Improved Parametric Expressions for Acoustic Source Strength Level and Impedance of Turbocharged Diesel Engine Exhaust System

The present article aims at a possible integration of design of an engine with the muffler to ensure adequate overall insertion loss (IL) of the muffler. Acoustic source characteristics of the engine exhaust system of turbocharged diesel generator (DG) sets running at a fixed shaft speed are estimated using a recently developed novel direct evaluation method. Each cylinder of a multi-cylinder engine is modelled individually as an acoustic source, which allows estimation of the source characteristics for different arrangements of exhaust runners. Parametric expressions of the acoustic source strength level (SSL) and the internal impedance of each cylinder are proposed for full load condition of a 4-cylinder and a 6-cylinder turbocharged (TC) engines. Using the appropriate transfer and combination of source strength level (with proper phase) and source impedance, source characteristics of the complete engine are computed. These source characteristics are used to predict the unmuffled exhaust SPL spectrum which compares well with the measured spectrum. The methodology described here for the DG set engines can be readily extended to automotive engines.