Multi-fuel injector and method

Abstract

A fuel injector (12) capable of injecting a plurality of different fuels in a single fuel injection event includes a body (15) including a main fuel path and a pilot fuel path, and a first plunger (14) in fluid communication with the pilot fuel path. The fuel injector (12) further includes a second plunger (20) in fluid communication with the main fuel path and with the pilot fuel path, a hydraulic control chamber (40) within the pilot fuel path, and an injection valve (26) at which the main fuel path and the pilot fuel path are connected to each other.

Description

Technical Field

[0001] The present disclosure generally relates to methods and systems for internal combustion engine components, and more particularly, to fuel injectors configured to inject two different fuels. Background Art

[0002] Although engines operating by burning conventional fuels such as gasoline or diesel fuel are used in many applications, there is increasing interest in making engines suitable for so-called "alternative fuels". Examples of alternative fuels include alcohol-containing fuels such as methanol and ethanol. These fuels can provide benefits, for example, due to their environmentally friendly qualities and the ability to be produced from renewable energy sources. However, compared to conventional fuels, the complete combustion of alternative fuels including methanol can be more challenging. For example, methanol may have a reduced energy density, a slower vaporization time, a lower cetane number, and / or other challenges. To address these drawbacks, some internal combustion engines are designed to inject two different fuels, including a pilot fuel that generates a pilot flame that burns the alternative fuel in a more complete and predictable manner.

[0003] Although multi-fuel internal combustion engines can improve combustion, the presence of alternative fuels as a primary energy source can introduce problems within the fuel injector itself. For example, the presence of alternative fuels such as methanol can cause increased cavitation damage, seat wear, and guide surface scratching. These problems can be caused by differences in the nature of alternative fuels, including a reduced lubricating ability compared to conventional fuels.

[0004] An exemplary high-pressure fuel injector is described in U.S. Patent 5,209,403 to Tarr ("the '403 patent"). The fuel injector described in the '403 patent has an internal structure that defines a timing chamber between an upper plunger and a lower plunger. The timing chamber includes a pressure relief valve for discharging timing fluid during injection to control pressure at high-speed operation. Although the timing chamber and pressure relief valve of the fuel injector described in the '403 patent can be used to vary the amount of fuel injected by using timing fluid, it cannot inject two different types of fuel with a single injector and may not be able to protect the components of the fuel injector from wear and / or damage associated with alternative fuels.

[0005] The systems and methods of the present disclosure can solve one or more of the above problems and / or other problems in the art. However, the scope of the present disclosure is defined by the appended claims and not by the ability to solve any particular problem. Summary of the Invention

[0006] In one aspect, a fuel injector capable of injecting multiple different fuels in a single fuel injection event may include a body that includes a main fuel path and a pilot fuel path, and a first plunger in fluid communication with the pilot fuel path. The fuel injector may further include a second plunger in fluid communication with the main fuel path and with the pilot fuel path, a hydraulic control chamber within the pilot fuel path, and an injection valve where the main fuel path and the pilot fuel path are connected to each other.

[0007] In another aspect, a fuel injection method may include receiving main fuel with a main fuel path within a body of a fuel injector, receiving pilot fuel with a pilot fuel path within the body of the fuel injector, and pressurizing the pilot fuel within a hydraulic control chamber in the pilot fuel path. The method may further include supplying the main fuel to a nozzle portion of the fuel injector with a main fuel plunger connected to the hydraulic control chamber, supplying the pilot fuel to the nozzle portion of the fuel injector, and injecting the pilot fuel and the main fuel from the nozzle of the fuel injector.

[0008] In yet another aspect, a fuel injector may include a body, a main fuel connection configured to receive main fuel, a pilot fuel connection configured to receive pilot fuel, and a plunger isolated from the main fuel. The fuel injector may further include a hydraulic chamber defined at least in part with the plunger, the hydraulic chamber in fluid communication with the pilot fuel connection, and a second plunger configured to deliver the main fuel to a nozzle of the fuel injector when actuated. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A is a schematic cross-sectional view of a multi-fuel injector according to an aspect of the present disclosure.

[0010] Figure 1B is Figure 1A an enlarged cross-sectional view of the tip of the fuel injector of

[0011] Figure 2A is a schematic cross-sectional view of an alternative configuration of the multi-fuel injector shown in Figure 1A according to an aspect of the present disclosure.

[0012] Figure 2B is Figure 2A an enlarged cross-sectional view of the tip of the fuel injector of

[0013] Figure 3 is a flow chart depicting an exemplary fuel injection method according to an aspect of the present disclosure. DETAILED DESCRIPTION

[0014] The foregoing general description and the following detailed description are merely exemplary and explanatory and do not limit the claimed features. As used herein, the terms "comprises", "comprising", "having", "including" or other variations thereof are intended to cover a non-exclusive inclusion, such that a method or apparatus that comprises a series of elements does not include only those elements but may include other elements not expressly listed or inherent to such method or apparatus. In the present disclosure, relative terms, such as, for example, "about", "substantially", "generally" and "approximately" are used to indicate a possible variation of ±10% of the stated value or characteristic. As used herein, "upper" refers to the proximal direction of the fuel injector, and when compared with the (one or more) injection orifices of the injector, the proximal end is the farthest end of the injector. As used herein, "lower" refers to the distal direction of the fuel injector, and the distal end of the fuel injector includes the (one or more) injection orifices or is positioned closest to the (one or more) injection orifices. Thus, the terms "upper" and "proximal" can be considered interchangeable, and the terms "lower" and "distal" can be considered interchangeable.

[0015] Figure 1A An exemplary fuel injector 12 in accordance with aspects of the present disclosure is shown. The fuel injector 12 can be a multi-fuel injector configured to inject two different types of fuel in a single injection event (e.g., an injection event including a pilot injection, a main injection, and / or a post injection) via a single nozzle 16 formed by a distal end portion of the fuel injector 12. In some aspects, the two different fuels can both be liquid fuels. As used herein, a fuel is determined to be "liquid" or "gaseous" based on the state of the fuel when it is delivered to the fuel injector. For example, liquid methanol can be supplied as the main liquid fuel, while diesel fuel can be supplied as the pilot fuel. In contrast, a fuel delivered to the fuel injector as a gas can be considered a gaseous fuel, even if the gaseous fuel is stored in a liquid state.

[0016] As used herein, "main" fuel refers to a fuel that is injected in a volume of 50% or more of the total volume of fuel injected into a particular combustion chamber of an internal combustion engine during an injection event that includes a pilot injection (e.g., diesel fuel) and a main injection (e.g., methanol). "Pilot fuel" can refer to a fuel that is injected primarily or entirely before the main fuel during an injection event. Additionally, although the terms "pilot fuel" and "main fuel" are related to the order of these different fuel injections, it is understood that compared to some injection methods where the pilot injection and the main injection are separated by a period of time during which no fuel is injected, the pilot fuel injection and the main fuel injection can occur continuously and can include injecting a mixture of the two fuels over a period of time.

[0017] The multi-fuel injector 12 can have a configuration with multiple plungers. In Figure 1A the illustrated example, the injector 12 can include a mechanically driven (e.g., cam-driven) plunger 14, a hydraulic chamber 40 that forms a control chamber of the injector 12, a main fuel reservoir 36, a main fuel plunger 20 that causes main fuel injection, and an injection valve 26. The fuel injector 12 can include a plurality of fuel connections, including a pilot fuel connection 18 for supplying and discharging pilot fuel, and a main fuel supply connection 28. Although only the inlet connections 18 and 28 are shown in Figure 1A , it is understood that the fuel injector 12 can include an outlet connection 18 in the distal portion of the injector 12, and the outlet connection 28 is connected downstream of the overflow valve 62, as described below.

[0018] The fuel injector 12 can be part of a fuel injection system installed in an internal combustion engine. The system can include a plurality of fuel injectors 12 mounted in a series of bores fixed in one or more cylinder heads 70 of the engine. When installed in the engine, the injector 12 can have a main fuel supply connection 28 outside the cylinder head 70 (e.g., between the cylinder head 70 and the valve cover), while the supply and discharge connections 18 are inside the cylinder head 70. This can avoid the need to route alternative fuels (such as methanol) inside the cylinder head 70. The cylinder head 70 can be formed with one or more embedded (e.g., cast) fuel paths configured to circulate fuel to and from the connection 18.

[0019] In Figure 1A and 1B the illustrated exemplary configuration, the path for guiding main fuel within the fuel injector 12 (also referred to herein as the "main fuel path") can start at the fuel supply connection 28 and end at the nozzle orifice 58 ( Figure 1B ). The main fuel path can include a main fuel passage 30 downstream of the main fuel supply connection 28 such that the main fuel path bypasses the plunger 14 to isolate the plunger 14 from the main fuel. The main fuel path can descend from the main fuel passage 30 toward the distal end of the fuel injector 12 to a first main fuel valve 34 (e.g., a check valve) that connects the main fuel passage 30 to the main fuel reservoir 36. The main fuel path can extend downstream from the main fuel reservoir 36 to an optional second main fuel valve 38 ( Figure 1B ), and the second main fuel valve allows main fuel to flow to a fuel injection chamber 39 that surrounds at least a portion of an injection valve member 27 of the injection valve 26. When the injector 12 is installed in the cylinder head 70, one or more nozzle orifices 58 can form the downstream end of the main fuel path facing the combustion chamber.

[0020] In addition to the fuel injection chamber 39, a pilot fuel path isolated from the main fuel path may extend through a series of channels downstream of the supply connection 18 within the injector 12. The pilot fuel path may be divided into two parts, including a first part for controlling the pressurization of the hydraulic chamber 40. The second part of the pilot fuel path may direct the fuel flow directly from the connection 18 to the radial fill channels 52( Figure 1B ) or 53( Figure 2B ), as described below, for injecting the pilot fuel via the nozzle 16. Although these parts for supplying fuel to the chamber 40 and for supplying fuel to the nozzle 16 respectively may both be connected to the supply and discharge connection 18, the two parts may be isolated from each other such that the pressurization of the fuel within the chamber 40 substantially does not affect the pressure of the pilot fuel within the nozzle 16. For example, the overflow valve 62 may isolate the chamber 40 from the connection 18 and from the pilot fuel supply channel 44 when closed.

[0021] The first part of the pilot fuel path within the injector 12 may include a hydraulic chamber 40, a fill and overflow channel 42 connecting the hydraulic chamber 40 to the overflow valve connection channel 64, an overflow valve 62, and a supply / discharge path (not shown) connected to the overflow valve 62. The fill and overflow channel 42 may be connected to the overflow valve 62 and to the supply / discharge path to fluidly connect the channel 42 to the connection 18 via the overflow valve 62. The first part of the pilot fuel path may allow an electronic control module in communication with the interface 60 to control the pressurization of the fuel within the hydraulic chamber 40 using the position of the overflow valve 62, as described below.

[0022] The second part of the pilot fuel path may enable pilot fuel to be supplied to the nozzle 16 of the injector 12. The second part may include a pilot fuel supply channel 44 having a pilot fuel lubrication channel 46, a nozzle fill channel 50( Figure 1B ) connected downstream of the pilot fuel supply channel 44, one or more radial fill channels 52, a hollow internal channel 54 extending through the body of the injection valve member 27 formed within the injection valve member 27 downstream of the radial fill channels 52, and one or more radially extending outlet channels 56 at the distal end portion of the injection valve member 27. The pilot fuel supply channel 44 may be connected downstream of the pilot fuel connection 18 such that the pressure of the fluid introduced at the connection 18 can passively control (e.g., without using an electromagnetic valve within the injector 12) the amount of pilot fuel metered into the nozzle 16, as described below.

[0023] Check valves (such as the pilot fuel check valve 48) may be provided at one or more locations in the second part. In Figure 1BIn the configuration shown, the pilot fuel check valve 48 can be disposed within the nozzle fill passage 50 to prevent the pilot fuel within the passage 50 from moving upstream relative to the hollow inner passage 54 when the pressure relief valve 62 is energized and pressure begins to build within the chamber 40. The downstream end of the second portion of the pilot fuel path can extend within the fuel injection chamber 39 such that the pilot fuel can encounter and displace some of the main fuel present within the fuel injection chamber 39.

[0024] In some aspects, when the main fuel valve 38 is present within the main fuel path, the displaced main fuel can leak upstream of the main fuel valve 38 in a controlled manner to prevent excessive pressure within the fuel injection chamber 39. Although the main fuel valve 38 can include an orifice or other path for controlled leakage of the main fuel in the upstream direction, in at least some configurations, the main fuel valve 38 is a non-leaking check valve, as is the check valve 38 shown in Figure 2B . During an injection event when the nozzle orifice 58 is open, this pilot fuel and main fuel can exit the nozzle 16 via the nozzle orifice 58.

[0025] Within the main fuel path, the main fuel reservoir 36 can extend below the plunger 20 to store the main fuel injected via the nozzle orifice 58. Within the pilot fuel path, the hydraulic chamber 40 can extend above the plunger 20 to control the amount of force acting on the proximal end of the plunger 20. In particular, the main fuel plunger 20 can be fixed within the body 15 of the injector 12 such that the proximal narrowed end 22 of the plunger 20 defines the bottom end of the hydraulic chamber 40, while the enlarged distal end 24 having a diameter greater than the diameter of the proximal narrowed end 22 and greater than the diameter of the plunger 14 defines the upper end of the main fuel reservoir 36.

[0026] The main fuel plunger 20 can be formed from a material compatible with alternative fuels, such as alcohol-based fuels or fuels containing alcohol (e.g., fuels having 25% or more, 50% or more, or 75% or more alcohol by volume, such as methanol, ethanol, or a combination of two or more alcohols). Alternatively, the plunger 20 can include one or more materials generally considered incompatible with alcohol-based fuels (e.g., materials that may tend to corrode, scratch, and / or experience wear at an increased rate in the presence of methanol fuel), and the plunger 20 is coated with a material compatible with alcohol-based fuels.

[0027] The main fuel plunger 20 can be biased towards a position that maximizes the size of the main fuel reservoir 36, this position of the main fuel plunger 20 being in Figure 1Ais shown. In some aspects, the pressure of the fluid supplied to the main fuel reservoir 36 and the reduced pressure within the hydraulic chamber 40 due to the return of the plunger 14 can create a net positive pressure in the chamber 40 below the main fuel plunger 20 that is sufficient to return the main fuel plunger 20 to its rest position within a suitable time period after the end of an injection event, thereby allowing the main fuel reservoir 36 to refill for subsequent injections. However, if desired, a biasing element such as a spring can extend from the enlarged distal end 24 to the wall at the bottom of the main fuel reservoir 36 to bias the main fuel plunger 20 upward. For example, the biasing element can improve the responsiveness of the main fuel plunger 20.

[0028] In some aspects, the plunger 20 can be lubricated to reduce wear and prevent sticking. For example, the main fuel lubrication passage 32 can be configured to supply main fuel as a lubricant for the enlarged distal end 24. As the main fuel plunger 20 moves toward the bottom plate of the main fuel reservoir 36, the main fuel lubrication passage 32 can receive fuel, thereby allowing the fuel to surround a portion of the proximal end 22 that extends below the lubrication passage 32 (e.g., into the reservoir 36). The lubrication passage 32 can be connected to a discharge passage (not shown) to allow removal of the fuel around this portion of the end 22 when the main fuel plunger 20 returns toward its retracted rest position (upward in Figure 1A and 1B ).

[0029] The pilot fuel lubrication passage 46 can be configured to supply pilot fuel to an annular space of the narrowed end portion 22 to lubricate this portion of the main fuel plunger 20. Although the plunger 20 can be lubricated by both main fuel and pilot fuel, in at least some configurations, the main fuel plunger 20 can be lubricated with only pilot fuel.

[0030] If desired, the body 15 can also include one or more passages for supplying lubrication to the plunger 14. In some configurations, the plunger 14 can be isolated from the main fuel and lubricated only by pilot fuel. This can enable the plunger 14 to be constructed of one or more materials compatible with a conventional fuel such as diesel, without the need to manufacture the plunger 14 from materials compatible with an alternative fuel such as methanol.

[0031] The proximal end of the body 15 can be connected to an electrical control interface 60, which includes one or more electrical connections for controlling the fuel injector 12. For example, the electronic control module can control the solenoid of the spill valve 62 via the control interface 60. The spill valve 62 can be biased to an open position where the passage 42 is connected to the discharge port, from which fuel leaves the fuel injector 12 and circulates to the low-pressure fuel return system. Thus, activating the solenoid for valve 62 can cause the valve 62 to close. When the spill valve 62 is in the closed position, the passage 42 can be blocked to prevent discharge, enabling pressurization of the fluid within the hydraulic chamber 40.

[0032] Figure 2A and 2B A second exemplary embodiment of the fuel injector 12 is shown. In Figure 2A and 2B the construction shown, elements having the same structure and / or function as the corresponding features of Figure 1A and 1B are denoted by the same reference numerals.

[0033] As shown in Figure 2A the circumferential wall of the body 15 fixed within the cylinder head 70 can include a main fuel supply and discharge connection 118 in place of the connection 18 shown in Figure 1A . As described above, the main fuel connection 118 can be configured to connect the main fuel path to an alternative fuel source such as an alcohol-containing fuel. In particular, the connection 118 can be in fluid communication with a main fuel passage 130 that includes a first main fuel valve 34, a main fuel reservoir 36, and a fuel injection chamber 39 in a manner similar to the main fuel passage 30 described above with respect to Figure 1A and 1B .

[0034] The pilot fuel connection 128 can be connected to the injector 12 to supply pilot fuel from a passage external to the cylinder head 70. The pilot fuel connection 128 can be connected to the spill valve 62, which in turn is selectively connected to the fill and spill passage 42 and the pilot fuel supply passage 144. The fill and spill passage 42 can also be connected to the spill valve 62 and the spill valve connection passage 64 such that the spill valve 62 can control the pressurization of the fuel within the hydraulic chamber 40.

[0035] As shown in Figure 2B the nozzle fill passage 51 can extend from the pilot fuel supply passage 144( Figure 2A) extends downward to provide fuel supply to passage 54 of valve member 27. Passage 51 can be connected to passage 54 of valve member 27 via an annular fuel chamber 57 or through one or more additional passages (not shown) extending between passage 51 and passage 54. One or more radial passages 53 can be formed at or near the proximal end of passage 54 to enable communication with the annular fuel chamber 57. The spacer member 55 can define the proximal end of chamber 57 and form a seal that prevents fuel from flowing in the proximal direction (e.g., toward the spring mechanism for biasing valve member 27).

[0036] If desired, in Figure 2A and 2B the illustrated embodiment, the material of the cylinder head 70 can be selected to supply an alcohol-containing fuel such as methanol via connection 118. For example, methanol or another primary fuel can be supplied from the interior of the cylinder head 70 through one or more internal fuel supply passages of the cylinder head 70, which are formed of a methanol-compatible material or coating. The methanol-compatible material can also be used for connection 118 and each primary fuel passage downstream of connection 118. Similar to Figure 1A and 1B the construction, as in Figure 2A and 2B the injector 12 shown can include a primary fuel path that is isolated (except at the fuel injection chamber 39 within nozzle 16) from the pilot fuel path. Additionally, as described above, the plunger 14 can be isolated from the primary fuel path.

[0037] Although the fuel injector 12 can include a mechanically driven plunger 14 (e.g., driven via a camshaft) as shown in Figure 1A and 2A if desired, the plunger 14 can be driven by a different mechanism. For example, the plunger 14 can be hydraulically driven or otherwise driven in a direction to pressurize the fuel within the injector 12.

[0038] Industrial applicability

[0039] The multi-fuel injector 12 can be installed in any internal combustion engine suitable for multiple liquid fuels. Examples of suitable internal combustion engines include engines for generating power in stationary machines (e.g., generators or other power generation devices), in mobile machines (e.g., earthmoving equipment, haul trucks, drills, etc.), or in other applications where it may be beneficial to operate the engine with multiple different fuels. The internal combustion engine can generate electricity and / or power, such as for providing power to operate one or more associated systems (such as a hydraulic system).

[0040] During one or more injection events, injector 12 may inject pilot fuel and main fuel into a combustion chamber of an internal combustion engine. In some aspects, this may involve injecting pilot fuel via nozzle orifice 58 and then immediately injecting main fuel via the same nozzle orifice 58. To inject fuel with injector 12, overflow valve 62 may be closed while plunger 14 is mechanically, hydraulically, or otherwise driven downward to pressurize the pilot fuel within hydraulic chamber 40 of injector 12 and prevent the pressurized pilot fuel from discharging from injector 12.

[0041] Figure 3 A flowchart for an exemplary method 300 that may be performed during operation of an internal combustion engine including multi-fuel injector 12 is included. During method 300, injection of fuel may be facilitated with one or more electronic control valves such as overflow valve 62. During method 300, injection may occur due to the movement of two separate plungers within body 15. For example, driven plunger 14 may be pressed down by a cam that physically contacts the proximal end of plunger 14 or includes plunger 14 of a plunger assembly. Main fuel plunger 20 may be indirectly controlled via movement of overflow valve 62 and plunger 14. For example, when overflow valve 62 is closed, pressurized incompressible fluid within hydraulic chamber 40 may drive main fuel plunger 20 downward.

[0042] During method 300, the presence of pilot fuel within nozzle fill passage 50 downstream of pilot fuel check valve 48 may be controlled based on the pressure of the pilot fuel. Accordingly, fuel within fuel injection chamber 39 may be received via one or more radial fill channels 52, hollow internal channel 54, and one or more radially extending outlet channels 56 based on the pressure of the pilot fuel upstream of pilot fuel check valve 48. Thus method 300 may enable the use of plunger 14 isolated from main fuel, which may be an alternative fuel, and enable the use of a second plunger (main fuel plunger 20) lubricated with pilot fuel and main fuel. In some aspects, some moving components of injector 12, including at least a portion of plunger 14 and main fuel plunger 20, may be minimally exposed or not exposed to an alternative fuel used as main fuel that has a reduced viscosity, reduced lubricity, and / or may be more corrosive compared to conventional fuels or lubricants used in other injectors.

[0043] A first step 302 of method 300 may include receiving main fuel. The main fuel may be, for example, an alternative fuel that includes a fuel containing 25% or more, 50% or more, or 75% or more alcohol by volume such as methanol, ethanol, or an alcohol blend. During step 302, the main fuel supply connection 28 ( Figure 1A ) or the fuel supply connection 118 ( Figure 2A)Receive main fuel. The received fuel may have a first relatively low pressure established by one or more fuel pumps and / or pressure regulating valves connected upstream of injector 12. The main fuel may pass through injector 12 in a generally distal direction via main fuel passage 30 or 130. The fuel may flow into main fuel reservoir 36 through first main fuel valve 34.

[0044] Step 304 may include receiving pilot fuel with injector 12 and pressurizing the pilot fuel. For example, diesel pilot fuel may be received with connection 18 ( Figure 1A ) or with supply connection 128 ( Figure 2A ). Thus, based on the particular construction of injector 12, pilot fuel may be received from inside the cylinder head 70 (e.g., with connection 18 as shown in Figure 1A ) or from outside the cylinder head 70 (e.g., with connection 128 as shown in Figure 2A ). The pilot fuel may be directed by a pilot fuel path defined within injector 12. Referring to Figure 1A , a pilot fuel path supplied with pilot fuel from discharge connection 18 may direct the fuel to locations within fuel injector 12 including passage 42, passage 44, nozzle fill passage 50, hollow interior passage 54, and to the bottom end of fuel injection chamber 39 adjacent to the distal end of injection valve member 27, where the pilot fuel mixes with and displaces the main fuel. Referring to Figure 2A , main fuel may be received with main fuel connection 118. The fuel may be provided to main fuel passage 130, where the fuel may be directed to main fuel reservoir 36 in the manner described above for main fuel passage 30.

[0045] During step 304, the pressure of the pilot fuel within hydraulic chamber 40 may be changed to allow the pilot fuel to act as control fluid for injector 12. In particular, the pressure of the pilot fuel may be increased by holding overflow valve 62 in the closed position while mechanically depressing plunger 14. This may prevent the pilot fuel from returning from fill and overflow passage 42 to connection 18 ( Figure 1A ) or 118 ( Figure 2A ). As plunger 14 advances in the downward direction, the fuel pressure within hydraulic chamber 40 may increase until the pressure reaches a level to actuate main fuel plunger 20 and actuate injection valve member 27, as described below.

[0046] In addition, the amount of pilot fuel entering the nozzle 16 via the hollow internal passage 54 can be controlled based on the pressure of the pilot fuel. In particular, the amount of fuel within the passage 54 or otherwise within the nozzle 16 can be controlled by adjusting the pressure differential between the pilot fuel and the main fuel supplied to the injector 12 (where the pilot fuel has a greater pressure) and / or by adjusting the fill time corresponding to the amount of time between injection events. The amount of pilot fuel within the nozzle 16 can also be affected by the volume (i.e., capacity) of the fuel injection chamber 39 and the difference between the compressibility of the main fuel and the pilot fuel. When there is an orifice in the valve 38, the amount of pilot fuel in the nozzle 16 can be affected by the compressibility of the fuel within the reservoir 36.

[0047] For example, fluid can be supplied at a pressure sufficient to open the pilot fuel check valve 48 and supply fuel inside the injection valve member 27. The amount of pilot fuel exiting the injection valve member 27 via one or more radially extending outlet channels 56 and entering the fuel injection chamber 39 can also depend on the pressure at which the pilot fuel is supplied to the injector 12 and the time between injections. Accordingly, the pressure of the pilot fuel in the second portion of the pilot fuel path can be set based on the desired amount of pilot fuel for injection.

[0048] Step 306 can include actuating a main fuel plunger such as the main fuel plunger 20. The plunger 20 can be actuated with the fluid pressurized in step 304. When the overflow valve 62 is held in the closed position (e.g., by generating a command to energize the solenoid of the valve 62 with an electronic control module), the plunger 14 can apply pressure to the upper surface of the proximal narrowing end 22 and drive the main fuel plunger 20 downward because the pressure of the pilot fuel within the hydraulic chamber 40 can be significantly greater than the pressure of the main fuel within the main fuel reservoir 36. If desired, the dimensions of the proximal narrowing end 22 and the enlarged distal end 24 can be set in a manner based on the expected pressures generated in the hydraulic chamber 40 and the main fuel reservoir 36, the maximum expected fuel delivery, and the corresponding forces.

[0049] Step 308 can include injecting both the main fuel and the pilot fuel via the nozzle 16. In particular, step 308 can include injecting two different types of fuel from a single set of nozzle orifices 58 in a single tip of the nozzle 16. For example, the pilot fuel can enter the injection valve member 27 from the pilot fuel supply channel 44, the nozzle fill channel 50, and one or more radial fill channels 52. This fuel can travel downward within the hollow internal passage 54 and enter the fuel injection chamber 39 via one or more radially extending outlet channels 56, thereby displacing some of the main fuel at the end of the fuel injection chamber 39 in the upstream direction. Using a pilot fuel with a density higher than that of the main fuel can also be used to limit the upward flow of the pilot fuel in the chamber 39.

[0050] Also during step 308, the main fuel within nozzle 16 downstream of valve 38 may have an increased pressure as in step 306. This pressurized fuel within fuel injection chamber 39 may raise a hydraulic surface (not shown) on injection valve member 27 so as to raise member 27 from nozzle orifice 58, thereby opening nozzle orifice 58 to initiate an injection event. Additionally, pressurization of the main fuel may move check valve 48 ( Figure 1B ) to a proximal blocking position that prevents backflow of the pilot fuel. During the injection event, the pilot fuel may be injected mostly or completely before the main fuel. This injection may be a substantially continuous event of stratified charging of the two fuels supplied within nozzle 16. In at least some aspects, there may be a transition period during which a blended pilot fuel and main fuel are injected before transitioning to only the main fuel. After injecting the pilot fuel, the fuel may combust (e.g., via autoignition), thereby creating a pilot flame that promotes complete combustion of the main fuel.

[0051] The disclosed systems and methods can enable the injection of two different types of liquid fuels using a single fuel injector. The main fuel and the pilot fuel may be received at different locations, with one type of fuel supplied from one or more passages within the cylinder head and the other type of fuel supplied from a location external to the cylinder head. Except within the nozzle of the injector where a controlled amount of pilot fuel displaces the main fuel prior to injection, the two fuels may be isolated from one another. This can allow the pilot fuel to be injected into the combustion chamber first, thereby providing more complete combustion of the main fuel, which may be a fuel associated with environmental or other benefits. In some configurations, isolation of at least some of the moving components of the injector from the main fuel can avoid cavitation or other damage, can reduce seat wear, and can avoid scratching. Injector components that include portions exposed to the pilot fuel rather than the displaced main fuel can also achieve some or all of these benefits.

[0052] It will be apparent to those skilled in the art that various modifications and alterations can be made to the disclosed systems and methods without departing from the scope of the disclosure. By considering the specification and the systems and methods disclosed herein, other embodiments of the systems and methods will be apparent to those skilled in the art. The specification and examples are intended to be considered only exemplary, and the true scope of the disclosure is indicated by the appended claims and their equivalents.

Claims

1. A fuel injector (12) capable of injecting a plurality of different fuels during a single fuel injection event, the fuel injector comprising: a body (15) including a main fuel path and a pilot fuel path; a first plunger (14) in fluid communication with the pilot fuel path; a second plunger (20) in fluid communication with the main fuel path and with the pilot fuel path; a hydraulic control chamber (40) within the pilot fuel path; and an injection valve (26) where the main fuel path and the pilot fuel path are connected to each other.

2. The fuel injector (12) according to claim 1, wherein the first plunger (14) is isolated from the main fuel path.

3. The fuel injector (12) according to claim 1 or claim 2, further comprising an overflow valve (62) included in the pilot fuel path, the overflow valve (62) having a first position and a second position, in the first position fluid is configured to be discharged from the hydraulic control chamber (40), in the second position preventing fluid from being discharged from the hydraulic control chamber (40).

4. The fuel injector (12) according to any one of the preceding claims, wherein the second plunger (20) includes a stepped shape including a narrowed end (22) extending towards the hydraulic control chamber (40) and an enlarged portion (24) extending away from the narrowed end (22).

5. The fuel injector (12) according to claim 4, wherein the enlarged portion (24) includes a distal face configured to pressurize fuel within a main fuel chamber (36).

6. The fuel injector (12) according to claim 5, further comprising a valve positioned downstream of the main fuel chamber (36) and upstream of a fuel injection chamber (39), where the main fuel path and the pilot fuel path are connected to each other at the fuel injection chamber.

7. A fuel injection method, comprising: receiving main fuel with a main fuel path within a body (15) of a fuel injector (12); receiving pilot fuel with a pilot fuel path within the body (15) of the fuel injector (12); pressurizing the pilot fuel within a hydraulic control chamber (40) in the pilot fuel path; supplying main fuel to a nozzle (16) of the fuel injector (12) with a main fuel plunger (20) connected to the hydraulic control chamber (40); supplying pilot fuel to the nozzle (16) of the fuel injector; and injecting the pilot fuel and the main fuel from the nozzle (16) of the fuel injector (12).

8. The method according to claim 7, wherein the pilot fuel has a higher cetane number compared to the cetane number of the main fuel.

9. The method according to claim 7 or claim 8, wherein pressurizing the pilot fuel is performed with a hydraulic drive or a mechanical drive movement of an electronic control valve (62) and a plunger (14).

10. The method according to any one of claims 7-9, wherein the pilot fuel is injected after being transferred from the hollow interior (54) of the injection valve (27) to the interior of the nozzle (16).

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