Method for transition between operating modes

Abstract

A method of transitioning between operating modes in an engine includes operating the engine in a first operating mode where a main fuel comprises a majority of a total quantity of fuel on an energy basis introduced into a combustion chamber; transitioning to a second operating mode by splitting an introduction of the main fuel into an earlier introduction and a later introduction; where the main fuel is the same fuel in the first and second operating modes; and the main fuel is auto-ignited or the main fuel burns with a partially-premixed combustion mode in the second operating mode.

Description

METHOD FOR TRANSITION BETWEEN OPERATING MODESTechnical Field

[0001] The present application relates to a method for transitioning between operating modes in an internal combustion engine, and more particularly between operating modes employing the same main 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] Conventional internal combustion engines that operate in the diesel cycle with a gaseous fuel as a main fuel employ a pilot fuel, such as diesel, to ignite the gaseous fuel, such as natural gas, which is more difficult to ignite than the pilot fuel. Both the pilot fuel and the gaseous fuel are introduced later during a compression stroke in what is known as late-cycle injection and bum with diffusion-flame combustion. As emission standards evolve and carbon-based emission requirements become more stringent the need to reduce the consumption of the pilot fuel in these engines increases. The increasing availability of other gaseous fuels, such as hydrogen, also opens the possibility of operating with a reduced need or without the need of the pilot fuel, at least for some engine operating conditions.

[0004] In late-cycle-inj ection engines fueling with a gaseous fuel, a significant amount of the gaseous fuel can be left inaccessible in the storage tank when the gaseous fuel is stored as a compressed gas in a pressurized tank. As the engine consumes the gaseous fuel from the pressurized tank the storage pressure decreases and some point the storage pressure decreases to a value where the gaseous fuel can no longer be supplied to the engine (even when pressurized by a compressor) at a suitable pressure for late-cycle injection, at least for some engine operating conditions. Under thesecircumstances, different operating modes can be employed to reduce the amount of gaseous fuel left inaccessible in the storage tank.

[0005] Due to these reasons, diesel-cycle engines that employ gaseous fuel as the main fuel can be operated in multiple operating modes. These multiple operating modes can lead to significant changes in fuel injector actuation and combustion characteristics. Unmitigated transition from one operating mode to another may impact the smoothness of engine operation and even drivability of a vehicle powered by the engine.

[0006] The state of the art is lacking in techniques for transitioning between operating modes in an internal combustion engine, and more particularly between operating modes employing the same main fuel.

[0007] An improved method of transitioning between operating modes in an internal combustion engine includes operating the internal combustion engine in a first operating mode where a main fuel comprises a majority of a total quantity of fuel on an energy basis introduced into a combustion chamber of the internal combustion engine. The first operating mode includes introducing the main fuel directly into a combustion chamber of the internal combustion engine after 30 crank angle degrees in a compression stroke; introducing a pilot fuel into the combustion chamber whereby the pilot fuel auto-ignites; and igniting the main fuel with combustion of the pilot fuel in the first operating mode whereby the main fuel bums substantially in a diffusion-flame combustion mode. Beginning transitioning to a second operating mode by splitting the introduction of the main fuel into an early quantity in an earlier introduction and a later quantity in a later introduction of the main fuel. The terms “early quantity” and “earlier introduction” are used to differentiate timing from the respective “later quantity” and “later introduction” of the main fuel. The main fuel can be the same fuel in the first and second operating modes. The main fuel can be auto-ignited in the second operating mode or the main fuel can bum with a partially-premixed combustion mode in the second operating mode.

[0008] In some embodiments, the earlier introduction of the main fuel occurs between and including 120 crank angle degrees before top dead center in the compression stroke and 30 crankangle degrees before top dead center in the compression stroke and the later introduction of the main fuel occurs after 30 crank angle degrees. The method can further include determining an occurrence of knock due to the earlier introduction of the main fuel; and when knock is determined to occur, performing a knock mitigation technique. The earlier introduction of the main fuel can bum in the partially-premixed combustion mode and the later introduction of the main fuel can bum in a diffusion-flame combustion mode. The method can further include determining whether some of the main fuel is still introduced in the later introduction of the main fuel; and when some of the main fuel is still introduced in the later introduction of the main fuel, increasing the early quantity of the earlier introduction of the main fuel and decreasing the later quantity of the later introduction of the main fuel. In some embodiments, an increment of the early quantity of the earlier introduction of main fuel or a decrement of the later quantity of the later introduction of the main fuel is at least 1% of a total energy value of fuel introduced into the combustion chamber in an engine cycle. When all the main fuel introduced into the combustion chamber in an engine cycle is introduced during the earlier introduction of the main fuel, the earlier introduction of the main fuel bums in the partially-premixed combustion mode. In some embodiments, a quantity of the pilot fuel is up to 20% of a total quantity of fuel on an energy basis after the transition to the second operating mode. In some embodiments, a start of injection timing for introducing the pitot fuel into the combustion chamber is retarded in the second operating mode compared to the first operating mode. The start of injection timing for the pitot fuel can be retarded for each increment of the early quantity of the earlier introduction of the main fuel and decrement of the later quantity of the later introduction of the main fuel combination. In some embodiments, a majority of the pitot fuel is introduced during an expansion stroke of the internal combustion engine after the transition to the second operating mode.

[0009] In some embodiments, the earlier introduction of the main fuel occurs between and including 30 crank angle degrees before top dead center in a compression stroke and 10 crank angle degrees before top dead center in the compression stroke and the later introduction of the main fuel occurs after the earlier introduction. The later introduction can begin after the earlier introduction begins. The method can further include determining a change in torque is greater than a threshold value; and when the change in torque is a decrease in torque and greater than the threshold value, performing a misfire mitigation technique. The main fuel in the later introduction of the main fuel can bum in a diffusion-flame combustion mode and the main fuel in the earlier introduction can bum in the diffusion-flame combustion mode during the second operating mode. The method can furtherinclude retarding a start of injection timing of the pilot fuel; determining a change in torque is greater than a threshold value; and when the change in torque is a decrease in torque and greater than the threshold value, performing a misfire mitigation technique. The start of injection timing of the pilot fuel can be retarded by a value up to 30 crank angle degrees. The method can further include determining whether the start of injection timing of the pilot fuel is after introduction of the later quantity of the later introduction of the main fuel; and when the start of injection timing of the pilot fuel is after introduction of the later quantity of the later introduction of the main fuel, stopping the introduction of the pilot fuel and increasing the later quantity of the later introduction of the main fuel to compensate for the removal of the pilot fuel. The method can further include determining whether the start of injection timing of the pilot fuel is after a mid-point of the heat release of the combustion of the pilot fuel and the main fuel in the combustion chamber; and when the start of injection timing of the pilot fuel is after the mid-point of the heat release, stopping introduction of the pilot fuel and increasing the later quantity of the later introduction of the main fuel to compensate for the removal of the pilot fuel. The method can further include determining a heat release of combustion of the early quantity of the earlier introduction of the main fuel includes a rate of heat release above a threshold rate and a magnitude of an area under the curve of the heat release above a threshold magnitude; and when the rate of heat release is above the threshold rate and the magnitude of the area under the curve of the heat release is above the threshold magnitude, stopping introduction of the pilot fuel and increasing the later quantity of the later introduction of the main fuel to compensate for the removal of the pilot fuel. The method can further include retarding the start of injection timing and / or a start of combustion timing of the pilot fuel to after combustion of the early quantity of the earlier introduction of the main fuel. In some embodiments, after the transition the early quantity of the earlier introduction of the main fuel comprises between 5% and 50% of the main fuel introduced into the combustion chamber during an engine cycle and the later quantity of the later introduction of the main fuel comprises between 50% and 95% of the main fuel introduced in the combustion chamber during the engine cycle.

[0010] In some embodiments, the main fuel is a gaseous fuel and preferably includes hydrogen.The main fuel can be a majority hydrogen, or the main fuel can be substantially hydrogen.Brief Description of the Drawings

[0011] 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.

[0012] FIG. 1 is a cross-sectional schematic view of a combustion chamber of an internal combustion engine according to an embodiment.

[0013] FIG. 2 is a chart view of a pilot fuel injection and a gaseous fuel injection for a late-cycle, direct-injection operating mode for the internal combustion engine of FIG.l according to an embodiment.

[0014] FIG. 3 a chart view of a pilot fuel injection and a gaseous fuel injection for a mid-cycle, direct-injection operating mode for the internal combustion engine of FIG.l according to an embodiment.

[0015] FIG. 4 is a chart view of injections of a pilot quantity of gaseous fuel and a main quantity of gaseous fuel for a compression-ignition, direct-injection operating mode for the internal combustion engine of FIG.1 according to an embodiment.

[0016] FIG. 5 is a flow chart view of a transition algorithm between the late-cycle, direct-inj ection operating mode of FIG. 2 to the mid-cycle, direct-injection operating mode of FIG. 3 according to an embodiment.

[0017] FIGS. 6, 7, and 8 illustrate fuel injections for the late-cycle, direct-injection operating mode, fuel injections for an intermediate operating mode between the late-cycle, direct-injection operating mode and the mid-cycle, direct-injection operating mode, and fuel injections for the midcycle, direct-injection operating mode, respectively.

[0018] FIG. 9 is a flow chart view of a transition algorithm between the late-cycle, direct-inj ection operating mode of FIG. 2 and the compression-ignition, direct-injection operating mode of FIG. 4 according to an embodiment.

[0019] FIGS. 10, 11, and 12 illustrate fuel injections for the late-cycle, direct-injection operating mode, fuel injections for an intermediate operating mode between the late-cycle, direct-injection operating mode and the compression-ignition, direct-injection operating mode, and fuel injections for the compression-ignition, direct-injection operating mode, respectively.

[0020] FIG. 13 is a chart view of injections of a main quantity of gaseous fuel for a single-pulse, compression-ignition, direct-injection operating mode for the internal combustion engine of FIG.1 according to an embodiment.

[0021] FIGS. 14, 15, and 16 illustrate fuel injections for the dual-pulse, compression-ignition, direct-injection operating mode, fuel injections for an intermediate operating mode between the dualpulse compression-ignition, direct-injection operating mode and the single-pulse compressionignition, direct-injection operating mode, and fuel injections for the single-pulse compressionignition, direct-injection mode, respectively.Detailed Description

[0022] Referring 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 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, propane, and mixtures of these fuels. 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 have a diameter suitable for internal combustion engines. For example, in light duty engine applications the bore diameter can be less than 100 millimeters (mm), in medium duty and heavy-duty engine applications the bore diameter can range from 100 mm to 180 mm, and in high horsepower engine applications the bore diameter can be above 180 mm. Generally, as the bore diameter increases the maximum engine speed decreases, primarily due to the increase inmomentum 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 180. At the TDC position of piston 70 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 are part of a cam system. 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) and / or intake valve lift (IVL) of intake valve 100 and exhaust valve timing (EVT) and / or exhaust valve lift (EVL) of exhaust valve 120. The term “and / or” is used herein to mean “one or the other or both”.

[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 of the piston.

[0024] With reference to FIG. 1, in some embodiments fuel injector 160 is an in-cylinder, dualfuel injector that introduces the gaseous fuel and a pilot fuel directly into combustion chamber 20 and can introduce the gaseous fuel separately and independently from the pilot fuel, and the timing of the 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 fuelauto-ignites due to the pressure and temperature in combustion chamber 20 later in 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 those embodiments, 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, fuel injector 160 only introduces the gaseous fuel (that is, fuel injector 160 is a gaseous fuel injector) and an additional in-cylinder fuel injector (not shown) separate from fuel injector 160 can be employed to introduce the pilot fuel. 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 axis of 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, the pilot fuel, or both, into combustion chamber 20.

[0025] In some embodiments, internal combustion engine 10 includes a combustion sensor (not shown) for determining a heat release, and more particularly a rate of heat release in combustion chamber 20 during combustion. The combustion sensor can be an in-cylinder pressure sensor configured to detect pressure within combustion chamber 20. Alternatively, or additionally, the combustion sensor can be a vibration sensor, such as an accelerometer, configured to detect vibrations in engine block 50 or in a bearing cap (not shown), see Applicant’s United States patent no. 7,444,231, issued on October 28, 2008 for various techniques to mount an accelerometer. Controller 170 is operatively connected with the combustion sensor to receive signals representative of the pressure in combustion chamber 20 or the signals representative of vibrations in engine block 50 or the bearing cap, and the controller can be programmed to determine the heat release within combustion chamber 20 as a function of crank angle during the engine cycle, and particularly during the compression stroke and the expansion stroke, based on the signals representative of the pressure signals and / or the vibration signals. Other sensors measuring engine operating variables can also be employed in internal combustion engine 10. For example, sensors to detect intake manifold temperature (IMT)and intake manifold pressure (IMP) can be employed and operatively connected to controller 170 to send signals representative of the IMT and IMP, respectively, and the controller can be programmed to determine the IMT and the IMP based on these signals.

[0026] With reference to FIG. 2, a fuel -injection mass-flow for a late-cycle, direct-injection (LCDI) operating mode is illustrated where the fuel injected into combustion chamber 20 substantially bums with diffusion-flame combustion (where the fuel and the oxidizer are separate before burning). Pilot-fuel injection 200 introduces a pilot-fuel quantity 202 of the pilot fuel into combustion chamber 20 and main injection 210 introduces a main quantity 212 of the gaseous fuel into the combustion chamber during the LCDI operating mode. The pilot-fuel quantity 202 represents a total mass of the pilot fuel introduced during pilot-fuel injection 200, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 204 of the pilot-fuel injection and the engine speed of internal combustion engine 10. The main quantity 212 represents a total mass of the gaseous fuel introduced during the main injection 210, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 214 of the main injection and the engine speed of internal combustion engine 10. The pilot-fuel injection 200 is calibrated based on a differential pressure between a rail pressure of the pilot fuel and the cylinder pressure inside combustion chamber 20 (and other engine operating conditions), and is influenced by the geometry of a pilot-fuel injection valve (not shown) inside in-cylinder injector 160 (or other separate pilot fuel injector), and particularly a cross-sectional flow area through the pilotfuel injection valve as it opens, remains open, and then closes. Similarly, the main injection 210 of the gaseous fuel is calibrated based on a differential pressure between a rail pressure of the gaseous fuel and the cylinder pressure inside combustion chamber 20 (and other engine operating conditions), and is influenced by the geometry of a gaseous-fuel injection valve (not shown) inside in-cylinder injector 160, and particularly a cross-sectional flow area through the gaseous-fuel injection valve as it opens, remains open, and then closes. The pilot-fuel injection 200 and the main injection 210 begin later during the compression stroke such that the pilot fuel and the gaseous fuel do not have time to premix and thereby substantially bum by diffusion-flame combustion.

[0027] In the illustrated embodiment, pilot-fuel quantity 202 is introduced completely during the compression stroke, before main quantity 212 is introduced, and the main injection 210 begins during the compression stroke and ends during the expansion stroke. However, this is not a requirement. Forexample, in other embodiments, the pilot-fuel injection 200 can be overlapped with the main injection 210, and / or the pilot-fuel injection 200 can begin during the expansion stroke, and / or the main injection 210 can end during the compression stroke, provided in all cases the pilot fuel and main fuel substantially bum by diffusion-flame combustion. In some embodiments, a pilot-fuel ignition window 206 illustrates the range of crank angle degrees (CAD) in which ignition of the pilot-fuel quantity 202 can occur relative to the pilot-fuel injection 200 during the LCDI operating mode, and is between and including 15 CAD before top dead center (BTDC) in the compression stroke and 15 CAD after top dead center (ATDC) in the expansion stroke. In some embodiments, an ignition delay of the pilot fuel is 2 milliseconds (ms) or less, and typically less than 1 ms, for all operating modes employing the pilot fuel. In some embodiments, a main injection window 216 for the main quantity 212 measured in crank angle degrees, within which a start of injection timing followed by an end of injection timing of the main injection 210 can occur anywhere within this window during the LCDI operating mode, is between and including 30 crank angle degrees (CAD) BTDC during the compression stroke and 35 CAD ATDC during the expansion stroke. For example, the main quantity 212 of the gaseous fuel can be injected over the entirety of main injection window 216, or over a portion thereof. In the LCDI operating mode, the end of injection of the main quantity 212 is typically later than start of ignition of the main quantity. In some embodiments, the introduction of main quantity 212 can include a plurality of inj ections of the gaseous fuel, where the fuel introduced in the plurality of inj ections bums in the diffusion-flame combustion mode. An injection pressure for the gaseous fuel during the LCDI operating mode can be at least 250 bar and as high as the rated fdl pressure of a gaseous-fuel supply (not shown), which is typically defined by local jurisdictions (and is known to be as high as 700 bar). Exemplary injection pressures for the gaseous fuel during the LCDI operating mode can be around 300 bar or around 500 bar. In some embodiments, when the gaseous fuel is hydrogen, the injection pressure in the LCDI operating mode is at least 200 bar for high loads and at least 100 bar for low loads. A global fuel / air equivalence ratio in combustion chamber 20 can be less than or equal to 0.75 in the LCDI operating mode where both the gaseous fuel and the pilot fuel are included in the determination. The global fuel / air equivalence ratio is lean to achieve good mixing quality for diffusion-flame combustion.

[0028] In the LCDI operating mode, in some embodiments, the pilot-fuel quantity 202 can be up to 20% of a total quantity of fuel (both the pilot fuel and the gaseous fuel) introduced into combustion chamber 20 on an energy basis. That is, 20% of a total energy quantity of fuel introduced into thecombustion chamber can be from the pilot fuel, where the total energy quantity of fuel includes both the pilot fuel and the gaseous fuel. Typically, the pilot fuel accounts for at least 1% of the total energy quantity of the fuel introduced into the combustion chamber. The pilot fuel can account for a greater percentage of the total energy quantity of fuel introduced into combustion chamber 20 when internal combustion engine 10 is operating at low(er) loads, and as the engine load increases the percentage of the total energy quantity of fuel introduced attributable to the pilot fuel can decrease. In some embodiments, the pilot-fuel quantity 202 can be greater than 20% of the total energy quantity of fuel introduced into combustion chamber 20 on an energy basis; however, this is not desirable due to increased carbon-based emissions.

[0029] Referring now to FIG. 3, a mid-cycle, direct-injection (MCDI) operating mode is illustrated where the gaseous fuel injected into combustion chamber 20 has some time to premix such that it forms a partially-premixed gaseous-fuel / air mixture that bums with both diffusion-flame combustion (where the fuel and the oxidizer are separate before burning) and premixed-flame combustion (where the fuel and oxidizer are premixed), which is referred to collectively as partially- premixed combustion. In the MCDI operating mode, there are regions in combustion chamber 20 where a combustion rate is limited by a rate of diffusion and other regions where the combustion rate is controlled by a propagation of the flame. Main injection 220 introduces a main quantity 222 of the gaseous fuel into combustion chamber 20 and pilot-fuel injection 230 introduces a pilot-fuel quantity 232 of the pilot fuel into the combustion chamber during the MCDI operating mode. The main quantity 222 represents a total mass of the gaseous fuel introduced during the main injection 220, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 224 of the main injection and the engine speed of internal combustion engine 10. The main injection 220 begins earlier during the compression stroke compared to both the pilot-fuel injection 200 and the main injection 210 in the LCDI operating mode of FIG. 2, which allows the main quantity 222 of the gaseous fuel to partially premix with air. The pilot-fuel quantity 232 represents a total mass of the pilot fuel introduced during pilot-fuel injection 230, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 234 of the pilot-fuel injection and the engine speed of internal combustion engine 10. The pilot-fuel injection 230 occurs later during the compression stroke and / or the expansion stroke near the time at which start of ignition of the partially-premixed gaseous-fuel / air mixture is desired.

[0030] In some embodiments, a main injection window 226 for the main quantity 222 measured in crank angle degrees, within which a start of injection timing followed by an end of injection timing of the main injection 220 can occur anywhere within this window during the MCDI operating mode, is between and including 120 CAD BTDC during the compression stroke and 30 CAD BTDC during the compression stroke. For example, the main quantity 222 of the gaseous fuel can be injected over the entirety of main injection window 226, or over a portion thereof. The end of injection timing of the main injection 220 typically occurs before start of ignition timing of the main quantity 222 in the MCDI operating mode. A pilot-fuel ignition window 236 illustrates the range of crank angle degrees in which ignition of the pilot-fuel quantity 232 can occur relative to the pilot-fuel injection 230 during the MCDI operating mode and can be between and including 15 CAD BTDC in the compression stroke and 15 CAD ATDC in the expansion stroke. An injection pressure for the gaseous fuel during the MCDI operating mode can be at least 100 bar, and although the injection pressure during the MCDI operating mode can be as high as the rated fill pressure of the gaseous-fuel supply (not shown) it typically isn’t higher than a lower value (or a minimum value) of the main inj ection pressure during the LCDI operating mode since the gaseous fuel is injected earlier during the compression stroke in the MCDI operating mode than in the LCDI operating mode whereby cylinder pressure during injection can be less. An exemplary injection pressure range for the gaseous fuel during the MCDI operating mode is between 100 bar and 200bar, although this is not a requirement. In an exemplary embodiment, when the injection pressure is 295 bar during the LCDI operating mode, the injection pressure during the MCDI operating mode is 140 bar, whereby engine 10 can be operated at full engine load in the MCDI operating mode with little, even negligible, penalty on peak thermal efficiency. In some embodiments, when the gaseous fuel is hydrogen, the injection pressure in the MCDI operating mode is at least 150 bar for high loads and at least 50 bar for light loads. A global fuel / air equivalence ratio in combustion chamber 20 can be less than or equal to 0.75 in the MCDI operating mode where both the gaseous fuel and the pilot fuel are included in the determination. The global fuel / air equivalence ratio is lean to achieve improved combustion efficiency.

[0031] Referring now to FIG. 4, a compression-ignition, direct-injection (CIDI) operating mode is illustrated where only the gaseous-fuel is introduced into combustion chamber 20, in two stages, and bums with diffusion-flame combustion. Pilot injection 240 introduces a pilot quantity 242 of the gaseous fuel into combustion chamber 20 and main injection 250 introduces a main quantity 252 of the gaseous fuel into the combustion chamber during the CIDI operating mode. The pilotquantity 242 represents a total mass of the gaseous fuel introduced during the pilot injection 240, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 244 of the pilot-fuel injection and the engine speed of internal combustion engine 10. The main quantity 252 represents a total mass of the gaseous fuel introduced during the main injection 250, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 254 of the main injection and the engine speed of internal combustion engine 10. The pilot quantity 242 of the gaseous fuel is typically introduced into combustion chamber 20 prior to the main quantity 252 of the gaseous fuel, accordingly the pilot injection 240 is an earlier introduction of the gaseous fuel and the main injection 250 is a later introduction. In some embodiments, a pilot injection window 246 (measured in crank angle degrees) for the pilot quantity 242 during the CIDI operating mode, within which a start of injection timing followed by an end of injection timing of the pilot injection 240 can occur anywhere within this window, is between and including 30 CAD BTDC during the compression stroke and 5 CAD BTDC during the compression stroke. For example, the pilot quantity 242 of the gaseous fuel can be injected over the entirety of the pilot injection window 246, or over a portion thereof. In some embodiments, a main injection window 256 for the main quantity 252 measured in crank angle degrees, within which a start of injection timing followed by an end of injection timing of the main injection 250 can occur anywhere within this window during the CIDI operating mode, is between and including 20 CAD BTDC during the compression stroke and 35 CAD ATDC during the expansion stroke. For example, the main quantity 252 of the gaseous fuel can be injected over the entirety of the main injection window 256, or over a portion thereof. Pilot quantity 242 of the gaseous fuel experiences a long residence time in combustion chamber 20 allowing the pilot quantity to reach an autoignition temperature, which in some embodiments is before or shortly after the introduction of the main quantity 252. The timing of the pilot injection 240 and a magnitude of the pilot quantity 242 of the gaseous fuel can be dependent on various factors, for example, the gaseous fuel, engine load, engine speed, IMT, IMP, and gaseous-fuel injection pressure. In some embodiments, the start of injection (SOI) timing for the pilot injection 240 of the gaseous fuel is advanced (begins 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 injection 240 of the gaseous fuel to reduce and preferably prevent over leaning of a local equivalence-ratio of the pilot quantity 242 due to over advancement of injection timing.

[0032] The CIDI operating mode is a monofuel operating mode where only one fuel, which can be a mixture of fuels, is auto-ignited without the need of a positive ignition source, although in some circumstances an ignition assist (such as a heated surface) can be employed during the CIDI operating mode when the pressure and temperature environment in combustion chamber 20 later during the compression stroke in some circumstances does not support autoignition of the fuel. The pilot quantity 242 of gaseous fuel is not to be confused with the pilot-fuel quantity 202, 232 of the pilot fuel in the LCDI and MCDI operating modes, respectively. In some embodiments, both the pilot quantity 242 and the main quantity 252 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. The pilot injection 240 and the main injection 250 begin later during the compression stroke such that the pilot quantity 242 and the main quantity 252 do not have time to premix and thereby substantially bum only with diffusion-flame combustion. The pilot quantity 242 of the gaseous fuel auto-ignites due to the pressure and temperature within combustion chamber 20 near the end of the compression stroke, and main quantity 252 of the gaseous fuel auto-ignites due to combustion of the pilot quantity creating a pressure and temperature environment suitable for igniting the main quantity of the gaseous fuel.

[0033] In some embodiments, the pilot quantity 242 of the gaseous fuel can be up to 50% of a total quantity of the gaseous fuel introduced into combustion chamber 20 in an engine cycle in the CIDI operating mode. In some embodiments, the pilot quantity 242 of the gaseous fuel can be as low as 1% of the total quantity of the gaseous fuel introduced into combustion chamber 20 in an engine cycle in the CIDI operating mode. 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. The pilot quantity 242 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 mixing prior to ignition of the main quantity 252 of the gaseous fuel. In an exemplary embodiment, at lower loads the pilot quantity 242 can be up to 50% of the total quantity of the gaseous fuel introduced into the combustion chamber, and at higher loads the pilot quantity 242 can be as little as 5% of the total quantity of the gaseous fuel introduced into the combustion chamber. At lower engine loads the pilot quantity 242 is typically a greater percentage of the total quantity ofthe gaseous fuel compared to higher engine loads. A mass of the pilot quantity 242 of the gaseous fuel is significantly smaller than a mass of the main quantity 252 of the gaseous fuel (or smaller than a mass of the total quantity of the gaseous fuel) 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, even though the pilot quantity and the main quantity are the same gaseous fuel and therefore have the same auto-ignition temperature at any particular pressure. The smaller mass of the pilot quantity and the increased residence time of the pilot quantity in combustion chamber 20 both increase the likelihood of the pilot quantity auto-igniting.

[0034] Referring now to FIGS. 5 to 8 and first to FIG. 5, there is shown algorithm 300 for transitioning from the LCDI operating mode to the MCDI operating mode. In step 310 it is determined to initiate the transition from the LCDI to MCDI operating mode. Various criteria can be employed to determine when to transition from the LCDI to the MCDI operating mode. For example, in some embodiments when a storage pressure of the gaseous fuel in a storage tank (not shown) decreases below a threshold value, internal combustion engine 10 can be operated more efficiently in the MCDI operating mode than the LCDI operating mode, particularly when the energetic cost of pressurizing the gaseous fuel from the storage tank to an injection pressure suitable for the LCDI operating mode is substantial. In step 320 the introduction of the main quantity 212 (seen in FIG. 2) is split into an earlier introduction 211 of early quantity 213 of the gaseous fuel and a later introduction 215 of a later quantity 217 of the gaseous fuel (seen in FIG. 7). As used herein the term introduction can be used interchangeably with the term injection when the context is fuel injection. In some embodiments, the main quantity 212 is split evenly between the early quantity 213 and the later quantity 217. In some embodiments, the main quantity 212 is split unevenly between the early quantity 213 and the later quantity 217. In some embodiments, the early quantity 213 is initially greater than the later quantity 217, and in other embodiments the early quantity 213 is initially less than the later quantity 217. The injection timing of the earlier introduction 211 is within the same injection window as the main injection window 226 of the main injection 220 in the MCDI operating mode seen in FIG. 3, and the injection timing of the later introduction 215 is within the same injection window as the main injection window 216 of the main injection 210 in the LCDI operating mode seen in FIG. 2. In other embodiments, the injection timing of the earlier introduction 211 can span both the main injectionwindows 226 and 216, initially, but eventually the injection timing of the earlier introduction 211 is only within the main injection window 226. In some embodiments, the introduction of pilot-fuel quantity 202 as seen in FIG. 6 is retarded (that is, delayed) at the same time the main quantity 210 is split, such as illustrated by a retarded introduction 201 of pilot-fuel quantity 203 seen in FIG. 7. Initially, the pilot-fuel quantity 203 is equivalent to the pilot-fuel quantity 202, and may or may not be adjusted during the transition. Delaying the introduction of the pilot fuel can protect engine 10 from excessive cylinder pressure in combustion chamber 20. An ignition window within which the pilot-fuel quantity 203 can ignite is the same as the pilot-fuel ignition window 206 or 236, as seen in FIGS. 2 and 3, respectively for the LCDI and MCDI operating modes. In step 330 it is determined whether engine knock is detected, and more particularly that knock is detected due to the split injection of the gaseous fuel between the earlier introduction 211 and the later introduction 215Engine knock can occur when one or more pockets of a fuel / air mixture in combustion chamber 20 explode outside the envelope of the normal combustion front. Engine knock can also occur when there is an excessive rate of heat release and / or ringing in the heat release during combustion. When knock is detected control is transferred to step 340 where a knock mitigation technique is performed, which can include (but is not limited to) anyone or more of (i) delaying timing of the introduction of the pilot fuel, (ii) lowering gaseous-fuel rail pressure to reduce turbulence thereby reducing flame speed, (iii) increasing exhaust-gas recirculation, and (iv) lowering the temperature of the intake charge (for example, by employing a charge-air-cooler and / or an EGR cooler), and when knock mitigation is not successful the transition can be aborted and operation returned to the LCDI operating mode. In some embodiments, alternatively or additionally to detecting knock, engine speed can be monitored for changes in torque when the main quantity 212 is split into the early quantity 213 and the later quantity 217, and when each time the early quantity 213 is incremented. When knock is not detected control is transferred to step 350 where it is determined whether any gaseous fuel is introduced during the later introduction 215. When there is still gaseous fuel introduced in the later introduction 215 (a magnitude of the later quantity 217 is greater than zero), control is transferred to step 360 where a magnitude of early quantity 213 is increased and the magnitude of the later quantity 217 is decreased. In some embodiments, the magnitude of later quantity 213 is decreased to zero and the magnitude of the early quantity 217 is increased to a magnitude of main quantity 212 seen in FIG. 6. In some embodiments, the magnitude of later quantity 217 is decreased by a predetermined value, and the magnitude of the earlier quantity 232 is increased by the predetermined value. In some embodiments, the retarded introduction 201 of pilot-fuel quantity 203 is further retarded after the magnitudes ofearly quantity 213 and later quantity 217 are adjusted. After the earlier and later introductions 211 and 215, respectively are adjusted, control is transferred again to step 330 to detect knock. In some embodiments, the transition from the LCDI to the MCDI operating mode occurs in four steps of increments of the early quantity 213. For example, in a first step, a second step, a third step, and a fourth step the early quantity 213 can be 25%, 50%, 75%, and 100% of the main quantity 212, respectively. When the later quantity 217 is reduced to zero, control is transferred to step 370 where the transition is complete, and the earlier introduction 211 and the early quantity 213 now correspond to the main injection 220 and the main quantity 222, respectively, and the pilot-fuel injection 201 and the pilot-fuel quantity 203 correspond to the pilot-fuel injection 230 and the pilot-fuel quantity 232, respectively seen in FIGS. 3 and 8. The introduction of the pilot fuel can be delayed (that is, retarded) once or multiple times when transitioning from the LCDI to the MCDI operating mode. In an exemplary embodiment, the introduction of the pilot fuel is delayed each time the magnitude of the early quantity 213 is incremented, which helps with mitigating excessive heat release. The pilot-fuel quantity 232 can be equivalent to the pilot-fuel quantity 202, or may be different depending upon the calibration for the pilot-fuel quantity in the LCDI versus the MCDI operating mode, and when the pilot-fuel quantity 232 is different than the pilot-fuel quantity 202, the main fuel quantity 222 can be adjusted such that the total quantity of fuel (both the pilot fuel and gaseous fuel) is equivalent on an energy basis between the LCDI and MCDI operating modes. In some embodiments, the efficiency in the MCDI operating mode is less than the efficiency in the LCDI operating mode, such that for a given power demand the fueling quantity will be higher for the MCDI operating mode. In these embodiments, the main quantity 222 seen in FIG. 8 can be higher than the main quantity 212 seen in FIG. 6, and the increase in the fueling of the gaseous fuel due to the difference between the main quantity 222 and the main quantity 212 can be distributed over one or more of the increments of the early quantity 213 seen in FIG. 7 when transitioning from the LCDI to the MCDI operating mode.

[0035] The steps outlined above for algorithm 300 in FIG. 5 can be reversed to transition from the MCDI operating mode to the LCDI operating mode. Alternatively, since the LCDI operating mode does not (typically) experience problems with knock, it is possible to transition from the MCDI operating mode back to the LCDI operating mode in a single engine cycle. That is, the timing for the injection of the gaseous fuel can be switched from the main injection 220 seen in FIG. 8 to the main injection 210 seen in FIG. 6, and the timing for the injection of the pilot fuel can be switched from the pilot-fuel injection 230 seen in FIG. 8 to the pilot-fuel injection 200 seen in FIG. 6 in a singleengine cycle. It is possible that the operator of the internal combustion engine 10 (or vehicle powered by the engine) may notice some torque disturbances or hear noise associated with the switch from the MCDI to the LCDI operating mode, in which case, in some embodiments, the single cycle switch from the MCDI to the LCDI operating mode can occur one engine cylinder at a time to reduce and preferably minimize any torque disturbance or noise associated with the transition. For example, there can be a predetermined number of engine cycles or a predetermined time period between transitioning each cylinder from the MCDI to the LCDI operating mode.

[0036] Referring now to FIGS. 9 to 12 and first to FIG. 9, there is shown algorithm 400 for transitioning from the LCDI operating mode to the CIDI operating mode. In step 410 it is determined to initiate the transition from the LCDI operating mode to CIDI operating mode. Various criteria can be employed to determine when to transition from the LCDI to the CIDI operating mode, such as reducing pilot fuel consumption (for example due to regulatory reasons related to emissions) and whether the engine operating conditions are suitable for auto-ignition of the gaseous fuel are two such criteria. Typically, the gaseous fuel is auto-ignitable when the pressure and temperature within the combustion chamber 20 create an environment during the compression stroke suitable for autoignition of the gaseous fuel, and more particularly, when the temperature in the combustion chamber is equal to or greater than an auto-ignition temperature of the gaseous fuel at the pressure at the crank angle during the compression stroke or the expansion stroke when ignition is desired to occur. In step 420, the introduction of the main quantity 212 (seen in FIG. 10) is split into an earlier introduction 241 of an early quantity 243 of the gaseous fuel and a later introduction 251 of a later quantity 253 of the gaseous fuel (seen in FIG. 11). The main quantity 212 is typically split unevenly between the early quantity 243 and the later quantity 253, where the early quantity 243 is less than the later quantity 253. In some embodiments, when the transition from the LCDI operating mode to the CIDI operating mode occurs at very low engine loads, the early quantity 243 can be up to 50% of the main quantity 212. In some embodiments, when the transition occurs at medium and higher engine loads the early quantity 243 can be up to 20% of the main quantity 212, and preferably it is around 10% of the main quantity 212. In some embodiments, the early quantity 243 is the same as pilot quantity 242 seen in FIG. 12. The injection timing of the earlier introduction 241 is within the same injection window as the pilot injection window 246 seen in FIG. 4, and the injection timing of the later introduction 251 is within the same injection window as the main injection window 256, also seen in FIG. 4. In some embodiments, the introduction of pilot-fuel quantity 202 is retarded at thesame time the introduction of the main quantity 212 is split, such as illustrated by a retarded introduction 205 introducing the pilot-fuel quantity 207 seen in FIG. 11. An ignition window within which the pilot-fuel quantity 207 as seen in FIG. 11 can ignite is the same as the pilot-fuel ignition window 206, as seen in FIG. 2. Initially, the pilot-fuel quantity 207 is equivalent to the pilot-fuel quantity 202.

[0037] Returning to FIG. 9, in step 430 it is determined whether a change in engine torque is detected, and more particularly whether engine torque has decreased by a predetermined amount due to splitting the main injection 210 between the earlier introduction 241 and the later introduction 251, and / or the retarding of the introduction of pilot quantity 207. Unless the engine operating conditions have changed, such as a reduced or increased demanded engine load, a change in engine torque is not to be expected due to splitting the main injection 210. Decreases in engine torque can be detected in a variety of ways, including (but not limited to) (i) reduction in engine speed, (ii) reduction in intake pressure (when operating with boost from a turbocharger), (iii) reduction in exhaust temperature, and (iv) reduction in turbine speed. When a substantial decrease in engine torque is detected, control is transferred to step 440 where a misfire mitigation technique is performed. When a substantial decrease in engine torque is not detected, control is transferred to step 450 where it is determined whether early quantity 243 auto-ignites without the assistance of pilot-fuel quantity 207 (seen in FIG. 11), and more particularly that the combustion of the early quantity 243 provides robust ignition of the later quantity 253. Determining whether the early quantity 243 auto-ignites can be done using different techniques. In some embodiments, it can be determined that early quantity 243 auto-ignites and provides robust ignition of later quantity 253 when the following two conditions are true, (1) there is not a substantial change in engine torque (already determined in step 430), and (2) when the retarded introduction 205 of the pilot-fuel quantity 207 occurs after a mid-point (that is, the 50% point by quantity) of the later introduction 251 of the later quantity 253. There would be a noticeable change in torque if the combustion of the pilot-fuel quantity 207 was responsible for igniting the later quantity 253 of gaseous fuel (that is, early quantity 243 is either not auto-igniting or not providing robust enough ignition for later quantity 253) while simultaneously being introduced after the later introduction 251 of the gaseous fuel. In using these criteria, when the conditions are both true, control is transferred to step 470, which will be discussed in more detail below. In using these criteria, when the retarded introduction 205 of the pilot fuel is not after the mid-point of the later introduction 251 of the gaseous fuel, control is transferred to step 460 where the retarded introduction 205 of the pilotfuel is retarded further after which control is transferred back to step 430 to monitor for changes in engine torque. In some embodiments, the introduction of pilot-fuel quantity 207 is retarded by a value of crank angle degrees between and including 1 CAD and 10 CAD. In some embodiments, the introduction of pilot-fuel quantity 207 is retarded to after the mid-point of the later introduction 251.

[0038] Alternatively, or additionally, it can be determined whether the early quantity 243 is not auto-igniting and the pilot-fuel quantity 207 is auto-igniting by detecting increases in exhaust temperature, reduction in torque (not due to misfire), and increases in turbine speed, all of which can occur due to later combustion than if the early quantity 243 was auto-igniting.

[0039] Alternatively, in some embodiments, it can be determined that the early quantity 243 auto-ignites and provides robust ignition of later quantity 253 when the heat release of the combustion of early quantity 243 is of a sufficient rate and magnitude. The heat release of the combustion of early quantity 243 can be determined by controller 170 using the signals from the combustion sensor representative of either or both the pressure in combustion chamber 20 and the vibration signals caused by combustion. Preferably the timing of the ignition and combustion of the pilot-fuel quantity 207 would be after the ignition and combustion of the early quantity 243, and typically when both quantities ignite this would be the case, since the pilot injection window 246 of the early introduction 241 and the pilot-fuel ignition window 206 of the retarded introduction 205 of the pilot fuel largely do not overlap; however, this is not a requirement since analysis of the heat release can determine whether the early quantity 243 of the gaseous fuel and the retarded quantity 207 of the pilot fuel ignite and combust even when the earlier introduction 241 and the retarded introduction 205 substantially overlap.

[0040] Returning to step 450, when the early quantity 243 auto-ignites and provides robust ignition of the later quantity 253, control is transferred to step 470 where the introduction of the pilotfuel quantity 207 is stopped and the later quantity 253 is increased by an amount to compensate for the loss of the pilot-fuel quantity, whereby a total energy value of the fuel introduced is the same. Control is then transferred to step 480 where the transition is complete, and early quantity 243 now corresponds to pilot quantity 242 and later quantity 253 corresponds to main quantity 252 seen in FIGS. 4 and 12.

[0041] In some embodiments, the efficiency in the LCDI operating mode is different than the efficiency in the CIDI operating mode, whereby for a given power demand the fueling in LCDI operating mode is not equivalent to the fueling in the CIDI operating mode on an energy basis. In this circumstance, the pilot quantity 242 and / or the main quantity 252 can be adjusted (that is, increased if the CIDI operating mode is less efficient and decreased when the CIDI operating mode is more efficient) to compensate for the difference in efficiency.

[0042] The steps outlined above for algorithm 400 in FIG. 9 can be reversed to transition from the CIDI operating mode to the LCDI operating mode. Alternatively, since the LCDI operating mode does not (typically) experience problems with misfire, it is possible to transition from the CIDI operating mode back to the LCDI operating mode in a single engine cycle. That is, the timing for the injection of the gaseous fuel can be switched from the pilot injection 240 and the main injection 250 seen in FIG. 12 to the pilot-fuel injection 200 and the main injection 210 seen in FIG. 10 in a single engine cycle. It is possible that the operator of the internal combustion engine 10 (or vehicle powered by the engine) may notice some torque disturbances or hear noise associated with the switch from the CIDI to the LCDI operating mode, in which case, in some embodiments, the single cycle switch from the CIDI to the LCDI operating mode can occur one engine cylinder at a time to reduce and preferably minimize any torque disturbance or noise associated with the transition. For example, there can be a predetermined number of engine cycles or a predetermined time period between transitioning each cylinder from the CIDI to the LCDI operating mode. In some embodiments, when internal combustion engine 10 is operating in the CIDI operating mode under a high load and then changes to a low load (such as idle), the internal combustion engine can transition from the CIDI to the LCDI operating mode, particularly when the conditions required for auto-ignition of the pilot quantity 242 do not exist under the low load.

[0043] Referring now to FIG. 13, a single-pulse CIDI operating mode is illustrated where the gaseous-fuel is introduced into combustion chamber 20 with a single introduction and bums with diffusion-flame combustion. A main injection 260 introduces a main quantity 262 of the gaseous fuel into the combustion chamber during the single-pulse CIDI operating mode. The main quantity 262 represents a total mass of the gaseous fuel introduced during the main injection 260, and in the illustrated embodiment, is equal to a function of the area under an instantaneous mass flow curve 264 of the main injection and the engine speed of internal combustion engine 10. In some embodiments,a main injection window 266 for the main quantity 262 measured in crank angle degrees, within which a start of injection timing followed by an end of injection timing of the main injection 260 can occur anywhere within this window during the CIDI operating mode, is between and including 30 CAD BTDC during the compression stroke and 35 CAD ATDC during the expansion stroke. For example, the main quantity 262 of the gaseous fuel can be injected over the entirety of the main injection window 266, or over a portion thereof.

[0044] It is preferable to transition from the LCDI to the dual-pulse CIDI operating mode instead of the single-pulse CIDI operating mode since the long residence time and relatively smaller magnitude of the pilot quantity 242 (seen in FIG. 4) increases the likelihood of robust ignition. Nevertheless, it is possible to transition from the LCDI operating mode directly to the single-pulse CIDI operating mode, which can be accomplished in a single engine cycle by eliminating the pilotfuel injection 200 and changing the main injection 210 (both seen in FIG. 2) to the main injection 260 (seen in FIG. 13). Preferably, the mid-point (50%) of the heat release is the same in the LCDI and the single-pulse CIDI operating modes. In this regard, the start-of-inj ection timing for main injection 260 (seen in FIG. 13) is earlier (advanced) than the start-of-inj ection timing for main injection 210 (seen in FIG. 2). The main quantity 262 in the single-pulse CIDI operating mode (seen in FIG. 13) is greater than the main quantity 212 in the LCDI operating mode by a quantity of the gaseous fuel equal to the pilot-fuel quantity 202 on an energy basis. When the efficiency of the single-pulse CIDI operating mode is different than the efficiency of the LCDI operating mode, the main quantity 262 can be adjusted accordingly. To reduce any torque disturbances or noises, each cylinder can be transitioned from the LCDI to the single-pulse CIDI operating mode separately, where there is a predetermined number of engine cycles or a predetermined time period between transitioning each cylinder. To transition from the single-pulse CIDI operating mode back to the LCDI operating mode, the steps of the above transition can be reversed. In some embodiments, the transition from the LCID to the singlepulse operating CIDI operating mode can occur in multiple steps, where the main injection 210 is first advanced then the pilot-fuel quantity 202 is reduced in two or more steps until zero (while simultaneously increasing the main quantity 262 in each step), while maintaining the mid-point of the heat release during the transition.

[0045] It is also possible to transition from the dual-pulse CIDI operating mode to the singlepulse CIDI operating mode. Referring now to FIGS. 14-16, two techniques of transitioning from theCIDI operating mode to the single-pulse CIDI operating mode will be discussed. A first transition technique involves switching from the injection timing of the dual-pulse CIDI operating mode, seen in FIG. 14, to the injection timing of the single-pulse CIDI operating mode, seen in FIG. 16, in a single engine cycle. The mid-point of heat release remains the same in the dual -pulse and the singlepulse CIDI operating modes, and in this regard the start of injection timing of the main injection 260 (seen in FIG. 16) is earlier than the start of injection timing of the main injection 250 (seen in FIG. 14). A second transition technique involves retarding the timing of the pilot injection 240, as seen in FIG. 15, two or more times until the injection of the pilot quantity 242 is essentially integrated into the main injection 250, thereby transforming the pilot and main injections 240, 250 into the main injection 260. Again, the mid-point of heat release remains the same between the dual-pulse and the single-pulse CIDI operating modes, and in this regard as the pilot injection 240 is retarded during the transition (as seen in FIG. 15) the main injection 250 is advanced. To transition from the single-pulse CIDI operating mode to the dual-pulse CIDI operating mode, the steps of the first or second transition techniques can be reversed.

[0046] 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 of transitioning between operating modes in an internal combustion engine comprising operating the internal combustion engine in a first operating mode where a main fuel comprises a majority of a total quantity of fuel on an energy basis introduced into a combustion chamber of the internal combustion engine; the first operating mode comprises, introducing the main fuel directly into a combustion chamber of the internal combustion engine after 30 crank angle degrees in a compression stroke; introducing a pilot fuel into the combustion chamber whereby the pilot fuel autoignites; and igniting the main fuel with combustion of the pilot fuel in the first operating mode whereby the main fuel bums substantially in a diffusion-flame combustion mode; beginning transitioning to a second operating mode by splitting the introduction of the main fuel into an early quantity in an earlier introduction and a later quantity in a later introduction of the main fuel; wherein the main fuel is the same fuel in the first and second operating modes; and wherein the main fuel is auto-ignited in the second operating mode or the main fuel bums with a partially -premixed combustion mode in the second operating mode.

2. The method as claimed in claim 1, wherein the earlier introduction of the main fuel occurs between and including 120 crank angle degrees before top dead center in the compression stroke and 30 crank angle degrees before top dead center in the compression stroke and the later introduction of the main fuel occurs after 30 crank angle degrees.

3. The method as claimed in claim 2, further comprising determining an occurrence of knock due to the earlier introduction of the main fuel; andwhen knock is determined to occur, performing a knock mitigation technique.

4. The method as claimed in claim 2, wherein the earlier introduction of the main fuel bums in the partially-premixed combustion mode and the later introduction of the main fuel bums in a diffusionflame combustion mode.

5. The method as claimed in claim 2, further comprising determining whether some of the main fuel is still introduced in the later introduction of the main fuel; and when some of the main fuel is still introduced in the later introduction of the main fuel, increasing the early quantity of the earlier introduction of the main fuel and decreasing the later quantity of the later introduction of the main fuel.

6. The method as claimed in claim 5, wherein an increment of the early quantity of the earlier introduction of main fuel or a decrement of the later quantity of the later introduction of the main fuel is at least 1% of a total energy value of fuel introduced into the combustion chamber in an engine cycle.

7. The method as claimed in claim 5, wherein when all the main fuel introduced into the combustion chamber in an engine cycle is introduced during the earlier introduction of the main fuel, the earlier introduction of the main fuel bums in the partially-premixed combustion mode.

8. The method as claimed in claim 7, wherein a quantity of the pilot fuel is up to 20% of a total quantity of fuel on an energy basis after the transition to the second operating mode.

9. The method as claimed in claim 7, wherein a start of injection timing for introducing the pilot fuel into the combustion chamber is retarded in the second operating mode compared to the first operating mode.

10. The method as claimed in claim 9, wherein the start of inj ection timing for the pilot fuel is retarded for each increment of the early quantity of the earlier introduction of the main fuel and decrement of the later quantity of the later introduction of the main fuel combination.

11. The method as claimed in claim 9, wherein a majority of the pilot fuel is introduced during an expansion stroke of the internal combustion engine after the transition to the second operating mode.

12. The method as claimed in claim 1, wherein the earlier introduction of the main fuel occurs between and including 30 crank angle degrees before top dead center in a compression stroke and 10 crank angle degrees before top dead center in the compression stroke and the later introduction of the main fuel occurs after the earlier introduction.

13. The method as claimed in claim 1, further comprising determining a change in torque is greater than a threshold value; and when the change in torque is a decrease in torque and greater than the threshold value, performing a misfire mitigation technique.

14. The method as claimed in claim 1, wherein the main fuel in the later introduction of the main fuel bums in a diffusion-flame combustion mode and the main fuel in the earlier introduction bums in the diffusion-flame combustion mode during the second operating mode.

15. The method as claimed in claim 1, further comprising retarding a start of injection timing of the pilot fuel; determining a change in torque is greater than a threshold value; and when the change in torque is a decrease in torque and greater than the threshold value, performing a misfire mitigation technique.

16. The method as claimed in claim 15, wherein the start of inj ection timing of the pilot fuel is retarded by a value up to 30 crank angle degrees.

17. The method as claimed in claim 15, further comprising determining whether the start of injection timing of the pilot fuel is after introduction of the later quantity of the later introduction of the main fuel; and when the start of injection timing of the pilot fuel is after introduction of the later quantity of the later introduction of the main fuel, stopping the introduction of the pilot fuel and increasing the later quantity of the later introduction of the main fuel to compensate for removal of the pilot fuel.

18. The method as claimed in claim 15, further comprising determining whether the start of injection timing of the pilot fuel is after a mid-point of a heat release of the combustion of the pilot fuel and the main fuel in the combustion chamber; and when the start of injection timing of the pilot fuel is after the mid-point of the heat release, stopping introduction of the pilot fuel and increasing the later quantity of the later introduction of the main fuel to compensate for the removal of the pilot fuel.

19. The method as claimed in claim 15, further comprising determining a heat release of combustion of the early quantity of the earlier introduction of the main fuel comprises a rate of heat release above a threshold rate and a magnitude of an area under a curve of the heat release above a threshold magnitude; and when the rate of heat release is above the threshold rate and the magnitude of the area under the curve of the heat release is above the threshold magnitude, stopping introduction of the pilot fuel and increasing the later quantity of the later introduction of the main fuel to compensate for the removal of the pilot fuel.

20. The method as claimed in claim 19, further comprising retarding the start of injection timing and / or a start of combustion timing of the pilot fuel to after combustion of the early quantity of the earlier introduction of the main fuel.

21. The method as claimed in claim 1, wherein after the transition the early quantity of the earlier introduction of the main fuel comprises between 5% and 50% of the main fuel introduced into the combustion chamber during an engine cycle and the later quantity of the later introduction of the main fuel comprises between 50% and 95% of the main fuel introduced in the combustion chamber during the engine cycle.

22. The method as claimed in any one of claims 1-21, wherein the main fuel is a gaseous fuel and comprises hydrogen.

23. The method as claimed in claim 22, wherein the main fuel is a majority hydrogen.

24. The method as claimed in any one of claims 1-21, wherein the main fuel is substantially hydrogen.

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