Abstract
The identification of source characteristics, commonly characterized as the source strength and source impedance, is essential for predicting the acoustic performance of an internal combustion (IC) engine exhaust system. This study contributes to a theoretical analysis of the effect of the acoustic parameters of loads (i.e., four-pole parameters, load impedance, and radiation impedance of the tailpipe) on the identification error of the source characteristics for an IC engine. A model based on the linear time-invariant hypothesis was constructed. A dispersion estimation function of the source strength and a deviation estimation function of the source impedance were established as indicators to test the identification accuracy. A three-dimensional (3D) multifield coupling numerical simulation method, which can thoroughly consider the influences of airflow and temperature, was applied to obtain the acoustic parameters of loads and compare them with those obtained by a one-dimensional (1D) analytical method. Then, the acoustic parameters of loads and the radiated sound pressure level of the tailpipe obtained in the measurement were substituted into the source characteristics identification model. Based on the analysis and calculation, the estimated error of the source characteristics acquired by using the 3D numerical simulation method is significantly lower than that by using the 1D analytical method. Moreover, the experiment and the 3D multifield coupling numerical simulation method were used to verify the identification results of the engine source characteristics. The results show that the far-field sound pressure level of the tailpipe predicted via the 3D numerical simulation method agrees well with the experimental results, indicating that accurate acoustic parameters of loads can effectively improve the source identification accuracy for an IC engine.
Highlights
An exhaust system is an essential component of an internal combustion (IC) engine; the exhaust system controls the noise of exhaust, thereby reducing the environmental noise pollution of motor vehicles, and adjusts the exhaust noise quality to meet human hearing requirements
When an engine exhaust system is assumed to have linear and time-invariant characteristics, the characteristics of the engine can be simplified into an equivalent acoustic source, which can be represented by the source strength PE and source impedance ZE
This study aims to investigate the effects of the acoustic parameters of loads on the identification of source characteristics
Summary
An exhaust system is an essential component of an internal combustion (IC) engine; the exhaust system controls the noise of exhaust, thereby reducing the environmental noise pollution of motor vehicles, and adjusts the exhaust noise quality to meet human hearing requirements. Increasing the number of acoustic loads and choosing an appropriate identification algorithm, such as the multiload method, can effectively improve the calculation accuracy of engine source characteristics [14]. Zheng et al [15] analyzed the load selection effect on the identification error of engine source characteristics based on a theoretical error analysis and proposed practical rules for selecting loads that can improve the source characteristics accuracy for an IC engine and reduce the required number of loads used in the measurement. For the identification of loudspeaker, compressor, and other sound source characteristics, the calculation of the acoustic parameters of loads by using the 1D analytical method generally does not cause large errors. THEORETICAL MODEL FOR SOURCE CHARACTERISTICS IDENTIFICATION A linear time-invariant model assumes that engine exhaust noise is produced in a steady state as a linear system and simplifies the entire engine into a black box with stable source characteristic parameters
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