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Number 22 2004GUIDELINESFOR DIESEL ENGINESLUBRICATIONOIL DEGRADATIONThe International Councilon Combustion EnginesConseil International desMachines à Combustion

CONSEIL INTERNATIONALDES MACHINES A COMBUSTIONINTERNATIONAL COUNCILON COMBUSTION ENGINESCIMAC is an international organisation, founded in 1950 by a Frenchinitiative to promote technical and scientific knowledge in the field ofinternal combustion engines (piston engines and gas turbines). This isachieved by the organisation of congresses and working groups.It is supported by engine manufacturers, engine users, technicaluniversitites, research institutes, component suppliers, fuel andlubricating oil suppliers and several other interested MACRecommendations still available are listed in the back of this publication.This document has been elaborated by the CIMAC Working Group „Marine Lubricants“ and approved by CIMAC in April 2004.

Foreward by the PresidentThe CIMAC Recommendations are produced by the CIMAC Working Groups inwhich experts in the various fields of combustion engines, contribute voluntarily,to formulate the related documents.The CIMAC Recommendations serve not only to consolidate the knowledge andexpertise in a particular field, but are also aimed to be of practical importance forengine users, manufacturers and related equipment suppliers.The present Recommendations on “Guidelines for Diesel Engine LubricationLubricating Oil Degradation” is targeted to all people related to large engines inmarine propulsion, land-based power generation and railroad industry.This Recommendation is one further product of the CIMAC Working Group No. 8.“Lubricants”, which can boast a very wide participation of experts from CIMACMembers and has been very fruitful in producing Recommendations over the pastyears.I wish to congratulate the Working Group No. 8 “Lubricants” for this finedocument, which I trust will be useful for the combustion engine community allover the world.Prof. Nikolaos P. KyrtatosApril 2004

GUIDELINES FOR DIESEL ENGINE LUBRICATIONLUBRICATING OIL DEGRADATION1

OIL DEGRADATIONCONTENTSPagePREFACE .41. INTRODUCTION .42. STRESSES IMPOSED ON THE ENGINE OILS BY ENGINE COMPONENTS .43. PRINCIPAL FUNCTIONS OF ENGINE OILS .74. TYPES OF LUBRICANT FOR LARGE DIESEL ENGINES ANDTHEIR REQUIREMENTS .74.1. Crosshead Engine Oils.84.1.1. Cylinder Oils .84.1.2. System Oils .84.2. Medium Speed Trunk Piston Engine Oils.94.3. High Speed Trunk Piston Engine Oils .105. CAUSES OF OIL DEGRADATION.115.1. General.115.2. Factors Affecting Oil Degradation .125.2.1. Specific Lube Oil Consumption .125.2.2. Specific Lube Oil Capacity .135.2.3. System Oil Circulation Speed.135.2.4. NOx Content in the Crankcase Atmosphere and Influence on Lubricant.135.2.5. Fuel Contamination in Trunk Piston Engines .155.2.6. Deposition Tendency on the Cylinder Liner Wall .155.2.7. Metals in Lubricant Systems .155.2.8. Oil Top-up Intervals .155.3. Summary of Factors Influencing Oil Degradation.166. LUBRICANT PERFORMANCE IN SERVICE AS INFLUENCED BY DEGRADATIONEFFECTS.186.1. Engine Impacts.186.1.1. Lube Oils for High and Medium Speed Trunk Piston Diesel Engines .186.1.2. Oils for Two-Stroke Crosshead Diesel Engines .196.2. Physical Stresses .196.3. Chemical Stresses .196.4. Physical Contamination .196.5. Oil Film Thickness .207. THE MECHANISM OF OIL DEGRADATION & MEASURABLE RESPONSES TOSTRESSES.207.1. Changes in Oil Viscosity.207.2. The Formation of Insolubles .247.3. Changes in BN (Base Number) .297.4. Increase of TAN (Total Acid Number) .357.5. Flash Point Reduction .377.6. Foaming .377.7. Chemical Changes .392

7.8. Change in Molecular Weight Distributions.407.9. Particle Size Distributions.407.10 Oxidation. .407.11. Process of Degradation of Characteristics of Oils in Use and their Control .418. PRACTICAL IMPLICATIONS AND INFERENCES .419. FUTURE TASKS.429.1. Designing More Stress-Resistant Lubricants .429.2. Environmental Issues .4210. ANALYTICAL METHODS FOR ASSESSING OIL DEGRADATION .4211. WARNING AND CONDEMNING LIMITS .4212. CONCLUSIONS .4313. APPENDICES .44Appendix 1. A Mathematical Model simulating Insolubles Build-Upin used Engine Oils .44Appendix 2. Oxidation Processes.48Appendix 3. What is Acid ?.5014. REFERENCES .5115. GLOSSARIES .5316. ACKNOWLEDGEMENT .603

OIL DEGRADATIONPREFACEThis document brings together insights into mechanisms and phenomena of oildegradation resulting from stress of the lubricant in large 4-stroke (medium speed andhigh speed) and 2-stroke diesel engines. Its objective is to contribute to the understandingof the complex processes resulting in oil degradation and thereby, to a degree, enablecontrol of them so that the engines, their treatment systems and the lubricant itself remainin an acceptable condition for an acceptable period.The intended readership of this document are all people related to large engines inmarine propulsion, land based power-generation and railroad industry - for exampleusers and producers of equipment, students and newcomers to the industry etc.1. INTRODUCTIONThe lubricating oil for a diesel engine needs a variety of properties. It must be able toclean engine components and keep them clean, it must neutralize acids, transfer heat,fight rust and corrosion in addition to its main job of lubricating the engine for a very longtime [1, 2]. Since lubricating oil is a product influenced in its quality by a variety ofstresses, monitoring of the oil quality, adequate oil maintenance, as well as its timelyreplacement if needed (partially or totally) must be ensured. Also, the selection of the typeand grade of lubricant to be used should be based on the relevant engine operatingconditions and service conditions.This document discusses the types, causes and counter measures of degradation oflarge engine lubricants during service. ”Oil degradation” in this document means thechange in physical and chemical properties of the lubricants during service that result indeterioration of performance. The change in oil quality is the result of a) accumulation ofcontaminants including combustion soot, acidic combustion blow-by products, rawresidual fuel, water, etc., and b) the influence of high temperature, aeration and NOx.This document gives advice on how to maintain oil properties within acceptable limits.2. STRESSES IMPOSED ON THE ENGINE OILS BY ENGINE COMPONENTSThis section compiles a list of the different stresses a lubricant experiences in an engine.It also serves as a guide for engineers to understand why attention needs to be paid tolubricant properties as part of routine engine maintenance. Some of the componentsmentioned in this section are marked in Fig.1 which shows a typical “Crosshead” and“Trunk Piston” diesel engine. [3].Stresses on the lubricant are listed in Table 1. A lubricant can degrade through a numberof routes, therefore users need to be aware of how engine operation can affect lubricantproperties and the importance of carrying out maintenance and preventive work tominimize engine wear and malfunctions.4

Figure 1: Engine Components relevant for Lubrication [3](Courtesy of Mitsubishi Heavy Industries and Niigata Power Systems)5

Table 1: Stresses on Lubricating Oils of Large Diesel EnginesN

3. Crankcase oils for medium or high speed trunk piston engines Table 2: Diesel Engine Classification Diesel Engine Classification Rotational Speed (rpm) Crosshead Below 300 Medium Speed Trunk Piston Below 1000 High Speed Trunk Piston Above 1000 Note : There are some older design engines of the two-stroke (trunk-piston) type with rpm of above .