Engine system and method for water injection

Abstract

A method of mitigating abnormal combustion characteristics in an internal combustion engine having a plurality of combustion chambers includes injecting a main fuel into each combustion chamber at least during respective compression strokes whereby the main fuel premixes or partially-premixes with intake air in the combustion chamber; igniting the main fuel in each combustion chamber with a respective positive ignition source; and for each combustion chamber, determining whether knock is occurring; and introducing water into the combustion chamber when knock is occurring such that a temperature of the combustion chamber is reduced due to the evaporation of the water therein thereby mitigating knocking; where water is only introduced into combustion chambers where knock is occurring.

Description

- 1 - 5 ENGINE SYSTEM AND METHOD FOR WATER INJECTION Technical Field

[0001] The present application relates to an engine system and method for water injection in an internal combustion engine. 10 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 15 date of the invention.

[0003] Internal combustion engines that operate with a gaseous fuel stored as a compressed gas in a pressurized cylinder at high pressure can operate in a variety of operating modes as the storage pressure of the gaseous fuel in the pressurized cylinder decreases. For example, when the storage pressure is high, the internal combustion engine can operate in a late-cycle, direct-injection (LCDI) 20 mode by injecting the gaseous fuel late in a compression stroke such that the gaseous fuel burns with diffusion-flame combustion. As the storage pressure continues to decrease, at some critical storage pressure to remain operating in the LCDI mode a compressor must be used to increase the pressure of the gaseous fuel above the storage pressure such that the gaseous fuel can continue to be injected late in the compression stroke. As the storage pressure continues to decrease below the critical storage 25 pressure the internal combustion engine may begin to employ a mid-cycle, direct-injection (MCDI) mode by injecting the gaseous fuel earlier during the compression stroke compared to the LDCI mode such that the gaseous fuel burns with both partially-premixed combustion, which is a combination of diffusion-flame combustion and premixed combustion. Initially the internal combustion engine may employ the MCDI mode during high fueling requirements where the compressor cannot keep up with 30 the fuel demand. However, as the storage pressure continues to decrease the MCDI mode is employed in ever more regions of the engine load / speed map until it is no longer possible to employ the LCDI operating mode whereby the MCDI mode may be used exclusively. The above process repeats for the MCDI operating mode in the following way. As the storage pressure continues to decrease the- 2 - 5 internal combustion engine may begin to employ an early-cycle, direct-injection (ECDI) mode by injecting the gaseous fuel earlier during the compression stroke compared to the MDCI mode such that the gaseous fuel burns with premixed combustion. Again, the internal combustion engine may employ the ECDI mode in those parts of the engine map having high fuel demand, and as the storage pressure continues to decrease more and more parts of the engine map will employ the ECDI mode 10 as the compressor cannot keep up with the fuel demand to operate in the MCDI mode. The internal combustion engine experiences problems that arise when operating in the LCDI, MCDI and ECDI operating modes.

[0004] Internal combustion engines fueled with a gaseous fuel and employing a positive ignition source can face several challenges. Premature ignition and knocking can occur under various 15 operating modes and engine operating conditions. As used herein, the terms preignition, premature ignition, knock, knocking, and engine knock are used interchangeably. Knocking is the uncontrolled ignition in the end gas mixture before the arrival of the flame front. Fuel injector tip temperatures may rise to a level requiring mitigation to prevent damage. Nitrous oxide (NOx) emissions can increase as cylinder temperature rises. Cylinder temperature, fueling, and exhaust gas recirculation 20 imbalances can lead to various abnormal combustion characteristics ranging from knock / preignition to retarded combustion and may artificially derate the power the internal combustion engine is capable of providing. Engine knock poses a significant threat to the safety and the durability of the engine. Internal combustion engines can suffer from rough combustion and higher coefficient of variation (COV) when fueling with a main fuel and a pilot fuel and while operating in the MCDI 25 operating mode.

[0005] The state of the art is lacking in techniques for an engine system and method for water injection in an internal combustion engine. Summary

[0006] An improved method of mitigating abnormal combustion characteristics in an internal 30 combustion engine having a plurality of combustion chambers includes injecting a main fuel into each combustion chamber of the plurality of combustion chambers at least during respective compression strokes whereby the main fuel premixes or partially-premixes with intake air in the combustion chamber; igniting the main fuel in each combustion chamber with a respective positive- 3 - 5 ignition source; and for each combustion chamber, determining whether knock is occurring; and introducing water into the combustion chamber when knock is occurring such that a temperature of the combustion chamber is reduced due to the evaporation of the water therein thereby mitigating knocking; whereby water is only introduced into combustion chambers where knock is occurring.

[0007] The method can include for each combustion chamber, determining a knock index; and 10 determining knock is occurring in the combustion chamber when the knock index is above a knock threshold. The method can also include for each combustion chamber, determining a start of combustion timing; and adjusting an ignition timing when the start of combustion timing is retarded beyond a desired start of combustion timing; whereby the start of combustion timing returns to the desired start of combustion timing due to the adjusted ignition timing. 15

[0008] In some embodiments, the method includes injecting the water directly into each combustion chamber where knock is occurring when only some of the combustion chambers are knocking; determining that all the combustion chambers are knocking; and injecting water into an intake manifold of the internal combustion engine when all the combustion chambers are knocking.

[0009] The main fuel can be directly injected into each of the plurality of combustion chambers. 20 The water can be directly injected into each of the plurality of combustion chambers. Alternatively, or additionally, the water can be injected into respective intake ports associated with each combustion chamber.

[0010] In some embodiments, the method includes providing a plurality of dual fluid injectors where each dual fluid injector is associated with the respective combustion chamber; whereby each 25 dual fluid injector directly injects the main fuel and the water into the respective combustion chamber and each dual fluid injector is operable to inject the main fuel separately and independently of the water and to inject the water separately and independently of the main fuel. In some embodiments, the method includes providing a water injector configured to inject water into an intake manifold of the internal combustion engine. 30

[0011] The method can include providing a plurality of main fuel injectors where each main fuel injector is associated with the respective combustion chamber; and providing a plurality of water injectors where each water injector is associated with the respective combustion chamber. In some embodiments, each water injector directly injects the water into the respective combustion chamber.- 4 - 5 In some embodiments, the method includes providing a plurality of intake ports; whereby each intake port is associated with the respective combustion chamber; and each water injector injects the water into the respective intake port associated with the respective combustion chamber. In some embodiments, the method includes providing an intake manifold water injector configured to inject the water into an intake manifold of the internal combustion engine. 10

[0012] Each combustion chamber can be associated with a respective cylinder of a plurality of cylinders. The method can further includes determining which cylinders of the plurality of cylinders are considered hot cylinders; and monitoring the hot cylinders differently compared to the cylinders that are not hot cylinders; whereby each hot cylinder has an average cylinder operating temperature that is greater than an average operating temperature of the plurality of cylinders by a predetermined 15 margin. In some embodiments, each hot cylinder is equipped with at least one additional sensor that the cylinders that are not hot cylinders are not equipped with including at least one of an exhaustport temperature sensor; an in-cylinder temperature sensor; a combustion sensor; and a knock sensor. When the internal combustion engine is equipped with a knock sensor, the method can further include configuring the knock sensor with respect to the internal combustion engine to detect 20 vibrations in the hot cylinders more sensitively than in the cylinders not considered the hot cylinders. The predetermined margin can be one or more standard deviations from the average operating temperature of the plurality of cylinders or an absolute temperature difference. In some embodiments, the method includes operating the internal combustion engine at an engine load and speed condition for a predetermined amount of time and / or until an engine temperature stabilizes; determining the 25 average cylinder operating temperature for each cylinder; and determining the average operating temperature of all the cylinders; such that the hot cylinders are determined by comparing the average cylinder operating temperature of each cylinder to the average operating temperature of all the cylinders. The method can further include operating the internal combustion engine at a plurality of engine load and speed conditions; for each engine load and speed condition of the plurality of engine 30 load and speed conditions determining the average cylinder operating temperature for each cylinder; and determining the average operating temperature of all the cylinders for the plurality of engine load and speed conditions.

[0013] Preferably, the water is injected at a water injection timing during the compression stroke such that the water evaporates before it reaches a wall of the combustion chamber.- 5 - 5 Brief Description of the Drawings

[0014] 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. 10

[0015] FIG. 1 is a schematic view of an engine system according to an embodiment.

[0016] FIG. 2 is a schematic view of an engine system according to an embodiment.

[0017] FIG. 3 is a schematic view of an engine system according to an embodiment.

[0018] FIG. 4 is a schematic view of an engine system according to an embodiment.

[0019] FIG. 5 is a chart view of a normal combustion characteristic, an abnormal combustion 15 characteristic due to engine knock, and an abnormal combustion characteristic due to retarded start of combustion timing.

[0020] FIG. 6 is a flow chart of an algorithm for mitigating abnormal combustion characteristics.

[0021] FIG. 7 is a flow chart of an algorithm for mitigating abnormal combustion characteristics.

[0022] FIG. 8 is a graphical view of cylinder temperature for the internal combustion engine of 20 FIG. 1, FIG. 2, FIG.3, or FIG. 4. Detailed Description

[0023] Referring to FIG.1 there is shown engine system 100 suitable for employing water mitigation strategies to solve problems associated with poor combustion characteristics in various 25 operating modes. Engine system 100 includes fuel system 110, internal combustion engine 120, intake air system 130, and exhaust system 140. Fuel system 110 supplies a main fuel and a pilot fuel to internal combustion engine 120. In some embodiments, the main fuel is a gaseous fuel and the pilot fuel is a liquid fuel. A gaseous fuel is any fuel that is in the gas phase at standard temperature- 6 - 5 and pressure, which is defined herein to be 0 degrees Celsius (°C) and 1 atmosphere (ATM). A liquid fuel is any fuel that is in the liquid phase at standard temperature and pressure. Examples of gaseous fuel include hydrogen, methane, propane, natural gas, and mixtures of these fuels. In an exemplary embodiment, the gaseous fuel is hydrogen or a mixture of gaseous fuels comprising hydrogen. Examples of liquid fuels include diesel, dimethyl ether (DME), and kerosine. Fuel system 110 10 supplies the pilot fuel at a pilot injection pressure PPI and supplies the main fuel at a main injection pressure PMI. The pilot injection pressure PPI and the main injection pressure PMI can vary based on engine operating conditions. The pilot fuel is a positive ignition source that auto-ignites and combusts within each combustion chamber 155 to create a suitable pressure and temperature environment for ignition of the main fuel. 15

[0024] Internal combustion engine 120 includes a plurality of cylinders 150, herein abbreviated to cylinders 150. In the illustrated embodiments internal combustion engine 120 includes four cylinders 150. In some embodiments, internal combustion engine 120 includes one, two, or three cylinders 150. In some embodiments, internal combustion engine 120 includes five or more cylinders 150. Internal combustion engine includes a plurality of combustion chambers 155, herein abbreviated 20 to combustion chambers 155. As is known by those skilled in the technology, each combustion chamber 155 is defined by a bore of the respective cylinder 150 in engine block 160, a respective piston (not shown) that reciprocates within the bore, and a cylinder head 170. Respective fuel injectors 180 are disposed to inject the pilot fuel and the main fuel directly into each of the respective combustion chambers 155 and in this regard fuel injectors 180 can be referred to as in-cylinder 25 injectors. The pilot fuel can be separately and independently injected from the main fuel, and the main fuel can be separately and independently injected from the pilot fuel. Fuel injectors 180 are also referred to as dual-fluid or dual-fuel injectors since they can inject two separate fluids. Fuel injectors 180 are fluidly connected with fuel system 110 to fluidly receive the pilot fuel at the pilot injection pressure PPI and fluidly receive the main fuel at the main injection pressure PMI suitable for injection 30 into combustion chamber 155. Knock sensor 460 is operatively connected with internal combustion engine 120 to detect signals representative of combustion chamber pressure, knocking, and / or preignition in each combustion chamber 155. In the illustrated embodiment there is one knock sensor 460. In some embodiments, there can be more than one knock sensor 460. Knock sensor 460 can also be referred to as a combustion sensor. In some embodiments, knock sensor 460 is an acoustic sensor- 7 - 5 capable of detecting vibration signals in internal combustion engine 120, particularly vibration signals due to combustion within combustion chambers 155.

[0025] Intake air system 130 fluidly directs the flow of intake air from the environment into combustion chambers 155 as well as exhaust gases returned to combustion chambers 155 by way of exhaust gas recirculation (EGR) system 190 (which will be described in more detail below). The 10 intake air from the external environment enters intake pipe 200. In some embodiments, throttle 210 can be employed to selectively and variably restrict the flow of the intake air that is fluidly communicated down intake pipe 200 when exhaust gases at a relatively low pressure are returned to intake air system 130 through EGR system 190. Turbocharger 220 includes turbine 230 and compressor 240, where the exhaust gases from combustion chambers 155 cause turbine 230 to spin 15 that in turn causes compressor 240 to compress the intake air and exhaust gases in intake pipe 200. As used herein, the mixture of intake air and exhaust gases admitted into combustion chambers 155 is referred to as an intake charge, which may contain intake air only, or a combination of intake air and exhaust gas. Heat exchanger 250 cools the intake charge that may have been elevated in temperature due to pressurization from compressor 240. The intake charge is cooled to remain below 20 an intake system temperature limit in order to protect the various components in intake air system 130 downstream from compressor 240. Heat exchanger 250 may also be referred to as a charge air cooler (CAC) and is used interchangeably herein. In some embodiments, charge air cooler 250 selectively cools the intake charge according to engine operating conditions. Throttle 260 is employed to fluidly restrict the flow of the intake charge, for example into intake manifold 270, 25 according to engine operating conditions, such as during low load conditions where it is desired to reduce the amount of intake charge drawn by suction into combustion chambers 155. Respective intake ports 280 are associated with each combustion chamber 155 to fluidly communicate the intake charge from intake manifold 270 into the respective combustion chamber 155 through a respective intake valve (not shown) associated with each combustion chamber 155. 30

[0026] Exhaust system 140 fluidly conducts the flow of exhaust gases leaving each cylinder 150 through a respective exhaust valve (not shown) into respective exhaust ports 285 into exhaust manifold 275 and towards tail pipe 290. The exhaust gases are fluidly directed through turbine 230 of turbocharger system 220 according to engine operating conditions. Bypass valve 300 when open permits at least a portion of the exhaust gas to bypass turbine 230 through passageway 310 into- 8 - 5 exhaust pipe 320. Bypass valve 300 can be referred to as a wastegate valve. In some embodiments, bypass valve 300 moves between a closed position and an open position. In some embodiments, bypass valve 300 can move from the closed position to two or more open positions each having different fluid flow capacities. The exhaust gas is fluidly communicated along exhaust pipe 320 through engine aftertreatment system 330, also referred to as EATS. Engine aftertreatment system 10 330 can include a variety of components that mitigate various emissions within the exhaust gas. In some embodiments, exhaust system 140 includes exhaust temperature sensors 470. Each temperature sensor 470 is configured to detect exhaust temperature in the respective exhaust port 285. In some embodiments, exhaust temperature sensors 470 are configured only in selectively predetermined exhaust ports 285 (that is, not all exhaust ports 285 are configured with an exhaust temperature 15 sensor), as will be discussed in more detail below.

[0027] Returning to EGR system 190, EGR valve 340 when open permits at least a portion of the exhaust gas to be recirculated from exhaust pipe 320 to intake pipe 200. In some embodiments, EGR valve 340 moves between a closed position and an open position. In some embodiments, EGR valve 340 can move from the closed position to two or more open positions each having different fluid flow 20 capacities. The exhaust gas is fluidly communicated from exhaust pipe 320 along EGR pipe 350 through heat exchanger 360 and into intake pipe 200. Heat exchanger 360 may also be referred to as EGR cooler / condenser herein and cools the exhaust gas to a temperature below the intake system temperature limit to protect components in intake system 130.

[0028] Engine system 100 further includes water system 370 that can include water storage and 25 water injection components. In some embodiments, heat exchanger 360 also captures condensation from the cooling of the exhaust gas, particularly water vapor content of the exhaust gas, and fluidly communicates the water condensate to a water reservoir 380 along condensate pipe 390. In some embodiments, fill receptacle 400 along with filling pipe 410 are employed to fluidly fill water reservoir from an external source of water. Pump 420 pressurizes the water fluidly received from 30 reservoir 380 into delivery conduit 430 to which intake-port water injectors 440 are fluidly connected to receive the water. Pump 420 pressurizes the water from a water storage pressure in reservoir 380 to an intake water-injection-pressure suitable for injecting the water upstream of the respective intake valves (not shown) of combustion chambers 155, such as into intake manifold 270 or intake port 280. Each intake-port water injector 440 is associated with the respective intake port 280 to inject water- 9 - 5 into the intake port at least during an intake stroke in the respective combustion chamber 155 when commanded. The water can be introduced into combustion chambers 155 that are experiencing engine knock as will be explained in more detail below. For each combustion chamber 155, a temperature of the combustion chamber can be reduced when water is introduced therein due to the enthalpy of vaporization of the water, where the water absorbs heat within the combustion chamber 10 in order to evaporate thereby reducing the temperature.

[0029] Controller 450 is operatively connected with engine system 100. In some embodiments, controller 450 is operatively connected with fuel system 110, internal combustion engine 120, intake air system 130, exhaust system 140, and water storage and injection system 370. In some embodiments, controller 450 is operatively connected with actuators and sensors in engine system 15 100. In the illustrated embodiment, controller 450 is operatively connected with fuel injectors 180, intake-port water injectors 440, knock sensor 460, and exhaust temperature sensors 470. Controller 450 can command each fuel injector 180 to inject the pilot fuel, the main fuel, or the pilot fuel and the main fuel. Controller 450 can command each intake-port water injector 440 to inject water in the respective intake port 280. In some operating modes, controller 450 can command all intake-port 20 water injectors 440 to inject the water into the respective intake port 280. Alternatively, controller 450 can command select intake-port water injectors 440 to inject the water into the respective combustion chambers 155 depending upon engine operating conditions (that is, controller 450 selectively commands one or more intake-port water injectors 440, but not all intake-port water injectors 440, to inject the water into the respective intake port 280), as will be described in more 25 detail below. Knock sensor 460 sends signals representative of a level of knock to controller 450 and controller 450 can determine the level of knock based on these signals. Knock sensor 460 can send signals representative of the pressure in each combustion chamber 155 to controller 450 and controller 450 can determine the combustion chamber pressure within the respective combustion chamber 155 based on these signals. Controller 450 can determine a start of combustion (SOC) timing 30 for each combustion chamber 155 based on the respective combustion chamber pressure. Each exhaust temperature sensor 470 sends signals representative of exhaust temperature in the respective exhaust port 285 to controller 450 and controller 450 can determine the exhaust temperature in the respective exhaust port 285 based on these signals. Controller 450 can include both hardware and software components. The hardware components can include digital and / or analog electronic 35 components. In some embodiments, controller 450 includes a processor and memories, including one- 10 - 5 or more permanent memories, such as FLASH, EEPROM and a hard disk, and a temporary memory, such as SRAM and DRAM, for storing and executing a program. As used herein, the terms algorithm and step refer to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described 10 functionality. The algorithms and steps that are performed by controller 450 can be part of the controller.

[0030] Referring now to FIG. 2, there is shown engine system 101 suitable for employing water mitigation strategies to solve problems associated with poor combustion characteristics in various operating modes. Engine system 101 is similar to engine system 100 and like parts in this and other 15 embodiments have like reference numerals and differences are discussed. Engine system 101 includes fuel system 111 that supplies the main fuel at the main injection pressure PMI to fuel injectors 180. Fuel injectors 180 fluidly receive the main fuel from fuel system 111. Fuel injectors 180 also fluidly receive the water from water system 371 instead of the pilot fuel. Igniter 480 can be employed to ignite the main fuel in combustion chamber 155, at least for portions of the engine load and speed 20 map, and at least for certain operating modes (such as during a warm-up period after a cold start). In some embodiments, engine system 101 can employ compression ignition to ignite the main fuel (that is, autoignition of the main fuel), at least for portions of the engine load and speed map, and at least for certain operating modes (such as after a warm-up period when cold starting the engine). Engine system 101 does not employ a pilot fuel to ignite the main fuel. Igniter 480 is a positive ignition 25 source. In some embodiments, igniter 480 is a spark igniter. In some embodiments, igniter 480 is a hot surface igniter.

[0031] Water system 371 includes high-pressure pump 425 that pressurizes the water fluidly received from pump 420 to an in-cylinder water-injection-pressure and fluidly supplies the water at the in-cylinder water-injection-pressure to fuel injectors 180. In an exemplary embodiment, the in- 30 cylinder water-injection-pressure is greater than the main injection pressure PMI. There is intakemanifold water injector 445 that injects water into intake manifold 270 upstream of throttle 260. In some embodiments, intake-manifold water injector 445 injects the water into intake manifold 270 downstream from throttle 260. Intake-manifold water injector 445 injects the water at the intake water-injection-pressure fluidly received from pump 420. Fuel injectors 180 can be employed to- 11 - 5 inject water directly into the respective combustion chambers 155. Controller 450 can command all fuel injectors 180 to inject the water into the respective combustion chambers 155. Alternatively, controller 450 can command select fuel injectors 180 to inject the water into the respective combustion chambers 155 depending upon engine operating conditions (that is, controller 450 selectively commands one or more fuel injectors 180, but not all fuel injectors 180, to inject the water 10 into the respective combustion chambers 155), as will be described in more detail below. Controller 450 can selectively command intake-manifold water injector 445 to inject the water into intake manifold 270 such that the water is distributed to each combustion chamber 155 through the respective intake ports 280, which can be referred to as global water injection since the water is effectively introduced into all combustion chambers 155. 15

[0032] Referring now to FIG. 3, there is shown engine system 102 suitable for employing water mitigation strategies to solve problems associated with poor combustion characteristics in various operating modes that is similar to engine system 101 in FIG. 2 and differences are discussed. Engines system 102 employs water injection in combustion chambers 155 through fuel injector 180 and does not employ intake-manifold water injector 445. The water is pressurized from the water storage 20 pressure in water reservoir 380 to the in-cylinder water injection pressure suitable for injection directly into combustion chambers 155. The water does not need to be pressurized to the intake manifold water injection-pressure (suitable for injection into intake manifold 270), which is significantly lower than the in-cylinder water injection-pressure. Accordingly, in some embodiments, pumps 420 and 425 can be replaced by a single pump that pressurizes the water from the water storage 25 pressure in water reservoir 380 to the in-cylinder water injection-pressure. Pumps 420 and 425 can be collectively referred to as the pump, for example a water-injection pump.

[0033] Referring now to FIG. 4, there is shown engine system 103 suitable for employing water mitigation strategies to solve problems associated with poor combustion characteristics in various operating modes that is similar to engine system 101 in FIG. 2 and differences are discussed. Fuel 30 injectors 182 directly injects the main fuel into the respective combustion chambers 155 and water injector 184 directly injects the water into the respective combustion chambers 155. Fuel injector 182 and water injectors 184 are in-cylinder injectors. Each fuel injector 182 is separate and distinct from the respective water injector 184. Although water injector 184 is illustrated disposed through cylinder head 170, in some embodiments water inject 184 is mounted in engine block 160 and through the- 12 - 5 wall of cylinder 150. In some embodiments, intake-manifold water injector 445 is not employed. In some embodiments, pumps 420 and 425 can be replaced by a single pump (for example, the waterinjection pump) that pressurizes the water from the water storage pressure in water reservoir 380 to the in-cylinder water-injection-pressure.

[0034] With reference to FIG. 5, there is shown curves 500, 510, and 520 representing different 10 combustion characteristics. Curve 500 represents a normal combustion characteristic for the combustion chamber pressure in combustion chamber 155 during the compression stroke and a power stroke, curve 510 represents an abnormal combustion characteristic for the combustion chamber pressure in combustion chamber 155 when experiencing knock, and curve 520 represents an abnormal combustion characteristic for the combustion chamber pressure in combustion chamber 15 155 when experiencing retarded start of combustion timing. In the illustrated example, all curves 500, 510, and 520 substantially share similar profiles (indicated by 501) up to around -10 crank angle degrees (CAD) after top dead center (ATDC) during the compression stroke. Note that a negative value for CAD ATDC is equivalent to a positive value for CAD of the same magnitude before top dead center (BTDC). At around -10 CAD ATDC, curve 500 begins to flatten as the piston (not shown) 20 approaches the end of the compression stroke and begins to slow down, and somewhere close to 0 CAD (top dead center) the main fuel ignites and begins to combust such that the pressure continues to rise even as a volume of combustion chamber 155 begins to increase as the piston moves downwards during the power stroke. An inflection point 502 occurs around 5 CAD ATDC where the pressure increases substantially due to combustion until a peak pressure of curve 500 is reached and 25 the pressure begins to decline. In contrast, curve 510 illustrates premature ignition around -8 CAD ATDC (the preignition knock), typically due to high temperatures within combustion chamber 155 or hotspots on the piston, cylinder 150, or cylinder head 170, whereby the combustion chamber pressure continues to increase due to the uncontrolled ignition and combustion until a peak pressure of curve 510 is reached that can be substantially higher than the peak pressure of curve 500. Curve 30 510 typically does not show the flattening seen in curve 500 prior to ignition. Curve 520 illustrating retarded start of combustion timing has a similar shape to curve 500 representing the normal combustion characteristic except that ignition and combustion are retarded whereby inflection point 522 is delayed compared to inflection point 502, and a peak pressure of curve 520 during the power stroke is substantially less compared to the peak pressure in curve 500. Depending upon the amount 35 of retardation in the start of combustion timing, combustion chamber and exhaust temperatures can- 13 - 5 be reduced resulting in lower NOx emissions and increased emissions in carbon monoxide and unburned fuel.

[0035] Referring now to FIG. 6, there is shown algorithm 600 for mitigating abnormal combustion characteristics by employing selective water injection into combustion chambers 155 of engine systems 100, 101, 102, or 103 illustrated in FIGS. 1, 2, 3, and 4 respectively. Algorithm 600 10 can be performed by controller 450. Algorithm 600 can be performed for each combustion chamber 155 separately in each engine cycle. The engine cycle in a four-stroke engine includes the intake stroke, the compression stroke, the power stroke, and an exhaust stroke. For each combustion chamber 155, in step 610 the main fuel is injected directly into the combustion chamber and ignited with the respective positive ignition source. In some embodiments, internal combustion engine 120 15 is operating in the ECDI operating mode where the main fuel is injected at least during a portion of the compression stroke whereby the main fuel premixes with the intake charge. In an exemplary embodiment, an injection window of the main fuel during the ECDI operating mode where the injection can begin and end anywhere within the injection window is between intake valve closing (IVC) and -120 CA° ATDC during the compression stroke. IVC can occur near the end of the intake 20 stroke, at bottom dead center, or near the beginning of the compression stroke. In some embodiments, internal combustion engine is operating in the MCDI operating mode where the main fuel is injected during the compression stroke whereby the main fuel partially-premixes with the intake charge. In an exemplary embodiment, the injection window of the main fuel during the MCDI operating mode where the injection can begin and end anywhere within the injection window is between -120 CA° 25 ATDC and -30 CA° ATDC during the compression stroke. In some embodiments, the positive ignition source is the pilot fuel. In some embodiments, the positive ignition source is igniter 480, which can be the spark igniter or the hot surface igniter. In step 620, the start of combustion timing and a knock index can be determined for each combustion chamber 155 using signals from knock sensor 460. In some embodiments, the SOC timing occurs when the fuel begins to burn within 30 combustion chamber 155. In some embodiments, the SOC timing is determined from the heat release rate (calculated based on the derivative of pressure and volume), which is sensitive to even a small deviation from a pure compression curve (that is, the combustion chamber pressure resulting from compression within combustion chamber 155 due to the piston movement when ignition does not occur), and to make measurement more robust, a threshold can be employed on the rate of heat release 35 or a percentage of integrated heat release can be employed to determine the SOC timing. The knock- 14 - 5 index represents a level of knock in combustion chamber 155. In some embodiments, the knock index can be an instantaneous knock index that occurs in the current engine cycle. In some embodiments, the knock index can be an average knock index for a plurality of engine cycles. In some embodiments, the knock index can be a moving average. In step 630, for each combustion chamber 155, it is determined whether knock is occurring. Knock occurs within a combustion chamber when the knock 10 index is above a knock threshold. For each combustion chamber 155 taken separately, control transfers to step 640 where water is introduced into the combustion chamber 155 where knock is occurring. Accordingly, water is injected only into those combustion chambers 155 where knock is occurring. With respect to engine system 100 seen in FIG. 1, controller 450 commands the intakeport water injectors 440 of the respective combustion chambers 155 where knock is occurring to 15 inject the water at least while the respective intake valves (not shown) are open, which can be during the intake stroke and early during the compression stroke. With respect to engines systems 101 and 102 seen in FIGS. 2 and 3, controller 450 commands fuel injectors 180 of the respective combustion chambers 155 where knock is occurring to inject the water during the intake stroke and / or during the compression stroke. Recall that in engine systems 101 and 102, fuel injectors 180 are dual-fluid 20 injectors that inject the main fuel separately and independently from water and inject water separately and independently from the main fuel. With respect to engines system 103 seen in FIG. 4, controller 450 commands water injector 184 of the respective combustion chambers 155 where knock is occurring to inject the water during the intake stroke and / or during the compression stroke. Only intake-port water injectors 440, fuel injectors 180, and water injectors 184 associated with 25 combustion chambers 155 experiencing knock are commanded to inject the water. Only in combustion chambers 155 where knock is occurring are temperatures reduced when water is injected such that the temperatures in combustion chambers 155 where knock is not occurring are not affected due to water injection since water injection is not occurring. It is advantageous to inject water only into combustion chambers 155 where knock is occurring since unnecessarily reducing the 30 temperature in combustion chambers where knock is not occurring by injecting water may negatively affect ignition and combustion of the main fuel, which may derate the available engine power. When directly injecting the water into combustion chambers 155, such as with fuel injectors 180 in engine systems 101 and 102 and with water injectors 184 in engine system 103, a water injection timing is selected during the compression stroke such that the injected water evaporates before it reaches a 35 wall of cylinder 150 and combustion chamber 155. Water injection into a high temperature environment is beneficial to reduce wall wetting, which will not only reduce the effectiveness of- 15 - 5 water injection, but also contaminate engine lube oil. Returning to step 630 seen in FIG. 6, for each combustion chamber 155, control transfers to step 650 when the knock index for the combustion chamber is below the knock threshold. For each combustion chamber 155, in step 650 it is determined whether the start of combustion timing is retarded compared to a desired start of combustion timing. Control transfers to step 660 when start of combustion timing is retarded compared to a desired start 10 of combustion timing, and ignition timing for the positive ignition source is adjusted such that the start of combustion timing occurs at the desired start of combustion timing. More particularly, ignition timing is advanced such that the SOC timing is advanced. When the positive ignition source is the pilot fuel, pilot fuel injection can be advanced to advance ignition timing such that the ignition and combustion of the pilot fuel occurs earlier to create the pressure and temperature environment 15 suitable for ignition of the main fuel sooner. When the positive ignition source is the igniter 480, the signals that command igniter 480 to ignite the main fuel can occur earlier.

[0036] Referring now to FIG. 7, there is shown algorithm 700 for mitigating abnormal combustion characteristics by employing selective water injection into combustion chambers 155 of engine systems 100, 101, 102, or 103 illustrated in FIGS. 1, 2, 3, and 4 respectively. Algorithm 700 20 is similar to algorithm 600 and differences are discussed. Control transfers from step 620 where the knock index and the start of combustion timing are determined for each combustion chamber 155 directly to step 710. In step 710 it is determined whether the knock index in each combustion chamber 155 is above the knock threshold indicating knock is occurring. When knock is occurring in all combustion chamber 155, control transfers to step 720 where water injection into intake manifold 25 270, into intake ports 280, or directly into combustion chambers 155 occurs. With respect to engine system 100 seen in FIG. 1, controller 450 commands each intake-port water injector 440 to inject the water into the respective intake port 280 at least before the respective intake valve (not shown) closes, and typically during the intake stroke of the respective combustion chamber 155. With respect to engine systems 101 and 103 seen in FIGS. 2 and 4, respectively controller 450 commands intake- 30 manifold injector 445 to inject the water into intake manifold 270 at least before the respective intake valve (not shown) closes, and typically during the intake strokes of the respective combustion chambers 155. When engines systems 101 and 103 do not employ intake-manifold water injector 445, controller 450 commands all fuel injectors 180 and all water injectors 184, respectively to inject the water directly into combustion chambers 155. With respect to engine system 102 seen in FIG. 2, 35 controller 450 commands all fuel injectors 180 to inject the water directly into combustion chambers- 16 - 5 155. Returning to step 710 in FIG. 7, when knock is not occurring in all combustion chambers 155, control transfers to step 630. In exemplary embodiments, algorithm 700 is employed in engine systems where there is a selection between directly injecting the water into the plurality of combustion chambers 155 or injecting the water into intake manifold 270.

[0037] Certain combustion chambers 155 in internal combustion engine 120 may run hotter than 10 other combustion chambers 155. With reference to FIG. 8, combustion chamber temperature distribution is shown for a four‐cylinder engine. In this circumstance, combustion chamber 155 labelled Cylinder Number 3 runs hotter than the other combustion chambers 155 (the cylinders labelled Cylinder Number 1, Cylinder Number2, and Cylinder Number 4). Note that each combustion chamber 155 is associated with the respective cylinder 150, and cylinder temperature can also be 15 referred to as combustion chamber temperature in this context. A temperature near and / or at the end of the compression stroke of Cylinder Number 3 is higher than a threshold value that can cause the main fuel to ignite in regions of Cylinder Number 3 before the advancing flame front due to controlled ignition has had time to start the ignition process, which is referred to as knocking. Knocking can occur in the MCDI operating mode (employing partially-premixed combustion) and the ECDI 20 operating mode (employing premixed combustion). Each cylinder 150 in internal combustion engine 120 (seen in FIGS. 1, 2, 3, and 4) is located in a different location in engine block 160 and accordingly would experience a different thermodynamic environment unique to its respective location. Additionally, internal combustion engine 120 employs a cooling system (not shown) that circulates a heat exchange fluid (such as water or engine coolant) around each cylinder 150 to extract heat from 25 the respective cylinders to keep an engine temperature below a threshold temperature. The engine temperature can be a temperature of the heat exchange fluid that circulates through the cooling system. The ability of the cooling system to extract heat from the respective cylinders 150 can vary from cylinder to cylinder. Accordingly, due to at least these reasons, for each steady state engine operating condition, cylinder operating temperature for the respective cylinders 150 and combustion 30 chamber temperature for the respective combustion chamber 155 can vary from cylinder to cylinder and combustion chamber to combustion chamber. The cylinder operating temperatures can be end of compression cylinder temperatures, which refers to the temperature of the combustion chamber at the end of the compression stroke or at some other point during the compression stroke, such as at the time of ignition of the fuel. The cylinder operating temperatures can be the exhaust temperatures 35 in the respective exhaust port 285 of each cylinder 150. The cylinder operating temperature can also- 17 - 5 be peak combustion chamber temperatures within the respective combustion chambers 155, which occurs during combustion of the fuel.

[0038] Referring now to FIG. 9, there is shown an algorithm 800 for determining whether some combustion chambers 155 operate at a higher temperature compared to the other combustion chambers 155, and more particularly at a statistically significant higher temperature than others. In 10 step 810, internal combustion engine 120 is operated at an engine load and speed condition for a predetermined amount of time and / or until the engine temperature stabilizes. The engine temperature stabilizes when it substantially remains at a value, and / or within a predetermined variance about the value. Preferably, the engine load and speed condition includes a relatively high engine load, for example above a 50% level of a rated power of internal combustion engine 120, or at or near a level 15 where knocking can occur. In step 820, an average cylinder operating temperature of each cylinder 150 and an average operating temperature of all the cylinders are determined. In some embodiments, steps 810 and 820 are repeated multiple times for a variety of engine load and speed conditions, and the average cylinder operating temperature for each cylinder 150 and the average operating temperature for all the cylinders 150 can be determined using the results from the variety of engine 20 load and speed conditions. For each cylinder 150, in step 830, the average cylinder operating temperature for each cylinder 150 is compared to the average operating temperature for all the cylinders, and when the average cylinder operating temperature for the cylinder 150 is greater than the average operating temperature for all the cylinders 150 by a predetermined margin then that cylinder 150 is considered a hot cylinder and added to a hot cylinder list in step 840, otherwise the 25 cylinder is added to a cold cylinder list in step 850. In some embodiments, the predetermined margin is one standard deviation. The standard deviation is a measure of an amount of variation of the values of a variable (the average cylinder operating temperature for each cylinder 150) about its mean (the average operating temperature of all the cylinders 150). In some embodiments, the predetermined margin is two standard deviations. In some embodiments, the predetermined margin is one or more 30 standard deviations. Other definitions of predetermined margins are contemplated, such as an absolute temperature difference from the average. In some embodiments, there are no hot cylinders since the average cylinder operating temperatures of all the cylinders are substantially the same. Note that the terms “hot cylinder” and “cold cylinder” in this context refers to the hot cylinders running hotter than the cold cylinders and not to an absolute temperature. In some embodiments, there is only 35 a hot cylinder list and by default all cylinders 150 not in the hot cylinder list are considered a cold- 18 - 5 cylinder. In some embodiments, there is only a cold cylinder list and by default all cylinders 150 not in the cold cylinder list are considered a hot cylinder. The cylinders 150 considered to be the hot cylinders can be treated differently than the cylinders 150 considered to be the cold cylinders. For example, the cylinders 150 considered to be hot cylinders can be equipped with additional sensors that the cylinders 150 considered to be cold cylinders do not have, such as being equipped with 10 exhaust temperature sensor 470 in exhaust port 285 or being equipped with an additional or dedicated combustion sensor, such as an in-cylinder combustion sensor or a combustion sensor mounted in a bearing cap (not shown) associated with that cylinder 150. Alternatively, or additionally, knock sensor 460 can be disposed on internal combustion engine 120 in a more optimal configuration for the cylinders 150 considered to be hot cylinders than for the cylinders considered to be cold cylinders. 15 A more optimal configuration for knock sensor 460 can be defined as more sensitive to vibrations emanating from the hot cylinders. Controller 450 can be programmed to monitor the cylinders 150 considered to be hot cylinder more closely and / or more frequently compared to the other cylinders, such as taking into consideration the extra sensors associated with the cylinders considered to be hot cylinders. Engine knock when it occurs will typically occur first in one of the cylinders 150 20 considered to be hot cylinders, and typically occurs in all of the cylinders 150 considered to be hot cylinders before it occurs in cylinders 150 considered to be cold cylinders, and when engine knock occurs, knock mitigation is performed only in cylinders 150 where knock has been detected.

[0039] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in the illustrated 25 embodiment(s)”, “in some embodiments”, “in an exemplary embodiment,” “in exemplary embodiments,” and “in some exemplary embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases “in other embodiments,” and “in another embodiment,” as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, 30 without departing from the scope of the invention.

[0040] The term “and / or” is used herein to mean “one or the other or both”. In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and / or,” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition,- 19 - 5 throughout the specification, the meaning of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. The term “substantially,” as modifying a parameter having a stated limit, is to be construed as meaning something that effectively possesses the same property or achieves the same function as that of the stated limit and includes exactly the stated limit as well as insignificant deviations therefrom. 10

[0041] Although exemplary embodiments are illustrated in the figures and described herein, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described herein. In cases where examples are listed, it is to be understood that combinations of any of the alternative examples are 15 also envisioned. The scope of the invention is not to be limited to the particular embodiments disclosed herein, which serve merely as examples representative of the limitations recited in the issued claims resulting from this application, and the equivalents of those limitations.

[0042] Various features may be grouped together in exemplary embodiments for the purpose of streamlining the disclosure, but this method of disclosure should not be interpreted as reflecting an 20 intention that any claimed embodiment requires more features than are expressly recited in a corresponding claim. Rather, inventive subject matter may lie in less than all features of a single disclosed exemplary embodiment or may combine features from different figures or different embodiments. Thus, the appended claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate disclosed embodiment. However, the present disclosure 25 shall also be construed as implicitly disclosing any embodiment having any suitable set of one or more disclosed or claimed features (i.e., a set of features that are neither incompatible nor mutually exclusive) that appear in the present disclosure or the appended claims, including those sets that may not be explicitly disclosed herein or disclosed in a single figure or embodiment. Conversely, the scope of the appended claims does not necessarily encompass the whole of the subject matter 30 disclosed herein.

[0043] 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

- 20 - 5 We claim:

1. A method of mitigating abnormal combustion characteristics in an internal combustion engine comprising a plurality of combustion chambers, the method comprising: injecting a main fuel into each combustion chamber of the plurality of combustion chambers at least during respective compression strokes whereby the main fuel premixes or partially- 10 premixes with intake air in the combustion chamber; igniting the main fuel in each combustion chamber with a respective positive ignition source; and for each combustion chamber: determining whether knock is occurring; and 15 introducing water into the combustion chamber when knock is occurring such that a temperature of the combustion chamber is reduced due to the evaporation of the water therein thereby mitigating knocking; wherein water is only introduced into combustion chambers where knock is occurring. 20 2. The method as claimed in claim 1, further comprising for each combustion chamber: determining a knock index; and determining knock is occurring in the combustion chamber when the knock index is above a knock threshold. 25 3. The method as claimed in claim 1, further comprising for each combustion chamber:- 21 - 5 determining a start of combustion timing; and adjusting an ignition timing when the start of combustion timing is retarded beyond a desired start of combustion timing; wherein the start of combustion timing returns to the desired start of combustion timing due to the adjusted ignition timing. 10 4. The method as claimed in claim 1, further comprising injecting the water directly into each combustion chamber where knock is occurring when only some of the combustion chambers are knocking; determining that all the combustion chambers are knocking; and injecting water into an intake manifold of the internal combustion engine when all the 15 combustion chambers are knocking.

5. The method as claimed in claim 1, wherein the main fuel is directly injected into each of the plurality of combustion chambers.

6. The method as claimed in claim 1, wherein the water is directly injected into each of the plurality of combustion chambers. 20 7. The method as claimed in claim 1, wherein the water is injected into respective intake ports associated with each combustion chamber.

8. The method as claimed in claim 1, further comprising providing a plurality of dual fluid injectors where each dual fluid injector is associated with the respective combustion chamber; 25 wherein each dual fluid injector directly injects the main fuel and the water into the respective combustion chamber and each dual fluid injector is operable to inject the main fuel separately and independently of the water and to inject the water separately and independently of the main fuel.- 22 - 5 9. The method as claimed in claim 1, further comprising providing a water injector configured to inject water into an intake manifold of the internal combustion engine.

10. The method as claimed in claim 1, further comprising providing a plurality of main fuel injectors where each main fuel injector is associated with 10 the respective combustion chamber; and providing a plurality of water injectors where each water injector is associated with the respective combustion chamber.

11. The method as claimed in claim 10, wherein each water injector directly injects the water into the respective combustion chamber. 15 12. The method as claimed in claim 10, further comprising providing a plurality of intake ports; wherein each intake port is associated with the respective combustion chamber; and each water injector injects the water into the respective intake port associated with the respective combustion chamber. 20 13. The method as claimed in claim 10, further comprising providing an intake manifold water injector configured to inject the water into an intake manifold of the internal combustion engine.

14. The method as claimed in claim 1, wherein each combustion chamber is associated with a respective cylinder of a plurality of cylinders, the method further comprising 25 determining which cylinders of the plurality of cylinders are considered hot cylinders; and monitoring the hot cylinders differently compared to the cylinders that are not hot cylinders;- 23 - 5 wherein each hot cylinder has an average cylinder operating temperature that is greater than an average operating temperature of the plurality of cylinders by a predetermined margin.

15. The method as claimed in claim 14, wherein each hot cylinder is equipped with at least one additional sensor that the cylinders that are not hot cylinders are not equipped with including at least one of 10 an exhaust-port temperature sensor; an in-cylinder temperature sensor; a combustion sensor; and a knock sensor.

16. The method as claimed in claim 14, wherein the internal combustion engine is equipped with a 15 knock sensor, the method further comprises configuring the knock sensor with respect to the internal combustion engine to detect vibrations in the hot cylinders more sensitively than in the cylinders not considered the hot cylinders.

17. The method as claimed in claim 14, wherein the predetermined margin is one or more standard deviations from the average operating temperature of the plurality of cylinders or an absolute 20 temperature difference.

18. The method as claimed in claim 14, further comprising operating the internal combustion engine at an engine load and speed condition for a predetermined amount of time and / or until an engine temperature stabilizes; determining the average cylinder operating temperature for each cylinder; and 25 determining the average operating temperature of all the cylinders; wherein the hot cylinders are determined by comparing the average cylinder operating temperature of each cylinder to the average operating temperature of all the cylinders.- 24 - 5 19. The method as claimed in claim 18, further comprising operating the internal combustion engine at a plurality of engine load and speed conditions; for each engine load and speed condition of the plurality of engine load and speed conditions determining the average cylinder operating temperature for each cylinder; and determining the average operating temperature of all the cylinders for the plurality of engine 10 load and speed conditions.

20. The method as claimed in claim 1, wherein the water is injected at a water injection timing during the compression stroke, such that the water evaporates before it reaches a wall of the combustion chamber. 15