The engine models has been to represent the processes in the engine to be able to simulate its behaviour. Hence, different designs and components can be tested in a computer environment without the need for expensive prototypes and test cell hours. Moreover, a reliable simulation model allows for reduction of engine calibration time. With the introduction of modern control methodologies, models suitable for control design were needed. As opposed to models for pure simulation purposes, control-orieneted models have to be of limited complexity such that standard software packets can be used and the designed controller can be implemented in real-time. The parameterisation of variable geometry turbochargers for mean-value modeling is typically based on compressor and turbine flow and efficiency maps provided by the supplier. At low turbocharger speeds, and hence low air flows, the heat exchange via the turbocharger housing affects the temperature-based measurements of the efficiencies. Therefore, the low-speed operating regime of the turbocharger is excluded from the supplied maps and mean-value models mainly rely on extrapolation into this region. However, operation in this region is commonplace. Indeed operation seldom takes place outside this region. Section 1.1 looks at this issue in more detail.
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