Engine system for liquid fuel with low cetane number

Abstract

An engine system including a fuel supply system and a fuel injection system for fueling with a main fuel and a pilot fuel, where the main fuel is a relatively low cetane number liquid fuel and the pilot fuel is a relatively higher cetane number fuel. The engine system can operate an LCDI operating mode with the main fuel and the pilot fuel or a monofuel operating mode with only the pilot fuel. The pilot fuel can be injected through main injection holes in the monofuel operating mode. A fuel injector can be adapted during manufacturing for the liquid fuel or for a gaseous fuel.

Description

ENGINE SYSTEM FOR LIQUID FUEL WITH LOW CETANE NUMBERTechnical Field

[0001] The present application relates to an engine system for liquid fuel with a low cetane number and a method to operate the engine system, and in particular a fuel supply system and a fuel injection system for a fuel injector including monofuel and dual fuel injector configurations for an internal combustion engine fueling with a liquid fuel with a low cetane number.Background

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the invention.

[0003] Methanol and ethanol are potential low-carbon fuels that can be used for a variety of applications, and notably for marine and mining applications to reduce greenhouse gas emissions. Late cycle, direct injection (LCDI) allows the introduction of methanol or ethanol at or near top dead center position during the compression and / or the expansion stroke directly into combustion chambers to take full advantage of an engine operating in the Diesel-cycle for improved efficiency. Methanol and ethanol are low cetane number fuels and have relatively high autoignition temperatures and high latent heats of vaporization, which makes it difficult to achieve autoignition in Diesel-cycle engines, thereby necessitating the use of a pilot fuel introduced into the combustion chamber by a second injector from that of the main fuel injector or from a dual fuel injector which introduces both a main fuel and a pilot fuel.

[0004] The methanol supply chain is not as robust or as extensive as the diesel fuel supply chain. There is the possibility of the unavailability of methanol when refilling a fuel system of an internal combustion engine under some circumstances.

[0005] The state of the art is lacking in techniques for engine systems fueling with liquid fuel having a low cetane number and methods to operate the engine systems for liquid fuel with a low cetane number.Summary

[0006] An improved fuel supply system for a main fuel and a pilot fuel for an internal combustion engine includes a main fuel supply, a first main pump pressurizing the main fuel from the main fuel supply to a main intermediate pressure, a second main pump pressurizing the main fuel from the main intermediate pressure to at least a main injection pressure, a main conduit for supplying the main fuel to the internal combustion engine at the main injection pressure, a pilot fuel supply, a first pilot pump pressurizing the pilot fuel from the pilot fuel supply to a pilot intermediate pressure, a second pilot pump fluidly receiving the pilot fuel from the first pilot pump and pressurizing the pilot fuel from the pilot intermediate pressure to at least a pilot injection pressure, a pilot conduit for supplying the pilot fuel to the internal combustion engine at the pilot injection pressure. The improved fuel supply system also includes at least one of (1) a first valve selectively fluidly connecting the second pilot pump with the main conduit whereby the pilot fuel at the pilot injection pressure can be fluidly communicated to the main conduit; (2) a second valve selectively fluidly connecting the first pilot pump with the second main pump whereby the pilot fuel at the pilot intermediate pressure can be fluidly communicated to the second main pump such that the second main pump can pressurize the pilot fuel further; and (3) a third valve selectively fluidly connecting the pilot fuel supply with the first main pump whereby the pilot fuel at a pilot tank pressure in the pilot fuel supply can be fluidly communicated to the first main pump such that the first main pump can pressurize the pilot fuel. In a first operating mode the main fuel is supplied to the main conduit for supplying the main fuel to the internal combustion, and the pilot fuel is supplied to the pilot conduit for supplying the pilot fuel to the internal combustion engine. In a second operating mode the pilot fuel is supplied to both the main conduit and the pilot conduit for supplying pilot fuel to the internal combustion engine.

[0007] The improved fuel supply system can further include any one or more of the following features including at least one of (1) a first check valve fluidly connecting the second main pump and the main conduit and allowing fluid flow from the second main pump to the main conduit andblocking fluid flow from the first valve to the second main pump; and (2) a second check valve fluidly connecting the first main pump and the second main pump and allowing fluid flow from the first main pump to the second main pump and blocking fluid flow from the second valve to the first main pump. The first valve, the second valve, and the third valve can be solenoid valves. The first valve and the second valve can be single-pole, single-throw valves; or ban be a single-pole, double-throw valve, where in a first position the first valve fluidly connects the second main pump with the main conduit and in a second position the first valve fluidly connects the second pilot pump with the main conduit. The second valve can be a single-pole, double-throw valve, where in a first position the second valve fluidly connects the first main pump with the second main pump and in a second position the second valve fluidly connects the first pilot pump with the second main pump. The third valve can be a single-pole, double-throw valve, where in a first position the third valve fluidly connects the main fuel supply with the first main pump and in a second position the third valve fluidly connects the pilot fuel supply with the first main pump. The third valve can include a first single pole, single throw valve and a second single pole, single throw valve; where the first single pole, single throw valve fluidly connects the main fuel supply with the first main pump and the second single pole, single throw valve fluidly connects the pilot fuel supply with the first main pump.

[0008] Additionally, the fuel supply system can further optionally include additional features such as a pressure regulator fluidly connecting the second main pump with the main conduit and regulate a pressure of the main fuel from the second main pump to the main injection pressure. The pressure regulator can regulate the pressure of the main fuel relative to the pressure of the pilot fuel in the pilot conduit. The pressure regulator can fluidly connect the second pilot pump with the pilot conduit and regulate a pressure of the pilot fuel from the second pilot pump to the pilot injection pressure where the pressure regulator can further regulate the pressure of the pilot fuel relative to the pressure of the main fuel in the main conduit. The main injection pressure can be less than the pilot injection pressure. The pilot injection pressure can be greater in the second operating mode compared to the first operating mode. The main fuel can be injected into a combustion chamber of the internal combustion engine through a main injection hole and the pilot fuel can be injected into the combustion chamber of the internal combustion engine through a pilot injection hole, the pilot injection pressure is less in the second operating mode compared to the first operating mode when the pilot fuel is injected through the main injection hole; and the pilot injection pressure is greater inthe second operating mode compared to the first operating mode when the pilot fuel is injected only through the pilot injection hole.

[0009] The pilot fuel can be diesel fuel, dimethyl either, kerosene, or mixtures of two or more of these fuels. The main fuel can be a liquid fuel which particularly includes alcohol fuels for example bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels.

[0010] An improved fuel injector for a main fuel including a nozzle having an inner surface and an outer surface, the nozzle including a main injection hole extending from the inner surface to the outer surface and a main valve seat on the inner surface of the nozzle. The main injection hole has a main injection hole diameter. The main valve member includes an inner surface and an outer surface with a main sealing surface on the outer surface of the main valve member. The main injection valve includes the main valve seat and the main sealing surface; the main injection valve is closed when the main sealing surface abuts the main valve seat and open when the main sealing surface is spaced apart from the main valve seat. The main injection valve has a main sealing diameter defined by the main valve seat and the main sealing surface and for each main injection pressure, the main injection hole diameter is greater when the main fuel is a gaseous fuel compared to when the main fuel is a liquid fuel. Additionally, the main sealing diameter of the main injection valve is the same within a margin for when the main fuel is a gaseous fuel and when the main fuel is a liquid fuel.

[0011] Additionally, one or more of the following features can be included in the improved fuel injector, including when the main fuel is liquid fuel, the main injection hole diameter can be between 0.3125 millimeters and 0.75 millimeters (mm). The margin can be + / -5% of a nominal value of the main sealing diameter. The fuel injector can further include a main valve lift length of the main valve member between the closed position and the open position of the main injection valve in which the main valve lift length can be less when the main fuel is a liquid fuel compared to when the main fuel is a gaseous fuel. The fuel injector can further include a match fit between the nozzle and the main valve member, in which a main match-fit diameter of the main valve member along the match fit remains the same whether the main fuel is a liquid fuel or the main fuel is a gaseous fuel. The fuel injector can further include a main control chamber disposed at an end of the main valve member providing closing hydraulic forces on the main valve member when pressurized with a control fluid; and a main fueling chamber can be disposed between a main fuel inlet of the fuel injector and the main injection valve such that the match fit extends between the main control chamber and the mainfueling chamber. The fuel injector can further include a liquid seal chamber extending around the main valve member, with the match fit extending between the liquid seal chamber and the main fueling chamber. The fuel injector can further include a main fueling chamber upstream of the main injection valve, a volume of the main fueling chamber when the main fuel is a gaseous fuel is substantially equal to a volume of the main fueling chamber when the main fuel is a liquid fuel. The fuel injector can further include a main injection chamber disposed between the main injection valve and the main injection hole, a volume of the main injection chamber when the main fuel is a gaseous fuel is substantially equal to a volume of the main injection chamber when the main fuel is a liquid fuel. The fuel injector can further include a main injection axis of the main injection hole, a longitudinal axis of the fuel injector, and a horizontal plane perpendicular to the longitudinal axis, such that a main injection angle of the main injection axis to the horizontal plane is within a range of 14 degrees to 30 degrees when the main fuel is a gaseous fuel and within a range of 10 degrees to 30 degrees when the main fuel is a liquid fuel. The fuel injector can further include a main valve seat angle(5), and the main valve seat angle when the main fuel is a gaseous fuel is substantially equal to the main valve seat angle when the main fuel is a liquid fuel. The main fuel can be a liquid fuel including alcohol fuels such as bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of these fuels.

[0012] The fuel inj ector with any one or more features described herein can be a dual fuel inj ector for injecting the main fuel and a pitot fuel. The main valve member can include a pilot injection hole extending from the inner surface to the outer surface and a pitot valve seat on the inner surface of the main valve member, and the dual fuel injector further can include a pitot valve member movable along a longitudinal axis of the dual fuel injector within the main valve member. The pilot valve member can include a pitot sealing surface on an outer surface of the pitot valve member; and a pitot injection valve can include the pitot valve seat and the pitot sealing surface, and the pitot injection valve is closed when the pitot sealing surface abuts the pitot valve seat and is open when the pitot sealing surface is spaced apart from the pitot valve seat. The pitot fuel can be diesel fuel, dimethyl either, or kerosene.

[0013] An improved method of making a fuel injector for introducing a main fuel into a combustion chamber of an internal combustion engine including making a nozzle having a valve seat on an inner surface of the nozzle; making a main valve member having a sealing surface on an outer surface of the main valve member; and when a gaseous fuel will be employed as the main fuel,forming a main injection hole in the nozzle having a first diameter and when a liquid fuel will be employed as the main fuel, forming the main injection hole in the nozzle having a second diameter; and forming a main injection valve between the valve seat of the nozzle and the sealing surface of the main valve member. The main injection valve has a main sealing diameter, with the main injection valve closed when the sealing surface abuts the valve seat and with the main injection valve open when the sealing surface is spaced apart from the valve seat. The main injection hole is downstream from the main injection valve, and the first diameter of the main injection hole is greater than the second diameter of the main injection hole, and the main sealing diameter is substantially the same within a margin whether the main fuel is gaseous fuel or liquid fuel.

[0014] The method of making the fuel injector further can include forming a match fit between at least a portion of the inner surface of the nozzle and at least a portion of an outer surface of the main valve member, the match fit upstream of the main injection valve and having a main match-fit diameter. The main match-fit diameter is substantially the same whether the main fuel is gaseous fuel or liquid fuel. Additionally, the method of making the fuel injector can also include a margin of at most +1-5% of a nominal value of the main sealing diameter.

[0015] An improved nozzle apparatus for a dual-fuel injector that injects a pilot fuel and a main fuel into a combustion chamber of an internal combustion engine includes twelve or more main injection holes, where each main injection hole can have a main injection hole diameter inclusively within a range of 0.33 millimeters and 0.41 millimeters; and twelve or more pilot injection holes, where each pilot injection hole can have a pilot injection hole diameter inclusively within a range of 0.10 millimeters and 0.15 millimeters. A pilot injection pressure for the pilot fuel can be between 1000 bar and 1500 bar, and a main injection pressure can be equal to a difference between the pilot injection pressure and a system bias pressure where the system bias pressure is within a range of 0 bar and 100 bar. The main fuel can be an alcohol fuel or a gaseous fuel that is injected in the liquid phase.

[0016] The main injection hole diameter of the improved nozzle apparatus can be within a range of 0.33 millimeters and 0.37 millimeters; or the main injection hole diameter of the improved nozzle apparatus can be within a range of 0.34 millimeters and 0.36 millimeters; or the main injection hole diameter of the improved nozzle apparatus can be substantially 0.35 millimeters. The pilot injection hole diameter of the improved nozzle apparatus can be inclusively within a range of 0.1 mm and 0.15mm, and preferably can be substantially 0.11 millimeters. The improved nozzle apparatus can be employed when the internal combustion engine has a power rating within a range of 50 to 150 kilowatts per cylinder. The improved nozzle apparatus can be employed when the alcohol fuel is bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels and the gaseous fuel is butane, liquefied petroleum gas, propane, or mixtures of two or more of these fuels.

[0017] An improved fuel injection method for a dual -fuel injector that injects a pilot fuel and a main fuel into a combustion chamber of an internal combustion engine, and where the dual-fuel injector includes pilot injection holes for the pilot fuel and main injection holes for the main fuel. The fuel injection method includes dividing an engine map between a first zone and a second zone, the first zone having a lower range of engine speeds for each engine load compared to the second zone and the first zone having a lower range of engine loads for each engine speed compared to the second zone; employing a first injection mode during a run-on-pilot mode when the internal combustion engine is operating in the first zone in the engine map where the pilot fuel is injected through the pilot injection holes only; and employing a second injection mode during the run-on- pilot mode when the internal combustion engine is operating in the second zone in the engine map where the pilot fuel is injected through the pilot injection holes and the main injection holes, a run- on-pilot pilot injection of the pilot fuel is employed to inject the pilot fuel through the pilot injection holes and a run-on-pilot main injection of the pilot fuel is employed to inject the pilot fuel through the main injection holes; where the pilot fuel bums with diffusion-flame combustion in the first injection mode and the second injection mode.

[0018] In the improved fuel injection method, for each pilot injection pressure, the engine map can be divided into the first zone and the second zone such that as the pilot injection pressure increases, the first zone increases in size and the second zone decreases in size.

[0019] In the improved fuel injection method, during the first injection mode, a pilot injection of the pilot fuel through the pilot injection holes can occur anywhere between a range inclusively between 15 crank angle degrees before top dead center during a compression stroke and 25 crank angle degrees after top dead center during a power stroke; and during the second injection mode, the run-on-pilot pilot injection where the pilot fuel is injected through the pilot injection holes occurs anywhere within a range inclusively between 20 crank angle degrees before top dead center during the compression stroke and top dead center at an end of the compression stroke, and the run-on-pilotmain injection where the pilot fuel is injected through the main injection holes occurs anywhere within a range inclusively between 5 crank angle degrees before top dead center during the compression stroke and 20 crank angle degrees after top dead center during the power stroke.

[0020] In the improved fuel injection method, the internal combustion engine can be operated at substantially a maximum rated power in the second injection mode in the run-on-pilot mode. The improved fuel injection method can further include employing a single value for a pilot injection pressure for a majority of the engine map except for when the engine load is below at most 10% of a maximum rated power. The improved fuel injection method can further include employing the single value for the pilot injection pressure for the majority of the engine map except for when the engine load is below at most 5% of the maximum rated power. The improved fuel injection method can further include providing each of the main injection holes with a main injection hole diameter inclusively within a range of 0.33 millimeters and 0.41 millimeters. The improved fuel injection method can further include providing the dual-fuel injector with at least twelve of the main injection holes.

[0021] In the improved fuel injection method, the main fuel can an alcohol fuel. The alcohol fuel can be bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels. In the improved fuel injection method where the main fuel is an alcohol fuel, a pilot injection pressure in the first injection mode and the second injection mode during the run-on-pilot mode can be inclusively within a range of 1000 bar and 1500 bar.

[0022] In the improved fuel injection method, the main fuel can be butane, liquefied petroleum gas, propane, or mixtures of two or more of these fuels, and in these circumstances, a pilot injection pressure in the first injection mode and the second injection mode during the run-on-pilot mode can be inclusively within a range of 575 bar and 1200 bar, or the pilot injection pressure in the first injection mode and the second injection mode during the run-on-pilot mode can be inclusively within a range of 1000 bar and 1500 bar.

[0023] The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the apparatus, systems, and methods and, together with the general description above, and the detailed description of the specific embodiments, serve to explain the principles of the apparatus, systems, and methods.

[0024] FIG. 1 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0025] FIG. 2 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0026] FIG. 3 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0027] FIG. 4 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0028] FIG. 5 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0029] FIG. 6 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0030] FIG. 7 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0031] FIG. 8 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0032] FIG. 9 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0033] FIG. 10 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0034] FIG. 11 is a schematic view of an engine system including a fuel supply system and a fuel injection system for an internal combustion engine according to an embodiment.

[0035] FIG. 12 is a schematic view of the fuel injection system and the internal combustion engine of FIGS. 1 to 11 according to an embodiment.

[0036] FIG. 13 is a schematic view of the fuel injection system and the internal combustion engine of FIG. 12, illustrating a main-fuel jet and a pilot-fuel jet in a combustion chamber.

[0037] FIG. 14 is a schematic view of a dual -fuel injector of the fuel injection system of FIG. 12 shown in a closed position for a main fuel and a closed position for a pilot fuel.

[0038] FIG. 15 is a detailed view of a nozzle portion of the dual-fuel injector of FIG. 14.

[0039] FIG. 16 is a schematic view of the dual-fuel injector of FIG. 14 shown in an open position for the main fuel and the closed position of the pilot fuel.

[0040] FIG. 17 is a detailed view of a nozzle portion of the dual-fuel injector of FIG. 16.

[0041] FIG. 18 is a detailed view of the nozzle portion of the dual -fuel injector of FIG. 15.

[0042] FIG. 19 is a detailed view of the nozzle portion of the dual -fuel injector of FIG. 15.

[0043] FIG. 20 is a flow diagram view of a method of making a fuel injector.

[0044] FIG. 21 is table view of a plurality of scenarios of computational fluid dynamic simulations where each scenario has a unique combination of engine operating parameters including operating mode, pilot injection pressure, main hole diameter, main hole number and whether a pilot injection is performed. The results of the simulations include indicated mean effective pressure (IMEP), indicated thermal efficiency (ITE), and nitrous oxide emissions (NOx).

[0045] FIG. 22 is a chart view of an engine operating map of an injection strategy including dividing lines between a first injection technique and a second injection technique.

[0046] FIG. 23 is a flow chart view of an injection method for the internal combustion engine FIGS. 12 and 13 when operating in a run-on-pilot mode.

[0047] FIG. 24 is a table view of the effect of pilot injection on a run-on-pilot mode of operation including a plurality of scenarios of computational fluid dynamic simulations where each scenario has a unique combination of engine operating parameters including operating mode, pilot injection pressure, main hole diameter, main hole number and whether a pilot injection is performed. The results of the simulations include indicated mean effective pressure (IMEP), indicated thermal efficiency (ITE), nitrous oxide emissions (NOx), and carbon monoxide emissions (CO). The pilot fuel is injected through the main injection holes in all the scenarios.

[0048] FIG. 25 is a schematic plan view of main jets and pilot jets in the combustion chamber of FIG. 1 according to an embodiment.

[0049] FIG. 26 is a schematic plan view of main jets and pilot jets in the combustion chamber of FIG. 1 according to an embodiment.

[0050] FIG. 27 is a schematic plan view of main jets and pilot jets in the combustion chamber of FIG. 1 according to an embodiment.

[0051] FIG. 28 is a schematic plan view of main jets and pilot jets in the combustion chamber of FIG. 1 according to an embodiment.

[0052] FIG. 29 is a schematic plan view of main jets and pilot jets in the combustion chamber of FIG. 1 according to an embodiment.

[0053] FIG. 30 is a schematic plan view of main jets and pilot jets in the combustion chamber of FIG. 1 according to an embodiment.

[0054] FIG. 31 is a chart view of a pilot inj ection and a main inj ection in the combustion chamber of FIG. 1 according to an embodiment.

[0055] FIG. 32 is a flow chart view of an algorithm for a method of the fuel injection and combustion for the internal combustion engine of FIG. 1 according to an embodiment.

[0056] FIG. 33 is chart view of computational fluid dynamic simulation results according to an embodiment.

[0057] FIG. 34 is a chart view of gross indicated efficiency for the computational fluid dynamic simulation results of FIG. 33.

[0058] FIG. 35 is chart view of computational fluid dynamic simulation results according to an embodiment.

[0059] FIG. 36 is a chart view of gross indicated efficiency for the computational fluid dynamic simulation results of FIG. 35.

[0060] FIG. 37 is chart view of computational fluid dynamic simulation results according to an embodiment.

[0061] FIG. 38 is a chart view of gross indicated efficiency for the computational fluid dynamic simulation results of FIG. 37.

[0062] FIG. 39 is chart view of computational fluid dynamic simulation results according to an embodiment.

[0063] FIG. 40 is a chart view of gross indicated efficiency for the computational fluid dynamic simulation results of FIG. 39.

[0064] FIG. 41 is a chart view of desired main injection pressure for a specified rated power per engine cylinder with different main injection hole diameters for a fuel injector nozzle with nine main injection holes.

[0065] Referring to FIG. 1, there is shown first engine system 10 including first fuel supply system 20 and fuel injection system 30 for internal combustion engine 40. First engine system 10 can bum a liquid fuel, such as an alcohol fuel, with a low cetane number as a main fuel in internalcombustion engine 40 and employs a pilot fuel to help ignite the main fuel. Main fuel supply 50 is a source of the main fuel. The main fuel can be a low cetane number liquid fuel such as alcohol fuels, for example, bioalcohol, butanol, ethanol, methanol, propanol, and mixtures of two or more of these fuels. In some embodiments, the latent heat of vaporization of the main fuel is greater than 575 kilojoules per kilogram (kJ / kgj.The cetane number of the main fuel is typically less than 40. In some embodiments, the cetane number of the main fuel is less than 15. In an exemplary embodiment, the main fuel is methanol with a cetane number of approximately 3. Other low cetane number liquid fuels are contemplated. The main fuel is pressurized in two stages by first main pump 60, which pressurizes the main fuel from a main tank pressure in main fuel supply 50 to a main intermediate pressure, and second main pump 70, which pressurizes the main fuel from the main intermediate pressure to a main injection pressure. In the illustrated embodiment, first main pump 60 is outside of the main fuel supply 50. In some embodiments, first main pump 60 is within main fuel supply 50. Pilot fuel supply 80 is a source of the pilot fuel. The pilot fuel can be, for example, diesel, dimethyl ether (DME), kerosene, and mixtures of two or more of these fuels. The pilot fuel is pressurized in two stages by first pilot pump 90, which pressurizes the pilot fuel from a pilot tank pressure in pilot fuel supply 80 to a pilot intermediate pressure, and second pilot pump 100, which pressurizes the pilot fuel from the pilot intermediate pressure to a pilot injection pressure. In the illustrated embodiment, first pilot pump 90 is outside of the pilot fuel supply 80. In some embodiments, first pilot pump 90 is within pilot fuel supply 80. The main intermediate pressure can be different, or the same as the pilot intermediate pressure. In some embodiments, the main and pilot intermediate pressures are less than 100 bar, preferably less than 50 bar, and most preferably less than 10 bar. In some embodiments, the main and pilot injection pressures are greater than 500 bar. In exemplary embodiments, the main injection pressure is between and including 1000 bar and 1500 bar when the main fuel is an alcohol fuel such as methanol and ethanol.

[0066] The main fuel at the main injection pressure and the pilot fuel at the pilot injection pressure are supplied to fuel injection system 30, and particularly to dual-fuel injector 110 by way of main conduit 120 and pilot conduit 130, respectively. In an exemplary embodiment, the main injection pressure is a desired main injection pressure, and the pilot injection pressure is a desired pilot injection pressure. In some embodiments, second main pump 70 can pressurize the main fuel to a pressure higher than the desired main injection pressure, whereby the pressure of the main fuel can be further regulated to the desired main injection pressure before being supplied to fuel injectionsystem 30, as will be described in more detail below. In some embodiments, second pilot pump 100 can pressurize the pilot fuel to a pressure higher than the desired pilot injection pressure, whereby the pressure of the pilot fuel can be further regulated to the desired pilot injection pressure before being supplied to fuel injection system 30, as will be described in more detail below. In the illustrated embodiment, there is one of the dual -fuel injector 110 that directly introduces the main fuel and the pilot fuel into combustion chamber 200. However, in other embodiments, there can be more than one of the dual -fuel injector 110 and more than one of the combustion chamber 200. Dual -fuel injector 110 will be described in more detail below. In some embodiments, there can be a main fuel injector and a pilot fuel injector (not shown) instead of the dual-fuel injector 110.

[0067] Internal combustion engine 40 can operate in a late cycle, direct injection (LCDI) operating mode when supplied with the main fuel over main conduit 120 and the pilot fuel over pilot conduit 130. The engine can operate over the full rated power range and at least 80% and preferably at least 95% of the fuel consumed on an energy basis is the main fuel. A minimum amount of the pilot fuel consumed on an energy basis depends upon the main fuel, since different main fuels have different ignition requirements. The main fuel and the pilot fuel both bum with diffusion-flame combustion in the LCDI operating mode, which will be described in more detail below. A total quantity on an energy basis of fuel consumed in the LCDI operating mode equals a sum of a main quantity on an energy basis of the main fuel and a pilot quantity on an energy basis of the pilot fuel. Under some circumstances, internal combustion engine 40 is fueled exclusively with the pilot fuel during a monofuel operating mode, also referred to as a run-on-pilot mode or a run-on-diesel mode. For example, while operating, the main fuel supply 50 can become depleted of fuel and the internal combustion engine 40 needs to continue to operate, or when main fuel supply 50 needs to be refdled but a source of the main fuel is unavailable, it is desirable to fuel with the pilot fuel alone. Internal combustion engine 40 can be supplied with the pilot fuel over main conduit 120 and pilot conduit 130 in the monofuel operating mode, where the internal combustion engine 40 can operate substantially over its full rated power range and 100% of the fuel consumed on an energy basis is the pilot fuel. The pilot fuel bums with diffusion-flame combustion in the monofuel operating mode. The LCDI operating mode and the monofuel operating mode are also referred to herein as first and second operating modes, respectively.

[0068] Referring now to FIG. 31, the LCDI operating mode where the fuel injected into combustion chamber 200 substantially bums with a diffusion-flame is described in more detail. Diffusion-flame combustion is characterized by the fuel and the oxidizer being separated from each other before burning. Pilot injection 700 introduces a pilot quantity 710 of the pilot fuel into combustion chamber 200 and main injection 740 introduces a main quantity 750 of the main fuel into combustion chamber 200 during the LCDI operating mode. The pilot quantity 710 is a total mass of the pilot fuel introduced during pilot injection 700, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 720 and the engine speed of internal combustion engine 40. The main quantity 750 is a total mass of the main fuel introduced during the main injection 740, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 760 and the engine speed of internal combustion engine 40. The pilot injection 700 is calibrated based on a differential pressure between the pilot injection pressure and the cylinder pressure inside combustion chamber 200 (and other engine operating conditions) and is influenced by the geometry of pilot injection valve 215 (seen in FIG. 12) inside dual-fuel injector 110 (or other separate pilot fuel injector), and particularly a cross-sectional flow area through the pilot injection valve 215 as it opens, remains open, and then closes. The pilot injection 700 begins at start of injection timing SOIPF. Similarly, the main injection 740 of the main fuel is calibrated based on a differential pressure between the main injection pressure and the cylinder pressure inside combustion chamber 200 (and other engine operating conditions) and is influenced by the geometry of main injection valve 210 (seen in FIG. 12) inside dual-fuel injector 110, and particularly a cross- sectional flow area through the main injection 210 valve as it opens, remains open, and then closes. The pilot injection 700 and the main injection 740 begin later during the compression stroke such that the pilot fuel and the main fuel do not have time to substantially premix and thereby substantially bum only by diffusion-flame combustion. In the illustrated embodiment of FIG. 31, the pilot quantity 710 is introduced completely during the compression stroke, before the main quantity 750 is introduced, and the main injection 740 begins during the compression stroke and ends during the expansion stroke. However, this is not a requirement. For example, in other embodiments, the pilot injection 700 can be overlapped with the main injection 740, and / or the pilot injection 700 can begin during the expansion stroke, and / or the pilot injection 700 can begin after the main injection 740, and / or the main injection 740 can end during the compression stroke, provided in all cases the pilot fuel and the main fuel substantially bum by diffusion-flame combustion. A pilot ignition window 730 illustrates the range of crank angle degrees (CAD) in which ignition of the pilot quantity 710 canoccur relative to the pilot injection 700 during the LCDI operating mode. In exemplary embodiments, the pilot ignition window 730 is between and including 15 CAD before top dead center (BTDC) in the compression stroke and 15 CAD after top dead center (ATDC) in the expansion stroke. In some embodiments, the pilot-ignition window can begin at 20 CAD BTDC at high engine speed, such as at or above 75% of maximum engine speed. An ignition delay of the pilot fuel is typically 2 milliseconds (ms) or less, and preferably less than 1 ms. A main injection window 770 for the main quantity 750 measured in crank angle degrees, within which start of injection timing SOIMF followed by end-of-inj ection timing EOIMF of the main injection 740 can occur anywhere within this window during the LCDI operating mode. In exemplary embodiments, the main injection window 770 is between and including 30 crank angle degrees (CAD) BTDC during the compression stroke and 35 CAD ATDC during the expansion stroke. For example, the main quantity 750 of the main fuel can be injected over the entirety of main injection window 770, or over any part thereof. In the LCDI operating mode, the end of injection timing EOIMF of the main quantity 750 is typically later than start of ignition of the main quantity. In some embodiments, the introduction of main quantity 750 can include a plurality of injections of the main fuel, where the fuel introduced in the plurality of injections bums in the diffusion-flame combustion mode. In some embodiments, a difference between the end of injection timing EOIMF and the start of injection timing SOIMF of the main fuel is between 14 and 25 CAD when the engine is operating at high load, such as at or above 75% of a maximum rated power of internal combustion engine 40, and the difference between the end of injection timing EOIMF and the start of injection timing SOIMF of the main fuel is between 14 and 20 CAD when the engine is operating below 75% of the maximum rated power.

[0069] With reference to FIG. 1, first fuel selector 140 can select whether the main fuel at the main injection pressure or the pilot fuel at the pilot injection pressure is supplied to main conduit 120. First fuel selector 140 includes first valve 150. In some embodiments, like the illustrated embodiment, first fuel selector 140 also includes check valve 170. In the LCDI operating mode, first valve 150 can be actuated to a closed position such that first main pump 60 and second main pump 70 can collectively supply the main fuel at the main injection pressure to main conduit 120. In some embodiments, actuating the first valve 150 to the closed position involves deenergizing the valve such that it returns to a biased condition, for example by a mechanical spring. In the monofuel operating mode, first valve 150 can be actuated to an open position to fluidly connect an outlet of second pilot pump 100 with main conduit 120 such that the first pilot pump 90 and the second pilotpump 100 can collectively supply the pilot fuel at the pilot injection pressure to main conduit 120, whereby the pilot fuel is supplied to fuel injection system 30 and particularly to dual-fuel injector 110 over main conduit 120 and pilot conduit 130. In an exemplary embodiment, first valve 150 is actuated by controller 160 to the open position. For example, first valve 150 can be a solenoid valve actuated by controller 160 between open and closed positions. In some embodiments, check valve 170 can be employed to reduce and preferably prevent back flow of the pilot fuel towards second main pump 70. In some embodiments, when second main pump 70 is disabled, it can function as check valve itself such that check valve 170 is not required. First valve 150 can be a single-pole, single-throw valve. In other embodiments, a single-pole, double-throw valve can be employed instead of first valve 150 and check valve 170 to fluidly connect second main pump 70 or second pilot pump 100 with main conduit 120. Other valve configurations are contemplated to make the fluid connection of second main pump 70 or second pilot pump 100 with main conduit 120. Controller 160 is operatively connected with first fuel selector 140 to command the first valve 150 closed to enter the LCDI operating mode, and to command the first valve 150 open to enter the monofuel operating mode. In the monofuel operating mode, first main pump 60 and second main pump 70 can be disabled from pressurizing the main fuel.

[0070] Referring now to FIG. 2, there is shown second engine system 11 that is similar to first engine system 10 and in this and all other embodiments like parts have like reference numerals and differences are discussed. Second fuel supply system 21 includes second fuel selector 141 that can select whether the main fuel at the main intermediate pressure or the pilot fuel at the pilot intermediate pressure is supplied to an inlet of second main pump 70. Second fuel selector 141 includes second valve 151, which is like first valve 150. In some embodiments, like the illustrated embodiment, second fuel selector 141 also includes check valve 171 to reduce and preferably prevent back flow of the pilot fuel towards first main pump 60. However, first main pump 60 may operate like a check valve when disabled such that check valve 171 is not required. In the LCDI operating mode, second valve 151 can be actuated to the closed position such that first main pump 60 and second main pump 70 can collectively pressurize and supply the main fuel at the main injection pressure to fuel injection system 30 over main conduit 120. In the monofuel operating mode, second valve 151 can be actuated to the open position to fluidly connect an outlet of first pilot pump 90 with the inlet of second main pump 70 such that the pilot fuel at the pilot intermediate pressure is supplied to the second main pump 70, whereby first pilot pump 90 and second main pump 70 collectively pressurize and supplythe pilot fuel at a desired run-on-pilot injection pressure to fuel injection system 30 and particularly to dual-fuel injector 110 over main conduit 120. In other embodiments, a single-pole, double-throw valve can be employed instead of second valve 151 and check valve 171 to fluidly connect first main pump 60 or first pilot pump 90 with second main pump 70. Other valve configurations are contemplated to make the fluid connection of first main pump 60 or first pilot pump 90 with second main pump 70. Controller 160 is operatively connected with second fuel selector 141 to command the second valve 151 closed to enter the LCDI operating mode, and to command the second valve 151 open to enter the monofuel operating mode. In the monofuel operating mode, first main pump 60 can be disabled from pressurizing the main fuel.

[0071] Referring now to FIG. 3, there is shown third engine system 12 that is similar to first engine system 10 and second engine system 11 and differences are discussed. Third fuel supply system 22 includes third fuel selector 142 that can select whether the main fuel from main fuel supply 50 or the pilot fuel from pilot fuel supply 80 can be supplied to an inlet of first main pump 60. Third fuel selector 142 includes third valve 152 in the illustrated embodiment. In the LCDI operating move, third valve 152 can be actuated to a first position to fluidly connect main fuel supply 50 with the inlet of first main pump 60 such that the main fuel at the main tank pressure is supplied to the first main pump, whereby first main pump 60 and second main pump 70 collectively pressurize and supply the main fuel at the main injection pressure to fuel injection system 30 over main conduit 120. In the monofuel operating mode, third valve 152 can be actuated to a second position to fluidly connect pilot fuel supply 80 with the inlet of first main pump 60 such that the pilot fuel at the pilot tank pressure is supplied to the first main pump, whereby first main pump 60 and second main pump 70 collectively pressurize and supply the pilot fuel at the desired run-on-pilot injection pressure to fuel injection system 30 over main conduit 120. In an exemplary embodiment, third valve 152 is actuated by controller 160 between the first and second positions. For example, third valve 152 can be a solenoid valve actuated by controller 160 between the first and second positions. Third valve 152 can be a single-pole, double-throw valve. In other embodiments, two single-pole, single-throw valves can be employed instead of a single-pole, double-throw valve. Other valve configurations are contemplated to fluidly connect main fuel supply 50 or pilot fuel supply 80 with first main pump 60. For example, third valve 152 can be replaced by two shut-off valves that can be controlled by controller 160 between open and closed positions, respectively. Controller 160 is operatively connected with third fuel selector 142 to command the third valve 152 into the first position to enterthe LCDI operating mode, and to command the third valve 152 to the second position to enter the monofuel operating mode.

[0072] Second fuel selector 141 and third fuel selector 142 in second fuel supply system 21 and third fuel supply system 22, respectively (seen in FIGS. 2 and 3) have an advantage of being in fluid contact with the main fuel and the pilot fuel at lower pressures compared to first fuel selector 140 in first fuel supply system 20 (seen in FIG. 1). Second fuel selector 141 fluidly switches the main fuel at the main intermediate pressure and the pilot fuel at the pilot intermediate pressure, and third fuel selector 142 fluidly switches the main fuel at the main tank pressure and the pilot fuel at the pilot tank pressure; whereas first fuel selector 140 fluidly switches the main fuel at the main injection pressure and the pilot fuel at the pilot injection pressure. Accordingly, second valve 151 and check valve 171 (seen in FIG. 2) and third valve 152 (seen in FIG. 3) can be rated for lower pressure operation compared to first valve 150 and check valve 170. First pilot pump 90 and second pilot pump 100 in first fuel supply system 20 (seen in FIG. 1 ) are sized and rated to supply the total quantity of fuel for operation of internal combustion engine 40 in the monofuel operating mode at the maximum rated power (that is, where the fuel is only the pilot fuel); whereas only first pilot pump 90 in second fuel supply system 21 (seen in FIG. 2) is sized and rated to supply the total quantity of fuel for operation in the monofuel operating mode at the maximum rated power. The first pilot pump 90 and the second pilot pump 100 in third fuel supply system 22 (seen in FIG. 3) are sized and rated for supplying the pilot quantity of the pilot fuel in the LCDI operating mode at the maximum rated power, which is at most 20% of the total quantity on an energy basis and preferably less than 5% and at least 2% (for alcohol fuels). First main pump 60 in first fuel supply system 20 and second fuel supply system 21 (seen in FIGS. 1 and 2) can be located either inside or outside of main fuel supply 50; whereas preferably, first main pump 60 is located outside of main fuel supply 50 in third fuel supply system 22 (seen in FIG. 3) for simplifying the fluid connection with pilot fuel supply 80.

[0073] As previously discussed, second main pump 70 can pressurize the main fuel to a pressure higher than the desired main injection pressure such that further pressure regulation can regulate the pressure of the main fuel to the desired injection pressure before supplying the main fuel to fuel injection system 30. Referring nowto FIGS. 4, 5, and 6, fourth engine system 10b, fifth engine system 11b, and sixth engine system 12b, respectively are shown where pressure regulator 180 regulates the pressure of the main fuel fluidly received at inlet 181 from second main pump 70 to the desired maininjection pressure (at outlet 182) based on the pressure of the pilot fuel in pilot conduit 130 fluidly received at reference inlet 183 when operating in the LCDI operating mode. Pressure regulator 180 is disposed in main conduit 120 such that main conduit 120 is split into upstream main conduit 120a upstream of pressure regulator 180 and downstream main conduit 120b downstream of pressure regulator 180. Pressure regulator 180 down regulates the pressure of the fuel in upstream main conduit 120a based on the pressure of the pilot fuel in pilot conduit 130. The fuel in upstream main conduit 120a can be the main fuel, when in the LCDI operating mode, or the pilot fuel, when in the monofuel operating mode. In the LCDI operating mode, in some embodiments, the desired pilot injection pressure is greater than the desired main injection pressure by a predetermined pressure differential, sometimes referred to as a system bias pressure. As used herein, the system bias pressure is positive when the desired pilot injection pressure is greater than the desired main injection pressure, and negative when the desired pilot injection pressure is less than the desired main injection pressure. When fourth engine system 10b, fifth engine system 11b, and sixth engine system 12b in FIGS. 4, 5, and 6, respectively are fueling with both the main fuel and the pilot fuel in the LCDI operating mode, the main fuel pressure in upstream main conduit 120a is typically above the desired main injection pressure whereby pressure regulator 180 regulates the main fuel pressure to the desired main injection pressure in downstream main conduit 120b. In fourth engine system 10b seen in FIG. 4, when first fuel selector 140 fluidly connects second pilot pump 100 with upstream main conduit 120a and pressure regulator 180, the pilot fuel pressure in upstream main conduit 120a is the same as the pilot injection pressure in pilot conduit 130. Accordingly, the pressure of the pilot fuel in downstream main conduit 120b will be reduced compared to the pressure in upstream main conduit 120a when the system bias pressure is positive such that the difference between the pressure of the pilot fuel in pilot conduit 130 and the pressure of the pilot fuel in downstream main conduit 120b is the system bias pressure. In fifth engine system 11b seen in FIG. 5, when second fuel selector 141 fluidly connects first pilot pump 90 with second main pump 70 in the monofuel operating mode, the pilot fuel pressure in upstream main conduit 120a can be higher than the pressure of the pilot fuel in pilot conduit 130 (for example, when second main pump 70 has a higher gain than second pilot pump 100, or is commanded to pressurize the pilot fuel in upstream main conduit 120a to a higher pressure than in pilot conduit 130) whereby pressure regulator 180 reduces the pressure of the pilot fuel in downstream main conduit 120b compared to the pressure in upstream main conduit 120a when the system bias pressure is positive, such that the difference between the pressure of the pilot fuel in pilot conduit 130 and the pressure of the pilot fuel in downstream main conduit 120b is the system biaspressure. Controller 160 can command the second main pump 70 to pressurize the pilot fuel in the monofuel operating mode to a desired inlet pressure for pressure regulator 180. In sixth engine system 12b seen in FIG. 6, when third fuel selector 142 fluidly connects pilot fuel supply 80 with first main pump 60, the pilot fuel pressure in upstream main conduit 120a can be higher than the pressure of the pilot fuel in pilot conduit 130 (for example, when a combined gain of first main pump 60 and second main pump 70 is higher than a combined gain of the first pilot pump 90 and the second pilot pump 100 or the first main pump 60 and the second main pump 70 are commanded to pressurize the pilot fuel in upstream main conduit 120a to a pressure higher than the pilot fuel in pilot conduit 130) whereby pressure regulator 180 reduces the pressure of the pilot fuel in downstream main conduit 120b compared to upstream main conduit 120a when the system bias pressure is positive, such that the difference between the pressure of the pilot fuel in pilot conduit 130 and the pressure of the pilot fuel in downstream main conduit 120b is the system bias pressure. Controller 160 can command the first main pump 60 and the second main pump 70 to pressurize the pilot fuel in the monofuel operating mode to the desired inlet pressure for pressure regulator 180.

[0074] Referring now to FIG. 7, seventh engine system lObb is shown that is like fourth engine system 10b seen in FIG. 4 except pressure regulator 180 is disposed upstream of first fuel selector 140, and more particularly upstream of check valve 170. Pressure regulator 180 regulates the pressure of the main fuel fluidly received at inlet 181 from second main pump 70 based on the pressure of the pilot fuel in pilot conduit 130 fluidly received at reference inlet 183 and is only operative during the LCDI operating mode. In the monofuel operating mode, first fuel selector 140 fluidly connects the outlet of second pilot pump 100 with main conduit 120. In the embodiment of FIG. 7, dual-fuel injector 110 is operable when the pressure of the fuel in main conduit 120 substantially equals the pressure of the fuel in pilot conduit 130, such as in the monofuel operating mode. In some embodiments, in the LCDI operating mode, dual-fuel injector 110 is operable when the pressure of the fuel in main conduit 120 is less than the pressure of the fuel in pilot conduit 130 by the system bias pressure. In some embodiments, in the LCDI operating mode, dual -fuel injector 110 is operable when the pressure of the fuel in main conduit 120 is substantially equal to the pressure of the fuel in pilot conduit 130 by the system bias pressure.

[0075] With reference to FIGS. 8, 9, and 10, eighth engine system 10c, ninth engine system 11c, and tenth engine system 12c, respectively are shown where pressure regulator 185 regulates thepressure of the pilot fuel fluidly received at inlet 186 from second pilot pump 100 to the desired pilot injection pressure (at outlet 187) based on the pressure of the main fuel in main conduit 120 fluidly received at reference inlet 188 when operating in the LCDI operating mode. Pressure regulator 185 is disposed in pilot conduit 130 such that pilot conduit 130 is split into upstream pilot conduit 130a upstream of pressure regulator 185 and downstream pilot conduit 130b downstream of pressure regulator 185. Pressure regulator 185 regulates the pressure of the pilot fuel in upstream pilot conduit 130a based on the pressure of the fuel in main conduit 120. The fuel in main conduit 120 can be the main fuel, when in the LCDI operating mode, or the pilot fuel, when in the monofuel operating mode. When eighth engine system 10c, ninth engine system 11c, and tenth engine system 12c in FIGS. 8, 9, and 10, respectively are fueling with both the main fuel and the pilot fuel in the LCDI operating mode, the pilot fuel pressure in upstream pilot conduit 130a is typically above the desired pilot injection pressure whereby pressure regulator 185 regulates the pilot fuel pressure to the desired pilot injection pressure in downstream pilot conduit 130b (based on the pressure of the main fuel in main conduit 120). In eighth engine system 10c seen in FIG. 8, when first fuel selector 140 fluidly connects second pilot pump 100 with main conduit 120, the pilot fuel pressure in main conduit 120 is substantially the same as the pilot fuel pressure in upstream pilot conduit 130a. In this circumstance, when the system bias pressure is positive, pressure regulator 185 can pass the pilot fuel through without further reducing the pressure (except for a small pressure drop inherent in the pass through). In some embodiments, the pilot fuel pressure in main conduit 120 and the pilot fuel pressure in downstream pilot conduit 130b can be substantially the same when operating exclusively with pilot fuel in the monofuel operating mode. In some embodiments, there can be a restriction orifice between upstream main conduit 130a and main conduit 120 (in series with valve 150) such that there is a pressure drop of the pilot fuel pressure across the restriction orifice in the monofuel operating mode that matches the pressure drop across pressure regulator 185. In ninth engine system 11c seen in FIG. 9, when second fuel selector 141 fluidly connects first pilot pump 90 with second main pump 70, the pilot fuel pressure in main conduit 120 can be set to a desired pilot fuel pressure in main conduit 120 by controlling the second main pump 70 and the pilot fuel pressure in upstream pilot conduit 130a can be set to another desired pilot fuel pressure by controlling the second pilot pump 100 whereby pressure regulator 185 can regulate the pressure of the pilot fuel to the desired pilot injection pressure in downstream pilot conduit 130b. In tenth engine system 12c seen in FIG. 10, when third fuel selector 142 fluidly connects pilot fuel supply 80 with first main pump 60, the pilot fuel pressure in main conduit 120 can be set to the desired pilot fuel pressure for main conduit 120 by controlling thefirst main pump 60 and the second main pump 70 and the pilot fuel pressure in upstream pilot conduit 130a can be set to the other desired pilot fuel pressure for upstream pilot conduit 130a by controlling the first pilot pump 90 and the second pilot pump 100 whereby pressure regulator 185 can regulate the pressure of the pilot fuel to the desired pilot injection pressure in downstream pilot conduit 130b.

[0076] Referring now to FIG. 11, eleventh engine system lOcc is shown that is like eighth engine system 10c seen in FIG. 8 except pressure regulator 185 is disposed upstream of first fuel selector 140, and more particularly upstream of first valve 150. The reference pressure for pressure regulator 185 fluidly received at reference inlet 188 is the pressure of the fuel downstream of check valve 170. Pressure regulator 185 regulates the pressure of the pilot fuel fluidly received at inlet 186 from second pilot pump 100 based on the pressure of the fuel in main conduit 120 fluidly received at reference inlet 188 and is operative during both the LCDI operating mode and the monofuel operating mode. In the monofuel operating mode, the pressure of the pilot fuel in downstream pilot conduit 130b substantially equals the pressure of the pilot fuel in main conduit 120. In some embodiments, in the LCDI operating mode, dual -fuel injector 110 is operable when the pressure of the fuel in main conduit 120 is less than the pressure of the fuel in pilot conduit 130 by the system bias pressure. In some embodiments, in the LCDI operating mode, dual-fuel injector 110 is operable when the pressure of the fuel in main conduit 120 is substantially equal to the pressure of the fuel in pilot conduit 130 by the system bias pressure.

[0077] In some embodiments, in addition to pressure regulator 180, other types of pressure regulators can regulate the pressure of the main fuel fluidly received from second main pump 70 in the LCDI operating mode or from the second pilot pump 100 in the monofuel operating mode. In some embodiments, in addition to pressure regulator 185, other types of pressure regulators can regulate the pressure of the pilot fuel fluidly received from second pilot pump 100 in the LCDI operating mode or the monofuel operating mode. For example, pressure regulators that are referenced with respect to atmospheric pressure can be employed instead of being referenced with respect to the pilot fuel pressure of the main fuel pressure. Pressure regulators that employ mechanical biasing (such as springs) and / or electronic techniques to determine the regulated pressure level can be used. Pressure regulators 180 and 185 can regulate the pressure of the main fuel or the pilot fuel by spilling the main fuel or the pilot fuel to a main return conduit or a pilot return conduit (not shown), respectively, which return the main fuel and the pilot fuel to the main fuel supply 50 or the pilot fuelsupply 80, respectively. When switching from the LCDI operating mode the monofuel operating mode, the pressure regulators 180 and 185 can switch from spilling fuel to the main return conduit to spilling fuel to the pilot return conduit.

[0078] In an exemplary embodiment, the desired main injection pressure can be 500 bar or higher. Preferably, the desired main injection pressure is within the range of 600 bar and 1500 bar, and more preferably within a range of 1000 bar and 1500 bar. In some embodiments, the system bias pressure is within a range of 0 bar to 100 bar. In some embodiments, the system bias pressure is within a range of 10 bar and 50 bar. An exemplary system bias pressure is 15 bar whereby the desired pilot injection pressure is equal to the desired main injection pressure plus 15 bar. Depending upon the design and / or operation of dual-fuel injector 110, there could be large pressure spikes internally since both the main fuel and the pilot fuel are liquid fuels, in which case higher system bias pressures are beneficial. The desired main injection pressure and the desired pilot injection pressure can change based on engine operating conditions, such as engine load and engine speed. Similarly, the system bias pressure can change based on engine operating conditions. The desired pilot injection pressure in the monofuel operating mode can be greater than the desired pilot injection pressure in the LCDI operating mode. For example, the desired pilot injection pressure can be 1000 bar or higher in the monofuel operating mode. Accordingly, the pilot injection pressure in pilot conduit 130 of first engine system 10, second engine system 11, third engine system 12, fourth engine system 10b, fifth engine system 1 lb, sixth engine system 12b, and seventh engine system lObb and downstream pilot conduit 130b in eighth engine system 10c, ninth engine system 11c, tenth engine system 12c, and eleventh engine system lOcc can be greater in the monofuel operating mode compared to the LCDI operating mode. In some embodiments, a compression ratio of internal combustion engine 40 is around 17, and preferably substantially 17.

[0079] Referring to FIG. 12, fuel injection system 30 and internal combustion engine 40 of first engine system 10, second engine system 11, third engine system 12, fourth engine system 10b, fifth engine system 1 lb, sixth engine system 12b, seventh engine system lObb, eighth engine system 10c, ninth engine system 11c, tenth engine system 12c, and eleventh engine system lOcc are shown in more detail. As previously disclosed, the main fuel can be a liquid fuel, such as an alcohol fuel, or in some embodiments can be a gaseous fuel in the liquid phase, both with a relatively low cetane number and the pilot fuel is a different fuel from the main fuel with a relatively high cetane number. The pilotfuel auto-ignites due to the pressure and temperature in combustion chamber 200 and the combustion of the pitot fuel creates a pressure and temperature environment inside the combustion chamber suitable for igniting the main fuel. The pilot fuel acts as a high energy ignition source to ignite the main fuel. At least in the LCDI operating mode, the main injection pressure can be within a pressure range defined by a lower injection pressure and an upper injection pressure. In exemplary embodiments, the tower injection pressure is 500 bar and the upper injection pressure is 1500 bar. This pressure range provides improved thermal efficiency for both higher values of an indicated mean effective pressure (IMEP) (such as 4-stroke engines) and tower values of the IMEP (such as 2-stroke engines).

[0080] First fuel supply system 20, second fuel supply system 21, third fuel supply system 22, fourth fuel supply system 20b, fifth fuel supply system 21b, sixth fuel supply system 22b, seventh fuel supply system 20bb, eighth fuel supply system 20c, ninth fuel supply system 21c, tenth fuel supply system 22c, or eleventh fuel supply system 20cc and fuel injection system 30 can include other components, as would be known by those skilled in the technology, but which are not illustrated for simplicity. Such components can include valves, sensors, and fuel rails, for example. Valves can include check valves, excess flow valves, inlet metering valves, one-way valves, pressure relief valves, and shut-off valves, among other valves. Sensors can include pressure sensors, temperature sensors, gas sensors, and mass-flow sensors, among other sensors.

[0081] Fuel injection system 30 further includes dual -fuel injector 110 that is configured as an in-cylinder fuel injector with nozzle 190 at least partially disposed within combustion chamber 200 whereby the fuel injector introduces fuel directly into the combustion chamber. Main injection valve 210 blocks the injection of main fuel into combustion chamber 200 when closed and permits the injection of the main fuel when open. Pitot injection valve 215 blocks the injection of pitot fuel into combustion chamber 200 when closed and permits the injection of pitot fuel when open. In the illustrated embodiment, dual-fuel injector 110 is a dual-fuel injector that introduces both the main fuel and the pitot fuel into combustion chamber 200. In exemplary embodiments, dual-fuel injector 110 introduces the main fuel separately and independently of the pitot fuel, and the timing of the injections of the main fuel and the pitot fuel are determined based on engine operating conditions and may or may not overlap, as will be discussed in more detail below. That is, main injection valve 210 can be actuated separately and independently of pitot injection valve 215. In some embodiments,dual-fuel injector 110 can be a concentric needle fuel injector including a main injection needle and a pilot injection needle (discussed in more detail below) whose longitudinal axes are substantially co-axial. Typically, the main injection needle is tubular with the pilot injection needle reciprocating therein. In some embodiments, dual-fuel injector 110 can include one injector body with side-by-side main fuel and pilot fuel injection assemblies (not shown). In some embodiments, dual -fuel injector 110 is replaced by the main fuel injector (now shown) that only introduces the main fuel and the pilot fuel injector (not shown) that introduces the pilot fuel. In the illustrated embodiment, dual-fuel injector 110 is shown disposed centrally in cylinder 220 through cylinder head 230, such that a longitudinal cylinder axis 240 of cylinder 220 is co-axial with a longitudinal injector axis 245 of dual-fuel injector 110. Although dual -fuel injector 110 is shown centrally mounted, it is possible that the fuel injector can be mounted offset from the longitudinal cylinder axis 240 whereby the longitudinal injector axis 245 is not co-axial with the longitudinal cylinder axis 240. Controller 160 is operatively connected with dual-fuel injector 110 to actuate the fuel injector to introduce the main fuel, the pilot fuel, or both the main fuel and the pilot fuel, into combustion chamber 200. More particularly, controller 160 is configured to actuate the main injection valve 210 and pilot injection valve 215. In some embodiments, the pilot fuel can operate as a sealing fluid for the main fuel in dual-fuel injector 110 in order to constrain the main fuel within the fuel injector.

[0082] Cylinder 220 is defined by cylinder wall 250 extending in engine block 260. Combustion chamber 200 is defined by cylinder wall 250, cylinder head 230, and piston 270 that reciprocates within cylinder 220. Cylinder wall 250 forms a bore having a diameter suitable for internal combustion engines. For example, in light duty engine applications the bore diameter can be less than 100 mm, in medium duty and heavy-duty engine applications the bore diameter can range from 100 mm to 180 mm, and in high horsepower engine applications the bore diameter can be above 180 mm. Generally, as the bore diameter increases the maximum engine speed decreases, primarily due to the increase in momentum of the piston that accompanies increases in its mass, as well as speed putting increased stress on engine components. Large cylinder bore engines, such as heavy-duty engines and high horsepower engines are particularly suitable for operation with alcohol and liquid fuels that are injected since the size of the cylinder bore reduces the likelihood of liquid-phase fuel droplets directly impinging on cylinder wall 250 and piston bowl 275, which leads to poor mixing and high particulate matter (PM) emissions when these phenomena occur. In the illustrated embodiment, piston 270includes the piston bowl 275 having an omega shape, although in other embodiments other piston bowl shapes are contemplated.

[0083] An air handling system includes intake port 280 and intake valve 285 on an intake side, and exhaust port 290 and exhaust valve 295 on an exhaust side. In some embodiments, the intake port 280, intake valve 285, and combustion chamber 200 cooperate to establish a swirl motion of intake air or intake charge in the combustion chamber. Swirl is a bulk motion of intake air or intake charge around the longitudinal cylinder axis 240 within combustion chamber 200. In exemplary embodiments, a swirl number between 2 and 4 is beneficial in improving combustion efficiency, particularly for high horsepower applications with large cylinder bore diameters. There can be a small gap at a top dead center (TDC) position of piston 270 between the top of the piston and fire deck 300. At the TDC position of piston 270, intake valve 285 and exhaust valve 295 can be aligned with recessed portions (not shown) in piston 270 such that the valves can be in an open position without interference with the piston. Intake valve 285 is actuated by intake valve actuator 310 and exhaust valve 295 is actuated by exhaust valve actuator 320. In some embodiments, intake valve actuator 310 and exhaust valve actuator 320 are part of a cam system. In some embodiments, intake valve actuator 310 and exhaust valve actuator 320 can be part of a variable valve actuation system (VVA system 330) that can be operatively connected with and commanded by controller 160 to adjust intake valve timing (IVT) and / or intake valve lift (IVL) of intake valve 285 and exhaust valve timing (EVT) and / or exhaust valve lift (EVL) of exhaust valve 295.

[0084] In some embodiments, VVA system 330 can employ camshaft-based systems or camless systems. Camshaft-based systems can be valve timing control (VTC), also known as variable valve timing (VVT) systems that change the timing of the intake and exhaust valve events without significantly altering the lift. Alternatively, camshaft-based systems can be variable valve event and lift control, also known as variable valve lift (VVL) that can provide a discrete or continuous range of lift and / or duration control between two limits, which can allow modest adjustments in phasing. Camshaft-based VVL and VTC systems can be combined to enable lift and timing control. Camless systems can include hydraulically actuated or electromagnetically actuated systems. Camless systems offer more flexibility compared to camshaft-based systems in valve lift and timing but can have an increased risk of interference between the intake or exhaust valve in the lifted position of the piston.

[0085] In some embodiments, controller 160 is operatively connected with first fuel supply system 20, second fuel supply system 21, third fuel supply system 22, fourth fuel supply system 20b, fifth fuel supply system 21b, sixth fuel supply system 22b, seventh fuel supply system 20bb, eighth fuel supply system 20c, ninth fuel supply system 21c, tenth fuel supply system 22c, or eleventh fuel supply system 20cc, intake valve actuator 310, exhaust valve actuator 320, and dual-fuel injector 110. Controller 160 can include both hardware and software components. The hardware components can include digital and / or analog electronic components. In some embodiments, controller 160 includes a processor and memories, including one or more permanent memories, such as FLASH, EEPROM and a hard disk, and a temporary memory, such as SRAM and DRAM, for storing and executing a program. As used herein, the terms algorithm and step refer to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality. The algorithms and steps that are performed by controller 160 can be part of the controller.

[0086] Referring now to FIG. 13, dual -fuel injector 110 includes main injection holes 340 and pilot injection holes 350. In the illustrated embodiment of FIG. 13, only one of the main injection holes 340 and one of the pilot injection holes 350 are shown; however, a plurality of the main injection holes 340 and a plurality of the pilot injection holes 350 can be employed. In some embodiments, there are between six and twelve of the main injection holes 340. In some embodiments there are twelve or more of the main injection holes 340. In some embodiments, when internal combustion engine 40 is operated in the monofuel operating mode frequently, the number of main injection holes 340 can be increased, for example there can be between 12 and 22 main injection holes, and a cross-sectional flow area through the main inj ection holes can be decreased as the number of main injection holes increases to improve the efficiency of atomization of the pilot fuel through the main injection holes 340 when operating in the monofuel operating mode. In exemplary embodiments, the main injection holes 340 are evenly distributed around a circumference of nozzle 190. Typically, there are an equal number of pilot injection holes 350 as there are main injection holes 340; however, in some embodiments there can be fewer of the pilot injection holes 350 compared to main injection holes 340. A main: pilot hole ratio is a ratio of main hole number over pilot hole number, where the main hole number is the number of main injection holes 340 and the pilot hole number is the number of pilot injection holes 350. The maimpilot hole ratio is one (1) whenthere are an equal number of main injection holes 340 and pilot injection holes 350. In some embodiments, there are half as many pilot injection holes 350 as there are main injection holes 340, such that the maimpilot hole ratio is 2 (2: 1), that is, in those embodiments with an even number Neven of main injection holes 340 there are Neven / 2 pilot-fuel injection holes 350, and in those embodiments with an odd number Nodd of main injection holes 340 there can be either floor(Nodd / 2) pilot injection holes 350 or ceil(Nodd / 2) pilot injection holes 350, where floor(Nodd / 2) represents the lower rounded integer and ceil(Nodd / 2) represents the upper rounded integer. Main jets 360 emanate from respective main injection holes 340 when dual-fuel injector 110 is actuated to inject the main fuel. Pilot jets 370 emanate from respective pilot injection holes 350 when dual-fuel injector 110 is actuated to inject the pilot fuel. In some embodiments, each of the main injection holes 340 is in the form of a cylindrical bore having a main injection hole diameter DMIH. In exemplary embodiments, an upper limit of the diameter of each of the main injection holes 340 can be 0.75 mm and a lower limit can be 0.3125 mm. The main injection pressure and the main injection hole diameter DMIH are selected to ensure adequate atomization of the main fuel for improved mixing and ignitability when the main fuel is a liquid fuel, such as an alcohol fuel. The upper limit of the main injection hole diameter DMIH is constrained by the need to atomize the main fuel sufficiently. In some embodiments, the upper limit of the main injection hole diameter DMIH is constrained by the need to atomize the pilot fuel sufficiently, when operating in the monofuel operating mode. The lower limit of the main injection hole diameter DMIH is constrained by the need to inject a sufficient amount of the main fuel to operate at full load, which is influenced by the main hole number and the main injection pressure. Each of the main jets 360 are injected along a respective main injection axis 365. Main injection axis 365 forms a main injection angle 0 relative to a plane 380 that is orthogonal to the longitudinal cylinder axis 240. In some embodiments, main injection angle 0 can vary between and including ten degrees (10°) and forty degrees (40°), particularly when piston bowl 275 has the omega shape, such as illustrated in FIGS. 12 and 13. In some embodiments, main injection angle 0 is between 14° and 30° when the main fuel is a gaseous fuel and between 10° and 40° when the main fuel is a liquid fuel. Each of the pilot jets 370 is injected along a respective pilot injection axis 375. Pilot injection axis 375 forms a pilot injection angle relative to plane 380. Pilot injection angle 0 of the pilot jets 370 can equal main injection angle 0 of the main jets 360, although this is not a requirement.

[0087] With reference now to FIGS. 14, 15, 16, and 17, dual-fuel injector 110 is illustrated as a concentric-needle dual-fuel injector according to an embodiment. Dual -fuel injector 110 includesnozzle 190, main valve member 390, and pilot valve member 400, which are concentrically disposed around longitudinal injector axis 245 along which main valve member 390 and pilot valve member 400 are each moveable when actuated. Main valve member 390 is the main injection needle and pilot valve member 400 is the pilot injection needle referred to above. Nozzle 190 and main valve member 390 are hollow, and in some embodiments, pilot valve member 400 may also be hollow although this is not a requirement. With reference to FIG. 15, nozzle 190 includes inner surface 420 and outer surface 425, main valve member 390 includes inner surface 430 and outer surface 435, and pilot valve member 400 includes outer surface 440 in the illustrated embodiment. The main valve member 390 and the pilot valve member 400 can be actuated for movement. Main valve member 390 is configured to selectively reciprocate along longitudinal injector axis 245 of dual -fuel injector 110. Similarly, pilot valve member 400 is also configured to selectively reciprocate along longitudinal injector axis 245 of dual -fuel injector 110. When the main valve member 390 is actuated to reciprocate, it automatically causes pilot valve member 400 to move with the main valve member along longitudinal injector axis 245. When only pilot valve member 400 is actuated to reciprocate (and not by movement of the main valve member 390), it does not cause main valve member 390 to move along with. Suitable actuation technologies can be employed to actuate the main valve member 390 and the pilot valve member 400, respectively depending upon the application. In illustrated embodiment, main valve member 390 and pilot valve member 400 are actuated by hydraulic forces. In some embodiments, the main and pilot valve members are actuated by mechanical forces, such as by a piezoelectric actuator. In some embodiments, the main and pilot valve members are actuated by electromagnetic forces.

[0088] Main injection valve 210 is formed between nozzle 190 and main valve member 390 and is shown in a closed position in FIGS. 14 and 15 and in an open position in FIGS. 16 and 17. More particularly, with reference to FIG. 17, main injection valve 210 includes valve seat 460 on inner surface 420 of nozzle 190 and sealing surface 465 on outer surface 435 of main valve member 390. In the closed position of main injection valve 210, sealing surface 465 abuts the valve seat 460, and in the open position the sealing surface 465 is spaced apart from valve seat 460 in the axial direction along longitudinal injector axis 245. In some embodiments, such as the illustrated embodiment, valve seat 460 and sealing surface 465 are annular whereby main injection valve 210 is an annular valve.

[0089] Pilot injection valve 215 is formed between main valve member 390 and pilot valve member 400 and is shown in a closed position in both FIGS. 14, 15, 16, and 17. More particularly, with reference to FIG. 17, pilot injection valve 215 includes valve seat 480 on inner surface 430 of main valve member 390 and sealing surface 485 on outer surface 440 of pilot valve member 400. In the closed position of pilot injection valve 215, sealing surface 485 abuts the valve seat 480, and in the open position (not shown) sealing surface 485 is spaced apart from valve seat 480 in the axial direction along longitudinal injector axis 245. In some embodiments such as the illustrated embodiment, valve seat 480 and sealing surface 485 are annular whereby pilot injection valve 215 is an annular valve.

[0090] Main injection valve 210 can be actuated to open independently and separately from pilot injection valve 215. Pilot injection valve 215 can be actuated to open independently and separately from main injection valve 210. Main injection valve 210 and pilot injection valve 215 can be open simultaneously. The time the main injection valve 210 is open can overlap the time the pilot injection valve 215 is open, at least partially.

[0091] Returning to FIG. 15, dual-fuel injector 110 includes main fueling chamber 490, formed between nozzle 190 and main valve member 390 upstream of main injection valve 210, and pilot fueling chamber 495, formed between main valve member 390 and pilot valve member 400 upstream of pilot injection valve 215. The main fueling chamber 490 and the pilot fueling chamber 495 can also be referred to as plenums. In the illustrated embodiment, the main fueling chamber 490 is an annular chamber extending around main valve member 390, and the pilot fueling chamber 492 is an annular chamber extending around pilot valve member 400. Main fueling chamber 490 is in fluid communication with a main fuel inlet (not shown) of dual-fuel injector 110 to receive the main fuel and pilot fueling chamber 495 is in fluid communication with a pilot fuel inlet (not shown) of the fuel injector to receive the pilot fuel. In some embodiments, the main fueling chamber 490 and the pilot fueling chamber 495 can receive the same fuel through the main and pilot fuel inlets, such as the pilot fuel in the monofuel operating mode. The fuel(s) supplied to dualfuel injector 110 can be at a range of pressures depending upon application requirements and engine operating conditions. The fuel supplied can be within a range of pressures, and can vary whether the main fuel is a gaseous fuel or the main fuel is a liquid fuel.

[0092] Dual-fuel injector 110 also includes main injection chamber 500, formed between nozzle 190 and main valve member 390 and disposed between main injection valve 210 and the main injection holes 340, and pitot injection chamber 505, formed between the main valve member 390 and the pilot valve member 400 and disposed between pitot injection valve 215 and pitot injection hole(s) 350. Main injection chamber 500 and pitot injection chamber 505 can both be referred to as a SAC. When main injection valve 210 is closed, main injection chamber 500 is fluidly isolated from the main fueling chamber 490, and when main injection valve 210 is open, main injection chamber 500 is in fluid communication with the main fueling chamber 490. Similarly, when pitot injection valve 215 is closed, pitot injection chamber 505 is fluidly isolated from the pitot fueling chamber 495, and when pitot injection valve 215 is open, pitot injection chamber 505 is in fluid communication with the pitot fueling chamber 495. In some embodiments such as the illustrated embodiment, when main injection valve 210 is an annular valve, main injection chamber 500 is an annular chamber. In the illustrated embodiment, pitot injection chamber 505 includes an annular portion and a distal portion below pitot valve member 400. The main injection holes 340 extend from main injection chamber 500 into inner surface 420 and through outer surface 425 of nozzle 190. In the illustrated embodiment, inlet orifice 345 of each of the main injection holes 340 is located closer to a distal, downstream end of main injection chamber 500 than a proximal, upstream end by main injection valve 210. Pitot injection holes 350 extend from pitot injection chamber 505 into inner surface 430 and through outer surface 435 of main valve member 390. In the illustrated embodiment, inlet orifice 355 of each of the pitot injection holes 350 is located closer to a distal, downstream end of the pitot injection chamber 505 than a proximal, upstream end by pilot injection valve 215.

[0093] With reference to FIG. 18, main valve seat angle 5 of valve seat 460 is the included angle between two axes (in the same plane) extending along the surface of the valve seat and through respective locations on the valve seat that are 180 degrees apart along a circumference of the valve seat centered around the longitudinal injector axis 245. In some embodiments, the main valve seat angle 5 is between a range of 60 degrees and 100 degrees. In some embodiments, the main valve seat angle 5 is between a range of 85 degrees and 95 degrees. In some embodiments, the main valve seat angle 5 when the main fuel is a gaseous fuel is substantially equal to the main valve seat angle when the main fuel is a liquid fuel, such as an alcohol fuel. Main injection angle a is the included angle between longitudinal axis 510 of each of the main injection holes 340 and a horizontal plane perpendicular to the longitudinal injector axis 245. In some embodiments, such asthe illustrated embodiments of FIGS. 12 and 13, main injection angle a is the same as main injection angle 0 when the longitudinal injector axis 245 is parallel to longitudinal cylinder axis 240. In some embodiments, the main injection angle a is between a range of 10 degrees and 30 degrees. In some embodiments, the main injection angle a is between a range of 18 degrees and 24 degrees. Referring now to FIG. 19, main injection hole diameter DMIH is the diameter of the main injection holes 340. In some embodiments, main injection hole diameter DMIH is the diameter of a cylindrical bore that forms the respective one of the main injection holes 340. In some embodiments, main injection hole diameter DMIH is the smallest diameter of the main injection holes 340. Pilot injection hole diameter DPIH is the diameter of pilot injection holes 350. In some embodiments, pilot injection hole diameter DPIH is the diameter of a cylindrical bore that forms the respective one of the pilot injection holes 350. In some embodiments, pilot injection hole diameter DPIH is the smallest diameter of pilot injection holes 350.

[0094] The main fuel can have a smaller volumetric energy density compared to the pilot fuel. For example, methanol has a smaller volumetric energy density compared to diesel fuel. In this circumstance, the main injection hole diameter DMIH of the main injection holes 340 can be larger than the pilot injection hole diameter DPIH of the pilot injection holes 350. The pilot injection pressure can be less in the monofuel operating mode compared to the LCDI operating mode when the pilot fuel is injected through the main injection holes 340 since the energy density of the pilot fuel is substantially greater than the energy density of the main fuel and a diameter of the main injection hole is substantially greater than a diameter of pilot injection holes 350, for comparable injection window for the pilot fuel the pressure is reduced in the monofuel operating mode. For example, in some embodiments, the pilot injection pressure decreases between 50 bar and 150 bar in the monofuel operating mode compared to the LCDI operating mode. The pilot injection pressure can be greater in the monofuel operating mode compared to the LCDI operating mode when the pilot fuel is only injected through pilot injection holes 350, for example, the pilot injection pressure can be increased above 1000 bar, for example as high as 2000 bar, or as high as 3000 bar. The pilot injection pressure refers to the pressure of the pilot fuel, which is injected through the pilot injection holes 350 during the LCDI operating mode, and can be injected through both the main injection holes 340 and the pilot injection holes 350 in the monofuel operating mode, or only through the pilot injection holes 350 in the monofuel operating mode. In an exemplary embodiment, the main injection hole diameter DMIH is 0.33 mm and the pilot injection holediameter is 0.21 mm when nozzle 190 has nine of the main injection holes 340 and nine of the pilot injection holes 350. In this circumstance, the pilot injection pressure can be between 500 bar and 1500 bar in the first operating mode and greater than 1000 bar in the second operating mode. In some embodiments, with the main injection pressure between 500 and 1500 bar, main injection hole diameter DMIH is between 0.3125 and 0.40625 mm when internal combustion engine 40 has a maximum power rating between 50 to 130 kilowatts (kW) per cylinder, main injection hole diameter DMIH is between 0. 40625 to 0.60 mm when internal combustion engine 40 has a maximum power rating between 130 to 225 kW per cylinder; and main injection hole diameter DMIH is at least 0.60 mm and preferably at most 0.75 mm when internal combustion engine 40 has a maximum power rating above 225 kW per cylinder.

[0095] With reference to FIG. 19, main sealing diameter DMS of main injection valve 210 is an effective diameter of a seal between valve seat 460 and sealing surface 465 when the main injection valve 210 is closed. Main sealing diameter DMS determines a pressure acting area of hydraulic and / or pneumatic forces on main valve member 390 when main injection valve 210 is closed, for example from opening hydraulic and / or pneumatic forces acting the main valve member 390 to cause the main injection valve 210 to open and closing hydraulic and / or pneumatic forces acting the main valve member 390 to cause the main injection valve to close. With reference to FIG. 14, main control chamber 520 located at end 395 of main valve member 390, for example a proximal end of the main valve member, is employed to apply hydraulic closing forces on main valve member 390 to cause main injection valve 210 to close and remain closed. Main control chamber 520 can be pressurized with a control fluid to apply the hydraulic force on main valve member 390 when main injection valve 210 is to be closed, and the main control chamber 520 can be depressurized of the control fluid when main injection valve 210 is to be open. In some embodiments, the control fluid is the pilot fuel. Match fit 530 between main valve member 390 and nozzle 190 extends between main control chamber 520 and main fueling chamber 490. In some embodiments, like the illustrated embodiment, match fit 530 extends between liquid seal chamber 550 and main fueling chamber 490. Liquid seal chamber 550 is defined by nozzle 190 and main valve member 390 and is an annular chamber extending around main valve member 390 that can be pressurized with the control fluid to act as seal to reduce and preferably prevent the main fuel fluidly communicating from the main fueling chamber 490 into main control chamber 520 and out of dual-fuel injector 110. Match fit 530 also limits theflow of the main fuel into main control chamber 520 by reducing the flow area therethrough. Main match-fit diameter DMMF is substantially the diameter of main valve member 390 along match fit 530.

[0096] Dual-fuel injector 110 can be employed in applications where the main fuel is a gaseous fuel. As used herein, a gaseous fuel is any fuel that is in the gas state (phase) at standard temperature and pressure, which is defined herein as a temperature of zero degrees Celsius (°C) and an absolute pressure of one hundred kilopascals (kPa), respectively. Examples of gaseous fuels include ammonia, biogas, butane, ethane, hydrogen, liquefied petroleum gas, methane, natural gas, propane, and mixtures of two or more of these fuels. Gaseous fuels typically have significantly lower volumetric energy density compared to liquid fuels, such as alcohol fuels, since liquid fuels have significantly higher density than gaseous fuels under typical storage conditions. As an example, 3.8 gallons of compressed natural gas (which is primarily methane) at a pressure of 3,600 pounds per square inch (psi) has the same energy as one gasoline gallon equivalent (GGE), whereas 2 gallons of methanol at substantially atmospheric pressure has the same energy as one GGE. The composition of natural gas can vary; however, the composition typically does not vary sufficiently to significantly affect the volumetric energy density, at least relative to the ratio of volumetric energy densities between gaseous fuel and liquid fuel. Accordingly, the volumetric energy density of the main fuel is significantly lower when the main fuel is a gaseous fuel compared to when the main fuel is a liquid fuel, such as an alcohol fuel.

[0097] Desired values of the main sealing diameter DMS of main injection valve 210 (seen in FIG. 19) when the main fuel is a gaseous fuel are larger compared to when the main fuel is a liquid fuel, such as an alcohol fuel. The cross-sectional flow area through main injection valve 210 when open at a predetermined lift of main valve member 390 is larger the greater the value of main sealing diameter DMS, that is, the cross-sectional flow area through main injection valve 210 when opened to the predetermined lift increases as the main sealing diameter DMS increases. The volumetric flow of fuel at a predetermined pressure through main injection valve 210 when open for a predetermined time increases as the cross-sectional flow area through the main injection valve increases. Accordingly, when the main fuel is a gaseous fuel, it is preferred to have larger values of the main sealing diameter DMS compared to when the main fuel is a liquid fuel, since gaseous fuels have lower volumetric energy densities compared to liquid fuels, such as alcohol fuels. Desired values for the main sealing diameter DMS for a particular fuel balance low load requirements, where a small amountof fuel needs to be injected accurately, versus high load requirements, where a large amount of fuel needs to be injected within a particular injection window.

[0098] Typically, when a fuel injector is actuated to inject fuel, it goes from a closed position to a fully open position in an opening time interval, stays in the open position for a holding time interval, and then goes from the fully open position to the closed position in a closing time interval. An injection interval is equal to the sum of the opening time interval, the holding time interval, and the closing time interval. The majority of the injection interval is spent in the holding time interval for the majority of injections in typical engine operation, for example during periods of medium load and high load engine operation, and even during periods of higher values of low load operation. The cross-sectional flow area through main injection valve 210 increases during the opening time interval; the cross-sectional flow area through main injection valve 210 is constant during the holding time interval; and the cross-sectional flow area through main injection valve 210 decreases during the closing time interval. There can be oscillations in the value of the cross-sectional flow area through main injection valve 210 when main valve member 390 reaches the fully open position or the fully closed position due to the main valve member 390 bouncing off hard stops. The accuracy of injecting a predetermined quantity of fuel is reduced as the value of the holding time interval approaches the sum of the opening and closing time intervals. At very low loads, dual-fuel injector 110 may enter what is known as a ballistic mode of operation where the fuel injector spends no time in the holding time interval, that is, the injection includes the opening time interval and the closing time interval, and injection accuracy is even further reduced. The main injection pressure can be decreased when internal combustion engine 40 operates at low loads to increase the holding time interval for a predetermined injection quantity of the main fuel compared to the holding time interval when not reducing the main injection pressure, particularly when the main fuel is a gaseous fuel since the volumetric energy density of gaseous fuels is affected more by pressure changes than the volumetric energy density of liquid fuels. Internal combustion engine 40 can enter into a skip fire mode at low engine loads where some cylinders are disabled and the fueling in remaining cylinders is increased, which improves injection accuracy by increasing the injection quantity and, accordingly, the holding time interval in the remaining cylinders. The holding time interval decreases as main sealing diameter DMS increases for injecting a predetermined quantity of the main fuel at a predetermined main injection pressure at a predetermined main injection timing. Accordingly, the larger the value of themain sealing diameter DMS the higher the engine load at which dual-fuel injector 110 fails to maintain a predetermined level of injection accuracy, all else remaining the same.

[0099] There are economic advantages to employing a substantially common nozzle for the nozzle 190 and a common value for main sealing diameter DMS of main injection valve 210 in dualfuel injector 110 whether the main fuel is a gaseous fuel or the main fuel is a liquid fuel, such as an alcohol fuel. Substantive design changes like changing the nozzle and the main valve member require significant modeling and sample validation, which requires substantial engineering resources. There can be a single fuel injector manufacturing process whether the main fuel is a gaseous fuel or a liquid fuel, thereby eliminating the need to double resources for manufacturing purposes. Main valve member 390 can have common main sealing diameters DMS (seen in FIG. 19) and main match-fit diameter DMMF (seen in FIG. 14) when the main fuel is either a gaseous fuel or a liquid fuel. In some embodiments, the main sealing diameter DMS can vary within a small range. In an exemplary embodiment, the main sealing diameter DMS is 5.9 + / - 0.03 mm. In some embodiments, the main sealing diameter DMS can vary +1-5% from a nominal value depending upon whether the main fuel is a liquid fuel or the main fuel is a gaseous fuel, while maintaining the nozzle 190 and main valve member 390 substantially the same, for example while maintaining main match-fit diameter DMMF the same. In some embodiments, the main match-fit diameter DMMF can vary within a small range; for example, the main match-fit diameter DMMF can be relaxed slightly for liquid fuels, although this is not a requirement. Previously, a desired volume of the main fueling chamber 490 was smaller when the main fuel was a liquid fuel compared to when the main fuel was a gaseous fuel. In some embodiments, a volume of main fueling chamber 490 when the main fuel is a gaseous fuel is substantially equal to the volume of the main fueling chamber when the main fuel is a liquid fuel, such as an alcohol fuel. Previously, a desired volume of the main injection chamber 500 was smaller when the main fuel was a liquid fuel compared to when the main fuel was a gaseous fuel. In some embodiments, a volume of the main injection chamber 500 when the main fuel is a gaseous fuel is substantially equal to the volume of the main injection chamber when the main fuel is a liquid fuel, such as an alcohol fuel. The main injection holes 340 in the main valve member can have different main injection hole diameters DMIH (seen in FIG. 19) when the main fuel is a gaseous fuel compared to liquid fuels, such as alcohol fuels, where the main injection hole diameter DMIH is smaller for liquid fuel such that the liquid fuel can be atomized more efficiently during fuel injection. The density of the main fuel and the heating value of the main fuel influence the main hole diameter DMIH. In someembodiments, a flow area through the main injection holes 340 when the main fuel is a liquid fuel, such as an alcohol fuel is 30% or less compared to the flow area through the main injection hole when the main fuel is a gaseous fuel. Since the flow area through a cylindrical hole is proportional to the square of the diameter (area = pi * dA2 / 4), the main injection hole diameter DMIH when the main fuel is a liquid fuel, such as an alcohol fuel is -55% or less compared to when the main fuel is a gaseous fuel. The main hole number can be different for gaseous fuels compared to liquid fuels, such as alcohol fuels.

[0100] Referring now to FIG. 16, main valve member 390 has a main valve lift when it travels from the closed position to the (fully) open position, and a length of the main valve lift is a main valve lift length LMVL. That is, main valve member 390 travels a distance of the main valve lift length LMVL when it travels from the closed position to the open position. The main valve lift length LMVL can be different when the main fuel is a gaseous fuel compared to when the main fuel is a liquid fuel. In an exemplary embodiment, the main valve lift length L VL is less when the main fuel is a liquid fuel, such as an alcohol fuel, compared to when the main fuel is a gaseous fuel. The cross-sectional flow area through main injection valve 210 increases when the main valve lift length LMVL increases. It is desirable to reduce the main valve lift length LMVL when the main fuel is a liquid fuel compared to when the main fuel is a gaseous fuel, since the volumetric energy density of liquid fuels is significantly greater than that of gaseous fuels, whereby for a commanded injection quantity on an energy basis the volumetric injection quantity is less when the main fuel is a liquid fuel compared to when the main fuel is a gaseous fuel, and by reducing the cross-sectional flow area through the main injection valve for liquid fuels, in some embodiments, allows for greater injection accuracy. In some embodiments, the main valve lift is limited by a hard stop of the main valve member 390, such as by surface 560 of barrel 540 (best seen in FIG. 14). In some embodiments, the main valve lift length LMVL can be increased by decreasing a length of the main valve member 390 such that the main valve member needs to travel further before abutting the surface 560 of barrel 540. In some embodiments, the main valve lift length LMVL can be increased by moving the surface 560 of barrel 540 further away from main valve member 390 such that the main valve member 390 needs to travel further before abutting the surface 560. The surface 560 can be moved further away, for example, by removing material from barrel 540 at surface 560. Alternatively, a spacer or a shim (not shown) can be inserted between the main valve member 390 and barrel 540 when the main fuel is a liquid fuel to reduce the main valve lift length LMVL, and the spacer or the shim can be removed when the mainfuel is a gaseous fuel to increase the main valve lift length LMVL. The shim or the space can be secured to the main valve member 390 or the barrel 540.

[0101] Referring now to FIG. 20, method 600 of making dual-fuel injector 110 for introducing the main fuel into combustion chamber 200 of internal combustion engine 40 is shown. The method includes, in step 610, making nozzle 190 having valve seat 460 on inner surface 420 thereof and, in step 620, making main valve member 390 having sealing surface 465 on outer surface 435 thereof. When the main fuel is a gaseous fuel, the method includes, in step 630, forming the main injection holes 340 in nozzle 190 having a first diameter. When the main fuel is a liquid fuel, the method includes, in step 640, forming the main injection holes 340 in nozzle 190 having a second diameter. Next the method includes, in step 650, forming the main injection valve 210 between valve seat 460 of nozzle 190 and sealing surface 465 of main valve member 390. Main injection valve 210 having main sealing diameter DMS. The main injection valve 210 is closed when sealing surface 465 abuts the valve seat 460 and main injection valve 210 is open when the sealing surface is spaced apart from the valve seat. The main injection holes 340 are downstream from main injection valve 210. The first diameter of the main injection holes 340 is greater than the second diameter of the main injection hole. The main sealing diameter DMS is substantially the same within a margin whether the main fuel is the gaseous fuel or the liquid fuel.

[0102] Referring now to FIG. 21, a series of computational fluid dynamic (CFD) simulations were conducted to identify nozzle designs for internal combustion engine 40 that retain maximum rated power capabilities while operating in the run-on-pilot mode. The nozzle design parameters that were varied were the main injection hole diameter DMIH and the main hole number. The main fuel in the LCDI mode is an alcohol based fuel, as disclosed above, for example methanol or ethanol. For the CFD simulations, a base engine was employed having six cylinders (6-cyl) for a total engine displacement of 13 liters, which was operated at an engine toad of maximum rated power and an engine speed of 2400 RPM. The differences in engine efficiency, heat release rate (HRR) and nitrous oxide (NOx) emissions were compared under various scenarios. In scenario 21.1, the base engine was configured for conventional diesel engine operation (with only diesel fuel injected) by employing a diesel injection pressure of 2134 bar (referred to as the pitot fuel pressure in the table of FIG. 21), a conventional diesel injection hole diameter of substantially 0.275 mm (referred to as the main hole diameter in the table of FIG. 21), seven diesel injection holes (referred to as the main hole numberin the table of FIG. 21), and since scenario 21.1 represents conventional diesel operation there was no pilot injection. In scenario 21.2, the base engine was configured to operate in the LCDI mode where methanol is the main fuel and with pilot injections, where the pilot fuel pressure is 1000 bar and the main fuel pressure is slightly higher than 1000 bar (that is, 1000 bar minus the system bias pressure, which can be around 15 bar), the main injection hole diameter DMIH is 0.39 mm, and where there are twelve of the main injection holes 340. In scenario 21.3, the base engine was operating in the run-on-pilot mode (that is, the monofuel operating mode) where the pilot fuel was only injected through the main injection holes 340, and the base engine was configured with the pilot fuel pressure being 1000 bar (that is, the pressure of the pilot fuel in main conduit 120), main injection hole diameter DMIH of 0.39 mm, and twelve of the main injection holes 340. Scenario 21.4 is like scenario21.2 except there are nine of the main injection holes 340 instead of 12. Scenario 21.5 is like scenario21.3 except there are nine of the main injection holes 340 instead of twelve. Scenario 21.6 is like scenario 21.2 except the main injection hole diameter DMIH is 0.35 mm instead of 0.39 mm. Scenario 21.7 is like scenario 21.3 except the main injection hole diameter DMIH is 0.35 mm instead 0.39 mm. Scenario 21.8 is like scenario 21.6 except the pilot fuel pressure is 1500 bar instead of 1000 bar, and where the main fuel pressure is around 1500 bar (less the system bias pressure) instead of around 1000 bar. Scenario 21.9 is like scenario 21.7 except the pilot fuel pressure is 1500 bar instead of 1000 bar. Scenario 21.10 is like scenario 21.3 except the pilot fuel is injected through both the main injection holes 340 and the pilot injection holes 350, and noting the pilot fuel pressure in main conduit 120 and pilot conduit 130 is 1000 bar. Scenario 21.11 is like scenario 21.9 except the pilot fuel is injected through both the main injection holes 340 and the pilot injection holes 350, and noting the pilot fuel pressure in main conduit 120 and pilot conduit 130 is 1000 bar. Based on these CFD simulations, the nozzle with twelve of the main injection holes 340 and with the main injection hole diameter DMIH of 0.35 mm was selected as an exemplary embodiment when the rail pressure varied between 1000 bar to 1500 bar. In some embodiments, for internal combustion engines inclusively within a power range of 50 to 150 kW per cylinder (which can include the endpoints), the main injection hole diameter DMIH can be inclusively within a range of 0.33 mm to 0.41 mm, and the pilot injection hole diameter DPIH can be inclusively within a range of 0.1 mm and 0.15 mm. More preferably, in some embodiments, for internal combustion engines inclusively within a power range of 50 to 150 kW per cylinder, the main injection hole diameter DMIH can be inclusively within a range of 0.33 mm to 0.37 mm. And even more preferably, in some embodiments, for internal combustion engines inclusively within a power range of 50 to 150 kW per cylinder, the main injection holediameter DMIH can be inclusively within a range of 0.34 mm to 0.36 mm. In general, exemplary embodiments include twelve or more of the main injection holes 340. In addition to increasing the main hole number, the methanol injection window can be longer compared to the base diesel injection window under identical operating conditions such that the main injection hole diameter DMIH can be reduced to improve the atomization of the main fuel and the pilot fuel, and particularly the pilot fuel when injected through the main injection holes 340 in the run-on-pilot mode for improved run-on- pilot capability. Diesel has a significantly higher heating value than typical alcohol fuels. For example, the heating value of diesel fuel is approximately 42-46 MJ / kg, while the heating value of methanol is approximately 22.7 MJ / kg. For identical injection pressure and injection hole size, the injection window for methanol needs to be longer compared to diesel to inject the same quantity of fuel on an energy basis. In some embodiments, the pilot injection pressure can be between 1000 bar and 1500 bar. In some embodiments, the pilot injection pressure can be any value between 1000 bar and 1500 bar and constant, at least for most of the engine map. That is, the pilot injection pressure can be reduced in a very low-load region of the operating map, as discussed below.

[0103] Referring now to FIG. 22, there is shown an engine operating map of an injection strategy 660 for internal combustion engine 40 operating in the run-on-pilot mode illustrating engine speed on the abscissa axis (the x-axis) and engine load fraction on the ordinate axis (the y-axis). The dualfuel injector 110 can employ any nozzle design disclosed herein, particularly those associated with FIG. 21. The injection strategy includes a first injection mode and a second injection mode. The first injection mode includes injecting the pilot fuel only through the pilot injection holes 350 during the run-on-pilot mode. In some embodiments, during the first injection mode, the pilot fuel can be injected anywhere within a range inclusively between 15 CAD BTDC during the compression stroke and 25 CAD ATDC during the power stroke. The second injection mode includes injecting the pilot fuel through both the pilot injection holes 350 and the main injection holes 340 during the run-on- pilot mode, whereby there is a two pulse strategy including a run-on-pilot pilot injection of the pilot fuel through the pilot injection holes 350 and a run-on-pilot main injection of the pilot fuel through the main injection holes 340. In some embodiments, during the second injection mode, the run-on- pilot pilot injection where the pilot fuel is injected through the pilot injection holes 350 can occur anywhere within a range inclusively between 20 CAD BTDC during the compression stroke and top dead center (TDC) at an end of the compression stroke, and the run-on-pilot main injection where the pilot fuel is injected through the main injection holes 340 can occur anywhere within a rangeinclusively between 5 CAD BTDC during the compression stroke and 20 CAD ATDC during the power stroke. The run-on-pilot main injection in the second injection mode is relatively short due to the relatively large size of the main injection hole diameter DMIH. In some embodiments, like the illustrated embodiment, the pilot injection hole diameter DPIH for the pilot injection holes 350 is 0. 11 mm. With reference to FIG. 22, line 670 divides the engine map 660 between a first zone 671 and a second zone 672 when the pilot injection pressure is 1000 bar, and line 680 divides the engine map 660 between a first zone 681 and a second zone 682 when the pilot injection pressure is 1500 bar. Each of the first zones 671 and 681 has a lower range of engine speeds for each engine load compared to the respective second zones 672 and 682, and each of the first zones 671 and 672 has a lower range of engine loads for each engine speed compared to the respective second zones 681 and 682. The first zone 681 is increased in size compared to the first zone 671 and the second zone 682 is decreased in size compared to the second zone 672 since the pilot injection pressure associated with the first zone 681 and the second zone 682 (1500 bar) is greater than the pilot injection pressure associated with the first zone 671 and the second zone 672 (1000 bar). In general, as the pilot injection pressure increases, a respective first zone increases in size and a respective second zone decreases in size. Line 670 represents a dividing line between the first injection mode and the second injection mode while operating in the run-on-pilot mode with the pilot injection pressure substantially equal to 1000 bar and line 680 represents another dividing line between the first injection mode and the second injection mode while operating in the run-on-pilot mode with the pilot injection pressure substantially equal to 1500 bar. The first injection mode is selected and performed when the internal combustion engine 40 is operating in the first zone 671 below line 670 or operating in the first zone 681 below line 680. The second injection mode is selected and performed when the internal combustion engine 40 is operating in the second zone 672 on or above line 670 or operating in the second zone 682 on or above line 680. In some embodiments, the pilot injection pressure during the run-on-pilot mode can be other values between 1000 bar and 1500 bar, and each pilot injection pressure would have a respective dividing line (not shown) between the first injection mode and the second injection mode on the chart of FIG. 24 accordingly. The pilot injection pressure can be a single value (that is, constant) for the maj ority of the engine map except for a very low-load region. In some embodiments, the very low-load region is when the engine load is below at most 10% of the maximum rated power of internal combustion engine 40. In some embodiments, the very low-load region is when the engine load is below at most 5% of the maximum rated power of internal combustion engine 40. In some embodiments, the pilot injection pressure can be reduced to at most 500 bar in the very low-loadregion of the engine map. In some embodiments, the pilot injection pressure can be reduced to at most 300 bar in the very low-load region of the engine map. In some embodiments, when the pilot injection hole diameter DPIH is greater than 0.11 mm, for example when the pilot injection hole diameter DPIH is greater than 0.11 mm and less than or equal to 0.15 mm, lines 670 and 680 shift upwards and to the right whereby the internal combustion engine 40 operates over a greater portion of the engine map in the run-on-pilot mode by employing the first injection mode with injecting the pilot fuel through the pilot injection holes 350 only compared to when the pilot injection hole diameter DPIH equals 0. 11 mm. In some embodiments, when the pilot injection hole diameter DPIH is less than 0.11 mm, for example when the pilot injection hole diameter DPIH is greater than or equal to 0.1 mm and less than 0.11 mm, lines 670 and 680 shift downwards and to the left whereby the internal combustion engine 40 operates over a smaller portion of the engine map in the run-on-pilot mode by employing the first injection mode with injecting the pilot fuel through the pilot injection holes 350 only compared to when the pilot injection hole diameter DPIH equals 0. 11 mm.

[0104] Referring now to FIG. 23, injection method 690 corresponding to the injection strategy 660 of FIG. 22 is illustrated. The injection method 690 includes, in step 692, dividing an engine map between a first zone and a second zone, the first zone having a lower range of engine speeds for each engine load compared to the second zone and the first zone having a lower range of engine loads for each engine speed compared to the second zone. Examples of the first zone are the first zone 671 and the first zone 681, which correspond to 1000 bar and 1500 bar values of the pilot injection pressure (that is, the pilot fuel pressure), respectively. In step 694, employing the first injection mode during the run-on-pilot mode when the internal combustion engine 40 is operating in the first zone in the engine map where the pilot fuel is injected through the pilot injection holes 350 only. In step 696, employing the second injection mode during the run-on-pilot mode when the internal combustion engine 40 is operating in the second zone in the engine map where the pilot fuel is injected through the pilot injection holes 350 and the main injection holes 340, the run-on-pilot pilot injection of the pilot fuel is employed to inject the pilot fuel through the pilot injection holes 350 and the run-no-pilot main injection of the pilot fuel is employed to inject the pilot fuel through the main injection holes 340. The pilot fuel bums with diffusion-flame combustion in the first injection mode and the second injection mode in the run-on-pilot mode.

[0105] Referring now to FIG. 24, a series of CFD simulations were conducted to determine the effect of the run-on-pilot pitot injections in the run-on-pilot mode for the same base engine as discussed above in relation to FIG. 21 operating at an engine toad of maximum rated power and an engine speed of 2400 RPM. With reference to FIG. 24, in scenario 23.1 the base engine was configured for conventional diesel engine operation by employing a diesel injection pressure of 2100 bar (referred to as pitot injection pressure in the table of FIG. 24), a diesel injection hole diameter of 0.275 mm (referred to as main hole diameter in the table of FIG. 24), seven of the main injection holes 340, and no pitot injection. In scenario 23.2, the base engine was operating in the run-on-pilot mode with the pitot fuel only injected through the main injection holes 340 (only the run-on-pilot main injections of the pilot fuel), the base engine was configured with the pitot injection pressure equal to 1000 bar, the main injection hole diameter DMIH equal to 0.39 mm, and with twelve of the main injection holes 340. Scenario 23.3 was like scenario 23.2 except the pitot fuel was injected through both the main injection holes 340 and the pitot injection holes 350 (both the run-on-pilot main injections of the pitot fuel and the run-on-pilot pilot injections of the pitot fuel, respectively). In scenario 23.4, the base engine was operating in the run-on-pilot mode with the pitot fuel only injected through the main injection holes 340 (only the run-on-pilot main injection of the pitot fuel), the base engine was configured with the pilot injection pressure equal to 1500 bar, the main injection hole diameter DMIH equal to 0.35 mm, and with twelve of the main injection holes 340. Scenario 23.5 was like scenario 23.4 except the pitot fuel was injected through both the main injection holes 340 and the pitot injection holes 350 (both the run-on-pilot main injections of the pitot fuel and the run- on-pilot pitot injections of the pilot fuel, respectively). As is illustrated in FIG. 24, NOx emissions are substantially reduced when injecting the pitot fuel through both the main injection holes 340 and the pitot injection holes 350 compared to injecting the pitot fuel through only the main injection holes 340. In this regard, it is beneficial to employ the second injection mode with both the run-on-pilot pitot injections of the pitot fuel through the pitot injection holes 350 and the run-on-pilot main injections of the pitot fuel through the main injection holes 340 when operating in the second zone, that is at points on the engine map of FIG. 22 in the second zone 672 on or above line 670 or in the second zone 682 on or above line 680 or in other ones of the second zones for other lines associated with different values of the pitot injection pressure. By employing the second injection mode in this way, the run-on-pilot pitot injections of the pitot fuel through the pitot injection holes 350 help to control the rate of heat release and make the combustion smoother.

[0106] The concentric needle design of the dual -fuel injector 110 dictates that leakage between the main fuel and the pilot fuel can occur through a match fit inside the injector. To reduce the quantity and control the direction of the leakage, a tightly controlled system bias pressure is maintained throughout the engine map and under various dynamic conditions. Large fluctuations of the fuel pressure in main conduit 120 and pilot conduit 130 as the engine going through transient modes can significantly affect the system bias pressure between the main fuel and the pilot fuel, which increases the complexity of fuel pressure control in main conduit 120 and pilot conduit 130. The low heating value of methanol and relatively long injection duration offers an opportunity of reducing or even eliminating the dynamic rail pressure control for a large part of the engine map. The range of the fuel pressure in main conduit 120 and pilot conduit 130 between the high and low load operation can be made substantially smaller. It is even possible to use a constant fuel pressure for all operating conditions for both the LCDI operating mode and the monofuel operating mode (that is, the run-on-pilot mode). For the 6 cylinder, 13L engine, the CFD results show that 1000-1500 bar rail pressure can satisfy most of the operating conditions. When operating in the run-on-pilot mode, a significant portion of the engine map can be covered by injecting the pilot fuel through the pilot injection holes only, which facilitates good mixing quality, avoids combustion chamber wall wetting and allows using a constant rail pressure for both low and high load operation. For high-load operation during the run-on-pilot mode, injecting part of the pilot fuel through the pilot hole helps control the rate of heat release and reduce NOx.

[0107] In the LCDI operating mode where the main fuel is an alcohol fuel such as methanol, the pilot quantity 710 of the pilot fuel on an energy basis consumed by internal combustion engine 40 can be between 2% and 5% of the total quantity of fuel (including the sum of the pilot quantity 710 of the pilot fuel and the main quantity 750 of the main fuel). In the CFD simulations here where methanol was the main fuel, the pilot quantity 710 of the pilot fuel on an energy basis was 2.5% of the total fuel quantity.

[0108] In some of the embodiments when the main fuel is a gaseous fuel, the main fuel is in the liquid phase from storage to injection, that is, the main fuel is stored in the liquid phase in main fuel supply 50 (for example, in a pressure vessel or a pressure cylinder), delivered to main conduit 120 in the liquid phase, and is injected in the liquid phase by dual-fuel injector 110 and then atomizes and evaporates within combustion chamber 200. A gaseous fuel is herein defined to be any fuel that isthe gas phase at standard temperature and pressure. Gaseous fuels that are in the liquid phase when stored, delivered, and injected include but are not limited to butane, liquefied petroleum gas, propane, or mixtures of two or more of these fuels. In an exemplary embodiment, the gaseous fuel is propane. In some embodiments, when the main fuel is a gaseous fuel that is injected in the liquid phase, the main injection pressure is between and including 500 bar and 1200 bar, and preferably the main injection pressure is between and including 575 bar and 650 bar. In some embodiments, the main injection pressure is between and including 575 bar and 1200 bar. Any gaseous fuel that is the liquid phase between and including 500 bar and 1200 bar and at a temperature of 75 °C, are included in the group of gaseous fuels that are in the liquid phase when stored, delivered, and injected as used herein. In light duty engine applications the bore diameter can be less than 100 mm, in medium duty and heavy-duty engine applications the bore diameter can range from 100 mm to 180 mm, and in high horsepower engine applications the bore diameter can be above 180 mm. Large cylinder bore engines, such as heavy-duty engines and high horsepower engines are particularly suitable for operation with gaseous fuel that is injected in the liquid phase since the size of the cylinder bore reduces the likelihood of liquid phase gaseous-fuel droplets directly impinging on cylinder wall 250 and piston bowl 275 in combustion chamber 200, which leads to poor mixing and high particulate matter (PM) emissions when these phenomena occur. In exemplary embodiments, there are between six and twelve of the main injection holes 340. In some embodiments, the main injection holes 340 are evenly distributed around a circumference of nozzle 190. In some embodiments, there are an equal number of main injection holes 340 and pilot injection holes 350, such that a ratio of a pilot hold number over a main hole number, (otherwise known as a pilotmain hole ratio) is 1 : 1. In some embodiments, there are half as many pilot injection holes 350 as there are main injection holes 340, such that the pilotmain hole ratio is ~1:2. A diameter of the cylindrical bore of each of the main injection holes 340 is less than an upper diameter. The diameter of the cylindrical bore of each of the main injection holes 340 is greater than a lower diameter. In exemplary embodiments, the upper diameter of the main injection holes 340 is 0.60 millimeters (mm) and the lower diameter of the main injection hole is 0.25 mm. The main injection pressure and the diameter of the main injection holes 340 are selected to ensure adequate atomization of the main fuel (and, more particularly, the gaseous fuel in the liquid phase) for improved mixing and ignitability. The diameter of the main injection holes 340 is at or near the upper diameter when the main injection pressure is at or near the lower injection pressure, and the diameter of the main injection holes 340 is at or near the lower diameter when the main injection pressure is at or near the upper injection pressure. In some embodiments, main injectionangle 0 can vary between and including ten degrees (10°) and thirty degrees (30°), particularly when piston bowl 275 has the omega shape, such as illustrated in FIGS. 12 and 13. Each of the pilot jets 370 is injected along a respective pilot injection axis 375. Pilot injection axis 375 forms an injection angle relative to plane 380. Injection angle 0 of the pilot jets 370 can equal injection angle 0 of the main jets 360, although this is not a requirement.

[0109] In some embodiments, each of the main jets 360 can overlap the respective one of the pilot jets 370, such as is illustrated in FIG. 25 where the pilotmain hole ratio is 1 : 1 and there are nine of the main jets 360 and nine of the pilot jets 370. In some embodiments, each of the main jets 360 is spatially interlaced with the respective one of the pilot jets 370, such as is illustrated in FIG. 26 where there are nine of the main jets 360 and nine of the pilot jets 370. In the embodiment of FIG. 26, each of the pilot jets 370 is angularly disposed with respect to the longitudinal injector axis 245 of dual-fuel inj ector 110 halfway between two of the main j ets 360, although this is not a requirement and in other embodiments each of the pilot jets 370 can be angularly disposed closer to one of the main jets 360. For example, in some embodiments, adjacent ones of the main jets 360 are angularly spaced apart by main-jet-spacing angle Q with respect to longitudinal injector axis 245 and each of the pilot jets 370 is angularly spaced apart from the respective one of the main jets 360 by main-pilot- jet-spacing angle <D, where the angles Q and <D can be expressed in radians or degrees. In some embodiments, angle <D is less than Q / 2. In some embodiments, angle <D is greater than Q / 2. In some embodiments, angle <D equals Q / 2. Spatially interlacing the pilot jets 370 with the main jets 360 can be advantageous when internal combustion engine 40 operates with swirl and the main jets 360 have a different start of injection timing than the pilot jets 370. Swirl causes a fuel jet to veer off its injection trajectory, typically in a spiral path around the longitudinal cylinder axis 240. Under the conditions of swirl and different start of injection timing for the pilot fuel and the main fuel, whichever of the main jets 360 or the pilot jets 370 is injected first can drift towards the injection trajectory of the subsequently injected respective one of the pilot jets 370 or the respective one of the main jets 360 resulting in the respective ones of the main jets 360 and the respective ones of the pilot jets 370 being more favorably spatially located for igniting the main jets 360. For example, if the main jets 360 seen in FIG. 26 were injected first along the respective ones of the main injection axis 365 into a clockwise swirl motion of intake air in combustion chamber 200, the swirl would cause the main jets 360 to spiral clockwise around the cylinder axis towards the respective ones of the pilot injection axis 375 of the subsequently injected adjacent one of the pilot jets 370, whereby the mainjets 360 would be in a more favorable position for ignition due to the combustion of the pilot jets 370. It must be noted that the main jets 360 and the pilot jets 370 in FIG. 26 are illustrated without the effects of a swirl motion of intake air in combustion chamber 200 on these jets. In some embodiments, there is a desire to reduce the amount of pilot fuel consumed by internal combustion engine 40. In these embodiments, when the pilotmain hole ratio is 1:1, after the pilot jets 370 have ignited and are combusting, it is possible that pilot flames can be quenched by respective ones of the main jets 360 since the ignition energy is reduced due to the reduced quantity of the pilot fuel. In this context, it is advantageous to spatially interlace the pilot jets 370 with the main jets 360 such that the main jets 360 do not quench the flame of the pilot jets 370. Under some circumstances, combusting the pilot jets 370 when combusting can be quenched by respective ones of the main jets 360 even when they are interlaced as in FIG. 26. In this context, with reference to FIG. 27, two of the pilot jets 370 can be angularly disposed between two adjacent ones of the mainjets 360 whereby the pilotmain hole ratio is 1:1. The combined ignition energy of the adjacent ones of the pilot jets 370 provides each combusting ones of the pilot jets 370 with more resilience from being quenched by the respective adjacent ones of the mainjets 360. In some embodiments, when the pilotmain hole ratio is 1:2, each of the pilot jets 370 is angularly disposed between two of the main jets 360, such as is illustrated in FIGS. 28, 29, and 30. With reference to FIG. 28, there are six of the mainjets 360 (an even number Neven) and three (3) pilot jets 370. With reference to FIG. 29, there are nine of the main jets 360 (an odd number Nodd) and four (4) pilot jets 370 (determined by the formula floor(Nodd)). With reference to FIG. 30, there are nine of the mainjets 360 (an odd number Nodd) and five of the pilot jets 370 (determined by the formula ceil(Nodd)). In those embodiments where it is desired to reduce the amount of pilot fuel consumed by internal combustion engine 40, it is advantageous to employ the pilotmain hole ratio of 1 :2 such that the quantity of the pilot fuel in each of the pilot jets 370 is increased (compared to employing the pilotmain hole ratio of 1:1 with the same pilot fuel fraction) thereby increasing the ignition energy from each of the pilot jets 370 whereby the pilot flame from the combustion of the pilot jets 370 has more resilience against quenching from the mainjets 360. However, the embodiment of FIG. 27 employing a pair of adjacent ones of the pilot jets 370 between adjacent ones of the mainjets 360 with the pilotmain hole ratio of 1: 1 may provide improved combustion stability compared to those embodiments with the pilotmain hole ratios of 1:2.

[0110] The main injection needle and the pilot injection needle (not shown) of dual-fuel injector 110 can be angularly fixed with respect to the longitudinal injector axis 245. In some embodiments, the main injection needle and the pilot injection needle can be free to rotate about the longitudinal injector axis 245 whereby, in some circumstances when the pilot: main hole ratio is ~1 :2, the varying interlace angle between the main jets 360 and pilot jets 370 may statistically improve ignition performance.

[0111] Referring now to FIG. 32, there is shown algorithm 800 for fuel injection and combustion of a liquefied gaseous fuel in internal combustion engine 40 according to an embodiment. The main fuel is pressurized in the liquid phase to at least the main injection pressure in step 810. The main injection pressure can be greater than or equal to 500 bar and less than or equal to 1200 bar. In some embodiments, the main injection pressure is greater than 575 bar and less than 1200 bar. In exemplary embodiments, the main injection pressure is greater than 575 bar and less than 650 bar. The main fuel is injected into combustion chamber 200 in step 820 (that is, the gaseous fuel is injected in the liquid phase) within the main injection window 770 (seen in FIG. 31) whereby the main fuel atomizes within the combustion chamber. In exemplary embodiments, the main fuel atomizes before contacting the cylinder wall 250 and piston bowl 275. In step 830, the pilot fuel is injected into combustion chamber 200 and ignites within the pilot ignition window 730 (seen in FIG. 30). In some embodiments, the start of injection timing SOIPF of the pilot fuel is before the start of injection timing SOIMF of the main fuel. In some embodiments, the start of injection timing SOIPF of the pilot fuel is after the start of injection timing SOIMF of the main fuel. In some embodiments, the start of injection timing SOIPF of the pilot fuel is the same as the start of injection timing SOIMF of the main fuel. The pilot fuel auto-ignites within the combustion chamber and bums with a diffusion flame thereby increasing the temperature and pressure within the combustion chamber. Accordingly, the main fuel ignites due to the combustion of the pilot fuel and bums with a diffusion flame.

[0112] A series of CFD simulations were conducted to compare the differences in engine efficiency between a baseline engine employing LCDI and operating with natural gas, and internal combustion engine 40 of FIGS. 12 and 13 operating with propane under multiple scenarios employing various design parameters. For the CFD simulations, both the baseline engine employing LCDI and internal combustion engine 40 were configured as 11.2 liter per cylinder engines operating at an engine speed of 1200 revolutions per minute (RPM).

[0113] With reference to FIGS. 33 and 34, the CFD simulation results for the baseline engine employing LCDI and operating with natural gas, and internal combustion engine 40 operating with propane is illustrated. Both engines employed a 300 bar main injection pressure, nine of the main injection holes 340, and nine of the pilot injection holes 350. There was no interlacing of the main jets 360 with pilot jets 370 whereby the main-pilot-jet-spacing angle <D was zero (0). Both engines employed a fuel injector like dual-fuel injector 110. The main injection hole diameter DMIH for internal combustion engine 40 was substantially smaller compared to the main injection hole diameter DMIH employed in the baseline engine so that the main fuel could be atomized sufficiently. Scenario 11.1 employed a later start of inj ection timing SOIMF of the main fuel compared to scenario 11.2; and scenario 11.3 employed an earlier start of injection timing SOIMF of the main fuel compared to scenario 11.4. The bar chart in FIG. 34 shows the normalized gross indicated efficiency for scenarios 11.1, 11.2, 11.3, and 11.4 tabulated in FIG. 33. The baseline engine employing LCDI and operating with natural gas exhibited significantly better gross indicated efficiency compared to internal combustion engine 40 operating with propane. The conclusion drawn from this simulation was that the operating parameters of internal combustion engine 40 operating with propane need to be adjusted further in order to improve performance.

[0114] Referring now to FIGS. 35 and 36, the CFD simulation results are illustrated for internal combustion engine 40 operating with propane and a variety of main injection pressures. All scenarios in FIG. 35 employed nine of the main injection holes 340 and nine of the pilot injection holes 350. The diameter of each of the main injection holes 340 was selected for each of the main injection pressures employed for improved atomization of the main fuel. Scenario 13.1 employed later start of injection timing SOIMF of the main fuel compared to scenario 13.2, although both scenarios 13.1 and 13.2 employed the same main injection pressure; and scenario 13.3 employed later start of injection timing SOIMF of the main fuel compared to scenario 13.4, although both scenarios 13.3 and 13.4 employed the same main injection pressure. The bar chart in FIG. 36 shows the normalized gross indicated efficiency for scenarios 13.1, 13.2, 13.3, 13.4, 13.5, and 13.6 tabulated in FIG. 35. Scenario 13.5 with the main injection pressure equal to 900 bar exhibited the highest efficiency followed by scenario 13.3 with the main injection pressure equal to 600 bar in a close second place. Scenarios 13.3, 13.4, 13.5, and 13.6 with the main injection pressure equal to and above 600 bar all exhibit relatively better performance compared to scenarios 13.1 and 13.2 with the main injection pressure equal to 300 bar. Injection pressure of 300 bar is employed for gaseous fuels injected in thegas phase, but for gaseous-fuel injected in the liquid phase this injection pressure did not produce good mixing quality and combustion efficiency. In some embodiments, it is preferable to select the main injection pressure within a range defined as greater than 575 bar and less than 650 bar rather than higher pressures, since the performance within this range is comparable to higher pressures but the cost of components and piping that are rated for this range is less than the cost of components and piping rate for higher pressures such as 900 bar.

[0115] With reference to FIGS. 37 and 38, the CFD simulation results for high gross indicated mean effective pressure (IMEP) operation is illustrated for the baseline engine employing LCDI and operating with natural gas, and internal combustion engine 40 operating with propane. All scenarios employed nine of the main injection holes 340 and nine of the pilot injection holes 350. A higher boost pressure was employed compared to simulations for lower gross IMEP operation (seen in FIGS. 33 to 36) to maintain an equivalence ratio at around 0.6. Scenario 15.1 employed later start of injection timing SOIMF of the main fuel and a larger diameter for the main injection holes 340 compared to scenario 15.2. Scenario 15.3 employed a higher main injection pressure compared to scenarios 15.1 and 15.2. The diameter of 0.56 mm of the main injection holes 340 for scenario 15.3 (of FIG. 15) was selected for improved atomization. The bar chart in FIG. 38 shows the normalized gross indicated efficiency for scenarios 15.1, 15.2, and 15.3 tabulated in FIG. 37. Internal combustion engine 40 operating with propane in scenario 15.3 exhibited the best gross indicated efficiency compared to the baseline LCDI engine.

[0116] Referring now to FIGS. 39 and 40, the CFD simulation results are illustrated for internal combustion engine 40 operating with propane and a variety of main injection pressures and number of the main injection holes 340. Scenarios 17.1 and 17.3 compared operating with nine and twelve of the main injection holes 340, respectively with the main injection pressure equal to 300 bar. The diameter of the main injection holes 340 was reduced in scenario 17.3 (with more main injection holes) compared to scenario 17.1. Scenarios 17.2 and 17.4 compared operating with nine and twelve of the main injection holes 340, respectively with the main injection pressure equal to 600 bar. The diameter of each of the main injection holes 340 was reduced in scenario 17.4 (with more main injection holes) compared to scenario 17.2. The bar chart in FIG. 40 shows the normalized gross indicated efficiency for scenarios 17.1, 17.2, 17.3, and 17.4 tabulated in FIG. 17. Scenarios 17.2 and 17.4 with higher main injection pressure exhibited significantly better gross indicated efficiencycompared to scenarios 17.1 and 17.3. Scenario 17.2 with fewer main injection holes exhibited significantly better gross indicated efficiency compared to scenario 17.4.

[0117] Referring now to FIG. 41, a CFD simulation was performed to determine the desired main injection pressure for a specified rated power per engine cylinder with different main injection hole diameters for a fuel injector nozzle with nine of the main injection holes 340. Three sizes for main injection holes 340 were selected: 0.25 mm, 0.325 mm, and 0.48 mm. For each size, nozzle 190 had nine of the main injection holes 340. Since the per-cylinder fuel flow rate is the most relevant value for the nozzle, the data were plotted against the per-cylinder power rating rather than the rated power for the engine. The minimum main injection pressure for rated power was set at 600 bar for acceptable atomization; although in other embodiments, the minimum main injection pressure can be set to values greater than 575 bar and less than 650 bar. The main injection holes 340 size selection is constrained by the maximum injection duration at high toad and minimum injection duration at idle. That is, no less than the desired amount of main fuel must be injected within the maximum injection duration at high toad, and no more than the desired amount of main fuel must be injected within the minimum injection duration at idle. For example, the nozzle with 0.48 mm for the main injection hole diameter DMIH may be less suitable for engines below a certain power rating due to violation of minimum injection duration at idle. Based on these and other similar CFD simulations, in some embodiments it has been determined that for engines between 2.0 to 3.0L per cylinder and operating with a maximum boost pressure between 2 and 4 bar absolute pressure, the main injection hole diameter DMIH can be between 0.25 mm and 0.35 mm, and for engines between 11 to 15L per cylinder and operating with a maximum boost pressure between 2 and 4 bar absolute pressure, the main injection hole diameter DMIH can be between 0.48 mm and 0.60 mm. In some embodiments, particularly when the number of main injection holes is nine, nozzle 190 with main injection holes 340 having the main injection hole diameter DMIH between 0.25 and 0.325 mm will be suitable when internal combustion engine 40 has a maximum power rating between 50 to 130 kilowatts (kW) per cylinder; nozzle 190 with main injection holes 340 having the main injection hole diameter DMIH between 0.325 to 0.48 mm will be suitable when internal combustion engine 40 has a maximum power rating between 130 to 225 kW per cylinder; and nozzle 190 with main injection holes 340 having the main injection hole diameter DMIH of at least 0.48 mm and preferably at most 0.60 mm will be suitable when internal combustion engine 40 has a maximum power rating above 225 kW per cylinder.

[0118] In the LCDI operating mode where the main fuel is a gaseous fuel injected into combustion chamber 200 in the liquid phase such as propane, the pilot quantity 710 of the pilot fuel on an energy basis consumed by internal combustion engine 40 can be between 1.5% and 5% of the total quantity of fuel (including the sum of the pilot quantity 710 of the pilot fuel and the main quantity 750 of the main fuel). In the CFD simulations herein where propane was the main fuel, the pilot quantity 710 of the pilot fuel on an energy basis was 2.5% of the total fuel quantity. When the main fuel is a gaseous fuel injected into combustion chamber 200 in the liquid phase such as propane, dual-fuel injector 110 can employ the nozzle design disclosed above for methanol in relation to FIG. 21. That is, the dual-fuel injector 110 can include twelve or more of the main injection holes 340, where the main injection hole diameter DMIH for each of the main injection holes 340 is inclusively within a range of 0.33 millimeters and 0.41 millimeters, and twelve or more of the pilot injection holes 350, where the pilot injection hole diameter DPIH of each of the pilot injection holes 350 is inclusively within a range of 0.10 millimeters and 0.15 millimeters. The injection strategy 660 for internal combustion engine 40 operating in the run-on-pilot mode can be employed when the main fuel is the gaseous fuel injected into combustion chamber 200 in the liquid phase, such as propane; and in this circumstance, in the LCDI operating mode, the main injection pressure can be inclusively within the range of 575 bar and 1200 bar, and in the run-on-pilot mode, in some embodiments, the pilot injection pressure can be within the 575 bar and 1200 bar range, and in some embodiments, the pilot injection pressure can be within the 1000 bar and 1200 bar range. This allows internal combustion engine 40 to operate at the maximum rated power in the run-on-pilot mode discussed above for alcohol fuel, like methanol. Alternatively, the pilot injection pressure can be within the 1000 bar and 1500 bar range when the main fuel is a gaseous fuel injected in the liquid phase, like propane, in the LCDI mode and the run-on-pilot mode, for improved atomization of the main fuel and the pilot fuel, particularly the pilot fuel.

[0119] It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It should be understood that the data so used may be interchanged under appropriate circumstances such that embodiments of the application described herein may be used. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a nonexclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list ofsteps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

[0120] Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention which are intended to be illustrative, and not restrictive.

[0121] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in an exemplary embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrase “in other embodiments,” as used herein does not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope of the invention. The term “and / or” is used herein to mean “one or the other or both.” In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and / or,” unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references.

[0122] Any reference in the specification to a method should be applied mutatis mutandis to a system capable of executing the method. Any reference in the specification to a system should be applied mutatis mutandis to a method that may be executed by the system.

[0123] While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

Claims

1. Claims1. A fuel supply system for a main fuel and a pilot fuel for an internal combustion engine comprising a main fuel supply; a first main pump pressurizing the main fuel from the main fuel supply to a main intermediate pressure; a second main pump pressurizing the main fuel from the main intermediate pressure to at least a main injection pressure; a main conduit for supplying the main fuel to the internal combustion engine at the main injection pressure; a pilot fuel supply; a first pilot pump pressurizing the pilot fuel from the pilot fuel supply to a pilot intermediate pressure; a second pilot pump fluidly receiving the pilot fuel from the first pilot pump and pressurizing the pilot fuel from the pilot intermediate pressure to at least a pilot injection pressure; a pilot conduit for supplying the pilot fuel to the internal combustion engine at the pilot injection pressure; and at least one of:(1) a first valve selectively fluidly connecting the second pilot pump with the main conduit whereby the pilot fuel at the pilot injection pressure can be fluidly communicated to the main conduit;(2) a second valve selectively fluidly connecting the first pilot pump with the second main pump whereby the pilot fuel at the pilot intermediate pressure can be fluidly communicated to the second main pump such that the second main pump can pressurize the pilot fuel further; and(3) a third valve selectively fluidly connecting the pilot fuel supply with the first main pump whereby the pilot fuel at a pilot tank pressure in the pilot fuel supply can be fluidly communicated to the first main pump such that the first main pump can pressurize the pilot fuel; wherein in a first operating mode the main fuel is supplied to the main conduit and the pilot fuel is supplied to the pilot conduit, and in a second operating mode the pilot fuel is supplied to the main conduit and the pilot conduit.

2. The fuel supply system as claimed in claim 1, further comprising at least one of(1) a first check valve fluidly connecting the second main pump and the main conduit and allowing fluid flow from the second main pump to the main conduit and blocking fluid flow from the first valve to the second main pump; and(2) a second check valve fluidly connecting the first main pump and the second main pump and allowing fluid flow from the first main pump to the second main pump and blocking fluid flow from the second valve to the first main pump.

3. The fuel supply system as claimed in claim 1 or 2, wherein the first valve, the second valve, and the third valve are solenoid valves.

4. The fuel supply system as claimed in any one of claims 1-3, wherein the first valve and the second valve are single-pole, single-throw valves.

5. The fuel supply system as claimed in claim 1, wherein the first valve is a single-pole, double-throw valve, where in a first position the first valve fluidly connects the second main pump with the main conduit and in a second position the first valve fluidly connects the second pilot pump with the main conduit.

6. The fuel supply system as claimed in claim 1, wherein the second valve is a single-pole, doublethrow valve, where in a first position the second valve fluidly connects the first main pump with thesecond main pump and in a second position the second valve fluidly connects the first pilot pump with the second main pump.

7. The fuel supply system as claimed in claim 1, wherein the third valve is a single-pole, doublethrow valve, where in a first position the third valve fluidly connects the main fuel supply with the first main pump and in a second position the third valve fluidly connects the pilot fuel supply with the first main pump.

8. The fuel supply system as claimed in claim 1, wherein the third valve comprises a first single pole, single throw valve and a second single pole, single throw valve; the first single pole, single throw valve fluidly connects the main fuel supply with the first main pump and the second single pole, single throw valve fluidly connects the pilot fuel supply with the first main pump.

9. The fuel supply system as claimed in any one of claims 1-8, further comprising a pressure regulator fluidly connecting the second main pump with the main conduit and regulating a pressure of the main fuel from the second main pump to the main injection pressure.

10. The fuel supply system as claimed in claim 9, wherein the pressure regulator regulates the pressure of the main fuel relative to the pressure of the pilot fuel in the pilot conduit.

11. The fuel supply system as claimed in any one of claims 1-8, further comprising a pressure regulator fluidly connecting the second pilot pump with the pilot conduit and regulating a pressure of the pilot fuel from the second pilot pump to the pilot injection pressure.

12. The fuel supply system as claimed in claim 11, wherein the pressure regulator regulates the pressure of the pilot fuel relative to the pressure of the main fuel in the main conduit.

13. The fuel supply system as claimed in any one of claims 1-12, wherein the main injection pressure is less than the pilot injection pressure.

14. The fuel supply system as claimed in any one of claims 1-13, wherein the pilot injection pressure is greater in the second operating mode compared to the first operating mode.

15. The fuel supply system as claimed in any one of claims 1-13, whereinthe main fuel is injected into a combustion chamber of the internal combustion engine through a main injection hole and the pilot fuel is injected into the combustion chamber of the internal combustion engine through a pilot injection hole, the pilot injection pressure is less in the second operating mode compared to the first operating mode when the pilot fuel is injected through the main injection hole; and the pilot injection pressure is greater in the second operating mode compared to the first operating mode when the pilot fuel is injected only through the pilot injection hole.

16. The fuel supply system as claimed in any one of claims 1-15, wherein the pilot fuel is diesel fuel, dimethyl either, or kerosene.

17. The fuel supply system as claimed in any one of claims 1-16, wherein the main fuel is a liquid fuel.

18. The fuel supply system as claimed in any one of claims 1-17, wherein the main fuel is an alcohol fuel.

19. The fuel supply system as claimed in claim 18, wherein the main fuel is bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels.

20. A fuel injector for a main fuel comprising: a nozzle having an inner surface and an outer surface, the nozzle including a main injection hole extending from the inner surface to the outer surface and a main valve seat on the inner surface thereof, the main injection hole having a main injection hole diameter; a main valve member including an inner surface and an outer surface, a main sealing surface on the outer surface thereof; a main injection valve including the main valve seat and the main sealing surface, the main injection valve is closed when the main sealing surface abuts the main valve seat and open when the main sealing surface is spaced apart from the main valve seat, the main injection valve having a main sealing diameter defined by the main valve seat and the main sealing surface;wherein for each main injection pressure, the main injection hole diameter is greater when the main fuel is a gaseous fuel compared to when the main fuel is a liquid fuel; and the main sealing diameter of the main injection valve is the same within a margin for when the main fuel is the gaseous fuel and when the main fuel is the liquid fuel.

21. The fuel injector as claimed in claim 20, wherein when the main fuel is a liquid fuel, the main injection hole diameter is between 0.3125 millimeters and 0.75 millimeters.

22. The fuel injector as claimed in claim 20 or claim 21, wherein the margin is + / -5% of a nominal value of the main sealing diameter.

23. The fuel injector as claimed in any one of claims 20-22, further comprising a main valve lift length of the main valve member between the closed position and the open position of the main injection valve; wherein the main valve lift length is less when the main fuel is a liquid fuel compared to when the main fuel is a gaseous fuel.

24. The fuel injector as claimed in any one of claims 20-23, further comprising a match fit between the nozzle and the main valve member, wherein a main match-fit diameter of the main valve member along the match fit remains the same whether the main fuel is a liquid fuel or the main fuel is a gaseous fuel.

25. The fuel injector as claimed in claim 24, further comprising a main control chamber disposed at an end of the main valve member providing closing hydraulic forces on the main valve member when pressurized with a control fluid; and a main fueling chamber disposed between a main fuel inlet of the fuel injector and the main injection valve;wherein the match fit extends between the main control chamber and the main fueling chamber.

26. The fuel injector as claimed in claim 25, further comprising a liquid seal chamber extending around the main valve member, wherein the match fit extends between the liquid seal chamber and the main fueling chamber.

27. The fuel injector as claimed in any one of claims 20-26, further comprising a main fueling chamber upstream of the main injection valve, a volume of the main fueling chamber when the main fuel is a gaseous fuel is substantially equal to a volume of the main fueling chamber when the main fuel is a liquid fuel.

28. The fuel injector as claimed in any one of claims 20-27, further comprising a main injection chamber disposed between the main injection valve and the main injection hole, a volume of the main injection chamber when the main fuel is a gaseous fuel is substantially equal to a volume of the main injection chamber when the main fuel is a liquid fuel.

29. The fuel injector as claimed in any one of claims 20-28, further comprising a main injection axis of the main inj ection hole, a longitudinal axis of the fuel inj ector, and a horizontal plane perpendicular to the longitudinal axis, wherein a main injection angle of the main injection axis to the horizontal plane is within a range of 14 degrees to 30 degrees when the main fuel is a gaseous fuel and within a range of 10 degrees to 30 degrees when the main fuel is a liquid fuel.

30. The fuel injector as claimed in any one of claims 20-29, further comprising a main valve seat angle(5), wherein a main valve seat angle when the main fuel is a gaseous fuel is substantially equal to the main valve seat angle when the main fuel is a liquid fuel.

31. The fuel injector as claimed in any one of claims 20-30, wherein the main fuel is a liquid fuel.

32. The fuel injector as claimed in any one of claim 20-31, wherein the main fuel is an alcohol fuel.

33. The fuel injector as claimed in any one of claims 20-32, wherein the main fuel is bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels.

34. The fuel injector as claimed in any one of claims 20-33, wherein the fuel injector is a dual fuel injector for injecting the main fuel and a pitot fuel.

35. The dual fuel injector as claimed in claim 34, wherein the main valve member includes a pitot injection hole extending from the inner surface to the outer surface and a pitot valve seat on the inner surface of the main valve member, the dual fuel injector further comprising: a pitot valve member movable along a longitudinal axis of the dual fuel injector within the main valve member, the pitot valve member including a pitot sealing surface on an outer surface thereof; and a pilot injection valve including the pitot valve seat and the pitot sealing surface, the pitot injection valve is closed when the pitot sealing surface abuts the pitot valve seat and open when the pitot sealing surface is spaced apart from the pitot valve seat.

36. The dual fuel injector as claimed in claim 34 or 35, wherein the pitot fuel is diesel fuel, dimethyl either, or kerosene.

37. A method of making a fuel injector for introducing a main fuel into a combustion chamber of an internal combustion engine, the method comprising making a nozzle having a valve seat on an inner surface thereof; making a main valve member having a sealing surface on an outer surface thereof; when a main fuel is a gaseous fuel, forming a main injection hole in the nozzle having a first diameter; when the main fuel is a liquid fuel, forming the main injection hole in the nozzle having a second diameter; forming a main injection valve between the valve seat of the nozzle and the sealing surface of the main valve member, the main injection valve having a main sealing diameter, the maininjection valve closed when the sealing surface abuts the valve seat and the main injection valve open when the sealing surface is spaced apart from the valve seat; wherein the main injection hole is downstream from the main injection valve, the first diameter of the main injection hole is greater than the second diameter of the main injection hole, and the main sealing diameter is substantially the same within a margin whether the main fuel is the gaseous fuel or the liquid fuel.

38. The method of making the fuel injector as claimed in claim 37, further comprising forming a match fit between at least a portion of the inner surface of the nozzle and at least a portion of an outer surface of the main valve member, the match fit upstream of the main injection valve and having a main match-fit diameter; wherein the main match-fit diameter is substantially the same whether the main fuel is the gaseous fuel or the liquid fuel.

39. The method of making the fuel injector as claimed in claim 37 or 38, wherein the margin is at most +1-5% of a nominal value of the main sealing diameter.

40. A nozzle apparatus for a dual-fuel injector that injects a pilot fuel and a main fuel into a combustion chamber of an internal combustion engine comprising twelve or more main injection holes, each main injection hole comprises a main injection hole diameter inclusively within a range of 0.33 millimeters and 0.41 millimeters; and twelve or more pilot injection holes, each pilot injection hole comprises a pilot injection hole diameter inclusively within a range of 0.10 millimeters and 0.15 millimeters; wherein a pilot injection pressure for the pilot fuel is between 1000 bar and 1500 bar, and a main injection pressure is equal to a difference between the pilot injection pressure and a system bias pressure where the system bias pressure is within a range of 0 bar and 100 bar; wherein the main fuel is an alcohol fuel or a gaseous fuel that is injected in the liquid phase.

41. The nozzle apparatus as claimed in claim 40, wherein the main injection hole diameter is within a range of 0.33 millimeters and 0.37 millimeters.

42. The nozzle apparatus as claimed in claim 40, wherein the main injection hole diameter is within a range of 0.34 millimeters and 0.36 millimeters.

43. The nozzle apparatus as claimed in claim 40, wherein the main injection hole diameter is substantially 0.35 millimeters.

44. The nozzle apparatus as claimed in claim 43, wherein the pilot injection hole diameter is within a range of 0.1 mm and 0.15 mm.

45. The nozzle apparatus as claimed in claim 40, wherein the internal combustion engine has a power rating within a range of 50 to 150 kilowatts per cylinder.

46. The nozzle apparatus as claimed in claim 40, wherein the alcohol fuel is bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels and the gaseous fuel is butane, liquefied petroleum gas, propane, or mixtures of two or more of these fuels.

47. A fuel injection method for a dual-fuel injector that injects a pilot fuel and a main fuel into a combustion chamber of an internal combustion engine, the dual -fuel injector comprising pilot injection holes for the pilot fuel and main injection holes for the main fuel, the fuel injection method comprising: dividing an engine map between a first zone and a second zone, the first zone having a lower range of engine speeds for each engine load compared to the second zone and the first zone having a lower range of engine loads for each engine speed compared to the second zone; employing a first injection mode during a run-on-pilot mode when the internal combustion engine is operating in the first zone in the engine map where the pilot fuel is injected through the pilot injection holes only; and employing a second injection mode during the run-on-pilot mode when the internal combustion engine is operating in the second zone in the engine map where the pilot fuel is injected through the pilot injection holes and the main injection holes, a run-on-pilot pilotinjection of the pilot fuel is employed to inject the pilot fuel through the pilot injection holes and a run-on-pilot main injection of the pilot fuel is employed to inject the pilot fuel through the main injection holes; wherein the pilot fuel bums with diffusion-flame combustion in the first injection mode and the second injection mode.

48. The fuel injection method as claimed in claim 47, wherein for each pilot injection pressure, the engine map is divided into the first zone and the second zone such that as the pilot injection pressure increases, the first zone increases in size and the second zone decreases in size.

49. The fuel injection method as claimed in claim 47, wherein during the first injection mode, a pilot injection of the pilot fuel through the pilot injection holes occurs anywhere between a range inclusively between 15 crank angle degrees before top dead center during a compression stroke and 25 crank angle degrees after top dead center during a power stroke; and during the second injection mode, the run-on-pilot pilot injection where the pilot fuel is injected through the pilot injection holes occurs anywhere within a range inclusively between 20 crank angle degrees before top dead center during the compression stroke and top dead center at an end of the compression stroke, and the run-on-pilot main injection where the pilot fuel is injected through the main injection holes occurs anywhere within a range inclusively between 5 crank angle degrees before top dead center during the compression stroke and 20 crank angle degrees after top dead center during the power stroke.

50. The fuel injection method as claimed in claim 47, wherein the internal combustion engine is operated at substantially a maximum rated power in the second injection mode in the run-on-pilot mode.

51. The fuel injection method as claimed in claim 47, further comprising employing a single value for a pilot injection pressure for a majority of the engine map except for when the engine load is below at most 10% of a maximum rated power.

52. The fuel injection method as claimed in claim 51, further comprising employing the single value for the pilot injection pressure for the majority of the engine map except for when the engine load is below at most 5% of the maximum rated power.

53. The fuel injection method as claimed in claim 47, further comprising providing each of the main injection holes with a main injection hole diameter inclusively within a range of 0.33 millimeters and 0.41 millimeters.

54. The fuel injection method as claimed in claim 53, further comprising providing the dual-fuel injector with at least twelve of the main injection holes.

55. The fuel injection method as claimed in claim 52, wherein the main fuel is an alcohol fuel.

56. The fuel injection method as claimed in claim 55, wherein the alcohol fuel is bioalcohol, butanol, ethanol, methanol, propanol, or mixtures of two or more of these fuels.

57. The fuel injection method as claimed in claim 56, wherein a pilot injection pressure in the first injection mode and the second injection mode during the run-on-pilot mode is inclusively within a range of 1000 bar and 1500 bar.

58. The fuel injection method as claimed in claim 53, wherein the main fuel is butane, liquefied petroleum gas, propane, or mixtures of two or more of these fuels.

59. The fuel injection method as claimed in claim 58, wherein a pilot injection pressure in the first injection mode and the second injection mode during the run-on-pilot mode is inclusively within a range of 575 bar and 1200 bar.

60. The fuel injection method as claimed in claim 58, wherein a pilot injection pressure in the first injection mode and the second injection mode during the run-on-pilot mode is inclusively within a range of 1000 bar and 1500 bar.

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