined as the inorganic residue that remains after combustion of the oil. It is a measure of the content of metal compounds and other inorganic components in oil. The sample is burned in accordance with the standard procedure and measures the ash content by methods: ISO 3987; ASTM D 874; DIN 51768 and 51450. If only combustion is done then it is oxide ash. When it is treated with sulfuric acid, sulphate ash is obtained. Sulphated ash usually introduces the content of the additive (based on metals Ca, Mg, Zn, Ba, etc.) in the fluid. Methods: oxides DIN EN 7; sulphates DIN 51575; iron DIN 51397; Ba, Ca, Zn according to DIN 51391; Mn- DIN 51431; Cl- DIN 51577; P- ASTM D 1091; Pb- ASTM D 810; Sn, Si, Al by ASTM D 811. |
| Water Content | Water Content in the oil is measured by the methods DIN 51777 in ppm (parts per million) or mg / kg. If the water appear in oil the cause can be from:
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| Wear metals | This analysis determines the presence of wear metals in the oil. The particles of the metal in the oil are highly abrasive and their presence increases wear and leads to the accelerated oxidation of the oil. The laboratory testing are used for determination of the amount of Fe (iron), Cr (chromium), Cu (copper), Al (aluminum), Pb (lead), Sn (tin). Metals that indicate the consumption of additives are: Zn (zinc), Ca (calcium), Ba (barium), Mg (magnesium). If a greater amount of Na (sodium), K (potassium) or B (boron) is present in the oil, it can be cause of pollution with coolant, because these elements are present in the coolant. The increased content of Si (silicon) or Ca (calcium), which are the present in dust, indicates a malfunction of the air filter. |
| FT-IR: Oxidation Products | In all lubricating systems, organic compounds exposed to high temperatures and pressures in the presence of oxygen will partially oxidize (react chemically with the oxygen). There are a variety of by-products produced during the combustion process such as ketones, esters, aldehydes, carbonates and carboxylic acids, and the exact distribution and composition of these products is complex. Some of these compounds are dissolved by the oil or remain suspended, owing to the dispersive additives in the oil. Carboxylic acids contribute to the acidity of the engine oil and deplete its basic reserve as neutralization takes place. The net effect of prolonged oxidation is that chemically the oil becomes acidic causing corrosion, while a physical increase in viscosity occurs..The level of oxidation can be accurately measured using FTIR spectroscopy. |
| Nitration Products | Nitration products are formed when organic compounds are exposed to high temperatures and pressures in the presence of nitrogen and oxygen. These are generally in the form of nitrogen oxides such as NO, NO2 and N2O4. In addition to causing oil thickening and some of these products being acidic, nitration products are the major cause of the buildup of varnish or lacquer. An increase of the nitration index of an engine oil can indicate mistuning (incorrect fuel/air ratios) or improper spark timing. It can also reflect operating conditions, such as high loads and low operating temperature, as well as piston ring blow-by. |
| Sulfation Products | Sulfate by-products such as SO2 and SO3 are formed by the oxidation of these sulfur-containing compounds. They subsequently escape into the lubrication system around the piston rings and seals and build up over of time. These compounds increase the production of varnish and sludges and generally degrade the oil. |
| Soot | Soot is created from the incomplete combustion of the diesel fuel. Burning a too-rich fuel/air mixture forms soot particulates. An increase in the soot content of the oil indicates combustion problems, or that the drain period may have been extended. Soot buildup is a problem in lubrication oils because it changes the viscosity and prematurely clogs the filters and oil galleries. With EGR (exhaust gas recirculation), one part of the exhaust gas is returned to the engine. Therefore, when analyzing oil from these engines, the appearance of larger quantities of soot is somewhat expected. With all other engines, it points to problems in operation (incomplete combustion). |
| API –American Petroleum Institute | The American Petroleum Institute (API) is the national trade association representing all facets of the oil and natural gas industry. API’s more than 625 members include large integrated companies, as well as exploration and production, refining, marketing, pipeline, and marine businesses, and service and supply firms. |
| ACEA – (Association des Constructeurs Européens d’Automobiles) | The European Automobile Manufacturers’ Association (ACEA) represents the 15 major Europe-based car, van, truck and bus makers. The first ACEA specifications for motor oils were issued in late 1995 under the mark of ACEA European Oil Sequences 1996. |
