ASTM 909 Standard Test Method for Supercharge Rating of Spark-Ignition Aviation Gasoline
4. Summary of Test Method
4.1 The supercharge method rating of a fuel is determined by comparing the knock-limited power of the sample to those for bracketing blends of reference fuels under standard operating conditions. Testing is performed at fixed compression ratio by varying the intake manifold pressure and fuel flow rate, and measuring IMEP at a minimum of six points to define the mixture response curves, IMEP versus fuel-air ratio, for the sample and reference fuels. The knock-limited power for the sample is bracketed between those for two adjacent reference fuels, and the rating for the sample is calculated by interpolation of the IMEP at the fuel-air ratio which produces maximum power (IMEP) for the lower bracketing reference fuel.
5. Significance and Use
5.1 Supercharge method ratings can provide an indication of the rich-mixture antiknock performance of aviation gasoline in aviation piston engines.
5.2 Supercharge method ratings are used by petroleum refiners and marketers and in commerce as a primary specification measurement to ensure proper matching of fuel anti-knock quality and engine requirement.
5.3 Supercharge method ratings may be used by aviation engine and aircraft manufacturers as a specification measurement related to matching of fuels and engines.
6. Interferences
6.1 Precaution - Avoid exposure of sample fuels to sunlight or fluorescent lamp UV emissions to minimize induced chemical reactions that can affect octane number ratings.
6.1.1 Exposure of these fuels to UV wavelengths shorter than 550 nm for a short period of time can significantly affect octane number ratings.
6.2 Electrical power subject to transient voltage or frequency surges or distortion can alter CFR engine operating conditions or knock measuring instrumentation performance and thus affect the supercharge rating obtained for sample fuels.
