Bridging the Knock Severity Gap to CFR Octane Rating Engines

It is widely acknowledged that the CFR octane rating engines are not representative of modern engines and that there is a gap in the quantification of knock severity between the two engine types. As part of a comprehensive study of the autoignition of different fuels in both the CFR octane rating engines and a modern, direct injection, turbocharged spark-ignited engine, a series of fuel blends were tested with varying composition, octane numbers and ethanol blend levels. The paper reports on the fourth part of this study where cylinder pressures were recorded under standard knock conditions in CFR engines under RON and MON conditions using the ASTM prescribed instrumentation. By the appropriate signal conditioning of the D1 detonation pickups on the CFR engines, a quantification of the knock severity was possible that had the same frequency response as a cylinder pressure transducer. The D1 signals were able to provide knock information far beyond the ASTM knock intensity readings and could rank the test fuels according to their expected real-world knock performance as measured by the magnitude of pressure oscillations. The paper suggests a pathway to combine standard octane ratings - needed to ensure backward compatibility of measurement - with minor additi0onal signal conditioning that will provide a forward-looking bridge between octane number tests and real-world knock severity.