Comparison of Methods of Measuring Knock Characteristics of Fuels 280008
NINE laboratories employing widely different methods have cooperated in the measurement of the knock characteristics of five selected motor fuels. Considerable divergencies are reported in the results obtained by different methods, particularly for certain fuels, although there is reasonable agreement for other fuels. Laboratories using the “bouncing-pin” method have shown consistent results among themselves. No system of rating the knock characteristics of fuels is in use at present by which the results of different laboratories are readily comparable. An analysis of the data obtained from the nine laboratories is included herein, and possible reasons for the divergencies are discussed.
First reviewing the circumstances that led to the investigation reported in his paper, the author names the laboratories which cooperated, describes the sample fuels and how they were prepared, and outlines the method or methods practised by each laboratory and the equipment used. The experimental results are tabulated and are presented also in the form of curves to make their meaning clearer, the coordinates being chosen so that the difference between fuels Nos. 1J and 5J equals 100.
In his general discussion of the results, the author points out that two distinct problems are involved in the data he presents. The first is the rating of fuels in terms of the quantity of tetraethyl lead needed to make the fuels equal to a standard better than they are. This is an important problem but it is not an actual rating of the fuels themselves, since two fuels requiring the same amount of tetraethyl lead to make them equal a certain standard may not be themselves exactly equal, though they are probably nearly equal to each other. The second problem is the rating of the fuels themselves in terms of some other standard fuel to which an antiknock or benzol has been added, or in some arbitrary system. This point is illustrated by the data from the Bureau of Standards, in which fuels Nos. 2J and 4J2 require the same amount of tetraethyl lead to make them equal fuel No. 5J, but their ratings are 94 and 97 respectively on the maximum power scale. For this reason the two sets of data are considered separately.