CHAPTER 4 RESULTS AND DISCUSSIONS
4.2 Intake Flow Analysis
4.2.2 Tumble Plane Analysis
The RMS values at 40 mm downstream from the valve seat on the swirl plane sampled along a line (y=0) were plotted in Figure 4.11. Its value for both velocity components in the radial direction of the sampled plane showed variations. At 3 mm intake valve lift, the variation along the sampling line was not much for medium tumble but with more opening of the intake valves its magnitude and spatial fluctuation became high. On the other hand, medium swirl and high swirl inductions showed RMS values of u and v velocity components on the swirl plane that has higher values on one half of the cylinder and lower on the other half. The higher values were recorded on the side of the valve with the adjustable SCV, and lower values on the swirling core center region side. Flow RMS values are related with the velocity magnitude and the level of turbulence as well. Therefore, this flow analysis indicates that the turbulence level of the medium tumble induction is the maximum of all the three induction levels. Medium tumble induction might have the highest turbulence decomposition in the early stage of compression. The structure of the tumble flow can be susceptible for easy decomposition during compression. Arcoumanis et al. [71]
observed in their study of in-cylinder flow in a combined swirl/tumble induction that the tumble structure was broken down in 90o to 60o BTDC during compression process, whereas the swirl flow structure still existed at 20o BTDC. The works of [14]
and [40] also discussed on the higher rate of decomposition of the tumbling flow structure during compression process. Geometrically the cylindrical combustion chamber can be convenient for a swirling flow structure so that it can persist longer during compression process. Depending on the swirl strength and its compactness observed in the current study, the medium swirl could stay longer than the high swirl induction case that had weak periphery and elliptic swirling core. The nature of rate of decomposition for the high swirl seems to be in between the medium tumble and the medium swirl induction case.
rotational direction in all cases of valve opening as shown in Figure 4.12. The vortex core created by the tumble circulation seemed moving from the center of the cylinder axis at lower valve lifts towards the left side of the cylinder at the higher valve lifts.
At 3 mm valve lift more than one weak vortex cores were observed. The more the valve lift the lower the number of vortices and the stronger the circulation became.
This tumble flow structure can be easily disintegrated into smaller eddy sizes during compression process in the engine; similar observation was also reported by Heywood [14].
Figure 4.12 Streamlines (left) and vortex strength (right) of medium tumble induction on a tumble plane at 3 mm, 5 mm and 7 mm valve opening
The results of the flow analysis for both swirl and tumble planes were compared in Figure 4.13 to 4.15. The velocity profiles that are shown in Figure 4.13 indicate that the maximum velocity values were recorded in the tumble plane in all induction cases, and the medium tumble induction was the maximum of all. This was obvious that the mean bulk flow should be axially down in the cylinder. For medium tumble intake, Figure 4.13 (a), the velocity profiles for both planes were similar, whereas on the medium and high swirl inductions there was a swirling flow on the swirl plane (the horizontal plane of the cylinder) that could reduce the flow velocity on the tumble plane. That can be seen in Figure 4.13 (b) and (c). Up to a maximum of 3.5 m/s velocity was recorded on the tumble planes of medium swirl and high swirl, and up to 5 m/s for the medium tumble.
(a) (b)
(c)
Figure 4.13 The swirl and tumble velocity at 40 mm downstream in the cylinder extracted along a common line for both planes on the x-axis
0 1 2 3 4 5 6
-40 -30 -20 -10 0 10 20 30 40
Velocity [m/s]
Radial axis [mm]
U_tmb_MT U_swr_MT
0 0.5 1 1.5 2 2.5 3 3.5 4
-40 -30 -20 -10 0 10 20 30 40
Velocity [m/s]
Radial axis [mm]
U_tmb_MS U_swr_MS
0 0.5 1 1.5 2 2.5 3 3.5 4
-40 -30 -20 -10 0 10 20 30 40
Velocity [m/s]
Radial axis [mm]
U_tmb_HS U_swr_HS
(a) (b)
(c)
Figure 4.14 x-coordinate velocity component on both swirl and tumble planes
The x-axis is a common coordinate axis for both swirl and tumble measurement planes. Therefore, x-component of the average velocity on the swirl and tumble plane should be the same. This was shown in Figure 4.14. The discrepancy between u_swirl and u_tumble on all induction strategies seemed dependant on the uRMS values of both planes shown in Figure 4.15. Hence, the u velocity component for high swirl induction case (with lower RMS values of all induction cases) showed more similar velocity records on both swirl and tumble planes. Since the data acquisition took place at different time on the planes, there could be calibration and imaging errors too.
(a) (b)
Figure 4.15 u component RMS values for (a) swirl plane (b) tumble plane
-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5
-40 -30 -20 -10 0 10 20 30 40
Velocity [m/s]
X coordinate [mm]
u_tmb_MT u_swr_MT
-2 -1.5 -1 -0.5 0 0.5 1
-40 -30 -20 -10 0 10 20 30 40
Velocity, m/s
X coordinate, mm
u_tmb_MS u_swr_MS
-1.5 -1 -0.5 0 0.5 1 1.5 2
-40 -30 -20 -10 0 10 20 30 40
Velocity, [m/s]
X coordinate [mm]
u_tmb_HS u_swr_HS
0 0.5 1 1.5 2 2.5
-40 -30 -20 -10 0 10 20 30 40
u_rms [m/s]
x coordinate [mm]
u_rms,MT u_rms,MS u_rms,HS
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
-40 -30 -20 -10 0 10 20 30 40
u_rms [m/s]
Radial axis [mm]
u_rms,MT u_rms,MS u_rms,HS