Acoustic transfer function in gasoline engines

The structure of an engine plays a key role in its performance on various NVH benchmarks. Materials used to manufacture engine casing quantify noise emissions. Previous studies have pointed out towards the nonlinear and time variant nature of sound attenuation properties of an engine. This paper aims to investigate the sound transfer function of a medium stroke gasoline engine. Data was acquired from a gasoline engine test rig to study the relationship between in-cylinder pressure development and the resulting radiated noise. The spectrum of noise emissions acquired was compared with the spectrum of in-cylinder pressure developed using cepstrum analysis in order to obtain the transfer function. This function, which represents the structural attenuation of an engine, is mainly dependent on the shape of the combustion chamber, fuel injection parameters and material properties of the engine structure. The test engine was operated at various conditions to see effects on the acoustics transfer function. Variations in the sound pressure levels (SPL) of the transfer function were found to be almost the same, in spite of variations in engine testing conditions. The major novelty of the discussed methodology shows versatility of application of cepstrum analysis technique which has been previously used for non-intrusive fault diagnosis methodology.