Abstract:
Apparatus for condensing return fuel in a fuel tank. The condenser comprises an elongated body having a passage therethrough in fluid communication with a fuel return line. A plurality of vent holes are spaced along the length of the body and communicated with the passage. The vent holes are sloped along the length of the passage so that gaseous fuel will tend to first exit vent holes toward a distal end of the passage. Both single and multiple passage condensers are disclosed.

Description:
CROSS REFERENCE 
     This is a Continuation-in-Part of U.S. patent application Ser. No. 08/855,217, filed May 13, 1997, now abandoned. 
    
    
     INCORPORATION BY REFERENCE 
     Applicant&#39;s U.S. Pat. Nos. 5,291,869; 5,325,838; and 5,423,303 are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to fuel injection systems and more particularly to in-tank condensers for cooling return fuel in such systems. 
     BACKGROUND OF THE INVENTION 
     Liquefied petroleum gas (“LPG”) fuel supply systems are known, for example as shown in Applicant&#39;s U.S. Pat. Nos. 5,291,869; 5,325,838; and 5,423,303. Such systems typically include a number of specialized fuel injectors which receive fuel from a high pressure tank. A fuel rail connected in-line with a series of injectors is often employed to deliver supply fuel to the injectors. In many systems, uninjected fuel is returned to the fuel tank. This is generally done to keep the supply fuel as cool as possible, particularly where it is intended to inject LPG in liquid rather than gaseous form. 
     One approach to injecting LPG without permitting it to vaporize is to pump high volumes of supply and return fuel. In this way, the supply fuel spends very little time near the heated engine compartment where it can vaporize. Another approach is to employ a refrigeration cycle as described in the Applicant&#39;s patents identified above. The evaporation of return fuel is used to cool supply fuel, thereby maintaining it in liquid form. 
     A problem with returning vaporized LPG to the fuel tank is that it can increase tank pressure substantially above the vapor pressure of the liquid in the tank. If the vapor does not condense before the pressure limit of the tank is exceeded, the pressure relief valve will release LPG vapor to the atmosphere. This is both unsafe and environmentally undesirable. 
     What has been needed is a way to cool return fuel in ILPG systems so as to reduce the high fuel tank pressures which can occur. 
     SUMMARY OF THE INVENTION 
     According to the present invention, an LPG fuel supply system, a method, and a condenser for fuel injection systems are provided. 
     In one aspect of the system, the LPG system includes a plurality of fuel injectors operably connected to a fuel rail. The fuel rail is in fluid communication with fuel supply and return lines. Both the fuel rail and injectors comprise an arrangement for cooling supply fuel with return fuel. A condenser in the return line cools return fuel. 
     In another aspect of the invention, the LPG fuel supply system comprises a plurality of fuel injectors in fluid communication with fuel supply and return lines. The fuel return line includes a mechanism for cooling return fuel. 
     In another aspect of the invention, the LPG fuel supply system comprises a plurality of fuel injectors in communication with a fuel supply line, which in turn communicates with a fuel tank. A condenser is positioned in the fuel tank. It comprises an elongated body having a passage therethrough in fluid communication with a fuel return line A plurality of vent holes spaced along the length of the body, for returning return fuel to the fuel tank, communicate with the passage. The vent holes are sloped relative to horizontal along the length of the body such that gaseous fuel will tend to first exit vent holes toward the distal end of the passage. 
     In another aspect of the invention, an apparatus for condensing return fuel in a fuel tank comprises an elongated body having a passage therethrough in fluid communication with a fuel return line. A plurality of vent holes spaced along the length of the body communicate with the passage. The body, passage, and vent holes are constructed and arranged such that gaseous fuel will tend to first exit vent holes toward the distal end of the passage. 
     In the method of the present invention, a liquefied petroleum gas fuel supply system is provided, comprising a plurality of fuel injectors in fluid communication with a fuel supply line and fuel return line. Vaporous fuel is produced in the fuel return line by the absorption of heat. The vaporous fuel is then cooled in the fuel return line prior to introducing it into the fuel in the fuel tank. 
     These and other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto. However, for a better understanding of the invention and its advantages, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter in which there is illustrated and described a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic diagram of a system according to the present invention; 
     FIG. 2 is a cross-sectional view of condensers according to the present invention; 
     FIG. 3 is a cross-sectional view of a second embodiment of an in-tank condenser according to the present invention, installed in a fuel tank and depicting a low thermal load scenario; 
     FIG. 4 is the in-tank condenser of FIG. 3, depicting a high thermal load scenario; and 
     FIG. 5 is a cross-sectional view of the in-tank condenser shown in FIG. 3, taken generally along lines  5 — 5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like numerals designate like parts throughout the figures, a fuel supply system  10  for providing LPG to an internal combustion engine  12  is shown. Applicant&#39;s U.S. Pat. Nos. 5,291,869 (“&#39;869 patent”), “LIQUEFIED PETROLEUM GAS FUEL SUPPLY SYSTEM,” 5,325,838 (“&#39;838 patent”), “LIQUEFIED PETROLEUM GAS FUEL INJECTOR,” and 5,423,303 (“&#39;303 patent”), “FUEL RAIL FOR INTERNAL COMBUSTION ENGINE” are also incorporated by reference and will be referred to herein as appropriate. 
     System  10  includes a fuel rail  14  which delivers fuel to a plurality of fuel injectors  16 . Although a fuel rail is shown in the preferred embodiment, one is not necessary within the principles of the invention. For example, separate supply lines branching from a main supply line could deliver fuel to each injector in parallel. 
     In the preferred embodiment, both fuel rail  14  and injector  16  include arrangements for cooling supply fuel with return fuel, such as those described in the &#39;869 patent generally, and more specifically in the &#39;303 patent for the fuel rail and the &#39;838 patent for the fuel injector. These arrangements involve evaporating return fuel in close proximity to supply fuel so as to extract heat from the supply fuel. In this way, supply LPG is maintained in liquid form when injected. It is not necessary. however, for the fuel rail or injectors to have such a refrigeration cycle, as there are other ways in which liquid LPG at injection can be achieved. 
     The main problem the present invention addresses is the high tank pressures which can result when heated LPG is returned to the fuel tank  18 . Under the present regulations in the United States, the maximum allowable tank pressure is 312.5 psi. A pressure relief valve (not shown) would be opened if this maximum pressure is reached. 
     Return fuel is heated in its passage through the engine compartment by the engine itself. It can also be heated if a refrigeration cycle such as that in the preferred embodiment is employed. If the return line is routed under the chassis, engine, transmission, exhaust and radiator heat will also tend to be absorbed there. The problem is most pronounced at high engine and ambient temperatures and at low fuel levels. 
     Referring to FIGS. 1 and 2, a system and method for addressing this problem will be described. In addition to the fuel injectors  16  and fuel rail  14  described above, system  10  includes fuel pump  20 , supply line  22  and return line  24 . As is generally the case, an engine control unit  26  controls injectors  16 . 
     Return fuel is cooled in the preferred embodiment by in-line  28  and in-tank  30  condensers in return line  24 . As shown in FIG. 2, condensers  28 ,  30  have external  32  and internal  34  fins to aid heat transfer. They are made of extruded aluminum. 
     In-line condenser  28 , and as much of return line  24  as possible, are preferably located away from the hot underchassis. Cooler air can then assist in extracting heat from return fuel in condenser  28 . If necessary, through ducting or otherwise, air can be forced across external fins  32  to further increase cooling. It may also be necessary to thermally insulate return line  24 , as for example by surrounding with foam rubber. 
     In-tank condenser  30  is immersed in fuel tank  18  at a terminal end of return line  24 . Condenser  30  is placed below the fuel level in the tank so heat can be transferred to the liquid fuel. It is preferably mounted at the bottom of tank  18  to maximize exposure. Condenser  30  is elevated by legs  36  at its distal end  38  and has a plurality of vent holes  40  from which return fuel enters the fuel in tank  18 . By this arrangement, gaseous fuel tends to be cooled along the entire length of condenser  30  before exiting near distal end  38 . Spreading vent holes across tank  18  reduces the localized heat which would otherwise occur. Vent holes  40  are also preferably small, on the order of 0.03-0.13 inches diameter, preferably 0.09 inches, to create smaller bubbles which will condense faster. The total flow area through vent holes  40  is at least twice and preferably four times the cross-sectional area of return line  24  to minimize back pressure. While vent holes  40  are shown at approximately the horizontal quadrant of condenser  30 , it may be preferable to position them lower to improve cooling. 
     A second embodiment of an in-tank condenser  130  is shown in FIGS. 3-5. Condenser  130  is in many ways similar to condenser  30 , and therefore like reference numerals (+100) are used where appropriate, and the below discussion will primarily discuss the differences between the two. 
     Condenser  130  has upper  150  and lower  152  passage portions communicating with one another at a distal end  138  of the body of the condenser. Plug  160 , made of plastic, closes lower passage  152  at its terminal or distal end, and has an opening therethrough so that return fuel can flow from return line  24  into upper passage  150 . Plug  162  closes off the opposite, distal end of the aluminum extrusion, leaving enough room between it and the end of dividing wall  154  so that communication between passages  150 ,  152  can occur. External  132  and internal  134  fins assist in heat transfer, both between the tank fuel and passages  150 ,  152  and between the passages  150 ,  152  themselves. 
     As with the first embodiment, condenser  130  is sloped so as to cause maximum phase change to liquid within the condenser. Support  136  elevates proximal end  139 , and bracket  164  is welded to tank  18  to secure distal end  138 . In conjunction with the double-passage arrangement, this significantly improves phase change. FIG. 3 shows a low thermal load scenario. Any vapor that enters condenser  130 , by buoyancy, stays in upper passage  150  so that, by the time the fuel reaches vent holes  140  in lower passage  152 , it is in liquid form. In the high thermal load scenario shown in FIG. 4, vapor similarly gravitates to the high, proximal end  139  of lower passage  152 . Fuel that does exit condenser  140  in vaporous form thus has been cooled along the longest possible path; the hottest vapors will also travel the longest distances due to their greater buoyancy, including along the length of internal fins  134  on the bottom side of dividing wall  154 . Uncondensed vapor also rides along the bottom side of dividing wall  154  within liquid fuel at the lower end of lower passage  152  until much of it too condenses and drops into that liquid. All of these factors contribute to maximum heat transfer before return fuel leaves the condenser. 
     Vent holes  140  are preferably located in the lower quadrant of condenser  130  so as to further maximize heat transfer before fuel exits condenser  130 . The size of vent holes  140 , and their total flow area, are preferably the same as those set forth above for the first embodiment. 
     Employing a multi-passage condenser like that of the second embodiment  130  has certain advantages compared to the first embodiment  30 . It allows the condenser to be shorter and to have the inlet located at the high end of the condenser, both of which save space that can be valuable in certain applications. Cooling on the order of 200 watts or higher can be obtained from the double pass condenser (second embodiment), compared to what is believed to be about half that amount for the single pass (first embodiment). It will be understood that a condenser employing three or more passages could also be used within the principles of the invention. 
     Sloping vent holes according to the invention greatly improves the performance of the in-tank condensers. Although the inventor has not yet conducted tests that quantify the performance advantage over a condenser without sloped vent holes, it is expected that the difference is significant because of the physics and thermodynamics involved, as discussed above. The preferred slope is about between 4-15 degrees. As can be seen in FIG. 1, the slope for the first embodiment is about 4 degrees. The preferred slope for the second embodiment, shown in FIGS. 3 and 4, is about 8 degrees. 
     It should be understood that the present invention is not limited to the preferred embodiments discussed above, which are illustrative only. For example, sloping vent holes could be achieved in a number of other ways, such as by having a horizontal condenser with vent holes formed progressively further down along the length of the body. The type and number of heat transfer devices and their size, shape and arrangement can also be varied within the principles of the invention. Other changes may be made in detail, especially in matters of shape, size, arrangement of the parts, order of steps or material of components within the principles of the invention, to the full extent indicated by the broad, general meanings of the terms in which the appended claims are expressed.