Separation of Combustion and Mechanical Noise Using Wiener Filter

The objective of this paper is to develop a robust methodology to study internal combustion (IC) engine block vibrations and to quantify the contribution of combustion pressure loads and inertial loads (mechanical loads) in overall vibration levels. An established technique for noise separation that, until recently, has not been applied to engine noise is Wiener filtering. In this paper, the harmonic part of the overall vibration response of the IC engine block is removed, resulting in a residual broadband response which is uncorrelated to the source signal. This residue of the response signal and the similarly calculated residue of the combustion pressure represent the dynamic portion of their respective raw signals for that specific operating condition (engine speed and load). The dynamic portion of the combustion pressure is assumed to be correlated only to the combustion event. A relation (frequency response function) between the source signal and residual broadband response of the block is developed for each cylinder pressure source signal. This relation is defined as the Wiener filter. The Wiener filter is then multiplied by the raw cylinder pressure signals to obtain the vibration of the engine block due to the combustion contribution. Finally, the engine vibration due to the mechanical sources is obtained using the difference of the raw block vibration and the combustion contribution. It is imperative that a condition-specific filter is computed in order to analyze the response signal at a specific operating condition.

This paper successfully demonstrates the process of developing a Wiener filter for a three-cylinder IC engine and identifying the partial contribution of combustion and mechanical excitation in the overall vibration response of the IC engine block. This study is not extended to the contribution analysis for the response due to the sound pressure generated by the engine although it is conceptually possible.