Professional paper
ENGINE OIL VISCOSITY INDEX IMPROVER BEHAVIOUR AT EXTENDED SHEAR STABILITY TEST
Višnja Mihaljuš Sklepić
; INA d.d. Zagreb, Rafinerija nafte Rijeka
Marijan Podobnik
; INA d.d. Zagreb, Rafinerija nafte Rijeka
Josip Bambić
; INA d.d. Zagreb, Rafinerija nafte Rijeka
Abstract
Multigrade engine oils among numerous additives, always contain also viscosity index improvers. These additives are special types of polymers, which in small concentration significantly improve engine oils rheological properties, especially viscosity and viscosity index. However, during engine oils utilization, degradation of viscosity index improvers ie. break down of polymeric molecules occures. It results in reduction of their molecular weight what leads to viscosity loss and oil film thickness decrease, which causes undesirable phenomena of friction and wear.
The shear stability of the viscosity index improvers that is the polymer resistance to mechanical degradation under shear stress is determined by measuring of the viscosity loss after repeated oil passing through the injector nozzle. The engine oil specifications define the minimal oil viscosity grade after the shear.
By introducing the new ACEA and API specifications, the requirements for the shear stability of engine oils have been changed and now they are accepted by engine and vehicle manufacturers. In order to achieve better correlation with engine oil application results, it is defined that the shear stability should be determined by standardized apparatus extending current testing of 30 to 90 cycles of oil passing through the nozzle.
The paper presents the shear stability testing of most important types of commercial viscosity index improvers on Orbahn diesel injector apparatus at extended shear stability test (90 cycles) with aim on meeting the new engine oil specifications.
Keywords
viscosity improvers; polyalkylmetacryilate VI improver (PAMA); multigrade motor oil; shear stability; viewpoint of increasing requirement
Hrčak ID:
23962
URI
Publication date:
30.4.2008.
Visits: 9.768 *