Knock thresholds and stochastic performance predictions: An experimental validation study 2019-01-1168
Knock control systems are fundamentally stochastic, regulating some aspect of the distribution from which observed knock intensities are drawn. Typically a simple threshold is applied, and the controller regulates the resultant knock event rate. Recent work suggests that the choice of threshold can have a significant impact on closed loop performance, but to date such studies have been performed only in simulation. Rigorous assessment of closed loop performance is also a challenging topic in its own right because response trajectories depend on the random arrival of knock events. The results therefore vary from one experiment to the next, even under identical operating conditions. To address this issue, stochastic simulation methods have been developed which aim to predict the expected statistics of the closed loop response, but again these have not been validated experimentally. The aim of this paper is therefore to investigate experimentally the effect of using two different knock thresholds, and to validate, to the extent possible, stochastic predictions for their closed-loop performance.
The paper is organized as follows. Experimental details are presented in Section 2. In Section 3, open loop spark sweep tests are used to estimate the knock characteristics of the engine which are needed for subsequent simulation work. The choice of knock threshold is discussed in Section 4, and several new robustness-related issues are highlighted. Closed loop steady state and transient results are presented in Section 5. The stochastic simulation method is described in Section 6 and used both to compare the performance of the controller with different knock thresholds, and to validate the simulation technique itself against experimental data. Finally, brief conclusions are given in Section 7.
Saeed Shayestehmanesh, Zhe Wang, James C. Peyton Jones, Robert Prucka
Villanova University, Clemson University