Abstract:
One strategy for reducing undesirable emissions from internal combustion engines relates to finding ways to better mix fuel and air prior to combustion. One such method is commonly referred to as homogenous charge compression ignition (HCCI); however, that strategy is problematic in both controlling ignition timing and avoiding overstressing the engine at higher speeds and loads. The present invention addresses these issues by mixing air and fuel vapor within an injector instead of within the engine cylinder. The air/fuel mixture is then injected into the engine cylinder at some desired timing and over some desired duration. Such a strategy permits for lower emissions due to better mixing of air and fuel, while also permitting control over some aspects of combustion timing and duration not apparently possible with a conventional HCCI strategy. The present invention is generally applicable to all internal combustion engines, but especially applicable to diesel engines.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to the operation of internal combustion engines, and more particularly to the injection of a mixture of fuel vapor and air into an engine cylinder.  
       BACKGROUND  
       [0002]     Engineers are constantly seeking ways to reduce undesirable emissions from engines. Over the years, engineers have come to recognize that cleaner burns tend to occur when there is a better mixing of fuel and air prior to combustion. One relatively recent strategy for improving fuel/air mixing is commonly referred to as homogenous charge compression ignition (HCCI). In an HCCI strategy, fuel is injected into the engine cylinder early in the compression stroke. The liquid fuel vaporizes in the engine cylinder and mixes with the air to produce a relatively lean homogenous mixture. As the compression stroke continues, the homogenous charge ignites when pressure and temperature in the cylinder reach the auto-ignition point. Although an HCCI strategy can produce a relatively clean burn with dramatic reductions in undesirable emissions, it remains problematic both in the ability to control ignition timing and operate a given engine in a HCCI mode at high load conditions.  
         [0003]     One method attempting to control ignition timing in a homogenous charge compression ignition engine is taught in U.S. Pat. No. 5,875,743 to Dickey. Dickey appears to assert that ignition timing can be controlled by injecting a controlled amount of water into the air brought into the cylinder through the intake valve. Although the usage of water may be a viable strategy in controlling ignition timing in an HCCI engine, there remains the problem of HCCIs&#39; general incompatibility with higher engine loads.  
         [0004]     At higher engine loads, when the amount of fuel injected is substantially higher than that at lower loads, the very efficient HCCI burn also becomes a liability. Apparently, when a HCCI charge burns, there is little or no flame front, and the entire charge combusts almost simultaneously over a relatively brief duration. With the burn duration being relatively short, the pressure spike produced by the burn can be destructively too high at higher engine loads. Thus, in order to make HCCI viable, ignition timing needs better control, and the combustion duration must be sufficiently long as to not overstress the engine, especially at higher loads.  
         [0005]     The present invention is directed to one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0006]     In one aspect, a method of operating an engine includes a step of mixing fuel vapor with air in an injector. The mixture of fuel vapor and air are then injected into an engine cylinder. The mixture is ignited in the engine cylinder.  
         [0007]     In another aspect, a fuel injector includes an injector body with an air/fuel mixing chamber and a liquid fuel chamber disposed therein. A first valve is at least partially positioned in the injector body and fluidly positioned between the liquid fuel chamber and the air/fuel mixing chamber. A second valve is at least partially positioned in the injector body and fluidly positioned between the air/fuel mixing chamber and an outside surface of the injector body.  
         [0008]     In still another aspect, a fuel injection system includes a source of liquid fuel and a nozzle body that includes an air/fuel mixing chamber at least partially disposed therein. A first valve is fluidly positioned between the air/fuel mixing chamber and an outside surface of the nozzle body. A second valve is moveable between a first position in which the air/fuel mixing chamber is fluidly connected to the source of liquid fuel, and a second position in which the air/fuel mixing chamber is closed to the source of liquid fuel.  
         [0009]     In still another aspect, an engine includes an engine housing with at least one cylinder. A fuel injector is attached to the engine housing and includes a nozzle tip position in the cylinder. The fuel injector includes an air/fuel mixing chamber at least partially disposed therein, and a valve fluidly positioned between the air/fuel mixing chamber and an outside surface of the nozzle tip. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an isometric view of an engine according to the present invention;  
         [0011]      FIG. 2  is a sectioned side diagrammatic view of a fuel injector according to one aspect of the present invention;  
         [0012]      FIG. 3  is a graph of valve  59  ( FIG. 2 ) position verses engine cylinder position for an example injection sequence according to one aspect of the present invention;  
         [0013]      FIG. 4  is a graph of piston  70  ( FIG. 2 ) position verses engine cylinder position for the example injection sequence;  
         [0014]      FIG. 5  is a graph of valve  69  ( FIG. 2 ) position verses engine cylinder position for the example injection sequence; and  
         [0015]      FIG. 6  is a graph of injection quantity verses engine cylinder position for the example injection sequence. 
     
    
     DETAILED DESCRIPTION  
       [0016]     Referring to  FIG. 1 , an internal combustion engine  10  includes an engine housing that defines one or more engine cylinders  17 , within which a piston  18  reciprocates in a conventional manner. A fuel injection system  11  is attached to engine  10  in a conventional manner to include an individual fuel injector  15  associated with each engine cylinder  17 . Each fuel injector  15  preferably includes a nozzle tip  29  located in engine cylinder  17  in a manner typical of that associated with a diesel type engine. Nevertheless, those skilled in the art will appreciate that, although the illustrated example shows a compression ignition engine, the present invention also contemplates other means of igniting a charge in an engine cylinder, including but not limited to spark ignition. Engine  10  generally, and fuel injection system  11  specifically, are controlled in a conventional manner by an electronic control module  20 . In the illustrated example, fuel injection system  11  is a dual fluid system that includes a fuel supply system  13  and an actuation fluid system  12 . Fuel supply system  13  preferably utilizes conventional distillate diesel fuel as its fuel medium, but could utilize any suitable liquid fuel. Actuation fluid system  12  preferably utilizes engine lubricating oil, but could use any suitable and available fluid for supplying hydraulic fluid pressure to different components within fuel injector  15 .  
         [0017]     Referring in addition to  FIG. 2 , each fuel injector  15  includes an electronically controlled fuel spray valve  26 , an electronically controlled actuation control valve  27  and an electronically controlled nozzle control valve  28  attached to an injector body  19 . Nevertheless, those skilled in the art will appreciate that these valves could be located at any suitable location in fuel injection system  11  without necessarily being attached to injector body  19 . Electronic control module  20  communicates with, and controls the positioning of, valves  26 ,  27 , and  28  via communication lines  22 ,  23  and  24 , respectively, in a conventional manner. Fuel spray control valve  26  controls the opening and closing of a needle valve  59 , which controls the spray of liquid fuel from a liquid fuel chamber  56  to a mixing chamber  75 . Actuation control valve  27  controls the application of either high pressure or low pressure actuation fluid onto a hydraulic surface  71  of a piston  70 . A portion of mixing chamber  75  is defined by a displacement surface  74  of piston  70 . Downward movement of piston  70  injects a fuel/air mixture in mixing chamber  75  into engine cylinder  17  via nozzle outlet  76 . Nozzle control valve  28  controls the application of either high pressure or low pressure actuation fluid on an opening hydraulic surface  61  of nozzle valve  69 .  FIG. 2  shows nozzle valve  69  in its downward open position that fluidly connects mixing chamber  75  to an outside surface of nozzle tip  29  via a frusto conically shaped nozzle outlet  76 . Those skilled in the art will appreciate that nozzle outlet  76  and nozzle valve  69  could have any suitable configuration known in the art besides the frusto conical shaped opening  76  shown in  FIG. 2 .  
         [0018]     Fuel supply system  13  includes a high pressure pump  46  that draws low pressure fuel from fuel tank  45  and supplies high pressure fuel to an accumulator  40 , which could be a high pressure common fuel rail in the case of a multi-cylinder engine. High pressure fuel is supplied from rail  40  to a fuel inlet  42  via a high pressure fuel supply passage  41 . Any fuel leakage and/or spillage is routed back to fuel tank  45  for recirculation via fuel outlet  43  and fuel drain  44 . Preferably, high pressure pump  46  is a variable output pump that is controlled by electronic control module  20  in a conventional manner via communication line  25 . Thus, in the illustrated embodiment, pressure in common fuel rail  40  is controlled by controlling the output of pump  46 . Nevertheless, those skilled in the art will appreciate that fuel pressure supplied to fuel injector  15  could be controlled in any suitable manner. For instance, the present invention is also compatible with a simple pump and line fuel supply system, a common rail, hydraulic pressure intensified systems, cam actuated fuel pressurization or any other suitable manner of pressurizing fuel. In other words, the present invention is compatible with fuel that is pressurized inside and/or upstream from fuel injector  15 . However, those skilled in the art will appreciate that because the injection of liquid fuel within injector  15  can occur at substantially lower pressures than those typically encountered in a conventional diesel fuel injector, fuel could be pressurized in fuel injection system  11  at levels substantially lower than that normally encountered in direct injection diesel type fuel injection systems.  
         [0019]     Actuation fluid system  12  includes a high pressure pump  36  that draws low pressure lubricating oil from low pressure reservoir  35  (oil pan) and supplies high pressure actuation fluid to an accumulator  30 , which is preferably a common actuation fluid rail in the case of a multi cylinder engine. High pressure actuation fluid is supplied to an actuation fluid inlet  32  of fuel injector  15  via a high pressure actuation fluid supply passage  31 . Used or leaked actuation fluid is returned to reservoir  35  via actuation fluid outlets  33  and  37  via actuation fluid drain  34  for recirculation. Pressure in common rail  30  is controlled by electronic control module  20  controlling the output of pump  36  in a conventional manner via communication line  21 .  
         [0020]     Referring in particular to  FIG. 2 , fuel spray control valve  26  is operable to fluidly connect a liquid fuel chamber  56  to either high pressure fuel inlet  42  or low pressure fuel outlet  43 . Valve  26  is preferably biased to a position that connects liquid fuel chamber  56  to low pressure fuel outlet  43 , but is moveable to its other position by energizing a first electrical actuator  50 . In the illustrated example, electrical actuator  50  is a solenoid, and valve  26  includes a spool valve member attached to the armature of valve  50 . Nevertheless, those skilled in the art will appreciate that other types of electrical actuators, such as piezos, could be substituted for the illustrated solenoid. In addition, although valve  26  has been illustrated as including a spool valve member, any suitable valve configuration including a poppet valve member or possibly even a pilot operated valve could be substituted in place of the illustrated valve. Needle valve member  54  is preferably biased toward a down position in contact with needle seat  65  by a biasing spring  57 . When in this position, liquid fuel chamber  56  is closed to mixing chamber  75 . When fuel pressure in liquid fuel chamber  56  is above a valve opening pressure sufficient to overcome biasing spring  57 , such as when valve  26  opens fuel inlet  42 , needle valve member  44  lifts away from needle seat  65  to allow liquid fuel to spray into mixing chamber  75  via spray passages  66 . Those skilled in the art will appreciate that needle valve  59  could take on other configurations without departing from the present invention. For instance, three way valve  26  could be rearranged to either supply high pressure fuel or low pressure fuel to the spring chamber within which biasing spring  57  is located and within which a closing hydraulic surface of needle valve member  54  is exposed to fluid pressure there. In such an alternative, liquid fuel chamber would always have an unobstructed fluid connection to fuel inlet  42 , but the opening and closing of needle valve  59  would be controlled by applying either high or low pressure to the back side or closing hydraulic surface of needle valve member  54 . In another variation is the potential for including a simple two way valve between the spring chamber and low pressure fuel outlet  43  while including appropriate flow restrictions that would result in substantial pressure changes when the valve either opens or closes low pressure fuel outlet  43  ( FIG. 1 ). Those skilled in the art will appreciate that any suitable means for controlling the spray of liquid fuel within fuel injector  15  is compatible with the present invention. In still another alternative, either high pressure or low pressure actuation fluid could be supplied to the spring chamber to control the opening and closing of needle valve  59 . Thus, the present invention contemplates a direct control needle valve.  
         [0021]     Turning now to nozzle control valve  28 , it controls the opening and closing of nozzle valve  69 , which is fluidly positioned between mixing chamber  75  and the engine cylinder  17 . A second electrical actuator  51 , which is preferably a solenoid but could be any other suitable actuator such as a piezo, is suitably located in the fuel injection system  11 , but is preferably attached to injector body  19 . Actuator  51  is operably coupled to nozzle control valve  28 , which is preferably a three way spool valve, but could be any other suitable type of valve such as a poppet valve. Preferably, when actuator  51  is deenergized, nozzle control valve  28  is biased to a position that fluidly connects control chamber  62  to low pressure actuation fluid outlet  37  ( FIG. 1 ). When in this position, low pressure is acting on opening hydraulic surface  61  of nozzle valve member  60 , resulting in nozzle valve member  60  moving upward under the action of biasing spring  63  to close nozzle outlet  76  and valve seat  68 . When actuator  51  is energized, nozzle control valve  28  is moved to a position that fluidly disconnects control chamber  62  from low pressure actuation fluid outlet  37 , and fluidly connects the same to high pressure actuation fluid inlet  32 . When this occurs, high pressure acting on opening hydraulic surface  61  is preferably sufficient to move nozzle valve member  60  downward away from valve seat  68  to open nozzle outlet  76 . Nozzle valve  69  is fully opened when nozzle valve member  60  comes in contact with stop  64 , as shown in  FIG. 2 . The various hydraulic and pneumatic surfaces as well as spring strengths and fluid pressures are preferably such that nozzle valve  69  can be opened by energizing actuator  51  at any desirable timing, including when the engine piston is at or near top dead center and pressure in the engine cylinder is peaking. Nozzle valve  69  is preferably the avenue through which the contents of mixing chamber  75  are injected into the engine cylinder via nozzle outlet  76 . In the illustrated embodiment, pressure in mixing chamber  75  and the engine cylinder  17  are maintained at a relative equilibrium via the inclusion of check valves  77  that are located in air inlet passages  78 . Thus, during a compression stroke, air from the engine cylinder is forced into mixing chamber  75  past check valves  77 . When the contents of mixing chamber  75  are being injected into the engine cylinder, check valve  77  returns to a closed position as shown in  FIG. 2 . Alternatively, check valves  77  might be eliminated in favor of utilizing nozzle valve  69  as the avenue through which air is fed into mixing chamber  75  and the air/fuel mixture in a chamber is injected into the engine cylinder. In an alternative embodiment in which check valves  77  are eliminated, fluid communication between the engine cylinder  17  and mixing chamber  75  is only available via nozzle outlet  76 .  
         [0022]     Turning now to actuation control valve  27 , its positioning controls whether high or low pressure is applied to hydraulic surface  71  of piston  70 . A third electrical actuator  52 , which is preferably a solenoid but could be any other suitable electrical actuator such as a piezo, is operably coupled to actuation control valve  27 , which is preferably a three way spool valve but could be any other suitable type of valve such as a poppet. Actuation control valve  27  is preferably biased to a position that fluidly connects hydraulic cavity  72  to low pressure actuation fluid outlet  33  ( FIG. 1 ). When in that position, low pressure acts upon hydraulic surface  71 , and return spring  73  urges piston  70  upward toward its retracted position. In  FIG. 2 , piston  70  is shown in motion moving downward a short distance from its upward retracted position. When actuator  52  is energized, hydraulic cavity  72  is connected to high pressure actuation fluid inlet  32  to supply a high pressure force on hydraulic surface  71 . The various hydraulic surfaces and spring strength are preferably sized such that when hydraulic surface  71  is exposed to high pressure from actuation fluid inlet  32 , piston  70  will be driven downward. Since mixing chamber  75  is partially defined by displacement surface  74 , which is a portion of piston  70 , the volume of mixing chamber  75  decreases when piston  70  is driven downward. If nozzle valve  69  is in an open position, as shown in  FIG. 2 , the contents of mixing chamber  75  will be injected into the engine cylinder when piston  70  is driven downward. If nozzle valve  69  is closed, a downward movement of piston  70  will compress the contents of mixing chamber  75 . The compressed contents of mixing chamber  75  can then be injected into the engine cylinder at any desired timing by moving nozzle valve  69  to an open position by energizing second electrical actuator  51 .  
       Industrial Applicability  
       [0023]     The present invention finds potential application in any internal combustion engine, and is especially applicable to diesel type engines in which fuel is injected directly into the engine cylinder. The present invention also preferably relies upon compression ignition to ignite the charge in the engine cylinder, but is also applicable to engines having an alternative means to ignite a fuel/air charge, such as spark ignition. Although the present invention is illustrated as a two fluid system, the present invention is also applicable to single fluid systems that utilize only fuel. For instance, in an alternative to the illustrated embodiment, pressurized fuel could be used as both the working actuation fluid and the fuel fluid medium with modest plumbing changes known in the art. The illustrated fuel injection system shows two common rails, one for actuation fluid and one for fuel; the fuel and/or actuation fluid could be pressurized in any suitable manner known in the art. In addition, while the illustrated embodiment shows actuation fluid pushing on a piston  70  to inject the air/fuel mixture from mixing chamber  75 , piston  70  could be moved in any suitable manner, including but not limited to cam actuation. In addition, the relative affective surface areas of hydraulic surface  71  and displacement surface  74  of piston  70  could be different such that piston  70  could be an intensifier piston, if desired. In such an alternative, the pressure in mixing chamber  75  could be made to be some multiple of the actuation fluid pressure acting on the top of the piston  70 . Although the illustrated embodiment shows three separate electrical actuators attached to a fuel injector  15 , those skilled in the art will appreciate that electrical control is desirable but not essential to the present invention. In addition, if electrically controlled valves are used, they can be located at any suitable location inside or outside of the injector body without departing from the present invention.  
         [0024]     Referring to  FIGS. 1 and 2 , and in addition to  FIGS. 3-6 , an example injection sequence according to the present invention will be described. At the beginning of the compression stroke, the engine piston is at bottom dead center, and all three electrical actuators,  50 ,  51 , and  52 , are deenergized. Thus, low pressure prevails within fuel injector  15 . In the illustrated embodiment, electronic control module  20  controls the pressure of both actuation fluid and fuel in their respective common rails  30  and  40  via control of their respective high pressure pumps  36 , and  46 . This preferred control allows the fuel pressure injected into mixing chamber  75  to be set independent of engine speed and load. Alternatively, the fuel system could be set at some predetermined pressure with known means and without the closed loop control shown in  FIG. 1 . In addition, by having the ability to control the actuation fluid pressure, the injection rate of the mixture from mixing chamber  75  can be controlled. In addition, the relative sizing of the surface areas of piston  70  along with the magnitude of the high pressure acting on its top surface can be utilized to control the injection pressure of the mixture from mixing chamber  75  into the engine cylinder. At some desired point or points during the compression stroke, liquid fuel is sprayed into mixing chamber  75  by energizing electrical actuator  50  to move needle valve  59  to an open position. In the illustrated example of  FIG. 3 , two injections take place relatively early in the compression stroke allowing for ample time for a thorough mixing with air and fuel vapor to occur. Those skilled in the art will appreciate that any number of internal liquid fuel injections of differing quantities can be performed with the fuel injector  15  illustrated in  FIG. 2 . Those skilled in the art will appreciate that a variety of strategies that may or may not be coordinated with the flow of air into mixing chamber  75  could be performed in order to use different strategies for obtaining a relatively homogenous air/fuel mixture in mixing chamber  75 . Those skilled in the art will appreciate that, although it would be desirable for the liquid fuel sprayed into mixing chamber  75  to be thoroughly vaporized and mixed with the air, in some instances, it might be desirable for some of the liquid fuel to remain in a liquid state when sprayed into mixing chamber  75 . In the illustrated embodiment, air will be continuously flowing into mixing chamber  75  throughout the compression stroke. In an alternative embodiment in which check valve  77  are omitted, the flow of air into mixing chamber  75  could be controlled by selectively opening and closing nozzle valve  69  to allow air into mixing chamber. It might be possible through selective openings and relative timings of the opening of needle valve  59  and nozzle valve  69  during the compression stroke to produce a very thorough mixing strategy. In order to inhibit auto ignition of the air/fuel mixture in mixing chamber  75 , the timing of the spraying of liquid fuel and the volume sizing of mixing chamber should be such that the air/fuel mixture is too rich to auto ignite within injector  15 .  
         [0025]     As the engine piston continues upward during the compression stroke, the air and fuel in mixing chamber  75  continue to mix. At some desired injection timing, both electrical actuators  51  and  52  are energized to open actuation control valve  27  and nozzle control valve  28  to the flow of high pressure actuation fluid. These two valves need not necessarily be energized simultaneously. In the illustrated example, electrical actuator  52  is energized shortly before piston top dead center in order to begin movement of piston  70  to compress the contents of mixing chamber  75 . This is illustrated in  FIG. 4  by the initial slopped portion of the curve in the region of TDC. At some desired injection timing thereafter, electrical actuator  51  is energized to open nozzle control valve  28  to cause nozzle valve  69  to move downward toward its open position to begin the injection of the air/fuel mixture into the engine cylinder. This is shown in  FIG. 5  by nozzle valve  69  moving from a closed position to an open position shortly before piston top dead center.  FIG. 6  shows that the actual injection event is contemporaneous with the opening and closing of nozzle valve  69 . At the desired end of the first injection event, electrical actuator  51  is deenergized to allow nozzle valve  69  to move to its closed position. In the illustrated example, electrical actuator  52  remains energized and actuation control valve  27  remains open to maintain pressure on the top side of piston  70 . Thus, when nozzle valve  69  closes, piston  70  continues moving downward until the pressure and spring forces reach an equilibrium causing the piston to stop movement. A short time later, a second injection event is initiated by again energizing needle control valve  28  to open nozzle valve  69 . When this occurs, the piston  70  continues moving downward injecting the remaining portion of the fuel/air mixture in mixing chamber  65 . In the preferred embodiment, the injection sequence is not finished until piston  70  reaches its fully advanced position covering air inlet passages  78 . In the illustrated example, this is accomplished with two separate injection events. One that begins shortly before top dead center and a second that happens later in the expansion stroke. Sometime thereafter, actuators  51  and  52  are deenergized and piston  70  retracts under the action of its return spring. However, it might be desirable to maintain piston  70  in its downward advanced position throughout the engines power stroke to avoid drawing post combustion products into mixing chamber  75 . On the other hand, in some instances it might be desirable to draw combustion products into mixing chamber  75  to produce some desired effect in a subsequent injection sequence.  
         [0026]     In the illustrated embodiment, the mixing chamber  75  is located entirely within fuel injector  15 . Nevertheless, those skilled in the art will appreciate that mixing chamber  75  could be located at least partially outside of injector body  19 . In addition, the illustrated embodiment shows that air for mixing chamber  75  is preferably drawn from engine cylinder  17 ; however, those skilled in the art will appreciate that air can be drawn from any suitable source. Air from the engine cylinder is preferred because it is already being pressurized by movement of the engine piston. Those skilled in the art will appreciate that the present invention provides a means of creating a homogenous charge of fuel vapor and air, and a means by which ignition timing and to some extent burn duration can be controlled. Ignition is controlled electronically by opening nozzle valve  69  at some desired timing while applying a downward hydraulic force on piston  70 . Upon leaving injector  15 , the mixture should shortly thereafter auto-ignite in a manner similar to conventional diesel engine operation. The burn duration can be somewhat controlled by the rate at which the air/fuel mixture is introduced into the engine cylinder as well as the number of injection events that are desired to occur, and when the timing of those events is made to happen. In other words, with the illustrated fuel injection system, an at least partially homogeneously charged gas mixture can be delivered into the engine combustion chamber at various rates and timings to control engine cylinder pressure and auto ignition timing to produce relatively low undesirable emissions while possibly improving brake specific fuel consumption at the same time. Depending upon the circumstances, the liquid fuel is partially or totally vaporized before being injected into the engine cylinder. The fuel and air will be mixed prior to injection into the combustion chamber, unlike conventional diesel engine operation. The fuel (vapor and liquid) and air mixture could be injected into the combustion chamber at various rates to control the auto-ignition timing. The present invention also allows for a relatively low fuel system pressure, since the fuel is injected internally within the injector into a mixing chamber that is preferably at a substantially lower pressure than that normally encountered in conventional diesel engine operation when injection occurs when an engine piston is at or near top dead center. Since the fuel vapor/air mixture burns relatively fast after injection, the fuel could be burned after top dead center to optimize the work output and to improve brake specific fuel consumption.  
         [0027]     It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.