Hybrid Approach to Predict Exhaust Noise of Naturally Aspirated Engine with Commercial Mufflers

In this paper, a hybrid approach is discussed. It combines the time-domain analysis of the non-linear, variable-geometry exhaust (or intake) source with the frequency-domain analysis of the muffler (or silencer) by means of a two-load method that evaluates the frequency-domain source characteristics making use of the time-domain model. The un-muffled exhaust noise is predicted by means of the commercial software AVL-BOOST and the muffled exhaust noise is then predicted by means of the source characteristics along with TMMP (the transfer matrix based muffler program) developed at the Facility for Research in Technical Acoustics (FRITA). This hybrid approach is applied to the naturally aspirated four-cylinder diesel engine. Comparisons have been made with the spectra of the measured values of exhaust noise and also with those predicted by AVL-BOOST, where available or applicable.