Abstract
The aim of the article was to analyze changes in the trends of selected physical, chemical and functional properties of lubricating engine oil operating in a diesel-engine vehicle equipped with DPF. The vehicle was operated mainly in urban driving conditions (app. 70%), which impeded the DPF regeneration cycle and caused dilution of oil with unburned fuel. Changes in the following physical and chemical properties were assessed: the DF level in engine oil, viscosity (kinematic, dynamic HTHS and structural CCS), total base num-ber, acid number as well as the degree of oxidation, nitration and sulphonation. The tests have shown that the amount of unburned fuel that goes to the engine crankcase due to the unfinished DPF regeneration cycle is as high as 26.0–34.6%. Dilution of the lubricating oil with fuel leads to a significant reduction of its viscosity – about 30% of the fuel content causes a decrease in the kinematic viscosity measured at 100°C to the level of 7.7 mm2/s. There was also a significant decrease in total base number (TBN) < 2 mg KOH/g, and an increase in the total acid number (TAN). Moreover, the results obtained were analyzed for potential effects that could have been caused during prolonged engine operation by assessing the content of trace elements in the samples taken.
Highlights
Stricter standards in the field of environmental protection have led, as far as compression ignition engines (CI) are concerned, to the widespread distribution of diesel particulate filters (DPFs), which require at least periodic regeneration processes to function properly
Considering the above-presented issues, the focus was on assessing the changes in physical, chemical and functional properties affecting the operational usefulness of motor oils, i.e. viscosity, total base number, acid number, DF content and oxidation, nitration and sulfonation
The determination of structural viscosity at low temperatures was carried out according to the PN-C-04150:2004 standard by means of a cold cranking simulator, by measuring the rotational speed of the impeller immersed in oil cooled down to –35oC (CE) and –30oC (PE)
Summary
Stricter standards in the field of environmental protection have led, as far as compression ignition engines (CI) are concerned, to the widespread distribution of diesel particulate filters (DPFs), which require at least periodic regeneration processes to function properly. Unfinished cycles of filter regeneration lead to the penetration of excess unburned fuel into the engine oil, which results in a significant deterioration of its physical, chemical and functional properties. The viscosity of the lubricating oil is systematically lowered as a result of diluting it with fuel and the leaching of elements included in the additives package follows. This contributes to an accelerated reduction of the base number, with the simultaneous increase in the acid number of the lubricating oil. The other is contamination with combustion products, due to solid particles such as dust, outer contaminants, abrasive metals, water and cooling liquid as well as to diluting the oil with unburned fuel
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