Experimental modeling of Wiener filters estimated on an operating diesel engine

• Wiener filters between cylinder and acoustic pressure are estimated on an operating diesel engine.
• Filters estimated in operation are compared to impact hammer tests.
• Two modal analysis techniques (LSCE and ESPRIT) are used to extract parameters.
• ESPRIT is implemented on transfer functions estimated on the operating and stopped engine.
• It is shown that the damping is overestimated at high rotational speed.

Sound source separation in diesel engines can be implemented using a Wiener filter, or spectrofilter, that can extract the combustion contribution in the overall noise. In this study this filter characterizes the transfer function between a cylinder pressure and a measurement point. An engine is characterized by several filters (one for each cylinder) which are estimated for many operating conditions (engine speed and load). The purpose of this work is to obtain an averaged spectrofilter allowing the synthesis of combustion noise in all operating conditions. This synthesis should be accurate enough to be used in perceptive studies. In order to refine the spectrofilter estimation in the medium frequency band, this paper consists in taking advantage of the multitude of information given by the estimations from different operating conditions. To do this, an experimental model is adopted so modal parameters are extracted from a great number of measured filters. Different procedures such as the ESPRIT method or the LSCE method (modal analysis) are used to decompose the impulse responses on a complex exponential basis. The spectrofilters estimated from different operating conditions are analyzed and compared in this reduced basis, in order to identify the underlying structural parameters. These parameters are compared to the results of an experimental characterization of the stopped engine. The accuracy of the synthesis (number of components of the filter) is an important issue because these filters will be used in perceptive applications, extracting combustion noises.This paper is an extended version of the work initially presented at the conference Surveillance 6 in November 2011 in Compiègne, France [1] (J. Drouet, Quentin Leclere, Etienne Parizet. Experimental modeling of Wiener filters estimated on an operating diesel engine, in: Proceedings of the Surveillance, vol. 6, Compi‘egne, France, 2011.).