Importance of mixture ratio in rating fuels for knock

Abstract

It is shown that the knock rating of the one fuel with respect to another may depend upon the carburetor setting at which the comparison is made. The influence of mixture strength is often so large that, unless careful attention is given to this factor during knock measurements, it is possible to obtain widely discordant results in spite of what may otherwise be the best of experimental technic.

If knock ratings of some fuels made by different laboratories are to be comparable, the different experimenters must agree upon some general specification as to the mixture ratio at which the measurements shall be made. Because it is both the point of highest intensity and one that can be located readily, it is proposed that knock measurements be made independently for each fuel at the mixture ratio giving its maximum degree of knock.