Abstract:
A method for mixture formation in an internal combustion engine with direct gasoline injection, and an internal combustion engine with direct gasoline injection, are proposed in which the fuel is sprayed at the piston bottom in a thin coherent stream, deflected there, and then atomized.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for generating a fuel-air mixture in internal combustion engines with direct gasoline injection, and to an internal combustion engine with direct gasoline injection. 
     2. Description of the Prior Art 
     In internal combustion engines with direct gasoline injection, in the partial-load range the goal is to form a cloud of an ignitable fuel-air mixture that fills part of the combustion chamber in the vicinity of the spark plug, while the remainder of the combustion chamber is as much as possible filled only with air. This decreases the specific fuel consumption in the partial-load range. 
     In the internal combustion engines known from the prior art (German Patent DE-PS 43 24 642 C2, German Published, Nonexamined Patent Application DE-OS 196 45 201 A1, or European Patent Disclosure EP 0 835 994 A2), the fuel on being injected is atomized in a conical pattern into many fine and superfine droplets of low impetus; that is, the mixture formation begins with the injection of the fuel into the combustion chamber. To reinforce the mixture formation, the walls of the combustion chamber or the air aspirated by the engine is used. 
     A disadvantage of the known internal combustion engines is that the conically atomized fuel strikes the cylinder wall or the piston bottom or face and forms a large-area wall film there, which in turn leads to a lagging course of combustion. The lagging course of combustion has disadvantages in terms of the specific fuel combustion and emissions. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is a primary object of the invention to furnish an improved method for generating a fuel-air mixture in internal combustion engines and to furnish an internal combustion engine with direct gasoline injection with improved partial-load performance as well as reduced specific fuel consumption and improved emission performance. 
     This object is attained according to the invention by a method for generating a fuel-air mixture in internal combustion engines with direct gasoline injection, in which 
     a virtually cylindrical fuel stream into the combustion chamber in the direction of the piston bottom is injected; 
     the fuel stream at the piston bottom, forming a wall film is deflected; 
     the deflected fuel stream into fuel droplets is broken down; and 
     the fuel is vaporized. 
     In the method of the invention, the fuel strikes a small area on the piston bottom at high impetus and is deflected by the piston bottom in the direction of the combustion chamber. The resultant wall film is thin and has a high flow velocity. After separating from the piston bottom, the wall film breaks down into fuel droplets of different size and speed and forms a cloud of fuel-air mixture. This cloud forms in the center of the combustion chamber and has no contact with the wall of the combustion chamber or with the piston bottom, and as a result no wall film of fuel forms, and the course of combustion is not lagging after the ignition of the mixture cloud. 
     Other advantages of this method are that it can be combined with wall-guided and air-guided combustion methods known per se, so that an especially favorable mixture formation ensues. 
     In a variant of the invention, the radial propagation of the fuel stream upon deflection is limited, so that the mixture cloud is prevented from striking the cylinder wall. 
     The radial propagation of the fuel stream upon deflection can be prevented by a concave indentation. 
     In a further feature of the invention, it is provided that the fuel-air mixture is ignited before reaching the wall of the cylinder head, thus reliably avoiding a wall film on the wall of the cylinder head. 
     The object stated above is also attained in accordance with the invention by an internal combustion engine with direct gasoline injection, having at least one cylinder, having a piston, and having a cylinder head, wherein an injection nozzle with an injection port is present in the cylinder head, wherein the fuel emerges from the injection port in the form of a virtually cylindrical stream, and wherein the longitudinal axis of the injection port extends parallel to the longitudinal axis of the cylinder, so that the fuel stream strikes the piston bottom at high velocity and with a small diameter and forms a small-area wall film that is deflected and atomized. In the atomization, fuel droplets of different size are formed; as a rule, the small droplets have a greater velocity than the somewhat larger droplets. The small droplets rapidly reduce their velocity, and the result is a mixture cloud with an adequately large volume in the middle of the combustion chamber. There is only slight deposition of fuel on the walls and the piston bottom. 
     Another advantage of the internal combustion engine of the invention is that it can be produced using production equipment for internal combustion engines of the prior art, since aside from the injection nozzle, the nozzle bore in the cylinder head, and the piston bottom, no modification of the engine is necessary. 
     In a further feature of the invention, the piston bottom has an indentation disposed concentrically to the longitudinal axis of the injection port, so that the fuel stream is deflected by virtually 180°, and the mixture cloud is created in the center of the combustion chamber. 
     In a further feature of the invention, the bottom face of the indentation is flat, so that minor deviations in terms of the direction or location of the fuel stream have only slight effects on the mixture formation. 
     In another feature of the invention, the indentation and the piston bottom are separated from one another by an encompassing protuberance, so that the fuel stream is deflected adequately well, and there is less weakening of the piston bottom from the indentation. The piston bottom in the region of the indentation can comprise a different material from the remainder of the piston bottom. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become apparent from the detailed description contained herein below, taken in conjunction with the drawings, in which: 
     FIG. 1 shows an internal combustion engine according to the invention with homogeneous mixture formation; and 
     FIG. 2 shows an internal combustion engine according to the invention with stratified mixture formation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, an internal combustion engine of the invention is shown, with a cylinder  1  and with a piston  3  that has a piston bottom  5  and an indentation  7 . The piston  3  is shown in a downward motion, represented by an arrow, and aspirates intake air through an opened inlet valve  9  from the inlet  11  into the combustion chamber  15 , which is defined by the piston bottom  5 , cylinder  1 , and cylinder head  13 . The air aspirated into the combustion chamber  15  through the inlet  11  is represented by the lines  17 . 
     An injection nozzle  19  is disposed in the cylinder head  13 . A stream  21  comprising fuel emerges from the injection nozzle  19 . The thin and virtually cylindrical stream  21  strikes a bottom face  23  of the indentation  7  at high velocity and forms a wall film there, which is deflected in the indentation  7  and is atomized at the edge of the indentation  7  into many fuel droplets  25 . The droplets  25  vaporize in the air in the combustion chamber  15  and form a homogeneous, ignitable mixture. 
     Because of the embodiment of an indentation  7  in the piston bottom  5 , the stream  21  is deflected in such a way that at the outlet from the indentation  7 , it has an annular cross section. This promotes both the atomization and the ensuing formation of an ignitable fuel-air mixture. 
     The mixture formation takes place during the intake stroke and the compression stroke, so that a homogeneous mixture in the combustion chamber  15  is established. This mode of operation is employed at high load and during the warmup phase of the engine. 
     FIG. 2 shows a further operating mode of an internal combustion engine of the invention. Identical components are identified by the same reference numerals as in FIG.  1 . In this engine, the injection takes place during the compression stroke with the inlet valve  9  and outlet valve  27  closed. Because of the shortness of time between injection and ignition, the cloud of ignitable mixture develops only in the center of the combustion chamber  15  and does not touch the wall of the combustion chamber  15 . The remainder of the combustion chamber  15  is filled with air. The mixture cloud is ignited by a spark plug, not shown in FIG. 1, before it reaches the wall of the cylinder  1  or of the cylinder head  13 . In this mode of operation, a stratified combustion thus occurs. It is especially well suited for partial-load operation. 
     It is common to both modes of operation that no significant fuel film remains in the indentation  7  or strikes the bottom of the piston  3 . This is partly due to the geometry of the indentation, to the velocity at which the fuel stream  21  strikes the piston bottom  5  or the indentation  7 , and the temperature of the piston  3 . 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.