Patent Application
20140311444
The present disclosure relates generally to dual fuel compression ignition engines, and more particularly to a common rail pressure control strategy during a load loss transient.
Natural gas is increasingly becoming an attractive alternative for fueling internal combustion engines. In one specific example, a compression ignition engine is fueled predominately with natural gas originating from a gaseous fuel common rail, and liquid diesel fuel from a liquid fuel common rail that are directly injected into each engine cylinder. Both fuels are injected from the same fuel injector, and the relatively large charge of gaseous fuel is ignited by compression igniting a small pilot injection quantity of liquid diesel fuel. When both fuels are injected from a single fuel injector, there is a possibility of gaseous fuel migrating into the liquid side, and vice versa, which can lead to undermining proper operation of the fuel system. Co-owned U.S. Patent Application Publication No. 2012/0285417 shows an example of such a dual fuel system. During typical operation, the liquid fuel pressure is maintained greater than the gaseous fuel pressure to inhibit migration of gaseous fuel into the liquid fuel side of the fuel system. Pressure in the liquid fuel common rail can be changed quickly due to the relative incompressibility of the liquid fuel. However, changing pressure in the gaseous fuel common rail is far different due to the highly compressible nature of the gaseous fuel. Reducing pressure in the gaseous fuel common rail during a load loss transient without venting substantial amounts of gas to atmosphere can be difficult, while maintaining a pressure differential that inhibits migration of gaseous fuel into the liquid fuel side of the fuel system.
The present disclosure is directed toward one or more of the problems set forth above.
In one aspect, a method of operating an engine includes injecting gaseous fuel and liquid fuel directly into an engine cylinder from a gaseous nozzle outlet set and a liquid nozzle outlet set, respectively, of a fuel injector. The injected liquid fuel is compression ignited to in turn ignite the gaseous fuel. Migration of gaseous fuel into liquid fuel within the fuel injector is inhibited by maintaining a liquid rail pressure greater than a gas rail pressure. The migration inhibiting step includes executing a first rail pressure control algorithm before and after a transient, and executing a second rail pressure control algorithm during the transient. The transient is initiated by changing from a high fuel demand state of a first speed and load to a low fuel demand state of a second speed and load.
In another aspect, an engine includes an engine housing that defines a plurality of cylinders within which a plurality of respective pistons reciprocate to define a compression ratio greater than 14:1. A gaseous fuel common rail and a liquid fuel common rail are fluidly connected to each of the plurality of fuel injectors, which each include a gaseous nozzle outlet set and liquid nozzle outlet set positioned for direct injection into one of the cylinders. A means for inhibiting migration of gaseous fuel into liquid fuel within the fuel injector includes an electronic controller configured to execute a first rail pressure control algorithm to maintain liquid pressure greater than a gas rail pressure before and after a transient, and execute a second rail pressure control algorithm to maintain a liquid rail pressure greater than a gas rail pressure during the transient. The transient includes changing from a high fuel demand state of a first speed and load to a low fuel demand state of a second speed and load.
Referring initially to
Although not necessary, the gaseous fuel common rail 40 and the liquid fuel common rail 41 may be made up of a plurality of daisy chained blocks 51 that are connected in series with liquid fuel lines 52 and gaseous fuel lines 53. The liquid and gaseous fuels may be supplied to the individual fuel injectors 30 with a coaxial quill assembly 54 that includes an inner quill 55 that is positioned within an outer quill 56. Liquid fuel is supplied to the fuel injector 30 through inner quill 55, and gaseous fuel is supplied to fuel injector 30 in the space between inner quill 55 and outer quill 54. A load adjusting clamp 57 may be utilized with each block 51 for pushing the coaxial quill assembly 54 so that both the inner quill 55 and the outer quill 56 seat on a common conical seat 27 of each fuel injector 30.
Referring in addition to
Injector body 100 defines a gaseous nozzle outlet set 103, a liquid nozzle outlet set 104 and a drain outlet 105. Disposed within injector body 100 are a first control chamber 106 and a second control chamber 107. A gaseous check valve member 110 has a closing hydraulic surface 112 exposed to fluid pressure in the first control chamber 106. The gaseous check valve member 110 is movable between a closed position, as shown, in contact with a first nozzle seat 108 to fluidly block the gaseous fuel inlet 101 to the gaseous nozzle outlet set 103, and an open position out of contact with the first nozzle seat 108 to fluidly connect the gaseous fuel inlet 101 to the gaseous nozzle outlet set 103. First control chamber 106 may be partially defined by a first sleeve 111.
A liquid check valve member 120 has a closing hydraulic surface 121 exposed to fluid pressure in the second control chamber 107. The liquid check valve member 120 is movable between a closed position, as shown, in contact with a second nozzle seat 113 to fluidly block the liquid fuel inlet 102 to the liquid nozzle outlet set 104, and an open position out of contact with the second nozzle seat 113 to fluidly connect the liquid fuel inlet 102 to the liquid nozzle outlet set 104. The second control chamber 107 may be partially defined by a second sleeve 122. Thus, injection of gaseous fuel through gaseous nozzle outlet set 103 is facilitated by movement of gaseous check valve member 110, while injection of a liquid fuel through liquid nozzle outlet set 104 is facilitated by movement of the liquid check valve member 120.
A first control valve member 130 is positioned in injector body 100 and is movable along a common centerline 125 between a first position in contact with first valve seat 150 at which the first control chamber 106 is fluidly blocked to the drain outlet 105, and a second position at which the first control chamber 106 is fluidly connected to the drain outlet 105. When first control chamber 106 is fluidly connected to drain outlet 105, pressure in first control chamber 106 drops, relieving pressure on closing hydraulic surface 112 to allow gaseous check valve member 110 to lift to facilitate an injection of the gaseous fuel through gaseous nozzle outlet set 103. A second control valve member 135 is positioned in the injector body 100 and movable along the common centerline 125 between a first position in contact with second valve seat 155 at which the second control chamber 107 is fluidly blocked to the drain outlet 105, and a second position at which the second control chamber 107 is fluidly connected to the drain outlet 105. When second control chamber 107 is fluidly connected to drain outlet 105, fluid pressure acting on closing hydraulic surface 121 is relieved to allow liquid check valve member 120 to lift to an open position to facilitate injection of the liquid diesel fuel through the liquid nozzle outlet set 104.
In the illustrated embodiment, the first and second control valve members 130, 135 are intersected by the common centerline 125. The respective control valve members 130, 135 may be moved to one of their respective first and second positions with first and second electrical actuators that include first and second coils 147, 148, respectively. The control valve members 130, 135 may be biased to the their respective first positions by a shared biasing spring 146. A first armature 141 may be attached to a pusher 145 in contact with first control valve member 130. A second armature 142 may be operably coupled to move the second control valve member 135 by way of a pusher 143. A shared stator 144 houses first and second coils 147, 148 and separates the first armature 141 from the second armature 142.
In the illustrated embodiment, the first control chamber 106 may always be fluidly connected to the high pressure in the liquid fuel inlet 102 via an F orifice 160 and a Z orifice 161. The upstream ends of respective F and Z orifices 160 and 161 may be fluidly connected to the liquid fuel inlet 102 via passages not visible in the sectioned views. The first control chamber 106 is fluidly connected to a control passage 133 via a so called A orifice 163. Thus, when first control valve member 130 lifts off of first valve seat 150, the second fuel inlet 102 becomes fluidly connected to the drain outlet 105 through a Z-A pathway 116 and an F pathway 117 that are fluidly in parallel with each other.
The second control chamber 107 may always be fluidly connected to the high pressure in liquid fuel inlet 102 via an F orifice 170 and a Z orifice 171. The upstream ends of respective F and Z orifices 170, 171 may be fluidly connected to the liquid fuel inlet 102 via passages not visible in the sectioned view. The second control chamber 107 is fluidly connected to a control passage 134 via a so-called A orifice 173. Thus, when the second control valve member 135 moves off of the second valve seat 155, the second fuel inlet 102 becomes fluidly connected to the drain outlet 105 through a Z-A pathway 126 and an F pathway 127 that are fluidly in parallel with each other.
Those skilled in the art will appreciate that the illustrated embodiment utilizes liquid diesel fuel to control movement of the gaseous check valve member 110 and the liquid check valve member 120 to facilitate control over gaseous fuel injection events and liquid diesel fuel injection events, respectively.
Apart from electronic controller 50 including various control algorithms for operating engine 20 in dual fuel modes at various speeds and loads, the present disclosure also teaches equipping the electronic controller with a means for inhibiting migration of gaseous fuel into liquid fuel within the fuel injector 30. This means includes electronic controller 50 being configured to execute a first rail pressure control algorithm to maintain liquid rail pressure greater than a gas rail pressure before and after a transient, and execute a second rail pressure control algorithm to maintain the liquid rail pressure greater than the gas rail pressure during the transient. Although those skilled in the art will appreciate that many different engine transitions exist, a transient according to the present disclosure includes changing from a high fuel demand state of a first speed and load to a low fuel demand state of a second speed and load.
In one specific example, a transient according to the present disclosure might include transitioning from a rated engine condition at which a liquid and gaseous rail pressures are controlled toward 40 MPa and 35 MPa, respectively, to an idle condition at which the respective liquid and gaseous fuel pressures are controlled to 25 and 20 MPa. These respective target pressures may be part of an overall engine design and stored in a lookup table available to electronic controller 50 based upon engine speed and load in a manner well known in the art. In general, pressure in either the liquid fuel common rail 41 or the gaseous fuel common rail 40 generally require injection events in order to reduce pressure. The nearly incompressible nature of liquid fuel makes lowering pressure quick even with only a small volume of injected fuel. However, the compressible nature of the gaseous fuel may require significantly larger volumes of fuel injection for a similar drop in pressure.
A first rail pressure control algorithm may be configured to control the liquid rail pressure toward a first predetermined target pressure based upon the first engine speed and load, and control the gaseous rail pressure toward a first gas pressure that is lower than the first predetermined target pressure prior to the transient. The first rail pressure control algorithm is also configured to control the liquid rail pressure toward a second predetermined target pressure based upon the second engine speed and load, and control the gaseous rail pressure toward a second gas pressure that is lower than the second predetermined target pressure after the transient. The second rail pressure control algorithm is configured to control the liquid rail pressure toward a transient target pressure that equals the gas rail pressure plus a bias pressure, and control the gaseous rail pressure toward the second gas pressure during the transient.
Those skilled in the art will appreciate that lowering the liquid rail pressure or the gaseous rail pressure may include reducing or temporarily stopping output from the liquid supply and pressure control devices 44 and the gas supply and pressure control devices 43, respectively. In some instances, depending upon hardware chosen, the cryogenic pump and maybe accumulator 33 may be sluggish in responding to temporarily stopping resupply of gaseous fuel common rail 40. Thus, the present disclosure might also teach the second pressure control algorithm being configured to close a shut off valve 45 during the transient. This strategy can quickly stop resupply of gaseous fuel to gaseous fuel common rail 40 allowing a quicker reduction in pressure. The shut off valve 45 may be reopened toward the end of the transient.
Another strategy that may be employed according to the present disclosure would be to inject fuel in less than all of the engine cylinders during the transient. In other words, a cylinder cutout strategy can result in proportionally more fuel in a given engine cycle being allocated to gaseous fuel rather than liquid fuel, assuming that there is a desire to inject at or near a minimum controllable liquid injection quantity at almost all engine operating conditions. The electronic controller 50 would likely cycle through different sets of active and inactive cylinders 22 if the cylinder cutout strategies were utilized. The second pressure control algorithm is preferably configured to avoid venting gas from the gaseous fuel common rail to atmosphere during the transient as a portion of a strategy for reducing pressure. However, the second pressure control algorithm could potentially include some gas venting to atmosphere without departing from the present disclosure in a less than preferred version of the present disclosure.
Referring now to
The present disclosure applies broadly to any engine that utilizes two fluidly distinct common rails to deliver gaseous and liquid fuels to a single fuel injector associated with each engine cylinder. The present disclosure is specifically applicable to a strategy for controlling pressures in the common rails as part of a transient pressure control strategy. Finally, the present disclosure is directed to a liquid rail pressure control strategy during a transient with reduced reliance on, and possible elimination of, a need to vent natural gas to atmosphere in order to transition through a rapid load loss transient.
Gaseous fuel is supplied from the gaseous fuel common rail 40 to each of the plurality of fuel injectors 30 by a respective co-axial quill assembly 54. Likewise, liquid fuel from a liquid fuel common rail 41 is supplied to each of the plurality of fuel injectors 30 by the same respective co-axial quill assemblies 54. When in operation, gaseous fuel is injected from each fuel injector 30 into an engine cylinder 22 responsive to a gaseous fuel injection signal communicated from electronic controller 50 to the fuel injector 30. In particular, a gaseous fuel injection event is initiated by energizing the upper electrical actuator (upper coil 147) to move armature 141 and first control valve member 130 downward out of contact with first valve seat 150. This fluidly connects control chamber 106 to drain outlet 105 to reduce pressure acting on closing hydraulic surface 112. The gaseous fuel check valve member 110 then lifts out of contact with first nozzle seat 108 to commence spray of gaseous fuel out of gaseous nozzle outlet set 103. The injection event is ended by de-energizing the upper electrical actuator to allow armature 141 and control valve member 130 to move upward under the action of spring 146 back into contact to close first valve seat 150. When this occurs, pressure abruptly rises in control chamber 106 acting on closing hydraulic surface 112 to push gaseous check valve member 110 back downward into contact with seat 108 to end the gaseous fuel injection event.
Also, liquid fuel from the fuel injector 30 is injected directly into engine cylinder 22 from the same fuel injector 30 responsive to a liquid fuel injection signal from electronic controller 50. In particular, a liquid fuel injection event is initiated by energizing the lower coil 148 to move armature 142 upward along common centerline 125. This causes pusher 143 to move second control valve member 135 out of contact with second valve seat 155. This in turn relieves pressure in control chamber 107 allowing liquid check valve member 120 to lift out of contact with second nozzle seat 113 to commence a liquid fuel injection event out of liquid nozzle outlet set 104. To end the liquid injection event, the lower electrical actuator (lower coil 148) is de-energized. When this is done, shared biasing spring 146 pushes armature 142 and second control valve member 135 back up into contact with second valve seat 155 to close the fluid connection between control chamber 107 and drain outlet 105. When this is done, pressure acting on closing hydraulic surface 121 quickly rises causing liquid check valve member 120 to move downward and back into contact with second nozzle seat 113 to end the liquid fuel injection event. Both liquid and natural gas injection events are ended by fluidly connecting the respective control chambers 107, 106 to the liquid fuel common rail 22 through respective F orifices 160, 170, and Z orifices 161, 171 that are fluidly in parallel.
Because of its high compression ratio (greater than 14:1) the injected liquid fuel will compression ignite in each of the respective engine cylinders 22. The injected gaseous fuel is ignited in a respective one of the engine cylinders responsive to the compression ignition of the liquid fuel.
The present disclosure also teaches that a higher ratio of gaseous fuel to liquid fuel may be injected in a given engine cycle by utilizing a cylinder cutout strategy in which the gaseous fuel and liquid fuel are injected in less than all of the engine cylinders 22 in an engine cycle. Proportionally more gaseous fuel may be injected and burned if maybe only half the cylinders are active. If this option is utilized, the electronic controller 50 may cycle through different combinations of active and inactive cylinders 22 in each engine cycle for reasons well known in the art.
Referring now to
If query 67 is positive, that indicates a rapid load loss transient, and the logic advances to block 71 to execute the second rail pressure control algorithm 70 according to the present disclosure. At block 71, a target liquid rail pressure is determined based upon the new lower engine speed and load. Next at block 72, a target gas rail pressure is determined by subtracting a pressure differential ΔP (e.g., 5 MPa) from the target liquid rail pressure. Next, at block 73, the gas rail pressure is controlled toward the target gas rail pressure. This step may or may not include closing shut off valve 45, and may include a cylinder cutout strategy to allocate more fuel injection to gaseous fuel from liquid fuel in order to meet the new lower engine speed and load fueling demand. In any event, this step primarily includes injection of as much gaseous fuel as possible during the transient 81 (
Because the liquid rail pressure is controlled with respect to the gaseous rail pressure during transient 81, the liquid rail pressure can be maintained greater than the gaseous rail pressure, even in the face of uncertain fueling demands by engine 20 during transient 81. This strategy should avoid instances, as in overlap region 83 shown in
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
