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
2015

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