Abstract:
A fuel injection system for internal combustion engines has at least one fuel injector which injects fuel into a combustion chamber delimited by a cylinder wall in which a piston is guided, and it has a spark plug which protrudes into the combustion space, and the fuel injector is designed so that a conical spray jet is produced in the combustion chamber. The conical spray jet has an angle cutout in the area of the spark plug.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuel injection system and a method of injection. 
     BACKGROUND INFORMATION 
     In internal combustion engines having spark ignition of a compressed fuel mixture with internal formation of the mixture, a “mixture cloud” which must have a certain fuel-air ratio in the ignitable range is required for stratified charge operation in the spark plug area. To this end, fuel injectors having nozzles which open toward the inside or the outside and produce a conical jet are used. 
     For example, German Published Patent Application No. 198 04 463 describes a fuel injection system for internal combustion engines having spark ignition of a compressed fuel mixture; this fuel injection system is provided with at least one fuel injector which injects fuel into a combustion chamber formed by a piston/cylinder arrangement and is equipped with a spark plug projecting into the combustion chamber. The fuel injector is provided with at least one row of injection holes distributed over the circumference of a nozzle body of the fuel injector. Through controlled injection of fuel through the injection holes, a jet-guided combustion method is implemented by the formation of a mixture cloud, at least one jet being directed in the direction of the spark plug. Other jets ensure that an at least approximately closed or coherent mixture cloud is formed. 
     German Patent No. 196 42 653 describes a method of forming an ignitable fuel-air mixture. An ignitable fuel-air mixture is formable in the cylinders of direct injection internal combustion engines, in that fuel is injected into each combustion chamber delimited by a piston, by way of an injector on opening of a nozzle orifice due to a valve element being lifted up from a valve seat surrounding the nozzle orifice. To permit formation of a mixture optimized for fuel consumption and emissions in each operating point of the entire engine characteristics map under all operating conditions of the internal combustion engine, in particular in stratified charge operation, the opening stroke of the valve element and the injection time are adjustable. 
     German Patent No. 38 08 635 describes a fuel injection device for direct injection of fuel into the cylinder of an internal combustion engine having compression of a fuel mixture. The fuel injection device includes a fuel injector which is situated in the cylinder wall at a distance from the cylinder head and opposite the exhaust opening and which has an outlet opening, with the axis of the jet of the injection valve being directed at the area around the spark plug situated in the cylinder head. The fuel injector here has a magnetically operated valve needle having helical swirl grooves to produce a swirl flow of the injection jet. The total cross-sectional area of the swirl grooves is smaller by at least one half than the cross-sectional area of the outlet opening, the fuel injector being situated above the flushing opening, and with its jet axis directed at the ignition point situated at the center of the cylinder head. 
     Most injection systems known from the publications cited above concern combustion methods with wall-guided fuel flow. This combustion method depends to a very great extent on the movement of incoming air which has the function of conveying an ignitable fuel-air mixture exactly into the electrode area of the spark plug over the entire stratified charge operation range of the engine characteristics map. In the wall-guided combustion method, fuel is carried to the spark plug with the support of more or less fractured combustion chamber geometries with simultaneous formation of the mixture. 
     Transport of the mixture to the spark plug is very incomplete in wall-guided and air-guided combustion methods in idling operation and in the lower partial load range, and in the middle partial load range of operation, it is possible in part only with unjustifiably low manufacturing tolerances of the high-pressure injectors used or the flow guidance through the intake manifold. The inadequate reproducibility is apparent in particular in increased emission of unburned hydrocarbons due to isolated instances of misfiring. These properties result in another serious disadvantage of the two combustion methods mentioned above: the engine cannot be operated unthrottled in the idling and lower partial load ranges because due to the great distance between the fuel injector and the spark plug, smaller injection quantities no longer reach the spark plug in the mixture concentration required for stable combustion. This means that the fuel-air mixture at the spark plug electrodes becomes too lean. However, the consumption advantage is reduced in comparison with internal combustion engines having compression of a mixture with spark ignition and intake manifold injection due to the intake air throttling. 
     SUMMARY OF THE INVENTION 
     The fuel injection system according to the present invention and the method according to the present invention have the advantage over the related art that the mixture in the area of the spark plug is not too rich due to the angle cutout. 
     It is also advantageous that the spark plugs do not develop as much soot, thermal shock load is reduced, and there is an improvement in the lack of sensitivity to the firing angle with a fixed injection time in the entire engine characteristics map in which stratified charge operation is carried out. Injection and ignition (or vice versa) may take place simultaneously. 
     It is also advantageous that the spark cannot be blown out due to the high injection rate because the droplet speed is greatest at the center of the jet, and on the angle bisectors of the two injection jets bordering the spark plug area, the spark conforms exactly to requirements regarding the quality of the fuel-air mixture and the rate of flow. 
     It is also advantageous that the depth of installation sensitivity of the spark plug is lower. 
     The injection jet is advantageously formed using a plurality of injection holes. Injection holes may be situated to advantage in several offset rows. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic axial section through an embodiment of a fuel injection system according to the present invention. 
     FIG. 2 shows the section labeled as II—II in FIG.  1  through the cylinder head of the embodiment of the fuel injection system according to the present invention as illustrated in FIG.  1 . 
     FIG. 3 shows a schematic diagram of a first jet pattern produced by the fuel injection system according to the present invention. 
     FIG. 4A shows a first illustration of a schematic diagram of a second jet pattern produced by another embodiment of the fuel injection system according to the present invention. 
     FIG. 4B shows a second illustration of a schematic diagram of a second jet pattern produced by another embodiment of the fuel injection system according to the present invention. 
     FIG. 4C shows the arrangement of injection holes to produce the jet patterns. 
     FIG. 5A shows a first diagram of the emissions of hydrocarbons and nitrogen oxide and the specific fuel consumption, each shown for a fuel injection system with and without the angle cutout according to the present invention for the spark plugs. 
     FIG. 5B shows a second diagram of the emissions of hydrocarbons and nitrogen oxide and the specific fuel consumption, each shown for a fuel injection system with and without the angle cutout according to the present invention for the spark plugs. 
     FIG. 5C shows a third diagram of the emissions of hydrocarbons and nitrogen oxide and the specific fuel consumption, each shown for a fuel injection system with and without the angle cutout according to the present invention for the spark plugs. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a detail of a sectional diagram of one embodiment of the fuel injection system according to the present invention. 
     Fuel injection system  1  includes a cylinder block having a cylinder wall  2  in which a piston  3  is guided. Piston  3  is guided up and down by a connecting rod  4  on cylinder wall  2 . Cylinder wall  2  is closed at one end by a cylinder head  5 . Cylinder wall  2 , piston  3  and cylinder head  5  enclose a combustion chamber  6 . 
     A fuel injection valve  7  is situated preferably centrally in cylinder head  5 . A spark plug  8  is inserted into a borehole in cylinder head  5  with a slight lateral offset. In addition, at least one intake valve  9  and at least one outlet valve  10  are also provided. The arrangement of fuel injector  7 , spark plug  8 , intake valve  9  and outlet valve  10  is shown in greater detail in FIG.  2 . 
     In the case of fuel injection system  1  which is in operation, a conical jet of fuel is sprayed into combustion chamber  6  through boreholes provided in fuel injector  7 . A mixture cloud  11  is formed by mixing fuel and air in combustion chamber  6 . Mixture cloud  11  is ignited by spark plug  8 . The shape of the conical jet and the recess on spark plug  8  according to the present invention are described in greater detail with reference to FIGS. 3 and 4. 
     FIG. 2 shows a section along line II—II in FIG.  1  through the embodiment of fuel injection system  1  according to the present invention as illustrated in FIG.  1 . Fuel injector  7  is situated centrally in a recess  12  in cylinder head  5 . Spark plug  8  is situated in a triangle formed by fuel injector  7  and two outlet valves  10 . Two intake valves  9  are situated symmetrically with outlet valves  10 . Intake and outlet valves  9 ,  10  may also be situated with the sides switched or in a cross pattern. 
     FIG. 3 shows schematically a jet pattern of fuel injector  7  producing a conical jet of fuel. Fuel injector  7  is situated at the center of the circle indicating lateral surface  13  of the cone. Since fuel injector  7  is designed as a multi-hole fuel injector, multiple injection jets  14  are sprayed into combustion chamber  6 . Injection jets  14  are represented symbolically as arrows directed outward. In the present embodiment, this is a fuel injector  7  having thirteen injection holes  16  producing thirteen injection jets  14  accordingly. Individual injection jets  14  are separated from one another by an angular distance β which amounts to 26° in the present embodiment. This does not include injection jets  14   a  which are injected at the right and left of spark plug  8 . Angle α of an angle cutout  17  between injection jets  14   a  enclosing spark plug  8  amounts to 30° to 60° or in the present embodiment 45°. Spark plug  8  is situated on an angle bisector  18  of angle α. This arrangement prevents spark plug  8  from being sprayed directly by injection jets  14  and  14   a  and therefore carbonization of spark plug  8  can be reduced significantly and the lifetime of spark plug  8  can be prolonged. 
     FIGS. 4A and 4B show the jet pattern of a second embodiment of fuel injection system  1 . 
     FIG. 4A shows the jet pattern in a top view like that in FIG.  3 . Fuel injector  7  is located at the center of the circle representing conical lateral surface  13 . In this case, mixture cloud  11  is produced by two different conical lateral surfaces  13   a  and  13   b . Angle α of angle cutout  17  between injection jets  14   a  enclosing spark plug  8  again amounts to approximately 45°. Angle β between two injection jets  14  which are outside and adjacent to angle section  17 , but in this embodiment are located in two different planes, amounts to approximately 20°. 
     FIG. 4B illustrates two conical lateral surfaces  13   a  and  13   b , which in this embodiment are covered by a total of seventeen injection holes. The cone angle of internal conical lateral surface  13   b  is 90°, while the cone angle of external conical lateral surface  13   a  amounts to 110°. Internal conical lateral surface  13   b  is covered by eight injection jets  14  while outer conical lateral surface  13   a  is covered by nine injection jets  14 . This produces a largely homogeneous mixture cloud  11  which does not have any lean pockets. 
     FIG. 4C shows a nozzle body  15  of multi-hole fuel injector  7  in a schematic diagram. The injection hole arrangement of nozzle body  15  is shown in a developed view at the side. To create a 45° angle cutout  17 , all that is necessary in this embodiment is to omit one of injection holes  16  situated in a first annular row  19   b , forming internal conical lateral surface  13   b . This in turn produces an angle cutout  17  which makes it possible to operate fuel injector  7  without directly spraying fuel onto spark plug  8 . Conversely, a gap may also be provided in the arrangement of injection holes  16  of a second annular row  19   a , producing outer conical lateral surface  13   a.    
     FIGS. 5A-5C show diagrams of hydrocarbon and nitrogen oxide emissions and the specific fuel consumption for a fuel injection system with and without angle cutout  17  for spark plug  8 . The consumption and emission values are plotted here as a function of the firing angle in units of the crank angle, measured on the crankshaft. The curve shown with a solid line represents measurement results for a fuel injection system without an angle cutout for the spark plug, and the curve shown with a broken line with asterisks represents the measurement results for a fuel injection system having an angle cutout for the spark plug. 
     In general, the diagrams in FIGS. 5A-5C show that the jet-guided combustion method is independent of the firing angle to a great extent. 
     FIG. 5A shows the hydrocarbon emissions in volume units for the respective injection systems as a function of the firing angle. The hydrocarbon emissions decrease significantly when using a fuel injection system having an angle cutout for the spark plug, in some cases as much as 50% in comparison with emissions in operation of a fuel injection system without an angle cutout for the spark plug. 
     FIG. 5B shows a corresponding diagram for the nitrogen oxides emissions, also plotted in volume units as a function of the firing angle. The emission values for nitrogen oxides remain almost the same for both fuel injection systems over the firing angle curve. 
     FIG. 5C shows the specific fuel consumption for the various fuel injection systems in units of grams per kilowatt hours as a function of the firing angle. Here again, a considerable improvement in consumption values can be achieved by using a fuel injection system having an angle cutout for the spark plug, the reduction in consumption amounting to as much as 15% in some cases. The present invention is not limited to the embodiments presented here and in particular it can also be applied to multi-hole fuel injectors having fewer or more injection holes. Likewise, the injection jets may be situated on more than two spray circles (rows) to thereby improve the homogeneity of the fuel-air mixture.