Investigation of the Effectiveness of Monoethanolamides as Low Sulfur Marine Fuel Lubricity Additives

Available online at www.sciencedirect.com

ScienceDirect Materials Today: Proceedings 5 (2018) 27563–27571

www.materialstoday.com/proceedings

PSCCE_2017

Investigation of the Effectiveness of Monoethanolamides as Low Sulfur Marine Fuel Lubricity Additives G. Anastopoulosa, P. Schinasa,b,*, Y. Zannikoua, D. Karonisa, F. Zannikosa, E. Loisa a

National Technical University of Athens, School of Chemical Engineering, Laboratory of Fuels Technology and Lubricants, Iroon Polytechniou 9, Athens 15780, Greece b National Technical University of Athens, School of Chemical Engineering, Environment and Quality of Life Laboratory, , Iroon Polytechniou 9, Athens 15780, Greece

Abstract In this study, six mixtures of monoethanolamides that were synthesized from various vegetable oils (Sunflower oil, Soybean Oil, Cotton Seed Oil, Olive oil, Tobacco seed oil, Used frying oil) were used as lubricating additives on a low sulfur Marine Gas Oil (MGO). All tribological measurements were carried out by using the HFRR test procedure, according to ISO 12156-1. The obtained wear results showed that all mixtures of monoethanolamides used provide satisfactory a mean wear scar diameter (WS 1.4) of less than 520 μm, at concentration levels of 80 - 140 ppm. The concentrations below 80 ppm had no effect on the fuel lubricity. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 11th Panhellenic Scientific Conference on Chemical Engineering. Keywords: Lubricity; MGO; Monoethanolamides; HFRR; Lubricating Additives

1. Introduction To reduce emissions from ships, various international regulations and Emission Control Areas (ECA) have been in force since 2005. Recently, new and stricter fuel sulfur content regulations promulgated by California and the EU have been developed and implemented [1]. The Californian Air Resource Board (CARB) has since 1 July 2009 enforced the use of diesel oils (MDO) or gas oils (MGO) in Californian waters [2]. In addition, when in berth in EU ports vessels must, as of 1 January 2010, use marine fuels with a sulfur content not exceeding 0.1% by mass [3].

* Corresponding author. Tel.: +30-2107723073; fax: +30-2107723163 E-mail address: [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 11th Panhellenic Scientific Conference on Chemical Engineering.

27564

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571

The practical effect of the above pollution control regulations is to oblige many ships to switch from viscous high-sulfur heavy fuel oil to thin distillate fuels such as marine gas oil (MGO). But, there is a technical difficulty. The three-screw pump is supposed to work under full-film running conditions, which means that the rotors are separated from each other and from the bores by an oil film that carries the load. To achieve a full-film condition, the pump needs to run with relatively high speed, and the oil needs to have a relatively high viscosity to carry the radial forces. Furthermore, the radial forces will increase with higher differential pressure. In order to find out if full-film condition is fulfilled, a Sommerfeld number can be calculated. A higher number means a stronger oil film [4,5]. When a three-screw pump operates with light fuel such as MGO, the Sommerfeld number is sometimes not high enough to fulfill the full oil film condition, and the pump operates in the boundary zone. This means that the moving parts are not separated by a film; consequently, some level of metallic contact will take place. When the pump is operating in this zone, the lubricity of the fuel is important [4,5]. In general, it remains the case that lubricity is little understood in the marine sector, with many misconceptions existing in the aftermath of the publication of the new specification. In the early1990s, when low sulfur diesel fuels were introduced to the automotive market, lubricity was likewise little understood and field issues rapidly followed, involving excessive and rapid fuel pump wear [6]. Traditionally fuel viscosity was used as an indicator of a fuel’s ability to provide wear protection, but since the introduction of low sulfur diesel fuels, even some fuels of higher viscosity have been found capable of producing wear [7]. It is true to say that, as viscosity reduces, lubrication will move from a hydrodynamic regime, through a mixed lubrication regime and then to a boundary regime where lubricity is critical. Past studies showed that diesel fuel lubricity is largely provided by trace levels of naturally occurring polar compounds which form a protective layer on the metal surface. Typical sulfur compounds do not confer this wear protection themselves, rather it is the heterocyclic aromatics and nitrogen and oxygen compounds that are the most important [8–10]. A complex mixture of polar compounds is found in diesel fuel and some are more active than others. The process of hydrotreating to reduce sulfur levels also destroys some of these natural lubricants. Other refinery processes also influence the concentration of the lubricity agents in the final fuel blend [11]. Lubricity additives have been developed to compensate for the deterioration in natural lubricity observed in low sulfur diesel fuels. A moderate dosage of chemically suitable additive is beneficial in most cases, but if the dosage is too high, some common diesel fuel additives can cause fuel injector deposits, water separation problems, or premature filter plugging. These problems are not always identified in the standard fuel specification tests, and result in field problems [12–15]. This study includes the evaluation of the lubricating properties of low sulfur marine gasoil, additized with six fatty acid monoethanolamide mixtures. Data were generated to identify the minimum concentration of the above compounds, which provide lubricity improvement down to the 520 μm wear scar diameter level. The value of 520 μm was proposed by the International Organization for Standardization (ISO), and generally adopted by the industry, as the minimum required for an acceptable field performance [16]. Oxygen containing compounds such as fatty acids and their derivatives are superior friction reducing agents [1731]. These compounds adsorb or react on rubbing surfaces to reduce adhesion between contacting asperities and limit friction, wear and seizure. Wei and Spikes considered, that the significant wear reduction was produced by oxygen compounds with phenolic – type or carboxylic acid groups and occurred at a concentration of just a few parts per million [32]. On the other hand the use of oxygen containing fuels, such as esters, assists in the reduction of particulate matter emissions. More generally, it has been mentioned in the literature that the oxygen – carbon ratio (O/C) of a fuel significantly affects particulate emissions; so to achieve low smoke emissions (lower than 0.5 in the Bosch range), the O/C ratio must be higher than 0.2 [33]. Although the impact of acid esters and amides on the lubricity of automotive diesel has been closely examined, their impact on the tribological properties of low sulfur middle gas oils for use in marine compression ignition engines has not been examined in detail. 2. Experimental Procedure 2.1. Materials Methanol, KOH, monoethanolamine and analytical reagents (e.g., standards for GC analysis) were of high grade and were supplied from Sigma Chemical Co. Commercial grade sunflower oil, soybean oil and olive oil were

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571

27565

purchased from a local grocery store. Cottonseed oil was obtained from Elin biofuels S.A, while the waste vegetable oil used in this work was a mixture of olive oil and sunflower oil collected from local fast food restaurants. The tobacco seed oil that was not commercially available was extracted from tobacco seeds in laboratory scale, and the procedure is as follows. The seeds were ground to a fine powder and then dried for 2 h at 100 °C. For the continuous extraction of a solid by a hot solvent, the Soxhlet extraction apparatus was employed. Hexane was used as a solvent in the extraction process where the temperature was kept at 65-70 °C and the overall process lasted 4 h. At the end of the process, the oil was separated from the organic solvent using a rotary vacuum evaporator, dried at 60 °C and weighed. The six vegetable oils were used as received without further purification. Table 1 presents their major quality properties, while table 2 gives their fatty acid profile. To assess the impact of the selected mixtures of monoethanolamides on the lubrication properties of low sulphur marine fuels, a MGO was obtained by a Greek refinery and was used for all the tribological experiments as a base fuel. The fuel properties are presented in table 3, along with the standard methods that were used for their determination. Table 1. Physicochemical properties of vegetable oils. Property Kinematic Viscosity at 40 °C (cSt) 3

Density at 15 °C (kg/m ) Flash Point (°C)

Sunflower oil

Soybean oil

Olive oil

Cotton seed oil

Used frying oil

Tobacco seed oil

Test method

32.6

33.07

29.4

28.4

40.2

27.7

EN ISO 3104

921.7

918.6

908.2

914.8

926

917.5

EN ISO 12185

272

246

268

234

286

220

EN 22719

Iodine Number (cg I2/g oil)

132

108

100

115

108

135

EN 14111

Acid Value (mg KOH/g)

0.33

1.02

0.25

0.16

1.7

0.48

EN 14104

Saponification Value (mg KOH/g)

192.1

170.4

196.2

190

193.2

193

AOCS CD3 1993

347

512

274

578

933

754

EN ISO 12937

Water Content (mg/kg) Sulfur Content (mg/kg)

0.23

3.0

2.6

3.2

5.7

8.2

EN ISO 20846

Carbon Residue (% m/m)

0.031

0.056

0.092

0.073

0.181

0.086

EN ISO 10370

-14

-16

-19

-14

-16

-15

ISO 3016

Pour point (°C)

Table 2. Fatty acid profile of vegetable oils, %m/m. Vegetable oil type Fatty acid

Chemical Structure

Sunflower Soybean oil oil

Olive oil

Cotton seed oil

Used frying oil

Tobacco seed oil

Lauric (C12)

CH3(CH2)10COOH

0.00

0.10

0.00

<0.01

1.98

<0.01

Myristic (C14)

CH3(CH2)12COOH

0.00

0.10

0.00

0.75

0.32

0.09

CH3(CH2)14COOH

6.20

11.3

11.6

22.23

15.65

10.96

CH3(CH2)5CH=CH(CH2)7COOH

0.10

0.00

0.90

0.44

0.31

0.2

Stearic (C18)

CH3(CH2)16COOH

3.70

4.10

3.10

2.17

3.10

3.34

Oleic (C18:1)

CH3(CH2)7CH=CH(CH2)7COOH

25.2

22.7

74.98

17.66

48.71

15.54

Palmitic (C16) Palmitoleic (C16:1)

Linoleic (C18:2)

CH3(CH2)3(CH2CH=CH)2(CH2)7COOH

63.1

52.6

7.80

55.77

22.39

69.49

Linolenic (C18:3)

CH3(CH2CH=CH)3(CH2)7COOH

0.30

7.40

0.60

0.13

1.04

0.69

Eicosenoic (C20)

CH3(CH2)8CH=CH(CH2)8COOH

0.20

0.50

0.01

0.20

0.11

0.25

Behenic (C22)

CH3(CH2)20COOH

0.70

0.50

0.10

<0.01

0.24

0.12

Erucic (C22:1)

CH3(CH2)7CH=CH(CH2)11COOH

0.10

0.20

0.00

0.02

0.02

<0.01

CH3(CH2)22COOH

0.20

0.20

0.50

0.01

0.30

0.04

Lignoceric (C24)

27566

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571 Table 3. Properties of the base fuel Property

Value

Test Method

Density (kg/m3, 15 C)

853.5

ISO 12185

Viscosity (cSt at 40 °C)

3.27

ISO 3104

°

Flash point ( C)

64

ISO 2719

Nitrogen content (mg/kg)

31

-

Sulfur content (mg/kg)

310

ISO 8754

-3

ISO 3015

°

Cloud point (°C) Pour point (°C)

-9

ISO 3016

Ash content (% m/m)

<0.01

ISO 6245

Carbon residue (% m/m)

0.006

ISO 10370

29

ISO 3733

49.7

ISO4264

Initial measurement, μm

645

ISO 12156-1

Repeated measurement, μm

641

Water content (mg/kg) Cetane index Lubricity

Distillation (°C) IBP

177

10%

231

50%

295

90%

352

FBP

378

ISO 3405

2.2. Preparation of Monoehanolamides The reaction was carried out in a round-bottom glass reaction flask submerged in an oil bath. The reaction flask was equipped with a mechanical stirrer, thermometer and condenser. Monoethanolamine was reacted with the oils at a molar ration of 6:1 (monoethylamine:oil) in the presence of potassium hydroxide (2% by weight of monoethanolamine and oil). The reactions were carried out at a temperature of 115 °C while the formation of monoethanolamides was monitored using Thin Layer Chromatography. At the end of each reaction, the reaction mixture was allowed to cool and later dissolved in diethyl ether in a separating funnel. The ether phase was washed with 5% aqueous hydrochloric acid. The ether layer was separated, washed with water and passed over sodium sulfate. The resulting ether layer was concentrated using a rotary evaporator. The scheme of this reaction is shown in figure 1.

  Fig. 1. General scheme for the synthesis of fatty acid monoethanolamides

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571

27567

2.3. Lubricity Measurements All tribological measurements were carried out using the HFRR apparatus (Figure 2), according to the ISO 12156-1 method. The test temperature was 60 °C and the volume of the fuel sample used was 2 ml. Relative humidity was kept between 52% and 57%, while the mean ambient temperature was 23 °C. The lubricating efficiency of the fuels was estimated by measuring the average WSD of the spherical specimen by using a photomicroscope. The wear scars quoted were corrected to give WS 1.4 values. The HFRR WS 1.4 parameter is the mean WSD normalized to a standard vapour pressure of 1.4 kPa. The repeatability was calculated using the following equation [16]: R = 139 - (0.1648 x WS1.4) The six monoethanolamide mixtures were dissolved to the base fuel, at the same concentration levels, i.e. 20, 40, 60, 80, 100, 120 and 140 ppm.

Fig.2. Schematic diagram of lubricity test by high frequency reciprocating test rig

3. Results and Discussion The base fuel was initially analyzed to determine its lubrication effectiveness. The corrected WSD value for the base fuel, on the first day of its production, is cited in Table 3. It is evident that the fuel has a wear scar diameter value much higher than the acceptable limit of 520 μm, and was characterized as fuel with poor lubricating properties. Repeated tribological measurement on the next day confirmed this conclusion. Consequently, this fuel was well suited to determine the lubricity of the additives. Figure 3 gives, in graphical form, the effect of the addition of the sunflower oil monoethanolamides mixture on the WS 1.4 of the base fuel. Small concentrations of sunflower oil monoethanolamides that ranged between 20 and 80 ppm practically caused no alteration on the corrected wear scar diameter of the base fuel. A substantial increase of the lubrication performance was shown with the addition of the sunflower oil monoethanolamides under observation in the concentration of 100 ppm. Yet, even in this case, the limit of 520 μm was not satisfied. When dealing with the increase of the concentration of sunflower oil monoethanolamides from 100 to 120 ppm, it was observed that there was an increasing effect on the lubricity of the base fuel, thus decreasing the wear scar diameter by 5 μm under the acceptable limit. The impact of soybean oil monoethanolamides on the lubricity of the base fuel is outlined in Figure 4. When analyzing the results, it is observed that the addition of soybean oil monoethanolamides mixture in the concentrations between 20 and 100 ppm even though it increased the lubricity of the base fuel, it did not reach the acceptable limit value of 520 μm. The desired improvement was realized as there was an increase in the

27568

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571

640

640

620

620

600

600

580

580 WS 1.4 (ì m)

WS 1.4 (ì m)

concentration of soybean oil monoethanolamides from 100 to 120 ppm, where the maximum permissible HFRR mean wear scar diameter of 520 μm, required for commercial marine fuels was satisfied.

560

540

560

540 520 ì m

520 ì m

520

520

500

500

480

480 20

40

60

80

100

120

140

Concentration (ppm)

Fig. 3. Impact of sunflower oil monoethanolamides addition on the lubrication properties of the base fuel

20

40

60

80

100

120

140

Concentration (ppm)

Fig. 4. Impact of soybean oil monoethanolamides addition on the lubrication properties of the base fuel 

Figure 5 shows, the influence of the olive oil monoethanolamides on the lubrication properties of the base fuel. On the basis of the HFRR test results, the addition of olive oil monoethanolamides mixture at the concentration levels lower than 80 ppm does not seem capable to increase the lubricity of the fuel to an acceptable level. Contrary, a significant reduction on the WS 1.4 to under the limit of 520 μm is observed when 80 ppm of olive oil monoethanolamides mixture is added, whereas extra addition of monoethanolamides seems to offer even better improvement on the lubrication properties of the base fuel. Thus, for concentrations between 100 and 140 ppm, the wear scar diameter illustrates an even higher decline, reaching 483 μm. Comparing tribological results that was admitted at the addition of olive oil monoethanolamides on the base fuel, to those that resulted from the addition of sunflower oil monoethanolamides, it is apparent that the olive oil monoethanolamides mixture have much better behavior on the fuel lubricity, which, may be due to the high content of mono-unsaturated monoethanolamides like those of oleic acid, even at the least higher concentration of monoethanolamide of palmitic acid. Figure 6 depicts the impact of the addition of the cottonseed oil monoethanolamides on the base fuel lubricity. As in the case of sunflower oil monoethanolamides mixture, Figure 3, similarly here, the required treat rate to obtain a satisfactory wear scar diameter (WS 1.4) of 520 μm was 120 ppm. However, a higher dosage of the cotton seed oil monoethanolamides led to a slight increase of the fuel lubricity. The careful assessment of the experimental results leads to the realization that cottonseed oil monoethanolamides mixture presents a slightly improved lubrication performance than sunflower oil monoethanolamides. Even though, both types of monoethanolamides provide an acceptable level of performance at a 120 ppm, however at this concentration level, the corrected wear scar diameter of sunflower oil monoethanolamides was 512 μm, while the WSD value of the cottonseed oil monoethanolamides was 490 microns. Thus the second mixture of monoethanolamides had a slightly better lubrication performance. A possible explanation for this may be that cottonseed oil monoethanolamides mixture; contains a higher content in palmitic acid diethanolamide in comparison to sunflower oil diethanolamides mixture. Consequently, the slightly better lubrication effectiveness of cotton seed oil monoethanolamides, is possibly due to the presence of saturated fatty acids.

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571 620

640

600

620

27569

600

580

580

560

560 520 ì m 520 500

WS 1.4 (ì m)

WS 1.4 (ì m)

540 540

520 ì m

520 500

480

480

460

460

440

440

420

420 20

40

60

80

100

120

140

20

40

Concentration (ppm)

60

80

100

120

140

Concentration (ppm)

Fig. 5. Impact of olive oil monoethanolamides addition on the lubrication properties of the base fuel

Fig. 6. Impact of cottonseed oil monoethanolamides addition on the lubrication properties of the base fuel

640

640

620 620 600 600

580

580

540 520 ì m 520

WS 1.4 (ì m)

WS 1.4 (ì m)

560

560

540

500

520 ì m

480

520

460 500

440 420

480 20

40

60

80

100

120

140

20

Concentration (ppm)

60

80

100

120

140

Concentration (ppm)

Fig. 7. Impact of used frying oil monoethanolamides addition on the lubrication properties of the base fuel  

40

Fig. 8. Impact of tobacco seed oil monoethanolamides addition on the lubrication properties of the base fuel  

Figure 7 illustrates the impact of the addition of used frying oil monoethanolamides on the WS 1.4 of the base fuel. At first glance, the particular type monoethanolamides improves the lubrication properties of the base fuel. The analysis of the trend curve shows that, the limit of 520 microns for the mean wear scar diameter (WS1.4) can be

27570

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571

attained at a monoethanolamides mixture concentration of 100 ppm or more. When comparing the HFRR test results of used frying oil monoethanolamides mixture to those of the monoethanolamides that contain high levels of C18:2, one can draw the conclusion that used frying oil monoethanolamides mixture has better lubricating ability. The better behavior of this type of monoethanolamides on fuel lubricity may be due to the higher total content of saturated and mono-saturated fatty acid monoethanolamides, which based on the results of Table 2, reaches about 70%. Figure 8 demonstrates the effect of the addition of tobacco seed oil monoethanolamides on the tribological properties of the base fuel. Similar behavior to that of sunflower and cotton seed oil monoethanolamides was presented by the monoethanolamides of the tobacco oil. Generally, small concentrations between 20 and 100 ppm did not have a positive influence on the lubrication properties of the base fuel. The desired improvement was achieved at the concentration of 120 ppm. Any increase in tobacco seed oil monoethanolamides mixture concentration led to a slight increase in the wear scar diameter values. It must be noted that tobacco seed oil monoethanolamides mixture have a slightly worse effect on the fuel lubricity in comparison to the sunflower oil and cotton seed oil monoethanolamides. This could be attributed to the high concentration of lineloic acid diethanolamide. Although, all types of fatty acid monoethanolamides tested in this series of experiments, had a beneficial impact on the lubricity of marine gasoil, an interesting conclusion is derived from the comparison of fatty acid composition. Among the individual types of fatty acid monoethanolamides, those derived from non-polyunsaturated oils, such as olive oil appeared to have better lubrication performance. The higher lubricity effect can be attributed to the higher amount of saturated and mono-unsaturated monoethanolamides. In saturated compounds, the molecules can align themselves easier in straight chains and are more closely packed on the surface, providing a strong lubricating layer. On the other hand, double bonds prevent rotation and force the chains to bend, making it more difficult to pack closely together and resulting in a weaker lubricating layer [27,28]. 4. Conclusions In an effort to investigate the impact of fatty acid monoethanolamides on the tribological properties of low sulfur marine fuel, six mixtures of monoethanolamides that were synthesized from various vegetable oils (sunflower oil, soybean oil, cotton seed oil, olive oil, tobacco seed oil, used frying oil) were added to a marine gas oil. The following conclusions can be drawn from this study:   

The low sulfur marine gas oil does not provide satisfactory lubrication and may lead to damage in the fuel pumps of the marine diesel engines. Small concentration levels of the fatty acid monoethanolamides ranging from 80–120 ppm, were necessary to bring the wear scar diameter value within the required limit of 520 microns, and any extra addition of the amides, did not give any significant improvement in the lubricity of the fuels. Among the individual types of fatty acid monoethanolamides, those derived from non-polyunsaturated oils, such as olive oil appear to be better lubricants.

References [1] [2] [3]

M. Vermeire, Development future marine fuels, Paris, France, 2012 S. Bengtsson, E. Fridell, K. Andersson, Energ. Pol. 36 (2012) 451-463. European-Commission: White paper road map to a single European transport area towards a competitive and resource efficient transport system. Brussels, 2011. [4] A.Miola, M. Marra, B. Ciuffo, Energ. Pol. 39 (2011) 5490-5498. [5] K. L. Andersen, F. Haase, M. Jandles, J. K. Paint, Project Reference SMIG 09004, 2011. [6] I. Crutchley, M. Green, MTZ industr. 2 (2012) 58-63. [7] R.H. Barbour, D.J. Rickeard, N.G. Elliott, SAE Technical Paper 2000-01-1918, 2000. [8] D.P. Wei, Acta Petrol. Sin. 2 (1986) 79–87. [9] D.P. Wei, Acta Petrol. Sin. 4 (1990), 90–99. [10] D.P. Wei, Acta Petrol. Sin. 6 (1990) 15–19. [11] R.F. Tucker, R.J. Stradling, , P.E. Wolveridge, K.J. Rivers, A. Unbbens, SAE Technical Paper 942016, 1994.

Anastopoulos et al. / Materials Today: Proceedings 5 (2018) 27563–27571

[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33]

27571

R. Caprotti, C. Bovington, W.J. Fowler, M.G. Taylor, SAE Technical Paper 922183, 1992. R.J. Batt, J.A. McMillan, I.P. Bradbury, SAE Technical Paper 961943, 1996. M. Nikanjam, E. Burk, SAE Technical Paper 940248, 1994. M. Nikanjam, SAE Technical Paper 942014, 1994. ISO12156-1: Diesel Fuel –Assessment of Lubricity using the High frequency Reciprocating Rig, 2006. F.P. Bowden, D. Tabor, Friction and lubrication of solids, Clarendo Press, Oxford, 1950. D. Karonis, G. Anastopoulos, E. Lois, S. Stournas, F. Zannikos, A. Serdari, SAE Technical Paper 1999-01-1471, 1999. G. Anastopoulos, E. Lois, A. Serdari, F. Zanikos, S. Stournas, S. Kalligeros, Energ. Fuel 15 (2001) 106-112. G. Anastopoulos, E. Lois, D. Karonis, S. Kalligeros, F. Zannikos, Energ. 30 (2005) 415-426. C. Kajdas, M. Majzner, Lubr. Sci. 14 (2001) 83-108. C. Kajdas, M. Majzner, SAE Technical Paper 2001-01-1929, 2001. D. P. Geller, J. W. Goodrum, Effect, Fuel 83 (2004) 2351-2356. K. S. Wain, J. M. Perez, E. Chapman, A. L. Boehman, Tribol. Int. 38 (2005), 313-319. L. G. Schumacher, B.T. Adams, ASAE Paper 02-6085, 2002. J. W. Goodrum, D. P. Geller, Bioresour. Technol. 96 (2005) 851-855. F. E. Ling, E. E. Klaus, R. S. Fein, Boundary Lubrications – An Appraisal of World Literature. American Society of Mechanical Engineers, New York, 1969, p 87. S. Bhuyan, S. Sundararajan, L. Yao, E. G. Hammond, T. Wang, Tribol. Lett. 22 (2006) 2-11. K. Wadumesthrige, M. Ara, S. O. Salley, K. Y. Simon Ng, Energ. Fuel 23 (2009) 2229-2234. J. Hu, Z. Du, C. Li, E. Min, Fuel 84 (2005) 1601–1606. G. Knothe, and K. R. Steidley, Energ. Fuel, 19 (2005), 1192-1200. D. Wei, H. Spikes, Wear 111 (1986) 217–235. T. Hashimoto, Y. Akasaka, Evaluation of Oxygenated Fuels Using Conventional and a New Type of Diesel Engines. Proceedings of the Ninth International Symposium on Alcohol Fuels, ISAF, Firenze, 1991, pp. 336 – 341