Prediction of source characteristics of engine exhaust manifolds

Abstract

Engine exhaust noise source is often described in frequency domain by the impedance and strength of an equivalent acoustic one-port source at a reference plane downstream of the exhaust manifold. These parameters can be measured by experimental methods, however, it is also desirable to develop methods for their prediction. A pre-requisite for the prediction of the equivalent one-port acoustic source parameters of an engine manifold is a linear mathematical model of the breathing noise generation mechanism at the valves. The present paper proposes new mathematical models for this source mechanism and the prediction of the one-port source characteristics of engine exhaust noise. The analysis is based on basic fluid dynamic equations for inviscid one-dimensional flow and encompasses both linear time-invariant, linear time-variant and non-linear one-port source models. A systematic procedure is presented for the calculation of one-port source characteristics of engine manifolds, with an application to a 4 cylinder engine exhaust manifold. The theory of the paper is applicable, with almost no modification, also to the prediction of one-port source characteristics of engine intake noise and the pressure fluctuations associated with discharge and suction processes in compressors.