The CFR test engine unit was modified by the use of a variable fuel needle jet, instead of the carburetor main jet of standard size (ASTM research and motor method), as well as by an additional heating system for the air/fuel mixture pre-heating device (ASTM motor method). This enables octane ratings of pure alcohols and gasoline-alcohol blends without changing engine operating conditions as specified by ASTM. The applicability of the newly developed supplementary devices was verified and found appropriate by the members of a FAM Task Group, organized within the German Institute for Standardization (DIN).
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I. Hunwartzen (1982) studied this question.