Patent Publication Number: US-11644000-B2

Title: Fuel injector clamp assembly for offset clamping bolt and cylinder head assembly with same

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a fuel injector structured for clamping to a cylinder head, and more particularly to arranging a bolt hole for clamping the fuel injector at an offset location. 
     BACKGROUND 
     Internal combustion engines are well-known and widely used throughout the world for diverse purposes ranging from vehicle propulsion and on-highway, off-highway, and marine applications to electrical power generation and operation of pumps, compressors, and all manner of industrial equipment. Many internal combustion engines can be classified generally based upon the manner in which a fuel is ignited in the engine. In spark-ignited engines an electrical spark is used to trigger ignition of a liquid fuel or a gaseous fuel at a desired timing. In compression-ignition engines in-cylinder pressure is increased to an autoignition threshold at which the fuel ignites without an additional external input of energy. A great many different variations and permutations of these general strategies including prechamber ignition, liquid fuel pilot ignition, and still others have been developed over the years. 
     In recent years increased research and development, especially in the case of compression-ignition engines, has been directed at increasing power density. Power density can be generally defined as the amount of output power that can be generated per unit volume of an engine. Relatively greater power density enables an engine to produce a given output power in a smaller spatial envelope with the attendant advantages of reduced weight and potentially reduced materials cost in engine construction. A multitude of commercial and practical advantages can be realized by employing engines with relatively greater power density as compared to predecessor platforms. 
     Efforts at increased power density have focused on a multitude of different improvements to features and operating aspects of engines, but have often created new challenges. In certain instances, increasing an amount of fuel that can be injected in an engine cycle can enable more fuel to be burned and thus increase power output of an engine of a given engine size. Increased fuel injection amounts, however, can require extremely high injection pressures and specialized equipment for handling highly pressurized fuel. Increased fuel injection amounts can also require enhanced cooling strategies to dissipate increased heat. Whenever combustion temperatures are elevated, as is commonly the case with high power density engines, component materials, placement, and component geometry may need to be carefully tailored to avoid overheating and/or thermal fatigue phenomena. Strategies for enhanced cooling or other temperature management schemes have also focused upon structures within combustion cylinders, including features of engine pistons and fuel injectors. United States Patent Application Publication No. 20160169153 is directed to a piston for an internal combustion engine where a ratio between a height of a top land surface and a nominal inner diameter of a cylinder bore is apparently optimized for increased heat release rate. Emissions considerations in high power density applications also remain as stringent as ever, and in the coming years regulations are expected to be ever more demanding, especially with regard to oxides of nitrogen and particulate matter or soot. U.S. Pat. No. 10,519,914 is directed to a fuel injection system where a positioning system for a fuel injector nozzle is adjusted in axial position based upon varying engine speeds and loads to optimize certain emissions. 
     SUMMARY 
     In one aspect, a fuel injector assembly includes a fuel injector defining a longitudinal axis extending between a first axial injector end, and a second axial injector end including a nozzle having spray outlets formed therein. The fuel injector further includes, between the first axial injector end and the second axial injector end, a first clamp face and a second clamp face together defining a middle plane and the longitudinal axis is within the middle plane. The fuel injector assembly further includes a clamp having a forked injector portion forming a slot receiving the fuel injector and in contact with each of the first clamp face and the second clamp face, and a bolting portion positioned radially outward of the fuel injector and having a bolt hole formed therein. The bolt hole defines a bolt hole axis oriented parallel to the longitudinal axis and offset from the middle plane. 
     In another aspect, a cylinder head assembly includes a cylinder head having an upper surface, a lower surface forming a fire deck, a total of four gas exchange openings in the fire deck arranged in a quadrilateral pattern, an injector bore centered within the quadrilateral pattern and extending from the upper surface to the lower surface, and a bolt bore extending downwardly from the upper surface. The cylinder head assembly further includes a fuel injector within the injector bore and defining a longitudinal axis, and a clamp clamping the fuel injector to the cylinder head and including a bolt hole formed therein. The total of four gas exchange openings defines a cylinder head middle plane extending vertically through the cylinder head and the fuel injector, and the bolt hole and bolt bore are coaxially arranged along a common bolt hole axis offset from the cylinder head middle plane. 
     In still another aspect, a fuel injector clamp includes a forked injector portion including a first prong having a first inside prong surface and a second prong having a second inside prong surface, and a bolting portion attached to the forked injector portion and having a bolt hole formed therein defining a bolt hole axis extending between an upper bolt head side of the fuel injector clamp and a lower bolt shaft side of the fuel injector clamp. The first inside prong surface and the second inside prong surface are oriented parallel to one another, and together form a slot for receiving a fuel injector. The bolting portion extends outwardly of the bolt hole to a terminal nose, and defines a clamp axis extending through the terminal nose and oriented diagonal to each of the first inside prong surface and the second inside prong surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagrammatic view of an internal combustion engine system, according to one embodiment; 
         FIG.  2    is a sectioned side diagrammatic view of an internal combustion engine system, according to one embodiment; 
         FIG.  3    is a top view of a cylinder head assembly, according to one embodiment; 
         FIG.  4    is a top view of a cylinder head assembly, according to one embodiment; 
         FIG.  5    is a bottom view of a cylinder head assembly, according to one embodiment; 
         FIG.  6    is a diagrammatic view of a fuel injector assembly, according to one embodiment; 
         FIG.  7    is a diagrammatic view of a fuel injector assembly, according to one embodiment; 
         FIG.  8    is a diagrammatic view of a fuel injector clamp, according to one embodiment; 
         FIG.  9    is a top view of a fuel injector clamp, according to one embodiment; 
         FIG.  10    is a sectioned side diagrammatic view of a fuel injector assembly, according to one embodiment; 
         FIG.  11    is a side diagrammatic view of a fuel injector, according to one embodiment; 
         FIG.  12    is a side diagrammatic view of a fuel injector, according to one embodiment; 
         FIG.  13    is a side diagrammatic view of a combustion system, according to one embodiment; 
         FIG.  14    is a diagrammatic view, in perspective, of a nozzle assembly for a fuel injector in a cylinder head, according to one embodiment; 
         FIG.  15    is an end view of a fuel injector, according to one embodiment; 
         FIG.  16    is a diagrammatic view of combustion state in an engine, according to one embodiment; and 
         FIG.  17    is a diagrammatic view of combustion state in an engine, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1   , there is shown an internal combustion engine system  10  according to one embodiment. Engine system  10  includes an engine  12  having a cylinder block  14  with a combustion cylinder  18  formed therein, within a cylinder liner  16  in the illustrated embodiment. Components of engine  12  including cylinder block  14 , cylinder liner  16 , and a cylinder head  34  together form an engine housing. A piston  20  is movable within combustion cylinder  18  between a bottom-dead-center position and a top-dead-center position to increase a pressure within combustion cylinder  18  to an autoignition threshold for injected liquid fuel and air, as further described herein. Piston  20  is coupled to a connecting rod  22 , in turn coupled to a crankshaft  24  in a generally conventional manner, to power a load such as an electrical generator, a pump, a compressor, or for propelling a vehicle, to name a few examples. In a practical implementation engine system  10  is operated in a conventional four-stroke engine cycle. Combustion cylinder  18  may be one of any number of combustion cylinders in engine  12 , in any suitable arrangement, such as an in-line pattern, a V-pattern, or still another. Engine system  10  may include a compression-ignition engine system, configured for improved power density, efficiency, and reduced emissions along with other properties as will be further apparent from the following description. 
     Engine system  10  further includes an intake system  26  having an air inlet  28 , and an intake manifold  30  structured to receive a flow of filtered intake air from air inlet  28  and convey the same by way of an intake runner  32  to cylinder head  34  in a cylinder head assembly  35 . Additional intake runners can be structured to supply a feed of intake air to other combustion cylinders in engine  12 . In a practical implementation, the intake air may be compressed by way of a turbocharger compressor in a generally conventional manner. In addition to intake air recirculated exhaust gas could be supplied into a feed of compressed air conveyed to combustion cylinder  18 . Engine system  10  further includes an exhaust manifold  60  structured to receive exhaust from combustion cylinder  18 . In  FIG.  1    an intake valve  52  coupled with a valve return spring  56  is supported in cylinder head  34  to open and close fluid communications between intake runner  32  and combustion cylinder  18 . An exhaust valve  54  is similarly supported in cylinder head  34  and coupled with a valve return spring  58  to control fluid communications between combustion cylinder  18  and exhaust manifold  60 . In a typical implementation two exhaust valves and two intake valves will be associated with combustion cylinder  18 . A valve cover  36  may be attached to cylinder head  34 , again in a generally conventional manner. 
     Engine system  10  further includes a liquid fuel system  40  having a fuel supply or tank  42 , and in the illustrated embodiment a low-pressure pump  44  structured to transfer a liquid fuel from fuel tank  42  to a high-pressure pump  46  that pressurizes the transferred liquid fuel to an injection pressure. High-pressure pump  46  may feed a common rail or other pressurized fuel reservoir  48 , and a fuel conduit  49  extends from pressurized fuel reservoir  48  to a fuel injector  50  supported in cylinder head  34 . The liquid fuel may be any suitable compression ignition liquid fuel such as a diesel distillate fuel, other liquid compression ignition fuels or blends, or a liquid fuel with a cetane enhancer, for instance. Fuel injector  50  may be electronically controlled and will typically include a solenoid-actuated control valve (not shown) operably coupled to an outlet check (not shown) such as a direct controlled needle check. Additional or alternative internal fuel injector components could be used, and the present disclosure is not limited with regard to the internal valve components manner, or control of fuel injector operation. In other embodiments a cam-actuated or hydraulically actuated unit pump fuel injector could be used. An electronic control unit  62  is in control communication with fuel injector  50 , and may also be in communication with high-pressure pump  46  and various other apparatus in engine system  10  including sensors, actuators, or still others. 
     Referring also now to  FIG.  2   , there are shown additional features of engine system  10 , and notably those of cylinder head assembly  35 . Cylinder head  34  may include a one-piece cylinder head casting  64  having an upper surface  66 , and a lower fire deck surface  68  forming a fire deck  70 . A head gasket  104  may be clamped between cylinder head  34  and cylinder block  14 . Also depicted in  FIG.  2    is a valve bridge  106  coupled to exhaust valve  54 , and to another exhaust valve not visible in  FIG.  2   . Another valve bridge, also labeled with a reference numeral  106 , is analogously coupled to intake valve  52  and to another intake valve not visible in  FIG.  2   . An intake conduit  94  is formed in cylinder head casting  64  and coveys an incoming flow of compressed intake air, or compressed intake air and other gases such as recirculated exhaust gas, to combustion cylinder  18 . An exhaust conduit  96  is also formed in cylinder head casting  64  and conveys an outgoing flow of exhaust from combustion cylinder  18  to exhaust manifold  60 . It can also be seen from  FIG.  2    that fuel injector  50  is received in an injector sleeve  98 , and a crush washer  100  is positioned between fuel injector  50  and injector sleeve  98 . Bolts  102  clamp cylinder head casting  64  to cylinder block  14 . 
     Cylinder head casting  64  further has formed therein an injector bore  72  defining an injector bore center axis  74  and extending through cylinder head casting  64  between upper surface  66  and lower surface  68 . Referring also now to  FIGS.  3 - 5   , cylinder head casting  64  further includes a total of four gas exchange openings  78 ,  80 ,  82 , and  84  formed in fire deck  70 . In the illustrated embodiment gas exchange openings  78  and  84  include intake openings, and gas exchange openings  80  and  82  include exhaust openings. Cylinder head casting  64  further has formed therein a bolt bore  86  defining a bolt bore center axis  88  parallel to injector bore center axis  74 . Cylinder head casting  64  also has formed therein a glow plug bore  92  defining a plug bore center axis  92  extending through cylinder head casting  64  between upper surface  66  and lower surface  68 . The four gas exchange openings  78 ,  80 ,  82 , and  84  are arranged at twelve o&#39;clock, three o&#39;clock, six o&#39;clock, and nine o&#39;clock positions, respectively, circumferentially around injector bore center axis  74 . 
     Bolt bore  86  originates in upper surface  66  and terminates at a location inward of lower surface  68 . Thus, bolt bore  86  opens at upper surface  66  but does not extend through to lower surface  68 . Bolt bore  86  is positioned angularly between the twelve o&#39;clock position and the three o&#39;clock position, circumferentially around injector bore center axis  74 . Glow plug bore  90  originates in upper surface  66  and terminates in lower surface  68 , thus extends fully through cylinder head casting  64 . A glow plug (not shown) of any suitable configuration can be positioned in glow plug bore  90  for conventional purposes including cold starting, with a heating element of the glow plug positioned to be impinged by a spray plume or jet of injected fuel, for instance by an outer periphery of a spray plume in some embodiments. Glow plug bore  90  is positioned angularly between the three o&#39;clock position and the six o&#39;clock position, circumferentially around injector bore center axis  74 . It can also be noted from  FIG.  1    that fuel injector  50  includes a nozzle tip  252  within combustion cylinder  18 , an arrangement and structure of which are further discussed herein. Spray outlets described later are formed in nozzle tip  252 . 
     It can also be noted from  FIG.  4    in particular that bolt bore  86  may be located closer to the twelve o&#39;clock position than to the three o&#39;clock position, circumferentially around injector bore center axis  74 . Glow plug bore  90  may be located closer to the three o&#39;clock position than to the six o&#39;clock position, circumferentially around injector bore center axis  74 . Glow plug bore  90  defines a plug bore center axis  92  as noted above. Plug bore center axis  92  may be oriented diagonal to injector bore center axis  74 , and extends between a radially outward location in upper surface  66  and a radially inward location in lower surface  68 . This arrangement can be seen by comparing relative locations of glow plug bore  90  and plug bore center axis  92  in  FIGS.  4  and  5   . 
     With continued focus on  FIG.  4   , it can be seen that a circle  110  is defined by center axes  116 ,  118 ,  120 , and  122  of each of the four gas exchange openings  78 ,  80 ,  82 , and  84 . In the illustrated embodiment each of bolt bore  86  and glow plug bore  90  is within circle  110 . Gas exchange openings  78 ,  80 ,  82 , and  84  may also be arranged in a quadrilateral pattern, a rectangular pattern in the illustrated embodiment, with injector bore  72  centered in the quadrilateral pattern. A midline  112  is defined by the four gas exchange openings  78 ,  80 ,  82 , and  84 . In the arrangement shown in  FIG.  4    gas exchange openings  78  and  84  at the respective twelve o&#39;clock and nine o&#39;clock positions are upon a first side of midline  112 . Gas exchange openings  82  and  80  at the respective three o&#39;clock and six o&#39;clock positions are upon a second side of midline  112 . It will be recalled gas exchange openings  78  and  84  may be intake openings and gas exchange openings  80  and  82  may be exhaust openings. Among other things, the relatively tight and precise arrangement of the respective gas exchange openings, glow plug bore, and bolt bore enables these features and the components with which they are associated to be confined within a relatively small footprint in cylinder head assembly  35  so that intake conduit  94  and exhaust conduit  96  can be made relatively large to provide large, optimal flow areas for exchange of intake and exhaust gases while preserving optimal wall thickness, in a high power density application. 
     Engine system  10  and cylinder head assembly  35  may further include a clamp  124 , features of which are further described herein, coupled to fuel injector  50 , and a bolt  126  within bolt bore  86  and extending through clamp  124  to clamp fuel injector  50  to cylinder head  34  within injector bore  72 . Also, in the illustrated embodiment fuel injector  50  is bisected by midline  112 , and clamp  124  is canted relative to midline  112 . An offset angle  114 , circumferentially around injector bore center axis  74 , is defined between midline  112  and bolt bore center axis  88 , as further discussed herein. 
     As noted above, achieving increased power density in an internal combustion engine can create various challenges, and one such challenge relates to packaging the various components in a cylinder head assembly. Fuel system  40  is a so-called “top feed” fuel injector so must be supported and supplied with fuel, as well as electrically connected to electronic control unit  62 , all from locations above cylinder head  34 . To this end, a canted configuration of clamp  124  can assist in enabling fuel injector  50  to be robustly attached to cylinder head  34  while still fitting clamp  124  in and amongst valvetrain components including intake valves  52  and exhaust valves  54 . Notably, relatively robust valve return springs necessitating large spring diameters can be used to ensure swift and reliable gas exchange valve closing, as may be desirable where relatively high pressures or pressure differences are experienced in combustion cylinder  18 , intake conduit  94 , intake conduit  96 , or elsewhere in engine system  10 . The canted configuration of clamp  124 , further described herein, assists in fitting fuel injector  50  and clamp  124  amid the relatively large valve return springs in a tightly confined packaging space, especially valve return spring  56  associated with the respective one of intake valves  52 . 
     As explained above, offset angle  114  is defined between midline  112  and bolt bore center axis  96 . While a canted configuration of clamp  124  provides a practical implementation strategy, in other embodiments a symmetrical or non-canted clamp could be used, with surfaces engaged by the clamp on fuel injector  50  being oriented to provide offset angle  114 . In still other embodiments, a bolt hole in clamp  124  could be offset, or some combination of these various features could be used. Also in a practical implementation strategy, offset angle  114  is 5° plus or minus 2.5°. With continued focus on  FIG.  4   , there can be seen a line  128  defined between center axes  116  and  120  of gas exchange openings  78  and  82  at the twelve o&#39;clock and three o&#39;clock positions, respectively. Bolt bore center axis  88  may be located radially inward of line  128 , relative to injector bore center axis  74 . 
     Referring also now to  FIGS.  6 - 12   , there are shown additional features of fuel injector  50  and clamp  124  together forming a fuel injector assembly  206 . Fuel injector  50  includes an injector housing  130  defining a longitudinal axis  132 . Longitudinal axis  132  will typically be colinear with injector bore center axis  74  when fuel injector assembly  206  is installed for service in cylinder head  34 . Longitudinal axis  132  extends between a first axial injector end  134  including a housing axial end surface  136  extending circumferentially around an electrical connector bore  138 , and a second axial injector end  140  including a downwardly extending nozzle  142  having a plurality of spray outlets  144  formed therein. Injector housing  130  further includes a fuel connector  146 , and an outer housing surface  148  extending circumferentially around longitudinal axis  132 . Outer housing surface  148  includes a cylindrical upper section  150  adjacent to housing axial end surface  136 , a cylindrical lower section  152 , and a middle section  154 . Injector housing  130  may also include an upper body piece  176  having cylindrical upper section  150 , cylindrical lower section  152 , and middle section  154  formed thereon. 
     Injector housing  130  also includes, between first axial injector end  134  and second axial injector end  140 , a first clamp surface  178  and a second clamp surface  180  formed on body piece  176  and extending axially between a connector axis  156  defined by fuel connector  146 , and cylindrical lower section  152 . Connector axis  156  may be understood as a transverse axis, and in some embodiments is oriented normal to longitudinal axis  132 . Connector axis  156  extends between a first or base connector end  158  attached to middle section  154 , and a second or terminal connector end  160  radially outward of outer housing surface  148 , relative to longitudinal axis  132 , and having a fuel inlet  162  formed therein. Fuel inlet  162  can include a conical or spherical inlet structured to engage with suitable connecting features of pressurized fuel conduit  49 . Fuel connector  146  further includes an outer connector surface  164  extending circumferentially around connector axis  156  and having an unthreaded base section  166  adjacent to first connector end  158 , and an externally threaded end section  168  adjacent to terminal connector end  160 . As depicted in  FIG.  3   , pressurized fuel conduit  49  includes a nut  190  engaged with externally threaded end section  168  to clamp fuel connector  146  to pressurized fuel conduit  49  and fluidly connect fuel injector  50  to a supply of pressurized fuel, such as pressurized fuel reservoir  48 . 
     With continued focus on  FIG.  3   , pressurized fuel conduit  49  may include an incoming linear section  192  arranged coaxially with fuel connector  146 , parallel to midline  112 , and clamped to fuel connector  146  by way of nut  190 . Pressurized fuel conduit  49  may also include a second linear section  194  forming an acute angle  196  with incoming linear section  192  and arranged diagonally relative to both connector axis  156  and longitudinal axis  132 , in and out of the page in  FIG.  3   . Pressurized fuel conduit  49  may also include a bend section  198  connecting between incoming linear section  192  and second linear section  194 . The arrangement of pressurized fuel conduit  49  can assist in feeding pressurized fuel under valve cover  36  to the relatively confined space where fuel injector  50  and clamp  124  reside amongst the intake valves and exhaust valves and related apparatus. 
     It will be recalled electrical connector bore  138  may be formed in first axial injector end  134 . In an implementation, electrical connector bore  138  could be internally threaded, and an electrical connector  170  threaded engaged to attach to injector housing  130  and body piece  176  within electrical connector bore  138 . Electrical connector  170  may be located entirely within a cylinder defined by cylindrical upper section  150 , enabling an electrical connection between electronic control unit  62  and one or more solenoid actuators in fuel injector  50  during installation or servicing to be performed vertically within the confined packaging space available. Electrical connector  170  may include upwardly projecting electrical prongs  172 , and a centrally located dividing wall  174  arranged between upwardly projecting electrical prongs  172 . 
     As described above, injector housing  130 , upon body piece  176 , includes first clamp face  178  and second clamp face  180 . First clamp face  178  and second clamp face  180  may be planar and parallel, and define a middle plane  182  as shown in  FIG.  12   . Midline  112  may be within middle plane  182 . Connector axis  156  and longitudinal axis  132  may also be oriented normal to one another as described above, and may each lie within middle plane  182 . Connector axis  156  may be located axially between cylindrical upper section  150  and each of first clamp face  178  and second clamp face  180 . Injector housing  130  further includes a connector base  184  extending peripherally around fuel connector  146  and transitioning between fuel connector  146  and each of first clamp face  178  and second clamp face  180 . Fuel connector  146  and connector axis  156  may be located angularly between first clamp face  178  and second clamp face  180 , circumferentially around longitudinal axis  132 , and fuel connector  146  may be spaced from first axial injector end  134  by way of cylindrical upper section  150 . 
     With focus on  FIGS.  11  and  12   , fuel injector housing  130 , within body piece  176 , defines a full diameter (FD)  186  of fuel injector  50 . A distance of protrusion  188  of fuel connector  146 , radially outward of injector housing  130 , between outer housing surface  148  and terminal connector end  160  may be equal to or greater than FD. It should also be appreciated that for purposes of the present description body piece  176  may be understood to define a longitudinal axis colinear with longitudinal axis  132 , and commonly labeled. Moreover, first axial injector end  134  may also be understood as a first axial body end of body piece  176  having axial end surface  136  thereon. A second axial body end  177  of body piece  176  is shown adjacent to other injector housing components further described herein. 
     First clamp face  178  and second clamp face  180  may be parallel as noted above, and define middle plane  182 . First clamp face  178  and second clamp face  180  may also be understood to define a minor diameter (MD)  200  therebetween. Fuel connector  146  defines a second diameter  202 , as in  FIG.  7   , and second diameter  202  may be less than (MD)  200 . Connector base  184  may define a third diameter  204  parallel to minor diameter  200 . Third diameter  204  may be greater than second diameter  202  and less than MD  200 . Fuel connector  146  may be partially overlapping in axial extent with each of first clamp face  178  and second clamp face  180 , and positioned opposite to a bolting portion of clamp  124 , circumferentially around longitudinal axis  132 . First clamp face  178  and second clamp face  180  may be positioned opposite to one another circumferentially around longitudinal axis  132 . 
     Focusing now on  FIGS.  8  and  9    clamp  124  includes a forked injector portion  208  forming a slot  210  receiving fuel injector  50  and in contact with each of first clamp face  278  and second clamp face  280 . Clamp  124  also includes a bolting portion  212  positioned radially outward of fuel injector  50  in fuel injector assembly  206  and having a bolt hole  214  formed therein defining a bolt hole axis  216  oriented parallel to longitudinal axis  132  and offset from middle plane  182  defined by first clamp face  278  and second clamp face  280 . Forked injector portion  208  may include a first prong  226  in contact with first clamp face  278  and a second prong  228  in contact with second clamp face  280 . Clamp  124  also includes a center section  233  having formed thereon a bolt boss  237  extending circumferentially around bolt hole axis  216 . It will be understood that bolt hole axis  216  in clamp  124  and bolt bore center axis  88  can be understood as a common bolt or bolt hole axis when injector assembly  206  is installed in cylinder head assembly  35 . A peripheral surface  239  of center section  233  extends radially outward, relative to bolt hole axis  216  to a first outside surface  241  of clamp  124  and to a second outside surface  243  of clamp  124 . Clamp  124  further includes a lower bolt shaft side  238  and an upper bolt head side  236 . Each of first prong  226  and second prong  228  is sloped downward upon upper bolt head side  236  in a direction of first prong tip  226  and second prong tip  228 , respectively. Bolting portion  212  extends from bolt hole  214  to a terminal nose  242  and defines a clamp axis  244 . Clamp axis  244  extends through terminal nose  242  and through bolt hole axis  216  and is oriented diagonally to middle plane  182  in each of a longitudinal aspect and a circumferential aspect, relative to longitudinal axis  132 . 
     As can be seen in  FIGS.  11  and  12   , for example, injector housing  130  further includes a first step  218  and a second step  220  each extending peripherally along first clamp face  278  and second clamp face  280 , respectively. A third step  222  is opposite first step  218 , and a fourth step  224  is opposite second step  220 , in the illustrated embodiment. First prong  226  is in contact with first step  218  and second prong  228  is in contact with second step  220  when clamp  124  is coupled to fuel injector  50 . First prong tip  230  is in axial facing contact with first step  218 , and second prong tip  232  is in axial facing contact with second step  220 . A contact length  238  of first prong tip  230  and second prong tip  232  to each respective first step  218  and second step  220  may be less than a majority of a full length  240  of each respective first step  218  and second step  220 . 
     It will be recalled that gas exchange openings  78 ,  80 ,  82 , and  84  define midline  112 . Midline  112  may lie within a cylinder head middle plane commonly labeled with reference numeral  112  that extends vertically through cylinder head  34  and fuel injector  50 . Fuel injector  50  may be bisected by the cylinder head middle plane  112 . Bolt hole  214  and bolt bore  86  are coaxially arranged along common axis  216 / 88 , which is offset from the cylinder head middle plane  112 . When fuel injector assembly  206  is installed for service in cylinder head assembly  35 , the cylinder head middle plane  212 , fuel injector middle plane  182 , and a clamp middle plane (not numbered) defined between a first inside prong surface  246  of first prong  226  and a second inside prong surface  248  of second prong  228  may all be coplanar. Returning focus to  FIGS.  8  and  9   , it will be recalled that clamp  124  may be canted. Canted means offset, and in the top view of  FIG.  9    the canting of forked injector portion  208  relative to bolting portion  212  is readily apparent. Clamp axis  244  may be diagonal to each of first inside prong surface  246  and second inside prong surface  248 , in a projection plane as depicted in  FIG.  9    oriented normal to bolt hole axis  216 . 
     Focusing now on additional proportional and dimensional attributes of fuel injector  50 , it will be recalled that fuel injector  50  is structured for installation in a relatively tight packaging space amongst valvetrain components in cylinder head assembly  35 . Fuel injector  50  may be relatively longer or taller relative to its diameter in comparison to certain known fuel injectors, and has various relative proportions of parts of injector housing  130  adapted for fitting into the available packaging space without compromising other factors such as functionality or serviceability. It will be recalled injector housing  130  includes a nozzle  142  having a nozzle terminal tip  252 . Injector full diameter (FD)  186  is defined by body piece  176 . An axial distance (AD)  254  is defined between an intersection of connector axis  156  and longitudinal axis  132 , and nozzle terminal tip  252 . A ratio of AD to FD may be from 4.8 to 5.1. In a refinement, the ratio of AD to FD may be from 4.88 to 5.06. In one practical implementation FD is equal to 30 millimeters within a tolerance of plus 0.8 millimeters or minus 0.0 millimeters, and AD is equal to 151.16 millimeters within a tolerance of plus 0.7 millimeters or minus 0.65 millimeters. 
     Electrical connector  170  may further include a connector terminal tip  256 . An injector axial length (AL)  258  is defined between connector terminal tip  256  and nozzle terminal tip  252 . A ratio of AL to FD may be from 6.9 to 7.2. In a refinement, the ratio of AL to FD is from 6.94 to 7.19. In a practical implementation AL is equal to 214.86 millimeters within a tolerance of plus 0.9 millimeters or minus 0.85 millimeters. 
     Injector housing  130  may further include a nozzle case  260 , and a middle body piece  262  between nozzle case  260  and upper body piece  176 . A reduced diameter (RD)  270  is defined by nozzle case  260 . Middle body piece  262  may include an upper section  264  having a diameter  266  equal to FD, and a lower section  268  having a diameter  272  equal to RD. The respective diameters may be equal within tolerances applied to the injector housing diameters, hence applying tolerances associated with FD to the described relationships relative to FD means that “equal” is satisfied within plus 2×0.8 millimeters or minus 2×0.0 millimeters. From  FIGS.  11  and  12    it will also be appreciated that FD is normal to MD, and that RD is greater than MD and less than FD. 
     Injector housing  130  may further include a locating surface  273  spaced axially inward of nozzle terminal tip  252  and extending circumferentially around nozzle  142 . An exposed tip length axial distance (TL)  274  is defined between locating surface  273  and nozzle terminal tip  252 . A ratio of AD to TL may be from 8.06 to 8.34. In a refinement the ratio of AD to TL may be from 8.07 to 8.32. A ratio of AL to TL may be from 11.48 to 11.86. In the illustrated embodiment, crush washer  100  forms locating surface  273 . In one practical implementation TL is equal to 18.36 millimeters within a tolerance of plus 0.3 millimeters or minus 0.15 millimeters. As will be further apparent from the following description the disclosed proportional and dimensional attributes relative to elongate nozzle  142  can assist in precisely positioning nozzle terminal tip  252  within combustion cylinder  18  such that nozzle  142  will not likely overheat while also presenting spray outlet features that are matched to features of piston  20  to achieve desirable performance goals. 
     Referring also now to  FIGS.  13 - 15    a protrusion distance (PD)  276  is defined between lower fire deck surface  70  and nozzle terminal tip  252 . A ratio of TL to PD may be from 8.67 to 8.89. In one practical implementation PD is equal to 2.1 millimeters, within a tolerance of plus 0.3 millimeters or minus 0.15 millimeters, for example. Nozzle case  260  may further include an axial end surface  278 . A distance  280  from axial end surface  278  to nozzle terminal tip  252  may be 19.86 millimeters, within a tolerance of plus 0.3 millimeters or minus 0.15 millimeters. It will be appreciated axial end surface  278  is a surface obscured by crush washer  100  when positioned about nozzle  142 . Spray outlets  144  may be of uniform size, uniform shape such as cylindrical, and uniformly distributed about a center axis  288  defined by elongate nozzle  142 . Nozzle terminal tip  252  may be hemispheric in shape as can be seen in  FIGS.  13  and  14   . 
     Spray outlets  144  may define spray axes  284  defining a spray angle of 130° plus or minus a tolerance of 0.75°, for example. Spray axes  284  may further define a spray axis apex  282  within nozzle  142 . A distance  286  from spray axis apex  282  to nozzle terminal tip  252  may be 1.1 millimeters. A tip full length (FL) is defined between axial end surface  278  and nozzle terminal tip  252 . Spray axes  284  may each define a center point  292  at a respective spray outlet exit location. A base-apex axial dimension (BA)  294  is defined between axial end surface  278  and spray axis apex  282 . A base-center point axial dimension (BC)  296  is defined between axial end surface  278  and center points  292 . A ratio of FL to BA may be from 1.06 to 1.10, and a ratio of FL to BC may be from 1.04 to 1.08. In one practical implementation FL is equal to 19.86 millimeters within a tolerance plus 0.3 millimeters or minus 0.15 millimeters. 
     Focusing now on  FIG.  13   , there is shown a combustion system  360  including fuel injector  50  and piston  20 . As noted above features of fuel injector  50  including dimensions, proportions, and other geometric attributes can be understood to work cooperatively with features of piston  20  to obtain desirable and unexpectedly advantageous results. Piston  20  includes a piston end face  302  forming an annular piston rim  304  extending circumferentially around a piston center axis  350 . Annular rim  304  may include an outer rim surface  306  and a sloped inner rim surface  308 . In some embodiments annular rim  304  may include pockets to accommodate intake valves. Piston end face  302  further forms a combustion bowl  310  having a bowl floor  316  and a bowl outer wall  318 . A center cone  312  formed by piston end face  302  is within combustion bowl  310  and defines a cone angle  322 . Spray axes  284  define a spray angle  298 , smaller than cone angle  322 . Spray angle  298  may be 130° plus or minus 0.75°, for example. Cone angle  322  may be 140° plus or minus 0.75°, for example. A difference between spray angle  298  and cone angle  322  may be 10° plus or minus 1.5°. A peak  313  of center cone  312  is generally centered on piston center axis  350 . Piston  20  further includes a reentrant protrusion  320  extending circumferentially around combustion bowl  310 . Annular rim  304  and bowl outer wall  318  intersect at reentrant protrusion  320 . Bowl floor  316  is radiused to form a toroidal shape and is intersected by spray axes  284  at the top dead center position of piston  20 , approximately as shown in  FIG.  13   . In one practical implementation outer rim surface  306  is flat or planar as described, and sloped inner rim surface  308  is radiused. In a refinement, sloped inner rim surface  308  forms a chamfius, a combined chamfered and radiused profile, adjoining reentrant protrusion  320 . The sloped profile of inner rim surface  308  is formed by the chamfius at least in part. Reentrant protrusion  320  may include a sharp edge that defines a radius of curvature smallest among all radiuses of curvature formed by piston end face  302 . In one embodiment reentrant protrusion  320  includes a deburred edge. As further discussed herein, features of fuel injector  50  and piston  20  form a glancing spray jet impingement pattern upon center cone  312  when piston  20  is at the top-dead-center position. 
     INDUSTRIAL APPLICABILITY 
     As discussed above, features of fuel injector  50  and piston  20  can be understood to be matched to provide desirable power density, efficiency, and emissions. To these ends, positioning, orientation, and number of spray outlets  144  are highly precise relative to fire deck  70  and features of piston  20 . Configuring fuel injector  50  in this manner enables spray plumes of fuel to advance in a desirable pattern that limits plume-plume interaction between adjacent spray plumes or jets of fuel, also limits interaction of any one spray plume with itself, and supports a combustion strategy that optimizes the use of available oxygen within combustion cylinder  18  even with relatively larger quantity highly pressurized fuel injections. 
     It has been discovered that employing a number of spray outlets greater than seven can be associated with greater risk of interaction between spray plumes and present challenges, particularly respecting emissions during transient engine conditions, resulting in excess soot production. Using more than seven outlets can be also associated with insufficient penetration of spray plumes into the cylinder for optimal combustion, at least without other compensation that can create still other challenges. It has further been discovered that use of a number of spray outlets less than seven can also present different challenges, namely, higher soot emissions generally, and likely for the reason that larger outlets result in greater penetration of spray plumes into the cylinder than is desired, resulting in potential wall wetting and/or excessive curling back of the plumes upon themselves and thus limiting exposure of the fuel to otherwise available oxygen. The use of exactly seven spray outlets configured according to the present disclosure provides a desirable balance of distribution of injected fuel into the available combustion space, providing sufficient but not excessive spray penetration while minimizing both plume-plume and intra-plume interaction risks. The features of spray outlet arrangement and number also cooperate with piston features, as further discussed below. 
     Referring also now to  FIGS.  16  and  17   , operating engine  12  can include moving piston  20  between its bottom dead-center-position and top-dead-center position in combustion cylinder  18 , and increasing in-cylinder pressure in combustion cylinder  18  based on the moving of piston  20  to an autoignition threshold for air and injected liquid fuel. Operating engine  12  can further include directly injecting the liquid fuel into combustion cylinder  18  through exactly seven spray outlets  144  in fuel injector  50  to produce spray jets advanced outwardly and downwardly from fuel injector  50  into combustion bowl  310  formed by piston end face  302 . 
     As depicted in  FIG.  16   , spray jets or plumes  400  are shown as they might appear at, or just after, the top-dead-center position of piston  20 , having propagated outwardly and downwardly from fuel injector  50  and first impinging at an impingement location  410  that is upon a slope of center cone  314 . In particular, impingement location  410  may be within a middle one third of the slope between cone peak  313  and a bottom of combustion bowl  310  formed by bowl floor  316 . Thus, at a top-dead-center position, approximately as shown in  FIG.  16   , spray jets  400  are targeted at a bottom of combustion bowl  310 . Upon and after the initial, first impingement spray jets  400  may be understood as glancing against the slope of center cone  314 . The glancing hit of spray jets  400  can be understood to initiate a gliding flow of the injected fuel along bowl surfaces, smoothly guiding the fuel while limiting any reduction in momentum that might occur as a result of a more direct impingement, and helping ensure fuel flow will continue robustly as jets  400  continue along the bowl surfaces. Put differently, the described strategy conserves momentum such that mixing of fuel and air can optimally continue late in the injection cycle. 
     Fuel of the glanced spray jets  400  can be guided along outer bowl surface or wall  318  upwardly toward reentrant protrusion  320 . At reentrant protrusion  320  the guided fuel is split into a detached minor flow  408  that is advanced upwardly and outwardly from reentrant protrusion  320  over sloped inner rim surface  308 . Forming inner rim surface  308  with a slope, and in particular with a chamfius, assists in controlling detachment of minor flow  408  so as to not be excessive, while making use of available oxygen in the space between piston rim  304  and fire deck  70 . A circulated major flow  406  is advanced upwardly and inwardly from reentrant protrusion  320  toward fire deck surface  70  in engine  12 . Splitting of the guided fuel can further include apportioning the guided fuel in a manner limited self re-entrainment (intra-plume interaction) of the circulated major flow. In  FIGS.  16  and  17    regions of fuel shown at  402  are not yet combusting or have just begun to combust, while regions shown at  404  are actively combusting and at high temperatures. Regions shown at  405  are still actively combusting but proceeding to somewhat cooler temperatures as combustion approaches completion. 
     The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.