Abstract
The effects of valve strokes on the spray shapes of a GDI injector with six holes were studied. Two kinds of strokes that change the shapes to be either cone-shaped or bell-shaped were selected to investigate the flow characteristics that caused the shapes to change. Fuel-spray behaviors were first observed with an experimental setup; strokes of 100 percent (full stroke) and 26 percent were selected assuming the multiple injection of fuel. The 26 percent stoke was selected as a representative example of narrow stroke. To investigate the flow characteristics that caused the cone and bell shapes, computational fluid simulation was applied to study the fluid flows around the holes and sprays in the air region. It was found that the stroke of 26 percent formed a narrow space upstream of the hole inlets, so the velocity component in the radial direction at the hole inlets increased. The velocity component in the radial direction also increased at the hole outlets, so each spray plume became wider and the spaces between the plumes narrower. Due to the narrower spaces, the mixture of the plumes caused the spray to become bell-shaped. The velocity component in the radial direction at the hole outlets was an important factor that determined the spray shape in the air region.
