Reconstruction of Pressure Signals on Structure-borne Sound for Knock Investigation

Knocking combustions decrease the efficiency of an SI engine and can cause damages in combustion chambers. The in-cylinder pressure signal provides an insight into the combustions. Due to cost and installation reasons, vibration signals are used for knock analysis in conventional engines; however, vibration signal analysis is less effective than pressure signal analysis. The aim of this paper is to approximate the pressure signal, which is more suitable for knock investigation, from structure-borne sound. Therefore, new models for pressure and vibration signals, related to each other, are presented. These models consist of constructional specific signal components and combustion specific random parameters. The signal components need to be determined only once for an engine by using ordinary mathematical tools. A least-squares method, applied on vibration signals, leads to estimates of the random parameters. With the knowledge of the signal components and the estimates of the random parameters, the pressure signal can be reconstructed. Furthermore, the described methods are applied on measured data.