Patent Application
20140238353
This disclosure relates generally to dual fuel common rail systems, and more particularly to a diesel only method of operation that includes strategies to address liquid fuel leakage into the gas fuel side of the system.
Diesel engines are the most popular type of compression ignition engines. Diesel engines introduce fuel directly into the combustion chamber. Diesel engines are very efficient because they provide high compression ratios without knocking, which is the premature detonation of the fuel mixture inside the combustion chamber. Because diesel engines introduce fuel directly into the combustion chamber, the fuel injection pressure must be greater than the pressure inside the combustion chamber. For liquid fuels such as diesel, the pressure must be significantly higher so that the fuel is atomized for efficient combustion.
Diesel engines are favored by industry because of their excellent combination of power, performance, efficiency and reliability. For example, diesel engines are generally much less expensive to operate compared to gasoline fueled, spark-ignited engines, especially in commercial applications where large quantities of fuel are used. However, one disadvantage of diesel engines is pollution, such as particulate matter (soot) and NOx gases, which are subject to increasingly stringent regulations that require NOx emissions to be progressively reduced over time. To comply with these increasingly stringent regulations, engine manufacturers are developing catalytic converters and other after-treatment devices to remove pollutants from diesel exhaust streams.
Improvements to diesel fuels are also being introduced to reduce the amount of sulfur in diesel fuel, to prevent sulfur from de-activating the catalysts of catalytic converters and to reduce air pollution. Research is also being conducted to improve combustion efficiency to reduce engine emissions, for example by making refinements to engine control strategies. However, most of these approaches add to the capital cost of the engine and/or the operating costs.
Other recent developments have been directed to substituting some of the diesel fuel with cleaner burning gas fuels such as, for example, natural gas, methane, butane, propane, hydrogen, and blends thereof. Since gas fuels typically do not auto-ignite at the same temperature and pressure as diesel fuel, a small amount of pilot diesel fuel can be introduced into the combustion chamber to auto-ignite and trigger the ignition of the gas fuel. Another approach for consuming gas fuel on board a vehicle involves introducing the gas fuel into the engine's intake air manifold at relatively low pressures. However, this approach has been unable to match the performance and efficiency of currently available diesel engines, particularly at high gas:diesel ratios. Thus, fuel injectors have been developed that provide a simultaneous delivery of both diesel fuel and gas fuel to combustion chambers, with the diesel acting as a pilot fuel.
For example, U.S. Pat. No. 7,627,416 appears to teach a dual fuel common rail system in which liquid diesel fuel and natural gas fuel are both injected from a single fuel injector associated with each engine cylinder. This reference recognizes that there may be instances in which the engine will need to operate solely on liquid diesel fuel due to exhaustion of the natural gas fuel supply or possibly some fault in the natural gas portion of the system. However, one problem this reference does not recognize is the migration of diesel or the liquid fuel into the gas fuel delivery system or gas rail. If liquid fuel migrates or leaks into the gas rail, the gas:liquid fuel ratio changes, engine performance suffers and damage to the engine is possible.
Thus, there is a need for a methods and systems for detecting when liquid fuel has leaked or migrated into the gas rail so the operation of the engine can be changed to mitigate or prevent damage and/or so the operator can be notified that such a problem exists.
In one aspect, a method for detecting leakage of a liquid fuel into a gas rail of a dual-fuel system for an internal combustion engine is disclosed. The method may include sending an injection signal from the controller to a fuel injector and injecting gas fuel and liquid fuel into a cylinder for combustion. The method may further include detecting the pressure in the gas rail over a pre-determined time period after the injection event. The method may further include measuring pressure fluctuations in the gas rail over the pre-determined time period and, if the pressure in the gas rail fluctuates by more than the pre-determined amount, the method may further include taking at least one mitigating action.
In another aspect, a system for detecting leakage of a liquid fuel into a supply of a gas fuel of a dual-fuel internal combustion engine is disclosed. The system may include a gas rail that is coupled to a pressure sensor. The gas rail may also be in communication with a gas nozzle chamber of a fuel injector for delivering gas fuel to the gas nozzle chamber. The system may also include a liquid rail in communication with a liquid nozzle chamber of the fuel injector for delivering a liquid fuel to the liquid fuel chamber. Further, the system may include a controller linked to the pressure sensor. The controller may have a memory programmed to receive signals from the pressure sensor and to determine if the pressure in the gas rail is fluctuating more than the pre-determined amount. The memory may also be programmed to initiate a mitigating action if the pressure in the gas rail is fluctuating more than the pre-determined amount.
A vehicle is also disclosed which may include an engine which may include a plurality of cylinders and a plurality of fuel injectors. Each cylinder may be in communication with one of the fuel injectors. Each fuel injector may include a liquid nozzle chamber and a gas nozzle chamber for simultaneously injecting liquid fuel and gas fuel respectively into its respective cylinder. Each fuel injector may also be in communication with a gas rail and a liquid rail. The gas rail may be used for delivering gas fuel from a gaseous fuel tank to the plurality of fuel injectors. The liquid rail may be used for delivering liquid fuel from a liquid fuel tank to the plurality of fuel injectors. The gas rail may be coupled to a pressure sensor. The pressure sensor may be linked to the controller. The controller may have a memory programmed to receive signals from the pressure sensor and to determine if a pressure in the gas rail is fluctuating more than a pre-determined amount. The memory may also be programmed to initiate a mitigating action if the pressure in the gas rail is fluctuating more than a pre-determined amount.
Referring initially to
The gas fuel common rail 25 may be in communication with a manifold 27 which may be in communication with an isolation valve 28. The isolation valve 28 may be used to shut off the gas fuel supply in the event that the gas fuel pressure drops to an undesirable level and the engine 20 must convert to a “limp home” mode where the engine 20 runs on liquid fuel only. The isolation valve 28 may be connected to a fuel conditioning module 29 which may be linked with the isolation valve 28 to the controller 31. The controller 31 may be an engine control module (ECM). A filter 32, an accumulator 33, a pump 35 and a pressurized cryogenic gas fuel tank 36 may be disposed upstream of the conditioning module 29. The fuel tank 36 may be equipped with a pressure relief valve 37. The controller 31 may also be linked to a gas fuel rail pressure sensor 38 that monitors the pressure in the gas rail 25.
The liquid fuel common rail 26 may also be in communication with a manifold 27 which may be in communication with a high pressure fuel pump 41. The fuel pump 41 may be linked to the controller 31 and may also be disposed upstream or downstream from a filter 42. In the embodiment shown in
The controller 31 may control each fuel injector 24, the isolation valve 28, the fuel conditioning module 29, and the pump 41 in a known manner. The gas fuel pump 35 may be a unidirectional variable displacement cryogenic pump while the liquid fuel pump 41 may be a unidirectional variable displacement hydraulic pump. The fuel conditioning module 29 may be used to control the supply and pressure of gas fuel to gas fuel common rail 25.
Turning to
Each block 45 of each co-axial quill assembly 44 may define a segment of the gas common rail 25 which may be oriented perpendicular to the axis 51 of the inner quill 46. One end of a gas fuel passage 52 opens at the gas fuel common rail 25, proceeds through the check valve 53, passes between the inner quill 46 and the outer quill 47 before opening at its other end into the gas fuel inlet 54 of the fuel injector 24. Thus, a segment of the gas fuel rail 25 is located between the inner quill 46 and the outer quill 47. Each of the blocks 45 also defines a segment of liquid fuel common rail 26. One end of a liquid fuel passage 55 opens at the liquid common rail 26, and may open at its opposite end into liquid fuel inlet 56 of the fuel injector 24.
Referring to
Returning to
The liquid check valve 72 has a closing hydraulic surface 73 (
Thus, an injection of a gas fuel (e.g., natural gas) to a cylinder 23 through the gas nozzle outlet 58 is facilitated by movement of the gas check valve 66, while an injection of a liquid fuel (e.g., diesel) through the liquid nozzle outlet 61 is facilitated by movement of the liquid check valve 72. Those skilled in the art will appreciate that the gas and liquid nozzle outlets 58, 61 might be expected to each include several nozzle outlets arranged around respective centerlines in a manner well known in the art. However, the gas and liquid nozzle outlets 58, 61 could each include as few as one nozzle outlet or any number of nozzle outlets in any arrangement without departing from the scope of this disclosure.
A gas control valve 77 may be positioned in the injector body 63 and may be movable axially between a closed position in contact with a seat 78 at which the gas control chamber 64 is fluidly blocked from the gas drain outlet 60, and an open position where the gas control chamber 64 is fluidly connected to the gas drain outlet 60 via the control passage 76 as shown in
A liquid control valve 81 may be positioned in the injector body 63 and movable axially between a closed position in contact with a seat 82 so the liquid control chamber 65 is fluidly blocked from the liquid drain outlet 62 as shown in
In the illustrated embodiment, the gas and liquid control valve members 77, 81 may be moved to one of their respective closed and open positions with the gas and liquid electrical actuators 83, 84 respectively. The control valves 77, 81 may be biased to their closed position by a spring(s) or biasing member(s) 85. A liquid armature 86 may be attached to a pusher 87 in contact with the liquid control valve 81. The liquid armature 86, the pusher 87 and the liquid control valve 81 may be biased to the position shown in contact with the seat 82 by the spring 85. Thus, the liquid armature 86 can be thought of as being operably coupled to move the liquid control valve 81. Similarly, a gas armature 88 may be operably coupled to move the gas control valve 77 by way of the pusher 91. A common stator 92 separates the liquid armature 86 from the gas armature 88.
The liquid control valve 81 may be in contact and out of contact with the seat 82 in its open and closed positions respectively. Likewise, the gas control valve 77 may be in contact and out of contact with the seat 78 in its closed and open positions, respectively. The liquid control valve 81 may be coupled to move with the liquid armature 86 in response to a de-energizing of the liquid actuator 84 mounted in the common stator 92. When the liquid actuator 84 is energized, the armature 86 and pusher 87 are lifted upward (or shifted to the right in
The gas nozzle chamber 94 may be fluidly connected to gas fuel inlet 54 via the passage 71 (see
Dual fuel common rail fuel systems may also have a single fuel mode of operation in which only liquid diesel fuel is utilized to power the engine 20. This mode of operation may be referred to as a “limp home” mode, as this mode of operation may only be preferable when there is some fault in the gas fuel system. A fault may include a malfunction of one or more of gas supply pressure control devices such as the pressure relief valve 37, the pump 35, the heat exchanger 34, the filter 32, the fuel conditioning module 29 or the isolation valve 28. A malfunction may also simply relate to a lack of sufficient gas fuel in the tank 36 to continue operating in a regular mode. When operating in a limp home mode, the controller 31 may maintain the liquid rail 26 at a high pressure (e.g., 80 MPa), whereas the pressure in gas rail 25 may be allowed to decay, and may slowly drop as low as atmospheric pressure.
During the limp home mode, the engine 20 is operated as a conventional diesel engine in which liquid diesel fuel is injected through the liquid nozzle outlets 61 in sufficient quantities and at timings to compression ignite the liquid fuel. On the other hand, during the regular mode of operation, one might expect a relatively small pilot liquid injection through the liquid nozzle outlets 61 to be compression ignited to ignite a much larger charge of gas fuel injected through gas nozzle outlets 58 to power the engine 20 in a regular mode of operation. Due to the higher pressure differential between the liquid fuel and the gas fuel that exists during the limp home mode of operation, more leakage of liquid fuel from the upper liquid nozzle chamber 102 to the gas nozzle chamber 94 is expected as opposed to a regular mode of operation with a smaller pressure differential between the two fuels.
Referring back to
Turning to
Further, while leakage from the liquid nozzle chamber 96 to the gas nozzle chamber 94 may be the primary location where liquid fuel leaks into the gas rail 25, other areas of the disclosed injectors 24 and other fuel injectors that differ in design from the disclosed injector 24 may be the source of such leakage and those skilled in the art will be able to examine a fuel injector design and determine where such leakage may occur.
A system and method for detecting liquid fuel leakage from the liquid rail 26 to the gas rail 25 is disclosed. When such leakage occurs, the pressure in the gas rail 25 will fluctuate and such fluctuations can be detected by the gas rail pressure sensor 38 and may be communicated to the controller 31. The gas rail pressure sensor 38 may be in continuous or regular communication with the controller 31.
Therefore, a dual fuel system is disclosed that is configured to: (1) monitor the pressure in the gas rail 25; (2) evaluate pressure waves in the gas rail 25 after injections to determine if liquid fuel is present in the gas rail 25; and (3) take one or more mitigating actions. Detecting liquid fuel or diesel in the gas rail 25 will allow the engine controller 31 to take any one or more of the following mitigating actions, such as: (1) entering a diagnostic mode to determine the leak location; (2) entering a liquid fuel or diesel only mode operation; (3) reducing fuel delivered to the effected cylinder(s) to prevent or reduce engine damage; (4) derating the engine or reducing the power output of the engine to prevent engine damage; and/or (5) notifying the operator that a problem exists. The controller 31 may be programmed to take other corrective actions as well, as will be apparent to those skilled in the art.
