Increasing knock detection sensitivity by combining knock sensor signal with a control oriented combustion model

Abstract

Knock phenomenon reduces the thermal efficiency and restricts performance improvement in spark-ignited engines. Reliable and rapid knock recognition is crucial for the engine knock control. Among the wide set of knock detection techniques, those based on in-cylinder pressure sensors provide the most precise recognition. However, pressure sensors are still affected by challenges such as durability and cost. For on-board applications, knock is usually detected by vibration signal, but the accuracy is limited due to natural vibration and external noises.In this paper, a novel knock recognition method based on knock sensor signal is proposed. The method consists of the comparison of a resonance index obtained through the knock sensor signal and a combustion model capable of estimating the fraction of mass burned, and thus being able to estimate if the amplitude in the knock sensor signal is produced by the auto-ignition of certain amount of fuel. The proposed method was compared with a fixed threshold for knock sensor resonance intensity, the improvements were quantified by using as reference a high sensitive knock recognition method based on cylinder pressure. Results show that the proposed method is able to improve the accuracy in over a 10 % of knock detection than using one set threshold over the entire cycle.