Patent Publication Number: US-8522752-B2

Title: Co-axial quill assembly for dual fuel common rail system

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to dual fuel common rail systems, and more particularly to a co-axial quill assembly for fluidly connecting first and second common rails to a fuel injector. 
     BACKGROUND 
     Common rail fuel systems are well known in the art of compression ignition engines. A typical common rail fuel system includes a common fuel rail that supplies fuel injectors for an engine via individual quill tubes. Because of the high pressures involved, some jurisdictions require a double wall containment strategy for capturing leaked fuel. For instance, co-owned U.S. Patent application 2005/0166899 teaches a high pressure line connection strategy for fluidly connecting a common rail to fuel injectors. Common rail fuel systems can be found that utilize either distillate diesel fuel or heavy fuel oil as the fuel medium. Increasingly, industry has turned toward common rail fuel systems as one strategy for improving burn characteristics to reduce the production of undesirable emissions, including NOx, unburnt hydrocarbons and the like in order to relax demands on aftertreatment systems. 
     Gaseous fuel engines are known for their ability to burn relatively clean relative to their compression ignition engine counterparts. However, gaseous fuels are well known for the difficulty in attaining successful ignition. Some gaseous fuel engines utilize a spark plug, whereas other engines are known for utilizing a small amount of distillate diesel fuel that is compression ignited to in turn ignite a larger charge of gaseous fuel. Practical spatial limitations in and around an engine often make it difficult to find space for all of the plumbing and hardware associated with supplying two different fuels to each combustion chamber. In this regard, Canadian patent 2,635,410 is of interest for teaching a dual fuel connector that relies upon a single quill that includes two different internal passages to facilitate fluid connection to two different fuel inlets of a fuel injector. However, this reference fails to teach a practical strategy for inhibiting fuel leakage between the two different fuels and from either fuel supply to atmosphere where the illustrated tube contacts the fuel injector. 
     The present disclosure is directed toward one or more of the problems set forth above. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, a co-axial quill assembly for a dual fuel common rail fuel system includes a quill at least partially positioned in a block. The quill defines a first fuel passage extending between a first fuel inlet and a first fuel outlet, and a second fuel passage extending between a second fuel inlet and a second fuel outlet. An outer tube has one end extending into the block and is fluidly connected to the second fuel outlet of the quill. An inner tube is positioned inside the outer tube and is fluidly connected to the first fuel outlet of the quill. A first compression load adjuster is attached to the block and operably coupled to adjust a compression load on the inner tube. A second compression load adjuster is attached to the block and operably coupled to adjust a compression load on the outer tube. 
     In another aspect, a method of supplying fuels to a fuel injector with a co-axial quill assembly includes moving a first fuel at a first pressure from a first common rail through a first fuel passage of a quill, through an inner tube and into a fuel injector. A second fuel is moved at a second pressure from a second common rail through a second fuel passage of the quill, through a space between the outer tube and the inner tube, and finally into the fuel injector. Leakage of the second fuel into the first fuel is inhibited by setting the first pressure higher than the second pressure. Leakage of the first fuel into the second fuel is inhibited by setting a compression load on the inner tube above a first predetermined threshold with the first compression load adjuster. Leakage of the second fuel to atmosphere is inhibited by setting a compression load on the outer tube above a second predetermined threshold with the second compression load adjuster. 
     In still another aspect, a dual fuel common rail fuel system includes a quill that defines first and second fuel passages therethrough. A fuel injector defines a first conical seat concentrically surrounding a second conical seat, and includes a first fuel inlet surrounded by the first conical seat, and a second fuel inlet positioned between the first conical seat and the second conical seat. An outer tube is compressed between the quill and the fuel injector, and fluidly connects a second fuel outlet of the quill to the second fuel inlet of the fuel injector. An inner tube is positioned in the outer tube and is compressed between the quill and the fuel injector, and fluidly connects a first fuel outlet of the quill to the first fuel inlet of the fuel injector. A first compression load adjuster is operable to adjust a load of the inner tube on the first conical seat, a second compression load adjuster is operably coupled to adjust a load of the outer tube on the second conical seat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectioned side view of a dual fuel common rail system according to the present disclosure; and 
         FIG. 2  is a pictorial isometric view of the co-axial quill assembly shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a dual fuel common rail system  10  includes a coaxial quill assembly  18  fluidly connecting a fuel injector  12  with first and second common rails  14 ,  16 , respectively. Although the concepts of the present disclosure could apply to a variety of fuels for different types of engines, the illustrated embodiment is particularly suited for a gaseous fuel engine that utilizes distillate diesel fuel for compression ignition. In other words, an engine associated with dual fuel common rail system  10  might primarily burn liquefied natural gas supplied form second common rail  16 , and ignite that charge in the engine combustion space by compressor igniting a smaller charge of distillate diesel fuel from common rail  14  during a combustion event. 
     Coaxial quill assembly  18  includes a quill  30  at least partially positioned in a block  20 . The quill includes a first fuel passage  32  extending between a first fuel inlet  33 , which is fluidly connected to first common rail  14 , and a first fuel outlet  34 . Quill  30  also defines a second fuel passage  35  extending between a second fuel inlet  36 , which is fluidly connected to second common rail  16 , and a second fuel outlet  37 . Quill  30  is fluidly connected to rails  14  and  16  using known hardware (e.g., fittings) and techniques. Fuel from first common rail  14  is moved through an engine head (not shown) via inner tube  50 , while fuel from second common rail  16  is moved to fuel injector  12  in the space  49  between inner tube  50  and an outer tube  40 . Inner tube  50  may be of a familiar construction to those skilled in the art, in that it includes rounded or conical ends that are compressed between a conical seat  38  of quill  30  and an inner conical seat  55  of fuel injector  12 . Thus, the fluid passage within inner tube  50  extends between first fuel outlet  34  of quill  30  and an inner fuel inlet  57  of fuel injector  12 . Second tube  40  has an inner diameter larger than an outer diameter of inner tube  50  in order to define an elongate annular space  49  that opens on one end to second fuel outlet  37  of quill  30  and at its other end to an outer fuel inlet  48  of fuel injector  12 . Outer tube  40  includes a rounded or conical end that is compressed into sealing contact with outer conical seat  46  of fuel injector  12 . The outer fuel inlet  48  opens between the inner diameter of tube  40  and the outer surface of inner tube  50 . Thus, fuel injector  12  defines an outer conical seat  46  that concentrically surrounds an inner conical seat  55 . In addition, the fuel injector  12  includes an inner fuel inlet  57  surrounded by the inner conical seat  55 , and an outer fuel inlet  48  positioned between the inner conical seat  57  and the outer conical seat  46 . 
     Outer tube  40  is compressed between quill  30  and the fuel injector  12 . In particular, outer tube  40  includes a rounded or conical end in sealing contact with outer conical seat  46  and an opposite end received in a bore defined by quill  30 . One end  41  outer tube  40  is sealed via an O-ring  80  that is positioned in a space  45  between outer tube  40  and quill  30 . O-ring  80  is maintained in place against the pressure from second common rail  16  by a back up ring  86  held in place by a cap  87  threaded to quill  30 . Outer tube  40  is compressed onto outer seat  46  of fuel injector  12  by an axial force applied to a load shoulder  42  by a compression load adjuster  60  that includes a contact surface  64  in contact with load shoulder  42 . Compression load adjuster  60  includes outer threads  65  that mate with a set of inner threads defined by base  21  of block  20 , and includes a tool engagement surface  62  located in hollow interior  24  of block  20  to facilitate adjusting a compression load on outer tube  40 . Thus, leakage of the second fuel from common rail  16  to atmosphere is inhibited by setting a compression load on the outer tube  40  with compression load adjuster  60  above a predetermined threshold to facilitate a seal at outer conical seat  46 . 
     Sealing at opposite ends of inner tube  50  is facilitated by a separate load adjuster  70  that includes threads  75  mated to internal threads defined by base  21  of block  20 . Load adjuster  70  includes a tool engagement surface  72  located outside of block  20  that facilitates movement of compression load adjuster  70  along a common centerline  54 . In other words, compression load adjuster  70  pushes along common centerline  54  against quill  30  to compress inner tube  50  between conical seat  38  of quill  30  and conical seat  55  of fuel injector  12 . Because one end  41  of outer tube  40  can slide within quill  30 , the respective compression loads on inner tube  50  and outer tube  40  can be adjusted independently to better insure proper sealing at all of the conical seats  38 ,  55  and  46 . Thus, leakage of the first fuel originating from common rail  14  into the second fuel is inhibited by setting a compression load on the inner tube  50  above a predetermined threshold with compression load adjuster  70 . In addition, leakage of the second fuel from common rail  16  into the first fuel from common rail  14  may include setting the pressure in common rail  14  higher than the pressure in common rail  16 . Outer tube  40 , inner tube  50 , compression load adjuster  60 , compression load adjuster  70 , conical seat  38 , inner conical seat  55  and outer conical seat  46  all share a common centerline  54 . 
     As shown, quill  30  may be at least partially positioned within block  20 , which includes a base  21  and a cover  22  that may be attached to base  21  by a plurality of fasteners  26 . Base  21  may include a flange ( FIG. 2 ) that facilitates attachment of block  20  to an engine head via bolts  28 . As shown in the Figures, the first fuel inlet  33  and the second fuel inlet  36  of quill  30  may be located outside of block  20 . A shim  27  may be included to adjust the distance between conical seat  38  and conical seat  57  to compensate for geometrical tolerances in the fuel system and engine components. Any of the second fuel that manages to leak past O-ring  80  into hollow interior  24  of block  20 , may be vented to atmosphere via vent opening  23 . Thus, vent opening  23  might be eliminated in a case where the fuel in common rail  16  is not gaseous at atmospheric pressure. Except for vent opening  23 , hollow interior  24  may be substantially closed via an O-ring  81  that is in contact with quill  30  and block  20  and surrounds first fuel passage  32 . In addition, a second O-ring  82  may be in contact with quill  30  and block  20  and surround the second fuel passage  35 . Thus, vent opening  23  extends between hollow interior  25  and an outer surface  25  of block  20 , which is exposed to atmosphere. 
     Coaxial quill assembly  18  may also include a flange  90 , collar  92  and bolts  91  to facilitate a sealed fluid connection between quill  30  and common rail  14 . Although co-axial quill assembly  18  is illustrated as including a separate block  20  and quill  30 , those skilled in the art will appreciate that the functions and structures of those two components could be merged into a single component without departing from the present disclosure. 
     Industrial Applicability 
     The dual fuel common rail system  10  of the present disclosure finds general applicability to any engine that utilizes two fuels in the combustion space of an associated engine. These two fuels may be the same fuel at two different pressures, or may, as in the illustrated embodiment be different fuels. Although the present disclosure could apply to spark ignited engines utilizing appropriate fuels, the present disclosure finds particular applicability in gaseous fuel engines that utilize a relatively large charge of natural gas that is ignited via compression ignition of a small charge of distillate diesel fuel originating from common rail  14 . The coaxial quill assembly  18  of the present disclosure can facilitate movement of both fuels to a fuel injector  12  mounted in the head of an engine via a single bore through the engine head associated with each fuel injector of the engine. This strategy conserves valuable space in and around the engine. 
     By utilizing a block  20  that is bolted to the outer surface of the engine head, separate load adjusters  60  and  70  can be utilized to independently load the inner tube  50  and outer tube  40  onto the conical seats  57  and  46 , respectively of fuel injector  12  to inhibit fuel leakage between the fuels and to inhibit fuel leakage outside of fuel injector  12 . In the event that system  10  was being utilized with two liquid fuels, an additional outer wall containment strategy (not shown) could be added to comply with double walled pressure containment regulations associated with certain jurisdictions. 
     When in operation, the first fuel at a first pressure moves from first common rail  14  through the first fuel passage  32 , through inner tube  50  and into fuel injector  12 . The second fuel at a second pressure is moved from the second common rail  16  through the second fuel passage  35 , through the space  49  between outer tube  40  and inner tube  50  and into fuel injector  12 . Leakage of the second fuel to the first fuel may be inhibited by setting the pressure in common rail  14  (maybe about 40 MPa) higher than the pressure in common rail  16  (maybe about 35 MPa). Leakage of the first fuel into the second fuel includes setting a compression load on the inner tube  50  above a first predetermined threshold with the compression load adjuster  70  to create appropriate sealing forces on both ends of quill  50 . Leakage of the second fuel to atmosphere includes setting a compression load on the outer tube  40  above a second predetermined threshold with the second load adjuster  60  to create a seal between outer tube  40  and fuel injector  12 . 
     The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.