An integrated numerical procedure has been developed in order to predict the noise radiation of small engine for automotive and general purpose applications.
In exhaust system of single or multi-cylinder small engine, complex shape elements are always included (junction, compact chamber), where non-planar higher-order modes exist. Besides, the amplitude of pressure wave, propagating inside such exhaust systems, is generally not bounded by linear acoustic limit.
For these reasons, aimed at providing realistic and accurate description of their fluid dynamic and acoustic behaviour, an integrated multi-code methodology, based on 0D, 1D and 3D models, has been set up; the investigation of the flow conditions all throughout the exhaust system, allows to predict the sound emission.
The developed approach retains the advantages of all methods: detailed information of flow behaviour as it is able to accurately predict, with the 3D scheme, the propagation of the pressure waves through complex elements, such as junctions, avoiding the significant limitations that a one-dimensional schematization always introduces, as well as fast processing typical of 1D and 0D schemes devoted to the analysis of ducts and volumes.
The multi-code method, set up and tested, has been applied on a typical small four stroke Diesel engine. The evaluation of the noise emission has been carried out and the results have been compared with experimental measurements.