Knock Behavior of SI-Engines: Thermodynamic Analysis of Knock Onset Locations and Knock Intensities

A general definition and an index for the assessment of different engine knock behavior have been developed. The knock onset locations have been determined by piezoresistive pressure actuators and optical fiber probes in full load engine operation mode. The thermodynamic conditions at the knock onset locations have been quantified by CFD-calculations. Therefore the local fuel concentration, mixture temperature and residual gas concentration have been considered. These calculated thermodynamic conditions were further used to calculate the necessary volume of an exothermal center for the generation of the maximal measured pressure amplitudes.