A Comparison of Methods for Determining Gum Contents of Gasolines
WIDESPREAD adoption of crude-oil cracking processes to provide an adequate supply of gasoline of high antiknock value has introduced the gum problem. The solution of this depends upon the development of a satisfactory method for determining the true gum-content of a fuel at the time of test and for predicting the content of a gasoline stored for a given time under specified conditions, and upon the correlation of data obtained by these methods with the results of engine tests.
Several methods proposed and used for determining the gum content of gasolines are described and data obtained by means of them are compared. Because published data from these methods do not establish that any of them or modifications of them are satisfactory and reproducible, the Bureau of Standards, with the cooperation of the Army Air Corps, undertook an investigation of test methods, as part of an extensive program for the study of the gumming characteristics of gasolines, with the purpose of applying to them a rational criterion for their accuracy and to amass further information regarding their reproducibility.
The paper is a report on this work. In the preliminary tests, data were secured by three methods on 20 gasolines and blends, and these data are compared, no relationship between the results being apparent. As time required for evaporation is a variable, tests were made with the air-jet method for accelerated evaporation and the comparative data are presented in tables and charts. Further tests were made with different volumes of gasoline and in inert atmospheres of carbon dioxide and nitrogen. More convenient apparatus for evaporating the samples under a nitrogen jet in a nitrogen oven is under construction.
The paper concludes with an analysis of the problem of determining the gum content of a gasoline and sets forth the three styles of a logical mode of attacking it.