Modeling of a Diesel Engine with VGT and EGR capturing Sign Reversal and Non-minimum Phase Behaviors
A mean value model of a diesel engine with VGT and EGR is developed
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 dynamics in the manifold
pressures, turbocharger, EGR, and actuators with few states in order
to have short simulation times. Therefore the model has only eight
states: intake and exhaust manifold pressures, oxygen mass fraction in
the intake and exhaust manifold, turbocharger speed, and three states
describing the actuator dynamics. The model is more complex than e.g.
the third order model in [12] that only describes the pressure and
turbocharger dynamics, but it is considerably less complex than a
GT-POWER model or a Ricardo WAVE model. Many models in the literature,
that approximately have the same complexity as the model proposed
here, use three states for each control volume in order to describe
the temperature dynamics. However, the model proposed here uses only
two states for each manifold. Model extensions are investigated
showing that inclusion of temperature states and pressure drop over
the intercooler only have minor effects on the dynamic behavior and
does not improve the model quality. Therefore, these extensions are
not included in the proposed model. Model equations and tuning methods
are described for each subsystem in the model. In order to have a low
number of tuning parameters, flows and efficiencies are modeled using
physical relationships and parametric models instead of look-up
tables. To tune and validate the model, stationary and dynamic
measurements have been performed in an engine laboratory at Scania CV
AB. Static and dynamic validations of the entire model using dynamic
experimental data show that the mean relative errors are 12.7 % or
lower for all measured variables. The validations also show that the
proposed model captures the essential system properties, i.e. a
non-minimum phase behavior in the channel EGR-valve to intake manifold
pressure and a non-minimum phase behavior, an overshoot, and a sign
reversal in the channel VGT to compressor mass flow.
Johan Wahlström and Lars Eriksson
2009
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Last updated: 2021-11-10
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