Towards understanding the effect of compression on swirl and tumble in the context of turbulence and mixing
(English)Manuscript (preprint) (Other academic)
The rotational motions of different strength and tilt angles in a generic heavy duty Diesel engine during compression are investigated using Large Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) decreases whereas the effect of tumble breakdown increases with the tumble number. For rotational motions with similar BDC tumble numbers the presence of swirl has a dampening effect on peak turbulence during compression but not on turbulence level at TDC.In detail, we show that peak turbulence levels are strongly affected by BDC tumble number, while a local maximum turbulence level at TDC was found for a tilted rotational motion with a tilt angle of 61 deg and BDC tumble number of 0.9. The effect of tilt and BDC total kinetic energy on TDC total kinetic energy and mixing is presented. It is observed that a small tilt angle is necessary in order to obtain a radially stratified mixture, e.g. stratified EGR.The combined effect of a rotational strength and tilt on turbulence and mixing during compression is investigated. This knowledge is important both for a better theoretical understanding of the compression process, and for engine development.
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-164886OAI: oai:DiVA.org:kth-164886DiVA: diva2:806422
QS 20152015-04-202015-04-202015-04-20Bibliographically approved