Physicochemical properties of a mineral-based gasoline engine oil have been monitored at 0, 500, 1000, 2000, 3500, 6000, 8500, and 11500 kilometer of operation. Tracing has been performed by inductively coupled plasma and some other techniques. At each series of measurements, the concentrations of twenty four elements as well as physical properties such as: viscosity at 40 and 100°C; viscosity index; flash point; pour point; specific gravity; color; total acid and base numbers; water content have been determined. The results are indicative of the decreasing trend in concentration of additive elements and increasing in concentration for wear elements. Different trends have been observed for various physical properties. The possible reasons for variations in physical and chemical properties have been discussed.
Oil analysis involves sampling and analyzing oil for various properties and materials to monitor wear and contamination in an engine, transmission, or hydraulic system [
The first use of used oil analysis dates back to the early 1940s by the railway companies in the Western United States. Prompted by the purchase of a fleet of new locomotives, technicians used simple spectrographic equipment and physical tests to monitor locomotive engines [
At present oil analysis regards an important part of condition monitoring in advanced industrial countries. By employment of such programs, considerable saving in time and costs has been obtained [
In an oil analysis, the concentration of a number of elements as well as the quantity of some of the physical properties such as viscosity, viscosity index, density, flash point, pour point, total acid and base numbers, and water content [
We have recently been involved in the investigation of lubrication oils [
Base oil SN-500 and gasoline oil Speedy SL from Sepahan Oil Company were used directly. Methanol, hydrochloric acid, perchloric acid, different buffers, propane-2-ol, chloroform, potassium hydroxide, acetic acid, acetic anhydride, chlorobenzene, sodium perchlorate, xylene, acetone, and solid carbon dioxide were purchased from Merck Company and used without any processing. Spex multielement primary standards set were used for ICP-OES elemental analysis.
The test methods were followed as: ASTM D-445 for viscosity at 40°C and 100°C, ASTM D-2270 for viscosity index, ASTM D-92 for flash point, ASTM D-97 for pour point, ASTM D-1298 for specific gravity, ASTM D-1500 for color, ASTM D-664 for total acid number, and ASTM D-6304 for water content.
All of the viscosities, viscosity indices and specific gravities were determined by viscometer Anton Paar model SVM 3000. Flash points were evaluated by flash point tester Herzog model HC 852. Pour points were determined by pour point tester Herzog model HC 852. The colors were determined by Dr. Long instrument. TBNs were determined by robotic titrosampler Metrohm model Dosiono 800. TANs were determined by titrator Metrohm model Titrino MPT 789. FTIR spectrum was recorded on a FTIR spectrum Perkin Elmer model Spectrum 65 using KBr pellet. The elemental analysis of the base oil, that is, SN-500 and formulated oil (Speedy SL) was performed by ICP-OES Perkin Elmer model Optima 5300 V. The detection limits (DLs) were obtained under simultaneous multielement conditions with the axial of a dual-view plasma using a cylonic spray chamber and a concentric nebulizer. All detection limits are given in microgram per liter and were determined using organometallic standards. The selected wavelengths and the values of DL (values in parentheses) for each element are as shown in Table
At each running kilometer the sampling [
The concentrations of twenty-four element in lubrication oil and at different kilometers have been determined by ICP-OES. The corresponding values are given in Table
The concentration of elements containing in additives, at different distances. Values in parenthesis are due to base oil.
No. | Element | Kilometer of operation | |||||||
0 | 500 | 1000 | 2000 | 3500 | 6000 | 8500 | 11500 | ||
(1) | S (7000) | 1108.3 | 970.4 | 964.7 | 957.5 | 960.0 | 940.0 | 935.4 | 907.1 |
(2) | Zn (6.1) | 784.0 | 743.2 | 711.6 | 650.1 | 580.9 | 467.5 | 355.6 | 249.9 |
(3) | P (5.7) | 811.2 | 793.9 | 773.5 | 738.0 | 686.6 | 603.5 | 505.1 | 411.9 |
(4) | Mg (0.3) | 228.9 | 228.3 | 227.6 | 225.4 | 223.2 | 222.1 | 214.7 | 202.7 |
(5) | Si (3.1) | 61.4 | 60.9 | 60.1 | 59.1 | 59.1 | 51.5 | 50.7 | 50.1 |
(6) | Ca (<DL) | 56.7 | 53.5 | 51.9 | 46.9 | 43.7 | 36.4 | 29.4 | 22.3 |
(7) | Ba (<DL) | 29.4 | 29.1 | 28.4 | 27.8 | 26.9 | 23.8 | 23.7 | 23.4 |
(8) | B (6.5) | 6.7 | 6.2 | 5.7 | 5.3 | 4.8 | 3.8 | 3.5 | 3.3 |
(9) | Mo (6.4) | 6.5 | 6.5 | 6.5 | 6.6 | 7.5 | 8.2 | 8.6 | 8.8 |
(10) | Al (5.2) | 5.1 | 5.2 | 5.4 | 5.9 | 5.9 | 7.0 | 7.3 | 8.9 |
(11) | Ag (1.6) | 1.7 | 2.1 | 2.2 | 2.2 | 2.3 | 2.2 | 2.3 | 2.3 |
(12) | Cr (1.1) | 1.1 | 1.6 | 1.9 | 2.1 | 2.2 | 2.3 | 2.4 | 2.7 |
(13) | Ni (1.2) | 1.1 | 1.2 | 1.3 | 1.4 | 1.6 | 1.6 | 1.7 | 2.0 |
(14) | Na (0.4) | 0.5 | 0.7 | 0.8 | 1.0 | 1.1 | 1.0 | 1.2 | 1.2 |
(15) | Mn (<DL) | <DL | 0.8 | 1.1 | 1.4 | 2.6 | 3.2 | 4.5 | 15.5 |
(16) | Fe (<DL) | <DL | 2.4 | 3.7 | 5.2 | 6.9 | 8.6 | 10.1 | 11.8 |
(17) | Cu (<DL) | <DL | 0.4 | 0.8 | 1.2 | 1.8 | 1.8 | 2.1 | 2.5 |
(18) | Sn (<DL) | <DL | 0.4 | 0.8 | 0.8 | 0.9 | 1.0 | 1.3 | 1.4 |
(19) | Ti (<DL) | <DL | 0.4 | 0.8 | 1.1 | 1.8 | 1.8 | 1.9 | 1.9 |
(20) | V (<DL) | <DL | 0.5 | 0.7 | 1.3 | 1.8 | 1.8 | 1.8 | 1.9 |
(21) | Pb (<DL) | <DL | <DL | <DL | <DL | 0.1 | 0.2 | 0.2 | 0.6 |
(22) | Cd (<DL) | <DL | 0.5 | 0.5 | 0.5 | 0.6 | 0.6 | 0.6 | 0.6 |
(23) | Sb (<DL) | <DL | 0.3 | 0.5 | 0.6 | 0.7 | 0.7 | 0.8 | 0.8 |
(24) | K (<DL) | <DL | <DL | <DL | <DL | <DL | <DL | <DL | 7.4 |
Standard deviations of the data of Table
No. | Element | Kilometer of operation | |||||||
0 | 500 | 1000 | 2000 | 3500 | 6000 | 8500 | 11500 | ||
(1) | S (±0.3) | ±0.3 | ±0.5 | ±0.2 | ±0.1 | ±0.1 | ±0.3 | ±0.7 | ±0.3 |
(2) | Zn (±0.9) | ±0.1 | ±0.1 | ±0.5 | ±0.8 | ±0.6 | ±0.3 | ±0.2 | ±0.1 |
(3) | P (±0.8) | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 |
(4) | Mg (±0.6) | ±0.1 | ±0.1 | ±0.1 | ±0.9 | ±0.4 | ±0.6 | ±0.3 | ±0.5 |
(5) | Si (±0.6) | ±0.4 | ±0.1 | ±0.7 | ±0.5 | ±0.2 | ±0.2 | ±0.6 | ±0.1 |
(6) | Ca (—) | ±0.3 | ±0.7 | ±0.6 | ±0.3 | ±0.5 | ±0.9 | ±0.1 | ±0.3 |
(7) | Ba (—) | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 | ±0.3 |
(8) | B (±0.1) | ±0.6 | ±0.1 | ±0.1 | ±0.7 | ±0.8 | ±0.1 | ±0.5 | ±0.9 |
(9) | Mo (±0.3) | ±0.1 | ±0.1 | ±0.4 | ±0.2 | ±0.1 | ±0.1 | ±0.3 | ±0.3 |
(10) | Al (±0.3) | ±0.3 | ±0.6 | ±0.3 | ±0.7 | ±0.1 | ±0.3 | ±0.4 | ±0.5 |
(11) | Ag (±0.1) | ±0.5 | ±0.2 | ±0.1 | ±0.5 | ±0.6 | ±0.5 | ±0.4 | ±0.5 |
(12) | Cr (±0.1) | ±0.1 | ±0.3 | ±0.4 | ±0.5 | ±0.6 | ±0.6 | ±0.3 | ±0.1 |
(13) | Ni (±0.1) | ±0.3 | ±0.2 | ±0.3 | ±0.4 | ±0.4 | ±0.3 | ±0.3 | ±0.9 |
(14) | Na (±0.2) | ±0.1 | ±0.1 | ±0.2 | ±0.2 | ±0.1 | ±0.2 | ±0.2 | ±0.3 |
(15) | Mn (—) | — | ±0.2 | ±0.1 | ±0.3 | ±0.1 | ±0.1 | ±0.1 | ±0.5 |
(16) | Fe (—) | — | ±0.2 | ±0.5 | ±0.3 | ±0.3 | ±0.6 | ±0.1 | ±0.2 |
(17) | Cu (—) | — | ±0.1 | ±0.2 | ±0.6 | ±0.5 | ±0.1 | ±0.2 | ±0.2 |
(18) | Sn (—) | — | ±0.2 | ±0.1 | ±0.1 | ±0.3 | ±0.1 | ±0.2 | ±0.3 |
(19) | Ti (—) | — | ±0.5 | ±0.7 | ±0.4 | ±0.2 | ±0.1 | ±0.1 | ±0.3 |
(20) | V (—) | — | ±0.3 | ±0.1 | ±0.4 | ±0.2 | ±0.1 | ±0.1 | ±0.3 |
(21) | Pb (—) | — | — | — | — | ±0.1 | ±0.1 | ±0.1 | ±0.2 |
(22) | Cd (—) | — | ±0.1 | ±0.1 | ±0.1 | ±0.2 | ±0.2 | ±0.2 | ±0.3 |
(23) | Sb (—) | — | ±0.1 | ±0.1 | ±0.1 | ±0.3 | ±0.4 | ±0.1 | ±0.2 |
(24) | K (—) | — | — | — | — | — | — | — | ±0.3 |
One of the sources of the elements in fresh oil is additives, that are, the compounds which are employed in the oil formulation and do have the role of enhancement of the physicochemical properties of the oils [
The other source of the elements in the fresh lubricant oil are those elements, which in the process of base oil production are incorporated. Because of the organic character of the base oil, it is anticipated that its metallic elements are less than the nonmetallic ones.
Thus, the elements of no. 1–14 in fresh oil originate from two sources of base oil and additives. In the case of metallic elements it is anticipated that the base oil has minor contribution and the main part is due to additives. In other cases such as sulfur and phosphorus, the contribution of both sources may be considerable.
In order to have a better understanding of the sources of the elements in the fresh oil, it was also examined for different elements. The obtained results are given in the second column of Table
As the data shown in the fresh oil S does have the most concentration. This can be attributed to (i) high level of S in the base oil and (ii) application of ZDDP, which is a sulfur-containing additive and normally is employed in crankcase oil formulations.
Zinc and phosphorous are the second and third highest concentration elements (Table
The elevated levels of Mg, Si, Ca, and Ba can be related to the application of additives such as basic phenates or magnesium sulfonate, silicon antifoam, calcium sulfonate, and barium sulfonate [
Comparison of the concentrations of the elements no. 7–14 in the base oil with those of fresh oil (Table
None of the elements no. 16–24 (Table
The concentrations of elements no. 1 to 7, which are incorporated in additive structures, versus the running kilometer are given in Table
Wear metals will appear in the oil because of wearing of different parts of engine, Fe is the most common of the wear metals. Present in some form in virtually all equipment. Its widespread presence means that there are many sources of the wear particles. It can be found in cylinder liners, piston rings, valve train, crankshaft, rocker arms, spring gears, lock washers, nuts, pins, connecting rods, engine blocks, and oil pump. Cu is widely used as an alloying element, copper is prized because of its materials properties, very ductile and excellent thermal and electrical conductivity. It is heavily used in bearing systems, as well as heat exchangers. In the engine, it can be found in valve train bushing, wrist pin bushing, cam bushings, oil cooler core, thrust washers, governor, connecting rods bearings, and valve gear train thrust buttons. Tin is used as an alloying element with copper and lead for sacrificial bearing liners. In the engine, it can be found in valve train bushing, wrist pin bushing, cam bushings, oil cooler core, thrust washers, governor, connecting rods bearings, and valve gear train thrust buttons. Aluminum is valued in equipment because of it high strength to weight ratio and excellent corrosion resistance. Being alloyed with other elements improves its wear and temperature resistance. It is widely specified for equipment manufacture nowadays. In engine, it can be found in engine blocks, pistons, blowers, oil pump bushings, bearings (some), cam bushings (some), and oil coolers (some). Chromium is used as an engineering material for its great hardness and corrosion resistance. It is found in many systems operating under harsh conditions. In engine it can be found in rings, liners, exhaust valves, and zinc chromate from cooling system inhibitor. Lead is used in a soft metal used for sacrificial wear surfaces such as journal bearings. Lead-based babbitts are widely used. Silver has exceptional thermal conductivity and is an excellent bearing plate material, providing minimum friction. It is susceptible to corrosive attack by zinc-based additives. In engine, it can be found in valves, valve guides, cylinder liners, and bearings. The other elements can also find in different parts of engine [
The data in Table
The decreasing trend of boron concentration may be due to the formation of boron compounds in oil matrix, which are absorb in oil filters.
The concentrations of the elements, which are neither due to base oil, nor due to additive, are given in Table
Consistency, flow properties, or viscosity in the case of oils are key parameters to create lubrication efficiency and the application of lubricants [
As it can be seen from the Table
Physical properties at different running kilometer.
Property | Test method | Running Kilometer | |||||||
0 | 500 | 1000 | 2000 | 3500 | 6000 | 8500 | 11500 | ||
Viscosity at 40°C | ASTM D-445 | 141.6 | 140.0 | 138.3 | 135.3 | 137.2 | 137.8 | 142.2 | 143.4 |
Viscosity at 100°C | ASTM D-445 | 16.5 | 16.3 | 16.0 | 15.8 | 15.9 | 16.1 | 16.3 | 16.5 |
Viscosity index | ASTM D-2270 | 125.0 | 126.2 | 127.3 | 129.5 | 128.0 | 127.5 | 123.0 | 122.2 |
Flash point | ASTM D-92 | 222 | — | — | — | — | — | — | 223 |
Pour point | ASTM D-97 | −26 | — | — | — | — | — | — | −26 |
Specific gravity | ASTM D-1298 | 0.8910 | 0.8935 | 0.8942 | 0.8943 | 0.8950 | 0.8963 | 0.8994 | 0.9011 |
Color | ASTM D-1500 | 2.0 | 2.8 | 3.1 | 3.9 | 5.1 | 5.9 | 6.3 | 7.5 |
TAN (mg KOH/g) | ASTM D-664 | 1.52 | 1.88 | 1.94 | 2.05 | 2.33 | 2.61 | 2.79 | 3.00 |
TBN (mg KOH/g) | ASTM D-664 | 12.37 | 12.13 | 12.03 | 11.80 | 11.22 | 10.97 | 10.82 | 10.33 |
Water content | ASTM D-6304 | 22.1 | 35.2 | 43.0 | 50.1 | 54.9 | 61.4 | 63.0 | 63.0 |
Element | Wavelength | Element | Wavelength | Element | Wavelength | Element | Wavelength |
---|---|---|---|---|---|---|---|
S (10.0) | 181.6 | Ba (0.03) | 233.5 | Ni (0.5) | 231.6 | Ti (0.4) | 334.9 |
Zn (0.2) | 206.2 | B (1.0) | 249.7 | Na (0.5) | 589.6 | V (0.5) | 290.9 |
P (4.0) | 213.6 | Mo (0.5) | 202.1 | Mn (0.1) | 257.6 | Pb (1.0) | 230.3 |
Mg (0.04) | 285.2 | Al (1.0) | 396.1 | Fe (0.1) | 238.2 | Cd (0.1) | 328.8 |
Si (10.0) | 251.6 | Cr (0.2) | 267.7 | Cu (0.4) | 327.4 | Sb (2.0) | 206.8 |
Ca (0.05) | 317.9 | Ag (0.6.0) | 328.1 | Sn (2.0) | 189.9 | K (1.0) | 766.5 |
IR spectrum of the oil after 11500 km operation.
The observed bands in the IR spectrum of used oil (Figure
The flash point is the lowest temperature at which an ignition source causes the vapors of the specimen (lubricant) to ignite under specified conditions [
Fuel dilution causes the decrease the specific gravity. In contrast, silicon contamination or oxidation causes its increase [
The total acid number is a measure of the acidic constituents in petroleum products. The acidity of unused oils and fluids is normally derived from the type and concentration of specific additive material, whereas the acidity of used oil is of interest to measure the degree of oxidation of the fluid. The total base number (TBN) characterizes the alkaline reserve in petroleum products [
The plots of TAN and TBN versus kilometers of operation are shown in Figure
Plots of TAN (bottom) or TBN (top) versus running kilometers.
In contrast, to TAN a lessening drift is observed for TBN (Figure
Considering that, TBN is a measure of alkaline reservation of lubricant [
Water is the most common contaminant found in lubricating oils. It is also one of the most damaging to bearings and other lubricated components. It causes corrosion to metal surfaces, lubricant degradation, and poor lubrication. Water can be present in three forms of dissolved, emulsified, and free in lubricating oils. The concentration of dissolved water is less than 100 ppm and is not harmful nor does it affect the appearance or performance of the lubricant. Emulsified water exists in more than 150 ppm and causes milky appearance of the oil. It is the most harmful. Water droplets are the third kind of water in lubricating oils. This form of water in oil is also very harmful to lubricated parts but is also the easiest to separate [
Based on the observed results it can be concluded that through different operation kilometers the following changes are happened: the additives depletion; minor wear; some oxidation; increase and decrease in rheological properties; increase of TAN and decrease of TBN due to oxidation; a few water contaminations; not many coolant leakage.
In addition, the soot formation and fuel contamination do not happen.
The financial support for this work by Azad University of Shahreza is highly appreciated. The authors also thank Sepahan Oil Company due to lab support for this work. The authors were also partially supported by the