Optimal stationary control of diesel engines using periodic control
Measurements and optimal control are used to study whether the fuel economy
of a diesel engine can be improved through periodic control of the
wastegate, illustrating how modern optimal control tools can be used to
identify non-trivial solutions that can improve performance. The
measurements show that the pumping torque of the engine is changed when the
wastegate is controlled in a periodic manner versus stationary even if the
mean position is the same. If this decreases the fuel consumption or not is
seen to be frequency and operating point dependent. The measurements
indicate that the phenomenon occurs in the time scales capturable by mean
value engine models (MVEM). The operating points are further analyzed using
a MVEM and optimal control. It is shown that whether the optimal solution
exhibits periodic oscillations or not is operating point dependent, but is
not due to the instantaneous nature of the controls. Even if an actuator
model is added the oscillations persist for reasonable time constants, the
frequency of the oscillations is however affected. Further it is shown that
the periodic control can be predicted by optimal periodic control theory and
that the frequency of the control affects the resulting efficiency.
Martin Sivertsson and Lars Eriksson
Proceedings of the Institution of Mechanical Engineers, Part D, Journal of Automobile Engineering,
2017
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