A critical analysis of classical severity-based knock control strategies

Abstract

A common variant of classical knock control strategies replaces fixed magnitude control moves with control actions that depend on the knock severity of the prior cycle. Though appealing to notions of proportional control, it is unclear whether such strategies offer benefit given the random nature of knock events. In this paper a new generalized event-based framework is developed and used to extend both time domain simulation and stochastic analysis methods for analyzing the closed loop behavior of such systems. These tools are then used to perform a rigorous analysis and comparison between standard advance-retard and severity-based control strategies. The analysis is also repeated using a lower knock threshold definition. The results show that the performance of severity-based knock control differs minimally from a similarly tuned standard advance-retard controller, and there is little benefit to recompense the additional complexity of severity-based control.