The change in Diesel Engine Oil Properties During Performance

: Infrared (IR) and differential scanning calorimetric (DSC) analytical tests have been used to study the change in diesel engine oil properties during performance, in addition to the changes in physical and chemical properties. Two types of diesel engine oils (petroleum base) that are used in bus vehicles were examined in bus diesel engines travelling distances up to 5000 km. The results show the characterization of the oil as the changes in chemical composition and physical properties with the travelling distances increase. Also, the results show the changes that take place in the diesel engine oils during use up to 5000 km depend on choosing the type of oil that bears such heavy duty engines as the bus vehicle, and the period required to change the oil to avoid damage to the different parts of the engine.


Introduction
Lubrication is a process in which a lubricant is placed between rubbing surfaces to control friction and reduce wear.The manufacture and classification of lubricating oil base stocks, including refined petroleum stocks, are used in internal combustion engines, whether in light or heavy duty engines (HD).These oils are consist of a base oil chosen with specifications that suit the place of use.However, these oils do not withstand the operating conditions, especially when exposed to extremely high temperatures (up to 800 °C in the cylinder walls) and pressures (up to 1000 psi in the bearings) in the air environment [1,2,3].Base oils are mixed with chemical additives to improve the specifications, and to enhance oxidation stability, corrosion resistance, wear reduction, friction modification, viscosity-temperature improver and other important performance characteristics to enhance lubrication in extreme environments [4, 5.6] .
The continuous aging of used oil is caused by the action of oxygen in the air, which readily reacts with hydrocarbons.As a result of their oxidation, compounds with the composition of alcohols, aldehydes, organic acids, and resin products are formed, which lead to the formation of double bonds, then cause polymerization.After a long period of use, the oxidation process is accelerated by the high temperature causing thermal decomposition of base oil hydrocarbons and altering viscosity, then the oil turns light and black, and becomes unable to lubricate anything [7,8].
During service, the properties of oil change and may come to the state that the oil fails to keep the engine performing efficiently and safely.A portion of the heat generated during combustion is eventually transferred to the oil which, with prolonged time of operation, deteriorates the oil properties by firstly reducing the viscosity at high temperature, and secondly by increasing the oxidation rate with a subsequent formation of organic compounds which may attack bearing materials.Moreover, other reactions may occur between oil molecules that result in asphaltic compounds which contribute to the formation of sludge; water, fuel, soot, residues, metallic wear particles and environmental dirt particles may pollute the oil as a result of combustion, engine wear and filtration.These are actually functions of engine life.For these situations, deteriorating oil should be replaced by new oil [9].A study of over a 100 hour lube oil aging in different passenger cars diesel engine shows the emissions decrease first up to 50 hr. of oil age, and then increased as the oil ageing up to 100 hr, and the contamination of diesel engine oil with particles, water or by other liquids effect on bearing life through wear, while water can damaging the ball and other roller bearing [10]. .
The effects of water contamination on the filtration of HD diesel engine oils [11], indicates that further work is required before bench tests can be established to predict filter plugging tendencies of water contaminated HD engine oils in service and shows that one of the great indicated on the efficiency of internal combustion engines and largely determine their reliability and durability as well as environmental impact is the wear resistance of friction pairs, which directly depends on the metal physical characteristics of the friction surfaces as well as the physical and chemical properties of engine oils [12].
For these reasons, the researchers went to search for oils that are more resistant to oxidation and bear the difficult conditions that oil is exposed to when used in internal combustion engines.Some of them who worked on the use of synthetic oils such as alpha olefin oil and different types of esters, and some of them went to use vegetable oils to solve problems or blend them with conventional oil.
Synthetic engine oils like esters, poly alpha olefins (PAO) and bio-based lubricants offer several advantages over conventional oil.First, it lasts longer because oil takes longer to break down.It also performs better in extreme temperatures, and needs lower levels of additives compared to conventional motor oils.Most notable are reduced quantities of viscosity improvers because of the inherently high viscosity index (VI) of synthetic oil.A high VI means that synthetic oil retains its viscosity when hot, and lower pour point [13].
In this study, about the changes that occur to the oils used in internal combustion engines such as public transport vehicles (heavy duty engines), it was found that it is a result of continuous use and the nature of use, in addition to environmental conditions, oils are affected quickly, so they need to be replaced for a period of 4500-5000 km, in addition to continuous maintenance and work to replace filters to preserve engine parts.

Field test program
Two double decker buses were selected and subjected to normal maintenance of their depot and have the following specifications: 220 h.p, 2200 r.p.m., 6 cylinders (D-2566 muh) -MAN type.Oil samples were fully drained from bus vehicles at intervals of 1000 km up to 5000 km for both diesel engine oils (A) and (B).The main properties of fresh diesel oils are listed in Table 1.

Table 1. The main properties of fresh diesel engine oils A & B
The specifications and changes that occurred in diesel engine oils A and B were studied after use for periods of 1000-5000 km.The properties are listed in Tables 2 and 3.

Infrared Analysis
The IR spectra of fresh and used diesel engine oils are carried out with PYE Unicom infra-red spectrophotometer SP-300 fitted with a data processor type SP3-050 and PYE printer type PU-8501.The test was done with a KBr cell of 0.02 mm.

Results and Discussion
The infrared spectrum for each of the diesel engine oils A and B is shown in Figures 1, 2. As for Figure 3, it shows the intensities and the changes in absorption bands that occurred in the oils during use up to 5000 km.The different chemical groups and their corresponding IR absorption spectra are listed in Table No  The change in the absorption bands increase as the running distance increases, and the changes occur within the same oil and between the different oils.It is possible to compare the stability of the different chemical groups, also.

diesel engine oil A
The absorption spectrum at 720 cm-1 shows the degradation of long-chain paraffinic compounds into compounds of smaller chain, and the absorption spectrum at 1300-1150 cm -1 , which is related to compounds that contain heterogeneous atoms.There was an increase at a low rate with the increase of the traveled distance up to 5000 km.Then, a rapid change occurred, which indicates a rapid degradation of the oil components as shown in Figure 1.It was also noticed that the rate of change in the absorption spectrum at 1600 cm -1 for aromatic compounds, and the spectrum at 850-820 cm -1 for aromatic compounds that contain substituted groups are less than what occurs in paraffinic compounds.
This indicates that the aromatic compounds and the naphthenic compounds are more stable compared to the various paraffinic compounds.After 5000 km, a rapid change occurred, which indicates that the oil has changed completely, Figure 2.

diesel engine oil B
The absorption spectra at 750 cm -1 and 1300-1150 cm -1 show the degradation of the long paraffinic chains into smaller ones.This increased at a rapid rate as soon as the oil was used, then became slower with the increase in the distance of travel.The rate of chemical change in absorption spectra for shown aromatic compounds, 970 cm -1 for naphthenic compounds, and 850-820 cm -1 for substituted aromatic compounds were higher than that observed with paraffinic and heteroatom compounds as shown in Figure 3.The absorption spectrum at 664 cm -1 for P=S of Zinc-dialkyldithiophospate ( Zn-DDP ) in paraffinic, aromatic, and naphthenic compounds has shown a smooth and slow change rate with increasing running distance that indicates a good stability of Zn-DDPh additive.
From the above observations we can say that the stability of diesel engine oil A is higher in stability than diesel engine oil B during performance in a diesel engine while traveling up to 5000 km, Figure 4.

Differential scanning Calometric (DSC) analysis for used diesel engine oils
Thermo-oxidation stability of diesel engine oil during performance could be estimated by plotting the initial degradation temperature (Ti) against the running distance.Such a plot for diesel engine oil A and diesel engine oil B has been obtained by DSC analysis and is presented in figure 5`.
In comparison between the two plots, it can be concluded that the thermo-oxidation stability of diesel engine A is higher in stability than diesel engine B. This higher stability is characterized by an induction period up to 4000 km traveled.The induction period was followed by a slow decrease in oil stability up to 5000 km.Then there continued to decline in stability.
On the other hand, diesel engine oil B shows no induction period.Its degradation started early.The stability declined at a higher rate from the first 1000 km, then a lower rate of decline was observed at the interval of 1000-3000 km, while a sharp decrease was observed after 3000 km.The degradation temperature (T) at 5000 km was 187 o C.This finding was agreed with the results of infra-red spectroscopic analysis.

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Technium Vol. 13, pp.68-78 (2023) ISSN: 2668-778X www.techniumscience.comA showed more resistance, and its loss of lubrication was gradual, up to a distance of 5000 km.We also notice the same behavior of the viscosity of the diesel engine oils at a temperature of 100 o C. Figure 7.

Flash point
From Figure 8, we notice in both diesel engine oils A and B a decrease in the degree of flash point with the increase in the distance traveled as a result of the degradation of the oil inside the engine, and that the diesel engine oil A showed a gradual degradation and breakdown of the components, while diesel engine oil B was faster in degradation, but in both cases the degradation produces as light materials and compounds that lower the degree of flash point.

Acidity
Acidity is considered one of the important specifications that indicate the unfitness of the oil for use if it exceeded the permissible limit because of the corrosion it causes to the equipment as a result of the formation of organic and mineral acids.Figure 9 shows that there is an increase in the acidity of both oils with increasing distance traveled.In the case of diesel engine oil A, we notice the increase appearing from the beginning of use, but gradually, while diesel engine oil B, the increase is rapid, and in both cases, the increase in acidity continues to a distance of 5000 km.

Conclusion
Because diesel engines must withstand higher peak combustion chamber forces than gasolinepowered engines, more durable construction features are used.They include heavier pistons and stronger crankshafts, valve trains, and gear trains.Infra-red and differential scanning calorimetry (DSC) can predict the stability and aging tendency of diesel engines at travelling distances.
The improvement in the quality and composition of engine oils helped the engine reach high durability milestones. Changing the oil filter as infrequently as twice a year. In heavy duty diesel engines, the required oil must be high in quality. The usage period for diesel engine oil in bus engines must be in the range of 4500-5000 km to keep the engine safe. Environmental pollution may play a role in accelerating oil degradation.

2. 3 .
Differential Scanning Calorimetric measurement 10 mg of oil samples were weighted in Aluminum crucibles by heating them at 10oC heating rate in static air to 350 o C. Aluminum oxide was used as a reference material.The experimental error was within ± 2 o C.

Figure 1 .Figure 2 .
Figure 2. The change in the absorption spectra with increasing traveling distance for diesel engine A

Figure 3 .
Figure 3. Infrared spectrum of diesel engine B

Figure 4 .
Figure 4 .The change in the absorption spectra with increasing traveling distance for diesel engine B

Figure 6 CFigure 5 .
Figure6shows a comparison of the viscosity measured at 40 o C for both types of oils at a distance of 5000 km, as the graphic shows the rapid change in the viscosity of oil B with an increase in the distance traveled, which indicates the loss of the oil's ability to lubrication at the distance of 2000 km.While oil

Figure 6 .Figure 7 .
Figure 6.Comparison in Viscosity at 40 o C for diesel engine Oils A and B

Figure 9 .Figure 8 .
Figure 9.Comparison in the acidity for diesel engine Oils A and B

Table 2 .
The main properties of diesel engine oil A at different running distances

Table 3 .
The main properties of diesel engine oil A at different running distances

Table 4 .
The IR absorption spectra and their corresponding chemical groups.