Influence of a High-Swirling Helical Port with Axisymmetric Piston Bowls on In-Cylinder Flow in a Small Diesel Engine

摘要

This paper deals with a numerical investigation on swirl generation by a helical intake port and its effects on in-cylinder flow characteristics with axisymmetric piston bowls in a small four-valve direct injection diesel engine. The novelty of this study is in determining the appropriate design and orientation of the helical port to generate high swirl. A commercial CFD software STAR-CD is used to perform the detailed three dimensional simulations. Preliminary studies were carried out at steady state conditions with the helical port which demonstrated a good swirl potential and the CFD predictions were found to have reasonably good agreement with the experimental data taken from literature. For transient cold flow simulations, the STAR-CD code was validated with Laser Doppler Velocimetry (LDV) experimental velocity components’ measurements available in literature. Influence of helical port geometry and the effects of port orientation on swirl ratio were then investigated to identify the configuration generating highest swirl. From the five helical port designs, the port design - 1 oriented tangentially to the cylinder wall produced the highest swirl ratio. With this high swirling helical intake port configuration, a directed intake port was incorporated and further analysis has been carried out with three piston bowl shapes namely flat, toroidal and re-entrant bowls. Results indicated that the intensification of swirl and turbulence are higher in case of re-entrant piston bowl followed by toroidal and flat bowl. Further, the increase in engine speed resulted in an overall reduction of the temporal variation of swirl ratio irrespective of the piston bowl shape. From this study, it was concluded that for high swirl and turbulence requirements, the combination of helical port design - 1 with re-entrant bowl piston configuration is most ideal.