In order to evaluate different port concepts for modern Compression-Ignition engines, usually quantities as the swirl level and the flow coefficient are evaluated, which are measured on a stationary flow test bench. As additional criterion, in this work, the homogeneity of the swirl flow is introduced and defined quantitatively. Different valve lift strategies are evaluated using three-dimensional Particle Imaging Velocimetry in a stationary flow configuration and transient In-Cylinder CFD simulation using both the Reynolds Averaged Navier Stokes equation and the Large Eddy simulation approach.
1.5 2.0 PIV measurements of stationary intake port flow
both ports active - 1.6 mm valve lift tangential Port filling Port
Swirl Velocity Distribution RMS Velocity Fluctuation filling port deactivated - 3.2 mm valve lift Swirl Velocity Distribution RMS Velocity Fluctuation
CU C A 1.73 0.67
tivated 3.2 mm
3.94 3.79
Computational Setup
STAR-CD is used for the transient calculations of
the intake and compression stroke with moving
valves and piston. On the intake and exhaust port
flange positions, pressure boundary conditions
from GT-Power gas exchange calculations were
employed. The calculation were performed from
360°CA to 720°CA. Two different turbulence
models, the LES Smagorinsky [
in-cylinder flow field different cut sections perpendicular to the cylinder axis are considered. Each of the considered cut sections is divided into concentric rings, shown in Figure 4.
1 2 3 4 5 6
Simulation results using RANS and LES
– (1)
Swirl ratio incylinder Engine . (2)
valve lift and port strategies are shown in Figure 5. It can be seen that the in-cylinder swirl ratio can be increased to the same level either by reducing the maximum valve lift to 4.8mm or by port deactivation. 8.0 mm maximum valve lift 6.4 mm maximum valve lift 4.8 mm maximum valve lift 3.2 mm maximum valve lift
Filling port closed 9 8 7 -] 6 [ io 5 t ra 4 ilr 3 Sw2 1 0 360 tr pog esd in lo ll c i F
t m lif .48m lavve tr pog esd in lo ll c i F
t m lif .48m lavve 420
480 540 600 Crank angle [°CA ATDC] 660 720
Inhomogeneity of in-cylinder flow
Figure 6 compares the cut sections of the tangential velocity field of each strategy at the middle of the piston bowl which is simulated using the k-ε model in STAR-CD at 2280 rpm.
Using LES model
Tangential velocity [m/s]
no difference between the two cases in terms of predicting the in-homogeneity of the flow field.
the middle of the bowl is shown also in Figure 6 for the same valve lift strategies using the LES model. The LES turbulence model captures turbulent flow structures while in RANS only the mean flow is resolved.
field between these valve strategies can be distinguished using the LES turbulence model rather than the k-ε model. The investigations with the LES model show that the 4.8 mm valve lift produces more homogeneous swirl than port deactivation. This is also in agreement with experimental investigations at the 3D PIV flow test.
Summary and conclusions
valve lifts and with and without deactivated filling port were observed for a single-cylinder engine. Measurements on a stationary flow bench and CFD calculation both assessed the swirl level for the different concepts. While in particular a maximum valve lift of 4.8 mm for both intake ports produces the same swirl level as the maximum valve lift of 8 mm with the filling port deactivated, the soot emissions are significantly different and higher for the latter configuration
Therefore it was argued that next to the swirl ratio, another important parameter, describing these discrepancies, is required. An approach to evaluate the in-homogeneity of in-cylinder flow by means of PIV and CFD simulation was developed and presented. While in CFD, the RANS approach could not show visible differences in the inhomogeneity of in-cylinder flow, the LES approach in CFD and the 3D-PIV method showed differences between two cases in a way that the inhomogeneity in the case filling port closed is higher than a maximum valve lift of 4.8 mm for both valves.