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4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.orgSAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR6056 AEROSPACE INFORMATION REPORT AIR6056 Issued 2014-08 Gas Turbine Engine Lub
5、ricant Specifications: Current Technical Review and Future Direction RATIONALE Qualification of a turbine oil formulation to AS5780 is now recognized as an integral part of most aviation equipment manufacturers oil approval processes. The E-34 Committee identified the need to develop this document b
6、ased on inputs, questions, and concerns from gas turbine lubricant customers, equipment manufacturers, military authorities, and civil aviation authorities. The intent is to provide a clear and concise reference which will help guide the direction of the committees efforts in refining AS5780. FOREWO
7、RD Background: During the decade beginning in 2000, there were significant events and milestones that shaped the means by which synthetic turbine oils are approved for engine and other aircraft component use. There were high visibility, in-service events that focused both the Civil Aviation Authorit
8、ys and Original Equipment Manufacturers (OEMs) attention on improving the processes used to approve synthetic turbine oils. An E-34 meeting with representatives of the global Airworthiness Authorities was held on September 11, 2003 to discuss Turbine Oil Approval and Control. Coincident to this scru
9、tiny, and after a decade long effort, AS5780 was released in November 2004. AS5780 consolidates the majority of OEM chemical, physical and rig performance requirements short of model specific engine tests. AS5780 also drove the formation of a Qualified Products Group made up of OEM representation th
10、at maintains the AS5780 Qualified Product List and oversees change management of the listed products. While these milestones set a framework for OEMs to mutually specify and control oil formulations, in-service events pointed to several gaps in AS5780 that require further development. Regulations: T
11、o understand the role of specifications in the aviation industry, an examination of engine OEM responsibility for certificating engines is necessary. Industry guidance on approving lubricants (and fuels) for certificated aircraft engines is provided by the U.S. Federal Aviation Administration in the
12、 form of an Advisory Circular No. 20-24C (see Reference 2.1.1): Engine operating limitations are established during the certification of an engine. One such operating limitation is the lubricants which are declared and substantiated during the certification of the engine model. Approved lubricants a
13、re listed (or referenced) on the engine models Type Certificate Data Sheet (TCDS). Each engine model or engine model series requires separate approval. The approved lubricant must be identified and defined by a specification which adequately details its physical properties and associated limits and
14、controls its composition. If qualification to a specification alone is not sufficient to approve the synthetic lubricants used in gas turbine engines, then they may be individually approved by formulation and brand name. SAE INTERNATIONAL AIR6056 Page 2 of 34 The Process (see Reference 2.1.1) by whi
15、ch new oils are approved involves: a. The Oil Manufacturer providing analysis and performing component, rig or engine testing necessary to comply with the applicable airworthiness standards such to show the new oil will not result in harmful build-up of carbon deposit. In the USA, these standards ar
16、e 14CFR Part 33 for engines, Parts 23 and 25 for airplanes, and Parts 27 and 29 for rotorcraft accomplished by any combination of engine test, rig test, and analysis based on prior service, experience, or testing. b. The FAA accepting data that was generated during the AS5780 qualification process t
17、o document that the lubricant has undergone sufficient testing to demonstrate that it will be compatible with the applicable engine. This data will typically address chemical, physical, compatibility and rig performance testing. OEMs have the responsibility to bridge testing gaps to show that, under
18、 the conditions in which the lubricant will be used in the aircraft it is compatible with the applicable engine and engine materials, if these are not tested during qualification to AS5780. c. The engine test facility documenting the test conditions, oil consumption, analysis of oil before and after
19、 engine test, evidence of wear, deposits or attack/deterioration/change of metal or non-metal components. d. Responsible parties identifying and controlling the lubricant by the specific oil brand name unless the engine OEM has substantiated that any oil qualified to AS5780 is acceptable for use on
20、the subject engine (see Reference 2.1.2). New oil formulations seeking approval to a certificated engine model are approved by Engineering Changes to that model which in turn amends its existing Type Certificate. European airworthiness regulations applicable to turbine engine oil are specified in EA
21、SA CS-E 570 (g). Motivation: An engine experiencing an uncontained turbine blade release related to the use of a novel engine/oil combination has focused much attention on the adequacy of aviation industry specifications and OEM engine/oil approval processes. Following an investigation of this incid
22、ent, the U.S. NTSB issued a Safety Recommendation (see Reference 2.1.3) to revise AC 20-24B to include guidance that ensures new engine/oil combinations are inspected where there is an identified risk for (porous) carbon formation and subsequent hazardous engine behavior. The FAA issued AC 20-24C in
23、 response to the NTSB recommendation and has committed to work with E-34 to develop and incorporate enhanced qualification test methods into AS5780 to assess the long-term thermal stability of oil and in particular, the longer term coking of turbine engine lubricants (see Reference 2.1.4). E-34 Stra
24、tegy: The E-34 committee determined that it was valuable to produce this AIR as a vehicle toward improving the current specification by: Documenting the AS5780 specification requirements in terms of each tests purpose, history, applicability and future direction. Critically examining the specificati
25、on requirements contained in AS5780 in light of current engine designs, operating conditions and maintenance programs for adequacy in maximizing safety and reliability. Developing plans for future revisions of AS5780 to bridge performance gaps: a. First priority: carbon formation per the NTSB Safety
26、 Recommendation b. Second priority: rationalize and refine current requirements where there are multiple methods and OEMs are coping with emerging issues (e.g., elastomer compatibility and oil oxidation). Additionally, it is hoped this document serves as a useful reference to educate in this special
27、ized technical field of synthetic turbine oils. SAE INTERNATIONAL AIR6056 Page 3 of 34 TABLE OF CONTENTS 1. SCOPE 4 2. REFERENCES 4 2.1 Applicable Documents 4 3. History of Aviation Gas Turbine Engine Lubricants 4 4. Specification Property Reviews 5 4.1 Physical Properties . 5 4.1.1 Kinematic Viscos
28、ity at 40 C and 100 C, ASTM D445/IP71 6 4.1.2 Viscosity Stability (Low Temperature), ASTM D2532 . 6 4.1.3 Viscosity Index (VI), ASTM D2270/IP226 . 7 4.1.4 Pour Point, ASTM D97/IP 15 or ASTM D5950 . 7 4.1.5 Flash Point, ASTM D92/IP 36 . 8 4.1.6 Evaporation Loss, ASTM D972 . 8 4.1.7 Foaming Tendency,
29、ASTM D892/IP146 . 9 4.1.8 Shear Stability, ASTM D2603 . 10 4.1.9 Density, ASTM D4052 . 11 4.1.10 Heat Capacity, ASTM E1269 11 4.1.11 Thermal Conductivity, ASTM D2717 . 12 4.1.12 Electrical Conductivity, ASTM D2624/IP274 . 12 4.2 Chemical Properties 13 4.2.1 Total Acid Number, ARP5088 . 13 4.2.2 Sedi
30、ment/Ash, FED-STD-791, Method 3010 14 4.2.3 Trace Metals by AES 14 4.2.4 Hydrolytic Stability, DEF STAN 05-50(Part 61), Method 6 . 15 4.3 Compatibility 15 4.3.1 Lubricant Compatibility, FED STAN 3403 Mod/Def Stan 05-50(Part 61) Method 24 . 16 4.3.2 Elastomer Compatibility, FED-STD-791, Method 3604 1
31、7 4.3.3 Elastomer Compatibility, Def Stan 05-50(Part 61) Method 22 18 4.3.4 Fluorocarbon Compatibility, Snecma Method . 19 4.4 Stability Properties 20 4.4.1 Oxidation and Corrosion Stability, FED-STD-791 Method 5308 (mod)/ASTM D4636 Alt Procedure 2 mod . 20 4.4.2 Thermal Stability and Corrosivity, F
32、ED-STD-791 Method 3411b 22 4.4.3 Oxidative Stability , Def Stan 05-50 (Part 61) Method 9 . 22 4.4.4 Thermal Aging , Turbomeca Method 23 4.4.5 Particulate Generation, P the possibility that an increase in viscosity during the soak could influence engine reliability was also considered. The U.S. Air F
33、orce, therefore, developed Federal Standard 791 Test Method 307 (FTM 307) and a viscosity change limit was introduced to the specification MIL-L-7808 edition current at the time. The FTM 307 was standardized by ASTM in 1966 as Method D2532, and in 2000 a requirement for testing by the latter method
34、was included in the AS5780 5 cSt oil specification. Applicability: Method ASTM D2532 is applicable to aviation gas turbine lubricants meeting the AS5780 specification and also to lubricants meeting the U.S. DOD and UK Defense Standards for 3 cSt and 5 cSt gas turbine oils. Current Test Method: Test
35、Method ASTM D445 requires the kinematic viscosity of a sample to be determined at low temperature at time intervals of 3 hours and 72 hours. Presently for AS5780, only the data generated at 72 hours is required and reported. Precision for the test is established for a soaking temperature of minus 53
36、.9 C only. However, the test is also applied at minus 40 C for those oils that are not fluid at the lower temperature. In such cases the same precision limits are recommended. SAE INTERNATIONAL AIR6056 Page 7 of 34 Future Development: No work is currently taking place to develop a new method, as the
37、 current test is considered adequate for use in specifications and for investigation of service events. 4.1.3 Viscosity Index (VI), ASTM D2270/IP226 Viscosity Index is an arbitrary scale for lubricating oils that indicates how viscosity varies with respect to temperature over a specific temperature
38、range. History: E W Dean and G H B Davis first proposed the use of a Viscosity Index scale in 1929 using a seven points scale based upon Pennsylvanian and Gulf Coast crudes. The scale was used for many years before the method was refined and became ASTM D567 in 1965. The more recent method, ASTM D22
39、70, incorporating changes to simplify the scale, was introduced in 1964 and quickly became the industry standard. Aims/Purpose: The viscosity index is a widely used and accepted measure of the variation in kinematic viscosity due to changes in the temperature of lubricating oil between 40 C and 100
40、C. A high VI indicates a small decrease in kinematic viscosity with increasing temperature whereas a low VI signifies a larger change of viscosity with increasing lubricant temperature. Applicability: The viscosity of a lubricant, and how the viscosity changes with variations in temperature are fund
41、amental properties of a lubricant that are required for bearing and gear design and for heat to oil calculations. Current Test Method: The method for calculating the VI Scale, and the precision attached to it is described in ASTM D2270 (jointed with IP226): The method details how to calculate the VI
42、 of petroleum products and related materials from their kinematic viscosities at 40 C and 100 C. The practice does not apply to petroleum products with kinematic viscosities less than 2.0 mm2s-1at 100 C. Future Development: Method ASTM D2270 and IP 226 are established methods under the purview of AS
43、TM and the Institute of Petroleum. The methods are stable and no significant changes are anticipated in the foreseeable future. 4.1.4 Pour Point, ASTM D97/IP 15 or ASTM D5950 The pour point of a liquid is the lowest temperature at which a sample of the fluid shows flow characteristics under defined
44、conditions. History: First generation synthetic oils were based on dicarboxylic acid esters having a viscosity of 3 to 3.5 mm2/s at 100 C with an operating temperature of -54 to 177 C. The pour point specification for such oils was -60 C maximum. Development of more fuel-efficient turbine engines re
45、sulted in higher operational engine temperatures, and those higher temperatures required a superior ester-based lubricant. Thus, the Type II MIL-PRF-23699 5 mm2/s polyol ester based oils were developed. However, in order to achieve stability at the higher temperatures, the low temperature requiremen
46、ts had to be relaxed, and the approval authorities increased the pour point limit to -54 C maximum. The change to the pour point requirement did not result in any in-service issues and the requirement still remains in the MIL-PRF-23699 specification. AS5780 incorporated the pour point requirement of
47、 -54 C maximum for grandfathered and new generation civil gas turbine oils which are based on 5 mm2/s polyol esters. Aims/Purpose: In order to circulate in an engine immediately after it starts, the lubricating oil must be capable of free flow. High pour point oils could channel and fail to flow if
48、the engine was operated below the pour point temperature of the oil. That could result in seizure of moving parts and serious damage to the engine. The pour point determination correlates to the storage of the oil under low temperature conditions, or where the oil is stationary in an engine oil tank
49、, and exposed to low temperatures, during an overnight stop for instance. Applicability: The manual pour point test procedure provides adequate precision for the specification requirements and, after completion of a Round Robin and the study of a plethora of data, the committee elected to also include the automated pour point method, ASTM D5950, into the latest revision of the specification, AS5780B. Current T
