Time and frequency domain modelling of vehicle intake and exhaust systems

A method is described for the computer prediction of the noise radiating from vehicle intake and exhaust systems when mounted to a given IC engine undergoing normal operation. A new methodology has been developed which couples a time domain treatment of the in-cylinder combustion and gas flows through the valves, with a frequency domain analysis of the acoustic characteristics of the intake and exhaust systems. In this way, robust predictions of the noise radiated have been made and compared favourably with measurement. Full consideration has been made of the thermo-chemical operation of spark ignition engines. A simple combustion model has been implemented, along with suitable treatment of the heat flux throughout the engine. Every effort has been made, through the use of appropriate assumptions, to keep computational requirements to a minimum. The resulting computer software, written in FORTRAN, runs efficiently on an IBM PC and has demonstrated run times significantly lower than other competitor codes, without apparent loss of integrity.