Optimized pilot injection quantity dual fuel engine combustion control strategy

Abstract

An engine system operation and control strategy includes causing a directly injected pilot fuel to auto-ignite to ignite a main fuel in a cylinder (16) in a first engine cycle. The strategy also includes comparing data indicative of heat release in the cylinder in the first engine cycle to a phase error criterion for an earlier pilot injection of pilot fuel and a later injection of pilot fuel. The quantity of one or more pilot injections in a subsequent engine cycle is changed based on the comparison. The pilot injection quantity can be changed in a closed loop manner to obtain a desired combustion phasing characteristic, such as when the characteristic of the main fuel is altered during operation. Related apparatus and control logic are also disclosed.

Description

Technical Field

[0001] This disclosure relates generally to a dual-fuel engine control strategy, and more specifically to altering the amount of pilot fuel injected based on a phase error criterion. Background Technology

[0002] Internal combustion engines are well-known and widely used worldwide for vehicle propulsion, power generation, pump and compressor operation, and various other industrial applications. In conventional operating schemes, fuel and air burn within the engine cylinders to generate a rapid increase in pressure, driving pistons connected to the crankshaft. Spark-ignition engines typically use liquid petroleum fraction fuels (such as gasoline) or certain gaseous fuels (such as natural gas, methane, propane, and various mixtures). Compression-ignition engines typically utilize fuels such as diesel fractions and biodiesel. In recent years, the industry has conducted extensive research on engines and operating strategies that offer flexibility in fuel utilization, particularly gaseous fuels. Fuel prices can fluctuate significantly, and various fuels (such as gaseous fuels) may possess desirable combustion or emission properties that remain to be utilized.

[0003] One type of engine design that can reduce the production of certain emissions and offers flexibility in terms of fuel type combines both compression-ignition fuels (such as diesel) and gaseous fuels (such as natural gas). Compression-ignition fuels and spark-ignition gaseous fuels each have their own advantages and disadvantages, and dual-fuel engine strategies attempt to balance these factors. Diesel fuel is relatively easy to compress-ignite but tends to produce some undesirable emissions. The quality of gaseous fuels can vary depending on the type and source of the gaseous fuel. For example, gaseous fuels with a relatively high methane content tend to be relatively less compressible than those containing certain longer-chain hydrocarbons, and therefore, different fuel blends may have varying degrees of knock tendency or a tendency to produce other forms of undesirable combustion.

[0004] In dual-fuel applications, it is generally desirable to use as little liquid fuel (such as diesel) as feasible, because even small amounts of diesel combustion can produce undesirable emissions and are more expensive than gaseous fuels. While combustion scientists have attempted to use relatively small amounts of diesel to ignite larger amounts of gaseous fuel, practical and commercial success has often been difficult to achieve, especially when the quality or composition of the available gaseous fuel varies, further complicating the issue. U.S. Patent No. 6,032,617 (Willi et al.) discloses an example of a dual-fuel engine that uses diesel to ignite natural gas. Summary of the Invention

[0005] In one aspect, a method of operating an engine system includes: injecting earlier and later injections of ignition fuel directly into a cylinder of the engine during a first engine cycle; and causing the ignition fuel to auto-ignite to ignite the main fuel in the cylinder during the first engine cycle. The method further includes: receiving data indicating heat release in the cylinder during the first engine cycle; and comparing the data with a first phase error criterion for the earlier injection and a second phase error criterion for the later injection. The method further includes: based on the comparison of the data with the first and second phase error criterions, changing the amount of at least one injection of the ignition fuel in a subsequent engine cycle.

[0006] On the other hand, an engine system includes an engine having a cylinder formed therein and a piston movable within the cylinder. The engine system further includes: a direct fuel injector arranged to inject an ignition injection of ignition fuel directly into the cylinder; and a main fuel feed valve for introducing main fuel into the cylinder for combustion. The engine system also includes a fuel control system having a sensor and a fuel supply control unit, the sensor being configured to generate data indicating heat release in the cylinder. The fuel supply control unit is configured to compare the data with a phase error criterion for an earlier injection and a later injection of the ignition fuel in a first engine cycle. The fuel supply control unit is also configured to, based on the comparison of the data with the phase error criterion, change the amount of at least one injection of the ignition fuel in a subsequent engine cycle.

[0007] In another aspect, a dual-fuel control system includes a fuel supply control unit configured to receive data indicating the heat release from combustion of fuel charge in a cylinder during a first engine cycle, the fuel charge including main fuel and multiple injections of auto-ignition fuel. The fuel supply control unit is further configured to: compare the data with a phase error criterion for multiple auto-ignition injections of directly injected auto-ignition fuel; and generate a combustion phase error signal based on the comparison of the data with the phase error criterion. The fuel supply control unit is also configured to output an auto-ignition fuel injection command based on the combustion phase error signal, the auto-ignition fuel injection command altering the amount of at least one injection of the auto-ignition fuel in a subsequent engine cycle. Attached Figure Description

[0008] Figure 1 This is a schematic view of a dual-fuel internal combustion engine system according to one embodiment;

[0009] Figure 2 It is a graph comparing the heat release data during the engine cycle with the expected heat release;

[0010] Figure 3 This is another graph comparing the heat release data during the engine cycle with the expected heat release;

[0011] Figure 4 This is another graph comparing the heat release data during the engine cycle with the expected heat release, illustrating the unwanted combustion phase characteristic regions; and...

[0012] Figure 5 This is a flowchart illustrating an example method and logic flow according to one embodiment. Detailed Implementation

[0013] refer to Figure 1 The figure illustrates a dual-fuel internal combustion engine system 10 according to one embodiment. The engine system 10 includes an internal combustion engine 12 having an engine housing 14, wherein a plurality of cylinders 16 are formed. Pistons 18 are located within the cylinders 16 and are movable in a conventional manner between bottom dead center and top dead center positions to rotate a crankshaft 20. The engine system 10 can be used in a variety of applications, such as rotating generators, operating transmission systems in land vehicles or ships, or operating pumps or compressors.

[0014] The engine housing 14 also includes a cylinder head 22. The cylinder head 22 forms an intake port 24 and an exhaust port 26 associated with each respective cylinder 16. One or more intake valves 28 and one or more exhaust valves 30 are supported in the cylinder head 22 and are movable to open and close fluid communication between the respective cylinder 16 and the respective intake port 24 and exhaust port 26. An exhaust manifold 32 receives exhaust gas from the cylinders 16 and directs it to a turbine 34 in a turbocharger 36. The turbocharger 36 includes a compressor 38 for pressurizing the intake air and directing it to the intake manifold 30. An intake manifold 42 extends between the intake manifold 30 and each intake port 24. The engine system 10 may include any number of cylinders in any suitable arrangement, such as inline, V-shaped, or any other suitable arrangement. Unless otherwise stated, the discussion and description herein of the singular form of cylinder 16 or other elements or components should be understood as referring to any of a plurality of similar elements or components. Engine system 10 can operate in a conventional four-stroke cycle, but this disclosure is not limited thereto and includes alternatives of various forms of variable valve actuation (VVA) timing within the scope of this disclosure.

[0015] Engine system 10 also includes fuel system 44. Fuel system 44 includes a main fuel supply unit 46 containing suitable main fuels, including but not limited to natural gas, methane, ethane, propane, E85, gasoline, methanol, ethanol, or naphtha. In some embodiments, main fuel supply unit 46 stores the main fuel, such as liquefied natural gas (LNG), in a cryogenic liquefied state. In other embodiments, the main fuel may be stored in a pressurized gaseous state and / or supplied, for example, from a commercial gas distribution network, mine, landfill, or wellhead as so-called "pipeline gas." It should be understood that engine system 10 can operate using various blends of hydrocarbon gaseous fuels, hydrocarbon gaseous fuels blended with gaseous hydrogen molecules, etc.

[0016] The fuel system 34 also includes devices 50, such as vaporization and / or pressurization devices for the main fuel, which direct the main fuel to a plurality of fuel feed valves 52, each associated with a cylinder 16. In the illustrated embodiment, the feed valves 52 are arranged to introduce gaseous fuel into the intake manifold 32 or directly into the intake port 24. Other embodiments may include introducing gaseous fuel into the intake manifold 40, or possibly directly into the cylinder 16 via direct injection.

[0017] Fuel system 44 also includes an ignition fuel supply unit 54. The ignition fuel supply unit 54 contains suitable compression-ignition liquid fuels, such as diesel fraction fuels, renewable diesel fuels, biodiesel, various blends of these fuels, or possibly low-cetane fuels blended with a cetane enhancer. Fuel system 44 also includes a low-pressure delivery pump 56 and a high-pressure pump 58, the high-pressure pump being configured to pressurize the ignition fuel to the injection pressure for direct injection into each corresponding cylinder 16 in multiple injections, as discussed further herein. Engine system 10 can also operate in a so-called pure diesel mode, as is well known to those skilled in the art.

[0018] It has been observed that certain fuel characteristics can vary due to supplier, operator preferences, or natural variations in composition or contaminants, processing techniques, or other factors. For example, the energy content of a gaseous fuel supply can vary based on the relative proportions of various hydrocarbon components. Engine system 10 can operate in a relatively stoichiometric lean manner for various purposes, including emissions optimization. An engine operating in a relatively stoichiometric lean manner may be relatively sensitive to disturbances in fuel energy content, such as those leading to undesirable emission levels, abnormal combustion, and / or reduced efficiency. As will become further apparent from the following description, engine system 10 can be configured to achieve optimal operation and compensate for variations in fuel characteristics by adjusting the amount of pilot fuel injected.

[0019] For this purpose, engine system 10 also includes a dual-fuel control system 70. The dual-fuel control system 70 includes a sensor 72 configured to generate data indicating heat release in cylinders 16. In one embodiment, each cylinder 16 is equipped with a sensor 72. Each sensor 72 may be an in-cylinder pressure sensor configured to monitor cylinder pressure during the engine cycle that has a known or determinable direct relationship with the heat release in cylinder 16 caused by the combustion of a fuel charge comprising main fuel and auto-ignition fuel injected multiple times. Monitoring in-cylinder pressure enables tracking of the heat release rate (HRR) associated with combustion during the engine cycle. It should be understood that the tracked HRR relative to engine timing (such as crank angle timing) represents the combustion phase.

[0020] The dual-fuel control system 70 also includes a fuel supply control unit 74. The fuel supply control unit 74 may include: a memory 76 storing computer-executable instructions; and a data processor 78 configured to execute the instructions to cause the dual-fuel control system 70 to operate the engine system 10 according to this disclosure. The fuel supply control unit 74 may include any number of computer-readable memories and any number of data processors, which may reside on the same device or be distributed across multiple devices. Any suitable volatile or non-volatile computer-readable memory (such as RAM, ROM, FLASH, etc.) and any suitable data processor (such as a microprocessor or microcontroller) may be used.

[0021] The fuel supply control unit 74 may be configured to receive data indicating the heat release generated by combustion of fuel charge in cylinder 16 during a first engine cycle, as discussed herein. The fuel supply control unit 74 may also be configured to compare the data with phase error criteria for multiple auto-ignition injections of directly injected pilot fuel. In one embodiment, the fuel supply control unit 74 compares the data with a first phase error criterion for earlier injections and a second phase error criterion for later injections. Each of the first and second phase error criteria may include HRR-based limits, which include a first HRR-based limit and a second HRR-based limit, which are associated with and specific to earlier and later injections, respectively. For example, the HRR observed based on data from sensor 72 may be compared with a threshold HRR associated with undesirable timing or magnitude of combustion phase.

[0022] A first HRR-based limit for earlier injections may include an HRR-based limit for later crank angle timing, and a second HRR-based limit for later injections may include an HRR-based limit for earlier crank angle timing. The fuel supply control unit 74 may generate one or more combustion phase error signals based on a comparison of data with a phase error criterion. For example, the fuel supply control unit 74 may perform a comparison to determine whether the observed HRR is below a threshold HRR for a predetermined crank angle timing, and if so, generate a combustion phase error signal. Various extensions and alternatives to implementing the HRR-based limits associated with earlier and later injections are within the scope of this disclosure. For example, the first HRR-based limit for earlier injections and the second HRR-based limit for later injections may be determined empirically. The fuel supply control unit 74 may also be configured to output an ignition fuel injection command based on the combustion phase error signal, which alters the amount of ignition fuel injected at least once in a subsequent engine cycle.

[0023] The described strategies reflect insights into combustion phase characteristics that can vary due to factors such as insufficient injection quantity and / or inconsistent spray characteristics of different injections of ignition fuel. In other words, the nature of the combustion phase error associated with earlier injection of ignition fuel may differ from that associated with later injection of ignition fuel.

[0024] It should also be recognized that certain engine systems (engine system 10 being one example) may be relatively sensitive to variations in the characteristics of the primary fuel. Variations in the characteristics of the primary fuel may be caused by differences in blending ratios, contaminants, or other external factors, as discussed herein. Changes in fuel characteristics may also occur simply because the operator chooses to switch from one fuel type to a second fuel type, or from one fuel supply source, based on factors such as cost, availability, applicable emission requirements, or others.

[0025] Engine system 10 can be understood as being configured to compensate for such variations in fuel characteristics. As discussed above, fuel supply control unit 74 outputs an ignition fuel injection command that alters the amount of ignition fuel injected once or multiple times in subsequent engine cycles. In a practical implementation, fuel supply control unit 74: outputs an ignition fuel injection command based on a combustion phase error signal associated with an earlier ignition injection in the first engine cycle, which alters the amount injected earlier in subsequent engine cycles; and outputs an ignition fuel injection command based on a combustion phase error signal associated with a later injection in the first engine cycle, which alters the amount injected later in subsequent engine cycles. These principles will become more apparent in light of the examples discussed further below.

[0026] refer to Figure 2 The figure shows graph 100 illustrating an earlier ignition injection 110 and a later ignition injection 120 of the ignition fuel. Curve 130 shows an example desired combustion phase curve indicated by HRR data obtained from associated cylinders in the engine cycle. Curve 140 is based on actual test data of HRR observed under conditions of insufficient earlier ignition injection. It can be noted that curve 140 is roughly similar in initial shape to curve 130, but exhibits an increased HRR in the later stages of the engine cycle compared to curve 130. One way to characterize the difference between curve 140 and curve 130 is by an increase in the CA50-70 parameter, which means that the crank angle range corresponding to approximately 50% to 70% of the total fuel burned in the engine cycle represented by curve 140 is shifted backward in time relative to curve 130. The fuel supply control unit 74 can detect and act upon observing such a shift to bring the combustion phase closer to the desired combustion phase of curve 130.

[0027] Now for reference Figure 3 The figure shows a graph 200 illustrating an earlier injection 210, a later injection 220, a desired combustion phase curve represented by curve 230, and a curve 240 based on test data, where the amount of igniting fuel in the later injection is insufficient or the quality of the later ignition injection is poor, for example due to variations in the fuel spray jet between the spray plumes during the later injection. It can be noted that curve 240 shows a delay in heat release at a relatively earlier stage in the engine cycle compared to curve 230. One way to characterize the difference between curve 240 and curve 230 is the CA10 parameter delay, which means that the crank angle corresponding to approximately 10% of the total fuel burned in the engine cycle represented by curve 240 shifts in time relative to curve 230. The fuel supply control unit 74 can detect and act upon observing such a shift to bring the combustion phase closer to the combustion phase of the desired curve 230.

[0028] Will Figure 2 and Figure 3 By comparison, it can be observed that HRR disturbances are often observed at relatively early crank angle timing when late injection errors of ignition fuel occur, and at later crank angle timing when early injection errors of ignition fuel occur.

[0029] Now go to Figure 4 The figure shows the desired combustion phase curve at curve 330, which roughly corresponds to... Figure 2 The curve 345 of the middle curve 140 and roughly corresponding to the curve 140 Figure 3 Another curve of curve 340 in the middle curve is graph 300. Figure 4 Region 350 is also illustrated, in which undesirable HRR properties may be observed due to earlier injection errors of the ignition fuel, and region 360, in which undesirable HRR properties occur due to later injection errors of the ignition fuel. In this context, "error" in fuel injection can be understood as including, but not limited to, insufficient quantity or consistency variations, such as inhomogeneity between spray plumes. This disclosure contemplates controlling the amount of at least one injection of ignition fuel in subsequent engine cycles based on data indicating heat release obtained from a first engine cycle. Changing the amount of at least one ignition injection in a subsequent engine cycle can include increasing that amount, thereby altering at least one of the timing or amplitude parameters of the HRR curve in the subsequent engine cycle.

[0030] Therefore, in the illustrated embodiment, upon receiving HRR data indicating that the combustion phase has shifted into or beyond region 360, an error signal can be generated, and a fuel injection command can be output based on this error signal to change the amount of later injection of ignition fuel in subsequent engine cycles. Upon receiving HRR data indicating that the combustion phase has shifted into or beyond region 350, an error signal can be generated, and a fuel injection command can be output based on this error signal to change the amount of earlier injection of ignition fuel in subsequent engine cycles. It should be understood that in some cases, HRR data may prompt adjustments to both earlier and later injections within the same subsequent engine cycle.

[0031] Changing the amount of at least one injection of ignition fuel in a subsequent engine cycle may also include changing the amount based on at least one timing-based fuel combustion index. In a practical implementation, changing the amount may also include changing the amount of an earlier ignition injection based on a first index and changing the amount of a second ignition injection based on a second index different from the first index. Each of the first and second indices may include a timing-based fuel combustion index. The first index may include a crank angle index for relatively large fuel combustion amounts (such as 50% or more). The second index may include a crank angle index for relatively small fuel combustion amounts (such as less than 50%). As an example, the fuel supply control unit 74 may increase the amount of a later injection in a closed-loop manner based on the CA10 index and may increase the amount of an earlier injection in a closed-loop manner based on the crank CA50-70 index.

[0032] Industry Applicability

[0033] Refer to the attached diagram for general information, but now focus on Figure 5The diagram shows a flowchart 400 illustrating an example method and logical flow. Flowchart 400 begins at block 410: Engine 12 is operated, and main fuel is introduced into cylinder 16 via fuel feed valve 52 through intake port 24. At the desired timing, the electrically actuated direct fuel injector 60 injects earlier and later injections of ignition fuel. More than two injections of ignition fuel may be injected. The earlier injection may be injected at least 35 degrees (possibly about 60 degrees) before the top dead center crank position of piston 18. The later injection of ignition fuel may be injected close to the top dead center crank position of piston 18 (possibly a few degrees before that position). The compression ignition of the directly injected ignition fuel triggers the ignition of the main fuel, typically achieved through two combined flame fronts generated by the combustion of the corresponding earlier and later injections.

[0034] Flowchart 400 continues from box 410 to box 420: Switching the primary fuel. Switching the primary fuel may include switching from operating with one primary fuel or one primary fuel supply in a previous engine cycle to operating with a second primary fuel or a second primary fuel supply in a subsequent (first) engine cycle. As also discussed herein, switching the primary fuel may be performed intentionally or unintentionally for a variety of reasons, but in either case, it will change the characteristics of the primary fuel, such as its energy content. Flowchart 400 continues from box 420 to box 430: Receiving data indicating the HRR in the first engine cycle, as discussed herein. Flowchart 400 continues from box 430 to box 440: Comparing the data with a phase error criterion, as discussed herein. The comparison may include numerical comparisons, for example, determining whether a first value indicating heat release or HRR is equal to or less than a second value indicating a combustion phase error criterion. Various strategies may be employed in the comparison performed at box 440, including ranges, ratios, multiple numerical factors, multidimensional graph queries, complex calculations, or other factors and / or techniques. Return to Reference Figure 4 Execution block 440 may include determining whether the observed HRR falls within one or both of regions 350 and 360. Flowchart 400 continues from block 440 to block 450: generating a combustion phase error signal. The error signal may be generated in response to the observed HRR being at or below a predetermined threshold HRR, as discussed herein.

[0035] Flowchart 400 continues from block 450 to block 460: Outputting one or more ignition fuel injection commands to the direct fuel injector 60 based on the error signal. Flowchart 400 can return from block 460 to block 430: Controlling the combustion phase in a closed-loop manner to reduce combustion phase errors until the desired combustion phase profile is obtained. As discussed herein, the fuel supply control unit 74 can output multiple fuel injection commands in each of multiple subsequent engine cycles in multiple subsequent engine cycles, based on a crank-angle timing-based fuel combustion index for each of the earlier and later ignition injections, which modify the amount of at least one ignition injection.

[0036] This specification is for illustrative purposes only and should not be construed as limiting the scope of this disclosure in any way. Therefore, those skilled in the art will understand that various modifications can be made to the currently disclosed embodiments without departing from the full and reasonable scope and spirit of this disclosure. Other aspects, features, and advantages will become apparent from a study of the accompanying drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items and may be used interchangeably with “one or more.” The term “an” or similar language is used where only one item is intended. Furthermore, as used herein, the term “having” is intended to be an open-ended term. Further, the phrase “based on” is intended to mean “at least partially based on”, unless otherwise explicitly stated.

Claims

1. A method of operating an engine system (10), the method comprising: In the first engine cycle, the earlier and later injections of ignition fuel are directly injected into the cylinder (16) of the engine (12); In the first engine cycle, the ignition fuel is auto-ignited to ignite the main fuel in the cylinder; Receive data indicating the heat release in the cylinder during the first engine cycle; The data is compared with a first phase error criterion for the earlier injection and a second phase error criterion for the later injection; as well as Based on comparing the data with the first phase error criterion and the second phase error criterion, the amount of the ignition fuel injected at least once in subsequent engine cycles is changed.

2. The method of claim 1, wherein receiving data includes receiving data indicating heat release rate (HRR) generated via an in-cylinder pressure sensor; Each of the first phase error criterion and the second phase error criterion includes a different HRR-based limit, and changing the amount includes increasing the amount, thereby changing at least one of the timing parameter or amplitude parameter of the HRR curve in the subsequent engine cycle.

3. The method of claim 1 or 2, wherein changing the amount comprises changing the amount of the earlier injection according to a first indicator and changing the amount of the second injection according to a second indicator different from the first indicator.

4. The method of claim 3, wherein the change includes a closed-loop change, and each of the first index and the second index includes a timing-based fuel combustion index.

5. The method of claim 4, wherein the first index includes a crank angle index with a relatively large fuel combustion amount, and the second index includes a crank angle index with a relatively small fuel combustion amount.

6. The method according to any one of claims 1 to 5, wherein the ignition fuel comprises a compression-ignition liquid fuel, and the main fuel comprises a gaseous fuel; and The method further includes changing the characteristics of the main fuel between a previous engine cycle and the first engine cycle, wherein the amount of change compensates for the change in the characteristics of the main fuel.

7. An engine system (10), said engine system comprising: An engine (12) having a cylinder formed therein and a piston (18) capable of moving in the cylinder. A direct fuel injector (60) is arranged to inject ignition fuel directly into the cylinder; Main fuel feed valve (52), the main fuel feed valve is used to introduce main fuel into the cylinder for combustion; A fuel control system (70) includes a sensor (72) and a fuel supply control unit (74), the sensor being configured to generate data indicating heat release in the cylinder; The fuel supply control unit is configured to: The data is compared with the phase error criteria for earlier and later injections of the ignition fuel in the first engine cycle; as well as Based on comparing the data with the phase error criterion, the amount of the ignition fuel injected at least once in subsequent engine cycles is changed.

8. The engine system of claim 7, wherein the phase error criterion includes a limit based on the heat release rate (HRR); and The fuel supply control unit is further configured to change the amount by increasing the amount, thereby changing at least one of the timing parameter or amplitude parameter of the HRR curve in the subsequent engine cycle.

9. The engine system according to claim 7 or 8, wherein: The phase error criterion includes a first limit based on heat release rate (HRR) and a second limit based on HRR for the earlier and later injections, respectively; and The first HRR-based limit includes the HRR-based limit at a later crank angle, and the second HRR-based limit includes the HRR-based limit at an earlier crank angle.

10. The engine system according to any one of claims 7 to 9, wherein the fuel supply control unit is further configured to change the amount according to at least one timing-based fuel combustion index.

11. The engine system of claim 10, wherein the at least one timing-based fuel combustion index includes a first crank angle index for the earlier injection for a relatively larger fuel combustion volume, and the second index includes a second crank angle index for the later injection for a relatively smaller fuel combustion volume.

12. The engine system of claim 11, wherein the relatively large fuel combustion volume includes 50% or more of the fuel combustion volume, and the relatively small fuel combustion volume includes less than 50% of the fuel combustion volume.

13. A dual-fuel control system (70), the dual-fuel control system comprising: A fuel supply control unit (74) is configured to receive data on the heat release generated by the combustion of fuel charge in a first engine cycle in an indicating cylinder (16), the fuel charge including main fuel and multiple injections of auto-ignition fuel; The fuel supply control unit is also configured to compare the data with a phase error criterion for multiple auto-ignition injections of directly injected ignition fuel; The fuel supply control unit is also configured to generate a combustion phase error signal based on the comparison of the data with the phase error criterion; and The fuel supply control unit is also configured to output an ignition fuel injection command based on the combustion phase error signal, the ignition fuel injection command changing the amount of ignition fuel injected at least once in a subsequent engine cycle.

14. The dual-fuel control system of claim 13, wherein the phase error criterion includes a first HRR-based limit and a second HRR-based limit, the first HRR-based limit and the second HRR-based limit being specific to an earlier and a later injection in the multiple injections of the first engine cycle, respectively.

15. The dual-fuel control system of claim 13 or 14, wherein the fuel supply control unit is further configured to output a plurality of ignition fuel injection commands, the plurality of ignition fuel injection commands changing the amount of ignition fuel injected at least once in each of a plurality of subsequent engine cycle closed loops according to a timing-based fuel combustion index.

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