Search Results

It is necessary to understand the entrainment process of ambient air into diesel sprays for the combustion process. This study focused on the entrainment process of non-combusting and combusting hydrogen jets instead of evaporated fuel sprays because of ease with measurement for fundamental research. Spatial and temporal changes of the air entrainment into the jets were obtained using flow visualization technique. The experimental results showed that the total air mass entrained into the flame jet is nearly equal to that into the cold jet. The rate of entrainment per unit area of the flame jet is smaller than that in the cold jet. When a transient jet is separated into side and front parts, the rate of air mass entrained from the front part of the jet decreases with time while the rate into the side of the jet per unit area is almost the same. The total air mass entrained into the jet can be approximately explained by the momentum theory.

A turbulent gas jet impinging on a flat wall was visualized by a laser sheet method. Velocity fields were determined from the images with a high speed video system by processing them in terms of the cross correlation method for the jet and particle tracking method for the ambient air from the same images. The vortex flow near the transient jet tip impinging on the wall was visualized and analyzed successfully. The velocity field obtained from the above methods was compared to that determined with a laser Doppler anemometer. The path line of a certain period which was taken with a CCD camera with controlled shutter was analyzed and the mean rate of air entrainment was determined quantitatively. The spatial and temporal change of the entrainment rate was estimated and it was found that the entrainment rate near the upstream part of the jet tip region is larger because of the vortex.