Intake and exhaust system development is an important step in automotive design. The intake system must allow sufficient air to flow into the engine, and the exhaust system must allow exhaust gases to depart at the rear of the vehicle, without excessive pressure loss. These systems must also attenuate the acoustic pressure pulsations generated by the engine, such that the noise emitted from the intake and exhaust orifices is constrained within reasonable limits, and exhibits a sound quality in keeping with the brand and vehicle image. Pressure loss and orifice noise tend to be in conflict, so an appropriate trade-off must be sought. Simulation of both parameters allows intake and exhaust systems to be designed effectively, quickly, cheaply and promptly. Linear simulation approaches have been widely used for intake and exhaust acoustic prediction for many decades. The frequency domain characteristics of ducts and mufflers are extremely well established, and calculation times are very short. However, such simulations are only correct for small amplitudes, it is not straightforward to determine the source characteristics, and care is required to account for gas flow effects. Additionally, a separate simulation approach must be used to predict flow pressure loss. Recently, there have been developments in linear simulation approaches. The exact same intake and exhaust system model geometrical network can be used for both non-linear and linear simulations. Thus both linear acoustic and flow simulations are easy to formulate. Convenient tools are now available to characterise a non-linear engine representation as a linear acoustic source to excite a linear representation of intake or exhaust system. These developments eliminate many of the disadvantages of the linear simulation approach, and provide one key additional advantage: the engine manufacturer no longer needs to provide his confidential non-linear engine model to the intake and exhaust system suppliers. This paper illustrates and evaluates the process of developing exhaust acoustics using the improved linear simulation approach.
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