Contents

The Influence of Fatty Acids and Fatty Acids Mixtures on the Lubricity of Low-Sulfur Diesel Fuels

Czeslaw Kajdas
Central Petroleum Laboratory in Warsaw, Poland
Warsaw University of Technology, Institute of Chemistry, Poland

Marzena Majzner
Warsaw University of Technology, Institute of Chemistry, Poland


Published in: SAE TECHNICAL PAPER SERIES 2001-01-1929

ABSTRACT

Research described in this work relates to tribological properties of fatty acids and fatty acids mixtures and aims at providing more information on and better understanding of the wear process in the presence of low-sulfur fractions containing these substances at very low concentration under boundary lubrication conditions in the steel-on-steel system.

Experiments were carried out using the ball-on-disc friction machine. To get detailed information on interaction of diesel fuel components with individual fatty acids and mixtures of acids, low-sulfur diesel fuel cuts as well as their mixtures and two model hydrocarbons were used as the base fluids.

Although the overall picture of the obtained results is very complex, it can be concluded that: (a) Tribological properties of base diesel fuels are determined by the highest fractions and heterogeneous compounds present in these fractions; (b) Fatty acids and their equimolar mixtures - added to the "reformulated diesel fuels" at the adequate concentration - show excellent antiwear properties; (c) Both the chemical structure and viscosity of base fluids influence the wear behavior of fatty acids and their mixtures.

All the findings are challenging from the view-point of their interpretation as well as from their relation to the diesel fuel constitution. Obtained results also evidently confirm the complexity of the boundary lubrication approach.

INTRODUCTION

There are several different models of how boundary lubrication prevents the high shear stresses associated with the localized seizures of the surfaces. In fuel injection equipment the mechanism by interposing - either by chemisorption or physical adsorption - a layer on the surfaces to reduce the number of points at which true metal to metal contact occurs, has been considered the most important [1].

In the 1960s and 1970s a number of serious aviation fuel pump problems were encountered in service. After considerable research it was realized that a prime cause of those problems was an increase in the severity of refinement of aviation kerosene by processes such as hydrotreatment and clay treatment refining process [2]. Nitrogen containing impurities such as pyrolles, indoles, carbazoles, basic pyridines and trace quantities of oxygen-containing impurities such as phenols and certain naphthenic acids were removed. That situation reduced the inherent lubricating properties of fuels. Those problems were overcome by incorporating lubricity additives, for example such as a mono-, di- and trimers of C18 fatty acids [3].

Wei and Spikes [4] carried out a study on the diesel fuel lubricity in the early 1980s, in anticipation of possible future lubricity problems. They investigated main factors influencing the lubricity of diesel fuels by carrying out tests on diesel fuels, diesel fuel fractions and model fuels. It has been found that diesel fuel lubricity is to a large extent determined by oxygen-containing polar impurities (some oxygen-containing compounds such as hydroxyquinolines and carboxylic acids reduced wear at concentration of a few parts per million (ppm)).

In the late 1980s and early 1990s environmental concern about the toxic and harmful emission from diesel engines led to large reductions in the level of sulfur and aromatic hydrocarbons in diesel fuels and the development of so-called "reformulated diesel fuels". Almost at once, fuel pump failures began to occur in Sweden and regions of the United States and Canada, where major reduction in sulfur levels for diesel fuels had been introduced. Lubricity of "reformulated diesel fuels" was the subject of a number of studies [1, 5-14]; one of the most significant conclusion was as follows: both low viscosity and the lack of sufficient trace components, such as oxygen- and nitrogen-containing compounds and certain aromatic compounds, can be responsible for equipment wear.

Fatty acids are the most thoroughly studied compounds from the view-point of the boundary lubrication. However, the major emphasis has almost always been put on their antifriction properties [15-21]. Moreover, sufficient evidence exists in the literature to indicate that antiwear properties of these additives mostly concern tests carried out with rather higher concentration, usually more than 0,5 % (5000 ppm) [16, 22]. Additionally, the major tested fatty acids relate to higher molecular weight compounds, mostly from lauric acid (C12) to stearic acid (C18) [16, 22-24].

Wei and Spikes [4] have found that the significant wear reduction was produced by fatty acids that were introduced into hydrotreated fuel at low concentration: caproic acid (C6) (100 ppm) and palmitic acid (C16) (1 - 300 ppm).

Results of the influence of 50 - 1000 ppm fatty acids C6 - C22 solutions in the diesel fuel components, their fractions and other solvents obtained from tribological tests carried out using ball-on-disc tester and HFR2 apparatus allowed to prove that [25]:

  • fatty acids added to low-sulfur diesel fuel components at the concentration range of 50 - 1000 ppm show excellent antiwear properties;
  • the tribological wear does not decrease with the increase of fatty acid concentration in the tested diesel fuel component;
  • for 500 ppm solutions of C6 - C22 acids in the tested diesel fuel component the wear does not decrease with growth of fatty acid molecular weight;
  • antiwear behavior of fatty acids is the result of complex interaction between molecules of the acid and particular types of hydrocarbons; such thesis has been confirmed by the results obtained for palmitic acid solutions in n-hexadecane, 1-methylnaphthalene and the mixture of these hydrocarbons at equivoluminal ratio;
  • antiwear behavior of fatty acids under boundary lubrication conditions is influenced by the rate of acid molecule diffusion to the friction surface; this conclusion was drawn from the test results obtained for systems lubricated with palmitic acid solutions in synthetic oils (polyalphaolefins) possessing various viscosity; it has also been found, that in some cases structure of the solvent molecule has a predominant influence on the wear (e. g., interaction between molecules of n-hexa-de-cane and fatty acid).
All the research described in the present work relates to tribological properties of fatty acids and fatty acids mixtures and aims at providing more information on and a better understanding of the wear process in the presence of low-sulfur fractions containing these substances at very low concentration under boundary lubrication conditions in the steel-on-steel system.

AIM OF RESEARCH

    The objective of this paper is:
  1. to present tribological properties of low-sulfur diesel fuels and determine the influence of fatty acids and fatty acids mixtures on their tribological properties;
  2. to describe the influence of fatty acids on the wear of systems lubricated with (a) fractions obtained by fractional distillation of a diesel fuel and (b) mixtures of these fractions;
  3. to demonstrate how the chemical structure and the viscosity of base fluids influence the antiwear and "prowear" behavior of fatty acids and mixtures of fatty acids.

EXPERIMENTAL TECHNIQUE

LUBRICANT MATERIALS

Base fluids

Three low-sulfur diesel base fuels were tested:

  • low-sulfur fraction from Installation of Diesel Fuel Desulfurisation containing 76 ppm of sulfur (denoted in this work as HON);

  • diesel base fuel containing 390 ppm of sulfur (denoted in this work as diesel base fuel S 390);

  • diesel base fuel containing 420 ppm of sulfur (denoted in this work as diesel base fuel S 420).
Properties of diesel base fuels are presented in Table 1 (all tables are in Appendix A).

Tribological tests were also carried out for distillation fractions obtained by fractional separation of HON (ten equivoluminal fractions were collected). Physical and chemical properties of these fractions are summarized in Table 2. The chemical constitution of selected fractions was analyzed by gas chromatography combined with infrared detection (AutoSystem 2000 GC/FTIR); parameters of this analysis are listed in Table 3. Tribological properties of some mixtures of the narrow distillation fractions were examined as well.

Additionally, to investigate in more detail the influence of fatty acids on the wear behavior of fuels, model fluids were used. They included: one pure paraffin hydrocarbon (n-hexa-decane), one pure aromatic hydrocarbon (1-meth-yl-naphthalene) and mixtures of n-hexadecane and 1-methyl-naphthalene in the following voluminal ratio: 25 : 75, 50 : 50, 75 : 25, 85 : 15.

Additives

The following aliphatic fatty acids:

  • caproic acid (hexanoic acid);
  • caprylic acid (octanoic acid);
  • capric acid (decanoic acid);
  • lauric acid (dodecanoic acid);
  • myristic acid (tetradecanoic acid);
  • palmitic acid (hexadecanoic acid);
  • stearic acid (octadecanoic acid);
  • arachidic acid (eicosanoic acid);
  • behenic acid (docosanoic acid)

    and equimolar mixtures of:

  • caproic acid + palmitic acid;
  • caprylic acid + palmitic acid;
  • capric acid + palmitic acid;
  • lauric acid + palmitic acid;
  • myristic acid + palmitic acid;
  • stearic acid + palmitic acid;
  • arachidic acid + palmitic acid;
  • behenic acid + palmitic acid
were used as additives. Table 4 presents molecular weight and purity of applied fatty acids. All of them were used as received, without further purification. Fatty acids and their mixtures were added into base fluids in the concentration range of 50 - 1000 ppm.

APPARATUS AND EXPERIMENTAL PROCEDURE

Wear tests were carried out with the ball-on-disc contact machine in which a stationary ball was loaded by a dead weight on a rotating disc. Prior to use, the test specimens were cleaned in acetone in an ultrasonic bath for 20 minutes. Sliding velocity and temperature were recorded continuously during the test. The test conditions (summarized in Table 5) were designed to result in boundary lubrication at the sliding interface. Minimum five tests were performed for each fluid.

INTERPRETATION OF OUTPUTS

The volume of material worn from the ball was calculated from the diameter of the spherical segment removed (wear scar diameter); this was measured after unloading the specimens, using a photomicroscope. Wear results obtained for each lubricant - collected in Tables 6 - 9 - include the wear scar diameter and the relative wear. The relative wear is the ratio of the volume ball wear obtained for a lubricant containing an additive and the volume ball wear for the base fluid, multiplied by 100 %. All other details relating to this procedure are described elsewhere [27].

RESULTS AND DISCUSSION

THE INFLUENCE OF FATTY ACIDS AND FATTY ACIDS MIXTURES ON WEAR BEHAVIOR OF LOW-SULFUR DIESEL FUELS

The results presented in Figure 1 (all figures are in Appendix B) show the wear performance differences for the tested fuels. Figure 1 reveals that the wear increase relates to both the sulfur content and the viscosity decrease. According to [4] usually fuels characterized by the higher density and viscosity contain larger amount of heterogeneous compounds, so the effects of the separate factors can not be distinguished.

Tribological tests for 100, 500, 750, 1000 ppm stearic acid solutions in these fuels were performed to determine the influence of the additive on their antiwear performance. Examining the relationship between properties of the base fuels and the effectiveness of stearic acid, one can say that the acid added to the heaviest fuel shows the lowest wear reduction effect as compared to the fuels of the lower density and viscosity (Figure 2).

In our previous work [25] HON, containing the lowest level of sulfur, was chosen as a base fluid to prepare solutions of C6 - C18 fatty acids. Tests results for those solutions showed that the wear does not decrease regularly with the acid concentration increase and no specific influence of the molecular weight on wear values was found (some minima and maxima were observed).

HON was also used as a base fuel for solutions of fatty acids mixtures at the concentration range of 50 - 1000 ppm. The obtained data reveal that the wear does not decrease regularly when the concentration of the solution increases for each tested mixtures of acids. It is also to note that in this case the wear does not decrease regularly when the average molecular weight of mixture increases for each examined concentration. However, the equimolar mixtures of fatty acids are very effective antiwear additives for the low-sulfur diesel fuel (Table 6). One can not state that the amount of the wear - caused in the presence of the mixture - is always the average of the wear produced in the presence of individual acids creating the mixture. Comparison of the wear value for HON containing fatty acids mixtures and individual acids in the amount of 500 ppm is shown in Figure 3. Typical synergetic effect appears for capric acid and palmitic acid (C10 + C16). On the other hand, the mixture of myristic acid and palmitic acid (C14 + C16) demonstrates an excellent example of an antagonistic effect.

THE INFLUENCE OF FATTY ACIDS ON WEAR BEHAVIOR OF SEPARATED FRACTIONS AND MIXTURES OF THESE FRACTIONS

HON was studied in detail and was separated into ten fractions (fractions I - X) by vacuum distillation. Clear evidence was found that only the last fraction (fraction X) provided lower wear than HON and for lighter fractions the wear did not correlate neither with the sulfur content nor with the viscosity (Figure 4) [25].

The application of GC-FTIR analysis for fraction I, V, IX demonstrated that most of compounds present in these fractions are n-paraffin and cycloparaffin hydrocarbons. In fraction I, which causes the smallest wear amongst heavier consecutive eight fractions, a kind of oxygen-containing compound was detected. The FTIR spectrum for a signal, obtained during chromatographic separation of fraction I, is presented in Figure 5. It has been known, e. g., that 200 - 370 C fraction of Californian crude oil contains benzofurans [26]. Hydrogenation of an aromatic ring can lead to the formation of a lacton or an aliphatic ester. Signals 1769 cm -1, 1218 cm -1 and 1053 cm -1 shown in Figure 5 can be assigned to the stretching vibration of C=O and the stretching vibration of C-O (two bands: symmetric and asymmetric). In fraction I, a substance arising from hydrogenation of an aromatic oxygen-containing compound can exist. No heterogeneous compounds were detected in fractions V and IX. It must be underscored that signals characteristic for C-S and S-S bands vibration are very weak, so the presence of a small amount of sulfur-containing compounds can not be excluded.

The comparison of the wear in the system lubricated with fractions I - X and the wear in the system lubricated with 500 ppm solutions of stearic acid in these fractions let notice that addition of small amount of stearic acid into fractions I - IX produced marked wear reduction, but did not influence on tribological properties of fraction X [25].

Four fractions were chosen to prepare mixtures: fraction I, fraction V, fraction IX and fraction X. Fractions I, V, IX have different sulfur content and viscosity, but cause comparable amount of the wear (Figure 4). The addition of fraction X to fractions I, V, IX in voluminal ratio 1 : 1 brings out significant reduction of wear. The wear in the system lubricated with aforementioned mixtures of fraction is comparable to the wear in the system lubricated with fraction X (Figure 6). It points out that higher fractions determine lubricity of a diesel fuel.

However, results obtained for solutions of stearic acid in mixtures of fractions indicate that influence of higher fractions on antiwear properties of fatty acids is disadvantageous. The wear in the system lubricated with 500 ppm solutions of stearic acid in the mixture of fractions V + X and in the mixture of fractions IX + X is lower than the wear in the system lubricated with neat mixtures of fractions (Table 7), but is larger than the wear in the system lubricated with 500 ppm solutions of stearic acid in individual fractions V and IX (Figure 7). The reduction of the stearic acid effectiveness seems to be influenced by viscosity of base fluids. On the other hand, the wear in the system lubricated with 500 ppm solution of stearic acid in the mixture of fractions I + X is lower than the wear in the system lubricated with the neat mixture of these fractions and is lower than the wear in the system lubricated with 500 ppm solution of stearic acid in the fraction I (Figure 8). Assuredly, heteroorganic constituents from fraction X and added fatty acid work in the lightest mixture better than fatty acid in the lightest fraction.

THE INFLUENCE OF FATTY ACIDS AND MIXTURES OF FATTY ACIDS ON WEAR BEHAVIOR OF MODEL HYDROCARBONS

Previous research [27] - in which n-hexadecane was used as the base fluid - revealed the existence of a new phenomenon concerning a very specific "prowear" and antiwear behavior of fatty acids at 50 - 1000 ppm concentration range. Two kinds of events were distinguished:

  • a clear "prowear" effect of myristic acid, palmitic acid and stearic acid at 750 ppm concentration;
  • a distinct antiwear effect of caproic acid at 500 ppm concentration.
Tribological tests carried out for solutions of equimolar mixtures of fatty acids in n-hexadecane (Table 8) allowed the observation of a similar kind of phenomenon as mentioned above. Additionally, considering the tribological wear plotted versus the concentration of these fatty acids mixtures and versus concentration of acids creating this mixture, one can say that there is a characteristic interaction between molecules of two fatty acids. In the concentration region, where both acids work as antiwear additives, their mixture has antiwear properties and in most cases works better than individual acids. In the concentration area, where at least one of the acids has "prowear" properties, the mixture functions as "prowear" additive and causes grater wear than individual acids (Figure 9-10).

It is interesting that the relationship between the wear and the concentration for some fatty acids mixtures diluted in n-hexadecane and HON is similar (Figure 11-12). This similarity can be related to highly paraffin character of hydrocarbons in HON.

Previous research carried out for 1-methylnaphthalene and equivoluminal mixture of n-hexadecane and 1-methyl-naphthalene containing palmitic acid at 50, 100, 500, 750, 1000 ppm concentration demonstrated that (Figure 13) [25]:

  • 100 - 500 ppm concentration of palmitic acid reduced the ball wear for both lubricants very significantly;
  • for the solution of palmitic acid in the mixture of aromatic and paraffin hydrocarbons the maximum wear appeared at the same concentration (750 ppm) as for n-hexadecane;

    no wear maximum existed for 1-methylnaphthalene.

Additionally, it appears that in the case of 750 ppm solutions of palmitic acid in mixtures of n-hexadecane and 1-methylnaphthalene the increase of 1-methylnaphthalene content in the solvent (base fluid) causes the decrease of ball relative wear (Table 9).

The ball relative wear values plotted against the number of carbon atoms in the molecule of the fatty acid that creates a mixture with palmitic acid for 500 ppm solutions of mixtures in n-hexadecane, HON and 1-methylnaphthalene are presented in Figure 14. The relationship has similar characteristics for n-hexadecane and HON, but is different from that one for aromatic base fluid.

The comparison of the wear values in the system lubricated with solutions of fatty acids in n-hexadecane, 1-methyl-naphthalene, equimolar mixture of these fluids (Figure 13) and mixtures of fatty acids in n-hexadecane, 1-methyl-naphthalene and HON (Figure 14) provides the evidence for the negative influence of pure paraffin hydrocarbons on tribological properties of fatty acids.

Former test results obtained for solutions of palmitic acid in mineral base oil SN 400 and saturated hydrocarbons separated from the SN 400 base oil also indicated that the chemical constitution of base fluids influenced the relationship between the wear and the concentration and decided about the wear value [28]. For high viscous base fluids: saturated paraffin-naphthenic hydrocarbons separated from the mineral base oil SN 400 and the mineral base oil SN 400, at the 100 ppm addition of the acid, a clear maximum wear value was found (Figure 15). When the concentration of palmitic acid was increased to 1000 ppm, the antiwear behavior of both oils was improved (relative wear around 30 %). In that case, the fluid viscosity controls the tribological behavior of fatty acids used in the lowest concentration. On the other hand, the low viscous fluid - n-hexade-cane - also made the antiwear properties of palmitic acid worse. It seemed to be caused by the molecular interaction between fatty acid molecules and the chemistry of base fluids, but not only by the viscosity of the base fluid.

CONCLUSIONS

  1. Tribological properties of base diesel fuels are determined by their highest fractions and heterogeneous compounds existing in these fractions.
  2. Fatty acids and their equimolar mixtures, added to the "reformulated diesel fuels" at the adequate concentration, provide excellent antiwear properties.
  3. The following factors seem to control wear behavior of fatty acids:
    • viscosity of the base fluids;
    • chemical composition of the base fluids.
  4. Tests carried out with fatty acids mixtures dissolved in n-hexadecane point out the existence of the phenomenon concerning a very specific "prowear" and antiwear behavior of these compounds; this phenomenon was discovered for solutions of acids earlier.
  5. All the above discussed findings are challenging from the view-point of their interpretation as well as from their relation to the diesel fuel constitution.
  6. Obtained results evidently confirm the complexity of the boundary lubrication approach.

REFERENCES

  1. Tucker, R. F., Stradling, R. J., Wolveridge, P. E., River, K. J., Ubbens, A., "The Lubricity of Deeply Hydrogenated Diesel Fuels - the Swedish Experience", SAE Technical Paper 942016.
  2. Spikes, H. A., Wei, D. P., "Fuel Lubricity - Fundamentals and Review", Proceedings of 1st International Colloquium "Fuels" 1997, Esslingen, Germany, 249-258.
  3. Margaroni, D., "Fuel Lubricity", Industrial Lubrication and Tribology, 1998, 50, 3, 108-118.
  4. Wei, D., Spikes, H. A., "The Lubricity of Diesel Fuels", Wear, 1986, 111, 217-235.
  5. Nikanjam, M., Burk, E., "Diesel Fuel Additive Study", SAE Technical Paper 942014.
  6. Nikanjam, M., Henderson, P. T., "Lubricity of Low Aromatic Diesel Fuel", SAE Technical Paper 920825.
  7. Lacey, P. I., Westbrook, S. R., "Diesel Fuel Lubricity", SAE Technical Paper 950248.
  8. Wang, J. C., Cusamo, C. M., "Predicting Lubricity of Low Sulfur Diesel Fuels", SAE Technical Paper 952564.
  9. Mitchell, K. J., "The Lubricity of Winter Diesel Fuels - Part 2: Pump Rig Test Results", SAE Technical Paper 961180.
  10. Mitchell, K. J., "Diesel Fuel Lubricity - A Survey of 1994/95 Canadian Winter Diesel Fuels", SAE Technical Paper 961181.
  11. Mitchell, K. J., "The Lubricity of Winter Diesel Fuels - Part 3: Further Pump Rig Test Results", SAE Technical Paper 961944.
  12. Hitchings, G. J., Pearson, M., Robertson, S. D, "Lubricity Additives for Low Sulfur Diesel Fuels", Proceedings of 1st International Colloquium "Fuels" 1997, Esslingen, Germany, 213-230.
  13. Cameron, F., "Lubricity of California Diesel Fuel", SAE Technical Paper 981362.
  14. Mitchell, K. J., "Continued Evaluation of Diesel Fuel Lubricity by Pump Rig Tests", SAE Technical Paper 981353.
  15. Bowden, F. P., Tabor, D., "Friction and Lubrication of Solids", Clarendon Press, Oxford, 1950.
  16. Kajdas, C., Luczkiewicz, J., Ozimina, D., Wawak-Pardyka, E., "The Influence of Concentration of Alcohols and Acids on Tribological Properties of Paraffin Oil", Tribologia, 1980, 11, 6, 22-24 (in Polish).
  17. Jahanmir, S., "Chain Length Effect in Boundary Lubrication", Wear, 1985, 102, 331-349.
  18. Beltzer, M., Jahanmir, S., "An Adsorption Model for Friction in Boundary Lubrication", ASLE Transactions, 1986, 29, 3, 423-430.
  19. Beltzer, M., Jahanmir, S., "Role of Dispersion Interactions Between Hydrocarbon Chain in Boundary Lubrication", ASLE Transactions, 1987, 30, 1, 47-54.
  20. Nakayama, K., Studt, P., "The Adsorption of Polar Cyclic Compounds on Iron Surfaces from Hydrocarbon Solutions and Their Lubricating Properties", Wear, 1987, 116, 107-118.
  21. Minami, I., Kikuta, S., Masuka, M., Okabe, H., "Lubricating Functions of Dicarboxylic Acids in Polar Base Oils", Japanese Journal of Tribology, 1990, 35, 4, 505-511.
  22. Wachal, A., "The Influence of Chemical Structure of Additives on Antiseizure and Antiwear Properties of Oils", Tribologia, 1977, 8, 5-6, 161-163 (in Polish).
  23. Hironaka, S., Yahagi, Y., Sakurai, T., "Effect of Adsorption of Some Surfactants on Antiwear Properties", ASLE Transactions, 1978, 21, 3, 231-235.
  24. Masuko, M., Ohmori, T., Okabe, H., "Antiwear Properties of Hydroxycarboxylic Acid with Straight Alkyl Chains", Tribology International, 1988, 21, 4, 199-203.
  25. Kajdas, C., Majzner, M., "Boundary Lubrication of Low-Sulfur Diesel Fuel in the Presence of Fatty Acids", Proceedings of 2nd International Colloquium "Fuels" 1999, Esslingen, Germany, 219-238.
  26. Kajdas, C., "Petrochemical Technology. Part I. Constitution of Crude Oil", Wydawnictwo Politechniki Warszawskiej, Warsaw, 1984 (in Polish).
  27. Kajdas C., Majzner M., Konopka M., "The Effect of Fatty Acids at Low Concentrations in n-Hexadecane on Wear of Steel in Boundary Lubrication", Tribologia, 1997, 153, 3, 221-237 (in Polish).
  28. Kajdas C., Majzner M., "Influence of Fatty Acids Solutions in Hydrocarbons and Petroleum Fractions on the Antiwear Properties of the Steel-on-Steel System", Tribologia, 1998, 159, 3, 285-317 (in Polish).

APPENDIX A

Table 1. Properties of low-sulfur diesel base fuels
PropertyHONDiesel base fuel S 390Diesel base fuel S 420
Density at 20 C, g/cm30,8130,8290,835
Kinematic viscosity at 40 C, mm2/s1,692,183,00
Sulfur content, ppm76390420
Distillation

50 % (V/V) recovered at, C

% (V/V) recovered at 250 C, % (V/V)

% (V/V) recovered at 350 C, % (V/V)

-

-

-

244

53,7

96,7

279

30,9

93,0

Table 2. Selected properties of distillation fractions obtained from HON
FractionInitial boiling point, CFinal boiling point, CKinematic viscosity at 40 C, mm2/sSulfur content, ppm
Fraction I1732011,0846
Fraction II2012161,1858
Fraction III2162211,3046
Fraction IV2212271,4046
Fraction V2272381,5350
Fraction VI2382421,7156
Fraction VII2422561,7944
Fraction VIII2562702,0778
Fraction IX2702872,4499
Fraction X287-3,34153

Table 3. Parameters of the GC/FTIR analysis performed to determine chemical constitution of fractions I, V, IX
ParameterFraction IFraction VFraction IX
Characteristics of parameters
Parameters of furnace work150 C (60 s) 210 C (60 s)
5 C/60 s
150 C (60 s) 220 C (60 s)
5 C/60 s
190 C (60 s) 270 C (60 s)
5 C/60 s
Injector temperature, C250250300
Sample volume, ml0,50,50,5
Column type
Column length, m
Rtx-5
30
Rtx-5
30
Rtx-5
30
Carrier gas type
Carrier gas pressure, kPa
Helium 5,5
40
Helium 5,5
40
Helium 5,5
40
Detector type
Detector temperature, C
FTIR (light pipe)
250 C
FTIR (light pipe)
250 C
FTIR (light pipe)
250 C

Table 4. Characteristics of fatty acids
Fatty acidChemical structureMolecular weightPurity, %
Caproic acidCH3-(CH2)4-COOH116,1699
Caprylic acidCH3-(CH2)6-COOH144,2198
Capric acidCH3-(CH2)8-COOH172,27~ 99
Lauric acidCH3-(CH2)10-COOH200,32> 99
Myristic acidCH3-(CH2)12-COOH228,38≥ 99
Palmitic acidCH3-(CH2)14-COOH256,43> 97
Stearic acidCH3-(CH2)16-COOH284,49≥ 90
Arachidic acidCH3-(CH2)18-COOH312,5498
Behenic acidCH3-(CH2)20-COOH340,59-

Table 5. The ball-on-disc experimental set-up and test conditions
Material system52100 steel-on-52100 steel
GeometrySphere-on-flat (the fixed ball on the rotating disc)
Specimens
- ball
- disc

Diameter: 3,18 mm; Ra = 0,3 - 0,35 mm; hardness: 63 HRC
Diameter: 25,4 mm; Ra = 0,2 mm; hardness: 58 - 63 HRC

Wear track radius, mm8
Applied load, N9,81
Sliding velocity, m/s0,25
Sliding distance, m500
Temperature, C25

Table 6. The tribological wear in the system lubricated with 50 - 1000 ppm solutions of equimolar mixtures of fatty acids C6 - C22 and palmitic acid C16 in HON
Mixture constitutionMixture concentration in HONWear scar diameterVolume ball wearBall relative wear
ppmm10-13 m3%
Average valueStandard deviation
HON04763916,01100,0
Caproic acid + palmitic acid50276211,7911,2
100205360,553,4
500219170,714,4
750239301,006,3
1000211310,623,8
Caprylic + palmitic acid500267461,589,9
Capric acid + palmitic acid50210140,603,8
100179340,322,0
500155150,181,1
75018180,342,1
1000168140,251,6
Lauric acid + palmitic acid50260321,418,8
100211280,623,8
500160310,201,3
750208370,583,6
1000171360,271,7
Myristic acid + palmitic acid500293762,2814,2
1000250640,567,6
Stearic acid + palmitic acid50232221,215,6
100178160,311,9
500191410,412,6
750196310,462,8
1000167200,241,5
Arachidic acid + palmitic acid500274891,7510,9
Behenic acid + palmitic acid500220640,724,5
1000237480,986,1

Table 7. The influence of the addition of 500 ppm stearic acid C18 on tribological properties of mixtures of fractions I + X, V + X, IX + X
Lubricating substanceWear scar diameter, mmVolume ball wear,
10 -13 m3
Ball relative wear, %
Average valueStandard deviation
HON4763916,01100,0
Fractions I + X265491,549,61)
Fractions V + X244561,106,92)
Fractions IX + X243541,086,73)
500 ppm stearic acid solution in the mixture of fractions I + X19480,4428,44)
500 ppm stearic acid solution in the mixture of fractions V+ X202320,5146,65)
500 ppm stearic acid solution in the mixture of fractions IX+ X191320,4138,16)

1), 2), 3) ball relative wear calculated referring to the wear in the system lubricated with HON,
4), 5), 6) ball relative wear calculated referring to the wear in the system lubricated with the neat mixture of fractions.

Table 8. The tribological wear in the system lubricated with 50 - 1000 ppm solutions of equimolar mixtures of fatty acids C6 - C22 and palmitic acid C16 in n-hexadecane
Mixture constitutionMixture concentration
in n-hexadecane
Wear scar diameterVolume ball wearBall relative wear
ppmm10-13 m3%
Average
value
Standard
deviation
n-Hexadecane029282,25100,0
Caproic acid + palmitic acid10026731,5769,7
30024311,0847,8
50024441,0948,5
60025841,3760,8
70031382,98132,0
800293452,27100,6
900311642,90128,5
1000340424,15184,1
Caprylic acid + palmitic acid100239291,0245,1
300269781,6171,4
500306622,72120,8
600342154,23187,5
70025941,4062,2
800288382,1294,2
900289522,1595,3
1000278471,8682,6
Capric acid + palmitic acid10026281,4664,9
30025231,2555,6
50026551,5367,8
60027281,6974,8
700325333,44152,6
800350354,63205,2
900350344,67207,2
1000290522,1896,8
Lauric acid + palmitic acid100237130,9743,1
300229220,8537,5
500206150,5624,8
60025341,2656,1
700299152,46109,1
8002842120,189,0
900266321,5568,7
1000220300,7231,9
Myristic acid + palmitic acid100307172,76122,6
300293172,27100,7
50035544,91217,6
60038326,64294,6
70041829,47420,1
80039847,79345,7
90037746,26277,5
100040188,04356,5
Stearic acid + palmitic acid10027211,6974,8
30023110,8838,8
50019310,4319,2
60022590,7935,1
70024021,0345,6
80030822,77122,9
90036235,31235,6
100027841,8682,3
Arachidic acid + palmitic acid10026841,6171,2
30030262,59114,8
50035334,80213,0
60032923,64161,5
700353124,80212,8
800374166,06268,9
900406168,41373,2
1000371255,88260,7
Behenic acid + palmitic acid10020210,5223,0
300247251,1651,3
500306102,71120,4
600287202,0992,6
700358105,12227,1
80025691,3258,6
90035264,78211,9
100037976,38283,1

Table 9. The tribological wear in the system lubricated with 50 - 1000 ppm solutions of palmitic acid C16 in 1-methylnaphthalene, n-hexadecane and mixtures of these hydrocarbons
Mixture of 1-methylnaphthalene and n-hexadecanePalmitic acid concentration in base fluidWear scar diameterVolume ball wearBall relative wear
n-Hexadecane content, % (V/V)1-Methylnaphthalene content, % (V/V)m10-13 m3%
ppmAverage valueStandard deviation
01000385136,84100,0
50279221,8727,4
100208370,588,4
500215160,669,6
75019270,426,1
100017490,294,2
25750329123,64100,0
75020880,5715,8
50500364214,43100,0
50268471,6036,0
100178110,317,0
50017870,3129,5
750255521,3123,4
1000241631,0423,4
7525028351,99100,0
750265571,5377,1
8515026121,44100,0
75026181,4399,1
10000261101,43100,0
750272321,70118,7

APPENDIX B

APPENDIX C