Exhaust pressure modelling for feedforward active control of internal combustion engine exhaust noise

This paper reports work on modelling the exhaust noise pressure of a small single-cylinder spark ignition (SI) engine. The model will ultimately be used for on-line prediction of exhaust noise in an active control system with a single-error microphone. The frequency properties of the engine exhaust noise generated by this SI engine are characterized by harmonic components related to engine firing conditions. The frequencies of the harmonic components depend only on the engine firing frequency while the amplitudes of the harmonic components vary with the engine load. Twenty harmonic components at the lower frequency band were included to model the exhaust pressure pulse which is a two-dimensional function of engine speed and load. The model is represented by a double Chebyshev polynomial. The instantaneous exhaust pressure at steady state for a fixed position in the exhaust pipe was predicted using this model and compared with the experimental data. The result of this comparison is regarded as satisfactory.