A Study on the Impact of Corrosion under Insulation(CUI) on the Acoustic Performance of an Absorptive Muffler of Automobiles 2023-01-1087

One of the basic functions of an Exhaust system of an automobile is the attenuation of noise generated by the engine combustion and additionally the noise generated due to the flow of the exhaust gas through the various ducts and orifices in the Exhaust system. One of the solutions to mitigate the noise generated due to the latter is by means of an absorptive muffler comprising a fibrous acoustic medium, which helps to absorb noise of certain frequencies which are sensitive to the human ear. Typically, the construction of such a system consists of the fibrous acoustic medium encompassing a perforated inner pipe on the inside and enclosed by an outer metal case on the outside. The temperature limitations of the acoustic medium sometimes necessitate the placement of the fibrous acoustic system away from the engine source, in order to prevent any damage to the fibers upon direct contact with the exhaust gas. However, this results in a potential for condensation of Exhaust gas in and around the inner pipe – fibrous system interface leading to a corrosive environment.This eventually results in the formation of rust on the inner pipe, a condition commonly known as corrosion under insulation (CUI). The corrosion over a period of time causes deposits to generate on the perforations causing them to partially or fully close which subsequently results in the deterioration of the acoustic performance of the absorptive muffler. This paper deals with the various factors that promote CUI conditions in a typical absorptive muffler of an automobile, by means of a market case study. It also dwells on various guidelines for mitigating the impact of rust formation which can lead to noise deterioration, from both design and manufacturing perspectives.