Question

How does turbulent intensity change according to 4 stroke engine’s cycle? What are some bulk motion you can do to increase the turbulent intensity?

Answer 1

in-cylinder flow transition and turbulence characteristics near the spark location
during compression stroke were measured and evaluated by using particle image velocimetry (PIV)
and laser Doppler anemometry (LDV) in order to understand the generation of in-cylinder bulk flow
during the intake stroke, cascade transition during compression stroke and optimize turbulence flow
field at ignition timing. Spatial distribution of in-cylinder flow characteristics were evaluated by
PIV and time-frequency analysis of flow at local point was made by LDV. Two dimensional
velocity distribution and qualitative turbulent distribution are obtained from PIV measurement. the other hand, time series velocity fluctuation and qualitative turbulent intensity at local point are
obtained from LDV measurement. Both techniques are used to evaluate the balk flow inside the
cylinder and turbulent characteristics around the spark location. The following conclusions can be
drawn:
1) The velocity and turbulent intensity distribution inside the pent roof were measured by PIV. The
in-cylinder flow field near the spark location during the compression stroke was obtained.
2) The PIV results were compared to LDV measurement results. The tendency of the time change
of velocity and turbulent intensity measured by PIV were agree with that measured by LDV.
Therefore, the flow and turbulent field can be evaluated qualitatively by PIV.
3) The turbulent intensity near the spark location was measured by LDV. During the compression
stroke, the turbulent intensity increased the near the TDC due to the tumble flow collapse by
cascade transition of turbulent. The turbulent intensity was higher for high engine speed condition
because the higher bulk flow velocity had the higher potential to generate the turbulence.
4) Combination of PIV and LDV enables to evaluate time change of in-cylinder flow, distribution
of qualitative turbulent intensity and quantitative evaluation of turbulence intensity and scale at
local point. These data are valuable for engine design (such as intake port, piston, and intake valves),
control optimization and CAE validation.