EP4735752A1

EP4735752A1 - Apparatus and method for supplying gaseous fuel to and operating an internal combustion engine

Info

Publication number: EP4735752A1
Application number: EP24829680.8A
Authority: EP
Inventors: Jian Huang; Adrian Post
Original assignee: Cespira Canada LP
Current assignee: Cespira Canada LP
Priority date: 2023-06-28
Filing date: 2024-06-26
Publication date: 2026-05-06
Also published as: WO2025000091A1; CN121420129A

Abstract

An apparatus for supplying a gaseous fuel and operating an internal combustion engine includes a supply storing the gaseous fuel as a compressed gas; a compressor selectively pressurizing the gaseous fuel received from the supply; a pressure regulator receiving the gaseous fuel selectively from the supply or from the compressor; a gaseous-fuel rail fluidly receiving the gaseous fuel from the pressure regulator; an in-cylinder injector receiving the gaseous fuel from the gaseous-fuel rail and directly introducing the gaseous fuel into a combustion chamber; the in-cylinder injector commanded in a first operating mode when the gaseous-fuel rail pressure is equal to or greater than a desired injection pressure; and the in-cylinder injector commanded in a second operating mode when the gaseous-fuel rail pressure is less than the desired injection pressure.

Description

APPARATUS AND METHOD FOR SUPPLYING GASEOUS FUEL TO AND OPERATING AN INTERNAL COMBUSTION ENGINE

Technical Field

[0001] The present application relates to an apparatus and method for supplying gaseous fuel to and operating an internal combustion engine, and in particular to applications employing a gaseous fuel stored as a compressed gas.

Background

[0002] Internal combustion engines that are fueled with gaseous fuels stored in the gas or supercritical state in pressurized storage tanks, such as compressed hydrogen (CH2) and compressed natural gas (CNG), can employ in-cylinder injectors to directly introduce the gaseous fuel into combustion chambers of the engine after intake valves close to increase engine power. Engine efficiency also increases when the gaseous fuel is injected late in a compression cycle of the engine such that the gaseous fuel bums in a diffusion combustion mode in what is known as a Diesel-cycle, where the compression ratio can be increased without the risk of premature ignition (knock) compared to when the gaseous fuel is injected early during the compression stroke where the gaseous fuel bums in a premixed combustion mode. In the Diesel-cycle there is a desired value of an injection pressure of the gaseous fuel that is characterized by an optimal or near to optimal efficiency that is capable for the engine. That is, as the rail pressure increases above the desired injection pressure the engine efficiency only marginally increases, whereas as the rail pressure decreases below the desired injection pressure the engine efficiency substantially decreases. The desired injection pressure can be a function of the engine load and engine speed.

[0003] When the storage tanks are refilled, they are typically pressurized to a pressure of 350 bar or 700 bar, although other pressures are contemplated. In an exemplary embodiment the desired injection pressure is around 300 bar. As the gaseous fuel is consumed by the engine the pressure in the storage tanks decreases, and as the storage tank pressure drops below the desired injection pressure, a compressor can be employed to pressurize the gaseous fuel to the desired injection pressure. Even though the compressor is a parasitic load on the engine, it can increase the overall engine efficiency by pressurizing the gaseous fuel to the desired injection pressure. As the storage tank pressure continues to decrease, the parasitic load of the compressor continues to increase since more work is required to compress the gaseous fuel to the desired injection pressure. Eventually the energetic cost of the parasitic load of the compressor is greater than the improvements in engine efficiency by injecting at the desired injection pressure. Additionally, or alternatively, eventually the storage tank pressure drops to a value where the compressor is either incapable of pressurizing the gaseous fuel to the desired injection pressure (to a pressure ratio of the compressor) or is incapable of providing a demanded mass flow rate of the gaseous fuel to the engine.

[0004] The size of the compressor also influences the operation of the engine. A larger compressor can provide a mass flow rate of the gaseous fuel at the desired injection pressure required by the engine to operate at maximum rated power at lower values of storage tank pressure compared to a smaller compressor. However, the larger compressor is typically a larger parasitic load on the engine compared to the smaller compressor for storage tank pressures within a range below and up to the desired injection pressure.

[0005] Two or more injection pressures can be used for distinct parts of the engine map to reduce the losses from the parasitic load of the compressor, since the optimal injection pressure is also a function of engine load. For example, at lower engine loads a first pressure regulator can be employed to provide a lower injection pressure and a second pressure regulator can be used to provide a higher injection pressure at higher engine loads, whereby during the lower engine loads the storage tank pressure is increased to the lower injection pressure and the work required from the compressor to pressurize to the lower injection pressure is reduced compared to pressurizing to the higher injection pressure. Instead of different pressure regulators, a variable pressure regulator can also be employed to provide two or more regulated pressures. These solutions increase the cost of the engine system through increased component count and fuel system complexity.

[0006] The state of the art is lacking in techniques for supplying gaseous fuel to and operating an internal combustion engine. The present apparatus and method provide a technique for improving the supply of gaseous fuel to and operating an internal combustion engine. Summary

[0007] An improved apparatus for supplying a gaseous fuel to and operating an internal combustion engine includes a first supply of the gaseous fuel storing the gaseous fuel as a compressed gas at a first supply pressure; a compressor selectively pressurizing the gaseous fuel fluidly received from the first supply to a pressurized pressure; a pressure regulator fluidly receiving the gaseous fuel selectively from the first supply at the first supply pressure or from the compressor at the pressurized pressure and fluidly providing the gaseous fuel at a delivery pressure; a gaseous-fuel rail fluidly receiving the gaseous fuel from the pressure regulator; an incylinder injector fluidly receiving the gaseous fuel from the gaseous-fuel rail and configured to directly introduce the gaseous fuel into a combustion chamber of the internal combustion engine, the in-cylinder injector injecting the gaseous fuel at a gaseous-fuel rail pressure PGFR; a controller operatively connected with the in-cylinder injector and programmed to command the in-cylinder injector in a first operating mode when the gaseous-fuel rail pressure PGFR is equal to or greater than a desired injection pressure; and command the in-cylinder injector in a second operating mode when the gaseous-fuel rail pressure PGFR is less than the desired injection pressure. In the first operating mode the pressure regulator fluidly receives the gaseous fuel from the first supply when the first supply pressure is greater than or equal to the desired injection pressure, and from the compressor when the first supply pressure is less than the desired injection pressure. In the first operating mode both the first supply and the compressor can deliver a demanded mass flow rate of the gaseous fuel by the internal combustion engine whereby the gaseous-fuel rail pressure PGFR is equal to the desired injection pressure. In the second operating mode the first supply pressure is less than the desired injection pressure such that the pressure regulator fluidly receives the gaseous fuel from the compressor. In the second operating mode the demanded mass flow rate of the gaseous fuel is greater than a mass flow rate of the gaseous fuel delivered by the compressor whereby the gaseous-fuel rail pressure PGFR is less than the desired injection pressure.

[0008] In some embodiments, the gaseous fuel bums in a diffusion combustion mode in the first and second operating modes. In some embodiments, a start of injection timing is earlier in a compression stroke and an injection duration is greater in the second operating mode compared to the first operating mode for a commanded injection mass. In some embodiments, the internal combustion engine can operate at a maximum rated power in the first and second operating modes. In some embodiments, in the first operating mode the gaseous-fuel rail pressure PGFR equals the desired injection pressure for both a low-power demand and a high-power demand of the internal combustion engine. In some embodiments, the pressure regulator fluidly receives the gaseous fuel from the first supply in the second operating mode when the first supply pressure is less than the desired injection pressure and greater than or equal to a parasitic threshold pressure PPT. The parasitic threshold pressure PPT can be in a range of 150 to 300 bar. In some embodiments, in the second operating mode the pressure regulator fluidly provides the gaseous fuel to the gaseous-fuel rail at an unregulated pressure since the mass flow rate of the gaseous fuel from the compressor is less than the demanded mass flow rate of the gaseous fuel by the internal combustion engine. In some embodiments, in the second operating mode the gaseous-fuel rail pressure PGFR continues to decrease further below the desired injection pressure after each injection by the in-cylinder injector.

[0009] In some embodiments, the controller is further programmed to command the incylinder injector to switch from the second operating mode to a third operating mode when the gaseous-fuel rail pressure PGFR is less than a mid-cycle direct injection threshold pressure PMCDI-T. In the third operating mode the pressure regulator can fluidly receive the gaseous fuel from the compressor and the demanded mass flow rate of the gaseous fuel by the internal combustion engine can be greater than the mass flow rate of the gaseous fuel delivered by the compressor. In the third operating mode, the gaseous fuel bums in a partially premixed combustion mode, a start of injection timing is earlier in a compression stroke and an injection duration is greater in the third operating mode compared to the second operating mode for a commanded injection mass, and the internal combustion engine can operate at a maximum rated power. In some embodiments, the first operating mode is commanded when the first supply pressure is greater than or equal to the desired injection pressure or when the first supply pressure is less than a parasitic threshold pressure PPT and greater than or equal to a compressor threshold pressure PCT; the second operating mode is commanded when the first supply pressure is less than the desired injection pressure and greater than or equal to the parasitic threshold pressure PPT, or when the first supply pressure is less than the compressor threshold pressure PCT and when the gaseous-fuel rail pressure PGFR is greater than or equal to the mid-cycle direct injection threshold pressure PMCDI-T, and wherein the pressure regulator fluidly receives the gaseous fuel from the first supply bypassing the compressor in the second operating mode when the first supply pressure is less than the desired injection pressure and greater than or equal to the parasitic threshold pressure PPT; and the third operating mode is commanded when the gaseous-fuel rail pressure PGFR is less than the mid-cycle direct injection threshold pressure PMCDI-T. The compressor threshold pressure PCT can be less than or equal to 350 bar and greater than or equal to 100 bar. The mid-cycle direct injection threshold pressure PMCDI- T can be 35 bar to 45 bar above a peak cylinder pressure, and preferably around 40 bar above the peak cylinder pressure.

[0010] In some embodiments, the apparatus further includes a bypass valve configured to fluidly communicate the gaseous fuel around the pressure regulator when the bypass valve is in an open position, and the controller is further programmed to, when the first supply pressure is greater than the desired injection pressure, command the bypass valve to the open position such that the in-cylinder injector receives the gaseous fuel from the first supply at the first supply pressure; and command the in-cylinder injector in a fourth operating mode. In the fourth operating mode, the gaseous fuel bums in a diffusion combustion mode, a start of injection timing is later in a compression stroke and an injection duration is smaller in the fourth operating mode compared to the first operating mode for a commanded injection mass, and the internal combustion engine can operate at a maximum rated power.

[0011] In some embodiments, the desired injection pressure is in a range of 200 to 400 bar. In some embodiments, the apparatus further includes a second supply of the gaseous fuel storing the gaseous fuel as a compressed gas at a second supply pressure, and the pressure regulator and the compressor fluidly receive the gaseous fuel selectively from the first supply or the second fuel supply. In some embodiments, when the first supply is fluidly supplying the gaseous fuel to the in-cylinder injector, the first supply pressure is less than the desired injection pressure and the second supply pressure is greater than the desired injection pressure, and the gaseous-fuel rail pressure PGFR drops below the desired injection pressure in the first operating mode, then the controller is programmed to command the pressure regulator to fluidly receive the gaseous fuel from the second supply.

[0012] In some embodiments, the internal combustion engine operates at a first power demand and at a second power demand that is greater than the first power demand, the desired injection pressure is at a first value in the first power demand and at a second value in the second power demand, the second value is greater than the first value, when the internal combustion engine switches from operating with the first power demand to the second power demand, the gaseous- fuel rail pressure (PGFR) increases from the first value to the second value, when the gaseous-fuel rail pressure PGFR decreases below the second value of the desired injection pressure while operating at the second power demand, the internal combustion engine switches from the first operating mode to the second operating mode.

[0013] In some embodiments, the internal combustion engine operates at a first power demand and at a second power demand that is greater than the first power demand, the desired injection pressure is at a first value in the first power demand and at a second value in the second power demand, the second value is greater than the first value, when the internal combustion engine switches from operating at the second power demand in the second operating mode to the first power demand, the gaseous-fuel rail pressure PGFR decreases to the first value and the internal combustion engine switches to the first operating mode.

[0014] In some embodiments, a start of injection timing and an injection duration are stored in one or more arrays indexed by the gaseous-fuel rail pressure (PGFR) and the commanded injection mass. In some embodiments, a start of injection timing and an injection duration are determined analytically as a function of the gaseous-fuel rail pressure (PGFR) and a commanded injection mass. In some embodiments, the gaseous fuel is selected from the group containing biogas, hydrogen, methane, natural gas, and mixtures thereof.

[0015] An improved method for supplying a gaseous fuel to and operating an internal combustion engine includes commanding an in-cylinder injector in a first operating mode when a gaseous-fuel rail pressure PGFR in a gaseous-fuel rail is equal to or greater than a desired injection pressure; and commanding the in-cylinder injector in a second operating mode when the gaseous- fuel rail pressure PGFR is less than the desired injection pressure; in the first operating mode a pressure regulator fluidly receives the gaseous fuel from a first supply when a first supply pressure is greater than or equal to the desired injection pressure, and from a compressor when the first supply pressure is less than the desired injection pressure, in the first operating mode both the first supply and the compressor can deliver a demanded mass flow rate of the gaseous fuel by the internal combustion engine whereby the gaseous-fuel rail pressure PGFR is equal to the desired injection pressure, and in the second operating mode the first supply pressure is less than the desired injection pressure such that the pressure regulator fluidly receives the gaseous fuel from the compressor, in the second operating mode the demanded mass flow rate of the gaseous fuel is greater than a mass flow rate of the gaseous fuel delivered by the compressor whereby the gaseous- fuel rail pressure PGFR is less than the desired injection pressure.

[0016] In some embodiments, the method further includes commanding the in-cylinder injector to switch from the second operating mode to a third operating mode when the gaseous- fuel rail pressure PGFR is less than a mid-cycle direct injection threshold pressure PMCDI-T, in the third operating mode the pressure regulator fluidly receives the gaseous fuel from the compressor and the demanded mass flow rate of the gaseous fuel by the internal combustion engine is greater than the mass flow rate of the gaseous fuel delivered by the compressor, and the gaseous fuel bums in a partially premixed combustion mode in the third operating mode.

Brief Description of the Drawings

[0017] The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate exemplary embodiments of the apparatus, systems, and methods and, together with the general description above, and the detailed description of the embodiments, serve to explain the principles of the apparatus, systems, and methods. In the figures, like reference numbers refer to like elements or acts throughout the figures.

[0018] FIG. 1 is a schematic view of a fuel system for supplying the gaseous fuel to an internal combustion engine according to an embodiment.

[0019] FIG. 2 is a schematic view of a fuel system for supplying gaseous fuel to the internal combustion engine of FIG. 1 according to an embodiment.

[0020] FIG. 3 is a schematic view of a fuel system for supplying gaseous fuel to an internal combustion engine according to an embodiment.

[0021] FIG. 4 is a schematic view of a fuel system for supplying gaseous fuel to an internal combustion engine according to an embodiment. [0022] FIG. 5 is a flow chart view of an algorithm for operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment.

[0023] FIG. 6 is a flow chart view of an algorithm for operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment.

[0024] FIG. 7 is a flow chart view of an algorithm for operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment.

[0025] FIG. 8 is a graphical view of supply pressure and gaseous-fuel rail pressure versus time corresponding to the algorithm of FIG. 7 according to an embodiment.

[0026] FIG. 9 is a flow chart view of an algorithm for operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment.

[0027] FIG. 10 is a graphical view of supply pressure and gaseous-fuel rail pressure versus time corresponding to the algorithm of FIG. 9 according to an embodiment.

[0028] FIG. 11 is a flow chart view of an algorithm for operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment.

[0029] FIG. 12 is a graphical view of supply pressure and gaseous-fuel rail pressure versus time corresponding to the algorithm of FIG. 11 according to an embodiment.

[0030] FIG. 13 is a flow chart view of an algorithm for operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment.

[0031] FIG. 14 is a graphical view of supply pressure and gaseous-fuel rail pressure versus time corresponding to the algorithm of FIG. 13 according to an embodiment.

[0032] FIG. 15 is a graphical view of operating the internal combustion engine of FIGS. 1, 2, 3, or 4 according to an embodiment. [0033] FIG. 16 is a graphical view of brake thermal efficiency versus compression ratio of the internal combustion engine of FIGS. 1, 2, 3, or 4 for a variety of gaseous-fuel rail pressures according to an embodiment.

Detailed Description

[0034] Referring to FIG. 1, there is shown fuel system 10 for supplying gaseous fuel to fuel consumer 20, which can be an internal combustion engine, or more particularly a fuel injection system of the internal combustion engine, according to an embodiment. As used herein, a gaseous fuel is any fuel that is in the gas state (phase) at standard temperature and pressure, which in the context of this application is zero degrees Celsius (0 °C) and one hundred kilopascals (100 kPa), respectively. The gaseous fuel herein can be a single gaseous fuel or a mixture of gaseous fuels. Exemplary gaseous fuels include but are not limited to biogas, hydrogen, methane, naturals gas, and mixtures thereof. Fuel system 10 includes first supply 30 of the gaseous fuel that stores the gaseous fuel as a compressed gas. The term internal combustion engine can be used interchangeably with the term engine herein. A typical storage pressure after refill for first supply 30 is between 350 bar to 700 bar after filling; however, different storage pressures after refilling (both higher and lower) are contemplated. First supply 30 can include one or more gas cylinders as storage vessels that can be connected in serial and/or in parallel arrangements. The term “and/or” is used herein to mean “one or the other or both.” A gas cylinder is a pressure vessel for storage and containment of gaseous fluids at pressures above atmospheric pressure. High-pressure gas cylinders can be called bottles. In the illustrated embodiments, the contents inside the gas cylinders are compressed above atmospheric pressure and in the gas state. In some embodiments, the gas cylinder can be elongated. In some embodiments, the gas cylinder can be lying horizontal or standing upright in a rack, with the valve and fitting at one end or the top, respectively, for connecting to the receiving apparatus. Fuel system 10 supplies the gaseous fuel stored in first supply 30 at a first storage pressure Psi to gaseous-fuel rail 40 in engine 20 at a delivery pressure PD, which is also known as gaseous-fuel rail pressure PGFR herein, and which is abbreviated to rail pressure PGFR. In-cylinder injector 50 selectively injects the gaseous fuel into combustion chamber 60 when commanded by controller 70. Gaseous-fuel rail 40 can be a conduit for fluidly conveying the gaseous-fuel from fuel system 10, or from components therein, to in-cylinder injector 50. Fuel system 10 will now be described in more detail.

[0035] In some embodiments, pressure regulator 80 fluidly receives the gaseous fuel, selectively, directly from first supply 30 or from compressor 90, and fluidly supplies the gaseous fuel to gaseous-fuel rail 40 at the rail pressure PGFR. The rail pressure PGFR is a regulated pressure when a mass flow rate of the gaseous fuel from first supply 30 or a mass flow rate of the gaseous fuel from compressor 90 matches a demanded mass flow rate of the gaseous fuel by engine 20. As used herein the demanded mass flow rate of the gaseous fuel by the internal combustion engine is also referred to as engine demand. First supply 30 fluidly supplies the gaseous fuel at the first storage pressure Psi to pressure regulator 80 (minus pressure drops, if any, in other components along the way). Compressor 90 pressurizes the gaseous fuel from first supply 30 at the first storage pressure Psi to a pressurized pressure when commanded by controller 70. In some embodiments, shut-off valve 100 selectively allows fluid communication of the gaseous fuel between first supply 30 and pressure regulator 80 and shut-off valves 100 and 110 selectively allow fluid communication between first supply 30 and compressor 90. Shut-off valve 100 is a general shutoff valve for fuel system 10 whereas shut-off valve 110 controls the flow of gaseous fuel to compressor 90 only. Shut-off valves 100 and 110 can be selectively commanded by controller 70 as will be described in more detail below. In some embodiments, check valve 120 allows fluid communication of the gaseous fuel from first supply 30 towards pressure regulator 80 and reduces and preferably prevents back flow of gaseous fuel from compressor 90 towards first supply 30.

[0036] In some embodiments, controller 70 can be operatively connected with compressor 90 to effectively turn the compressor on or off. Compressor 90 can be different types of pumps, for example compressor 90 can be a reciprocating piston pump, a diaphragm pump, or a centrifugal pump, although other types of pumps are contemplated and depending upon the application one type of pump may be more suitable. Compressor 90 can be actuated by several methods, for example the compressor can be actuated hydraulically, pneumatically, mechanically, or electromagnetically. Compressor 90 can be configured in a variety of ways, for example the compressor can be configured in terms of single acting pump, double acting pump, and quad acting pump, as well as in terms of single stage and double stage (or even more stages). When compressor 90 is hydraulically actuated, a hydraulic motor (not shown) can fluidly provide a selective hydraulic fluid flow that can actuate compressor 90, where in some embodiments the hydraulic motor can be a fixed displacement hydraulic pump or in other embodiments a variable displacement hydraulic pump. In an exemplary embodiment compressor 90 is a double stage, hydraulically actuated, reciprocating piston pump driven by a variable displacement hydraulic pump. This type of compressor allows an instantaneous mass flow of the gaseous fuel from compressor 90 to be controlled proportional to the pressurized pressure (that is, the compressor outlet pressure) to reduce and preferably minimize pressure fluctuations in buffer 130 in the illustrated embodiment, which is in fluid communication with pressure regulator 80. In those embodiments where compressor 90 is hydraulically actuated and driven by a hydraulic pump, controller 70 can control compressor 90 (and particularly the mass flow of the gaseous fuel from the compressor) by modulating the hydraulic fluid flow from the hydraulic pump and can effectively turn the compressor off by reducing the hydraulic fluid flow to the compressor to zero (that is, by shutting off the hydraulic fluid flow). The mass flow rate of the gaseous fuel from compressor 90 can depend upon a pressure and a temperature of the gaseous fuel at an inlet of the compressor, a volume of a compression chamber (not shown), and a frequency of compression cycles.

[0037] In some embodiments, controller 70 can be an engine controller when fuel consumer 20 is an internal combustion engine, or in other embodiments controller 70 can be a fuel system controller that communicates with an engine controller of the internal combustion engine. In some embodiments, controller 70 can include both hardware and software components. The hardware components can include digital and/or analog electronic components. In some embodiments, controller 70 can include a processor and one or more 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, module 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, modules and steps that are performed by controller 70 can be part of the controller. Double-arrowed lines adjacent controller 70, when illustrated, can represent communication channels, which can be either bidirectional or unidirectional, to the components that controller 70 either or both receives status information from and sends command information to, and these components can also have adjacent double-arrowed lines.

[0038] In some embodiments, buffer or accumulator 130 is downstream from compressor 90 and can function to store a volume of the gaseous fuel at the pressurized pressure and to limit pressure surges coming from compressor 90 (since a mass output from the compressor per compression cycle is dispersed over the volume of the buffer thereby limiting the pressure rise). In some embodiments, buffer 130 can be in a direct fluid communication pathway between first supply 30 and pressure regulator 80 that fluidly bypasses compressor 90, and buffer 130 can also be in a direct fluid communication pathway between compressor 90 and pressure regulator 80. However, this is not a requirement and in other embodiments buffer 130 can be in the direct fluid communication pathway from compressor 90 but not in the direct fluid communication pathway from first supply 30 that bypasses compressor 90. As an example, with reference to gaseous-fuel system 11 in FIG. 2 according to another embodiment where like parts in this and all other embodiments have like reference numerals, buffer 130 is in the direct fluid communication pathway between compressor 90 and pressure regulator 80 but not in the direct fluid communication pathway between first supply 30 and pressure regulator 80 that bypasses compressor 90. Check valve 140 can be employed to fluidly isolate buffer 130 from the direct fluid communication pathway between first supply 30 and pressure regulator 80 that bypasses compressor 90.

[0039] Returning to FIG. 1, in some embodiments bypass valve 150 can be commanded by controller 70 to selectively fluidly bypass the gaseous fuel from first supply 30 and compressor 90 around pressure regulator 80, as will be described in more detail below. In some embodiments, all shut-off valves and bypass valves herein can be commanded by controller 70 to either an open position or to a closed position, and in exemplary embodiments can be solenoid-type valves or hydraulically-actuated type valves. In some embodiments, pressure sensor 160 emits signals representative of first supply pressure Psi in first supply 30 to controller 70 that can be programmed to determine the first supply pressure Psi accordingly. In some embodiments, pressure sensor 170 emits signals representative of unregulated delivery pressure PUD upstream of pressure regulator 80 to controller 70 that is programmed to determine the unregulated delivery pressure PUD accordingly. When compressor 90 is pressurizing the gaseous fuel from first supply 30 into buffer 130, the unregulated delivery pressure PUD also represents the pressurized pressure due to compressor 90. In some embodiments, pressure sensor 175 emits signals representative of delivery pressure PD to controller 70 that is programmed to determine the delivery pressure PD and rail pressure PGFR accordingly.

[0040] In some embodiments, controller 70 commands in-cylinder injector 50 to inject a demanded mass of the gaseous fuel into combustion chamber 60. Each injection can have a start of injection (SOI) timing and an injection duration (that can also be referred to as a pulse width) determined by controller 70 based on engine operating condition variables, and primarily by the engine demand and the rail pressure PGFR. The rail pressure PGFR can be representative of actual injection pressure, which is defined herein as the pressure of the gaseous fuel to be injected inside in-cylinder injector 50. In some embodiments, controller 70 can determine the SOI timing and the injection duration by employing empirical data in one or more fueling maps 180 that can be stored in a memory 185 accessible by controller 70. The memory 185 can be part of controller 70. The empirical data can be determined during a calibration of the internal combustion engine where the operation of the engine is set up to achieve the best possible or desired performance and emission characteristics. The fueling maps 180 can be tables or arrays indexed by the engine demand and the rail pressure PGFR to retrieve the start of injection timing and the injection duration. Alternatively, in some embodiments controller 70 can analytically determine start of injection timing and an injection duration as a function of the gaseous-fuel rail pressure (PGFR) and a commanded injection mass. In some embodiments, controller 70 can employ mathematical functions representative of the empirical data in the fueling maps 180 and having the engine demand and the rail pressure PGFR as arguments and having the SOI timing and the injection duration as respective outputs. In some embodiments, other engine operating condition variables can be employed to additionally index into fueling maps 180 or as arguments in the mathematical functions.

[0041] Referring now to FIG. 3, there is shown fuel system 12 according to another embodiment and only differences are discussed. Second supply 35 of the gaseous fuel can store the gaseous fuel as a compressed gas. In some embodiments, first supply 30 can include one or more pressurized gas cylinders, and second supply 35 can also include one or more pressurized gas cylinders. In some embodiments, shut-off valve 105 selectively allows fluid communication of the gaseous fuel between second supply 35 and pressure regulator 80, and shut-off valves 105 and 110 selectively allow fluid communication between second supply 35 and compressor 90. Shut-off valve 105 can be selectively commanded by controller 70 to the open position or the closed position. In some embodiments, pressure sensor 165 emits signals representative of second supply pressure Ps2 in second supply 35 to controller 70 that is programmed to determine the second supply pressure Ps2 accordingly. In some embodiments, check valve 125 functions to reduce and preferably prevent back flow from second supply 35 to first supply 30 in the event both shut-off valves 100 and 105 are open at the same time, particularly in those embodiments when second supply pressure Ps2 is typically greater than first supply pressure Psi during operation of engine 20.

[0042] Referring now to FIG. 4 there is shown fuel system 13 according to another embodiment and only differences are discussed. Fuels system 13 includes both a gaseous-fuel system 190 and a pilot-fuel system 200. In the illustrated embodiment, gaseous-fuel system 190 is like fuel system 12 in FIG. 3. In some embodiments, pressure regulator 80 can include a pressure regulator that regulates that gaseous fuel at the unregulated delivery pressure PUD to an intermediate pressure and a fuel injector commanded by controller 70 to inject the gaseous fuel at the intermediate pressure into gaseous-fuel rail 40. Pilot-fuel system 200 can supply a pilot fuel to pilot fuel rail 210 of engine 23 at pilot-fuel rail pressure PPFR. The pilot fuel can be a liquid fuel or a gaseous fuel. In exemplary embodiments the pilot fuel can be biodiesel, diesel, dimethyl ether (DME), and kerosene, although other suitable pilot fuels can be employed. In the illustrated embodiment, the pilot fuel is stored in pilot supply 220 as a liquid. In some embodiments, pilotfuel system 200 employs a two stage pumping apparatus including low-pressure pump 230 (also referred to as a transfer pump) that pressurizes the pilot fuel from atmospheric pressure to a pressure suitable for high-pressure pump 240 (also referred to as a common rail pump) that pressurizes the pilot fuel to an unregulated pilot-fuel delivery pressure PUPFD, which is greater than pilot-fuel rail pressure PPFR in pilot-fuel rail 210. In some embodiments, pilot-fuel regulator 250 regulates unregulated pilot-fuel delivery pressure PUPFD to pilot-fuel rail pressure PPFR based on gaseous-fuel rail pressure PGFR such that a differential pressure between gaseous-fuel rail pressure PGFR minus pilot-fuel rail pressure PPFR is within a predefined range. In-cylinder injector 55 can be a dual fuel injector that is supplied both the gaseous fuel from the gaseous-fuel rail 40 and the pilot fuel from the pilot-fuel rail 210 and can inject both the gaseous fuel and the pilot fuel into combustion chamber 60. The gaseous fuel can be injected separately and independently from the pilot fuel. In some embodiments, the pilot fuel can be employed in in-cylinder injector 55 to control a gaseous-fuel injection valve (not shown) and a pilot fuel injection valve (not shown), and to reduce and preferably prevent leakage of the gaseous fuel from in-cylinder injector 55 (for example, by using liquid seals). Pilot fuel can be returned to pilot supply 220 through pilot return 260. In some embodiments, pilot-fuel regulator 250 can spill excess pilot fuel into pilot return 260 to regulate pilot-fuel rail pressure PPFR and the differential pressure. In-cylinder injector 55 can fluidly communicate pilot fuel that has been employed as a controlling fluid for the gaseous-fuel injection valve and the pilot fuel injection valve to pilot return 260. In some embodiments, pressure sensor 270 can emit signals representative of the unregulated pilot-fuel delivery pressure PUPFD to controller 70 that can be programmed to determine the unregulated pilot-fuel delivery pressure PUPFD accordingly. In some embodiments, pressure sensor 275 can emit signals representative of pilot-fuel rail pressure PPFR in pilot-fuel rail 210 to controller 70 that can be programmed to determine the pilot-fuel rail pressure PPFR accordingly.

[0043] Referring now to FIG. 5, there is shown algorithm 500 for operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment. In some embodiments, algorithm 500 and all other algorithms disclosed herein can be stored in and performed or executed by controller 70. The algorithm can start in step 505 in some embodiments when, for example, the engine is started. In some embodiments, rail pressure PGFR can be compared to desired injection pressure PDI in step 510. A first operating mode can be entered in step 515 when the rail pressure PGFR is greater than or equal to the desired injection pressure PDI. A second operating mode can be entered in step 520 when the rail pressure PGFR is less than the desired injection pressure PDI. AS used herein, the desired injection pressure PDI is defined as that value of the rail pressure PGFR (for a given value of a compression ratio of the engine) where when the rail pressure PGFR increases above the desired injection pressure PDI an increase in an efficiency of the engine for operating at the higher pressure is less than a first predetermined value, and when the gaseous-fuel rail pressure PGFR decreases below the desired injection pressure PDI a decrease in the efficiency of the engine for operating at the lower pressure is greater than a second predetermined value, where a ratio between the second predetermined value over the first predetermined value is greater than a third predetermined value, which in an exemplary embodiment can be one (1). Alternatively, the desired injection pressure PDI can be defined as that value of the gaseous-fuel rail pressure PGFR (for a given value of a compression ratio of the engine) where, as the gaseous-fuel rail pressure is increased from a low value by small increments in pressure, the increase in the efficiency of the engine due to operating at a value of the gaseous fuel rail pressure PGFR that is greater by the small increment in pressure is less than the first predetermined value. The low value of the gaseous-fuel rail pressure PGFR can be a minimum value required for fuel injection. In some embodiments, the desired injection pressure PDI can be a function of engine load and engine speed. In some embodiments, there can be a discrete number of values of the desired injection pressure PDI that can be selected based on engine load and engine speed. In some embodiments, the desired injection pressure PDI is lower for a low engine demand (that is, a low-power demand) than for a high engine demand (that is, a high-power demand).

[0044] The rail pressure PGFR decreases below the desired injection pressure PDI triggering a transition from the first operating mode to the second operating mode and continues decreasing in the second operating mode. In some embodiments, when the condition that caused the rail pressure PGFR to decrease is removed, specifically when the engine demand is reduced, the rail pressure PGFR can start to increase back towards the desired injection pressure PDI and when the rail pressure PGFR equals the desired injection pressure PDI the engine transitions to operating in the first operating mode again. In some embodiments, the phase between the rail pressure PGFR beginning to increase again while in the second operating mode to when the rail pressure PGFR equals the desired injection pressure PDI and the engine transitions to the first operating mode can be referred to as a recharge operating mode. The recharge operating mode is like the second operating mode in that the gaseous fuel bums in a diffusion combustion mode, a start of injection timing is earlier in the compression stroke, and an injection duration is greater in the recharge operating mode compared to the first operating mode for a commanded injection mass, and the engine can operate at a maximum rated power. However, unlike the second operating mode, in the recharge operating mode the gaseous-fuel mass flow rate from compressor 90 is greater than the engine demand, whereby the rail pressure PGFR increases. The rate of increase of the rail pressure PGFR in the recharge mode is directly proportional to the size of compressor 90 and the first supply pressure Psi, and indirectly proportional to the engine demand. In some embodiments, when the first supply pressure Psi is close to the desired injection pressure PDI from the low side, the recharge operating mode is short in duration since the rail pressure PGFR tends to increase quickly after the conditions causing it to decrease are removed. Returning to algorithm 500 in FIG. 5, in some embodiments, when the rail pressure PGFR is less than the desired injection pressure PDI in step 510, the algorithm transitions to step 520, and in step 520 when the rail pressure PGFR is decreasing the engine is in the second operating mode and when the rail pressure PGFR is increasing the engine is in the recharge operating mode. In both the second operating mode and the recharge operating mode incylinder injector 50 or 55 selects the SOI timing and the injection duration based on the gaseous fuel rail pressure PGFR. Step 520 is characterized in part by the rail pressure PGFR being less than the desired injection pressure PDI and being unregulated, while the gaseous fuel bums in the diffusion combustion mode in combustion chamber 60 and the engine still capable of being operated at the maximum rated power.

[0045] In some embodiments, in the first operating mode, pressure regulator 80 can fluidly receive the gaseous fuel from first supply 30 when the first supply pressure Psi is greater than or equal to the desired injection pressure PDI, and pressure regulator 80 can fluidly receive the gaseous fuel from compressor 90 when the first supply pressure Psi is less than the desired injection pressure PDI. Additionally, in the first operating mode a mass flow rate of gaseous fuel from first supply 30 or a mass flow rate of gaseous fuel from compressor 90 can match (or exceed) the engine demand such that the rail pressure PGFR is equal to (or greater than) the desired injection pressure PDI. In some embodiments, in the second operating mode, pressure regulator 80 can fluidly receive the gaseous fuel from compressor 90 when the first supply pressure Psi is less than the desired injection pressure PDI. Additionally, in the second operating mode the engine demand is greater than the mass flow rate of the gaseous fuel delivered by compressor 90 such that the rail pressure PGFR is less than the desired injection pressure PDI and the rail pressure PGFR continues to decrease while the engine operates in the second operating mode. That is, in the second operating mode the rail pressure PGFR is an unregulated pressure (since engine gaseous-fuel mass demand is greater than delivered gaseous-fuel mass) as it decreases after each injection of gaseous fuel by in-cylinder injector 50 or 55. The gaseous fuel bums in a diffusion combustion mode in the first and second operating modes, which is also referred to as a late-cycle direction injection (LCDI) mode. The SOI timing is earlier in the compression stroke and the injection duration is greater in the second operating mode compared to the first operating mode for a commanded injection mass of the gaseous fuel. As used herein, the commanded injection mass can also be referred to as a demanded injection mass. In some embodiments, an injection window suitable for the diffusion combustion mode where injection can begin and end is between 30 crank angle degrees (CA°) before top dead center (BTDC) during the compression stroke and 35 CA° after top dead center (ATDC) during an expansion stroke. The first operating mode can be referred to as high pressure LCDI, and the second operating mode can be referred to as low pressure LCDI, where the terms high pressure and low pressure are used in relation to each other rather than as absolute pressure references. Engine 20 or 23 can operate at a maximum rated power in the first and second operating modes, which is particularly advantageous with regard to the second operating mode since heretofore a previous internal combustion engine would be derated in power when a mass flow rate of fuel from a compressor could not match a demanded mass flow rate of the fuel from the previous internal combustion engine. In the first operating mode the rail pressure PGFR equals the desired injection pressure PDI for both a low-power demand and a high-power demand of the internal combustion engine, where in some embodiments, the desired injection pressure PDI can change based on engine load and engine speed. In some embodiments, the second operating mode can allow compressor 90 to be purposively undersized more so than previously possible such that for brief excursions in the second operating mode the engine continues to operate at maximum rated power, whereby by under-sizing compressor 90 the parasitic energy costs of operating the compressor during the first operating mode are reduced. Similarly, the second operating mode can increase the available operating time of the engine or allow for range extension when the engine propels a vehicle while simultaneously allowing the engine to operate at maximum rated power. This contrasts with operating the engine only in the first operating mode where the engine would lose the ability to operate at the maximum rated power sooner as the first supply pressure Psi decreases then if the engine could operate selectively in both the first and second operating modes.

[0046] Referring now to FIG. 6, there is shown algorithm 501 for operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment and differences are discussed. Step 511 is like step 510 in algorithm 500 in FIG. 5, except when it is determined not to operate in the first operating mode, control is transferred to step 525 where it is determined whether to operate in the second operating mode or in a third operating mode. In some embodiments, control is transferred to step 520 where the engine is commanded to operate in the second operating mode when rail pressure PGFR is greater than or equal to a mid-cycle direct injection (MCDI) threshold pressure PMCDI-T. In some embodiments, control is transferred to step 530 where the engine is commanded to operate in the third operating mode when rail pressure PGFR is less than the MCDI threshold pressure PMCDI-T. In some embodiments, in the third operating mode, the first supply pressure Psi is less than the desired injection pressure PDI such that pressure regulator 80 fluidly receives the gaseous fuel from compressor 90. Additionally, in the third operating mode the engine demand is greater than the mass flow rate of the gaseous fuel delivered by compressor 90 such that the rail pressure PGFR is less than the desired injection pressure PDI and the rail pressure PGFR continues to decrease while the engine operates in the third operating mode. That is, in the third operating mode the rail pressure PGFR is an unregulated pressure (since the engine gaseous-fuel mass demand is greater than the delivered gaseous-fuel mass) as it decreases after each injection of gaseous fuel by in-cylinder injector 50 or 55. The gaseous fuel bums in an MCDI combustion mode in the third operating mode, which is a partially-premixed combustion mode where portions of an air-fuel mixture in combustion chamber 60 (seen in FIGS. 1, 3, and 4) bum with diffusion combustion and other portions of the air-fuel mixture bum with premixed- flame combustion. The MCDI threshold pressure PMCDI-T represents a value of the gaseous-fuel rail pressure PGFR where with injection pressures higher than or equal to that value LCDI combustion can be employed at maximum rated power, and with injection pressures lower than that value, not enough gaseous fuel can be introduced to operate at maximum rated power with LCDI combustion whereby earlier injection timings are employed to operate in the MCDI combustion mode. The SOI timing is earlier in the compression stroke and the injection duration is greater in the third operating mode compared to the first operating mode and the second operating mode for a commanded injection mass of the gaseous fuel. The engine can operate at a maximum rated power in the third operating mode as long as the rail pressure PGFR is high enough to allow the demanded mass of the gaseous fuel to be injected during an injection window suitable for the MCDI combustion mode. In some embodiments, the MCDI threshold pressure PMCDI-T is between 35 bar to 45 bar above a peak cylinder pressure, where the peak cylinder pressure is defined as a maximum pressure due to combustion of fuel within combustion chamber 60. In some embodiments, an injection window suitable for the MCDI combustion mode where injection can begin and end is between 120 CA° BTDC during the compression stroke and 30 CA° BTDC during the compression stroke.

[0047] Referring now to FIGS. 7 and 8, there is shown algorithm 600 for operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment. The algorithm starts in step 610 when, for example, engine 20 or 23 is started. In some embodiments, the first supply pressure Psi of first supply 30 is compared to desired injection pressure PDI in step 615. The first operating mode is entered in step 620 when first supply pressure Psi is greater than or equal to desired injection pressure PDI whereby the gaseous fuel is fluidly communicated from first supply 30 directly to pressure regulator 80 without pressurization from compressor 90. This corresponds to the portion of the first supply pressure Psi to the left of timestamp T1 in the graph of FIG. 8. The graph of FIG. 8 represents a simplified operating cycle (or duty cycle) where, for example, the engine continuously operates at the maximum rated power until it can no longer do so, which is a useful way to graphically illustrate the first and second operating modes. Note that algorithm 600 and all other algorithms herein can be operated in other embodiments where the engine demand varies randomly. While in the first operating mode the first supply pressure Psi is continuously monitored and compared to the desired injection pressure PDI. In some embodiments, when first supply pressure Psi is less than the desired injection pressure PDI control transfers to step 625 where the gaseous fuel is fluidly communicated to pressure regulator 80 through compressor 90 whereby the gaseous fuel is pressurized such that the unregulated delivery pressure PUD is equal to or greater than the desired injection pressure PDI, and preferably a difference between the unregulated delivery pressure PUD minus the rail pressure PGFR is equal to or greater than a pressure margin preferred by pressure regulator 80 to correctly regulate the rail pressure PGFR at the desired injection pressure PDI. In some embodiments, compressor 90 can be selectively operated according to the engine demand to maintain the rail pressure PGFR at the desired injection pressure PDI. While fluidly communicating the gaseous fuel through compressor 90 to gaseous- fuel rail 40, the rail pressure PGFR can be compared to the desired injection pressure PDI in step 630, in some embodiments, and the engine can be operated in the first operating mode in step 635 when the rail pressure PGFR is greater than or equal to the desired injection pressure PDI, which corresponds to the portion of the gaseous-fuel pressure PGFR between timestamps T1 and T2 in the graph of FIG. 8, and operated in the second operating mode in step 640 when the rail pressure PGFR is less than the desired injection pressure PDI, which corresponds to the portion of the gaseous- fuel pressure PGFR to the right of timestamp T2 in the graph of FIG. 8. In some embodiments, the first supply pressure Psi at timestamp T2 in FIG. 8 equals a compressor threshold pressure PCT, which represents the first supply pressure Psi at which the mass flow rate of gaseous fuel from compressor 90 cannot match the engine demand such that the rail pressure PGFR begins to decrease. The compressor threshold pressure PCT can be a function of the load on the engine, whereby the compressor threshold pressure PCT can be the highest for the maximum rated engine load and decreases for lesser loads. In some embodiments, the compressor threshold pressure PCT can be less than or equal to 350 bar and greater than or equal to 100 bar. The compressor threshold pressure PCT can depend upon a variety of factors, such as the mass flow rate of the gaseous fuel from compressor 90 and a volume of accumulator 130. The probability of entering the second operating mode increases as the first supply pressure Psi decreases.

[0048] Referring now FIGS. 9 and 10, there is shown algorithm 601 for operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment. Algorithm 601 is like algorithm 600 and differences are discussed. Step 616 is like step 615 in algorithm 600 in FIG. 7, except in step 616, when first supply pressure PSI is less than the desired injection pressure PDI, control transfers to step 645 (instead of step 625 in algorithm 600). In some embodiments, the first supply pressure Psi can be compared to a parasitic threshold pressure PPT in step 645, and when the first supply pressure Psi is greater than or equal to the parasitic threshold pressure PPT control can be transferred to step 650 where the engine can be operated in the second operating mode. The parasitic threshold pressure PPT is less than the desired injection pressure PDI and is now discussed in more detail. An improvement in the efficiency of the engine by increasing the first supply pressure Psi from a value anywhere from the parasitic threshold pressure PPT to the desired injection pressure PDI is less than a parasitic energy cost of operating compressor 90. The parasitic threshold pressure PPT is that value of first supply pressure Psi where an increase in the efficiency of the engine by operating with the rail pressure PGFR equal to the desired injection pressure PDI is less than a decrease in the efficiency of the engine due to the parasitic energy cost of operating compressor 90 to raise the first supply pressure Psi to the desired injection pressure PDI. When the first supply pressure Psi is below the parasitic threshold pressure PPT, the increase in efficiency by operating with the rail pressure PGFR equal to the desired injection pressure PDI is greater than the decrease in efficiency due to the parasitic energy cost of operating compressor 90 to raise the first supply pressure Psi to the desired injection pressure PDI. In some embodiments, the gaseous fuel is fluidly communicated from first supply 30 directly to pressure regulator 80 (bypassing compressor 90) in the second operating mode when the first supply pressure Psi is less than the desired injection pressure PDI and greater than or equal to the parasitic threshold pressure PPT. This corresponds to a portion of the gaseous-fuel pressure PGFR curve in FIG. 10 between timestamps T1 and T3. Control can be transferred to step 625 when the first supply pressure Psi is less than the parasitic threshold pressure PPT. The portion of the gaseous-fuel pressure PGFR curve in FIG. 10 between timestamps T3 and T4 corresponds to the recharge operating mode, where compressor 90 is turned on such that the rail pressure PGFR can be increased to the desired injection pressure PDI. The portion of the gaseous-fuel pressure PGFR curve in FIG. 10 between timestamps T4 and T5 corresponds to step 635 where the engine is operating in the first operating mode with the gaseous fuel being fluidly communicated to pressure regulator 80 through compressor 90 whereby the gaseous fuel is pressurized to the desired injection pressure PDI. The portion of the gaseous-fuel pressure PGFR curve in FIG. 10 to the right of timestamp T5 corresponds to step 640 where the engine is operating in the second operating mode with the gaseous fuel being fluidly communicated to pressure regulator 80 through compressor 90 whereby the gaseous fuel is pressurized towards the desired injection pressure PDI, but since the gaseous-fuel mass flow rate from compressor 90 is less than the engine demand in the second operating mode the rail pressure PGFR is less than the desired injection pressure PDI.

[0049] Referring now FIGS. 11 and 12, there is shown algorithm 602 for operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment. Algorithm 602 is like algorithm 600 and differences are discussed. Step 631 is like step 630 in algorithm 600 of FIG. 7, except when the rail pressure PGFR is less than to the desired injection pressure PDI, in some embodiments control can be transferred to step 655 (instead of step 640 in algorithm 600). The rail pressure PGFR can be compared to the MCDI threshold pressure PMCDI-T in step 655, and in some embodiments when the rail pressure PGFR is greater than or equal to the MCDI threshold pressure PMCDI-T control can be transferred to step 660 where the engine is operated in the second operating mode, and when the rail pressure PGFR is less than the MCDI threshold pressure PMCDI-T control can be transferred to step 665 where the engine is operated in the third operating mode. With reference to FIG. 12, the first operating mode corresponds to portions of the rail pressure PGFR curve to the left of the timestamp T2, the second operating mode corresponds to portions of the rail pressure PGFR curve between timestamps T2 and T6, and the third operating mode corresponds to portions of the rail pressure PGFR curve to the right of timestamp T6. In some embodiments, in the first operating mode, the gaseous fuel can be fluidly communicated from first supply 30 directly to pressure regulator 80 when operating to the left of timestamp Tl, since first supply pressure Psi is greater than or equal to the desired injection pressure PDI, and the gaseous fuel is fluidly communicated from first supply 30 through compressor 90 to pressure regulator 80 when operating between timestamps Tl and T2, since first supply pressure Psi is less than the desired injection pressure PDI. In some embodiments, the gaseous fuel can be fluidly communicated from first supply 30 through compressor 90 to pressure regulator 80 when operating in the second operating mode (between timestamps T2 and T6) and in the third operating mode (to the right of timestamp T6), since first supply pressure Psi is less than the desired injection pressure PDI. Algorithm 602 allows for increased operating time or range extension of a vehicle by employing the MCDI operating mode when the rail pressure PGFR is too low for efficient or maximum rated power operation in the second operating mode.

[0050] Referring now FIGS. 13 and 14, there is shown algorithm 603 for operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment. Algorithm 603 combines features of algorithms 600, 601, and 603. With reference to FIG. 14, in some embodiments the first operating mode corresponds to portions of the rail pressure PGFR curve to the left of the timestamp Tl, and between timestamps T4 and T5, the recharge operating mode corresponds to the portion of the rail pressure PGFR curve between timestamps T3 and T4, the second operating mode corresponds to portions of the rail pressure PGFR curve between timestamps Tl and T3, and between timestamps T5 and T7, and the third operating mode corresponds to portions of the rail pressure PGFR curve to the right of timestamp T7. In some embodiments, in the first operating mode, the gaseous fuel can be fluidly communicated from first supply 30 directly to pressure regulator 80 when operating to the left of timestamp Tl, since first supply pressure Psi is greater than or equal to the desired injection pressure PDI, and the gaseous fuel can be fluidly communicated from first supply 30 through compressor 90 to pressure regulator 80 when operating between timestamps T4 and T5, since first supply pressure Psi is less than the desired injection pressure PDI. In some embodiments, in the second operating mode, the gaseous fuel can be fluidly communicated from first supply 30 directly to pressure regulator 80 between timestamps Tl and T3, since first supply pressure Psi is less than the desired injection pressure PDI and greater than or equal to the parasitic threshold pressure PPT, and the gaseous fuel can be fluidly communicated from first supply 30 through compressor 90 to pressure regulator 80 between timestamps T5 and T7, since first supply pressure Psi is less than the parasitic threshold pressure PPT and greater than or equal to the MCDI threshold pressure PMCDI-T. In some embodiments, in the third operating mode the gaseous fuel can be fluidly communicated from first supply 30 through compressor 90 to pressure regulator 80 to the right of timestamp T7, since first supply pressure Psi is less than the desired injection pressure PDI. [0051] With reference to fuel systems 12 and 13 in FIGS. 3 and 4, respectively, in some embodiments second supply 35 can operate as a surge tank or high pressure tank whereby, when rail pressure PGFR drops below the desired injection pressure PDI while fluidly drawing the gaseous fuel from first supply 30, controller 70 can be programmed to switch to operating from second supply 35 to increase rail pressure PGFR to the desired injection pressure PDI (or higher), or to increase the unregulated delivery pressure PUD to a value above the desired injection pressure PDI such that pressure regulator 80 can regulate the rail pressure PGFR at the desired injection pressure PDI. Algorithms 500, 501, 600, 601, 602, 603 can be performed whenever second supply 35 cannot increase unregulated delivery pressure PUD when required to maintain the rail pressure PGFR at the desired injection pressure PDI, and these algorithms can be entered at respective steps therein according to the value of first supply pressure Psi or second supply pressure Ps2 depending upon which of the first supply 30 or second supply 35 is supplying the gaseous fuel. First supply pressure Psi can be replaced by second supply pressure Ps2 in the algorithms 500, 501, 600, 601, 602, 603 when the gaseous fuel is fluidly drawn from second supply 35 while operating one of these algorithms.

[0052] Referring now to FIG. 15, there is shown a simplified graphical view of operating engine 20 or 23 with respective fuel systems 10, 11, 12, or 13 according to an embodiment. In some embodiments, the desired injection pressure PDI can be a function of the engine load and the engine speed, where for example the desired injection pressure PDI can increase, linearly or non- linearly, or discretely, as the engine load increases . In the illustrated embodiment, the engine load increases at time T9 from a medium load to a full rated load, and then decreases at time T11 from the full rated load to another medium load. With reference to fuel system 10 in FIG. 1 (although in other embodiments fuel systems 11, 12, or 13 can be employed), buffer 130 fluidly supplies enough of the gaseous fuel to increase the desired injection pressure PDI at time T9 from a lower value PDI-L, specific for the medium load, to a higher value PDI-H specified for the higher engine load, whereby the unregulated delivery pressure PUD (that is, the pressure substantially in buffer 130 and upstream of pressure regulator 80) decreases and the rail pressure PGFR increases accordingly. In some embodiments, the unregulated delivery pressure PUD is maintained between high and low setpoints, for example between 325 bar and 300 bar, although other setpoints are contemplated. Note that since the first supply pressure Psi is less than the unregulated delivery pressure PUD between time interval T8 and T9, the gaseous fuel is fluidly communicated from first supply 30 to buffer 130 through compressor 90, such that there may be pressure surges from compressor 90 into buffer 130, which are not illustrated in FIG. 15. In some embodiments, pressure regulator 80 can be a variable pressure regulator when the desired injection pressure PDI is a function of the engine load whereby the delivery pressure PD from pressure regulator 80 can be adjusted according to the engine load. Engine 20 operates in the first operating mode in the time interval between time T8 and T9. During the time interval between time T9 and T10, engine 20 is also operating in the first operating mode, however the unregulated delivery pressure PUD begins to decrease during this interval indicating that compressor 90 cannot meet the engine demand, but the combined flow from compressor 90 and buffer 130 can meet the engine demand such that the rail pressure PGFR equals the higher value PDI-H of the desired injection pressure PDI after rising from the lower value PDI-L during the time interval between T9 and T10. At time T10, pressure regulator 80 can no longer maintain the desired injection pressure PDI at the higher value PDI-H since compressor 90 cannot meet engine demand and buffer 80 has depleted enough such that the unregulated delivery pressure PUD has decreased below a value required for pressure regulator 80 to properly regulate the delivery pressure PD at the higher value PDI-H, whereby the rail pressure PGFR begins to decrease below the higher value PDI-H of the desired injection pressure PDI, whereby engine 20 switches to operating in the second operating mode at time T10, and continues in this mode in the time interval between T10 and Ti l. At time T11, the engine load decreases from the full rated load to the other medium load, whereby the desired injection pressure PDI decreases from the higher value PDI-H to the lower value PDI-L. Accordingly, the rail pressure PGFR is allowed to decrease to the lower value PDI-L of the desired injection pressure PDI, for example through consumption by engine 20 of the gaseous fuel in gaseous-fuel rail 40. In illustrated embodiment, compressor 90 is employed to increase the unregulated deliver pressure PUD back to the higher setpoint after the engine load is decreased. Engine 20 returns to operating in the first operating mode at time Ti l since the engine demand is being met and the rail pressure PGFR is greater than or equal to the desired injection pressure after time Til. Algorithms 500, 501, 600, 601, 602, and 603 are representative of the operation of engine 20 or 23 illustrated in FIG. 15 when considering the increase in the rail pressure PGFR after the step change in the engine load is substantially instantaneous, particularly when the buffer pressure is nearer to the higher setpoint.

[0053] Brake thermal efficiency (BTE) of engines 20 or 23 is a function of the compression ratio of the engine and the rail pressure PGFR. AS the rail pressure PGFR decreases the injection duration increases and a mixing quality of the gaseous fuel with the air inside combustion chamber 60 (seen in FIGS. 1 to 4) is reduced. The reduction in the mixing quality and increase in the injection duration eventually offsets the benefit of the higher cylinder pressure due to the higher compression ratio. For a given value of the rail pressure PGFR, there may exist an optimal compression ratio corresponding to a best brake thermal efficiency for given circumstances. Accordingly, the desired injection pressure PDI can be selected as a function of the compression ratio. With reference to FIG. 16, there is shown a plot of the BTE versus the compression ratio at 100% of engine load where each curve Cl, C2, C3, C4, C5, and C6 is associated with a discrete value of the rail pressure PGFR. In the illustrated embodiment, curve Cl has a greater value of the rail pressure PGFR than curve C2, and curve C2 has a greater value of the rail pressure PGFR than curve C3, and curve C3 has a greater value of the rail pressure PGFR than curve C4, and curve C4 has a greater value of the rail pressure PGFR than curve C5, and curve C5 has a greater value of the rail pressure PGFR than curve C6. Accordingly, the order of decreasing value of the rail pressure PGFR are the curves Cl, C2, C3, C4, C5, and C6. For each discrete value of the rail pressure PGFR, there is a value of the compression ratio that results in a best value of the BTE shown as best BTE points PTB-BTEI, PTB-BTE2, PTB-BTE3, PTB-BTE4, PTB-BTES, and PTB-BTE6 for a predefined range of compression ratios. Moreover, typically as the rail pressure PGFR decreases, the compression ratio associated with the best BTE point also decreases. In the illustrated embodiment, rail pressures curves Cl and C2 have best BTE points PTB-BTEI and PTB-BTE2, respectively, at a common value of 20 of the compression ratio due to the maximum illustrated compression ratio being that value of 20 in the graph of FIG. 16, and if the maximum value of the compression ratio was extended enough beyond 20 a compression ratio for the best BTE point PTB-BTEI would be greater than the compression ratio for the best BTE point PTB-BTE2, since the rail pressure PGFR is greater for curve Cl than the curve C2. Accordingly, engines 20 and 23 can employ variable valve timing (VVT) such that while operating algorithms 500, 501, 600, 601, 602, and 603, the compression ratio of the engine 20 or 23 can be selected to match the value of the best BTE for the respective rail pressure PGFR, and typically the compression ratio can be decreased as the rail pressure PGFR decreases, and increased as the rail pressure PGFR increases. When the variable valve timing provides two or more discreate values of the compression ratio, while operating algorithms 500, 501, 600, 601, 602, and 603, the compression ratio of the engine 20 or 23 can be selected to achieve the best BTE possible under these circumstances. For example, in an exemplary embodiment, the compression ratio can have the values of 16, 18, and 20. Under these circumstances, in the illustrated embodiment of FIG. 16, when the rail pressure PGFR equals the value of curve Cl, curve C2, or curve C3, the compression ratio can be set to 20, and when the rail pressure PGFR equals the value of curve C4, the compression ratio can be set to 18, and when the rail pressure PGFR equals the value of curve C5 or curve C6, the compression ratio can be set to 16. When the best BTE point is on a plateau of BTE, as it is with curve C5 (where the BTE is equivalent at compression ratios of 16 and 17), the higher compression ratio is preferably selected at which to operate since when the engine runs at a lower load, for example at 50% or 25% of the full load, the higher compression ratio offers better thermal efficiency, particularly when the engine includes a turbocharger (not shown). This is due to when operating at the lower load, the boost pressure from the turbocharger is lower whereby so too is the cylinder pressure, which influences the mixing quality in addition to the rail pressure PGFR. In other embodiments, when the first supply pressure Psi is greater than the desired injection pressure PDI, or when the first supply pressure Psi is within a range of pressures greater than the desired injection pressure PDI, bypass valve 150 (seen in FIGS. 1-4) can be commanded to the open position such that the gaseous-fuel rail 40 and in-cylinder injector 50 or 55 fluidly receives the gaseous fuel from first supply 30 at the first supply pressure Psi. The in-cylinder injector can be commanded in a fourth operating mode where the gaseous fuel bums in the diffusion combustion mode, a start of injection timing is later in the compression stroke and the injection duration is shorter for the commanded injection mass compared to the first operating mode, and the engine can operate at the maximum rated power in the fourth operating mode.

[0054] 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

What is claimed is:

1. An apparatus for supplying a gaseous fuel to and operating an internal combustion engine comprising: a first supply of the gaseous fuel storing the gaseous fuel as a compressed gas at a first supply pressure; a compressor selectively pressurizing the gaseous fuel fluidly received from the first supply to a pressurized pressure; a pressure regulator fluidly receiving the gaseous fuel selectively from the first supply at the first supply pressure or from the compressor at the pressurized pressure and fluidly providing the gaseous fuel at a delivery pressure; a gaseous-fuel rail fluidly receiving the gaseous fuel from the pressure regulator; an in-cylinder injector fluidly receiving the gaseous fuel from the gaseous-fuel rail and configured to directly introduce the gaseous fuel into a combustion chamber of the internal combustion engine, the in-cylinder injector injecting the gaseous fuel at a gaseous-fuel rail pressure (PGFR); a controller operatively connected with the in-cylinder injector and programmed to command the in-cylinder injector in a first operating mode when the gaseous-fuel rail pressure (PGFR) is equal to or greater than a desired injection pressure; and command the in-cylinder injector in a second operating mode when the gaseous- fuel rail pressure (PGFR) is less than the desired injection pressure; wherein in the first operating mode the pressure regulator fluidly receives the gaseous fuel from the first supply when the first supply pressure is greater than or equal to the desired injection pressure, and from the compressor when the first supply pressure is less than the desired injection pressure, in the first operating mode both the first supply and the compressor can deliver a demanded mass flow rate of the gaseous fuel by the internal combustion engine whereby the gaseous-fuel rail pressure (PGFR) is equal to the desired injection pressure, and in the second operating mode the first supply pressure is less than the desired injection pressure such that the pressure regulator fluidly receives the gaseous fuel from the compressor, in the second operating mode the demanded mass flow rate of the gaseous fuel is greater than a mass flow rate of the gaseous fuel delivered by the compressor whereby the gaseous-fuel rail pressure (PGFR) is less than the desired injection pressure.

2. The apparatus as claimed in claim 1, wherein the gaseous fuel bums in a diffusion combustion mode in the first and second operating modes.

3. The apparatus as claimed in claim 1, wherein a start of injection timing is earlier in a compression stroke and an injection duration is greater in the second operating mode compared to the first operating mode for a commanded injection mass.

4. The apparatus as claimed in claim 1, wherein the internal combustion engine can operate at a maximum rated power in the first and second operating modes.

5. The apparatus as claimed in claim 1, wherein in the first operating mode the gaseous-fuel rail pressure (PGFR) equals the desired injection pressure for both a low-power demand and a high- power demand of the internal combustion engine.

6. The apparatus as claimed in claim 1, wherein the pressure regulator fluidly receives the gaseous fuel from the first supply in the second operating mode when the first supply pressure is less than the desired injection pressure and greater than or equal to a parasitic threshold pressure (PPT).

7. The apparatus as claimed in claim 6, wherein the parasitic threshold pressure (PPT) is in a range of 150 to 300 bar.

8. The apparatus as claimed in claim 1, wherein in the second operating mode the pressure regulator fluidly provides the gaseous fuel to the gaseous-fuel rail at an unregulated pressure since the mass flow rate of the gaseous fuel from the compressor is less than the demanded mass flow rate of the gaseous fuel by the internal combustion engine.

9. The apparatus as claimed in claim 8, wherein in the second operating mode the gaseous-fuel rail pressure (PGFR) continues to decrease further below the desired injection pressure after each injection by the in-cylinder injector.

10. The apparatus as claimed in claim 1, wherein the controller is further programmed to command the in-cylinder injector to switch from the second operating mode to a third operating mode when the gaseous-fuel rail pressure (PGFR) is less than a mid-cycle direct injection threshold pressure (PMCDI-T), wherein in the third operating mode the pressure regulator fluidly receives the gaseous fuel from the compressor and the demanded mass flow rate of the gaseous fuel by the internal combustion engine is greater than the mass flow rate of the gaseous fuel delivered by the compressor, the gaseous fuel bums in a partially premixed combustion mode in the third operating mode, a start of injection timing is earlier in a compression stroke and an injection duration is greater in the third operating mode compared to the second operating mode for a commanded injection mass, and the internal combustion engine can operate at a maximum rated power in the third operating mode.

11. The apparatus as claimed in claim 10, wherein the first operating mode is commanded when the first supply pressure is greater than or equal to the desired injection pressure or when the first supply pressure is less than a parasitic threshold pressure (PPT) and greater than or equal to a compressor threshold pressure (PCT); the second operating mode is commanded when the first supply pressure is less than the desired injection pressure and greater than or equal to the parasitic threshold pressure (PPT), or when the first supply pressure is less than the compressor threshold pressure (PCT) and when the gaseous-fuel rail pressure (PGFR) is greater than or equal to the mid-cycle direct injection threshold pressure (PMCDI-T), and wherein the pressure regulator fluidly receives the gaseous fuel from the first supply bypassing the compressor in the second operating mode when the first supply pressure is less than the desired injection pressure and greater than or equal to the parasitic threshold pressure (PPT); and the third operating mode is commanded when the gaseous-fuel rail pressure (PGFR) is less than the mid-cycle direct injection threshold pressure (PMCDI-T).

12. The apparatus as claimed in claim 11, wherein the compressor threshold pressure (PCT) is less than or equal to 350 bar and greater than or equal to 100 bar.

13. The apparatus as claimed in claim 11, wherein the mid-cycle direct injection threshold pressure (PMCDI-T) is 35 bar to 45 bar above a peak cylinder pressure.

14. The apparatus as claimed in claim 1, further comprising a bypass valve configured to fluidly communicate the gaseous fuel around the pressure regulator when the bypass valve is in an open position, the controller is further programmed to, when the first supply pressure is greater than the desired injection pressure, command the bypass valve to the open position such that the in-cylinder injector receives the gaseous fuel from the first supply at the first supply pressure; and command the in-cylinder injector in a fourth operating mode; wherein the gaseous fuel bums in a diffusion combustion mode in the fourth operating mode, a start of injection timing is later in a compression stroke and an injection duration is smaller in the fourth operating mode compared to the first operating mode for a commanded injection mass, and the internal combustion engine can operate at a maximum rated power in the fourth operating mode.

15. The apparatus as claimed in claim 1, wherein the desired injection pressure is in a range of 200 to 400 bar.

16. The apparatus as claimed in claim 1, further comprising a second supply of the gaseous fuel storing the gaseous fuel as a compressed gas at a second supply pressure; wherein the pressure regulator and the compressor fluidly receive the gaseous fuel selectively from the first supply or the second fuel supply.

17. The apparatus as claimed in claim 16, wherein when the first supply is fluidly supplying the gaseous fuel to the in-cylinder injector, the first supply pressure is less than the desired injection pressure and the second supply pressure is greater than the desired injection pressure, and the gaseous-fuel rail pressure (PGFR) drops below the desired injection pressure in the first operating mode, then the controller is programmed to command the pressure regulator to fluidly receive the gaseous fuel from the second supply.

18. The apparatus as claimed in claim 1, wherein the internal combustion engine operates at a first power demand and at a second power demand greater than the first power demand, the desired injection pressure at a first value in the first power demand and at a second value in the second power demand, the second value greater than the first value, when the internal combustion engine switches from operating with the first power demand to the second power demand, the gaseous-fuel rail pressure (PGFR) increases from the first value to the second value, when the gaseous-fuel rail pressure (PGFR) decreases below the second value of the desired injection pressure while operating at the second power demand, the internal combustion engine switches from the first operating mode to the second operating mode.

19. The apparatus as claimed in claim 1, wherein the internal combustion engine operates at a first power demand and at a second power demand greater than the first power demand, the desired injection pressure at a first value in the first power demand and at a second value in the second power demand, the second value greater than the first value, when the internal combustion engine switches from operating at the second power demand in the second operating mode to the first power demand, the gaseous-fuel rail pressure (PGFR) decreases to the first value and the internal combustion engine switches to the first operating mode.

20. The apparatus as claimed in any one of claims 1-19, wherein a start of injection timing and an injection duration are stored in one or more arrays indexed by the gaseous-fuel rail pressure (PGFR) and the commanded injection mass.

21. The apparatus as claimed in any one of claims 1-19, wherein a start of injection timing and an injection duration are determined analytically as a function of the gaseous-fuel rail pressure (PGFR) and a commanded injection mass.

22. The apparatus as claimed in any one of claims 1-21, wherein the gaseous fuel is selected from the group containing biogas, hydrogen, methane, natural gas, and mixtures thereof.

23. A method for supplying a gaseous fuel to and operating an internal combustion engine comprising: commanding an in-cylinder injector in a first operating mode when a gaseous-fuel rail pressure (PGFR) in a gaseous-fuel rail is equal to or greater than a desired injection pressure; and commanding the in-cylinder injector in a second operating mode when the gaseous-fuel rail pressure (PGFR) is less than the desired injection pressure; wherein in the first operating mode a pressure regulator fluidly receives the gaseous fuel from a first supply when a first supply pressure is greater than or equal to the desired injection pressure, and from a compressor when the first supply pressure is less than the desired injection pressure, in the first operating mode both the first supply and the compressor can deliver a demanded mass flow rate of the gaseous fuel by the internal combustion engine whereby the gaseous-fuel rail pressure (PGFR) is equal to the desired injection pressure, and in the second operating mode the first supply pressure is less than the desired injection pressure such that the pressure regulator fluidly receives the gaseous fuel from the compressor, in the second operating mode the demanded mass flow rate of the gaseous fuel is greater than a mass flow rate of the gaseous fuel delivered by the compressor whereby the gaseous-fuel rail pressure (PGFR) is less than the desired injection pressure.

24. The method as claimed in claim 23, wherein the gaseous fuel bums in a diffusion combustion mode in the first and second operating modes.

25. The method as claimed in claim 23, wherein a start of injection timing is earlier in a compression stroke and an injection duration is greater in the second operating mode compared to the first operating mode for a commanded injection mass.

26. The method as claimed in claim 23, wherein the internal combustion engine operates at a maximum rated power in the first and second operating modes.

27. The method as claimed in claim 23, wherein in the first operating mode the gaseous-fuel rail pressure (PGFR) equals the desired injection pressure for both a low-power demand and a high- power demand of the internal combustion engine.

28. The method as claimed in claim 23, further comprising commanding the in-cylinder injector to switch from the second operating mode to a third operating mode when the gaseous-fuel rail pressure (PGFR) is less than a mid-cycle direct injection threshold pressure (PMCDI-T), wherein in the third operating mode the pressure regulator fluidly receives the gaseous fuel from the compressor and the demanded mass flow rate of the gaseous fuel by the internal combustion engine is greater than the mass flow rate of the gaseous fuel delivered by the compressor, and the gaseous fuel bums in a partially premixed combustion mode in the third operating mode.

29. The method as claimed in claim 28, wherein a start of injection timing is earlier in a compression stroke and an injection duration is greater in the third operating mode compared to the second operating mode for a commanded injection mass.

30. The method as claimed in claim 28, wherein the internal combustion engine operates at a maximum rated power in the third operating mode.