Standard Knock Intensity Revisited: Atypical Burn Rate Characteristics identified in the CFR Octane Rating Engine

The paper studied the burn rate of fuels in the CFR engine at standard knock intensity. Burn duration was found to increase with compression ratio, and knocking pressure traces exhibited a distinct change in slope, thought to be the onset of knock. A criterion was developed to identify this knock-point. The knock-point was related to the mass fraction bunt and it was found that the mass fraction burnt at the knock-point decreases as the compression ratio decreases, to as little as 30%. It is proposed that the nature of knock in the CFR engine is unique in that a large fraction of the trapped mass participates in the autoignition. The paper also presented a functional descriptor for the mass fraction burnt and illustrated the suitability thereof through the application in an engine model.