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Bridging the Knock Severity Gap to CFR Octane Rating Engines
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
It is widely acknowledged that the CFR octane rating engines are not representatively 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 prepared with varying composition, octane numbers and ethanol blend levels. The paper reports on the forth part of this study where cylinder pressures were recorded under standard knock conditions in the CFR engines under RON and MON conditions using the ASTM prescribed instrumentation. By the appropriate signal conditioning of the D1 detonation pick-up on the CFR engine, a quantification of the knock severity was achieved that matched that of a cylinder pressure transducer as well as exhibiting the same frequency response. The D1 signals were able to provide knock information far beyond merely the knock intensity readings and could rank the test fuels according to their real-world knock performance as measured in a single-cylinder research engine (SCRE). The paper suggests a pathway to combine standard octane ratings - needed to ensure backwards compatibility of measurement - with minor additional signal condition that will provide a forward-looking bridge between octane numbers and real-world knock severity.