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).
Technical paper discussing the benefits of blending castor oil with mineral oil to reduce crankcase dilution and contamination.
| Identifier | ExFiles\Box 32\4\ Scan196 | |
| Date | 29th December 1924 guessed | |
| A BLEND OF CASTOR OIL WITH MINERAL OIL TO REDUCE CRANKCASE DILUTION AND CONTAMINATION It is undoubtedly true that various controllable factors in a motor, affect the rate of dilution and consumption of the lubricant. We believe however, that it is possible to reduce the amount of dilution to a minimum without the need of redesigning the motor. Something should be done for the fifteen million automobiles now in daily use. Different oils of different viscosities, respond differently to dilution. But with all of them there is a point beyond which dilution does not increase. At least, this is true of a given oil in a given motor. As the oil thins out, the motor temperature rises until evaporation offsets the dilution and a point of equilibrium is reached. This diluted oil, if uncontaminated, may still serve as a lubricant. But the thinned out film between piston, piston rings and cylinder walls is not as good a seal as the original oil. The natural result is increasing contamination as the combustion chamber is the point of origin for the bulk of contaminating matter. With mineral oil, the oil film on the cylinder walls above the piston on the intake stroke, is subjected to a bombardment of gasoline particles and due to its affinity for gasoline, is diluted, partially vaporized and to a considerable extent, becomes a part of the fuel itself. The oil thus vaporized and mixed with the gasoline, reduces the ignition point and also increases the end point of the compressed fuel. Only the more volatile portion of this mixture is consumed in the combustion chamber, the remaining portion being subject to destructive distillation. With the small amount of oil left on the cylinder walls, only a partial seal is made and these heavy unconsumed fractions pass the rings and find their way to the crankcase, carrying with them, impurities introduced with the gasoline. As dilution increases the film on the cylinder wall is more easily absorbed with ever increasing resultant contamination. It is needless to enumerate the evil effects of contamination. Dilution which, of itself, is not necessarily harmful, leads to contamination. Castor oil blended with a highly refined mineral oil, reduces crankcase dilution thereby reducing contamination to a minimum. Castor oil has great adhesive properties for hot metal. Its repelling characteristic for hydrocarbons is such that it tends to prevent the gasoline from absorbing the film of oil on the cylinder walls, thus correcting the most prolific cause of crankcase dilution as well as reducing the principal cause of contamination. With castor oil, the carbon produced in the combustion chamber is soft and easily expelled through the exhaust port. Appended is a report on a blend of castor and mineral oil used in a motor car driven continuously, over 100 hours in the traffic of the Metropolitan district. | ||