Abstract:
A dual fuel system for an engine is disclosed. The dual fuel system may have a first fuel supply providing a first fuel to the engine, and a second fuel supply providing a second fuel. The dual fuel system may also have a regulator configured to pass the second fuel from the second fuel supply to the engine, with the regulator also in fluid communication with the first fuel supply. The dual fuel system may further have a damper in fluid communication with the first fuel supply and an output of the regulator.

Description:
TECHNICAL FIELD  
       [0001]    The present disclosure is directed to a dual fuel system and, more particularly, to a dual fuel system having a damper. 
       BACKGROUND  
       [0002]    Dual fuel systems supply the combustion chamber of an engine with two different types of fuel. In many cases, one of these fuels will be a liquid such as diesel fuel, and the other will be a gaseous fuel such as natural gas. Such systems often use a dome loaded regulator to control a pressure of the natural gas. This type of regulator is controlled by a reference pressure, for example, a pressure of the diesel fuel. By using a reference pressure, the engine can be supplied with each fuel in the proper pressure ratio. 
         [0003]    However, the diesel fuel pressure is subject to fluctuations due to its incompressibility. Fuel pumps and fuel injectors can create fluctuations in this fuel pressure that would typically be passed on to the gaseous fuel pressure, since the diesel fuel pressure serves as the reference for the gaseous fuel pressure. Because the gaseous fuel&#39;s density is sensitive to these pressure fluctuations, engine operation may suffer as a result of the fluctuating pressures. 
         [0004]    One attempt to address fuel system pressure fluctuations is described in U.S. Pat. No. 7,463,967 issued to Ancimer et al. on Dec. 9, 2008. The &#39;967 patent describes a system that measures gaseous fuel pressure and adjusts fuel injection pulsewidth in order to correct for differences between a target fuel pressure and the measured fuel pressure. This system uses an engine map and calculations performed by an engine controller to modify the injector pulsewidth to a value that is calculated to provide the correct mass of fuel to the engine for a given engine parameter. 
         [0005]    While the system of the &#39;967 patent may provide some control over gaseous fuel pressure, it does so with sensors and a controller that are complex and require separate programming. Further, because the system of the &#39;967 patent relies on electronic signals and calculations, there may be an increased potential for error, malfunction, and lag in the control system. 
         [0006]    The present disclosure is directed toward one or more of the problems set forth above and/or other problems of the prior art. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the present disclosure is directed to a dual fuel system for an engine. The dual fuel system may include a first fuel supply providing a first fuel to the engine and a second fuel supply providing a second fuel. The dual fuel system may also include a regulator configured to pass the second fuel from the second fuel supply to the engine, with the regulator also in fluid communication with the first fuel supply. The dual fuel system may further include a damper in fluid communication with the first fuel supply and an output of the regulator. 
         [0008]    In another aspect, the present disclosure is directed to a method of providing two fuels to an engine. The method may include directing a first fuel into the engine, and directing the first fuel to a regulator and to a damper in parallel. The method may further include directing a second fuel through the regulator into the engine and to the damper in parallel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a diagrammatic illustration of an exemplary disclosed dual fuel system. 
           [0010]      FIG. 2  is a cross sectional illustration of a damper that may be used in the dual fuel system of  FIG. 1 . 
           [0011]      FIG. 3  is a cross sectional illustration of an alternative damper that may be used in the dual fuel system of  FIG. 1 . 
           [0012]      FIG. 4  is a cross sectional illustration of another alternative damper that may be used in the dual fuel system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates an exemplary dual fuel system  10  having a first fuel supply  15  and a second fuel supply  20  that together fuel an engine  25 . In the depicted example, the first fuel supply  15  contains diesel fuel, and the second fuel supply  20  contains natural gas (or another gaseous fuel). However, it is contemplated that other fuels such as biodiesel, liquefied petroleum gas, or hydrogen may also be used. 
         [0014]    Engine  25  may take in air and the two fuels and ignite a mixture thereof. The resulting combustion generates mechanical work and exhaust gasses. The work can then be transferred from the engine to a machine such as a truck or generator in order to provide power to move a vehicle or generate electricity. After the combustion of the fuels, the byproducts are exhausted from the engine, and the cycle starts again. 
         [0015]    Fuel system  10  is an important component of engine  25 . Fuel must be delivered to engine  25  in order for combustion to occur and for power to be produced. Fuel system  10  may include a regulator  30  connected to first fuel supply  15  by a pilot line  35 . Fuel supply  15  is also connected to an injector  40 , which in turn is connected to engine  25 . Second fuel supply  20  may be fed to engine  25  via regulator  30 , regulator output  45 , and injector  40 . Regulator output  45  may feed into damper  50  on one side, and pilot line  35  may feed into damper  50  on an opposing side. 
         [0016]    First fuel supply  15  may be a diesel fuel tank with a centrifugal pump located in the tank. Alternatively, first fuel supply  15  may be a diesel fuel tank with an in-line fuel pump disposed outside of the fuel tank. Second fuel supply  20  may be a tank of liquefied natural gas or other liquefied gaseous fuel. In order to maintain the fuel in a liquefied state the tank may be chilled, for example to below about −165 degrees Celsius (about −265 degrees Fahrenheit). In some embodiments, the liquefied gaseous fuel may be warmed and vaporized. Vaporization causes expansion and an increase in pressure that may result in no pump being needed. Alternatively, a pump may be employed. Even if second fuel supply  20  is natural gas in a gaseous state, the gas may be compressed in order to save space. 
         [0017]    Regulator  30  may be a dome loaded regulator or another type known in the art. The pressure in pilot line  35  may be used as a reference pressure for regulating second fuel supply  20 . Regulator output  45  may be maintained at a pressure that is substantially the same as or otherwise related to the pressure of pilot line  35 . For example, the pressure of regulator output  45  may be regulated to be about 5 MPa lower than the pressure of pilot line  35 . 
         [0018]    Injector  40  may inject both gaseous and diesel fuels into engine  25 . Injector  40  may be a series of injectors that inject both fuels, or it could be a series of injectors with each only injecting one type of fuel. Injector  40  may be connected to engine  25  at, for example, a cylinder head, such that the injection is directly into a combustion chamber of the engine. Alternatively, one or more of the injectors may be connected to the engine at the intake manifold to provide injection at an intake port. 
         [0019]      FIG. 2  illustrates an exemplary embodiment of damper  50 . Damper  50  may have a housing  55  with a central bore  60  formed therein. Further, damper  50  may have a first port  65  at one end of central bore  60  that is connected to first fuel supply  15 , and a second port  70  at the other end of central bore  60  that is connected to second fuel supply  20 . Disposed between those ports may be piston  75 . Piston  75  may have a first end  80  and a second end  85 . The piston&#39;s first end  80  may be in contact with the fuel from pilot fuel line  35 , and second end  85  may be in contact with the fuel from regulator output  45 . 
         [0020]    In the illustrated embodiment, a diameter of first end  80  may be smaller than a diameter of second end  85 , such that a ratio of areas of the ends is about the same as a ratio of desired pressures of the fuels. By sizing the piston ends this way, the forces of the fuels on piston  75  may be balanced under normal conditions. When the force of one of the fuels on piston  75  is not balanced by the force of the other fuel, piston  75  may slide within central bore  60 . 
         [0021]    Damper  50  may further be structured to inhibit mixing of the fuels. A seal  90  may be disposed around the piston&#39;s second end  85 . Seal  90  may be a nonmetallic annular seal suitable for being in contact with diesel fuel and natural gas, as well as for sliding in bore  60  without seizing or wearing down bore  60 . A drainage port  95  may also be included in damper  50  and connected back to first fuel supply  15 . Drainage port  95  may be located elsewhere on damper  50 , as long as it is on the same side of seal  90  as first port  65 . 
         [0022]      FIG. 3  illustrates an alternative embodiment of a damper  100 . As in the previous embodiment, damper  100  may have a housing  105  with a central bore  110  formed therein. Further, damper  50  may have a first port  115  at one end of central bore  110  that is connected to first fuel supply  15 , and a second port  120  at an opposing end of central bore  110  that is connected to second fuel supply  20 . Disposed between those ports may be a first piston  125 , a second piston  130 , and a rod  135  operatively connecting the pistons. A diameter of first piston  125  may be smaller than a diameter of second piston  130 , but larger than a diameter of rod  135 . First piston  125  may have a first end  140 , and second piston  130  may have a second end  145 . A seal  150  may be disposed around the second piston  130 , and a drainage port  155  may be located in housing  105  between first piston  125  and seal  150  on the second piston  130 . 
         [0023]      FIG. 4  illustrates an alternative embodiment of a damper  160 . As in the previous embodiments, damper  160  may have a housing  165  with a central bore  170  formed therein. Further, damper  160  may have a first port  175  at one end of central bore  170  that is connected to first fuel supply  15 , and a second port  180  at an opposing end of central bore  170  that is connected to second fuel supply  20 . Disposed between those ports may be a first piston  185 , a second piston  190 , and a rod  195  operatively connecting the pistons. First piston  185  may have a first end  200 , and second piston  190  may have a second end  205 . A seal  210  may be disposed around second piston  190 , and a drainage port  215  may be located in housing  165  between first piston  185  and seal  210  on the second piston  190 . 
         [0024]    In this embodiment, first piston  185  and second piston  190  may have about the same area in contact with the fuels. To account for the pressure differential, damper  160  may include a spring  220  located between first piston  185  and a spring perch  225 . This spring  220  may be calibrated to bias first and second pistons in a neutral position between two different fuel pressures until a pressure spike occurs. 
       INDUSTRIAL APPLICABILITY 
       [0025]    The disclosed dual fuel system may be applicable to any dual fuel engine where improved fuel pressure control is desired. The system may provide for stability in the pressure of the second fuel through the use of a damper. The operation of dual fuel system  10  will now be described. 
         [0026]    During operation of dual fuel system  10 , first fuel supply  15  may be used to regulate the pressure of second fuel supply  20 , and then both fuels may be directed into an engine  25 . Second fuel supply  20  may be directed into regulator  30  to regulate its pressure before being fed to the injector  40 . First fuel supply  15  may be directed to both the injector  40  and the regulator  30 . Regulator  30  may use the first fuel supply&#39;s pressure as a reference pressure to modulate the pressure of the second fuel supply. Regulator output  45  and first fuel supply  15  may then be directed through injector  40  into engine  25 . 
         [0027]    Damper  50  may help to reduce the incidence of pressure variations in the first fuel supply  15  so that the regulator output  45  is more stable. Regulator output  45  may be directed into one side of damper  50 , and first fuel supply  15  may be directed to an opposing side of damper  50 . In the embodiment of  FIG. 1 , first fuel supply  15  is directed from pilot line  35  to damper  50 , but other methods may be employed. Piston  75  of damper  50  may typically be balanced between the pressures of the different fuels, but when a pressure spike in the first fuel supply  15  is experienced, piston  75  may move to reduce the pressure spike. 
         [0028]    As an example, diesel fuel from pilot line  35  may enter first port  65  at a pressure of about 40 MPa, while natural gas may enter second port  70  at a pressure of about 35 MPa. When first fuel supply  15  exhibits pressure variations, a pressure spike in pilot line  35  can result. When the pressure spike reaches the first end  80  of piston  75 , the force of that pressure spike may be greater than the opposing force of the natural gas at second end  85  of piston  75 . This imbalance of forces may cause piston  75  to move axially within central bore  60 , which can help to reduce the pressure of the diesel fuel pressure spike in pilot line  35 . When the pressure variation in the first fuel supply  15  subsides, piston  75  may return to its starting position by the natural gas pressure. 
         [0029]    Seal  90 , together with drainage port  95 , may help to prevent the two fuels from mixing within damper  50 . If the first fuel leaks past the first end  80  of piston  75 , this leakage should be captured in drainage port  95  and returned to first fuel supply  15 . Second fuel supply  20 , which may be a gaseous or liquefied gaseous fuel, should be on an opposing side of seal  90  from drainage port  95  in order to prevent its escaping to the atmosphere. Unlike the liquid fuel of first fuel supply  15 , which will remain in a liquid state and may be contained and returned to first fuel supply  15  without the use of pressurized lines, second fuel supply  20  may be a pressurized tank of a liquefied gaseous fuel. Because of its gaseous state, the second fuel may not be easily returned to second fuel supply  20  if it were to leak past second end  85  of the piston  75 . Damper  100  and damper  160  may function similarly to damper  50 . 
         [0030]    After damping first fuel supply  15  and regulating second fuel supply  20 , both fuels may then be directed into injector  40 . Injector  40  may then inject the fuels into engine  25  by any suitable method known in the art. One such method may include directing both fuels to a dual fuel injector that injects both fuels through a single port. Another suitable method may include having separate diesel injectors and natural gas injectors. 
         [0031]    The disclosed system may be used to provide two fuels to an engine at stable pressures for controlled combustion. The improved pressure stability may make the amount of fuel injected easier to control. With an easier to control fuel supply, proper air/fuel ratios may be more readily achieved. These ratios may allow for reduced emissions and increased fuel economy. 
         [0032]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed dual fuel system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed dual fuel system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.