The lubricating properties of used engine oil

The lubricating properties of used engine oil

195 Wear, 77 (1982) 195 - 202 THE LUBRICATING PROPERTIES MASUHIKO KAWAMURA, OIL KENJI FUJITA and KIYOSHI NINOMIYA Toyota Central Research and D...

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195

Wear, 77 (1982) 195 - 202

THE LUBRICATING

PROPERTIES

MASUHIKO KAWAMURA,

OIL

KENJI FUJITA and KIYOSHI NINOMIYA

Toyota Central Research and Development Prefecture, 480-l 1 (Japan) (Received September 4,198l;

OF USED ENGINE

Laboratories

Inc., Nagakute-cho,

Aichi

in revised form September 28,198l)

Summary

The lubricating properties of oil samples from four cars using either leaded or unleaded gasolene were examined using a cross-pin-type lubricant tester and a JIS four-ball tester. The zinc dialkyldithiophosphate (ZnDTP) content in the oil samples was determined by thin layer chromatography (TLC). The wear scar diameter increased with running distance up to 2000 km. At running distances above 2000 km, the wear scar diameter decreased for oil from cars using unleaded gasolene but increased for oil from cars using leaded gasolene. The load-carrying capacity also varied depending on the type of fuel used. The TLC spot characteristic of ZnDTP disappeared after running distances of 3000 km with both fuels. However, another spot, characteristic of lead dialkyldithiophosphate (PbDTP), appeared below the ZnDTP spot for oil from cars using leaded gasolene. These results indicate that the differences in the lubricating properties of oils from cars using leaded and unleaded gasolene are due to the formation of PbDTP.

1. Introduction

The lubricating properties of engine oil change with running time owing to the effects of such factors as oxidation, thermal degradation, reaction with sliding surfaces, contamination by engine blow-by and additive depletion. Since these changes start as soon as an engine is used, almost all engines should be considered to be lubricated by used oil. Therefore investigations of engine lubrication should be carried out using both fresh and used oils, but little work on used oils has been reported [l]. In this paper we report changes in the lubricating properties with running time for cars using either leaded or unleaded gasolenes, and we discuss their variation with the type of fuel used. Four cars using either leaded or unleaded gasolene were subjected to fleet tests. Samples of engine oil were subjected to lubrication tests and chemical analysis at running distance intervals of 1000 km. The lubrication tests were carried out 0043-1648/82/0000-0000/$02.75

@ Elsevier Sequoia/Printed in The Netherlands

196

using a cross-pin-type lubricant tester and a JIS four-ball lubricant The content of the anti-wear additive zinc dialkyldithiophosphate was analysed by thin layer chromatography (TLC).

2. Experimental

tester. (ZnDTP)

de&Is

2.1. Oil samples SAE low-30 SE grade engine oil was used to lubricate four cars, which were run in urban areas. 100 ml samples of the used oil were taken from the port for the oil-level stick at running distance intervals of 1000 km. No fresh oil was added during the test. The cars used are listed in Table 1. Cars 1 - 3 used unleaded gasolene, and car 4 used leaded gasolene. 2.2. Lubrication tests Lubrication tests were carried out using a cross-pin-type lubricant tester and a JIS K2519 four-ball lubricant tester. The test conditions are summarized in Table 2. The critical part of the cross-pin-type lubricant tester, which is described in detail elsewhere [2], is shown in Fig. 1. The relation between the wear scar diameter obtained in the cross-pin test and the cam wear of an engine is shown in Fig. 2. The wear scar diameter correlates well with cam wear. TABLE 1 Cars used 1

2

3

4

Model

Toyota Corolla

Toyota Corolla

Toyota Corona

Toyota Corolla

Engine

3K (1200 cmq

3K (1200 cm3)

6R (1700 cm3)

TB (1400 cm3)

Fuel

Unleaded

Unleaded

Unleaded

Leaded

TABLE 2 Test conditions Test

Sliding materials

Load and speed

Temperature

Test

Wear scar diameter by the cross-pin tester

SUJ-2 rods 20 mm in diameter

12.4 kgf; 600 rev min-l

80 “C

60 min

Load-carrying capacity by the JIS four-ball tester

SUJ-2 balls 0.75 mm in diameter

Step up; 200 rev mine1

Room temperature

Until seizure

duration

197

Air cylinder Semiconductor strain gage

Fig. 1. Cross-pin-type

lubricant tester.

0 30

0

/

low-40

0 low-40

low- 30

/

a

0 /2cow-40 4t

3o

I

I

0.8

0.9

Wear scar diameter by the cross-pin

I

1.0 tester,

(nun)

Fig. 2. Wear scar diameter us. cam wear.

2.3. Chemical analysis The ZnDTP content in the oil samples was determined by TLC using activated silica-gel-coated TLC plates. 3 ~1 of each oil sample was spotted on the starting point of the TLC plate. The less polar constituents such as the base oil were removed from the analytical area of the TLC plate

198

using n-hexane (clean-up treatment). The ZnDTP spot was developed by a developing solvent mixture containing 80% n-hexane, 5% acetic acid and 15% methylethyl ketone. The plate was dried in air and sprayed with a colour-producing agent consisting of 0.5% palladium chloride dissolved in dilute hydrochloric acid. The sprayed TLC plate was photographed after being allowed to stand overnight. A brown colour developed at the ZnDTP spot in which phosphorus and zinc were detected by an ammonium molybdate reagent and by emission spectroscopy respectively.

3. Results and discussion 3.1. Lubricatingproperties Wear scar diameters obtGned with the cross-pin-type lubricant tester are shown in Fig. 3. The results for oil samples from cars 1 - 3, which used unleaded gasolene, show that the wear scar diameters increased with running distance up to 2000 km and then decreased. However, the wear scar diameters obtained for oil samples from car 4, which used leaded gasolene, continued to increase for running distances up to 4000 km. Wear scar diameters obtained for an oil sample heated at 150 “C in an oil bath (Fig. 4) initially increased with heating time up to 20 h and then decreased. This behaviour is similar to that obtained for oils from cars using unleaded gasolene.

T 0

.

.

1000

2000

Running

distance,

. 3000

4

4000

km

Fig. 3. Wear scar diameter: o, car 1; l, car 2; A, car 3 ; 0,

car

4.

5000

199

1.0

.

0

I

I

I

I

I

20

40

60

80

100

Heating time,

hr.

Fig. 4. Wear scar diameter of the heat-treated oil

The load-carrying capacity determined by the four-ball tester increased with the running distance up to 1000 km (Fig. 5). It then decreased up to a running distance of 2000 km and finally became almost constant. Oil samples from the car using leaded gasolene showed a higher loadcarrying capacity than those from cars using unleaded gasolene. The results show that the lubricating properties of the engine oil change with running distance, and that these changes are dependent on the type of fuel used. We believe that the constituents of the oils were changed in different ways by the different fuels. 3.2. Analytical results Since ZnDTP is the most effective additive influencing the lubricating properties of .engine oil, the ZnDTP content was determined by TLC. Chromatograms of oil samples from car 1 (unleaded gasolene) are shown in Fig. 6. ZnDTP was detected for running distances up to 2000 km but had disappeared by 3000 km. Similar results were obtained using oil samples from cars 2 and 3. Results from the oil samples of car 4 (leaded gasolene) are shown in Fig. 7. The spots characteristic of ZnDTP were observed for running distances up to 2000 km and then disappeared. A new spot was observed beneath the ZnDTP spot after a running distance of 1000 km. The new spot was the same colour as the ZnDTP spot. The material of the new spot was separated from the oil sample by the TLC preparation method. An absorption peak of about 1000 cm-l due

200

Running distance, km

Fig. 5. Load-carrying

Spotby ZnDTP

capacity:

o, car 1; l, car 2; 4 car 3; 0, car 4.

.@F

Fig. 6. Thin layer chromatograms

for oil samples from car 1 (unleaded).

201

Fig. 7.

from car4 (leaded).

to a CUP group was observed in the IR spectra of the separated material, and lead instead of zinc was detected by emission spectroscopy. These analytical results show that the ZnDTP in the initial oil had been changed into lead dialkyldithiophosphate (PbDTP) during the running of the car fuelled with leaded gasolene. Allum and Forbes [ 31 reported that the wear scar diameter obtained with PbDTP was larger than that obtained with ZnDTP, and that the load-carrying capacity with PbDTP was higher than that with ZnDTP. This behaviour was similar to that observed in the present results. Fuchs [ 41 reported that 4% - 6% Pb was detected in drained oil following the Ford sequence VC test with leaded gasolene. Lead in the drained oil may come from engine blow-by, and the most probable forms of lead compounds are PbO and the unburned lead.additive. Therefore ZnDTP in the engine oil may react with PbO and/or with the lead additive to form PbDTP. To confirm the reaction between ZnDTP and PbO or the lead additive in engine oil, 6% PbO or 20% leaded gasolene was mixed with fresh engine oil and refluxed to 100 “C. The thin layer chromatograms showed a new spot beneath the ZnDTP spot, as in the oil samples from car 4. Other fleet tests were carried out using different cars with different engine oils, and similar results were obtained.

Acknowledgments We are sincerely grateful to Dr. Heihachiro Okabe, Tokyo Institute Technology, for continuing interest and encouragement. We thank

of

202

Dr. Koichi Nakajima, Toyota Technological cussions and for reviewing the manuscript.

Institute,

for valuable

dis-

References 1 T. Yoshimoto, M. Kawamura and K. Ninomiya, Performance of engine oils used on gasolene and LPG-powered cars, J. Jpn. Sot. Lubr. Eng., 15 (8) (1970) 504 - 509 (in Japanese). 2 M. Kawamura and K. Fujita, Organic sulphur and phosphorus compounds as extreme pressure additives, Wear, 72 (1981) 45 - 53. 3 K. G. Allum and E. S. Forbes, The load-carrying capacities of metal dialkyl dithiophosphates: the effects of chemical structure, Proc., Inst. Mech. Eng., London, 183 (3P) (1968 - 1969) 7 - 14. 4 E. J. Fuchs, Unleaded versus leaded fuel results in laboratory engine tests, SAE (Sot. Automot. Eng.) Tech. Pap. 710676, 1971.