Effect of Humidity and Air Temperature on Octane Numbers of Secondary Detonation-Standards 310022

AFTER stating briefly the requirements that reference fuels used in determining the detonation values of test fuels should meet, the tests conducted by the Bureau of Standards to ascertain the effect that atmospheric conditions have upon the relations between the primary scale and each of a number of secondary detonation-standards are described. All tests were made with a Cooperative Fuel-Research engine having a 6:1 compression-ratio L-head. Varying the throttle opening gave the desired intensity of detonation, which was estimated by the bouncing-pin apparatus. Air-conditioning apparatus, used in previous tests, controlled the air temperature and humidity.
Four sets of secondary standards, (α) Michigan gasoline to which tetraethyl lead and benzol were added, (b) Cabin Creek gasoline with similar additions, (c) heptane plus benzene and (d) Texas Spirits plus California aviation gasoline, were compared at a number of compositions with the primary-standard scale, iso-octane and normal heptane. The results of these comparisons are presented graphically and in tables.
While the effect of air temperature was investigated on only two secondary-scales-Michigan gasoline and Texas Spirits-California aviation gasoline-the effect is inferred for the Cabin Creek gasoline plus benzol and heptane plus benzene secondary-scales, since the principal effect noted is attributable to the decreased antiknock value of benzol at higher temperatures. In the case of the first three secondary-standards investigated, normal variations in atmospheric humidity had no appreciable effect on the relation between the primary and secondary scales. Humidity had a large effect on the last secondary-scale and an apparent one on the two constituents, Texas Spirits and California aviation gasoline, hence the effect of atmospheric conditions on any materials intended for use as secondary-standard detonation-scales should be studied.


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