Modelling diesel engines with a variable-geometry turbocharger and exhaust gas recirculation by optimization of model parameters
for capturing non-linear system dynamics
A mean-value model of a diesel engine with a variable-geometry turbocharger
(VGT) and exhaust gas recirculation (EGR) is developed, parameterized, and
validated. The intended model applications are system analysis, simulation,
and development of model-based control systems. The goal is to construct a
model that describes the gas flow dynamics including the dynamics in the
manifold pressures, turbocharger, EGR, and actuators with few states in
order to obtain short simulation times. An investigation of model complexity
and descriptive capabilities is performed, resulting in a model that has
only eight states. A Simulink implementation including a complete set of
parameters of the model are available for download. To tune and validate the
model, stationary and dynamic measurements have been performed in an engine
laboratory. All the model parameters are estimated automatically using
weighted least-squares optimization and it is shown that it is important to
tune both the submodels and the complete model and not only the submodels or
not only the complete model. In static and dynamic validations of the entire
model, it is shown that the mean relative errors are 5.8 per cent or lower
for all measured variables. The validations also show that the proposed
model captures the system properties that are important for control design,
i.e. a non-minimum phase behaviour in the channel EGR valve to the intake
manifold pressure and a non-minimum phase behaviour, an overshoot, and a
sign reversal in the VGT to the compressor mass flow channel, as well as
couplings between channels.
Johan Wahlström and Lars Eriksson
Proceedings of the Institution of Mechanical Engineers, Part D, Journal of Automobile Engineering,
2011
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