Evaluation of knock begin in spark ignition engines by least squares

In order to detect knock in spark ignition engines, usually structure-borne sound signals measured by acceleration sensors mounted on the engine housing are analyzed. However, the sound signal is distorted and disturbed, whereas expensive measuring of the in-cylinder pressure signal provides best information of combustions. Based on a vibration signal model, a least-squares method is applied to estimate the model parameters from structure-borne sound. Afterwards the estimated parameters can be used in an appendant in-cylinder pressure model for pressure approximation. For a good approximation of pressure signals it is essential to estimate accurately the starting time of knock, which is incapable of measurement. In this paper a theoretical evaluation of the estimated knock begin is provided. Additionally, a reference for the knock begin, based on the pressure model, is derived, such that an evaluation can be given for measured data.