FUEL ANTIKNOCK PERFORMANCE IN HIGH-COMPRESSION ENGINES

The trend toward motor fuels of higher antiknock quality and increased use of aromatic components from catalytic reforming prompted an investigation of the effects of Research and Motor octane numbers and composition on antiknock behavior in high-compression engines. Olefinic and aromatic blends covering a wide octane spread were knock-rated in the laboratory by a procedure designed to eliminate the abnormal ignition timing encountered when fuels are rated on the road.

Engine ratings approached or exceeded Research octane number as octane level increased, and decreased with increasing spread between Research and Motor octane numbers. Compression ratio had no effect on engine ratings, but combustion-chamber design apparently affected the performance of highly aromatic fuels. Ratings of all fuels decreased with increase in engine speed, but aromatic blends decreased much less than olefinic blends. Thus, information on composition as well as Research and Motor octane numbers is needed to predict fuel antiknock performance in high-compression engines.