Modeling and Control of Co-Surge in Bi-Turbo Engines
Using a bi-turbocharged configuration makes for better utilization of the exhaust energy and a
faster torque response in V-type engines. A special surge phenomenon that should be avoided
in bi-turbocharged engines is co-surge, which is when the two interconnected compressors
alternately go into flow reversals. If co-surge should occur, the control system must be able
to quell the oscillations with as little disturbance in torque as possible. This paper presents a
model of a bi-turbocharged engine based on a Mean Value Engine Model that includes a More-
Greizer compressor model for surge. The model is validated against measured data showing that
it captures the frequency and amplitude of the co-surge oscillation. The effect of momentum
conservation in the pipes is investigated by adding this feature to the control volumes before
and after the compressor. This gives a slightly better mass flow shape with the drawback of
increased simulation time, due to more states and a higher frequency content in the model.
A sensitivity analysis is performed to investigate which model parameters have most influence
on the co-surge behavior. It is shown that the largest influence comes from the turbocharger
inertia, the volumes after the compressor and the "zero mass flow pressure ratio" during flow
reversal in the compressor. The model is used to investigate principles for control strategies to
detect and quell co-surge. The detection algorithm is evaluated on measured data.
Andreas Thomasson and Lars Eriksson
2011
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