G Index: A Novel Knock Detection Method that is Simpler and Calibration-Free, Based on Angular Position of Combustion Parameters

Stringent emission legislations have pushed engine operation to borderline knock. Knocking combustion limits engine efficiency, putting a threshold in carbon emission reduction that impairs further decarbonization of the transport sector. In this way, online knock monitoring is very important during engine development and calibration to allow operation with higher efficiency levels. Commonly, knock detection methods require complex calculations with high computational cost. Furthermore, these methods normally need previous calibration of a threshold value for each specific engine to indicate the knock limit, requiring important engineering resources and time. Hence, this paper proposes a novel methodology for knock detection that is simple, does not require prior calibration and can be used for sensorless knock detection. The method is applied by relating the crank angle of maximum pressure rise rate (AMPRR) with the angle of 50% of fuel mass burned (CA50), the so-called G Index (GI). The results were compared in respect to the ringing intensity methodology, showing good correlation in detecting knocking combustion. In general, the results showed that a negative average value means knock-free operation and a positive average value means a knocking combustion operating condition.