Patent Publication Number: US-10767610-B2

Title: Liquid fuel injector having dual nozzle outlet sets, fuel system, and method

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a liquid fuel injector for a fuel system in an internal combustion engine and relates more particularly to a liquid fuel injector having dual outlet checks and dual nozzle outlets supplied by a common nozzle supply cavity. 
     BACKGROUND 
     Fuel systems used in state-of-the-art internal combustion engines are relatively complex and sophisticated electromechanical systems. The associated engines can be direct-injected where fuel injectors extend into the engine cylinders, port-injected where fuel is delivered into a port in communication with an engine cylinder, or structured according to yet another strategy. In the case of compression ignition diesel engines it is typical for liquid fuel injection pressures to be as high as several hundred megapascals (MPa). Injections can occur multiple times per second, necessitating rapid travel of moving parts within the fuel injector in response to electromagnetic actuation forces and/or rapid pressure changes, and resulting in relatively intense, repetitive impacts, and in some instances a tendency toward liquid cavitation. The timing and manner of injection of fuel is typically relatively tightly controlled, with opening and closing of valves desirably quite rapid to produce so-called “square” injection rate shapes, ramp shapes, and still others. 
     Pressurization of the fuel to be injected can take place within the fuel injector itself, such as by way of a hydraulically actuated or cam-actuated plunger, or externally such that pressurized fuel is stored in a common rail or the like and a reservoir of pressurized fuel maintained for multiple fuel injectors. Due to the foregoing and other factors, fuel injectors are often purpose-built for certain fuel injection strategies and combustion recipes. One example fuel injector for an internal combustion engine is known from U.S. Pat. No. 7,556,017 to Gibson et al. 
     SUMMARY OF THE INVENTION 
     In one aspect, a liquid fuel injector for an internal combustion engine includes an injector body defining an inlet passage, a first set of nozzle outlets, a second set of nozzle outlets, a first control chamber, and a second control chamber each in fluid communication with the inlet passage, and a low-pressure space. The liquid fuel injector further includes a first outlet check having a closing hydraulic surface exposed to a fluid pressure of the first control chamber and movable between a closed position blocking the first set of nozzle outlets, and an open position. The liquid fuel injector further includes a second outlet check having a closing hydraulic surface exposed to a fluid pressure of the second control chamber and movable between a closed position blocking the second set of nozzle outlets, and an open position. The liquid fuel injector still further includes a first injection control valve positioned fluidly between the first control chamber and the low-pressure space, and a second injection control valve positioned fluidly between the second control chamber and the low-pressure space. The first set of nozzle outlets form a narrower spray angle and have a first combination of outlet number and outlet size, such that the first set of nozzle outlets produces a relatively greater steady flow of fuel for injection. The second set of nozzle outlets form a wider spray angle and have a second combination of outlet number and outlet size, such that the second set of nozzle outlets produces a relatively lesser steady flow of fuel for injection. The injector body further defines a common nozzle supply cavity in fluid communication with the inlet passage, and the first set of nozzle outlets and the second set of nozzle outlets being in fluid communication with the common nozzle supply cavity at the open position of the first outlet check and the second outlet check, respectively. 
     In another aspect, a fuel system for an internal combustion engine includes a liquid fuel supply, and a plurality of liquid fuel injectors each defining an inlet passage, a first set of nozzle outlets, a second set of nozzle outlets, and a low-pressure space. The plurality of liquid fuel injectors each include a first direct-operated outlet check movable between a closed position blocking the first set of nozzle outlets, and an open position, and a second direct-operated outlet check movable between a closed position blocking the second set of nozzle outlets and an open position. The plurality of liquid fuel injectors each further include a first injection control valve coupled with the first direct-operated outlet check and a second injection control valve coupled with the second direct-operated outlet check. The first set of nozzle outlets in each one of the plurality of liquid fuel injectors form a narrower spray angle and have a first combination of outlet number and outlet size, such that the first set of nozzle outlets produces a greater steady flow of fuel for injection. The second set of nozzle outlets in each one of the plurality of liquid fuel injectors form a wider spray angle and have a second combination of outlet number and outlet size different from the first combination, such that the second set of nozzle outlets produces a lesser steady flow of fuel for injection. 
     In still another aspect, a method of operating an engine includes supplying liquid fuel to a liquid fuel injector positioned at least partially within a cylinder in the engine, and injecting a first charge of the liquid fuel into a cylinder in the engine using a first set of nozzle outlets in a fuel injector, such that spray jets of the first charge of the liquid fuel are oriented at a relatively narrower spray angle. The method further includes autoigniting the first charge of the liquid fuel such that the first charge of the liquid fuel combusts by diffusion burning within the cylinder in a first engine cycle. The method further includes injecting a second charge of the liquid fuel into the cylinder using a second set of nozzle outlets in the fuel injector, such that spray jets of the second charge of liquid fuel are oriented at a relatively wider spray angle, and autoigniting the second charge of the liquid fuel such that the second charge of liquid fuel combusts by diffusion burning within the cylinder in a second engine cycle. The method still further includes transitioning operation of the engine from a relatively higher engine load in the first engine cycle to a relatively lower engine load in the second engine cycle, and decreasing fueling of the engine based on the transitioning of the operation of the engine, such that an amount of the second charge of liquid fuel is smaller than an amount of the first charge of liquid fuel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially sectioned side diagrammatic view of an internal combustion engine system, according to one embodiment; 
         FIG. 2  is a sectioned side view of a fuel injector suitable for use in the internal combustion engine system of  FIG. 1 ; 
         FIG. 3  is a sectioned view through an orifice plate taken along line  3 - 3  of  FIG. 4 , according to one embodiment; 
         FIG. 4  is a perspective view of an orifice plate, according to one embodiment; 
         FIG. 5  is a sectioned view taken along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is a sectioned view taken along line  6 - 6  of  FIG. 4 ; 
         FIG. 7  is an enlarged sectioned view of a portion of a liquid fuel injector, according to one embodiment; 
         FIG. 8  is a diagrammatic view of liquid fuel injection, and associated apparatus at a first set of conditions; and 
         FIG. 9  is a diagrammatic view of liquid fuel injection, and associated apparatus at another set of conditions. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown an internal combustion engine system  8  (hereinafter “engine system  8 ”), according to one embodiment. Engine system  8  can include a compression ignition internal combustion engine system structured to operate on liquid fuel. In an implementation, the liquid fuel can include diesel distillate fuel, however, other liquid hydrocarbon fuels such as biodiesel or blends might be used. Engine system  8  includes an internal combustion engine  10  having a housing  12  with a plurality of combustion cylinders  14  formed therein. Cylinders  14  can be of any number and in any suitable arrangement such as an in-line arrangement, a V-configuration, or still another arrangement. A piston  16  is movable within each one of combustion cylinders  14  to rotate a crankshaft  18  in a generally conventional manner. Engine system  8  can further include an intake conduit  26  structured to feed air for combustion to combustion cylinders  14  by way of a turbocharger  20  including a compressor  22  and a turbine  24 . An aftercooler  28  is positioned downstream of compressor  22  and conveys cooled and compressed air to an intake manifold  30 . A plurality of intake runners  32  extend between intake manifold  30  and each of combustion cylinders  14 , again in a generally conventional manner. Engine system  8  further includes a fuel system  44 . 
     Fuel system  44  includes a liquid fuel supply  46  such as a fuel tank, and can include at least one pump structured to convey the liquid fuel to engine  10 . In the illustrated embodiment a low-pressure transfer pump  48  receives fuel from supply  46  and transitions the fuel to a high-pressure pump  50  that feeds a pressurized fuel reservoir  52  such as a common rail. Fuel reservoir and common rail are terms used interchangeably herein. For purposes of the present disclosure common rail  52  can be understood to itself be, or be a part of, a fuel supply. It should be appreciated that a single monolithic pressurized fuel reservoir could be used, as well as a plurality of separate pressure accumulators, or still another strategy such as a plurality of unit pumps. An electronic control unit  54  may be coupled with a plurality of liquid fuel injectors  56  of fuel system  44 . A mass flow sensor  55  may be coupled with electronic control unit  54  to monitor incoming air flow for determining or estimating engine load indirectly, the significance of which will be further apparent from the following description. Liquid fuel injectors  56  may each be coupled with engine housing  12  and positioned so as to extend at least partially into each one of combustion cylinders  14 . Each liquid fuel injector  56  can include twin or dual outlet checks, as further discussed herein, structured to inject liquid fuel in different quantities, at different spray angles or different spray patterns, for example, and for different purposes, including a first liquid fuel charge that serves as a main charge during operating engine  10  in a higher portion of its load range, and a second charge of liquid fuel that serves as a main charge during operating engine  10  in a lower portion of its load range. As will be further apparent from the following description, it is contemplated that separate control and separate design of the two outlet checks enables optimization for their different intended purposes. 
     Referring also now to  FIG. 2 , there is shown a sectioned view through a liquid fuel injector  56  of a type suitable for use in engine system  8 . Fuel injector  56  includes an injector body  58  defining a high-pressure inlet passage  60  connected with a high-pressure inlet  62 . Inlet  62  may fluidly connect with reservoir/common rail  52 , for example, by way of a so-called quill connector in one embodiment. Injector body  58  further defines a first set of nozzle outlets  64 , a second set of nozzle outlets  66 , a first control chamber  68 , and a second control chamber  70  each fluidly connected to inlet passage  60 . Injector body  58  also defines a low-pressure space  72  that can be a low-pressure outlet or drain, or multiple low-pressure outlets or drains, within injector body  58  or the space outside injector body  58 . Fuel injector  56  further includes a first outlet check  74  having a closing hydraulic surface  76  exposed to a fluid pressure of first control chamber  68  and movable between a closed position blocking first set of nozzle outlets  64 , and an open position. Fuel injector  56  also includes a second outlet check  78  having a closing hydraulic surface  80  exposed to a fluid pressure of second control chamber  70  and movable between a closed position blocking second set of nozzle outlets  66 , and an open position. In the illustrated embodiment first outlet check  74  and second outlet check  78  are arranged side-by-side, and first set of nozzle outlets  64  has at least one of a spray angle, an outlet size, or an outlet number that is different from a spray angle, an outlet size or an outlet number of second set of nozzle outlets  66 . First set of nozzle outlets  64  may form a narrower spray angle  114 , and has a first combination of outlet number and outlet size, such that nozzle outlets  64  produce a greater steady flow of fuel for injection. Second set of nozzle outlets  66  may form a second, wider spray angle  116 . Nozzle outlets  66  have a second combination of outlet size different from the first combination, such that nozzle outlets  66  produce a lesser steady flow of fuel for injection. Both of outlet number and outlet size may differ between the respective sets, although the present disclosure is not thereby limited, and only one of outlet number and outlet size might differ. Steady flow means a rate of flow that is observed if the same conditions are applied to/experienced by the respective nozzle outlet sets, irrespective of time. A greater number of outlets, a greater size of outlets, or both, can give a greater steady flow, whereas a lesser number of outlets, a lesser size of outlets, or both, results in a lesser steady flow. 
     Fuel injector  56  further includes a first electrically actuated injection control valve  82  in a first control valve assembly  81 . Injection control valve  82  can be a first two-way injection control valve and is positioned fluidly between first control chamber  68  and low-pressure space  72 . A control passage  83  extends between control valve assembly  81  and first control chamber  68 . Control valve  82  is movable between a closed position blocking fluid communication between control passage  83  and low-pressure space  72  and an open position at which control passage  83  is fluidly connected to low-pressure space  72 . Control valve  82  is thus structured to connect or disconnect a total of two passages. Fuel injector  56  also includes a second electrically actuated injection control valve  85  in a control valve assembly  84 . Injection control valve  85  can be a second two-way injection control valve and is positioned fluidly between second control chamber  70  and low-pressure space  72 . Instead of two-way injection control valves, three-way injection control valves, or still another valve configuration could be used. A control passage  87  extends between second control chamber  70  and control valve assembly  84 . Control valve assembly  84  can function analogously to control valve assembly  81 . In the illustrated embodiment each of control valve assembly  81  and control valve assembly  84  is a solenoid actuated control valve assembly structured to vary between a deenergized state where the respective control valves  82  and  85  are at their closed positions, and an energized state where control valves  82  and  85  move in opposition to a spring biasing force to an open position. Certain components are shared among control valve assembly  81  and control valve assembly  84 , however, the present disclosure is not thereby limited. It can also be seen from  FIG. 2  that control passage  83  and control passage  87  extend through a number of components of injector body  58 , and may be out of plane in the view illustrated. Each of injection control valve  82  and injection control valve  85  can include a ball valve or a half-round, hemispheric valve structured to move into and out of contact with a flat valve seat, however, the present disclosure is not thereby limited. Those skilled in the art will be familiar with the design technique of providing for flow to low-pressure space  72  between or among the various components in injector body  58  between injection control valve assemblies  81  and  84  and low-pressure space  72  when injection control valves  82  and  85  are opened. 
     Injector body  58  further includes a casing  92  and a stack  94  positioned within casing  92 . Injector body  58  also defines a common nozzle supply cavity  90  in fluid communication with inlet passage  60 . Common nozzle supply cavity  90  can be understood as part of inlet passage  60 , which in turn can be understood to extend from inlet  62  to each of nozzle outlets  64  and nozzle outlets  66 . First set of nozzle outlets  64  and second set of nozzle outlets  66  are fluidly connected to common nozzle supply cavity  90  at the open position of first outlet check  74  and second outlet check  78 , respectively. Common nozzle supply cavity  90  may be formed within stack  94 , and each of first outlet check  74  and second outlet check  78  extends through common nozzle supply cavity  90 . Stack  94  also includes a tip piece  95 , positioned within casing  92  and having first set of nozzle outlets  64  and second set of nozzle outlets  66  formed therein. Tip piece  95  has therein a first guide bore  102  that receives first outlet check  74  and forms a first nozzle supply passage  104  with first outlet check  74 . Tip piece  95  also has therein a second guide bore  106  that receives second outlet check  78  and forms a second nozzle supply passage  108  with second outlet check  78 . A first M-orifice  110  is formed within tip piece  95  to limit flow through first nozzle supply passage  104 . A second M-orifice  112  is formed within tip piece  95  to limit flow through second nozzle supply passage  108 . A spacer  96 , which can be cylindrical in shape, is positioned to abut tip piece  95  and includes a wall  99  extending circumferentially around first outlet check  74  and second outlet check  78  so as to form common nozzle supply cavity  90 . Yet another stack piece  98  is positioned at least partially within casing  92 , and an orifice plate  100  is sandwiched between stack piece  98  and spacer  96 . Each of first outlet check  74  and second outlet check  78  can include opening hydraulic surfaces (not numbered) exposed to a fluid pressure of common nozzle supply cavity  90 . Each of first outlet check  74  and second outlet check  78  is further biased closed by way of spring biasing in a generally known manner. 
     Injector body  58  still further defines a first set of orifices  86  arranged in an A-F-Z pattern among inlet passage  60 , low-pressure space  72 , and first control chamber  68 . An “A” orifice is positioned fluidly between a check control chamber and an outlet to low pressure, whereas a “Z” orifice is fluidly between incoming high pressure and a check control chamber, and an “F” orifice fluidly connects a high pressure supply for the Z-orifice to an outlet of the A-orifice. A second set of orifices  88  is arranged in an A-F-Z pattern among inlet passage  60 , low-pressure space  72 , and second control chamber  70 . Referring also now to  FIGS. 3 and 4 , there are shown additional details of orifice plate  100 . Orifice plate  100  includes a one-piece orifice plate body  120  defining a center axis  122  extending between an upper plate body side  124  and a lower plate body side  126 . Orifice plate body  120  also includes an outer peripheral edge  128  extending circumferentially around center axis  122 . In the illustrated embodiment, outer peripheral edge  128  includes a first linear segment  130 , a first arcuate segment  132 , a second linear segment  134 , and a second arcuate segment  136 . First and second arcuate segments  132  and  136  are in an alternating arrangement with first and second linear segments  130  and  134 . Orifice plate body  120  also has a plurality of raised sealing surfaces including a first raised sealing surface  138 , a second raised sealing surface  140 , and a third raised sealing surface  142 . It can be seen from  FIG. 4  that sealing surface  138  and sealing surface  142  are arranged adjacent to first arcuate segment  132  and second linear segment  134 , respectively. Orifice plate body  120  also includes a recessed surface  144  positioned axially inward of raised sealing surfaces  138 ,  140 , and  142 . Orifice plate body  120  further has a first inlet passage  146  and a second inlet passage  148  extending between upper plate body side  124  and lower plate body side  126 , for feeding high-pressure fuel to first control chamber  68  for first outlet check  74  and second control chamber  70  for second outlet check  78 , respectively. 
     Orifice plate body  120  also includes a first outlet passage  150  and a second outlet passage  152  extending between lower plate body side  126  and upper plate body side  124 , for connecting first and second control chambers  68  and  70  to low-pressure space  72 . First set of orifices  86  in orifice plate body  120  is also shown in  FIG. 3  and include a first A-orifice  154  formed in first outlet passage  150 , a first Z-orifice  156  formed in first inlet passage  146 , and a first F-orifice  158 . F-orifice  158  is out of plane in  FIG. 3 , but described and illustrated elsewhere hereinafter. Second set of orifices  88  in orifice plate body  120  is also shown in  FIG. 3  and includes a second A-orifice  160  formed in second outlet passage  152 , a second Z-orifice  162  formed in second inlet passage  148 , and a second F-orifice  164 . First and second F-orifices  158  and  164  fluidly connect first and second outlet passages  150  and  152  to lower plate body side  126  to fluidly connect common nozzle supply cavity  90  in fuel injector  56  to each of first and second control chambers  68  and  70 . Provision of F-orifices  158  and  164  assists in refilling of control chambers  68  and  70  at the end of fuel injection, as further discussed herein. It should be appreciated that F-orifices  158  and  164  could connect to high-pressure inlet passage  60  by another architecture. In other words, in a practical implementation strategy F-orifices  158  and  164  connect to common nozzle supply cavity  90 , but could be configured otherwise without departing from the scope of the present disclosure. The various orifices described herein could also be positioned in components of stack  94  other than orifice plate  100  in other embodiments. 
     It can also be noted from  FIG. 4  that a first connector channel  166  is formed in upper plate body side  124  and fluidly connects first inlet passage  146  to second inlet passage  148 . First connector channel  166  may have a C-shaped configuration, although the present disclosure is not thereby limited. A second connector channel  168  is formed in upper plate body side  124  and fluidly connects first outlet passage  150  to first F-orifice  158 . A third connector channel  170  is formed in upper plate body side  124  and fluidly connects first outlet passage  150  to second F-orifice  164 . Each of second connector channel  168  and third connector channel  170  may be linear in shape. It can also be noted that each of first, second, and third connector channels  166 ,  168 , and  170  is formed in raised sealing surface  140 . The axial depth between raised sealing surfaces  138 ,  140 , and  142  and recessed surface  144  can provide a space that is connected to high pressure when fuel injector  56  is assembled for service. First and second inlet passages  146  and  148  and first and second outlet passages  150  and  152  may be in an alternating arrangement between first and second linear segments  130  and  134  of outer peripheral edge  128 . 
     Referring also now to  FIG. 5  and  FIG. 6 , there are shown sectioned views taken along lines  5 - 5  and  6 - 6  of  FIG. 4 . It will also be noted that the sectioned view in  FIG. 3  includes subject matter of orifice plate  100  taken along line  3 - 3  of  FIG. 4 . It can be seen from  FIG. 5  and  FIG. 6  that F-orifices  158  and  164  each extend at an angle from the corresponding connector channel  168  and  170 , relative to center axis  122 . It will be recalled that F-orifices  158  and  164  provide fluid connections between outlet passages  150  and  152  and common nozzle supply cavity  90 . A first fluid passage  163  extends between upper plate body side  124  and lower plate body side  126 , and a second fluid passage  152  also extends between upper plate body side  124  and lower plate body side  126 . First fluid passage  163  includes first F-orifice  158  and opens at lower plate body side  126 , whereas second fluid passage  152  includes second F-orifice  160  and opens at lower plate body side  126 . It can also be noted from  FIG. 35  that each of first and second A-orifices  154  and  160  and each of first and second Z-orifices  156  and  162  is formed adjacent to lower plate body side  126 . Each of first and second F-orifices  156  and  158  can be formed adjacent to upper plate body side  124 . Sizes of each of the A, F, and Z-orifices herein may be within an order of magnitude of one another. 
     Referring also now to  FIG. 7 , there is shown a close-up view of a portion of fuel injector  56 , illustrating side-by-side arrangement of outlet check  74  and outlet check  78 . Outlet check  74  and outlet check  78  are shown in closed positions and structured to lift and return along a first check axis  61  and a second check axis  63 , respectively, with axes  61  and  63  being parallel to one another and parallel to a longitudinal axis  59  of fuel injector  56  itself. In one example configuration, nozzle outlets  66  are straight and substantially cylindrical, from 6 to 8 in number, and have a hole diameter  67  that is about 300 microns or 0.003 millimeters. Nozzle outlets  66  may be arranged circumferentially about axis  63 , have uniform orientations at the subject spray angle and may be evenly spaced from one another. Nozzle outlets  64  might also be straight and substantially cylindrical, be from 4 to 6 in number, and have a hole diameter  65  that is from about 25% to about 50% of hole diameter  67 . In one implementation hole diameter  65  is 150 microns or 0.0015 millimeters. Nozzle outlets  64  may be circumferentially and uniformly spaced about axis  61 , and have uniform orientations at the subject spray angle. Spray angle  116  may be from about 130° to about 140°, and spray angle  114  from about 140° to about 150°. As used herein, the term “about” can be understood in the context of conventional rounding to a consistent number of significant digits. Thus, “about 300” is from 250 to 349, “about 25%” is from 24.5% to 25.4%, and so on. 
     Referring also now to  FIG. 8 , spray jets of liquid fuel, in the context of the present description the first charge of liquid fuel, may be targeted along a surface of a combustion bowl in a piston within the corresponding cylinder. In  FIG. 8  piston  16  is shown, illustrating a piston top surface  17  that has a middle or inner convex section  19 , an outer rim section  23  that forms a piston rim  27 , and a concave bowl section  21  extending between section  19  and section  17  and forming a combustion bowl  25 . A fuel spray jet is shown at  400  with an arrow indicating an approximate direction of targeting of fuel spray jet  400  toward a target  300  approximately in the middle or close to the lowest point of combustion bowl  25 . Different combustion strategies and objectives might have substantially different targets, which could be constant for a given engine or class of engines, or change depending upon a presently desired or required outcome. In other words, the targeting could be varied cycle to cycle. It will be understood that piston  16  is reciprocating up and down within the corresponding cylinder  14 , such that a position of piston  16  relative to spray jet  400  can vary with varying engine speed or varying velocity of spray jet  400  as it advances through cylinder  14 . A velocity of spray jet  400  can depend upon injection pressure, including injection pressure relative to an internal pressure and/or density of fluid within cylinder  14 . Thus, a density of fluids within cylinder  14 , including air and potentially gaseous fuel and/or recirculated exhaust gas, can affect the speed and extent of penetration of spray jets of injected liquid fuel. It will therefore be appreciated that turbocharger boost pressure, engine speed, and injection timing and amount can all bear upon the manner in which fuel spray jets advance through an engine cylinder. To obtain desired combustion results, engineers typically target certain features within an engine cylinder as noted above. In the illustration of  FIG. 8 , spray jet  400  is targeted along surface  17 , in particular along the portions of surface  17  forming combustion bowl  25 , toward target  300 . In at least some instances fuel injection design properties can be based on a 100% load or rated condition. For operation in a higher portion of an available engine load range, such as 50%-100% load, it can be desirable to limit entrainment of air into fuel spray jets to obtain a desired balance between production of oxides of nitrogen, or NOx, and soot. Spray angle  116 ′, shown relative to a cylinder centerline, may be about 65°. Referring also to  FIG. 9 , there is shown fuel injector  56  positioned in proximity to piston  16 , with a fuel spray jet  410  shown directed from nozzle outlets  64  toward a different target  320 . A spray angle  114 ′ relative to the cylinder centerline may be about 75°. At lower load conditions, such as less than 50% load, production of NOx may be of less concern, and it is thus desirable to entrain more air to promote more complete burning and minimize soot. 
     Industrial Applicability 
     Referring to the drawings generally, during operating engine system  8  outlet check  78  can be controlled by way of injection control valve assembly  84  to open and close to inject a first charge of liquid diesel fuel into cylinder  14  in an engine cycle, using nozzle outlets  66  such that spray jets of the first charge of liquid fuel are oriented at relatively narrower spray angle  116 . The first charge can be autoignited within cylinder  14  such that the first charge combusts by diffusion burning within cylinder  14  in the first engine cycle. Embodiments are also contemplated wherein both of second outlet check  78  and first outlet check  74  are operated by way of control valve assembly  84  and control valve assembly  81 , respectively, to cooperate in injection of a charge of liquid diesel fuel, provide successive injections within the same engine cycle, such as pilot injections, pre-injections, or post-injections. Injection control valve assembly  84  can be energized to lift injection control valve  85  from its seat to cause a drop in pressure in second control chamber  70 , in turn enabling pressure acting on opening hydraulic surfaces of outlet check  78  in common nozzle supply cavity  90  to lift outlet check  78  to open nozzle outlets  66 . When injection is to be ended, or just prior to when injection is to be ended, injection control valve assembly  84  is deenergized, to close injection control valve  85  and enable pressure to increase in second control chamber  70  and act upon closing hydraulic surface  80  to cause outlet check  78  to close. Piston  16  moves in a conventional four-phase cycle to intake, compress, combust, and exhaust the mixture of air and diesel fuel. As noted above, outlet check  74  can be operated generally analogously to operation of outlet check  78  so as to inject a second charge of liquid diesel fuel into cylinder  14  using nozzle outlets  66 , such that spray jets of the second charge of liquid fuel are oriented at a relatively wider spray angle. The second charge is autoignited in a manner generally analogous to that of the first charge. 
     Operation of engine  10  may be transitioned from a relatively higher engine load in the first engine cycle to a relatively lower engine load in the second engine cycle. Operation of engine  10  can of course be transitioned in the reverse, from one engine cycle where engine load is relatively lower to another engine cycle where engine load is relatively higher. Data produced by sensor  55  enables electronic control unit  54  to determine or estimate a present engine load and changes in engine load. In one implementation, transitioning of the operation of engine  10  includes transitioning from greater than a 50% load to less than a 50% load, using nozzle outlets  66  when engine  10  is operated at greater than 50% load and using nozzle outlets  64  when engine  10  is operated at less than 50% load. Other operating strategies could transition between the use of the respective sets of nozzle outlets at load thresholds other than 50%. In still other instances, a threshold for transitioning between use of nozzle outlets  64  and nozzle outlets  66  could vary cycle to cycle based upon factors such as engine speed, boost pressure, or still others. Fueling of engine  10  may be decreased based on the transitioning of the operation of engine  10 , such that an amount of the second charge of liquid fuel is smaller than an amount of the first charge of liquid fuel. Analogously, when operation of engine  10  is transitioned from a lower load to a higher load, fueling of engine  10  may be increased. 
     As noted above, employing dual outlet checks can enable separation of design of each outlet check for different purposes, namely, different injection characteristics at different parts of an engine load range. A liquid fuel charge during lower load operation may be injected at a relatively shallower angle, whereas a charge for higher load operation can be injected at a somewhat deeper angle into cylinder  14  as discussed herein. It is believed that the deeper/narrower angle during higher load operation enables spray jets to somewhat limit entrainment of air such that NOx production is limited, and also to reduce risk of the spray jets impinging upon a cylinder liner. At lower load operation some of the constraints as to NOx production and liner impingement are relaxed. 
     It will also be recalled that orifice sets  86  and  88  affect the nature of fuel injection, and can be sized to various ends. F-orifices can be employed to slow a rate of pressure drop in the control chambers when connected to low pressure, and can hasten the rate of pressure build at the end of injection. As a result, the F-orifices can assist in obtaining a relatively square rate shape to an end of injection, or tailored to obtain another rate shape. Z-orifices can analogously assist in obtaining a relatively square end of injection shape, for example. Varying a size of a Z-orifice within the present context tends to have a relatively larger effect on end-of-injection properties than varying the size of an F-orifice. The M-orifices are controlled clearances around the outlet checks that act to retard the start of injection. The A-orifices also tend to affect start of injection, assisting in controlling spilling of pressure from the associated control chamber. 
     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.