The primary objective of this thesis is to compare various Wiener filtering techniques documented in the literature for decomposing total engine noise into its combustion and mechanical components, as well as to introduce and evaluate an innovative methodology that combines aspects of the existing techniques. The Wiener filtering technique consists of a coherence method in which the in-cylinder pressure is taken as a reference for the combustion process. By analyzing the coherence between the in-cylinder pressure and the engine noise, the combustion contribution to the engine noise can be estimated. This study is conducted on an internal combustion diesel engine. A brief introduction to the combustion process and the engine noise contribution has been provided, including the use of in-cylinder pressure as a reference for assessing combustion noise.