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Effects of Pulsating Flow on Mass Flow Balance and Surge Margin in Parallel Turbocharged Engines

The paper extends a mean value model of a parallel tur- bocharged internal combustion engine with a crank angle resolved cylinder model. The result is a 0D engine model that includes the pulsating flow from the intake and exhaust valves. The model captures variations in turbo speed and pressure, and therefore variations in the compressor oper- ating point, during an engine cycle. The model is used to study the effect of the pulsating flow on mass flow balance and surge margin in parallel turbocharged engines, where two compressors are connected to a common intake mani- fold. This configuration is harder to control compared to single turbocharged systems, since the compressors inter- act and can work against each other, resulting in co-surge. Even with equal average compressor speed and flow, the en- gine pulsations introduce an oscillation in the turbo speeds and mass flow over the engine cycle. This simulation study use the developed model to investigates how the engine pulsations affect the in cycle variation in compressor op- erating point and the sensitivity to co-surge. It also shows how a short circuit pipe between the two exhaust manifolds could increase surge margin at the expense of less available turbine energy.

Andreas Thomasson and Lars Eriksson


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