Intake airflow characteristics are essential for the performance of diesel
engines. However, previous investigations of these airflow characteristics were
mostly performed on two-valve engines despite the difference between the airflow
of two-valve and four-valve engines. Therefore, in this study, particle image
velocimetry (PIV) investigations were performed on a four-valve diesel engine.
The investigations were conducted under different engine speeds and helical port
openings using a swirl control valve (SCV). The results suggest that the position
of the swirl center does not significantly shift with different engine speeds and
helical port openings, as the dynamics of the flow remained closely similar. The
trends of the airflow characteristics can be best observed during the compression
stroke. A higher engine speed increases the angular velocity of the engine more
compared to the increase of the airflow velocity and results in a lower swirl ratio
of the flow. On the other hand, a higher engine speed leads to a higher mean
velocity and the variation of velocity results in a larger turbulence intensity of the
flow. Increasing the helical port opening brings a reduction in the swirl ratio and
turbulence intensity as more airflow from the helical port disturbs the airflow from
the tangential port.
