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 article discussing the development and application of the octane number scale for measuring anti-knock quality in gasoline.
| Identifier | ExFiles\Box 27a\4\ Scan066 | |
| Date | 1st November 1931 | |
| NOVEMBER, 1931 A Gulf Publishing Company Publication 87 of about 212° F.{Mr Friese} is secured, and that without any attention on the part of the operator. In order to insure consistency and to prevent the formation of localized pockets of steam, a belt-driven water pump has been inserted in the system to give positive circulation of the cooling liquid. OCTANE NUMBER SCALE For any form of quantitative measurement, it is necessary to have a scale of some kind. Anti-knock quality is a measure of one of the most important and most variable properties of gasoline. But, although people have been speaking of anti-knock quality now for several years, it is only within the past 18 months that there has been any common scale of expression for it. Before that, each man had his own language, and usually it was not even possible to translate the language of one observer into that of another. The common scale of reference which we now have, and which is expressed in terms of octane numbers, has come into use as a result of the work of this sub-committee. It is based upon the suggestion made in 1926 by Graham Edgar, who is one of the members of the sub-committee, that anti-knock quality be rated in terms of two pure paraffin hydrocarbons, one (normal heptane) of very low anti-knock quality, and another (iso-octane, 2, 2, 4-trimethyl pentane) of high anti-knock quality.² Although the adoption of the octane-number scale occurred prior to the year just past, the general acceptance of it has taken place during the past year. And, in view of the fact that little has thus far been published about the octane-number scale, it seems desirable to discuss it briefly here. Experience has shown that the most satisfactory and dependable scale of anti-knock quality is one that is based not upon some engine factor, but upon a fuel, and upon a fuel of definite and determinable composition. The conditions that influence knock are many and so variable that the expression of anti-knock quality in terms of some engine factor, such as the compression ratio, the compression pressure, or the spark setting, at which knock just begins, is not a universal, nor even an altogether dependable method. The reason for this is that these engine factors vary too much from engine to engine, and too much even from day to day in the same engine. It is thus because engine conditions are so variable that it has been found best to use a fuel, rather than an engine, as the basis of a scale of anti-knock quality. But, of course, it will not do to use merely some selected gasoline as a primary reference fuel, because the composition of no gasoline can be known with certainty, and it cannot, therefore, be reproduced with exactitude. It is this difficulty that has been overcome by making the reference fuel out of two pure gasoline hydrocarbons, one of low anti-knock quality and the other of high. Not only are both of these hydrocarbons of the general type present in conventional gasoline, but both have also practically the same boiling point and other physical properties. They differ in any essential manner only in anti-knock quality, and in this respect they differ widely. SOURCES OF HEPTANE AND OCTANE The source of normal heptane, the hydrocarbon of low anti-knock quality, is the Jeffrey pine, a tree that grows in the mountains along the Pacific Coast. For some strange reason, heptane can be obtained from this pine much as turpentine is obtained from some other pines. Heptane is distilled directly out of the pitch of the Jeffrey pine in a high degree of purity. This same heptane is present to some extent in gasoline. But the Jeffrey pine is the place to get it pure and uncontaminated by other hydrocarbons. The source of iso-octane, the hydrocarbon of high anti-knock quality and the one from which the name octane number has been taken, is tertiary butyl-alcohol. Iso-octane is made synthetically and in a pure state from tertiary butyl-alcohol. And again this same octane is of the type of compounds present in gasoline. It is made from butyl-alcohol as a means of getting it away from other members of the same family in a condition pure enough to serve as a reference material. As is indicated in footnote 4 of Appendix II, the heptane and octane used thus far have been supplied by the Ethyl Gasoline Corporation, which company had limited supplies of both of these compounds that were gathered for its own use. These materials it has been making available to industry in general, with the result that the supply is now running rather short. One activity of the sub-committee has, consequently, been the effort to provide adequate sources of these two primary reference fuels for the future. The group working on this was headed by Graham Edgar, who originally suggested the use of these hydrocarbons and who has had experience producing them. As a result of the work of this group, heptane for the future is being produced, and is now for sale, by the California Chemical Corporation, San Francisco. This company has already prepared a 250 gallon batch of heptane; and, in accordance with arrangements made by the sub-committee group to insure the purity of the reference fuels, a sample of this product was sent to the U. S. Bureau of Standards for test. The manufacturer has been authorized to attach to each container the following statement: “The manufacturer of this material guarantees that the contents of this container are a part of a batch prepared by............, and that samples of the same batch of containers have been submitted to the U. S. Bureau of Standards for tests, results of which tests are as follows: (statement of results.”) In addition to the provision stated above, the Bu- | ||