Co-Surge in Bi-Turbo Engines - Measurements, Analysis and Control
In parallel turbocharged V-engines, with two separate air paths
connected before the throttle, an oscillation in the flow can occur.
If the compressor operates close to the surge line, typically during
low speed and high load, and a disturbance alters the mass flow
balance, the compressors can begin to alternately go into surge. This
phenomenon is called co-surge and is unwanted due to high noise and
risk for turbocharger destruction. Co-surge is measured on a test
vehicle in a chassis dynamometer and the system analyzed and modeled
using a mean value engine model. The investigation shows that the
alternating compressor speeds have an important role in the prolonged
oscillation. A~reconstruction of the negative flow from measurements
is made and compared to simulation results, showing similar
amplitudes, and supports the model validation. A new co-surge
detection algorithm is presented, suitable for a pair of sensors
measuring either mass flow, boost pressure or turbo speed in the two
air paths. Furthermore, a new controller is proposed that uses a
model based feedforward for the throttle, together with wastegate
actuation to force the compressor speeds together and improve balance
at the recovery point. This has shown to be sufficient with moderate
to high pressure ratios over the throttle, only for zero or very low
pressure drop the use of bypass valves are necessary. The advantage of
not opening the bypass valves is a smaller drop in boost pressure
which also reduces the torque disturbance. The performance of the
controller is evaluated both in simulation and in the test vehicle.
Andreas Thomasson and Lars Eriksson
Control Engineering Practice,
2014

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Last updated: 2021-11-10