Modeling of a turbocharged SI engine

Control Engineering Practice

2014

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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.

Section: Control Oriented Engine Modelmentioning

confidence: 99%

Co-surge in bi-turbo engines: Measurements, analysis and control

Control Engineering Practice

2014

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“…The modeling approach taken is the component based Mean Value Engine Model (MVEM) outlined in Eriksson et al (2002);Eriksson (2007). A complete turbocharged spark ignited engine with these components is implemented and evaluated in Andersson (2005).…”

Section: Engine Modelmentioning

confidence: 99%

Co-Surge Detection and Control for Bi-Turbo Engines with Experimental Evaluation

IFAC Proceedings Volumes

2013

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A V-type engine with a bi-turbocharger configuration utilizes the exhaust energy well which gives a fast torque response. An unwanted instability, called co-surge, can occur in such engines where the two interconnected compressors alternately go into flow reversals. If cosurge occurs, the control system must quell the oscillations with as little disturbance in engine torque as possible. A model of a bi-turbocharged engine is presented, combining a mean value engine model and a Moore-Greizer compressor model for surge. The model is validated against measurements on a vehicle dynamometer, showing that it captures the frequency and amplitude of the co-surge oscillation. The model is used to develop detection and control strategies for co-surge that rapidly returns the turbo to a stable operating point. Both simulations and experimental evaluation on the vehicle show that the developed strategies are successful in rapidly detecting and quelling co-surge. The selection of actuators is also studied. With no or small pressure drops over the throttle, it is necessary to use the bypass valves. However, for operating conditions with moderate and high pressure drops over the throttle, it is shown that it is sufficient to only open the throttle. This has the advantage, compared to opening the bypass valves, that it reduces the drop in boost pressure and thus reduces the drop in engine torque.

“…The modeling approach taken is the component based Mean Value Engine Model (MVEM) outlined in Eriksson et al (2002);Eriksson (2007). This uses control volumes, that contain states for pressure and temperature, and restrictions that govern the mass flow.…”

Section: Engine Modelmentioning

confidence: 99%

Modeling and Control of Co-Surge in Bi-Turbo Engines*

IFAC Proceedings Volumes

2011

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Abstract: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 MoreGreizer 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.