Investigating the dynamic effects on flow structures generated during the intake stroke in heavy-duty diesel engines using Large Eddy Simulations
(English)Manuscript (preprint) (Other academic)
The aim of this work is to investigate whether a quasi-steady assumption is applicable for the flow entering a heavy-duty diesel engine. That is, what errors can be expected when a steady swirl test rig is used to characterize the flow structures entering the cylinder. The main conclusion is that the dynamic effects have an effect on the flow generated during intake.In detail, we show that the swirl coefficient is higher during fluid deceleration as compared to during fluid acceleration. The swirl coefficient was also found to be around 40~\% higher during valve closing as compared to similar lifts during valve opening. The flow of angular momentum into the cylinder is found to be delayed by the time it takes to empty the volume above the valves. A new ratio, port delay ratio (Rp), is proposed to account for this phenomena. Minimizing the port delay ratio during engine design is likely to lead to a stronger and more homogeneously distributed swirling motion.Taken together, the dynamic effects on swirl and mass flow expected during the intake have been investigated. This knowledge is important when measured mean swirl numbers are used as initial condition in sector model simulations of combustion. Sector model simulations are very common during the optimization process of diesel combustion and a small difference between real and simulated swirl numbers may have a significant effect on engine performance.
Fluid Mechanics and Acoustics Vehicle Engineering
IdentifiersURN: urn:nbn:se:kth:diva-164888OAI: oai:DiVA.org:kth-164888DiVA: diva2:806423
QS 20152015-04-202015-04-202015-04-20Bibliographically approved