Engine oil viscosity index

Oil viscosity index classification Using Table 1 (Appendix) and Chapter 2.5 as references, write viscosity index values for winter and summer engine oils. 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

Before 1925, there were a few compounded oils made for special purposes, such as lubrication of marine engines and steam cylinders, but additives were not used in automotive crankcase oils. In the 1930 s, chemical compounds made by condensation of chlorinated paraffin wax with naphthalene were found to lower the pour points of oils. Pour depressants (9) apparently are adsorbed on small wax crystals which separate from oils when they are chilled. The protective adsorbed layer of additive prevents the normal interlacing of larger wax crystals which forms a gel. In 1934 polymerized unsaturated hydrocarbons first came into large scale commercial use to lower the temperature coefficient of viscosity of oils. Other compounds for increasing the viscosity index of oils have since become common. 

In a fully synthetic oil, there is almost certainly some mineral oil present. The chemical components used to manufacture the additive package and the viscosity index improver (VI) contain mineral oil. When all these aspects are considered, it is possible for a "fully synthetic" engine oil to surpass mineral oil (Shubkin, 1993). Synthetic oils fall into general ASTM classification (a) synthetic hydrocarbons (poly-a-olefins, alkylated aromatics, cycloaliphatics) (b) organic esters (dibasic acid esters, polyol esters, polyesters) (c) other fluids (polyalkylene glycols, phosphate esters, silicates, silicones, polyphenyl esters, fluorocarbons). 

MV EG MVMA different viscosities at 100°C. Fluids with very high natural viscosity indexes, such as some synthetic fluids, are also classified as multiviscosity. Motor Vehicle Emission Group (Europe). Motor Vehicle Manufacturers Association (U.S. passengers cars). A North American OEM association. As part of ILSAC, it participates in promoting the ILSAC engine oil standards. 

The DEHZ basestock was selected as an efficient compromise for desired properties in a partial synthetic oil. An engine oil was formulated using 200 neutral oil, 100 neutral oil, polymethylmethacrylate viscosity index improver, an additive package, and 15% DEHZ. See Table VII under Current 5W-30. This 5W-30 formulation was then subjected to the various tests described in Table VI for qualification as an SF engine oil. The results are presented in Table VIII. 

Asymmetric stars have also been added to a variety of oils including crude oils, lubricating and fuel oils to produce oil compositions, generally having improved viscosity index characteristics. The newer engines place increased demands on the engine lubricants. Asymmetric stars are effective viscosity index improvers. 

Viscosity index, the customary basis for comparison of change of viscosity in hydrocarbon oils, becomes less satisfactory when applied to silicone oils, because the viscosity index varies with viscosity as well as with the temperature coefficient. In silicone oils the variation of viscosity with temperature is too small in relation to the viscosity itself. A true viscosity-temperature coefficient (VTC) has been proposed as a more satisfactory criterion [see Wilcock, Mechanical Engineering 66, 739 (1944)1. 

These oils must be changed at frequent intervals to remove the foreign matter collected during service. The stability of such oils is therefore of less importance than the stability of oils used in continuous service for prolonged periods without renewal. On the other hand, oils used in continuous service must be extremely stable, but their viscosity indexes may be low because the engines operate at fairly constant temperature without frequent shutdown and thermal stability (ASTM D-2070, ASTM D-2511, ASTM D-6205) is an important property. 

The viscosity index of multigrade automotive engine oils is typically in the range of 130-190, whereas monograde oils are usually between 85 and 105. The improved viscosity-temperature characteristics of multigrade oils enables, for example, an SAE 20W/50 oil to be formulated that spans SAE 20W viscosity characteristics at low temperatures and SAE 40 to 50 characteristics at the working temperature. 

Compared on an equal viscosity basis, the properties of a polybutene, a PAO and an ester, the polybutene is more volatile, less resistant to oxidation and has a lower viscosity index. This illustrates the limitations of polybutene as a true synthetic base oil. For example, it would be inappropriate to use a low-viscosity polybutene as the base oil for crankcase engine oils. Polybutenes are used as a major base fluid for... 

Exxon Research and Engineering Co. (1986) Ethylene Copolymer Viscosity Index Improver Dispersant Additive Useful in Oil Compositions , US Patent 4,632,769. 

Hillman, D.E., Lindley, H.M., Paul, J.I. and Pickles, D. (1975) Application of gel permeation chromatography to the study of shear degradation of polymeric viscosity index improvers used in automotive engine oils. Er. Polym. J. 1 397-407. 

Mueller, H.G. (1978) Mechanism of action of viscosity index improvers. Tribol. Int. 11 (3). Stewart, R.M. and Selby, TW (1977) The relationship between oil viscosity and engine performance - a literature search. SAE Trans. 86 Paper 770372. 

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