Apparatus and method for a compression ignition, direct injection, internal combustion engine

Abstract

A method for operating an internal combustion engine including introducing a pilot quantity of a gaseous fuel directly into a combustion chamber of the internal combustion engine; and introducing a main quantity of the gaseous fuel directly into the combustion chamber. The pilot quantity auto¬ ignites due to a temperature and a pressure within the combustion chamber and bums in a diffusion combustion mode, and the main quantity ignites due to combustion of the pilot quantity and the main quantity bums in the diffusion combustion mode.

Description

APPARATUS AND METHOD FOR A COMPRESSION IGNITION, DIRECT INJECTION, INTERNAL COMBUSTION ENGINETechnical Field

[0001] The present application relates to an apparatus and method for operating an internal combustion engine, and more particularly a compression ignition, direct injection internal combustion engine fueling with a gaseous fuel.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] Ignition is a key challenge for compression ignition, direction injection, gaseous fueled, internal combustion engines, and particularly those engines where the gaseous fuel is introduced later during a compression stroke. The autoignition temperature for gaseous fuel such as natural gas or hydrogen can be above the end of compression temperature for typical diesel-cycle engines. As a result, gaseous fuel engines require a positive ignition source such as a pilot fuel, a glow plug, or a spark plug to achieve reliable ignition. The use of pilot fuel increases the complexity of the fuel system since it has to store and deliver to the engine both the pilot fuel (for example, diesel fuel) and the gaseous fuel. The pilot fuel also increases the brake specific carbon dioxide (CO2) emission for the engine. The future of CO2 emission regulation for heavy-duty engines under consideration may demand near zero quantities of the pilot fuel. Spark plugs are more suited to premixed combustion where the gaseous fuel is introduced in the intake stroke or early in the compression stroke and suffer from reliability and durability issues when used to ignite gaseous fuel introduced later in the compression stroke that bums in a diffusion combustion mode. Glow plugs ignite the gaseous fuelover and around a finite surface area of the glow plug typically at a single location in the combustion chamber and require a high surface temperature and this can result in poor ignition and combustion characteristics and limit the life of the glow plug.

[0004] The state of the art is lacking in techniques for operating internal combustion engines, and more particularly compression ignition, direction injection, internal combustion engines fueling with a gaseous fuel introduced later in a compression stroke.Summary

[0005] An improved method for operating an internal combustion engine including introducing a pilot quantity of a gaseous fuel directly into a combustion chamber of the internal combustion engine; and introducing a main quantity of the gaseous fuel directly into the combustion chamber. In an exemplary embodiment, a start of injection of the pilot quantity and a start of injection of the main quantity are during a compression stroke. The pilot quantity of the gaseous fuel auto-ignites due to a temperature and a pressure within the combustion chamber and bums in a diffusion combustion mode, and the main quantity of the gaseous fuel ignites due to combustion of the pilot quantity of the gaseous fuel and the main quantity bums in the diffusion combustion mode. A global fuel equivalence ratio in the combustion chamber is less than one.

[0006] In some embodiments a local equivalence ratio of the pilot quantity of the gaseous fuel is greater than one when it auto-ignites. The pilot quantity and the main quantity of the gaseous fuel can be introduced through an injection hole (the same injection hole) of an in-cylinder fuel injector. Alternatively, the pilot quantity can be introduced through a first injection hole and the main quantity can be introduced through a second injection hole of another in-cylinder injector. A pilot injection window within which the pilot quantity of the gaseous fuel is introduced can be from and including thirty (30) crank angle degrees (CAD) before top dead center in a compression stroke to and including five (5) crank angle degrees (CAD) before top dead center in the compression stroke. The pilot quantity of the gaseous fuel can be introduced during a portion of the pilot injection window. A main injection window within which the main quantity of the gaseous fuel is introduced can be from and including twenty (20) crank angle degrees (CAD) before top dead center in a compression stroke to and including thirty -five (35) crank angle degrees (CAD) after top dead center in an expansion stroke.The main quantity of the gaseous fuel can be introduced during a portion of the main injection window. The pilot quantity can be up to 50% of a total quantity of the gaseous fuel introduced during an injection window, where the pilot quantity as a percentage of the total quantity is higher at lower engine loads and lower at higher engine loads.

[0007] In some embodiments, when a pressure and a temperature in the combustion chamber later in the compression stroke support ignition of a single introduction of the gaseous fuel during an engine cycle, then only a single quantity of the gaseous fuel is introduced into the combustion chamber rather than a separate pilot and main quantity introduction, and a magnitude of the single quantity is increased compared to the main quantity to compensate for the pilot quantity. A single injection window within which the single quantity of the gaseous fuel is introduced can be from and including thirty (30) crank angle degrees (CAD) before top dead center in a compression stroke to and including thirty-five (35) crank angle degrees (CAD) after top dead center in an expansion stroke. The single quantity of the gaseous fuel can be introduced during a portion of the main single injection window.

[0008] In some embodiments, the method further includes determining whether the pilot quantity of the gaseous fuel at a desired local equivalence-ratio is auto-ignitable. When the pilot quantity of the gaseous fuel at the desired local equivalence ratio is auto-ignitable, the method includes introducing the pilot quantity of the gaseous fuel such that a local equivalence-ratio of the pilot quantity of the gaseous fuel equals the desired local equivalence ratio when it auto-ignites. When the pilot quantity of the gaseous fuel at the desired local equivalence ratio is not auto-ignitable, the method includes performing a mitigation technique whereby the pilot quantity of the gaseous fuel auto-ignites. The pilot quantity of the gaseous fuel at the desired local equivalence-ratio is autoignitable when an ignition delay in the combustion chamber is less than or equal to two milliseconds. The mitigation technique can include determining an auto-ignitable equivalence-ratio whereby the pilot quantity of the gaseous fuel auto-ignites in the combustion chamber; and adjusting a start of injection timing of the introduction of the pilot quantity of the gaseous fuel, a magnitude of the pilot quantity of the gaseous fuel, the gaseous-fuel injection pressure, a cross-sectional flow area of an injection hole for the pilot quantity, or any combination of two or more of these, whereby the local equivalence-ratio of the pilot quantity of the gaseous fuel equals the auto-ignitable equivalence-ratio when it auto-ignites. Note that when the magnitude of the pilot quantity of the gaseous fuel is adjusted, a magnitude of the main quantity of the gaseous fuel is adjusted in an opposite manner (that is, when the pilot quantity is increased the main quantity is decreased, and vice versa), such that the totalquantity of the gaseous fuel remains substantially the same. Additionally, the ignitability of the pilot quantity of the gaseous fuel can be further improved by increasing the temperature in the combustion chamber, increasing the pressure in the combustion chamber, or both. The temperature and / or the pressure in the combustion chamber can be increased by bypassing at least a portion of intake air pressurized by a compressor of a turbocharging system around a charge air cooler, by bypassing at least a portion of exhaust gas returning to an intake manifold through an exhaust gas recirculation system around an exhaust-gas-recirculation cooler, by employing internal exhaust gas recirculation, by actuating a variable valve actuation system to trap exhaust gas in the combustion chamber after an exhaust valve closes, and / or by increasing an effective compression ratio of the internal combustion engine. The term “and / or” is used herein to mean “one or the other or both”.

[0009] In some embodiments, the method further includes determining whether the pressure and the temperature within the combustion chamber later during the compression stroke are suitable for autoignition of the pilot quantity of the gaseous fuel. When the pressure and the temperature within the combustion chamber are suitable for autoignition, the method can include introducing the pilot quantity of the gaseous fuel. When the pressure and the temperature within the combustion chamber are not suitable for autoignition within the combustion chamber later during the compression stroke, the method can include performing a mitigation technique whereby the pilot quantity of the gaseous fuel auto-ignites. The mitigation technique can include increasing the temperature in the combustion chamber, increasing the pressure in the combustion chamber, or both, such that the pressure and the temperature in the combustion chamber are suitable for autoignition of the pilot quantity of the gaseous fuel. The temperature in the combustion chamber can be increased by bypassing at least a portion of intake air pressurized by a compressor of a turbocharging system around a charge air cooler. The temperature in the combustion chamber can be increased by bypassing at least a portion of exhaust gas returning to an intake manifold through an exhaust gas recirculation system around an exhaust-gas-recirculation cooler. The temperature in the combustion chamber can be increased by actuating a variable valve actuation system to trap exhaust gas in the combustion chamber after an exhaust valve closes. The pressure and the temperature in the combustion chamber can be increased by increasing an effective compression ratio of the internal combustion engine. The effective compression ratio can be increased by adjusting an intake valve closing timing of an intake valve, wherein the intake valve closing timing occurs later in an intake stroke or earlier in the compression stroke. The method can further include determining that the mitigation technique cannot createconditions suitable for auto-igniting the pilot quantity of the gaseous fuel; and actuating an ignition assist to help ignite the pilot quantity or the main quantity of the gaseous fuel. The ignition assist can include a heated surface or a pilot fuel. The heated surface can be a glow plug. When the ignition assist is the pilot fuel, the method can further include introducing the pilot fuel into the combustion chamber whereby the pilot fuel auto-ignites due to the pressure and the temperature in the combustion chamber creating a pressure and temperature environment suitable for igniting the gaseous fuel. The pilot fuel can be selected from the group containing diesel fuel, dimethyl ether (DME), kerosene, and mixtures of these fuels.

[0010] In some embodiments, the method further includes actuating an ignition assist to help ignite the pilot quantity or the main quantity of the gaseous fuel when starting the internal combustion engine or when an ambient temperature is below a predetermined threshold.

[0011] In some embodiments, the gaseous fuel can be hydrogen or mixtures of hydrogen with one or more of ammonia, biogas, butane, ethane, liquefied petroleum gas, methane, natural gas, or propane.

[0012] 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.

[0013] FIG. 1 is a cross-sectional schematic view of a combustion chamber of an internal combustion engine according to an embodiment.

[0014] FIG. 2 is a schematic view of an air handling system of the internal combustion engine of FIG. 1.

[0015] FIG. 3 is a schematic view of a control system of the internal combustion engine of FIG.1.

[0016] FIG. 4 is a chart view of an introduction of a pilot quantity of a gaseous fuel and an introduction of a main quantity of the gaseous fuel into the combustion chamber of FIG. 1 according to an embodiment.

[0017] FIG. 5 is a chart view of an introduction of a single quantity of a gaseous fuel into the combustion chamber of FIG. 1 according to an embodiment.

[0018] FIG. 6 is a flow chart view of a control algorithm for operating the internal combustion engine of FIG. 1 according to an embodiment.

[0019] FIG. 7 is a flow chart view of a control algorithm for operating the internal combustion engine of FIG. 1 according to an embodiment.

[0020] FIG. 8 is a chart view of an ignition delay for various equivalence ratios of the gaseous fuel as a function of pressure and temperature.

[0021] FIG. 9 is a flow chart view of a control algorithm for operating the internal combustion engine of FIG. 1 according to an embodiment.Detailed Description

[0022] Referring to FIGS. 1 and 2, and first to FIG. 1, there is shown a cross-sectional view of combustion chamber 20 of internal combustion engine 10 fueling with a gaseous fuel. As used herein, a gaseous fuel is defined as any fuel that is in the gaseous state (phase) at standard temperature and standard pressure (also called standard temperature and pressure) which is defined herein as a temperature of zero (0) degrees Celsius (°C) and an absolute pressure of one hundred (100) kilopascals (kPa), respectively. Examples of gaseous fuels include ammonia, biogas, butane, ethane, hydrogen, liquefied petroleum gas, methane, natural gas, and propane. In exemplary embodiments the gaseous fuel can be hydrogen, or mixtures of hydrogen with one or more other gaseous fuels. Combustion chamber 20 is formed by cylinder wall 30 of cylinder 40 in engine block 50, cylinder head 60 and piston 70 that reciprocates within the cylinder. Cylinder wall 30 forms a bore that can be any size (diameter) suitable for internal combustion engines. For example, in light duty engineapplications the bore size is typically less than 100mm, in medium duty and heavy-duty engine applications the bore size can range from 100mm to 180mm, and in high horsepower engine applications the bore size is above 180mm. Generally, as the bore size increases the maximum engine speed decreases, primarily due to the increase in momentum of the piston that accompanies increases in its mass and speed putting increased stress on engine components, as would be known by those skilled in the technology. In the illustrated embodiment, piston 70 includes an omega-shaped piston bowl 80, although in other embodiments other piston bowl shapes are contemplated. An air handling system includes intake port 90 and intake valve 100, and exhaust port 110 and exhaust valve 120. In some embodiments at a top dead center (TDC) position of piston 70, there is a small gap between the top of piston 70 and fire deck 65. At this position intake valve 100 and exhaust valve 120 can be aligned with recessed portions (not shown) in piston 70 such that the valves can be in an open position without interference with the piston. Intake valve 100 is actuated by valve actuator 130 and exhaust valve 120 is actuated by valve actuator 140. In some embodiments, valve actuators 130 and 140 can be part of a variable valve actuation (VVA) system 150 that can be operatively connected with and commanded by controller 170 to adjust intake valve timing (IVT) of intake valve 100 and exhaust valve timing (EVT) of exhaust valve 120.

[0023] In some embodiments, VVA system 150 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 electromagnet! cally 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 and the piston.

[0024] Fuel injector 160 is an in-cylinder, gaseous-fuel injector that introduces the gaseous fuel directly into combustion chamber 20. In the illustrated embodiment fuel injector 160 is shown mounted centrally in cylinder 40 through cylinder head 60. Although fuel injector 160 is shown centrally mounted, it is possible that the fuel injector can be mounted offset from a longitudinal axisof cylinder 40. In some embodiments fuel injector 160 is mounted in engine block 50 through cylinder wall 30 (a side mount). The mounting location can be determined by application requirements and the specific architecture of an engine and the available space. Controller 170 is operatively connected with fuel injector 160 to actuate the fuel injector to introduce the gaseous fuel into combustion chamber 20.

[0025] In some embodiments and circumstances, the gaseous fuel will not or may not auto-ignite due to the pressure and temperature environment in combustion chamber 20 near or at the end of a compression stroke, as will be discussed in more detail below. Accordingly, in some embodiments fuel inj ector 160 is a dual fuel inj ector that introduces the gaseous fuel and a pilot fuel into combustion chamber 20 and can introduce the gaseous fuel separately and independently from the pilot fuel, and the timing of injections of the pilot fuel and the gaseous fuel are determined based on engine operating conditions and may or may not overlap. The pilot fuel is a different fuel from the gaseous fuel. The pilot fuel auto-ignites due to the pressure and temperature in combustion chamber 20 later in the compression stroke, and typically near or at the end of the compression stroke, and the combustion of the pilot fuel creates a pressure and temperature environment inside combustion chamber 20 suitable for igniting the gaseous fuel. The pilot fuel acts as a high energy ignition source to ignite the gaseous fuel. In some embodiments when fuel injector 160 is a dual fuel injector it can be a concentric needle fuel injector that can introduce pilot fuel separately and independently of the gaseous fuel. In an alternative embodiment, when fuel injector 160 is a dual fuel injector it can include one injector body with side-by-side gaseous fuel and pilot fuel injection assemblies. In some embodiments when fuel injector 160 only introduces the gaseous fuel, an additional in-cylinder fuel injector (not shown) separate from fuel injector 160 can be employed to introduce the pilot fuel.

[0026] Referring now to FIG. 2, internal combustion engine 10 is shown with six cylinders. In some embodiments internal combustion engine 10 has fewer than six cylinders and in other embodiments internal combustion engine 10 has more than six cylinders. In some embodiments intake air is received in intake manifold 180 through throttle 190, and in other embodiments there is no throttle. To improve power, in some embodiments turbocharger system 200 can boost the pressure in intake manifold 180 above ambient pressure to increase the mass of air (including oxygen) delivered to combustion chamber 20 during an intake stroke. Pressurized exhaust gas from exhaust manifold 210 causes turbine 220 spin that in turn drives compressor 230 to compress intake air to adesired level of boost. Compressed intake air leaving an outlet of compressor 230 is elevated in temperature as a result of compression, compared to fresh intake air, and accordingly can be communicated through charge air cooler (CAC) 240 where it can be cooled. In some embodiments CAC bypass valve 250 can be actuated by controller 170 between a closed position and a fully open position, or any intermediate position therebetween, such that at least a portion of the compressed intake air can bypass the charge air cooler 240. In some embodiments wastegate valve 270 can be actuated by electronic controller 170 between a closed position and a fully opened position, or to any position in between these positions, to allow at least a portion of exhaust gas to bypass turbine 220. In different embodiments other conventional turbocharging systems or supercharging systems can be employed.

[0027] In some embodiments exhaust gas from combustion chamber 20 is communicated through exhaust manifold 210 past exhaust gas oxygen sensor 280 that generates a signal 290 representative of an oxygen content in the exhaust gas in exhaust manifold 210 and the signal 290 is communicated to controller 170. In some embodiments exhaust gas from engine aftertreatment system 340 is communicated past exhaust gas oxygen sensor 285 that generates a signal 295 representative of an oxygen content in the exhaust gas downstream from aftertreatment 340 and the signal 295 is communicated to controller 170. The oxygen content in the exhaust gas can be representative of, or aid in the determination of, an air-fuel ratio in combustion chamber 20, and more particularly a global air-fuel ratio. The air-fuel ratio can change from cycle to cycle due to fluctuations in an amount of air that is fluidly drawn into combustion chamber 20 and the amount of fuel that is introduced. In some embodiments a compression ratio of internal combustion engine 10 is fixed, whereby there can be changes in the amount of air fluidly drawn into combustion chamber 20 during the intake stroke due to changes in air pressure and temperature, and changes in the bulk flow of intake air. In some embodiments an effective compression ratio of internal combustion engine 10 can be changed by VVA system 150 by varying an intake valve closing (IVC) timing, which can change the amount of air in combustion chamber 20 immediately after intake valve 100 closes. The effective compression ratio can be increased by retarding the IVC timing during the intake stroke or advancing the IVC timing during the compression stroke, and accordingly, the effective compression ratio can be decreased by advancing the IVC timing during the intake stroke or retarding the IVC timing during the compression stroke. The terms “compression ratio” and “effective compression ratio” can be used interchangeably herein.

[0028] During certain engine operating conditions, in some embodiments, a portion of the exhaust gas can be communicated to intake manifold 180 through exhaust gas recirculation (EGR) system 300. Controller 170 can command EGR valve 310 between a closed position and a fully open position, or any intermediate position therebetween, to control the EGR mass flow rate through EGR system 300, for a given back pressure in exhaust manifold 210. EGR cooler 320 can reduce the temperature of exhaust gas to protect the intake manifold and to lower in-cylinder temperatures. EGR cooler bypass valve 330 can be employed when it is desired that at least a portion of the recirculated exhaust gas bypasses EGR cooler 320. In the illustrated embodiment at least a portion of exhaust gas from all cylinders 40 can be recirculated to intake manifold 180. In other embodiments any other EGR system architecture can be employed, such as those that dedicate one or more cylinders, or one or more exhaust ports, to EGR, and which may have two or more exhaust manifolds. Exhaust gas not passing through EGR system 300 can be communicated through turbine 220 and / or wastegate valve 270 to engine aftertreatment system 340 before exiting the internal combustion engine.

[0029] Referring to both FIGS. 1 and 2, in some embodiments valve actuators 130 and 140 in VVA system 150 can be employed for internal EGR, also known as residual EGR, which is hot, incylinder EGR, in comparison to EGR system 300, which is an external EGR system (that can be either hot or cool depending upon how much EGR cooler 320 is employed to cool the exhaust gas). Internal EGR can be advantageous when the gaseous fuel includes hydrogen where EGR system 300 can be deteriorated due to water condensation and corrosion. In some embodiments VVA system 150 can control exhaust valve 120 to trap a desired amount of exhaust gas inside combustion chamber 20 after the exhaust valve closes, for example by closing exhaust valve 120 earlier in an exhaust stroke before all the exhaust gas has been evacuated from combustion chamber 20. In some embodiments VVA system 150 can control intake valve 100 to trap the desired amount of exhaust gas inside combustion chamber 20 after exhaust valve 120 closes, for example by opening intake valve 100 later during the exhaust stroke to allow a portion of the exhaust gas to flow into intake port 90, where the exhaust gas in intake port 90 later flows back into combustion chamber 20 during the intake stroke. In some embodiments VVA system 150 can control an exhaust valve closing (EVC) timing or an intake valve opening (IVO) timing, or both, to trap exhaust gas inside combustion chamber 20 after exhaust valve 120 closes.

[0030] In some embodiments an ignition assist can be employed for starting internal combustion engine 10 and for operating the internal combustion engine in cold ambient temperature conditions where in some circumstances the autoignition temperature of the gaseous fuel is not reached in combustion chamber 20 later during the compression stroke. The ignition assist can be a heated surface, such as a glow plug (not shown), configured in combustion chamber 20, or a pilot fuel that is injected and combusted in the combustion chamber, both of which assist in creating a pressure and temperature environment suitable for igniting the gaseous fuel. The pilot fuel can be introduced by fuel injector 160 when the fuel injector is a dual fuel injector introducing a gaseous fuel separately and independently of the pilot fuel, or another fuel injector that only introduces the pilot fuel can be employed. In exemplary embodiments, the plot fuel can be diesel fuel, dimethyl ether (DME), or kerosene.

[0031] Referring now to FIG. 3, controller 170 receives sensor information from sensors employed in internal combustion engines, illustrated on the left-hand side of the controller and commands actuators or components, illustrated on the right-hand side of the controller. Some actuators or components can also send status information to the controller, as would be known by those familiar with the technology. In some embodiments sensors include any of intake manifold temperature (IMT) sensor 400 that provides a signal representative of the temperature inside intake manifold 180 (seen in FIG. 2), intake manifold pressure (IMP) sensor 410 that provides a signal representative of the pressure in intake manifold 180, cylinder pressure sensor 420 that provides a signal representative of the pressure in combustion chamber 20, which can be an in-cylinder pressure sensor or a vibration sensor such as an accelerometer mounted external to combustion chamber 20 (such as on the engine block or bearing cap), an engine speed sensor 430 that provides a signal representative of the engine speed, a gaseous-fuel rail pressure sensor 440 that provides a signal representative of an injection pressure of the gaseous fuel, an engine coolant temperature sensor 450 that provides a signal representative of engine coolant temperature, oxygen sensor 280 that provides the signal representative of the oxygen content in exhaust manifold 210, oxygen sensor 285 that provides the signal representative of the oxygen content downstream from aftertreatment 340, and can include other sensors not shown but commonly employed in internal combustion engines. In some embodiments the actuators or components include any of VVA system 150, in-cylinder injector 160, throttle 190, CAC bypass valve 250, wastegate valve 270, EGR valve 310, EGR cooler bypass valve330, and ignition assist 335 and can include other actuators or components not shown but commonly employed in internal combustion engines.

[0032] In some embodiments controller 170 can comprise both hardware and software components. The hardware components can comprise digital and / or analog components. In some embodiments controller 170 can be a computer including a processor and memories, having one or more permanent memories, such as FLASH, EEPROM or a hard disk, and a temporary memory, such as volatile a memory, for example a random access memory (RAM), for storing and executing a program. In some embodiments controller 170 can include two or more computers or electronic controllers.

[0033] Referring now to FIG. 4, a chart view of a compression-ignition, direct-injection (CIDI) mode is illustrated where only the gaseous-fuel is introduced into combustion chamber 20 (seen in FIG. 1) by fuel injector 160, in two stages, and bums in a diffusion combustion mode, which is also referred to as diffusion-flame combustion, according to an embodiment of a method for operating internal combustion engine 10. Pilot injection 501 introduces a pilot quantity 500 of the gaseous fuel into combustion chamber 20 and main injection 511 introduces a main quantity 510 of the gaseous fuel into the combustion chamber during the CIDI mode. The pilot quantity 500 represents a total mass of the gaseous fuel introduced during the pilot injection 501, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 503 of the pilot-fuel injection and the engine speed of internal combustion engine 10. The main quantity 510 represents a total mass of the gaseous fuel introduced during the main injection 511, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 513 of the main injection and the engine speed of internal combustion engine 10. In some embodiments both the pilot quantity and the main quantity of the gaseous fuel are injected into combustion chamber 20 through an injection hole, and more particularly the same injection hole in fuel injector 160, although this is not a requirement and in other embodiments the pilot quantity can be injected through a different injection hole in fuel injector 160 than the main quantity of gaseous fuel. For example, a main injection hole for the main quantity can have a larger diameter (and cross-sectional flow area) than a pilot injection hole for the pilot quantity. In some embodiments pilot injection window 520 for the pilot quantity of gaseous fuel, within which a start of injection timing followed by an end of injection timing of the pilot quantity can occur anywhere within this window, is between and including thirty (30) crankangle degrees (CAD) before top dead center (BTDC) during the compression stroke and five (5) CAD BTDC during the compression stroke. For example, the pilot quantity 500 can be injected over the entirety of pilot injection window 520, or over a portion thereof. When injected during pilot injection window 520, the pilot quantity 500 of the gaseous fuel bums in a diffusion combustion mode when it auto-ignites. In the illustrated embodiment, the start of injection timing of the pilot quantity 500 occurs at crank angle 502, and the end of injection timing of the pilot quantity occurs at crank angle 504. The pilot quantity 500 of the gaseous fuel experiences a long residence time in combustion chamber 20 allowing the pilot quantity 500 to reach an autoignition temperature, which in some embodiments is before or shortly after the main injection starts. The timing and magnitude of the pilot quantity 500 of the gaseous fuel can be dependent on various factors, for example, engine load, engine speed, IMT, IMP, and gaseous-fuel injection pressure. In some embodiments, the start of injection (SOI) timing for the pilot quantity 500 of the gaseous fuel moves earlier with higher engine speeds, lower engine load, or lower IMT. A limit can be put in place on the SOI timing of the pilot quantity 500 of the gaseous fuel to reduce and preferably prevent over leaning of a local equivalence-ratio of the pilot quantity due to over advancement of injection timing. In some embodiments, main injection window 530 for the main quantity 510 of the gaseous fuel, within which a start of injection timing followed by an end of injection timing of the main quantity can occur anywhere within this window, is between and including 20 CAD BTDC during the compression stroke and 35 CAD after top dead center (ATDC) during an expansion stroke (also known as a power stroke). For example, the main quantity 510 can be injected over the entirety of main injection window 530, or over a portion thereof. When injected during main injection window 520, the main quantity 510 of the gaseous fuel bums in a diffusion combustion mode when it auto-ignites. In the illustrated embodiment, the start of injection timing of the main quantity 510 occurs at crank angle 512, and the end of injection timing of the main quantity occurs at crank angle 514. The pilot quantity 500 auto-ignites due to the pressure and temperature within combustion chamber 20 near the end of the compression stroke, and the main quantity 510 auto-ignites due to, in part, from combustion of the pilot quantity (that creates a pressure and temperature environment suitable for igniting the main quantity of the gaseous fuel). When the pilot quantity 500 and the main quantity 510 are employed, a total quantity of the gaseous fuel introduced into combustion chamber 20 during an engine cycle is a sum of the pilot quantity and the main quantity of the gaseous fuel. In some embodiments the pilot quantity 500 can be up to 50% of the total quantity of the gaseous fuel introduced into combustion chamber 20 in an engine cycle. In some embodiments, the pilot quantity 500 can be as low as 1% of the total quantity of the gaseousfuel introduced into combustion chamber 20 in an engine cycle. At lower engine loads the pilot quantity 500 is typically a greater percentage of the total quantity of the gaseous fuel compared to higher engine loads (for example, the pilot quantity can be up to 50% of the total quantity at engine idle and as low as 1% when the engine operates at full rated power). In some embodiments, the engine cycle is defined as the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke, as in a four-stroke engine. In some embodiments the pilot quantity 500 of the gaseous fuel can serve as a control lever to change a peak rate of heat release by regulating the strength of an ignition flame kernel and controlling the level of premixing prior to ignition of the main quantity of the gaseous fuel. The pilot quantity 500 is typically a significantly smaller mass than the total quantity of the gaseous fuel (except at lower loads where both the pilot quantity and the main quantity can be comparable masses) such that a rate of temperature rise of the pilot quantity after introduction into combustion chamber 20 is sufficient to allow the pilot quantity to reach an autoignition temperature in significantly less time compared to injecting the total quantity of the gaseous fuel in one introduction, which increases the probability of ignition significantly and reduces misfires.

[0034] In some embodiments, a local equivalence-ratio of the pilot quantity is greater than one when the pilot quantity auto-ignites, while a global equivalence-ratio is less than one. Within combustion chamber 20, there is both the local equivalence-ratio and the global equivalence-ratio, and these terms are now discussed in more detail. A fuel-air ratio is a ratio calculated as a quantity of fuel over a quantity of air. A stoichiometric fuel-air ratio is the fuel-air ratio when the quantity of air is just enough to bum the quantity of fuel. An equivalence ratio is calculated as a fuel-air ratio divided by the stoichiometric fuel-air ratio, whereby when the equivalence ratio is less than one there is more than enough air to bum all the fuel (a lean condition), when the equivalence ratio is greater than one there is not enough air to bum all the fuel (a rich condition), and when the equivalence ratio equals one there is just enough air to bum all the fuel (the stoichiometric condition). As used herein, the local equivalence-ratio is the equivalence ratio around a local volume within combustion chamber 20 (such as the local volume within which the gaseous fuel ignites), and the global equivalence-ratio is the equivalence ratio for combustion chamber 20 as a whole. A TDC volume VTDC is defined as the volume of combustion chamber 20 when piston 70 is at the top dead center position. The local volume can vary depending upon the magnitude of the TDC volume. In some embodiments the local volume is two orders of magnitude less than the TDC volume VTDC (VTDC / 100), or 1% of the TDC volume VTDC. In some embodiments, the local volume is three orders of magnitude less than the TDC volumeVTDC (VTDC / 1000), or 0.1% of the TDC volume VTDC. In some embodiments the local volume is between and including 50 cubic millimeters (mm3) to 200 mm3. The local equivalence-ratio can influence the ignition and combustion characteristics of the gaseous fuel even when the global equivalence-ratio remains substantially the same. For example, an ignition flame with the highest temperature would have the local equivalence-ratio at a value of one (stoichiometry), and as the local equivalence-ratio gets further away from the value of one (that is, either more lean or more rich) the flame temperature and the flame speed decrease. Preferably, the local equivalence-ratio for the pilot- quantity / air mixture should be close to or slightly higher than 1 at the time of ignition. Such a range of equivalence ratio helps create a more lasting high-temperature reaction zone after ignition, which increases the robustness for igniting the main quantity of the gaseous fuel. The local equivalenceratio can change from cycle to cycle depending upon various factors even when the global equivalence-ratio remains substantially the same, as will be explained in more detail below.

[0035] Referring now to FIG. 5, a chart view of a compression-ignition, direct-injection (CIDI) mode is illustrated where only the gaseous-fuel is introduced into combustion chamber 20 (seen in FIG. 1) by fuel injector 160, in a single stage, and bums in the diffusion combustion mode, according to an embodiment of a method for operating internal combustion engine 10. Single injection 541 introduces a single quantity 540 of the gaseous fuel into the combustion chamber during the single stage CIDI mode. The single quantity 540 represents a total mass of the gaseous fuel introduced during the single injection 541, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 543 of the single injection and the engine speed of internal combustion engine 10. That is, all the gaseous fuel introduced into combustion chamber 20 during an engine cycle is in single quantity 540. At a particular engine load and engine speed, a magnitude of single quantity 540 is increased compared to main quantity 510 to compensate for pilot quantity 500. In some embodiments single injection window (without pilot) 550 for the single quantity 540 of the gaseous fuel, within which a start of injection timing followed by an end of injection timing of the single quantity can occur anywhere within this window, is between and including 30 CAD BTDC during the compression stroke and 35 CAD after top dead center (ATDC) during an expansion stroke. For example, the single quantity 540 can be injected over the entirety of injection window 550, or over a portion thereof. When injected during single injection window 550, the single quantity of the gaseous fuel bums in a diffusion combustion mode when it auto-ignites. In the illustrated embodiment, the start of injection timing of the single quantity 540 occurs at crank angle 542, andthe end of injection timing of the single quantity occurs at crank angle 544. A sole injection of single quantity 540 without a pilot quantity of the gaseous fuel can occur when the pressure and temperature environment support a single injection, which typically requires hotter conditions within the combustion chamber in order to heat up the greater mass of the gaseous fuel that is injected compared to pilot quantity 500. In some embodiments, a more robust ignition of the gaseous fuel may include the introduction of both the pilot quantity 500 and the main quantity 510 even when the pressure and temperature within the combustion chamber support igniting a sole introduction of the single quantity 540 of the gaseous fuel.

[0036] Referring now to FIG. 6, there is shown a flow chart diagram of a control algorithm 600 for operating internal combustion engine 10 according to an embodiment. In some embodiments, control algorithm 600 is stored and executed by controller 170. In some circumstances the pressure and temperature in combustion chamber 20 in the compression stroke does not create an environment suitable for autoignition of the gaseous fuel, even when there is the introduction of the pilot quantity and the main quantity of the gaseous fuel. In these circumstances the air handling system of internal combustion engine 10 can be adjusted to create the pressure and temperature environment in combustion chamber 20 suitable for autoignition of the gaseous fuel. A condition for whether autoignition of the gaseous fuel is satisfied is determined in step 610, which receives as input the intake manifold temperature and the intake manifold pressure (that are measured and determined in step 620) and a map for the IMT and IMP required for achieving autoignition (that is, compression ignition without the assistance of a positive ignition source, such as ignition assist 335), which is supplied by controller 170 in step 630. In some embodiments, the map is indexed by the effective compression ratio and the engine coolant temperature since the IMP and the IMT required for autoignition can be influenced by these engine operating conditions. Additionally, or alternatively, in other embodiments other engine parameters or engine variables can be employed to index into the map. The pressure and temperature in combustion chamber 20 can be estimated at any crank angle degree during the compression stroke based on the IMT, the IMP, and the compression ratio of internal combustion engine 10. When the condition for autoignition of the gaseous fuel is determined to exist, control is transferred back to step 620 where IMT and IMP are measured. When the condition for autoignition is determined to not exist, control is transferred to step 640 where it is determined how to adjust the operation of internal combustion engine 10 to create the condition for autoignition. In some embodiments autoignition conditions exist when an ignition flame kernel is robust wherebycombustion is stable and predictable from cycle to cycle, and autoignition conditions do not exist when the probability of establishing a robust ignition flame kernel from cycle to cycle is below a desired threshold. Step 640 determines how to employ anyone of, or any combination of two or more of the following controls, (i) actuating charge air cooler bypass valve 250 seen in FIG. 2, (ii) actuating EGR cooler bypass valve 330, (iii) adjusting the effective compression ratio of internal combustion engine 10, and (iv) adjusting the equivalence ratio of the gaseous fuel. In some embodiments, only some of these controls are available. Regarding the first control, when at least a portion of the compressed intake air from compressor 230 (seen in FIG. 2), with elevated temperature due to compression, is bypassed around charge air cooler 240 through CAC bypass valve 250 the temperature of the intake air in intake manifold 180 increases as does the temperature of the intake air in combustion chamber 20. The conditions for autoignition improve with increasing combustion chamber temperature. Similarly, regarding the second control, when EGR is employed and when at least a portion of the exhaust gas from exhaust manifold 210 is bypassed around EGR cooler 320 through EGR cooler bypass valve 330 the temperature of an intake charge (including intake air and exhaust gas) in intake manifold 180 increases as does the temperature of the intake charge in combustion chamber 20. Alternatively, or additionally, instead of employing EGR system 300 at least a portion of exhaust gas can be retained in combustion chamber 20 by performing internal EGR using VVA system 150, which also increases the temperature within combustion chamber 20. Regarding the third control, increasing the effective compression ratio by actuating VVA system 150 increases the pressure and temperature environment within combustion chamber 20, thereby improving the conditions required for autoignition of a fuel-air mixture. Regarding the fourth control, adjusting the equivalence ratio changes the autoignition condition for a fuel-air mixture as will be explained in more detail below. In some embodiments the availability of the controls is a function of engine operating conditions. One of the controls (CAC bypass valve 250, EGR bypass valve 330, internal EGR, the effective compression ratio, and the equivalence ratio), or any combination of two or more of these controls, is actuated accordingly in step 650 to create the condition required for autoignition.

[0037] Referring now to FIG.7 there is shown a flow chart diagram of a control algorithm 602 for operating internal combustion engine 10 according to an embodiment. Control algorithm 602 is like control algorithm 600 in FIG. 6 where like parts in this and all other embodiments have like reference numerals and differences are discussed. In step 610, when the condition for autoignition is satisfied the internal combustion engine 10 enters a compression ignition, direct injection, monofueloperating mode where only the gaseous fuel is introduced into combustion chamber 20 and where the gaseous fuel auto-ignites, such as disclosed in FIGS. 4 and 5. In new step 670, it is determined whether step 640 determined if one of the controls (CAC bypass valve 250, EGR bypass valve 330, internal EGR, the effective compression ratio, and the equivalence ratio), or any combination of two or more of these controls, can be actuated to create the condition required for autoignition, without creating other adverse operating conditions, such as an unacceptable increase in emissions or decrease in efficiency. When step 670 is true (the controls can be actuated to create the condition for autoignition), then control is transferred to step 650 to actuate the controls accordingly. When step 670 is false (the controls cannot be actuated to create the condition for autoignition), then control is transferred to step 680 where an ignition assist operating mode is entered where ignition assist 335 is actuated to help create the conditions in combustion chamber 20 for autoignition. In some circumstances, the ignition assist 335 is actuated in addition to one or more of the controls in step 640 to create autoignition conditions in combustion chamber 20, which can help to reduce the energy requirement from the ignition assist. When ignition assist 335 is the glow plug, then the glow plug is actuated to heat up whereby its surface in combustion chamber 20 and the surrounding area increases in temperature, thereby creating a pressure and temperature environment suitable for igniting the gaseous fuel. When the ignition assist is the pilot fuel, then the internal combustion engine can enter a late cycle, direction injection (LCDI), pilot fuel operating mode, where the pilot fuel is employed as a positive ignition source for the gaseous fuel. Note that the pilot fuel is a fuel with a relatively high cetane value making it a more easily auto-ignitable fuel in typical combustion chamber environments in conventional diesel engines, and the pilot fuel is not to be confused with the pilot quantity of the gaseous fuel, which is a relatively small amount of the gaseous fuel whose combustion creates a pressure and temperature environment suitable for igniting the main quantity of the gaseous fuel, which is a relatively large amount of the gaseous fuel. The internal combustion engine 10 can switch back and forth between the compression ignition, direction injection, monofuel operating mode and the ignition assist operating mode accordingly whenever the conditions required for autoignition are or are not met. In some embodiments in the LCDI mode, the pilot fuel can be introduced between and including 15 CAD BTDC in the compression stroke and 15 CAD ATDC in the expansion stroke, and the gaseous fuel can be introduced between and including 30 CAD BTDC in the compression stroke and 35 CAD ATDC in the expansion stroke.

[0038] For a given fuel, the ignition delay of a fuel-air mixture is a function of the pressure and temperature environment in which that fuel-air mixture exists. With reference to FIG. 8, there are shown lines of different equivalence ratios of fuel-air mixtures that each have the same ignition delay, where the pressure of each fuel-air mixture is plotted along the x-axis and the temperature of each fuel-air mixture is plotted along the y-axis. The numerical values of the x-axis and y-axis in FIG. 8 are for illustrative purposes and in other embodiments the relevant values of the x-axis or the y-axis may be different than that illustrated in FIG. 8. Line 700 is a line of constant equivalence ratio 07oo, and similarly, lines 710, 720, 730, 740, and 750 are lines of constant equivalence ratios 07io, 0720, d>730, 0740, and 0750, respectively. Each fuel-air mixture of equivalence ratios 07oo, 07io, 0720, 0730, 0740, and 0750 have the same ignition delay along their respective pressure and temperature lines 700, 710, 720, 730, 740, and 750. As can be seen, for a fuel-mixture of a fixed equivalence ratio, such as equivalence ratio 07oo represented by line 700, as the pressure decreases the temperature must increase in order to achieve the same ignition delay, and vice versa, that is, as the pressure increases the temperature must decrease in order to achieve the same ignition delay. For two fuel-air mixtures of two different fixed equivalence ratios, such as equivalence ratio 07oo represented by line 700 and equivalence ratio 07io represented by tine 710, for a given pressure, the temperature to achieve the same ignition delay of the fuel-air mixture with equivalence ratio 07io is higher than the temperature of the fuel-air mixture with equivalence ratio 07oo. Accordingly, the target equivalence ratio range can be adjusted in some embodiments in order to achieve an autoignition condition for the fuel-air mixture within combustion chamber 20. Moreover, the equivalence ratio typically can be adjusted from engine cycle to engine cycle whereby autoignition conditions can be established within one engine cycle, whereas other controls that are employed to achieve autoignition conditions, such as adjusting the air handling system through CAC bypass valve 250 or EGR cooler bypass valve 330, typically takes more time and several engine cycles to achieve autoignition conditions. In some embodiments, the ignition delay is less than and including two (2) milliseconds (ms). In some embodiments, the ignition delay is in between and including one (1) ms and 2 ms. For the equivalence ratios illustrated in FIG. 8, the lines are shifted towards upper right in a corresponding chart that illustrates a smaller ignition delay, and the lines are shifted towards lower left in a corresponding chart that illustrates a larger ignition delay. For a given gaseous fuel, there is an equivalence ratio for a fuel-air mixture of that gaseous fuel that experiences the smallest ignition delay for that gaseous fuel, which is called herein a smallest-ignition-delay equivalence ratio 0SID. In the chart for the smallest-igniti on-delay equivalence ratio 0SID, corresponding to the chart of FIG. 8, there is only oneline. The smallest-ignition-delay equivalence ratio OSID is on the slightly lean side of stoichiometry, such that as the equivalence ratio of the fuel-air mixture moves away from the smallest-ignition-delay equivalence ratio OSID, either richer or leaner, the ignition delay increases for a particular pressure and temperature condition. The ignition delay is an indication of the auto-ignitability of a fuel-air mixture where ignition of a mass of fuel is required to occur under time constraints. For example, as the ignition delay for the fuel-air mixture decreases, its auto-ignitibility increases, and as the ignition delay for the fuel-air mixture increases, its auto-ignitibility decreases. A fuel-air mixture with a smaller ignition delay can ignite under certain time constraints that a fuel-air mixture with a larger ignition delay will not ignite under those time constraints. Extending this concept further, a fuel-air mixture with a smaller ignition delay can ignite in a pressure and temperature environment under fixed time constraints that a fuel-air mixture with a larger ignition delay cannot ignite in that pressure and temperature environment under the same fixed time constraints.

[0039] Referring now to FIG. 9, there is shown a flow chart diagram of a control algorithm 800 for operating internal combustion engine 10 according to an embodiment. In some embodiments, control algorithm 800 is stored and executed by controller 170. A condition for whether autoignition of the gaseous fuel is satisfied is determined in step 810, which receives as input the intake manifold temperature and the intake manifold pressure as well as the engine speed measured and determined in step 820 and a map for the IMT and IMP required for achieving autoignition of a fuel / air mixture having a desired local equivalence ratio, which is supplied by controller 170 in step 830. The map in step 830 can be indexed like the map in step 630, with the additional index of the desired equivalence ratio. In step 810 it is determined whether the pilot quantity of the gaseous fuel at the desired local equivalence ratio is auto-ignitable within the allowed time window at the current engine speed, IMT and IMP values, which as previously discussed for control algorithm 600, can be employed to determine the pressure and temperature at any crank angle degree in combustion chamber 20 during the compression stroke. More particularly, when the pilot quantity of the gaseous fuel is injected into combustion chamber 20, it begins to mix with air such that the local equivalence ratio decreases (from richer to leaner); as the pilot quantity penetrates further into the combustion chamber, the fuel-air mixture forms a range of local equivalence ratios along its trajectory. In some embodiments the desired local equivalence ratio is the average equivalence ratio in the TDC volume around the region of the trajectory of the pilot quantity where the fuel ignites. Considering again step 810, the pressure and temperature within the combustion chamber at a crank angle degree where a start of combustion(SOC) preferably should occur can be input into a map, a table, or an equation(s) representative of the chart of FIG. 8, and if the pressure and temperature point such as operating point OP1 in FIG. 8, is on or above an equivalence ratio line representing the desired equivalence-ratio then the desired equivalence ratio is auto-ignitable, otherwise the desired equivalence-ratio is not auto-ignitable. With respect to operating point OP 1 , equivalence ratios d>7oo, d>7io, and 720 are not auto-ignitable, whereas equivalence ratios d>73o, 740. and 750 are auto-ignitable. The map, the table, or the equation(s) representative of the chart of FIG. 8 can be for a desired ignition-delay or a maximum allowable ignition delay. In some embodiments, what is meant by auto-ignitable is having an ignition delay less than a maximum value, for example equal to or less than 2 ms. In some embodiments, what is meant by auto-ignitable is having an ignition delay less than a desired value or within a desired range, for example between and including 1ms to 2ms. In some embodiments, the lower limit in the desired range of ignition delay is indicative that ignition delays below the lower limit typically require extreme pressure and temperature environments that are simply not possible in conventional internal combustion engines. Returning to FIG. 9, when the pilot quantity of the gaseous fuel at the desired local equivalence ratio is auto-ignitable at the current IMT and IMP values, control is transferred to step 840 where the pilot quantity of the gaseous fuel is introduced into combustion chamber 20 such that the local equivalence-ratio of the pilot quantity equals the desired equivalence ratio when and where it auto-ignites, and subsequently or additionally the main quantity of the gaseous fuel is introduced into combustion chamber 20. When the pilot quantity of the gaseous fuel at the desired local equivalence ratio is not auto-ignitable at the current IMT and IMP values, control is transferred to step 850 where a mitigation technique is performed. In some embodiments, the mitigation technique includes determining an auto-ignitable equivalence ratio of the pilot quantity of the gaseous fuel in step 860 and determining controls necessary to obtain the auto-ignitable equivalence ratio in step 870. In some embodiments the auto-ignitable equivalence-ratio is leaner than the desired equivalence-ratio. In some embodiments the auto-ignitable equivalence-ratio is richer than the desired equivalence-ratio. In some embodiments the desired equivalence-ratio is an auto-ignitable equivalence ratio that was previously determined. The local equivalence-ratio of the pilot quantity can be adjusted from the desired equivalence-ratio to the auto-ignitable equivalence ratio by adjusting one or more of the start of injection (SOI) timing of the pilot quantity of the fuel, a magnitude of the pilot quantity of the gaseous fuel, an injection pressure of the pilot quantity of the gaseous fuel, and using different pilot injection hole having a different diameter or cross-sectional flow area. When the magnitude of the pilot quantity of the gaseous fuel is adjusted, a magnitude of the main quantity ofthe gaseous fuel is adjusted in an opposite manner (that is, when the pilot quantity is increased, the main quantity is decreased, and vice versa), such that the total quantity of the gaseous fuel remains substantially the same. Regarding the injection hole adjustment, when different injection holes are employed to inject the pilot quantity and the main quantity, it may be advantageous to employ the main injection hole for the main quantity to also introduce the pilot quantity in some circumstances. Either the SOI timing or the magnitude of the pilot quantity can be adjusted from engine cycle to engine cycle of internal combustion engine 10, whereas the injection pressure of the pilot quantity of the gaseous fuel typically takes more time to adjust. After step 870, control is then transferred to step 840 where the controls required to achieve the auto-ignitable equivalence ratio are employed to introduce the pilot quantity of the gaseous fuel. Alternatively, or additionally, in some embodiments the mitigation technique in step 850 further includes adjusting the controls employed in steps 640 and 650, where the temperature and / or the pressure in combustion chamber 20 can be increased by bypassing at least a portion of intake air pressurized by compressor 230 around charge air cooler 240, by bypassing at least a portion of exhaust gas returning to intake manifold 180 through EGR system 300 around EGR cooler 320, by actuating VVA system 150 to trap exhaust gas in combustion chamber 20 after exhaust valve 120 closes (internal EGR), and / or by increasing the effective compression ratio of the internal combustion engine. In some embodiments, algorithm 800 is performed when the main quantity 540 is introduced into combustion chamber 20 without a pilot quantity, and a desired local equivalence ratio of the main quantity 540 is employed in the algorithm instead of the desired local equivalence ratio of the pilot quantity 500.

[0040] 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

We claim:

1. A method for operating an internal combustion engine comprising, introducing a pilot quantity of a gaseous fuel directly into a combustion chamber of the internal combustion engine; and introducing a main quantity of the gaseous fuel directly into the combustion chamber; wherein the pilot quantity of the gaseous fuel auto-ignites due to a temperature and a pressure within the combustion chamber and bums in a diffusion combustion mode; the main quantity of the gaseous fuel ignites due to combustion of the pilot quantity of the gaseous fuel and the main quantity bums in the diffusion combustion mode; and a global fuel equivalence ratio in the combustion chamber is less than one.

2. The method as claimed in claim 1, wherein a local equivalence ratio of the pilot quantity of the gaseous fuel is greater than one when it auto-ignites.

3. The method as claimed in claim 1, wherein the pilot quantity and the main quantity of the gaseous fuel are introduced through an injection hole of an in-cylinder fuel injector.

4. The method as claimed in claim 1, wherein a pilot injection window within which the pilot quantity of the gaseous fuel is introduced is from and including thirty (30) crank angle degrees (CAD) before top dead center in a compression stroke to and including five (5) crank angle degrees (CAD) before top dead center in the compression stroke.

5. The method as claimed in claim 4, wherein the pilot quantity of the gaseous fuel is introduced during a portion of the pilot injection window.

6. The method as claimed in claim 1 , wherein a main inj ection window within which the main quantity of the gaseous fuel is introduced is from and including twenty (20) crank angle degrees (CAD) before top dead center in a compression stroke to and including thirty-five (35) crank angle degrees (CAD) after top dead center in an expansion stroke.

7. The method as claimed in claim 6, wherein the main quantity of the gaseous fuel is introduced during a portion of the main injection window.

8. The method as claimed in claim 1, wherein the pilot quantity is up to 50% of a total quantity of the gaseous fuel introduced.

9. The method as claimed in claim 1, wherein when a pressure and a temperature in the combustion chamber in the compression stroke support ignition of a single introduction of the gaseous fuel during an engine cycle, only a single quantity of the gaseous fuel is introduced into the combustion chamber and a magnitude of the single quantity is increased compared to the main quantity to compensate for the pilot quantity, wherein the single quantity bums in the diffusion combustion mode.

10. The method as claimed in claim 9, wherein a single injection window within which the single quantity of the gaseous fuel is introduced is from and including thirty (30) crank angle degrees (CAD) before top dead center in a compression stroke to and including thirty-five (35) crank angle degrees (CAD) after top dead center in an expansion stroke.

11. The method as claimed in claim 10, wherein the single quantity of the gaseous fuel is introduced during a portion of the single injection window.

12. The method as claimed in claim 1, further comprising, determining whether the pilot quantity of the gaseous fuel at a desired local equivalence-ratio is auto-ignitable; when the pilot quantity of the gaseous fuel at the desired local equivalence ratio is autoignitable, introducing the pilot quantity of the gaseous fuel such that a local equivalence-ratio of the pilot quantity of the gaseous fuel equals the desired local equivalence ratio when it autoignites; and when the pilot quantity of the gaseous fuel at the desired local equivalence ratio is not autoignitable, performing a mitigation technique whereby the pilot quantity of the gaseous fuel auto-ignites.

13. The method as claimed in claim 12, wherein the pilot quantity of the gaseous fuel at the desired local equivalence-ratio is auto-ignitable when an ignition delay is less than or equal to two milliseconds.

14. The method as claimed in claim 12, wherein the mitigation technique comprises determining an auto-ignitable equivalence-ratio whereby the pilot quantity of the gaseous fuel auto-ignites in the combustion chamber; and adjusting a start of injection timing of the introduction of the pilot quantity of the gaseous fuel, a magnitude of the pilot quantity of the gaseous fuel, a gaseous-fuel injection pressure, a cross-sectional flow area of an injection hole for the pilot quantity, or any combination of two or more of these, whereby the local equivalence-ratio of the pilot quantity of the gaseous fuel equals the auto-ignitable equivalence-ratio when it auto-ignites.

15. The method as claimed in claim 14, further comprising improving ignitability of the pilot quantity of the gaseous fuel by increasing the temperature in the combustion chamber, increasing the pressure in the combustion chamber, or both.

16. The method as claimed in claim 15, wherein the temperature and / or the pressure in the combustion chamber is increased by bypassing at least a portion of intake air pressurized by a compressor of a turbocharging system around a charge air cooler, by bypassing at least a portion of exhaust gas returning to an intake manifold through an exhaust gas recirculation system around an exhaust-gas- recirculation cooler, by employing internal exhaust gas recirculation, by actuating a variable valve actuation system to trap exhaust gas in the combustion chamber after an exhaust valve closes, and / or by increasing an effective compression ratio of the internal combustion engine.

17. The method as claimed in claim 1, further comprising determining whether the pressure and the temperature within the combustion chamber during the compression stroke are suitable for autoignition of the pilot quantity of the gaseous fuel; when the pressure and the temperature within the combustion chamber are suitable for autoignition, introducing the pilot quantity of the gaseous fuel; andwhen the pressure and the temperature within the combustion chamber are not suitable for autoignition within the combustion chamber during the compression stroke, performing a mitigation technique whereby the pilot quantity of the gaseous fuel auto-ignites.

18. The method as claimed in claim 17, wherein the mitigation technique comprises increasing the temperature in the combustion chamber, increasing the pressure in the combustion chamber, or both, whereby the pressure and the temperature in the combustion chamber are suitable for autoignition of the pilot quantity of the gaseous fuel.

19. The method as claimed in claim 18, wherein the temperature in the combustion chamber is increased by bypassing at least a portion of intake air pressurized by a compressor of a turbocharging system around a charge air cooler.

20. The method as claimed in claim 18, wherein the temperature in the combustion chamber is increased by bypassing at least a portion of exhaust gas returning to an intake manifold through an exhaust gas recirculation system around an exhaust-gas-recirculation cooler.

21. The method as claimed in claim 18, wherein the temperature in the combustion chamber is increased by actuating a variable valve actuation system to trap exhaust gas in the combustion chamber after an exhaust valve closes.

22. The method as claimed in claim 18, wherein the pressure and the temperature in the combustion chamber are increased by increasing an effective compression ratio of the internal combustion engine.

23. The method as claimed in claim 22, wherein the effective compression ratio is increased by adjusting an intake valve closing timing of an intake valve, wherein the intake valve closing timing occurs later in an intake stroke or earlier in the compression stroke.

24. The method as claimed in claim 17, further comprising determining the mitigation technique cannot create conditions suitable for auto-igniting the pilot quantity of the gaseous fuel; and actuating an ignition assist to help ignite the pilot quantity or the main quantity of the gaseous fuel.

25. The method as claimed in claim 24, wherein the ignition assist comprises a heated surface or a pilot fuel.

26. The method as claimed in claim 25, wherein the heat surface is a glow plug.

27. The method as claimed in claim 25, when the ignition assist is the pilot fuel, further comprising introducing the pilot fuel into the combustion chamber whereby the pilot fuel auto-ignites due to the pressure and the temperature in the combustion chamber creating a pressure and temperature environment suitable for igniting the gaseous fuel.

28. The method as claimed in claim 25, wherein the pilot fuel is selected from the group containing diesel fuel, dimethyl ether (DME), kerosene, and mixtures of these fuels.

29. The method as claimed in claim 1, further comprising actuating an ignition assist to help ignite the pilot quantity or the main quantity of the gaseous fuel when starting the internal combustion engine or when an ambient temperature is below a predetermined threshold.

30. The method according to one of claims 1 to 29, wherein the gaseous fuel is hydrogen or mixtures of hydrogen with one or more of ammonia, biogas, butane, ethane, liquefied petroleum gas, methane, natural gas, or propane.

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