PURPOSE: To prevent the liquefaction due to the collision of injected mists with a wall surface by intermittently feeding air for fine atomization and constituting a valve body and a valve seat so that the Coanda effect acts and reducing the penetration force of the injected mist according to the angle of the valve seat and the installation position.

CONSTITUTION: A unidirectional valve 19 is installed on a wall surface 24, and the injection length X after the lapse of a certain time after injection is measured. (h) is the position of the top edge of the valve 19 and the wall surface 24, and positive in the state where the top edge of the valve 19 projects from the wall surface, while negative when the top edge is recessed from the wall surface. When (h) is within ±0.8m the injected mist flows along the wall surface 24, and X reduces, and since the injected mists contact the wall surface 24, the injected mists are liquefied, and fine particle disorder is generated. When (h) is 1-2 or -1--2, the injected mists separate from the wall surface 24, and liquefaction is prevented, but X reduces because of the Coanda effect in which the injected mists are attracted to the wall surface 24 side. When (h) becomes less than 2, the influence of the wall surface is eliminated, and fuel is injected in the angle close to the angle of the valve seat of the valve 19, and X becomes constant. Further, when (h) becomes over -2, X is becomes constant according to the passage diameter determined according to the top edge diameter of the valve 19.