Acoustic and fluid-dynamic characterization of state-of-the-art exhaust after-treatment systems.

Abstract

Continuously tightening pollutant and noise emission regulations have been the key motivation for engine -and engine related technology-research, development and optimization. Such trend gave rise to the gradual introduction of after-treatment systems to reduce pollutant emissions in automotive applications. However, in the last two decades the level of restrictions have made the use of after-treatment systems intensive and mandatory, evolving from small individual devices to very complex systems often including more than one device.Even though the main purpose of after-treatment systems is pollutant emissions abatement, they also exert a strong influence on wave dynamics, back-pressure and acoustic behaviour of the exhaust line, therefore changing the flow, acoustic and pressure characteristics of the exhaust flow. This in turn redefines the boundary conditions for the main silencing device (muffler) placed downstream. A better understanding of the sound attenuation and pressure drop due to the presence of after-treatment systems could have beneficial impacts, allowing the optimized design of the devices and the complete exhaust lines, especially the muffler. It was considered that a promising approach to reach a better understanding on the matter would be to account for the influence that usual components and characteristics of after-treatment systems have on their actual behaviour.Experimental and modelling approaches were used to study and characterize the acoustic and fluid-dynamic behavior of a diverse set of state-of-the-art after-treatment systems and devices, covering a wide range of elements and characteristics representative of after-treatment applications of commercial use. Transmission loss and pressure drop were selected as the key parameters to account for the sound attenuation and back-pressure generated by each device. Well established measurement facilities and procedures were used for the experimental characterization. In parallel, 1D, 3D CFD and even coupled 1D-3D simulation approaches on the basis of the "virtual twinning" concept were implemented on commercial software, aiming to replicate the experimental results in order to provide additional information and help deepen the understanding of internal phenomena, three-dimensional flow and acoustic effects. i Funding Acknowledgements This research has been funded by the Programa de Ayudas de Investigación y Desarrollo PAID-01-19, from Universitat Politècnica de València (UPV), which granted my pre-doctoral contract. xvi "Investigar es ver lo que todo el mundo ha visto, y pensar lo que nadie más ha pensado". "Research is to see what everybody else has seen, and to think what nobody else has thought". -Albert Szent-Györgyi xvii * Pressure drop measurements in the cold flow test bench. * Transmission loss measurements in the impulse test rig.