Patent Publication Number: US-9845779-B2

Title: Coated high pressure gasoline injector seat to reduce particle emissions

Description:
FIELD 
     The invention relates to gasoline direct injection for vehicles and, more particularly, to providing a non-thermally conducting coating on a fuel injector tip to increase a temperature thereof and thus reduce particulate emissions. 
     BACKGROUND 
     Particulate emissions of gasoline engines will be newly regulated in Europe in 2014 with the introduction of EU6a regulations of 6×10 12  particles/km and further reduced to 6×10 11  particles/km with the introduction of EU6c in 2017. Similarly, United States regulations will impose similarly challenging standards with the introduction of LEVIII. Standards are assumed to be 10 mg/mi in 2014, 3 mg/mi in 2018 and 1 mg/mi in 2025. A major source of particulate emissions is known to be from a diffusion flame fed by fuel evaporating from the deposits on the fuel injector tip. 
     It is known that protruding the fuel injector further into the combustion chamber reduces the particulate emissions. Increasing injector tip protrusion raises injector tip temperature by exposing more injector tip surface area to hot combustion gases. This in turn enhances evaporation of any fuel remaining on the tip so there is no or little fuel remaining on the tip to be ignited when the flame front passes. The higher tip temperature also enhances oxidation of the deposits on the tip reducing the sponge-like surface of the deposits which hold the fuel. 
     Increasing tip temperature enhances evaporation on the external surfaces of the tip lowering particulate emissions, but it also increases the temperature of the fuel metering orifices or passages. This increases the risk of deposits being formed in the metering passages themselves. It is well known that fuel characteristics, tip (orifice) temperatures, fuel pressure and nozzle design affect deposit formation in injector flow passages. It is generally accepted that if the tip temperatures are kept below 120° C., that no problems with deposit related flow shift will be encountered. This guideline is only achievable with side mounted direct injectors. In centrally mounted injector applications, temperatures up to 300° C. can be seen. 
     Thus, there is a need to increase the injector tip temperature to lower particulate emissions while allowing the metering passages of the injector to be cooled by the fuel to prevent deposit formation in the passagers and thus prevent flow shift. 
     SUMMARY 
     An object of the invention is to fulfill the need referred to above. In accordance with the principles of the embodiments, this objective is obtained by providing a fuel injector having an inlet, an outlet, and a passageway providing a fuel flow conduit from the inlet to the outlet. The fuel injector includes a valve structure movable in the passageway between a first position and a second position. A seat, at the outlet, has at least one seat passage in communication with the passageway. The seat contiguously engages a portion of the valve structure in the first position thereby closing the at least one seat passage and preventing fuel from exiting the at least one passage. The valve structure in the second position is spaced from the at least one seat passage so that fuel can move through the passageway and exit through the at least one seat passage. The seat includes an outer tip surface through which the least one seat passage extends. A non-thermally conducting coating is provided on at least a portion of the outer tip surface and not on surfaces defining the at least one seat passage. The coating is constructed and arranged to be heated by combustion gases so that the outer tip surface reaches a temperature greater than a temperature that the outer tip surface would reach if the coating was not provided, so as to cause evaporation of fuel that contacts the outer tip surface after injection. The at least one seat passage is constructed and arranged to not be substantially heated by conduction from the outer tip surface and to be cooled by fuel passing there-through so as to prevent deposits of combustion from accumulating on surfaces defining the at least one seat passage. 
     In accordance with another aspect of a disclosed embodiment, a method reduces particulate emissions associated with a fuel injector. The fuel injector has an inlet; an outlet; a passageway providing a fuel flow conduit from the inlet to the outlet; a valve structure movable in the passageway between a first position and a second position; a seat, at the outlet, having at least one seat passage in communication with the passageway. The seat contiguously engages a portion of the valve structure in the first position thereby closing the at least one seat passage and preventing fuel from exiting the at least one passage. The valve structure in the second position is spaced from the at least one seat passage so that fuel can move through the passageway and exit through the at least one seat passage. The seat includes an outer tip surface through which the at least one seat passage extends. The method coats a non-thermally conducting material on at least a portion of the outer tip surface and not on surfaces defining the at least one seat passage. The coating is heated by combustion gases during operation of the fuel injector so that the outer tip surface reaches a temperature greater than a temperature that the outer tip surface would reach if the coating was not provided, thereby enhancing evaporation of fuel on the outer tip surface and thus reducing particle emission. The method cools surfaces defining the at least one seat passage with fuel passing there-through so that the surfaces are at a temperature less than a temperature of the outer tip surface to ensure that fuel remaining in the at least one passage after injection is in a liquid state, thereby preventing deposits of combustion from accumulating on surfaces defining the at least one seat passage. 
     Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which: 
         FIG. 1  is a view of gasoline direct fuel injector provided in accordance with an embodiment. 
         FIG. 2  is an enlarged view of the portion encircled at  2  in  FIG. 1 . 
         FIG. 3  is a plot showing the surface temperature of the injector tip surface at different points in the engine cycle. 
         FIGS. 4A-4D  show embodiments of an interface between the coating and an exit a metering passage. 
         FIGS. 5A-5C  show embodiments of coating of stepped metering passages. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     With reference to  FIG. 1 , a gasoline direct fuel injector is shown, generally indicated at  10 , in accordance with an embodiment of the invention. The fuel injector  10  has a fuel inlet  12 , a fuel outlet  14 , and a fuel passageway  16  extending from the fuel inlet  12  to the fuel outlet  14 . The injector  10  is of the conventional, solenoid-operated type, having an armature  18  operated by a coil  20 . Electromagnetic force is generated by current flow from the electronic control unit (not shown) through the coil  20 . Movement of the armature  18  also moves an operatively attached needle  22  and ball valve  24  to positions that are either separated from or contiguously engaged with a seat, generally indicated at  26 . The needle  22  and ball valve  24  define valve structure of the injector  10 . Instead of providing the ball valve  24 , it can be appreciated that the valve structure could only comprise the needle  22 , with an end of the needle engaging the seat  26 . 
     Movement of the ball valve  24  opens or closes, respectively, the at least one metering orifice or seat passage  28  ( FIG. 2 ) through the seat  24 , which permits or inhibits, respectively, fuel from flowing through the fuel outlet  14  of the fuel injector  10 . In the embodiment a plurality of metering seat passages  28  are shown. More or fewer passages  28  can be provided depending on the application. The passages  28  extend through an outer tip surface  30  of the seat  26 . The outer tip surface  30  defines an end of the fuel injector  10  and can be considered to be the injector tip face. 
     In accordance with an embodiment, an insulative coating  32  is provided on at least a portion of the outer tip surface  30 . The coating  32  permits the surface temperature of the tip surface  30  to increase and, at the same time, allows the seat passages  28  to be cooled more effectively by the fuel passing there-through. The hot tip surface  30  reduces particle emissions and the cool seat passages  28  minimize the risk of deposit related flow loss. In the embodiment, the coating  32  surrounds, without obstructing, all of the seat passages  28 . 
     It has been shown through measurements and modeling that the flow of fuel through the seat  26  has a major influence on the temperatures encountered on the seat  26 . The plot shown in  FIG. 3  shows the surface temperature of the injector tip surface  30  at different points in the engine cycle. The plot shows that the high temperatures of combustion raise the tip surface  30  temperature and the injection of fuel lowers it. 
     In the embodiment, the steel outer tip surface  30  is coated with a non-thermally conducting material  32 . The passages  28  are drilled through the more thermally conductive steel portion of the seat  26 . The outer tip surface  30  is coated in such a way to allow the fuel to exit the steel surfaces defining the passages  28  with minimal contact with the coated tip surface  30 . In this way, the passages  28  are cooled and wetted with fuel during injection but are not substantially heated through conduction from the large surface area of the tip surface  30  exposed to the heat of combustion. The low temperature (lower than that of the outer tip surface) in the passages  28  allows what fuel remains there after injection to remain liquid and not form deposit precursors. The coated tip surface  30 , being insulated, is readily heated by the combustion gases and reaches higher temperatures than the same geometry would reach if it was not coated. Any fuel that contacts this hot surface readily evaporates and is less likely to form deposits and/or a diffusion flame creating particulates. 
     The material of the coating  32  preferably falls into the class of materials known as thermal barrier coatings. These are typically ceramic coating systems most commonly containing yttria-stabilized zirconia or other rare earth zirconates. However, the coating is not limited to zirconia or zirconates. The thickness of the coating  32  depends on the material selection and application method. A target thickness is preferably less than 0.25 mm. 
       FIGS. 4A-4D  show various example shapes of surface features defining an exit of the passage  28 . In particular,  FIG. 4A  shows an exit surface feature  34  of the passage  28  to be of conical shape.  FIG. 4B  shows an exit surface feature  34 ′ of the passage  28  to be of stepped shape.  FIG. 4C  shows an exit surface feature  34 ″ of the passage  28  to be defined by an internal radius and  FIG. 4D  shows an exit surface feature  34 ′″ of the passage  28  to be defined by an external radius. The exit surface features  34 ,  34 ′,  34 ″ and  34 ′″ are preferably provided entirely within the coating  32  by machining, laser machining, masking or the like and define the interface between the insulating coating  32  and the cylindrical passage  28 . The embodiments of the exit surface features depend on the coating material, thickness and application method. 
       FIGS. 5A-5C  show example embodiments of stepped passages  28 ′. Depending on the nature of the coating  32 , its thickness and application method, a stepped passage  28 ′ may be masked, preventing application of the coating inside the step leaving a surface on the edge of the coating parallel to the step surface. This coating  32  can be applied to conical ( FIG. 5C ) or cylindrical ( FIG. 5A ) passages  28 ′. In the case of a cylindrical step, it may be desirable to coat the inside of the step ( FIG. 5B ) to enhance the evaporation of any fuel that may be left in the step after injection. The details of the exit surface feature at the exit of the metering passage  28 ′ at the bottom of the step could be the same as those depicted in  FIGS. 4A-4D . 
     Thus, the embodiments ensure that the temperature of the tip surface  30  is maintained as high as possible to lower particle emission and ensure that the temperature of the surfaces of the passages  28  is as low as possible so as to limit fuel deposits forming in the passages and thus prevent flow shift that is caused by fuel deposits. 
     The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.