Certification of Exhaust System Components

Abstract

Various regulatory agencies have recognized the need for a reliable yet uncomplicated system of certifying and identifying exhaust systems and their elements with respect to noise control capability. Experts have cautioned that such a system could prove unworkable in view of the complex mix of exhaust gas parameters and system configurations which influence the installed attenuation of individual system elements. The present paper recognizes the potential importance of these complicating factors, yet advocates that a system of toleranced muffler class ratings (M.C. ratings) that take into account frequency selective properties and attenuation capability will yield performance predictions which will remain consistent from vehicle to vehicle. The approach advocated does not attempt to develop an engineering tool for manufacturers; rather, the objective is merely one of establishing comparative classification indices which permit the selection of equivalent replacement components. A parametric study on an exhaust flow simulator would model the exhaust in an increasingly sophisticated manner until the measured insertion loss matches that measured on a sample of real engines to within an acceptable statistical tolerance, thus providing a means of assessing the relative cost/effectiveness of an increasingly complex simulation facility. Once the standard insertion loss test facility is established, insertion loss characteristics for a respresentative sample of existing mufflers would be tabulated and statistically reduced to determine the M.C. contours. Regulation of the acceptable standard deviation from these contours would provide an additional means of quality assurance on muffler performance, discouraging mufflers with passbands or extremely narrow filter characteristics.