IC-Engine Intake Acoustic Source Data from Non-Linear Simulations

Non-linear 1-D CFD time domain prediction codes are used to calculate the performance of the gas exchange process for IC-engines. These softwares give time-varying pressures and velocities in the exhaust and intake systems. They could therefore in principle be used to predict radiated orifice noise. However, the accuracy is not sufficient for them to be used as a virtual design tool. More accurate results might be provided by dividing the problem into a source domain and a transmission domain and use linear 3-D frequency domain codes to describe the transmission part. Radiated shell noise and frequency dependent damping could also be included in the frequency domain models. The simplest source model used in the low frequency plane wave range for simulation of dominating engine harmonics is the linear time invariant 1-port model. This acoustic source data is usually obtained from experimental tests where the multi-load methods and especially the two-load method are most commonly used. The main limitations of these tests are that they are time consuming, expensive and require physical hardware which prevents them from being used for early predictions. It would therefore be of interest to extract the acoustic source data from the existing 1-D CFD gas exchange models. This paper presents a comparison between acoustic source data, obtained applying the two-load technique to measurements on a six-cylinder personal car petrol engine, and to 1-D simulations of identical intake systems on the same engine. The degree of non-linearity in the results is discussed as well as the choice of source type and its relation to engine properties. The results show that it is possible to obtain reasonably accurate source strength as well as source impedance estimates, for the intake side, from 1-D gas exchange simulations.