Patent Publication Number: US-2010123031-A1

Title: Fluid oscillator assembly for fuel injectors and fuel injection system using same

Description:
TECHNICAL FIELD  
     The present disclosure generally relates to fuel injection systems and more particularly to fuel injection systems having the ability to spray fuel from a fuel injector into a combustion space in an oscillatory pattern to reduce undesirable emissions. 
     BACKGROUND  
     In most fuel injection systems, fuel from a fuel injector is sprayed into a combustion space through one or more relatively tiny nozzle orifices at relatively high pressures. Fuel injectors control the injection of fuel from the fuel injector by opening and closing a needle check valve. Before an injection event begins, the needle check valve is in a closed configuration, preventing fuel from leaving the nozzle orifices of the fuel injector. When an injection event is initiated, the needle check valve is lifted to an open configuration, thereby allowing fuel to flow through the nozzle outlet. In a typical injection sequence, the needle check valve moves to an open configuration allowing an amount of fuel to move from inside the fuel injector to outside the fuel injector into a combustion chamber, and the needle check valve then returns to the closed configuration to end the injection event. 
     Engineers are continuously striving to improve combustion efficiency in fuel systems resulting in reduced unburned hydrocarbons and harmful emissions such as NOx as well as soot and smoke. NOx is produced in the periphery of the plume and the large unburned center adds to the production of soot and smoke. Combustion efficiency may be improved by better mixing the fuel and air. One way of improving combustion efficiency has been to raise injection pressures. However, due to technological limitations, manufacturing designs that are able to sustain ever increasing injection pressures become increasingly expensive and less cost effective. 
     Another way of improving combustion efficiency has been to inject fuel as pulses. U.S. Pat. No. 6,109,533 seeks to improve combustion efficiency by rapidly opening and closing the needle check valve during each injection cycle. By rapidly opening and losing the nozzle outlet, fuel is cyclically intermittently sprayed into the combustion space in such a way that better mixing occurs, which results in a more efficient burn. 
     The present disclosure is directed to overcoming one or more of the problems set forth above, including improving combustion efficiency, and hence reducing undesirable emissions, by injecting fuel in a manner different from that of the prior art. 
     SUMMARY  
     In one aspect, a fuel injector includes a nozzle assembly. At least one passageway extends from inside the fuel injector to outside the fuel injector. At least one fluid oscillator is a part of the at least one passageway. 
     In another aspect, a method of operating a fuel injector with a nozzle assembly includes passing fuel from inside the fuel injector to outside the fuel injector by configuring the nozzle assembly to an open configuration. The passing fuel step includes oscillating fuel between a high injection rate and a low injection rate through at least one nozzle orifice. 
     In another aspect, a method of operating an engine includes compressing air inside a combustion chamber, and injecting fuel in to the combustion chamber from inside the fuel injector. The injecting step further includes oscillating fuel between a high injection rate and a low injection rate through at least one nozzle orifice. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a fuel injection system including a fuel injector partially disposed in a combustion chamber according to the present disclosure; 
         FIG. 2  is an enlarged front view of the nozzle tip shown in  FIG. 1 ; 
         FIG. 3  is an enlarged sectional top plan view of the nozzle tip shown in  FIG. 2  as viewed along section line  3 - 3 ; and 
         FIG. 4  is a schematic view of one of the fluid oscillators shown in  FIG. 3 . 
         FIG. 5   a  is a schematic view of one embodiment of a fluid oscillator according to the present disclosure; 
         FIG. 5   b  is a schematic view of another embodiment of a fluid oscillator according to the present disclosure; 
         FIG. 5   c  is a section view of yet another embodiment of a fluid oscillator according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION  
     The present disclosure relates to the use of a fluid oscillator inside a fuel injector to improve combustion efficiency. A fluid oscillator creates an oscillatory flow pattern for fuel entering a combustion chamber by breaking up the injection stream and allowing smaller parcels of fuel to better mix with the air and hence, burn more efficiently, which results in a much improved combustion efficiency. 
     Referring to  FIG. 1 , a fuel injection system  100  includes a common rail fuel injector  10  fluidly connected to a common rail  99  and partially disposed within a combustion chamber  98 . Because the present disclosure is applicable to a wide variety of fuel injectors, including common rail fuel injectors, cam actuated fuel injectors, hydraulically actuated fuel injectors among others, the common rail fuel injector shown in  FIG. 1  is not intended to limit the scope of the present disclosure but rather represents any fuel injector that may fall within the scope of the present disclosure. The present disclosure specifically relates to any fuel injector that includes a passageway that extends from inside the fuel injector to outside the fuel injector, while having at least one fluid oscillator as a part of the passageway. 
     The fuel injector  10  includes a solenoid assembly  20  including an armature assembly  15  and a solenoid coil  26  that is either in an energized state or a de-energized state. The armature assembly  15  includes an armature  18  that is movable between a first and second armature position. A control valve assembly  30  includes a control valve member  32 , which is operatively coupled to the armature assembly  15  and moves between an upper valve seat  33  and a lower valve seat  34 . The fuel injector  10  further includes a nozzle assembly  60  that includes a needle check valve  62  movable between an open and closed configuration, and a nozzle spring  69  that biases the needle check valve to the closed configuration. The needle check valve  62  has an opening hydraulic surface  64  exposed to fluid pressure inside a nozzle chamber  67 , and a closing hydraulic surface  65  exposed to fluid pressure inside a needle control chamber  50 . The needle check valve  62  and the nozzle spring  69  may be disposed inside the nozzle assembly  60 . 
     The control valve member  32  controls the movement of the needle check valve  62  by controlling the pressure in the needle control chamber  50 . The needle check valve  62  in turn, controls the flow of fuel passing through a nozzle tip  70  to outside the fuel injector  10 . The nozzle chamber  67  may receive fuel entering the fuel injector  10  from a rail inlet port  52  via a rail supply passage  42 . In the present disclosure, the nozzle chamber  67  may be fluidly connected to the common rail  99 , thereby maintaining rail pressure inside the nozzle chamber  67 . 
     A valve supply passage  41  establishes a fluid connection between the nozzle chamber  67  and the control valve assembly  30 . The valve supply passage  41  also fluidly connects the nozzle chamber  67  to the needle control chamber  50  via a first flow restrictor  46 . A second flow restrictor  47 , having a larger flow area than the flow area of the first flow restrictor  46 , fluidly connects the needle control chamber  50  to either high-pressure fuel in valve supply passage  41  or to a low-pressure fuel drain passage  44  via the control valve assembly  30 . The drain passage  44  is shown in dotted lines because the drain passage  44  lies in a plane not depicted in the section view shown in  FIG. 1 . Furthermore, the needle control chamber  50  remains fluidly connected to the nozzle chamber  67  via the first flow restrictor  46  regardless of the position of the control valve member  32 . 
     When the solenoid assembly  20  is in a de-energized state, the armature assembly  15  is at the first armature position and the control valve member  32  is at the lower valve seat  34 . A first annular opening  36  fluidly connects the high-pressure fuel from the nozzle chamber  67  to the needle control chamber  50  via the second flow restrictor  47  thereby increasing the pressure acting on the closing hydraulic surface  65  inside the needle control chamber  50  to rail pressure. The nozzle assembly  60  and the needle check valve  62  are in a closed configuration when the pressure acting on the closing hydraulic surface  65  is high enough to keep the needle check valve  62  in sealed contact with the nozzle tip  70 . This allows the needle check valve  62  to fluidly block fuel inside the nozzle chamber  67  from entering the nozzle tip  70 , thereby preventing any fuel from passing from inside the fuel injector  10  to outside the fuel injector  10 . 
     Upon energizing the solenoid assembly  20 , the armature assembly  15  moves to the second armature position and the control valve member  32  moves to the upper valve seat  33 . When the control valve member  32  is moved to the upper valve seat  33 , the second flow restrictor  47  fluidly connects the needle control chamber  50  to a low-pressure drain passage  44  via a second annular opening  37  and the pressure communication passage  43 , thereby relieving pressure inside the needle control chamber  50  because the second flow restrictor  47  has a larger flow area than the first flow restrictor  46 . The nozzle assembly  60  and the needle check valve  62  are in an open configuration when the pressure acting on the closing hydraulic surface  65  is reduced enough to move the needle check valve  62  out of sealed contact with the nozzle tip  70  and the pressure acting on the opening hydraulic surface  64  overcomes the combined force of the pressure acting on the closing hydraulic surface  65  and the force exerted by the nozzle spring  69 . This allows the fuel inside the nozzle chamber  67  to pass through the nozzle tip  70  to outside the fuel injector  10 . 
     Those skilled in the art may recognize that there are various ways of controlling the flow of fuel through the fuel injector  10  via the control valve assembly  30 , such as allowing the needle check valve  62  to be directly controlled by the movement of the control valve member  32  by varying the pressure acting inside the needle control chamber  50 . The present disclosure contemplates all fuel injectors that use alternate methods of controlling the flow of fuel through the fuel injector  10  as well. 
     Referring also to  FIGS. 2 and 3 , the nozzle assembly  60  further includes a nozzle tip  70 , which has an outer surface  72  and an inner surface  74 , which is in sealed contact with the needle check valve  62  when the needle check valve  62  is in the closed configuration. The outer surface  72  of the nozzle tip  70  defines at least one nozzle orifice  75 . Further, the nozzle tip  70  includes at least one passageway  78  extending from inside the fuel injector  10  to outside the fuel injector  10  via one of the at least one nozzle orifice  75 . In the present embodiment, the at least one passageway  78  may be fluidly connected to the nozzle chamber  67  when the needle check valve  62  is in the open configuration but may be fluidly blocked from the nozzle chamber  67  when the needle check valve  62  is in the closed configuration. 
     The present disclosure teaches the incorporation of a fluid oscillator in a passageway extending from inside the fuel injector to outside the fuel injector. At least one passageway extending from inside the fuel injector to outside the fuel injector includes at least one fluid oscillator. According to the present disclosure, a fluid oscillator is defined as a passive structure having no moving parts that allows fuel flowing through the fluid oscillator to produce an oscillatory spray pattern. The oscillatory spray pattern may oscillate between a high injection rate and a low injection rate, oscillate directionally, or oscillate in both injection rate and direction. 
     Referring to  FIG. 3  specifically, the present embodiment shows a nozzle tip  70  having six fluid oscillators  80 , each having a first diffuser leg  83  and a second diffuser leg  84 , separated by a Y-shaped flow splitter  85 . Each of the six first diffuser legs  83  is fluidly connected to a corresponding nozzle orifice  75 , while each of the six second diffuser legs  84  is fluidly connected to a corresponding nozzle orifice  75 ′, such that each nozzle orifice  75  or  75 ′ is fluidly connected to one diffuser leg  83  or  84  and each diffuser leg  83  or  84  is fluidly connected to one nozzle orifice  75  or  75 ′. Each of the six fluid oscillators  80  are equally spaced apart from the other fluid oscillators  80  and each of the six fluid oscillators  80  are separated from an adjacent fluid oscillator  80  by an equal angle  92  about a centerline (shown as dot  97  in section view) passing through the nozzle assembly  60 . 
     The nozzle tip  70  defines twelve passageways  78  and  78 ′, each of which extends from the inner wall  74  of the nozzle tip  70  to a respective nozzle orifice  75  or  75 ′, such that each nozzle orifice  75  and a corresponding first diffuser leg  83  defines one passageway  78 , and each nozzle orifice  75 ′ and a corresponding second diffuser leg  84  defines one passageway  78 ′. In  FIG. 3 , the lines labeled  78  and  78 ′ are two passageways that flow through each fluid oscillator  80 . Each fluid oscillator  80  is a part of two passageways  78  and  78 ′, such that one fluid oscillator  80  is shared between two separate passageways  78  and  78 ′. In the embodiment shown in FIG.  3 , the nozzle tip  70  includes six fluid oscillators  80  and twelve passageways  78  and  78 ′. 
     Referring now to  FIG. 4 , one of the fluid oscillators  80  defined in the nozzle tip  70  of  FIG. 3  is shown. The fluid oscillator  80  includes a main stem  82 , a Y-shaped splitter  85  and two diffuser legs  83  and  84 . The flow splitter  85  traditionally assumes a triangular or trapezoidal shape, with a narrow leading edge  86  directly in the path of the fuel injection stream entering from the main stem  82 . The flow splitter  85  partially defines the two diffuser legs  83  and  84  that diverge and exit the fuel injector  10 . The fluid oscillator  80  includes outer walls  93  and  94  which partially define the two diffuser legs  83  and  84 , as well as at least two feedback loops  87  and  88  leading from the diffuser legs  83  and  84  back into the main stem  82 . Each feedback loop  87  or  88  will be disposed along one of the diffuser legs,  83  or  84 , respectively. The diffuser legs  83  and  84  also fluidly connect to separate nozzle orifices  75  and  75 ′ positioned at the outer surface  72  of the nozzle tip  70 . Each fluid oscillator defines two passageways  78  and  78 ′. One passageway  78  flows from the main stem to the first diffuser leg  83  while the second passageway  78 ′ flows from the main stem to the second diffuser leg  84 . The two passageways  78  and  78 ′ are flow paths that flow out of nozzle orifices  75  and  75 ′, respectively. For the sake of simplicity however, the passageways and orifices throughout the application will be referred generally by the numerical references  78  and  75  respectively. 
     The present disclosure is not limited to embodiments described in this application but to other embodiments that may or may not yet be known that fall within the spirit of the disclosure.  FIG. 5   a - c  shows three embodiments of fluid oscillators that may be defined in a fuel injector that may be used to produce an oscillatory spray pattern. 
       FIG. 5   a  shows a fluid oscillator  240  that may produce a spray pattern that oscillates directionally. The fluid oscillator  240  includes a chamber  243  having an inlet  241  and outlet  242 . An obstacle or island  244  is positioned in the path of a fluid stream passing through the chamber  243  between inlet  241  and outlet  242 . Island  244  is shown as a triangle, in plan, with one side facing upstream (i.e. toward inlet  241 ) and the other two sides facing generally downstream and converging to a point along the longitudinal center line  249  of the oscillator  240 . Neither the shape, orientation, nor symmetry of the island  244  is limiting on the present embodiment. However, a blunt upstream-facing surface has been found to provide a greater vortex street effect than sharp, aerodynamically smooth configuration, while the orientation and symmetry of the island or obstacle has an effect on the resulting flow pattern issued from the fluid oscillator  240 . 
     The outlet  242  is defined between two edges  245  and  246 , which form a restriction proximate the downstream facing sides of island  244 . This restriction is sufficiently narrow to prevent ambient fluid from entering the region adjacent the downstream-facing sides of island  244 , the region where the vortices of the vortex street are formed. In other words, the throat or restriction between edges  245 ,  246  forces the liquid outflow to fill the region  242  therebetween and preclude entry of ambient fluid. The vortex street formed by island  244  causes the stream to cyclically sweep back and forth transversely of the flow direction. 
       FIG. 5   b  shows a fluid oscillator  260  having one input and one output, producing a pulsating spray pattern. The fluid oscillator  260  generally includes an oscillator body  261  having two attachment walls  262  defining an oscillating chamber  264  therebetween, an inlet  267  extended from the oscillating chamber  264 , an outlet  268  extended from the oscillating chamber  264 , a splitter  265  provided at the outlet  268 , and two feedback channels  266  communicating with the oscillating chamber  264 . When a flow of fluid passes to the oscillating chamber  264  through the inlet  267  to fill up the oscillating chamber  264 , the fluid is guided to split at the splitter  265  to flow towards the outlet  268  and back to the oscillating chamber  264  through the feedback channels  266 , such that the fluid is started to oscillate within the oscillating chamber  264 . The oscillating effect of the fluid in the oscillating chamber  264  produces an injection stream that oscillates between a high injection rate and a low injection rate. 
       FIG. 5   c  shows a more complex fluid oscillator that may be used in the present disclosure. The complex fluid oscillator includes an array  290  of fluid oscillators that include a first fluid oscillator  291 , a second fluid oscillator  292 , a third fluid oscillator and so on. Details of two exemplary oscillators are illustrated in  FIG. 5   c . The array  290  of fluid oscillators includes a shared feedback chamber formed by fusing a second feedback line  293  of the first fluid oscillator  291  with a third feedback line  294  of second fluid oscillator  292 . By this arrangement, the second feedback line  293  of the first fluid oscillator  291  and the third feedback line  294  of the second oscillator  292  supply the control fluid into the shared feedback chamber  296 . The shared feedback chamber  296  thus provides a feedback flow path for the control fluid to the first fluidic oscillator  291  and the second fluidic oscillator  292  and thereby puts the first fluidic oscillator  291  in fluidic communication with the second fluidic oscillator  292 . The array  290  of fluid oscillators may be fluidly connected to a series of passageways extending from inside the fuel injector to outside the fuel injector allowing fuel leaving the fuel injector to produce an oscillatory spray pattern. Fuel may flow through inlets  297  and flow out of the array  290  of fluid oscillators through outlets  298 . 
     Other embodiments that fall within the scope of the present embodiment include a fuel injector wherein, each of the at least one passageway includes at least one fluid oscillator, such that fuel inside the fuel injector flows through at least one fluid oscillator before flowing out of the fuel injector. In one embodiment, a fuel injector may include only one nozzle orifice and one fluid oscillator. In yet another embodiment, a fuel injector may include at least one nozzle orifice that is fluidly connected to a passageway that does not include a fluid oscillator, and at least one nozzle orifice fluidly connected to a passageway that includes a fluid oscillator. However, in all embodiments of the present disclosure, the fuel injector should include at least one passageway extending from inside the fuel injector to outside the fuel injector that includes at least one fluid oscillator. 
     Those skilled in the art may appreciate that modern machining techniques, such as electrical discharge machining (EDM) or laser cutting may be employed in defining the fluid oscillator  80  inside the nozzle tip  70  of the fuel injector  10 . Those skilled in the art may employ customary skill in the art to design such nozzle tips that include fluid oscillators. One way of manufacturing the nozzle tip is making the nozzle tip as two pieces and forming grooves of the fluid oscillator  80  in one piece or portions of each piece and attaching the two pieces together via suitable attachment methods known to those skilled in the art. Another way may include using EDM or lasers inserted through two nozzle orifices  75  to define the Y-shape and then rotating the electrodes or laser to make the feature at the junction of the Y-shaped splitter to produce the feedback loops. 
     Those skilled in the art may recognize that designing a suitable fluid oscillator for a desired oscillatory spray pattern may involve modeling and experimentation. The size of the passageway and the desired injection pressure among other factors, may be modeled and experimented with to reach the desired oscillatory spray pattern. The shape of the fluid oscillator and the sizes of its distinct portions may affect the direction and/or pressure of the oscillatory spray pattern. There may be further recognition by those skilled in the art of other issues that may affect oscillatory spray frequency and patterns include the fluid used and the injection pressure selected. Those skilled in the art may design fluid oscillators bearing in mind the fluid may be a nearly incompressible, slightly viscous, distilled diesel fuel and injection pressures are greater than 100 MPa. Additionally, spray patterns may vary when operating fuel injectors at different injection pressures and different fluids. 
     INDUSTRIAL APPLICABILITY  
     The present disclosure finds potential application in fuel injectors and fuel systems in any engine or machine. The present disclosure has a general applicability in all fuel injectors injecting fuel in combustion chambers, and a particular applicability in fuel injection systems, including fuel injectors that inject fuel into combustion chambers, wanting better fuel and air mixing to occur. 
     The present disclosure teaches the use of a fluid oscillator to allow for better mixing between the fuel and air. The use of a fluid oscillator may break up an injection stream into smaller fuel packets in order to provide better mixing between the fuel packets and air, reducing Nox emissions, soot and smoke. 
     The fuel injection system  100  described herein includes a common rail fuel injector  10  fluidly connected to the common rail  99  and partially disposed in the combustion chamber  98 . Typically, the fuel injector is electronically actuated to control the flow of fuel from inside the injector to outside the injector. Although the fuel injector  10  may include one of a variety of actuators, such as a solenoid or a piezo-electric actuator, to move the control valve assembly  30 , the present embodiment includes a solenoid assembly  20  that has a solenoid coil  25 , which is either de-energized or energized. 
     Before an injection event is initiated, the solenoid assembly  20  is in a de-energized state and the control valve member  32  is seated at the lower valve seat  34 . The control valve member  32  blocks the fluid connection between the second annular opening  37  and the pressure communication passage  43 , and instead allows the first annular opening  36  to fluidly connect the nozzle chamber  67  to the needle control chamber  50  via the pressure communication passage  43  allowing high pressure fuel to occupy both the nozzle chamber  67  and the needle control chamber  50 . The pressure acting on the closing hydraulic surface  65  of the needle control chamber  50  along with the preload of the nozzle spring  69  applies a force on the needle check valve  62  that is greater than the pressure force inside the nozzle chamber  67  acting on the opening hydraulic surface  64  of the needle check valve  62 . Because of the high pressure in the needle control chamber  50 , the needle check valve  62  is biased towards the closed configuration. In the closed configuration, the needle check valve  62  fluidly blocks any fuel inside the fuel injector  10  to flow through the nozzle tip  70  and out the fuel injector  10 . During this stage, no fuel is flowing through the fluid oscillator  80  or the nozzle orifices  75 . 
     Upon initiating an injection event, the solenoid assembly  20  is energized and the control valve member  32  moves towards the upper valve seat  33 . Once the control valve member  32  is seated at the upper valve seat  33 , the control valve member  32  blocks the fluid connection between the first annular opening  37  and the pressure communication passage  43 , and instead allows the second annular opening  36  to fluidly connect the needle control chamber  50  to the drain passage  44  via the pressure communication passage  43 . Because the drain passage  44  is at a lower pressure than rail pressure, the pressure difference allows fuel inside the needle control chamber  50 , to flow through the second flow restrictor  47  into the drain passage  44  via the second annular opening  36 . The second flow restrictor  47  has a greater flow rate than the flow rate of the first flow restrictor  46 . Therefore, fuel can leave the needle control chamber  50  via the second flow restrictor  47  faster than the fuel entering the needle control chamber  50  via the first flow restrictor  46 . Hence, the pressure inside the needle control chamber  50  is relieved. 
     As the pressure inside the needle control chamber  50  drops, the pressure acting on the closing hydraulic surface  65  also drops. Eventually, the pressure acting on the opening hydraulic surface  64  exceeds the combined force of the pressure acting on the closing hydraulic surface  65  and the preload of the nozzle spring  69 , causing the needle check valve  62  to move away from the nozzle tip  70 , thereby allowing fuel to flow through the nozzle tip  70  and out the nozzle orifices  75 . In order to initiate the injection event, the nozzle assembly is configured to an open configuration. 
     During the injection event, the nozzle chamber  67  expels the fuel as an injection stream into the nozzle tip  70  including the at least one passageway  78 . The injection stream then flows into the fluid oscillator  80 . Those skilled in the art may appreciate that the injection stream will cling to one side of main stem  82  due to a phenomenon called the Coanda effect. Thus, the fluid may flow through one of the two diffuser legs  83  and  84  at a time. Flow splitter  85  also helps guide the flow into either diffuser leg  83  or diffuser leg  84 . As the fluid flows through one diffuser leg such as diffuser leg  83 , feedback loop  87  will divert a portion of the fluid and return it to the main stem  82 . The fluid inside the feedback loop  87  will then disturb the fluid flow along the side of main stem  82  closest to diffuser leg  83 . This disturbance will cause the fluid flow to switch to the side of the main stem closest to fluid diffuser leg  84 . Fluid will thus leave from diffuser leg  84 , rather than from diffuser leg  83 . As a result, the fluid oscillator may emit pulses of fluid in succession from the two diffuser legs  83  and  84 , with diffuser leg  83  ejecting fluid at a higher injection rate than the diffuser leg  84  at a given time and diffuser leg  84  ejecting fluid at a higher injection rate than the diffuser leg  83  at another given time. 
     During an injection event according to the present disclosure, fuel moving from inside a fuel injector to outside the fuel injector moves in an oscillatory spray pattern through at least one nozzle orifice. The oscillatory spray pattern may oscillate between a high injection pressure and a low injection pressure, or oscillate directionally, or both depending on the fluid oscillator included in the nozzle tip. 
     During the injection event according to the present embodiment, the fuel injection stream oscillates between the two nozzle orifices  75  and  75 ′ fluidly connected to each fluid oscillator  80 , causing the injection rate of the nozzle orifice  75  and  75 ′ to oscillate between a high injection rate and a low injection rate. In one embodiment, fuel may eject from both nozzle orifices  75  and  75 ′ at a given time although the injection rate in the nozzle orifice  75  will be relatively large while the injection rate in the nozzle orifice  75 ′ will be relatively small. The injection rates in both the nozzle orifices  75  will oscillate between a high injection rate and a low injection rate as long as the nozzle assembly  60  is in an open configuration. In one embodiment, the total injection rate of the fuel injector  10  may remain the same, but the injection rate of each nozzle orifice  75  and  75 ′ oscillates between a high injection rate and a low injection rate. 
     To end the injection event, the solenoid assembly  20  is de-energized and the control valve member  32  moves back from the upper valve seat  33  to the lower valve seat  34 , thereby fluidly connecting the first annular opening  36  to the needle control chamber  50 . Because the needle control chamber  50  may no longer be fluidly connected to the low-pressure drain passage  44  but instead, to the nozzle chamber  67  via the valve supply passage  41 , high-pressure fuel begins to accumulate in the needle control chamber  50 , thereby increasing the pressure acting on the closing hydraulic surface  65  of the needle check valve  62 . This pressure acting on the closing hydraulic surface  65  combined with the preload of the nozzle spring  69  eventually exceeds the pressure acting on the opening hydraulic surface  64 , and forces the needle check valve  62  to return to its closed configuration and stop any fluid from exiting the fuel injector  10  through the nozzle tip  70 . Hence, no fuel will be flowing within the fuel injector  10  as the needle control chamber  50  and the nozzle chamber  67  are at the same fluid pressure and the drain passage  44  is no longer fluidly connected to the needle control chamber  50 . 
     The present embodiment may be used to operate an engine including the fuel injection system  100 . The fuel injector  10  may be partially disposed inside the combustion chamber  98  where air is being compressed. The fuel injector  10  injects fuel into the combustion chamber  98  from inside the fuel injector  10  when the nozzle assembly  60  is in an open configuration. The fuel injector  10  oscillates the injection pressure of the fuel being injected out from the nozzle orifices  75  and  75 ′ positioned on the outer surface  72  of the nozzle tip  70  of the fuel injector  10  by passing the fuel through at least one fluid oscillator  80 . In one embodiment, the combustion chamber  98  compresses the air beyond the auto-ignition condition of fuel. Furthermore, in another embodiment, the fuel injection system  100  may compression-ignite the fuel inside the combustion chamber  98 . Finally, in a common rail fuel injector system  100 , initiating the injection event includes moving fuel from the common rail  99  into the fuel injector  10 , and moving fuel from inside the fuel injector  10  to outside the fuel injector  10  by moving the needle check valve  62  to an open configuration. 
     In order to achieve higher combustion efficiencies, engineers have tried increasing injection pressures to reduce the size of fuel packets that leave the nozzle orifices of nozzle tips. Although high pressures may be important in producing smaller fuel packets, splitting up the injection stream by oscillating the flow of fuel between nozzle orifices may also improve combustion efficiency. By splitting an injection stream flowing through any nozzle orifice into fuel packets, and oscillating the fuel packets between nozzle orifices, each fuel packet may achieve better mixing with the air, resulting in a better combustion efficiency. Finally, the use of a fluid oscillator may produce an oscillatory spray pattern that may oscillate between a high injection pressure and a low injection pressure, or oscillate directionally, or oscillate both in direction and injection pressure, which may be desirable in many operations. 
     It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit 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 of the present disclosure. Other aspects, features and advantages can be obtained from a study of the drawings, and the appended claims