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    Methods for Reducing the Effect of Barometric Pressure in Measurement of Octane Number

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    Knock ratings made by the ASTM Motor, Research, and Aviation methods are affected by barometric pressure. Earlier experiments made at the National Bureau of Standards (1, 2) established the magnitude of rating variations in the pressure range of 21.0 to 30.0 in. of mercury, and indicated that some means of resolving the effect of barometric pressure on octane rating was needed. As a result of the earlier findings, pressurized induction and exhaust systems were tested in the altitude-chamber tests herein reported. While these schemes apparently would solve the problem, they were also beset with mechanical and operating difficulties. This prompted a third series of altitude chamber tests, in which inlet temperature and compression ratio were adjusted in combination to produce more uniform compression temperature-density relationships regardless of barometric pressure. The final results are presented in the form of tables of empirically determined operating conditions that will lead to substantially the same octane number when operated at any atmospheric pressure between 21.0 and 30.5 in. of mercury absolute.

    Author Information:

    Siegel, Bruno R.
    Guest worker, National Bureau of StandardsSinclair Research Laboratories, Inc., Harvey, Ill.

    Committee/Subcommittee: D02.01

    DOI: 10.1520/STP46848S