Visualization of Ambient Air Motion and Entrainment into a Transient Gas Jet Impinging on a Flat Wall

Ambient Air Entrainment into Transient Hydrogen Jet and its Flame Jet

For the study of the combustion in a transient gas jet used in gas diesel engines, it is very important to investigate the entrainment process of the surroundings of the jet. In this study, a path line method utilizing a CCD random shutter camera with various shutter times was applied. Large (40 μm), lightweight microballoon particles are used for scattering the path lines of the surroundings and fine particles (0.75 μm) are used for visualizing the approximate shape of the jet. The transient gas velocity was also measured with a two-component laser Doppler velocimeter (LDV). Consequently, (1) the jet configuration and the entrainment process could be visualized simultaneously, and (2) this path line method was found to be very useful for estimating the air mass entrained because of the good agreement with the values obtained using LDV.

Ambient Gas Entrainment into a Transient Gas Jet. (Visualization of Surrounding Air Motion and Estimation of Entrainment Amount by Path Line Method).

The purpose of this study is to clarify the jet tip velocity and mixing process between the jet and its surrounding fluid. The analysis was made with the time history of injection velocity which monotonously rises up just after the opening of injection valve and is steady later. The jet is injected into quiescent ambient air. The jet tip velocity first increases, then decreases, increases and last decreases with time lapses from injection. Therefore, the growing process of the jet is composed of four periods from the standpoint of the jet tip velocity. The jet tip velocity is maximum at the time boundary between the first and second growing periods, when the rate of increase of the injection velocity is maximum. The mixture between the jet and surrounding fluid is very active at this time. The growing period between the first period to the initiation of the fourth period corresponds to the unsteady period of injection velocity.

Tohru Sugita

Papers

Study on Characteristics of Transient Gas Jats. Jet Tip Velocity and Mixing Process in Front.