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Cetane Rating of Diesel Fuels
ISSN: 0148-7191, e-ISSN: 2688-3627
Published January 01, 1936 by SAE International in United States
Annotation ability available
IN the testing method described in this paper the moment of ignition is determined by a mechanism consisting of a diaphragm in the cylinder head, a phonograph “pick-up,” a short stiff wire transmitting the motion of the diaphragm to the pick-up, a thyratron relay, and a neon lamp protractor. When ignition occurs in the cylinder the flexing velocity of the diaphragm is sufficiently high so that the voltage generated in the coil of the pick-up trips the thyratron tube and permits a high-tension condenser discharge to be sent through the neon lamp which by its flashes then indicates the time of ignition.
Because of the absence of friction and arcing the action of the pick-up is more regular than that of a bouncing pin. A similar pick-up is used for indicating injection timing. Using this apparatus and the “fixed-ignition-lag method” the Diesel fuel testing in the C.F.R. engine has been so simplified that seven to eight fuels can be tested in an hour with a high degree of reproducibility.
Empirical ratings such as Aniline Point, Diesel Index, Viscosity-Gravity Index and Viscosity-Slope Index were applied to 19 fuels and none of them was found to offer a perfect substitute for engine testing. Some can, however, be recommended for approximate rating.
Combustion knock was found to decrease only slightly when the cetane number of the fuel exceeds 55. Cathode-ray oscillograms would indicate that the knock follows the maximum rate of pressure rise more than the ignition lag.