DUAL FUEL SYSTEM FOR AN ENGINE WITH FUEL-OPERATED FUEL PUMP AND METHOD

Abstract

A dual-fuel system (24) comprises a first pressurized fuel reservoir (26), a first fuel pump (28) fluidically connected to the first pressurized fuel reservoir, a second pressurized fuel reservoir (30), and a second fuel pump (32) comprising a pump outlet (34) fluidically connected to the second pressurized fuel reservoir, a pump chamber (36), an actuating fluid inlet (38) fluidically connected to at least one of the first fuel pumps or the first pressurized fuel reservoir, and at least one pumping element (40). The first fuel pump may, at least temporarily, have excess capacity to provide a pressurized first fuel to actuate the second fuel pump.The at least one pump element can include a pressure intensifier or pressure reducer piston, such that the flow rate of a second pressurized fuel from the second fuel pump differs from the flow rate of the first pressurized fuel from the first fuel pump, which acts as an actuating fluid for the second fuel pump. Corresponding devices and a method are also disclosed.

Description

Technical field

[0001] The present disclosure relates in general to a dual-fuel system for an internal combustion engine and in particular to the pressurization of two different fuels, while pumped fuel from a first pump is used to operate a second pump. State of the art

[0002] Dual-fuel combustion engine systems are well-known and increasingly used worldwide for purposes ranging from generating electricity to powering vehicles and industrial equipment. Engineers have developed many different strategies to take advantage of the combustion and emission characteristics of different fuel types simultaneously or during different engine cycles in a single engine cylinder. In one exemplary dual-fuel system, a relatively small pilot injection of diesel fuel is compression-ignited in one cylinder and used to trigger the ignition of a larger main charge of a gaseous fuel, such as natural gas. Other well-known strategies aim to utilize two different types of liquid fuels, for example, diesel fuel and an alcohol fuel such as methanol.Factors driving further research and development of dual-fuel engine systems include the desire to reduce certain emissions, save fuel, and reduce costs.

[0003] A significant disadvantage of certain dual-fuel engine implementations is the need for equipment to supply, store, pressurize, and manage two different fuel types. In a typical example, two separate and independent pumping systems are required for the two different fuel types, each comprising a low-pressure feed pump and a high-pressure pump, both driven by the engine's transmission. Injection pressures in dual-fuel applications can be very high, necessitating relatively large and powerful pumps that can be space-consuming and costly. A known dual-fuel system is described in U.S. Patent No. 9,664,122 B2, granted to Coldren et al. Brief description

[0004] In one aspect, a dual-fuel system comprises a first pressurized fuel reservoir, a first fuel pump fluidically connected to the first pressurized fuel reservoir, a second pressurized fuel reservoir, and a second fuel pump. The second fuel pump comprises a pump outlet fluidly connected to the second pressurized fuel reservoir, a pump chamber fluidly connected to the pump outlet, an actuating fluid inlet fluidly connected to at least one of the first fuel pumps or the first pressurized fuel reservoir, and at least one pumping element. The at least one pumping element comprises an actuating surface exposed to the fluid pressure of the actuating fluid inlet and a pumping surface exposed to the pump chamber.

[0005] In another aspect, a method for operating a dual-fuel system comprises supplying a pressurized first fuel from a first fuel pump to a first pressurized fuel reservoir and supplying the pressurized first fuel to an actuating fluid inlet of a second fuel pump. The method further comprises actuating the second fuel pump via the pressurized first fuel to pressurize a second fuel and supplying the pressurized second fuel to a second pressurized fuel reservoir.The method further comprises injecting the pressurized first fuel and the pressurized second fuel from a first fuel outlet set and a second fuel outlet set, each formed in at least one fuel injector, into each of a plurality of cylinders in an engine.

[0006] In yet another aspect, a dual-fuel engine system comprises an engine with a plurality of cylinders and a fuel system comprising a first pressurized fuel reservoir, a first fuel pump fluidically connected to the first pressurized fuel reservoir, a second pressurized fuel reservoir, and a second fuel pump fluidically connected to the second pressurized fuel reservoir. The fuel system further comprises at least one fuel injector assembly within each cylinder, each forming a first fuel outlet set and a second fuel outlet set, configured to be fluidically connected to the first and second pressurized fuel reservoirs, respectively.The second fuel pump further comprises a plurality of hydraulically actuated pump elements, each comprising an actuating surface, an actuating fluid inlet fluid connected fluidically to the first fuel pump, and a plurality of electrically actuated flow control valves, each arranged fluidically between the actuating fluid inlet and the actuating surface of one of the plurality of hydraulically actuated pump elements.

[0007] In another aspect, a fuel pump comprises a pump housing in which an actuating fluid inlet, an actuating fluid outlet, a valve seat fluidically arranged between the actuating fluid inlet and the actuating fluid outlet, a pump fuel inlet, a pump chamber, and a pump fuel outlet are formed. The fuel pump further comprises a flow control valve movable between a closed position blocking the valve seat and an open position, and at least one pumping element comprising an actuating surface with a smaller area exposed to the fluid pressure of the actuating fluid inlet and a pumping surface with a larger area exposed to the pump chamber.

[0008] In another aspect, a fuel pump comprises a pump housing containing an actuating fluid inlet, an actuating fluid outlet, a valve seat fluidically located between the actuating fluid inlet and the actuating fluid outlet, a pump fuel inlet, a pump chamber, and a pump fuel outlet. The fuel pump further comprises a flow control valve movable between a closed position, in which it blocks the valve seat, and an open position, as well as at least one pumping element. The at least one pumping element comprises an actuating surface with a smaller area exposed to the fluid pressure of the actuating fluid inlet and a pumping surface with a larger area exposed to the pump chamber. Brief description of the drawings Fig. Figure 1 is a schematic representation of a dual-fuel engine system according to one embodiment; Fig. Figure 2 is a cutaway, schematic sectional view of a section of the dual-fuel engine system as shown in Fig. 1; Fig. 3 is a cutaway, schematic side view of a fuel pump according to one embodiment; Fig. 4 is a cutaway schematic side view of a pump unit intended for use in the fuel pump of Fig. 3 is suitable; Fig. Figure 5 is a schematic view of a plurality of fuel pumps mounted in a housing, according to one embodiment; Fig. Figure 6 is a cutaway, schematic side view of a fuel pump according to one embodiment; and Fig. Figure 7 is a schematic view of the fuel pump of Fig. 6. Detailed description

[0009] With reference to Fig. Figure 1 shows a dual-fuel internal combustion engine system 10 according to one embodiment. Engine system 10 comprises an internal combustion engine 12 and a dual-fuel system 24. Engine 12 can be operated to drive a load such as an electric generator, a pump, a compressor, or a drive train in a mobile machine such as a ship. Additional devices relating to an air intake system, an exhaust system, an engine transmission, and various other components and subsystems of engine system 10 are shown in Figure 1. Fig. Not explicitly shown in Figure 1, but are understood to be included in the conventional sense. Engine system 10 can be operated with a variety of different fuel types, including compression-ignited liquid fuels such as diesel distillate and alcoholic fuels such as methanol, gasoline, naphtha, and various mixtures. In some embodiments, engine system 10 could be operated with compression-ignited liquid fuels and gaseous fuels such as natural gas. As will be further explained in the following description, engine system 10 can be designed for improved efficiency and a reduced overall footprint compared to certain known designs.

[0010] With reference also to Fig. 2, Engine 12 comprises a cylinder block 14 with a plurality of cylinders 18 formed therein, one of which is in Fig. Figure 2 illustrates this. A cylinder head 16 is attached to a cylinder block 14 and typically includes one or more intake valves and one or more exhaust valves, each assigned to a corresponding cylinder 18. The engine 12 also includes a plurality of pistons 20, one of which is in Fig. 2 is shown and is movable between a top dead center position and a bottom dead center position, typically in a four-stroke engine cycle, to increase the pressure of fluids in the cylinder 18 to a self-ignition threshold. The plurality of cylinders 18 can comprise any number in any suitable arrangement, such as an inline pattern, a V-pattern, or any other. Each piston 20 can have a combustion chamber recess 22, approximately as shown in Fig. 2 is shown, although the present disclosure is not thereby limited.

[0011] With further reference to additional features of the dual-fuel system 24, the fuel system 24 comprises a first pressurized fuel reservoir 26 and a first fuel pump 28, which is fluidly connected to the first pressurized fuel reservoir 26. The fuel system 24 may also comprise another pressurized fuel reservoir 27, which may be referred to here as a fourth pressurized fuel reservoir. The fuel system 24 further comprises a second pressurized fuel reservoir 30 and a second fuel pump 32, which has a pump outlet 34 that is fluidly connected to the second pressurized fuel reservoir 30. The fuel system 24 may further comprise a third pressurized fuel reservoir 31, which is also fluidly connected to the second fuel pump 32.The terms "first", "second", "third" and other numerical designations are not used here to prescribe an order or identity of components and serve only for ease of description. In the section on... Fig. In the embodiment shown in Figure 1, the first and second pressurized fuel reservoirs 26 and 30 can each contain a different pressurized fuel for injection into a first group or subset of cylinders 18, and the third and fourth pressurized fuel reservoirs 31 and 27 can analogously supply two fuels into a second group or subset of cylinders 18. In some embodiments, the pressurized fuel reservoirs can be arranged on opposite sides of the engine 12, for example as shown in Figure 1. Fig. 1 shown.

[0012] Fuel system 24 may further comprise a first fuel supply line 48 extending from the first fuel pump 28 to the first pressurized fuel reservoir 26. A connecting line 50 may fluidically connect the first pressurized fuel reservoir 26 to the fourth pressurized fuel reservoir 27. A drain line 52 may extend from the first pressurized fuel reservoir 26 back to the first fuel pump 28. A first fuel supply 46 contains a liquid compression ignition fuel, such as diesel distillate fuel, which is supplied to the first fuel pump 28. The first fuel pump 28 may comprise a high-pressure fuel pump that receives a fuel supply from a low-pressure transfer pump fluidically arranged between the first fuel supply 46 and the first fuel pump 28.In one embodiment, the first fuel pump 28 can be operated via a transmission cable (not shown) of the engine 12.

[0013] The first fuel pump 28 can also have a high-pressure pump outlet 54. Pump outlet 54 is in fluid communication with an actuating fluid line 56, which extends to an actuating fluid inlet 38 of the second fuel pump 32, the significance of which will become clear from the following description.

[0014] The second fuel pump 32 further comprises a pump inlet or fuel inlet 58, which receives a supply of a second fuel from a low-pressure transfer pump 60, which is fluidly connected to a second fuel supply 47. The second fuel supply 47 contains a second fuel, such as a liquid alcohol fuel comprising methanol or various mixtures, usually, but not necessarily, with methanol predominating. An outlet line 62 extends from the pump outlet 34 to a fuel distributor 64. The fuel distributor 64 is fluidically arranged between the second fuel pump 34 and both the second pressurized fuel reservoir 30 and the third pressurized fuel reservoir 31.Fuel distributor 64 comprises a housing 66 with two fuel outlets, including a first fuel outlet 68 which is in fluid communication with the second pressurized fuel reservoir 30, and a second fuel outlet 70 which is in fluid communication with the third pressurized fuel reservoir 31. A first check valve 72 and a second check valve 73 can be arranged within the distributor housing 66 and can each be fluidically connected between the outlet line 62 and the first pressurized fuel reservoir 30 and the third pressurized fuel reservoir 31, respectively, as shown in [Figure]. Fig. 1 shown.

[0015] Fuel distributor 64 may also include an air inlet 74, which receives an air supply from an electronically controlled air control valve 76. The pressurized fuel reservoirs considered herein may include so-called double-walled reservoirs or common rails, each arranged to supply pressurized fuel to a plurality of cylinders in an engine, and wherein an airflow is directed through an external passage or lower-pressure line to, for example, capture any fuel leakage and return it to the secondary fuel supply 47. Air lines 77 and 78 may extend from the fuel distributor 64 to the pressurized fuel reservoirs 30 and 31. An air outlet 79 receives an airflow that is directed through the double-walled structures.

[0016] Fuel system 24 can also include a purge gas supply 86, such as a nitrogen supply, and a purge gas line 88 extending from the purge gas supply 86 to a purge gas inlet 82 of the fuel distributor 64. The fuel distributor 64 can also include a purge gas valve 84 fluidically arranged between the purge gas inlet 82 and at least one of the second pressurized fuel reservoir 30 and the third pressurized fuel reservoir 31. A connecting line 80 fluidically connects the second pressurized fuel reservoir 30 to the third pressurized fuel reservoir 31.

[0017] Fuel system 24 also comprises a plurality of fuel injector assemblies 90 in a plurality of fuel injectors 92. Each cylinder 18 in the engine system 10 can comprise one fuel injector that can be operated to selectively inject the first fuel and / or the second fuel, or two separate fuel injectors that can be operated to selectively inject the first fuel and the second fuel. Embodiments are considered in which a single fuel injector comprises concentric double needles that can be actuated to inject each of the two fuels, as well as embodiments such as those shown in Fig. Figure 2 shows a configuration in which double needles arranged side by side are used. Each cylinder 18 in engine 12 will be assigned to at least one fuel injector assembly comprising a first fuel outlet set 94, a first injector 96 movable to open and close the respective first fuel outlet set 94 to the first pressurized fuel reservoir 26 or fourth pressurized fuel reservoir 27, a second fuel outlet set 104, and a second injector 106 movable to open and close the second fuel outlet set 104 to the second pressurized fuel reservoir 30 or third pressurized fuel reservoir.

[0018] In the illustrated embodiment, fuel injector 92 comprises a first fuel inlet 98, which receives a supply of the first fuel from the first pressurized fuel reservoir 26, and a second fuel inlet 112, which receives a supply of the second fuel from the second pressurized fuel reservoir 30. Fuel injector 92 includes a fuel chamber 102, which is in fluid communication with the first fuel inlet 98 and with the first fuel outlet 94 when the first injector 96 is open. A second fuel chamber 114 is in fluid communication with the fuel inlet 112 and with the second fuel outlet 104 when the second injector 106 is open.The first fuel injector 96 has a hydraulic control surface 100 that is exposed to the fluid pressure of the first pressurized fuel reservoir 26. The second injector 106 has a hydraulic control surface 108 that is exposed to the fluid pressure of the first pressurized fuel reservoir 26. It is thus evident that both the first fuel injector 96 and the second fuel injector 106 are controlled, at least in part, based on the fuel pressure of the first fuel contained in the first pressurized fuel reservoir 26 (or the fourth pressurized fuel reservoir 27, if used), which typically comprises diesel fuel. Fuel injector 92 further comprises an injection control valve assembly 110.The injection control valve arrangement 110 is electrically actuated and may include two magnetic actuators to separately and independently vary a closing hydraulic pressure on the hydraulic control surfaces 100 and 108 to control an injection start time, an injection end time, an injection quantity and possibly other features of the fuel injection.

[0019] It should be noted that the first fuel can be a diesel distillate fuel and the second fuel an alcohol fuel such as methanol. Diesel fuels have a higher energy density than methanol, which generally requires a relatively larger fuel injection quantity for a given engine power output. Engine system 10 can operate in a diesel-only mode or a pilot-ignited dual-fuel mode. In diesel-only mode, the engine power requirements are met by compression ignition combustion of diesel fuel only. Operation in such a mode involves the injection of diesel fuel only using injector 96. In dual-fuel mode, a relatively small diesel pilot injection is delivered to cylinder 18 to ignite a larger charge or injection of methanol using injector 106 via compression ignition.Fuel injector 92 is generally designed such that each respective first fuel outlet set 94 and each respective first injector 96 in the respective nozzle assembly 90 together define a lower steady-state nozzle flow, and each respective second fuel outlet set 104 and each respective second injector 106 together define a larger steady-state nozzle flow. Steady-state flow, including steady-state nozzle flow, is a known feature of fuel injectors and refers to a flow rate that is expected under equivalent conditions. Thus, for a given fuel pressure and opening time, a larger quantity of fuel could be expected to be injected through the second fuel outlet set 104, which has a larger steady-state flow than the steady-state nozzle flow of the first fuel outlet set 94.Individual fuel spray outlets or openings in the second fuel outlet set 104 may be larger in size and / or number than the size and / or number of individual outlets in the first fuel outlet set 94.

[0020] With current focus on features of the second fuel pump 32 and also with reference to the Fig. 3 and Fig. 4 It is recalled that the second fuel pump 32 has a pump outlet 34 which is fluidly connected to the second pressurized fuel reservoir 30. The second fuel pump 32 further has a pump chamber 36 which is in fluid communication with pump outlet 34, an actuating fluid inlet 38 which is in fluid communication with at least one of the first fuel pumps 28 or the first pressurized fuel reservoir 26, and at least one pumping element 40 which has an actuating surface 42 which is exposed to a fluid pressure of the actuating fluid inlet 38, and a pumping surface 44 which is exposed to the pump chamber 36. In the illustrated embodiment, the second fuel pump 32 has a plurality of individual pump units 116 positioned within a plurality of pump unit bores 124 formed in a pump body 120. The pump units 116 can be arranged in any suitable pattern, including an approximately circular arrangement as shown, in series, in two separate banks, or the like. The pump units 116 can be six in number, as shown, or a smaller number, for example four or five, or a larger number, for example seven or eight. The pump body 120 can include a fuel inlet 58 and a centrally located fuel cavity 122 that fluidically connects the fuel inlet 58 to each individual pump unit 116.The second fuel pump 32 can also include an actuating fluid distributor 118, which has an actuating fluid inlet 38 formed therein. The actuating fluid distributor 118 can be attached to any of the pump units 116, which may have a generally circumferential distribution in the pump body 120 around a centrally arranged pump 58, as shown, or another arrangement as explained above.

[0021] Fig. Figure 4 shows an example of one of the pump units 116 in further detail, including a pump unit housing 126 that forms a fuel inlet channel 128 to the pump chamber 36, and a pressurized fuel outlet channel 130 that extends from the pump chamber 36 to the fuel outlet 34. The pump unit housing 126 also forms an actuating fluid inlet channel 132, an actuating fluid outlet channel 134, and includes a flow control valve arrangement 136 therein or thereon.

[0022] Flow control valve assembly 136 comprises an electric actuator 138, such as a magnetic actuator, coupled to an armature 140, which in turn is coupled to an electrically actuated flow control valve 142. The electrically actuated flow control valve 142 can be fluidically arranged between the actuating fluid inlet 38 and the actuating surface 42. The actuating fluid inlet channel 132 can be understood as forming one of a plurality of actuating fluid supply ports in the second fuel pump 32, each of which is in fluid communication with one of the plurality of pump elements 40. Energizing the flow control valve assembly 136 can cause the flow control valve 142 to open a seat 144 against a preload force of a return spring 146.Opening the seat 144 allows a flow of pressurized actuating fluid, including the pressurized first fuel, to flow through the actuating fluid inlet channel 132 and act on the actuating surface 42, thereby driving the pumping element 40 downwards in a pumping stroke to pressurize the second fuel in the pumping chamber 36.

[0023] As mentioned above, a flow rate of the second fuel is desirablely greater than a flow rate of the first fuel, based at least partially on the lower energy density of the second fuel. To enable a flow rate of the second fuel from the second fuel pump 32 that is greater than a flow rate of the first fuel, which acts as the actuating fluid, the at least one pump element 40 can comprise a reversing booster piston, wherein the actuating surface 42 has a first region and the pumping surface 44 has a second region that differs from the first region, for example, being larger than it. In other embodiments, the pumped second fuel can be pressure-enhanced instead of being pressure-enhanced or pressure-reduced.A pumped second fuel, reduced in pressure, could have an energy density greater than that of the first fuel used as the actuating fluid. In other cases, the first and second fuels could have similar or substantially the same energy densities, in which case no pressure increase could be used and the ratio of the flow of the first fuel used for actuation to the pumped second fuel could be approximately 1:1.

[0024] Pump element 40 and each of the other pump elements in other pump units 116 can comprise a two-part piston having a first piston section 148 with an actuating surface 42 formed thereon and a separate second piston section 150 with a pumping surface 44 formed thereon. Alternatively, a single piston section could be used, having the respective surfaces differing in their area. In this way, a relatively lower flow rate of the first fuel generates a relatively higher flow rate of the second fuel. An annular space 152 can be formed in the pump unit housing 126 and extend around the second piston section 150 for lubrication and for collecting fuel that exits at a free space between the second piston section 150 and the pump unit housing 126. The annular space 152 can, as shown, be in fluid communication with the inlet channel 128.Moving the pump element 40 in one pump stroke, downwards in the representation of . Fig. 4, can be performed against the preload of a return spring 154. Suitablely arranged check valves (not numbered) can each be fluidically arranged between pump chamber 36 and inlet channel 128 and outlet channel 130.

[0025] With reference to the following Fig. Figure 5 shows a pump arrangement 214 suitable for use in a fuel system considered herein, comprising a plurality of pump units 216 mounted in a common housing 218. A plurality of clamps 220 are provided for clamping pump units 216, generally in a series configuration, in the pump arrangement 214. Clamps 220 can be attached to the pump housing 218 by means of suitable fasteners. An actuating fluid inlet 224 is formed in the pump housing 218 and can receive a supply of pressurized fluid for actuation, for example, a supply of pressurized fuel from the first fuel pump 47 in the pump arrangement 214. Fig. The system shown in Figure 1. An actuating fluid outlet 222 or drain is also formed in the housing 218. A common actuating fluid channel 226 extends through the housing 218 and provides a supply of pressurized fuel for actuation to a plurality of actuating fluid supply lines 228, each extending from the housing 218 to one of the pump units 216. A plurality of actuating fluid drain lines 230 extend from the pump units 216 back to the housing 218 to collect used actuating fuel and supply it to the actuating fluid outlet 222. Other arrangements of lines, pipes, and pump unit arrangements are within the scope of this disclosure.A pump fuel inlet 323 forms a pump fuel inlet and is coupled to the housing 218 to direct a fuel supply for pressurization, for example, the alcohol fuel described herein, to a common pump fuel supply channel 236. A pump fuel outlet channel 238 receives supplies of pressurized fuel from each respective pump unit 216 and directs them together to a pump fuel outlet 238. The pump fuel outlet 238 forms a pump fuel outlet to supply the now pressurized fuel to a plurality of fuel injectors, for example, via a pressurized fuel reservoir in some embodiments.

[0026] With reference to the following Fig. 6 and Fig. 7 are features of a fuel pump or pump unit 316 shown, which the in Fig. The pump units 216 shown in Figure 5 are similar to or possibly identical to those shown. Fuel pump 316 has a pump housing 318 in which an actuating fluid inlet 320 and an actuating fluid outlet 322 are formed. A valve seat 324 is also formed in the pump housing 318, which is fluidically arranged between the actuating fluid inlet 320 and the actuating fluid outlet 322. The pump housing 318 further comprises a pump fuel inlet 326, a pump chamber 327, and a pump fuel outlet 328. A flow control valve 330 is arranged in the pump housing 318 and is movable between a closed position, in which it blocks the valve seat 324, and an open position, in which it does not block the valve seat 324, generally analogous to other flow control valves described and considered herein.Fuel pump 316 further comprises an electrical actuator arrangement 332, which is similar to or identical with the analogous arrangements described herein and is operable to move the flow control valve 330 between its respective open and closed positions. Fuel pump 316 further comprises at least one pump element 334. Pump element 334 has an actuating surface 336, which has a smaller area and is exposed to the fluid pressure of the actuating fluid inlet 320, and a pumping surface 338, which has a larger area and is exposed to the pumping chamber 327. The operation of fuel pump 316 to amplify a flow of a second fuel by actuating the pump element 334 using a first fuel is generally analogous to that of other embodiments described and considered herein.

[0027] In the illustrated example, the pump housing 318 further comprises a valve body section 340. Actuating fluid inlet 320 and valve seat 324 can be formed in the valve body section 340. The pump housing 318 can also comprise a pump section 342 with a pump fuel inlet 326 and a pump fuel outlet 328 formed therein. Also in the illustrated example, a plurality of pump fuel inlets are provided, generally extending along radial directions relative to a reciprocating direction defined by the pumping element 334. As shown, a single, centrally arranged pump fuel outlet 328 can be provided. However, the present disclosure is not limited by this, and other arrangements and configurations of pump fuel inlets and outlets are considered.Pump fuel inlet or inlets 326 can receive fuel from a common supply line, such as the pump fuel supply channel 236. Pump housing 318 can also have a center piece 334 that forms a piston bore 346 which receives the pump element 334. In the illustrated example, piston bore 346 is partially formed by each of the valve body piece 340, the pump piece 342, and the center piece 344. Center piece 344 can have a clamping surface 354 that is positioned to be held by a clamp, such as one of the ones shown. Fig. The pump housing 318 can further comprise a drain piece 348 sandwiched between the electrical actuator assembly 332 and the valve body 340, with an outlet 322 formed therein. A first channel 350 extends in the valve body 340 to convey a flow of pressurized fuel past the valve seat 324 to actuate the pump element 334 when the flow control valve 330 is open. A second channel 352 extends substantially from the actuating surface 336 to the actuating fluid outlet 322. In the illustrated embodiment, the pump element 334 further comprises a two-part pump element, comprising a first piston 356 and a second piston 358, which contact each other but are otherwise not physically connected. A one-piece piston is also within the scope of protection of this disclosure. Commercial applicability

[0028] Referring to the drawings in general, but with particular emphasis on the embodiment of Fig.1. The engine system 10 described above can be operated in several different modes, including a dual-fuel mode in which a relatively small pilot injection of the first fuel is compression-ignited to ignite a larger injection of the second fuel in cylinder 18. It remains desirable for the engine system 10 to be capable of operating in a single-fuel mode, using only diesel fuel. For this reason, the first fuel pump 28 is typically designed with sufficient capacity to operate the engine system 10 exclusively on diesel fuel over the entire speed and load range.This means that the first fuel pump 28 has additional capacity at times, including in dual-fuel mode, which means that the first fuel pump 28 can be operated to pressurize the first fuel in the first pressurized fuel reservoir 26 and also to supply the first fuel for actuation of the second fuel pump 32.

[0029] In a dual-fuel mode, the operation of the dual-fuel system 24 can include supplying the pressurized first fuel from the first fuel pump 28 to the first pressurized fuel reservoir 26 and supplying the pressurized first fuel to the actuating fluid inlet 38 of the second fuel pump 32. By actuating the second fuel pump 32 via the pressurized first fuel pump, the second fuel is pressurized and can then be supplied to the second pressurized fuel reservoir 30. When both respective pressurized fuel reservoirs are pressurized, the pressurized first fuel and the pressurized second fuel can each be injected into any one plurality of cylinders 18 in engine 12 via the first fuel outlet set 94 and the second fuel outlet set 104, respectively.The pressurized first fuel can be injected in a relatively small pilot charge in a pilot quantity immediately before the respective piston 20 reaches top dead center, in order to ignite, by compression, the pressurized second fuel, which is usually supplied in a second injection of a larger quantity shortly after the pilot injection. As explained herein, the supply of the pressurized first fuel can include the supply of the pressurized first fuel at a first flow rate, and the supply of the pressurized second fuel can include the supply of the pressurized second fuel at a second flow rate greater than the first flow rate.The outlet pressure of the first fuel pump 28 can be greater than the outlet pressure of the second fuel pump 32, and the injection pressure of the first fuel can be greater than the injection pressure of the second fuel.

[0030] The present description serves only for illustration and should not be interpreted as limiting the scope of this disclosure in any way. Those skilled in the art will therefore appreciate that various modifications to the embodiments disclosed herein could be made without deviating from the intended and appropriate meaning and scope of this disclosure. Other aspects, features, and advantages will become apparent upon examination of the accompanying drawings and attached claims. As used herein, the articles "one" are intended to include one or more elements and can be used interchangeably with "one or more." When only one element is intended, the term "one" or similar language is used. Similarly, the terms "comprising," "exhibiting," "comprising," or the like are meant to be open-ended.Furthermore, the expression “based on” shall mean “at least partly based on” unless explicitly stated otherwise. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 9,664,122 B2

[0003]

Claims

[1] Dual fuel system (24), comprising: a first pressurized fuel reservoir (26); a first fuel pump (28) which is in fluid communication with the first pressurized fuel reservoir; a second pressurized fuel storage tank (30); and a second fuel pump (32, 116, 316) which includes a pump outlet (34, 130, 328), which is in fluid communication with the second pressurized fuel reservoir, a pump chamber (36, 327) which is in fluid communication with the pump outlet, an actuating fluid inlet (38, 132, 320) which is in fluid communication with at least one of the first fuel pump or the first pressurized fuel reservoir, and at least one pumping element (40, 334) with an actuating surface (42, 336) which is exposed to a fluid pressure of the actuating fluid inlet, and a pumping surface (44, 338) which is exposed to the pump chamber. [2] Dual fuel system according to claim 1, wherein the at least one pump element includes a reversing booster piston, wherein the actuating surface has a first surface and the pumping surface has a second surface which is larger than the first surface. [3] Dual fuel system according to claim 1 or 2, wherein: the second fuel pump includes an electrically operated flow control valve (142, 330), which is arranged fluidically between the actuating fluid inlet and the actuating surface; which includes at least one pump element from a multitude of pump elements and The second fuel pump further includes an actuating fluid distributor (118) which includes the actuating fluid inlet, and a plurality of actuating fluid supply ports (132, 320) which are in fluid communication with the plurality of pumping elements. [4] Dual fuel system according to any one of claims 1 to 3, further comprising a plurality of fuel injector assemblies (90) each comprising a first fuel outlet set (94), a first injector (96) movable to open and close the first fuel outlet set relative to the first pressurized fuel reservoir, a second fuel outlet set (104) and a second injector (106) movable to open and close the second fuel outlet set relative to the second pressurized fuel reservoir; wherein each corresponding first fuel outlet set and each first injector together define a lower steady-state flow, and each corresponding second fuel outlet set and each second injector together define a higher steady-state flow; and wherein each corresponding first injector and second injector includes a hydraulic control surface (108) which is exposed to a fluid pressure of the first pressurized fuel reservoir. [5] Dual fuel system according to any one of claims 1 to 4, further comprising: a third pressurized fuel storage tank (27); and a fuel distributor (64) which is arranged fluidically between the second fuel pump and the second pressurized fuel reservoir and the third pressurized fuel reservoir, respectively. [6] Dual fuel system according to claim 5, further comprising a connecting line (80) which fluidically connects the second pressurized fuel reservoir to the third pressurized fuel reservoir, and wherein the fuel distributor includes a purge gas inlet (82) and a purge gas valve (84) which is fluidically arranged between the purge gas inlet and at least one of the second pressurized fuel reservoir and the third pressurized fuel reservoir. [7] Method for operating a dual fuel system (24) comprising: Supply of pressurized first fuel from a first fuel pump (28) to a first pressurized fuel reservoir (26); Supply of the pressurized first fuel to an actuating fluid inlet (38, 132, 320) of a second fuel pump (32, 116, 316); Activating the second fuel pump via the pressurized first fuel to pressurize a second fuel; Supplying the pressurized second fuel to a second pressurized fuel reservoir (30); and Injection, into each of a plurality of cylinders (18) in an engine (12), of the pressurized first fuel and the pressurized second fuel from each of a first fuel outlet set (94) and a second fuel outlet set (104), each of which is formed in at least one fuel injector (92). [8] Method according to claim 7, further comprising compression ignition of the pressurized first fuel in the plurality of cylinders and ignition of the pressurized second fuel in the plurality of cylinders via compression ignition of the pressurized first fuel. [9] Method according to claim 7 or 8, wherein the injection of the pressurized first fuel includes the injection of a pilot quantity of the pressurized first fuel, and the injection of the pressurized second fuel includes the injection of a larger quantity of the pressurized second fuel. [10] Method according to any one of claims 7 to 9, wherein the pressurized first fuel comprises diesel fuel and the pressurized second fuel comprises alcohol fuel. [11] Method according to any one of claims 7 to 10, wherein actuating the second fuel pump includes actuating a piston (40, 334) having an actuating surface (42, 336) exposed to a fluid pressure of the pressurized first fuel and a pumping surface (44, 338) exposed to a pumping chamber (36, 327) containing the second fuel. [12] The method of claim 11, wherein the supply of the pressurized first fuel comprises the supply of the pressurized first fuel at a first flow rate, and the supply of the pressurized second fuel comprises the supply of the pressurized second fuel at a second flow rate which is greater than the first flow rate; and where the outlet pressure of the first fuel pump is greater than the outlet pressure of the second fuel pump. [13] Method according to any one of claims 7 to 12, further comprising supplying the pressurized second fuel to the second pressurized fuel reservoir and to a third pressurized fuel reservoir (27) via a fuel distributor (64) with a fuel inlet, two fuel outlets (68, 70) which are each fluidically connected to the second pressurized fuel reservoir and the third pressurized fuel reservoir, a purge gas inlet (82) and a purge gas valve (84) which is fluidically arranged between the purge gas inlet and at least one of the two fuel outlets. [14] Fuel pump (32, 116, 316), comprising: a pump housing (118, 120, 126, 318) in which an actuating fluid inlet (38, 132, 320), an actuating fluid outlet (134, 322), a valve seat (144, 324) arranged fluidically between the actuating fluid inlet and the actuating fluid outlet, a pump fuel inlet (128, 326), a pump chamber (36, 327) and a pump fuel outlet (130, 326) are formed. a flow control valve (142, 330) that is movable between a closed position, which blocks the valve seat, and an open position; and at least one pump element (40, 344) having an actuating surface (42, 336) with a smaller area exposed to a fluid pressure of the actuating fluid inlet and a pumping surface (44, 338) with a larger area exposed to the pump chamber. [15] Fuel pump according to claim 14, wherein: that at least one pump element includes a piston (40, 334); the piston includes a two-part piston (148, 150); and that at least one pump element is one of a plurality of pump elements in a plurality of pump units (116, 316) which are mounted in a common housing (120).

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