Knock-limited spark angle setting by means of statistical or dynamic pressure based methods

In spark-ignition engines, knock is a very rigid constraint because it prevents the use of optimal spark timing and it limits the compression ratio and/or the boost pressure. Unfortunately, during engine development, it is not easy to detect the transition through borderline knock. Therefore, large ‘‘safety limits” could be adopted in spark timing setting. That penalizes the engine fuel conversion efficiency. This paper deals with the effectiveness of two knock quantification methods. Both methods are based on the analysis of the in cylinder pressure trace. The first method determines knocking combustions by means of a threshold value. This threshold is set by the statistical analysis of a knock-free engine operating point. The second method does not need any a priori threshold setting to distinguish knocking combustions from non-knocking combustions. It dynamically resolves the knock intensity of an engine cycle within the same cycle. Experimental analyses show that both methods are able to detect knock occurrence in spark-ignition engines. In particular, the dynamic method can be a simple and reliable tool useful for setting knocklimited spark angle during engine development.