From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Properties and performance of different types of lubricating oils for engines.
| Identifier | ExFiles\Box 32\4\ Scan274 | |
| Date | 12th December 1927 | |
| N1588 o-to BJ. BY.{R.W. Bailey - Chief Engineer} Hs.{Lord Ernest Hives - Chair} Laboratory. H11/EA12.12.27. Lubricating Oils. - with respect to your memo. R1/M9.12.27. Relatively thin oils generally give better results even in engines with less accurate clearances than ours; this may be partly due to more rapid circulation owing to lower viscosity especially under cold or starting-up conditions. Compounding generally improves a mineral oil, especially if it is made up largely of paraffin hydrocarbons. On the other hand a large proportion of asphaltic base is undesirable. An over-refined oil may require more animal, vegetable or asphaltic base addition to produce a good lubricant than a less refined mineral oil. Mineral oils for lubrication are manufactured under very varying conditions, cracking and other processes being employed. Thus, a crude made up largely of paraffin base hydrocarbons may be more or less converted, under distillation etc., into asphaltic base hydrocarbons. In this manner it is possible to change a typically american oil into one high in asphaltic characteristics (more similar to some varieties of Russian oils and Trinidad oils, which latter have been found to produce an excellent lubricant). As to compounding with fatty oils, this may be satisfactorily replaced by careful selection of mineral oil or blend of mineral oils, with or without a microscopic addition of say about 0.2% non-corrodible fatty acid. With respect to fatty acid it may be taken that with Oleic acid and probably several others there is no greater tendency to engine corrosion than without it (numerous tests have been made to check this point). Further, under intermittent or continuous running conditions, when traces of water are present in the crankcase oil, it has a protective effect; on the other hand, it may be a disadvantage under storage conditions. Animal, vegetable and fish oils are undoubtedly more liable to decomposition than most mineral oils when used under the complex temperature conditions to which crankcase oil is subjected. The products do not cause corrosion under running conditions, if local stagnation is avoided, so long as there is a large excess of mineral oil compounded with them. It is possible that a pure mineral oil might be used for storage and that an addition might be made when going into service; uniformity of the mixture would soon be obtained on running. On the other hand, the oil used for "running-in" a new engine should not be chosen on account of its pure mineral nature, irrespective of its lubricating value. I conclude that most ball bearings are practically sealed off from oil used in other parts of the engine. If so, I agree that mineral oil is preferable, but it would be better that some part of this should be of asphaltic base since running is largely under boundary lubrication conditions (absence of film). | ||