Patent Publication Number: US-9897053-B2

Title: Fuel cooled injector tip

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 62/204,254, entitled “FUEL COOLED INJECTOR TIP,” filed on Aug. 12, 2015, the entire disclosure of which is hereby expressly incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to fuel injectors and more particularly to embodiments of a fuel injector having a tip cooled by low pressure fuel. 
     BACKGROUND 
     Diesel Dual Fuel (“DDF”) is a technology wherein a combination of methane or other natural gas and diesel is used in a compression ignited engine, thereby maintaining the high compression ratio of a diesel engine with the resulting benefits of thermal efficiency. However, the tip of the fuel injector may reach intolerable temperatures in DDF engines as a result of reduced diesel fuel flow through the injector. In dual fuel operation, as opposed to diesel operation, high loads do not necessarily imply a high flow of diesel through the injector nozzle. Accordingly, an approach is needed for reducing the temperature of fuel injector nozzle tips, especially during high load dual fuel operation. 
     SUMMARY 
     According to one embodiment, the present disclosure provides a fuel injector, comprising: an outer housing; a nozzle housing disposed within the outer housing; a flow path between the outer housing and the nozzle housing, the flow path being coupled to a low pressure fuel source; and a circumferential gap in flow communication with the flow path and extending about a tip of the fuel injector between an outer surface of the nozzle housing and an inner surface of a combustion shield adjacent the injector tip; wherein the circumferential gap is in flow communication with a drain gap between the outer housing and a bore for receiving the fuel injector, the drain gap routing the low pressure fuel away from the injector tip. In one aspect of this embodiment, the outer surface of the nozzle housing includes a first shoulder that contacts the combustion shield to define one end of the circumferential gap, and a second shoulder that contacts the combustion shield to define another end of the circumferential gap, the other end of the circumferential gap having an opening in flow communication with the flow path. In a variant of this aspect, the drain gap is in flow communication with the circumferential gap at a location between the ends of the circumferential gap. In another aspect, the nozzle housing comprises at least one injector orifice positioned at a distal end of the nozzle housing, the injector orifice being in flow communication with a high pressure fuel source to controllably inject fuel into a cylinder of an engine. Still another aspect further comprises an O-ring disposed between the outer housing and the bore, the drain gap being disposed between the injector tip and the O-ring. 
     In another embodiment, the present disclosure provides a method for cooling a fuel injector in a dual fuel engine application, comprising: providing low pressure diesel fuel to a double walled segment coupled to a plurality of fuel injectors; routing the low pressure diesel fuel from the double walled segment through a flow path between an injector nozzle housing and an injector outer housing; routing the low pressure diesel fuel from the flow path through a circumferential gap extending about a tip of the fuel injector between an outer surface of the injector nozzle housing and an inner surface of a combustion shield adjacent the injector tip; and draining the low pressure diesel fuel from the circumferential gap through a drain line coupled to a fuel tank. In one aspect of this embodiment, routing the low pressure diesel fuel from the flow path through a circumferential gap comprises routing the low pressure fuel through an opening defined at one end of the circumferential gap by a shoulder of the outer surface of the nozzle housing and an inner surface of the combustion shield. In another aspect, the drain line is in flow communication with the circumferential gap at a location between ends of the circumferential gap. 
     In yet another embodiment, the present disclosure provides a fuel injector, comprising: an outer housing; a nozzle housing disposed within the outer housing; a flow path between the outer housing and the nozzle housing, the flow path being coupled to a low pressure fuel source; a circumferential gap in flow communication with the flow path and extending along an upper surface of a combustion shield adjacent the injector tip; and an opening extending through the outer housing having one end in flow communication with the circumferential gap and another end in flow communication with a drain gap formed between the outer housing and a bore for receiving the fuel injector, the drain gap routing the low pressure fuel away from the injector tip. In one aspect of this embodiment, the nozzle housing comprises at least one injector orifice positioned at a distal end of the nozzle housing, the injector orifice being in flow communication with a high pressure fuel source to controllably inject fuel into a cylinder of an engine. Another aspect further comprises an O-ring disposed between the outer housing and the bore, the drain gap being disposed between the injector tip and the O-ring. 
     In still another embodiment, the present disclosure provides a method for cooling a fuel injector in a dual fuel engine application, comprising: providing low pressure diesel fuel to a double walled segment coupled to a plurality of fuel injectors; routing the low pressure diesel fuel from the double walled segment through a flow path between an injector nozzle housing and an injector outer housing; routing the low pressure diesel fuel from the flow path through a circumferential gap extending along an upper surface of a combustion shield adjacent an injector tip; and draining the low pressure diesel fuel from the circumferential gap through a drain line coupled to a fuel tank. In one aspect of this embodiment, providing low pressure diesel fuel to a double walled segment comprises providing the low pressure fuel to an outer line of the double walled segment surrounding an inner line of the double walled segment. A variant of this aspect further comprises providing high pressure fuel to the inner line of the double walled segment. In another aspect, routing the low pressure diesel fuel from the double walled segment through a flow path comprises routing the low pressure fuel from the double walled segment through a T-fitting coupled to one of the plurality of fuel injectors. Another aspect further comprises using a control module to control operation of the plurality of fuel injectors. In a variant of this aspect, using a control module to control operation of the plurality of fuel injectors comprises responding to an engine shut down when a fuel injector operating temperature is above a predetermined high temperature threshold by causing the flow of low pressure diesel fuel to the plurality of fuel injectors to discontinue. In another variant, using a control module to control operation of the plurality of fuel injectors comprises responding to an engine shut down when a fuel injector operating temperature is above a predetermined high temperature threshold by activating a pumping device coupled to the circumferential gap to pump low pressure diesel fuel from the circumferential gap. In yet another variant, using a control module to control operation of the plurality of fuel injectors comprises responding to an engine shut down when a fuel injector operating temperature is above a predetermined high temperature threshold by activating a pump for a period of time following engine shut down to pump low pressure diesel fuel through the circumferential gap to cool the injector tip. In still another variant, using a control module to control operation of the plurality of fuel injectors comprises responding to an engine shut down when a fuel injector operating temperature is above a predetermined high temperature threshold by causing the engine to idle for a period of time prior to actually shutting down the engine to permit the plurality of fuel injectors to cool before shut down. In a further variant, the period of time is one of a predetermined period of time or a period of time that depends upon a difference between the fuel injector operating temperature and the predetermined high temperature threshold. 
     In still another embodiment, the present disclosure provides a method for cooling a fuel injector, comprising: using a control module to respond to an engine shut down when an operating temperature of a fuel injector of an engine is above a high temperature threshold by causing the engine to idle for a period of time prior to actually shutting down the engine to permit the fuel injector to cool before shut down. In one aspect of this embodiment, the period of time is one of a predetermined period of time or a period of time that depends upon a difference between the operating temperature and the high temperature threshold. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features of this disclosure and the manner of obtaining them will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the present disclosure taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram of a fuel delivery system for an engine; 
         FIG. 2  is a cross-sectional side view of a fuel injector according to the principles of the present disclosure; 
         FIG. 3  is an enlarged cross-sectional side view of a portion of the fuel injector of  FIG. 2 ; 
         FIG. 4  is an enlarged cross-sectional side view of a portion of another embodiment of a fuel injector; and 
         FIG. 5  is a flow chart of a method of cooling a fuel injector according to the teachings of the present disclosure. 
     
    
    
     While the present disclosure is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The present disclosure, however, is not to limit the particular embodiments described. On the contrary, the present disclosure is intended to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims. 
     DETAILED DESCRIPTION 
     Methods and apparatuses for reducing the temperature of fuel injector nozzle tips are described below. It should be understood that by reducing the nozzle tip temperature in dual fuel applications, a reduced amount of diesel pilot fuel may be used in fuel injection events, thereby permitting an increased substitution ratio (i.e., the amount of fuel energy supplied by gas divided by the total fuel energy). In conventional approaches, reduced diesel pilot fuel resulted in higher operating temperature of the fuel injector tip (due to the increased percentage of natural gas used during combustion). This higher temperature resulted in, among other things, increased carboning of fuel injector spray holes. The present disclosure permits lower quantities of diesel pilot in dual fuel engines with reduced concern of carboning because of the reduced operating temperature of the fuel injectors. It should be understood, however, that the principles of the present disclosure may also be adapted by skilled artisans for use in other engine applications, including conventional (i.e., non-dual fuel) diesel engines. 
     Referring now to  FIG. 1 , an embodiment of a fuel supply system  10  configured to cool the tips of fuel injectors is shown coupled to an internal combustion engine  12  including a plurality of cylinders  14 , each housing a piston  16  that is movable in a reciprocating manner within its associated cylinder  14  as is known in the art. Fuel system  10  is a common rail configuration that supplies fuel to each of a plurality of daisy chained fuel injectors  18 ,  20  (only two shown), each of which is controlled to deliver timed charges of atomized fuel under high pressure to an associated one of cylinders  14 . 
     As shown in  FIG. 1 , fuel system  10  includes a low pressure (“LP”) fuel pump  22  that draws fuel from a fuel tank or reservoir (not shown) through a low pressure fuel line  24 . One fuel output from LP pump  22  may be passed through a filter (not shown) before being provided through conduit  26  to a high pressure (“HP”) fuel pump  28 , which provides fuel at high pressure to fuel injectors  18 ,  20  as is further described below. 
     In this embodiment, injectors  18 ,  20  are coupled together by a double walled segment  30  which includes an inner line  32  that forms a portion of a high pressure fuel passage, and an outer line  34  surrounding the inner line  32  to form an annular shaped low pressure fuel passage. As will be described below in detail, cool low pressure fuel may be provided to injectors  18 ,  20  through outer line  34  to cool the tips of fuel injectors  18 ,  20 . 
     As shown in  FIG. 1 , double walled segment  30  has one end sealingly connected to a T-fitting  38  coupled to fuel injector  18  and another end sealingly connected to a T-fitting  40  coupled to fuel injector  20 . T-fitting  38  is coupled to a high pressure fuel line  36  coupled as an output of HP fuel pump  28 . In this way, a continuous supply of high pressure fuel  52  is provided in the direction of dash tailed arrows depicted in  FIG. 1  from high pressure fuel line  36  of HP fuel pump  28  through inner line  32  of double walled segment  30  to the last fuel injector  20  in the plurality of fuel injectors. In the depicted embodiment, inner line  32  is terminated at an outlet of T-fitting  40  of fuel injector  20  with a coupler  42 . 
     Coupler  42  is also connected to a low pressure fuel line  44  from LP pump  22 . After the low pressure fuel  46  from LP pump  22  enters coupler  42 , it flows through outer line  34  of double walled segment  30  in the direction of solid tailed arrows depicted in  FIG. 1  to T-fitting  38 . The low pressure fuel is also routed through fuel injectors  18 ,  20  to cool the tips of the injectors as is described in detail below. The low pressure fuel exits fuel injectors  18 ,  20  through drain line  48  formed in cylinder head  50 , and is drained back to the fuel tank (not shown). 
     It should be understood by those skilled in the art with the benefit of the present disclosure that instead of providing high pressure fuel through line  36  to T-fitting  38  and low pressure fuel to coupler  42 , high pressure pump  28  could readily provide both high pressure fuel and low pressure fuel to T-fitting  38  via a double walled segment, thereby eliminating the need for line  44 . 
     As indicated by the dashed lines in  FIG. 1 , the operation of HP pump  28  and fuel injectors  18 ,  20  to provide timed and measured amounts of fuel to cylinders  14  is controlled by control module  54 , such as an engine control module (“ECM”). Control module  54  can sense several conditions of the engine  12  and fuel system  10 , including but not limited to sensing pressure and/or temperature of fuel in HP pump  28  and double walled segment  30 , and can control fuel injectors  18 ,  20  in response to these sensed conditions. It should be understood that while control module  54  is depicted as a single physical device, control module  54  may be implemented as multiple distributed devices without deviating from the principles of the present disclosure. 
     In certain embodiments, control module  54  includes one or more modules that functionally execute the operations of the control module. The description herein including modules emphasizes the structural independence of certain aspects of control module  54 , and illustrates one grouping of operations and responsibilities of the control module. Other groupings that execute similar overall operations are understood within the scope of the present disclosure. Modules may be implemented in hardware and/or as computer instructions on a non-transient computer readable storage medium, and modules may be distributed across various hardware or computer based components. 
       FIG. 2  provides a detailed cross-sectional view of a fuel injector according to embodiments of the present disclosure, such as fuel injector  18 . As shown, fuel injector  18  includes an injector body  56  which includes an injection control valve assembly  58 , a nozzle module  60 , an outer housing  62 , and a valve housing  64 . Outer housing  62  secures injection control valve assembly  58 , nozzle module  60  and other elements of fuel injector  18  in a fixed relationship. The structural and functional details of fuel injector  18  may be similar to those disclosed in U.S. Pat. Nos. 5,676,114 and 7,156,368, the entire disclosures of which are expressly incorporated herein by reference. 
     Nozzle module  60  includes a nozzle housing  66  positioned in outer housing  62  and an injector cavity  68  located within nozzle housing  66 . Nozzle housing  66  further includes one or more injector orifices  70  positioned at a distal end of nozzle housing  66 . Injector orifices  70  communicate with one end of injector cavity  68  to discharge high pressure fuel into the cylinder  14  of engine  12 . Nozzle module  60  further includes a nozzle or nozzle valve element  72  positioned in injector cavity  68  adjacent to injector orifices  70 . Nozzle valve element  72  is movable between an open position which denotes the beginning of an injection event because fuel may flow through injector orifices  70  into the cylinder  14  and a closed position which denotes the end of the injection event because fuel flow through injector orifices  70  is blocked or inhibited. 
     In  FIG. 2 , fuel injector  18  is shown coupled to T-fitting  38 , which includes an opening  74 , which is coupled to high pressure fuel line  36  of HP pump  28  as shown in  FIG. 1 , and an opening  76 , which is coupled to double walled segment  30  as shown in  FIG. 1 . Fuel injector  18  also includes a damper flange  78  coupled to T-fitting  38  which includes a drilling  80 . Drilling  80  extends through damper flange  78  to opening  76  so that the cooling fuel from double walled segment  30  is routed into fuel injector  18 . Fuel injector  18  further includes an accumulator  82  which is coupled to damper flange  78 . Accumulator  82  includes drilling  84  which is coupled at one end to drilling  80 . Cooling fluid from drilling  80  is routed through a slot on a face of damper flange  78 , into an annular gap  85  and then across a slot at an upper end of accumulator  82 . O-rings  87  on damper flange  78  and accumulator  82  prevent leakage of the fuel from the annular gap  85 . Drilling  84  is coupled at its other end to a circumferential gap  86  between outer housing  62  and valve housing  64 . 
     Referring now to  FIGS. 2 and 3 , gap  86  permits low pressure fuel to flow along a flow path  89  between nozzle housing  66  and outer housing  62 . As described in more detail below, low pressure fuel is routed to injector tip  92  where it flows in contact with a nozzle combustion shield  94  to absorb heat from shield  94  and cool nozzle tip  92 . The fuel is then routed to a drain gap  96  between outer housing  62  and an injector bore  90  formed in cylinder head  50  to common injector drain line  48 , which is in fluid communication with the fuel tank (not shown). Low pressure fuel is prevented from flowing out of injector bore  90  (other than through drain line  48 ) by an upper O-ring  88  that extends around outer housing  62  within injector bore  90 . 
     Referring now to  FIG. 3 , a more detailed view of the flow of low pressure fuel to cool nozzle tip  92  is shown. As indicated by the arrows in the figure, fuel flows through flow path  89  between nozzle housing  66  and outer housing  62 . As the fuel approaches nozzle tip  92 , it is routed into a circumferential gap  100  extending about nozzle housing  66  between an outer surface of nozzle housing  66  and an inner surface of combustion shield  94 . Gap  100  is closed at a lower end by a circumferential shoulder  102  and closed at an upper end (except at its interface—opening  103 —with flow path  89 ) by a partially circumferential shoulder  104 . As such, the only outlet from circumferential gap  100  is drain gap  96  which routes the fuel (after having absorbed heat from combustion shield  94  and nozzle housing  66 ) to drain line  48 . 
     In an alternative embodiment depicted in  FIG. 4 , cooling fuel flows across an upper end of combustion shield  94  instead of around nozzle tip  92 . As shown, outer housing  62  includes an opening  99  in flow communication with flow path  89  at one end and drain gap  96  at another end. As fuel flows along the upper end of combustion shield  94  from flow path  89  to drain gap  96 , heat is transferred to the fuel from the nozzle tip  92  via the combustion shield  94 . 
     In certain applications, the fuel injector tip is particularly susceptible to damage from fuel boiling and/or coking after high temperature engine shut down. In particular, when the engine is shut down after high temperature operation, residual fuel remaining in injector cavity  68  in the vicinity of orifices  70  may boil and/or coke, causing damage to fuel injector tip  92 .  FIG. 5  depicts a method for responding to a high temperature shut down situation to reduce potential damage to the fuel injector tip. As shown, method  110  includes providing low pressure diesel fuel to a double walled segment coupled to a plurality of fuel injectors at step  112 . At step  114 , low pressure diesel fuel is routed from the double walled segment through a flow path between an injector nozzle housing and an injector outer housing. At step  116 , the low pressure diesel fuel is routed from the flow path through a circumferential gap extending along an upper surface of a combustion shield adjacent an injector tip. At step  118 , the low pressure diesel fuel is drained from the circumferential gap through a drain line coupled to a fuel tank. 
     At step  120 , control module  54  determines whether an engine shut down command has been received. If not, operation continues at step  112 . If an engine shut down command has been received, control module  54  determines at step  122  whether an injector operating temperature is above a predetermined threshold. If not, control module  54  initiates an engine shut down at step  124 . If control module  54  determines that the injector operating temperature is above the predetermined threshold, then depending upon the embodiment of the present disclosure implemented, control is passed to one or more of steps  126 ,  128 ,  130  or  132 . 
     In one embodiment of the present disclosure, the low pressure fuel circulated through circumferential gap  100  ( FIG. 3 ) is vented or drained from the fuel injector tip  92  following high temperature shut down. In particular, when control module  54  identifies a fuel injector operating temperature above a predetermined high temperature threshold, control module  54  may respond to an engine shut down by discontinuing the flow of low pressure fuel to fuel injectors  18 ,  20  to limit the amount of low pressure fuel adjacent fuel injector tip  92  at shut down as indicated by step  126 . It should be further understood that control module  54  may instead, or in addition, activate a pumping device coupled to circumferential gap  100  through flow path  89  or drain line  48  to pump low pressure fuel from circumferential gap  100  when a high temperature shut down situation is identified as indicated by step  128 . Diesel only operation will also increase the amount of fuel flowing through injector orifices  70  which cools them and prevents carboning. 
     Alternatively, or in addition, in other embodiments control module  54  may operate a low pressure fuel pump, such as fuel pump  22  for a period of time following high temperature shut down as indicated by step  130 . In this manner, cool low pressure fuel is pumped through the above-described path around fuel injector tip  92  and out drain line  48  for a period of time to cool the fuel injector tip  92  even after the engine  12  is shut down. The time period of operation of the pump needed to prevent damage to the fuel injector tip  92  after high temperature shut down may be responsive to a model of the thermal characteristics of fuel injector  18 ,  20  or responsive to a sensed characteristic of the actual operation of fuel injector  18 ,  20 , such as, for example, a sensed temperature at fuel injector tip  92  or both. 
     Also, control module  54  may respond to a high temperature shut down situation by modifying an engine shut down algorithm in response to shut down temperature limits and/or operating conditions preceding the shut down. Such a modification may result in an engine idle time period prior to actual shut down to permit the engine to cool before shut down as indicated by step  132 . Again, the idle period may be responsive to a model or to actual sensed characteristics of engine parameters. In a modification of this embodiment, control module  54  may instead, or in addition, cause diesel only operation for some time period prior to actual shut down to cool the injector tip  92  before shut down. As is known, combustion of gas causes higher tip temperatures. Therefore, elimination of the gas fuel component (i.e., diesel only operation) will result in lower tip temperatures at shut down. 
     Other mechanisms and approaches for managing high temperature shut down situations are described in co-pending patent application Ser. No. 62/204,408, entitled “NOZZLE COMBUSTION SHIELD AND SEALING MEMBER WITH IMPROVED HEAT TRANSFER CAPABILITIES,” filed on Aug. 12, 2015, the entire disclosure of which being expressly incorporated herein by reference. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present disclosure. For example, while the embodiments described above refer to particular features, the scope of this disclosure also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present disclosure is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.