Turbine D has drawn a little heat for asking some questions, in the last few posts above. But nonetheless one of Turbine D's questions was of considerable interest to me, that regarding the specifications of the [QF32] engine oil. And Turbine D asked that question directly to
Shell Management, whom I think we are entitled to assume has the background to answer it more fully than he did. The exchange:
Question:
So what oils are approved for the Trent 900 series engines? It isn't clear in the Type Certification Document.
Answer, by Shell Mgmt, addressed to
DERG:
DERG
Refer to the Operating Instructions for information on approved oil specifications for the Trent 900 old chap.
Well, I see now the question was DERG's, restated by Turbine D. I find the answer to be a bit circular, at least to me in my ignorance. The AC Captain who posted in the original oil thread here that he'd been down the AC oil road once before and never wanted to go down it again has my full sympathy. I too have been down the oil road with the oil manufacturers. But here goes, yet again and ever hopeful:
1. The type certification document says that the oil shall be as specified by the manufacturer. [I omit mention of the reams I read as to which manufacturer [AC or engine], and as to whom holds the certificate, and whom incorporates it by reference; not to mention where the oil may be obtained.]
2. The AC manufacturer now says that MJO II or MJO 294 may be used; the AC QF32 was shipped with MJO II installed; the failed engine appears to have been using MJO 294 [I may have to correct the "memory item" 294 on edit]. When the changeover occurred may have been at the 3-year repair point, but I did not see this published anywhere. Some or all of the other engines on QF32 continued with the originally installed type of oil.
3. Now comes the problem. Perhaps the Operating Instructions contain the actual specs of the oil, which is only identified by name in the public documents. [My deduction at the moment is that the A380 Operating Instructions either are distributed need-to-know basis only, or do not yet exist.]
4. Of course, the Mobil (or ExxonMobil, which may or may not be the same thing) website for oil contains the specifications for the oil in question. The problem is, these voluminous specifications are next to useless in the jet engine context. I give one example at #5 and 6 ff:
5. Viscosity of the hot oil: 5 centistokes at 100-degrees Centigrade. Well, I don't think the viscosity at 100-C has been of any interest since pressure radiator caps were added to water-cooled automobile engines sometime in the 1930s.
6. What are we given instead: MJO-xxx (whatever) is provided with extended range viscosity stabilizers. Give me a break. What is the viscosity of these two oils at 180-C and 196-C?
7. On to another question. What is the base stock of these two oil types? Well, for MJO II it is fairly clearly identified as a highly refined mineral oil base. Okay, I'll accept that as an answer. But for MJO-294, the situation become murky indeed. It was identified on a document posted here [at least of quasi-official standing, I will look it up] as being an HPC oil. However, I located a MIL spec discussion in which MJO-294 [number from memory, will edit] is identified as an SPC oil, which whatever it is, is not an HPC oil.
8. I think the MJO-294 must be also a highly refined mineral oil base, but with the addition of PG additives, but what do I know? ExxonMobil describes it as an "advanced oil", IIRC.
9. The question of whether both these oils have a mineral oil base bears on two questions. One is the question of lubricity, at which the mineral oils excel. The other is the viscosity buildup that occurs to such oils when the evaporation rate removes the lighter fractions preferentially, and "topping up" is frequent. It will be frequent if the operation is at the specification operating limit temperature for evaporation-- a 12-hour flight to LAX would consume half the contents of the engine oil reservoir.
10. ExxonMobil have an HPC oil under development. It is unobtainable in the US as of December, if it is available anywhere.
11. I get the feeling there is a desire to have the oil last between major off-wing inspections/overhauls. Perhaps this is because MJO-294 (again, number subject to edit) is a potent orthophosphate insecticide. For crying out loud, even the US tv police sitcom "Castle" took notice of this within the last month. Where do these people find these things out, let alone accurately? [That's not a question that needs an answer.]
Shell Management, I assume you must know the answers to the questions and uncertainties I discussed above: Meaningful viscosity data, base oil and expected T-972 oil temps enroute LAX as it affects viscosity buildup due evaporation on the long-term hand, and viscosity loss at high temp in new oil on the short-term hand-- these are the uncertainties which I think need to be known. It would be helpful to know your views on oil change intervals. Your views on whether Engine #2 might have been operating with an oil likely to have insufficient lubricity would also be helpful.
Hopefully you will not be constrained in your position at Shell from discussing Exxon products. Or you might prefer to make a discussion from the standpoint of Castrol products, which perhaps are more likely to have been used by RR in the development of the engine. Thanks.