Abstract
Dynamic behavior of unburnt diesel sprays under no-evaporation and evaporation conditions were investigated by dual nano-spark shadowgraph photography method. This method enables obtaining two individual high definition shadowgraph images with short photographing interval. Details of temporal behavior can be obtained by comparing these two images. Image analysis was conducted by in-house developed image analysis algorism. As a first step, the raw image was converted into the image that emphasizes the degree of spatial fluctuation. This image shows obvious boundary of the evaporated fuel. This technic can extract not only the outer boundary in the diesel spray, but also the inner boundary between fluctuated region and high density region. In second step, the shapes of extracted boundary on the sprays photographed with certain time interval were compared and the movement of the boundary was calculated. Accordingly, this technic can extract the information of spray dynamic behavior about both of outer and inner boundary of diesel spray. In the present study, the following phenomena were observed. Air entrainment in upstream of the spray was observed only in no-evaporation condition. Spray tip in no-evaporation condition tended to penetrate parallel to the spray axis, instead of the spray tip in evaporation condition expanding wider angle to the axis. Inner core region of the spray moves faster than outer boundary movement.
