Assessment of the potential of a Wiener-Hilbert filter for automatic diagnosis of spark ignition engine faults

Abstract

In a spark ignition engine the time profiles of the pressures within the cylinders represent an ideal tool for detecting combustion anomalies. Unfortunately the pressure is not easily measurable outside a laboratory environment, so that simpler methodologies are most welcome. In a previous paper we proposed a methodology for obtaining the pressure profile by Wiener-Hilbert filtering the vibration signals which are easily measured in an industrial environment. In the present paper, after a brief résumé of the suggested procedure, we present the improvements introduced since then and report some results aimed at checking the validity of the method. In particular it has been found that the background may be measured with the engine running at minimum load and that the methodology can be applied to different engines and mountings. Moreover the pressure profile may be recovered either under cyclo-stationary conditions by varying the load, or under free acceleration running without any change in the engine status, so that the measurements can be performed in a few seconds. By switching from the time to the crank-shaft angular coordinate a single filter is sufficient to obtain the reconstructed pressure profile, whatever the engine angular speed. Thus the potential of the methodology as a manageable diagnostic tool is confirmed.