Experimental assessment of emission models used for IC engine exhaust noise prediction

One of the worst known factors in exhaust noise prediction is the emission model used, which always sheds some additional uncertainty on the results, thus complicating the interpretation of comparisons between measurement and modelling. In this paper, an evaluation of usual emission models has been performed, based on the estimation of the volume velocity fluctuation at the open end from instantaneous in-duct pressure measurement at points relatively close to the tailpipe exit. The experimental set-up used and the complementary measurements performed are described, and comments on the quality of the results obtained and an evaluation of the difficulties found are given. Directional effects are studied, the results indicating that they are highly dependent on the emission conditions. An extensive discussion of the accuracy of the emission model and its relation with the influence of inflow at low engine speeds is provided.

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