ARL-TN- 10 AR-007-112

AD-A267 088 ..-

DEPARTMENT OF DEFENCE

DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION

AERONAUTICAL RESEARCH LABORATORY

MELBOURNE, VICTORIA

Technical Note 10

EXTENSION OF OIL SERVICING INTERVALS

FOR THE LEOPARD AS-1 POWER PACK

by DTICG. G.McVea ELECT_

R.K. Solly JUL23 1993

EUApproved for public release.

© COMMONWEALTH OF AUSTRALIA 1993

MAY 1993

9 3 7 93-16619

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AR-007-112

DEPARTMENT OF DEFENCEDEFENCE SCIENCE AND TECHNOLOGY ORGANISATION

AERONAUTICAL RESEARCH LABORATORY

Technical Note 10

EXTENSION OF OIL SERVICING INTERVALSFOR THE LEOPARD AS-I POWER PACK

by

G. G. McVeaR.K. Solly

SUMMARY

The condition of the engine and transmission oils was determined at three monthly intervalsfor a period of 24 months for five armoured Leopard vehicles operated routinely by the 1stArmoured Regiment, Puckapunyal. For the trial vehicles, the maximum operating hours was270 and the minimum 56. All oil samples from the trial vehicles remained withinspecification requirements for new oil as determined by viscosity, total base number andpentane insoluble content. A small increase in the viscosity of both the engine oils and thetransmission oils was recorded over the period of the trial, but all determinations remainedwell below the maximum specified for new oil. There was no indication of storage orstanding deterioration of the oils during the two year period and it was concluded thatvehicle operating hours was the sole criterion for the variations that were determined. It wasrecommended that oil change intervals could be extended to a minimum of 300 operationalhours or two years elapsed time.

DSTO4A U S T R A t I A

@ COMMONWEALTH OF AUSTRALIA 1993

POSTAL ADDRESS: Director, Aeronautical Research Laboratory506 Lorimer Street, Fishermens Bend 3207Victoria Australia

W;

TABLE OF CONTENTS

1. BACKG ROU ND ................................................................................................... 1

2. CRANKCASE OIL DETERIORATION ............................................................ 1

3. FIELD PROG RA M M E ....................................................................................... 2

3.1 Vehicles ................................................................................................... 2

3.2 Oils .......................................................................................................... 2

3.3 O il Sam ples .............................................................................................. 2

4. LA BO RA TO RY ANALYSES ............................................................................. 2

5. RESULTS ............................................................................................................ 3

6. D ISCU SSIO N ........................................................................................................ 3

6.1 Engine O ils .............................................................................................. 3

6.2 Transm ission Oils .................................................................................... 4

7. CO NCLUSIO NS ................................................................................................... 4

8. RECOM M END ATIO NS ...................................................................................... 4

9. REFERENCES ..................................................................................................... 5Accesion For

FIGURES 1-5NTIS CRA&MDTIC TAB

TABLES 1-10 Unannounced DJustification

DISTRIBUTIONBy

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Avai aiidjorDist Special

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1. BACKGROUND

Extension of oil change intervals to two years for the Leopard Main Battle Tank (MBT) isunder consideration by NATO countries. At the 15th International Leopard VehicleTechnical Working Group meeting [1], a final report was provided on a European trialwhich involved the extension of oil change intervals for Leopard vehicles to periods inexcess of two years when operating with a multigrade 15W40 oil (Nato 0-236). Resultsfor 800 oil samples from more than 200 vehicles were summarized in this report. Nounacceptable deterioration of the oil or abnormal wear in the vehicles was found for oilchange intervals extending up to 30 months.

In Australia, a single grade SAE-30 oil, OMD-115 (Nato 0-238) is used for crankcaselubrication of AS-1 Leopard Powerpacks rather than the Nato 0-236 oil. Current Armypractice is to change the lubricant in the Leopard AS-1 every 6 months or 1000 kIn. Thisinterval was based on recommendations by the engine manufacturer (MTU), that the oilbe changed after 5000 litres of fuel had been consumed, which is approximately 1200 kmfor Australian operation conditions. Extension of the oil change interval would not onlyreduce expenditure on replacement oil, but also allow greater flexibility in servicingrequirements for the vehicles. This study, on the feasibility of extei|ding the oil changeintervals in the Leopard AS-1 vehicles when operating with OMD-115 oil underAustralian conditions, was carried out at the request of the Australian Army MaintenanceEngineering Agency (MEA).

2. CRANKCASE OIL DETERIORATION

Modern diesel engine oils are formulated to provide lubrication and corrosion protectionfor the current generation of high performance diesel engines. Effective lubrication andwear minimization is provided by a combination of fluid hydrodynamic factors andsurface modification following chemical interaction between oil components and metalsurfaces. Corrosion protection is achieved by neutralization of corrosive combustionproducts which may be deposited in the oil and also from the interactions between oilconstituents and metal surfaces.

Effective hydrodynamic lubrication is a function of the ability of the oil to form a liquidfilm between the moving components. The viscosity is the major oil property indetermining this ability. The viscosity range over which hydrodynamic lubrication willoccur is limited. Too high or too low a viscosity for the engine design will not allow aneffective liquid film to remain between moving components. With engine operation, theviscosity of the oil may be reduced by shearing of larger oil molecules, by shearing ofpolymer molecules formulated in the oil as viscosity improvers or by dilution with lowerviscosity fuel. An increase in oil viscosity may follow from degradation andpolymerization of the oil moleculcs add by deposition of fuel combustion products in theoil. The deposition of soot in the fuel has been shown to be a factor in increased oilviscosity [2]. The significance of soot deposition in the crankcase oil of diesel engines isrecognized by the formulation of engines oils with significant detergency properties. The'D' in the 'OMD' designation indicates an oil, mineral, containing a detergent additive.

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Acid combustion products deposited in the oil are generally considered by the oil industryto be the major factor in determining crankcase oil change periods. The presence ofsulphur species in the fuel, which are oxidized to components which form sulphuric acidin the oil, may lead to high rates of engine corrosion. The significance of the sulphurcontent of the fuel is recognized by oil formulators, acid neutralizing additives being animportant part of the formulation. Recommended crankcase oils for use with h~gh sulphurfuels contain higher proportions of acid neutralizing materials as measured by the totalbase number (TBN) of the oil.

Measurement of the viscosity and the "latent acidity" of the oil are the major means ofdetermining the deterioration of crankcase oils in service. "Latent acidity" may bedetermined as the change in Base Number of the oil, by direct measurement of carbonylabsorptions in the infrared spectra which may be associated with acid products [3], or bymeasurement of the concentrations of acid dissolved metal species in the oil [41. Thechange in viscosity, total base number and total insolubles have been determined for fiveLeopard vehicles which were operated for periods up to two years without changing theoil in the crankcase and gearbox assemblies.

3. FIELD PROGRAMME

3.1 Vehicles

Five Leopard vehicles were included in this trial at 1st Armoured Regiment, Puckapunyal.These comprised three Main Battle Tanks (MBT), one Recovered Vehicle (ARVM) andone Bridge Layer (AVLB). These vehicles represented a cross section of the Leopardfleet and were used routinely during the trial period.

3.2 Oils

The crankcase oil was OMD- 115, a monograde SAE30 diesel engine oil qualified toMIL-L-2104D. This is the standard diesel engine crankcase oil used by the AustralianArmy for almost all diesel powered vehicles. The transmission oil was 0X47, amonograde SAE10 hydraulic transmission fluid to Detroit Diesel Allison specificationTES 122.

3.3 Oil Samples

Oil samples were to be taken from the engine and transmission assemblies at the sixmonthly service and thereafter every three months. Sampling valves were fitted to thetrial vehicles with sampling procedures being specified to ensure that uncontaminated andrepresentative samples were obtained for analyses.

4. LABORATORY ANALYSES

The viscosity was measured at 400C and 1000 C with capillary viscometers by the methodof ASTM D445. A potentiometric method according to ASTM D2896 was used todetermine the total base number of the oil. Insoluble materials were precipitated from theoil by dilution with pentane following the procedure of ASTM D893. Centrifuging theoil/pentane solution separated the solids which were dried and determinedgravimetrically.

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5. RESULTS

Results for this trial are shown for each vehicle in Tables 1 to 10. The operating hours foreach oil sample in shown in Figure 1. Variations in the engine oils parameters are showngraphically in Figures 2 to 5.

6. DISCUSSION

6.1 Engine Oils

Viscosity increases were less than 10% for all engines in this trial. The viscosity of theengine oils remained within the specification limits for unused SAE30 grade OMD-1 15engine oil (maximum 12.5 mm 2 sec-1 and minimum 9.3 mm2 sec-1 at 1000C). Themaximum viscosity determined was 11.8 mm 2 sec-1, which was significantly less than themaximum allowed for new oil.

Further evidence for the small amount of degradation of the oils is seen in measurementsof the viscosity index (VI). The VI is a measurement of the variation of viscosity withtemperature. The larger the value, the smaller the change in viscosity with temperature.The specification for OMD- 115 oil calls for a minimum value of 75. Oil from all vehiclesshowed a small increase in VI over the period of the trial. These results would suggestthat there was no breakdown of the VI additive in the oil. Any deterioration of thelubricating oil would appear to have arisen from a small amount of oxidation of thebasestock oil itself to possibly form polymer material with natural VI properties. Thismaterial would cause a small increase in the viscosity at the higher temperature and asmall increase in the VI.

Only one sample of the engine oils indicated a decrease in viscosity during the samplingperiod. The decrease was reversed in the sample from the same vehicle during the nexttime period, when a small increase in viscosity was recorded. There was no evidence thatthe decrease in viscosity was caused by fuel dilution.

The increase in concentration of pentane insolubles was less than 1% for all trial samples.Previous studies have shown that an increase in the concentration of fuel combustioncarbon particles (soot) in the oil was the major factor in determining the life of the engineoil [2]. The soot, measured as the major component of the pentane insolubles, causes anincrease in the viscosity of the oil. Neither the pentane insolubles nor the viscosityincreased significantly in the samples from the trial.

Very little decrease in total base number (TBN) was recorded for the samples over theperiod of the trial. These results would indicate that the oil is still providing adequateprotection against engine chemical corrosion from acid combustion products.

The results obtained in this study were comparable with results reported in Appendix2.1.6 to Annexe A of reference 1. The multigrade oil used in the European study alsoremained satisfactory for continued operation after the two year period.

t

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6.2 Transmission Oils

Transmission oils are not subject to deterioration by deposited soot or acid combustionproducts. The major factors are changes in viscosity from oil oxidation and possibilityshear of base oil molecules. Oil oxidation may be accelerated by operating the vehiclesunder heavy loads, causing the transmissions to become overheated.

Changes in viscosity of all the transmission oils were less than 10% after 24 months ofoperation. The small change would indicate that oil oxidation and shear processes werenot a determining factor in the oil condition in the transmission assemblies during the trialperiod. All oil samples showed a small increase in viscosity from that of the original oilin the assemblies.

The increase in the pentane insoluble content of the transmissions oils was less than0.20%. The presence of oil degradation products, wear metals and ingested airborneparticulate matter were not significant in the oil condition.

The results from this study of the transmission oils was again similar to the much largerstudy in Europe [1]. Over the two year period, the viscosity of the transmission oilsincreased slightly and the amount of insolubles remained low.

7. CONCLUSIONS.

The criteria for acceptable oil life are generally based upon viscosity change, insolublesbuild-up, water contamination and depletion of additives. Results from the engine oils ofthe trial vehicles showed that deterioration was insignificant after operation for up to 269hours over a period of 24 months. Fo, the parameters determined in this study, all oilsamples met the specification requirements for the original unused oil.

The usage rate of the vehicles was relatively low over the trial period. After 24 months,all oils meet the requirements of unused oil which would suggest that there wasconsiderable oil life remaining. There was no indication that storage ageing from oilremaining in the vehicles over the two year period was contributing to its deterioration.These results are consistent with previous studies of the deterioration of the oil in ArmyMack Trucks [2]. Vehicles which had travelled small distances over a period of two yearsshowed little deterioration of the oil. For the trucks, the major factor in oil deteriorationwas the engine operation hours. An increase in pentane insolubles and an associatedincrease in the viscosity of the oil was correlated with operating hours of the oil.

8. RECOMMENDATIONS

1. Elapsed time was not found to be a significant factor in the deterioration of the oilfor the vehicles in this trial. Increasing the oil drain interval to 2 years isrecommendLi, especially for low usage vehicles.

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2. As variations in oil parameters over a period up to 269 operztional hours werewithin specification limits for new oil, it may be concluded that minimum risk willarise from extending oil change intervals to 300 hours.

3. Insufficient deterioration occurred in the engine and transmission oils in this trialto gauge the maximum operational life of these oils. Based on the limited numberof vehicles and samples in this trial, conservative recommendations have been putforward.

9. REFERENCES

1. Proceedings 15th International Leopard Vehicle Technical WorkingGroup Meeting, 1985. Germany, 18-22 March.

2. McVea, G.G. 1983. "Lubricant Deterioration in the Army Mack TruckDuring Extended Operation". Materials Research Laboratory, OCDReport No. 83/9.

3. Coates, J.P and Setti, L.C. 1985. "Infrared Spectroscopic Methods forthe Study of Lubricant Oxidation Products", ASLE Trans, 29, pp 394 -401.

4. Golden, G.S. 1971. "The Determination of Iron in Used LubricatingOils" Applied Spectroscopy, 25, 668.

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I&. AR NUIMER 1b. ESTAIUaOMENUMDM 2. DOCUMEN DATE 3. TAM NUMBER

AR-00-112 ARL-TN-10 MAY 1993 ARM 92/471

4. T5. CURM CIASSInCAMION 6. NO. PAGES

EXTENSION OF OIL SERVICING O A A.S.•ATIoNINTERVALS FOR THE LEOPARD AS-1 I BOXM M SzFr• 0CO. tC) 22POWER PACK •RESMCrIEC. LD rEM CU

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G.G. McVeaR.K. Solly Not applicable.

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14. DC•IV7CIFI 15. DWSCATSUBJC••

Leoprd manks CAE(TOF=5Lubricating oils 1108Engine maintenance 1903

16.

The condition of the engine and transmission oils was determined at three mnnhIN ipuerWls for a period of24 months for five armoured Leopard vehicles operated routinely by the i Armoured Regiment.Puckapunyal. For the trial vehicles, the maximum operating hours was 270 and the minimum 56. All oilsamples from the trial vehicles remained within specification requirements for new oil as determined byviscosity, total base number and pentane insoluble content. A small increase in the viscosity of both theengine oils and the transmission oils was recorded over the period of the trial, but all determinationsremained well below the maximum spec#1ed for new oil. There was no indication of storage or standingdeterioration of the oils during the two year period and it was concluded that vehicle operating hours wasthe sole criterion for the variations that were determined. It was recommended that oil change intervalscould be extended to a minimum of 300 operational hours or two years elapsed time.

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