Approximate empirical expressions for the aeroacoustic source strength level of the exhaust system of compression ignition engines

Abstract

Prediction of the un-muffled or muffled noise from internal combustion engines requires knowledge of the acoustic performance of the muffling system together with the engine source characteristics. The pressure time history downstream of the exhaust manifold or turbocharger is computed by means of a time-domain finite-volume numerical software. From this pressure time history, the electro-acoustic analogue source characteristics i.e. p_s and Z_s are determined indirectly using a multi-load method. This investigation has been conducted for both naturally aspirated and turbocharged diesel engines. Using this methodology and the resultant empirical relations one can analyze any compression-ignition IC-engine configuration for the prediction of the un-muffled noise without having to carry out the time-domain simulation of the exhaust source. The goal of this work is to parameterize the source characteristics of an engine in terms of basic engine parameters, so that a first assessment of the un-muffled noise can be made before a detailed design is taken up. Though this empirical approach may not be able to predict actual noise spectra precisely, yet this serves a useful purpose. One of the results has also been corroborated with the measured value in order to validate the methodology presented here.