Patent Publication Number: US-10767587-B2

Title: Methods and system for injecting water at different groups of cylinders of an engine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 15/226,615, entitled “METHODS AND SYSTEM FOR INJECTING WATER AT DIFFERENT GROUPS OF CYLINDERS OF AN ENGINE,” filed on Aug. 2, 2016. The entire contents of the above-referenced application are hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD 
     The present description relates generally to methods and systems for injecting water at an engine and adjusting engine operation based on the water injection. 
     BACKGROUND/SUMMARY 
     Internal combustion engines may include water injection systems that inject water into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions. 
     As explained above, water may be injected into different locations, including the intake manifold, intake ports of engine cylinders, or directly into engine cylinders. While direct and port injection may provide increased cooling to the engine cylinders and ports, intake manifold injection may increase cooling of the charge air without needing high pressure injectors and pumps. However, due to the lower temperature of the intake manifold, not all the water injected at the intake manifold atomizes properly. Condensed water from water injection may accumulate within the intake manifold and result in unstable combustion if ingested by the engine, Additionally, the inventors herein have recognized that manifold water injection may result in uneven water distribution amongst cylinders coupled to the manifold. For example, water injected upstream of a group of cylinders may not distribute evenly to each of the cylinders due to evaporation, mixing, and entrainment issues, in addition to the airflow maldistribution among cylinders. As a result, uneven cooling may be provided to the engine cylinders. 
     In one example, the issues described above may be addressed by a method for injecting a first amount of water upstream of a first group of cylinders and a different, second amount of water upstream of a second group of cylinders, the first amount determined based on operating conditions of the first group and the second amount determined based on operating conditions of the second group. Additionally, in one example, injecting the first amount of water may include pulsing a first water injector disposed upstream of the first group of cylinders to deliver the first amount of water. The pulsing may be synchronized to an intake valve opening timing of each cylinder of the first group of cylinders. Further, the first amount of water and/or the pulsing timing may be adjusted based on outputs of knock sensors coupled to each cylinder of the first cylinder group following injection of water. In this way, maldistribution of water between cylinders of a group of cylinders may be identified and the water injection pulses may be adjusted to reduce the variation in water injection amounts between the cylinders. As a result, desired charge air cooling may be provided to each engine cylinder and engine efficiency may be increased. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of an engine system including a water injection system. 
         FIG. 2  shows a schematic diagram of a first embodiment of a water injector arrangement for an engine. 
         FIG. 3  shows a schematic diagram of a second embodiment of a water injector arrangement for an engine. 
         FIG. 4  shows a schematic diagram of a third embodiment of a water injector arrangement for an engine. 
         FIG. 5  shows a flow chart of a method for injecting water into one or more locations in an engine. 
         FIG. 6  shows a flow chart of a method for selecting a location for water injection based on engine operating parameters. 
         FIG. 7  shows a flow chart of a method for adjusting water injection and engine operating parameters based on estimated vaporized and condensed portions of water injected at an engine. 
         FIG. 8  shows a flow chart of a method for adjusting water injection to a group of cylinders of an engine and adjusting water injection parameters based on a distribution of water injected upstream of a group of cylinders. 
         FIG. 9  shows a graph depicting adjustments to various engine operating conditions in response to estimated vaporized and condensed portions of water injected at an engine. 
         FIG. 10  shows a graph depicting adjustments to a water injection amount and timing based on an indicated distribution of water to a group of cylinders. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for injecting water at a selected location in an engine based on engine operating conditions of the engine and adjusting water injection parameters, as well as engine operating parameters, based on one or more of an estimated portion of water that condensed following injection, an estimated portion of water that evaporated following injection, and detected imbalances in water distribution from injection among a group of cylinders. A schematic depiction of an example vehicle system, including a water injection system, is shown in  FIG. 1 .  FIGS. 2-4  show alternate embodiments of an engine with example locations of water injectors for substantially the same engine system as the one shown in  FIG. 1 . Water injectors may be located in a manifold, upstream of multiple cylinders, in intake ports of the engine cylinders, and/or at each individual cylinder. During engine operation, water injection at selected locations may be requested depending on various operating conditions of the engine in order to increase charge air cooling, increase cooling to engine components, and/or increase dilution at the engine cylinders. Conditions influencing the amount of water to be injected may include engine load, spark timing, knock intensity, etc.  FIGS. 5-8  illustrate example methods for injecting water at various locations in the engine (e.g., such as an intake manifold or intake ports of cylinders) and subsequently adjusting engine operating parameters based on estimates of vaporized and condensed portions of the injected water. Specifically,  FIG. 5  shows a method for determining whether to inject water via one or more water injectors based on engine operating conditions. In  FIG. 6 , a method is shown for selecting water injection at different engine locations based on engine operating conditions. For example, water may be injected via one or more injectors disposed in a manifold (such as an intake manifold) upstream of a plurality of cylinders, in an intake port of individual cylinders, and/or directly into engine cylinders.  FIG. 7  shows a method for injecting water at the selected location and estimating the amount of water that evaporated and condensed following the injection. Additionally,  FIG. 7  shows a method for adjusting the amount of water injected during subsequent injection events and adjusting engine operating conditions based on these estimated amounts. For example, spark timing may be adjusted to compensate for greater amounts of injected water that condensed (e.g., remained liquid). In some examples, water may be injected upstream of a group (e.g., two or more) cylinders). However, due to different airflow amounts, pressures, and architectures of each cylinder, injected water may not be distributed evenly to all cylinders of the group. Thus, as shown in  FIG. 8 , a method may include detecting an imbalance in water distribution across cylinders in a group based on output from knock sensors and adjusting water injection parameters based on the detected imbalance. In this way, more even water distribution may be achieved among cylinders.  FIG. 9  graphically depicts changes to various engine operating parameters in response to estimated vaporized and condensed portions of water injected at the selected locations. Finally,  FIG. 10  graphically depicts adjusting the amount and timing of water injection pulses in response to uneven distribution across cylinders. In this way, water injection parameters may be selected based on estimates of how much of the injected water is vaporizing vs. condensing at the selected location, how much of the injected water is going to each cylinder, and engine operating conditions. As a result, desired charge air cooling and engine dilution may be provided to all engine cylinders. This may increase engine efficiency, decrease fuel consumption, and decrease emissions of the engine. 
       FIG. 1  shows an embodiment of a water injection system  60  and an engine system  100 , in a motor vehicle  102 , illustrated schematically. In the depicted embodiment, engine  10  is a boosted engine coupled to a turbocharger  13  including a compressor  14  driven by a turbine  16 . Specifically, fresh air is introduced along intake passage  142  into engine  10  via air cleaner  11  and flows to compressor  14 . The compressor may be a suitable intake-air compressor, such as a motor-driven or driveshaft driven supercharger compressor. In the engine system  100 , the compressor is shown as a turbocharger compressor mechanically coupled to turbine  16  via a shaft  19 , the turbine  16  driven by expanding engine exhaust. In one embodiment, the compressor and turbine may be coupled within a twin scroll turbocharger. In another embodiment, the turbocharger may be a variable geometry turbocharger (VGT), where turbine geometry is actively varied as a function of engine speed and other operating conditions. 
     As shown in  FIG. 1 , compressor  14  is coupled, through charge air cooler (CAC)  18  to throttle valve (e.g., intake throttle)  20 . The CAC may be an air-to-air or air-to-coolant heat exchanger, for example. Throttle valve  20  is coupled to engine intake manifold  22 . From the compressor  14 , the hot compressed air charge enters the inlet of the CAC  18 , cools as it travels through the CAC, and then exits to pass through the throttle valve  20  to the intake manifold  22 . In the embodiment shown in  FIG. 1 , the pressure of the air charge within the intake manifold is sensed by manifold air pressure (MAP) sensor  24  and a boost pressure is sensed by boost pressure sensor  124 . A compressor by-pass valve (not shown) may be coupled in series between the inlet and the outlet of compressor  14 . The compressor by-pass valve may be a normally closed valve configured to open under selected operating conditions to relieve excess boost pressure. For example, the compressor by-pass valve may be opened during conditions of decreasing engine speed to avert compressor surge. 
     Intake manifold  22  is coupled to a series of combustion chambers or cylinders  180  through a series of intake valves (not shown) and intake runners (e.g., intake ports)  185 . As shown in  FIG. 1 , the intake manifold  22  is arranged upstream of all combustion chambers  180  of engine  10 . Sensors such as manifold charge temperature (MCT) sensor  23  and air charge temperature sensor (ACT)  125  may be included to determine the temperature of intake air at the respective locations in the intake passage. In some examples, the MCT and the ACT sensors may be thermistors and the output of the thermistors may be used to determine the intake air temperature in the passage  142 . The MCT sensor  23  may be positioned between the throttle  20  and the intake valves of the combustion chambers  180 . The ACT sensor  125  may be located upstream of the CAC  18  as shown, however, in alternate embodiments, the ACT sensor  125  may be positioned upstream of compressor  14 . The air temperature may be further used in conjunction with an engine coolant temperature to compute the amount of fuel that is delivered to the engine, for example. Additional temperature sensors such as temperature sensor  25  may be included to determine the temperature proximate to a water injector. In some embodiments, an engine system  100  may include a plurality of temperature sensors  25  to determine the temperature at each water injector location in the engine  100 . Each combustion chamber may further include a knock sensor  183  for identifying abnormal combustion events. Further, as explained further below with reference to  FIG. 8 , outputs of the knock sensors of each combustion chamber  180  may be used to detect maldistribution of water to each combustion chamber  180 , where the water is injected upstream of all the combustion chambers  180 . In alternate embodiments, one or more knock sensors  183  may be coupled to selected locations of the engine block. 
     The combustion chambers are further coupled to exhaust manifold  136  via a series of exhaust valves (not shown). The combustion chambers  180  are capped by cylinder head  182  and coupled to fuel injectors  179  (while only one fuel injector is shown in  FIG. 1 , each combustion chamber includes a fuel injector coupled thereto). Fuel may be delivered to fuel injector  179  by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. Furthermore, combustion chamber  180  draws in water and/or water vapor, which may be injected into the engine intake or the combustion chambers  180  themselves by a plurality of water injectors  45 - 48 . In the depicted embodiment, the water injection system is configured to inject water upstream of the throttle  20  via water injector  45 , downstream of the throttle and into the intake manifold  22  via injector  46 , into one or more intake runners (e.g., ports)  185   s  via injector  48 , and directly into one or more combustion chambers  180  via injector  47 . In one embodiment, injector  48  arranged in the intake runners may be angled toward and facing the intake valve of the cylinder which the intake runner is attached to. As a result, injector  48  may inject water directly onto the intake valve (this may result in fast evaporation of the injected water and increase the dilution benefit of using the water vapor as EGR to reduce pumping losses). In another embodiment, injector  48  may be angled away from the intake valve and be arranged to inject water against the intake air flow direction through the intake runner. As a result, more of the injected water may be entrained into the air stream, thereby increasing the cooling benefit. 
     Though only one representative injector  47  and injector  48  are shown in  FIG. 1 , each combustion chamber  180  and intake runner  185  may include its own injector. In alternate embodiments, a water injection system may include water injectors positioned at one or more of these positions. For example, an engine may include only water injector  46 , in one embodiment. In another embodiment, an engine may include each of water injector  46 , water injectors  48  (one at each intake runner), and water injectors  47  (one at each combustion chamber). Water may be delivered to water injectors  45 - 48  by the water injection system  60 , as described further below. 
     In the depicted embodiment, a single exhaust manifold  136  is shown. However, in other embodiments, the exhaust manifold may include a plurality of exhaust manifold sections. Configurations having a plurality of exhaust manifold sections may enable effluent from different combustion chambers to be directed to different locations in the engine system. Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  136  upstream of turbine  16 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . 
     As shown in  FIG. 1 , exhaust from the one or more exhaust manifold sections is directed to turbine  16  to drive the turbine. When reduced turbine torque is desired, some exhaust may be directed instead through a waste gate (not shown), by-passing the turbine. The combined flow from the turbine and the waste gate then flows through emission control device  70 . In general, one or more emission control devices  70  may include one or more exhaust after-treatment catalysts configured to catalytically treat the exhaust flow, and thereby reduce an amount of one or more substances in the exhaust flow. 
     All or part of the treated exhaust from emission control device  70  may be released into the atmosphere via exhaust conduit  35 . Depending on operating conditions, however, some exhaust may be diverted instead to an exhaust gas recirculation (EGR) passage  151 , through EGR cooler  50  and EGR valve  152 , to the inlet of compressor  14 . In this manner, the compressor is configured to admit exhaust tapped from downstream of turbine  16 . The EGR valve  152  may be opened to admit a controlled amount of cooled exhaust gas to the compressor inlet for desirable combustion and emissions-control performance. In this way, engine system  100  is adapted to provide external, low-pressure (LP) EGR. The rotation of the compressor, in addition to the relatively long LP EGR flow path in engine system  100 , provides excellent homogenization of the exhaust gas into the intake air charge. Further, the disposition of EGR take-off and mixing points provides effective cooling of the exhaust gas for increased available EGR mass and increased performance. In other embodiments, the EGR system may be a high pressure EGR system with EGR passage  151  connecting from upstream of the turbine  16  to downstream of the compressor  14 . In some embodiments, the MCT sensor  23  may be positioned to determine the manifold charge temperature, and may include air and exhaust recirculated through the EGR passage  151 . 
     The water injection system  60  includes a water storage tank  63 , a water pump  62 , a collection system  72 , and a water filling passage  69 . In embodiments that include multiple injectors, water passage  61  may contain one or more valves to select between different water injectors. For example, as shown in  FIG. 1 , water stored in water tank  63  is delivered to water injectors  45 - 48  via a common water passage  61  that branches to water passages  90 ,  92 ,  94 , and  96  In the depicted embodiment, water from water passage  61  may be diverted through one or more of valve  91  and passage  90  to deliver water to injector  45 , through valve  93  and passage  92  to deliver water to injector  46 , through valve  95  and passage  94  to deliver water to injector  48 , and/or through valve  97  and passage  96  to deliver water to injector  47 . Additionally, embodiments that include multiple injectors may include a plurality of temperature sensors  25  proximate to each injector to determine engine temperature at one or more water injectors. Water pump  62  may be operated by a controller  12  to provide water to water injectors  45 - 48  via passage  61 . In an alternate embodiment, the water injection system  60  may include multiple water pumps. For example, the water injection system  60  may include a first water pump  62  to pump water to a subset of injectors (such as injectors  45  and/or  46 ) and a second water pump (not shown) to pump water to another subset of injectors (such as injectors  48  and/or  47 . In this example, the second water pump may be a higher pressure water pump and the first water pump may be a relatively lower pressure water pump. In addition, the injection system may comprise a self-pressurized piston pump which can perform both high pressure pumping and injection. For example, one or more of the injectors may include or be coupled to a self-pressurized piston pump. 
     Water storage tank  63  may include a water level sensor  65  and a water temperature sensor  67 , which may relay information to controller  12 . For example, in freezing conditions, water temperature sensor  67  detects whether the water in tank  63  is frozen or available for injection. In some embodiments, an engine coolant passage (not shown) may be thermally coupled with storage tank  63  to thaw frozen water. The level of water stored in water tank  63 , as identified by water level sensor  65 , may be communicated to the vehicle operator and/or used to adjust engine operation. For example, a water gauge or indication on a vehicle instrument panel (not shown) may be used to communicate the level of water. In another example, the level of water in water tank  63  may be used to determine whether sufficient water for injection is available, as described below with reference to  FIG. 5 . In the depicted embodiment, water storage tank  63  may be manually refilled via water filling passage  69  and/or refilled automatically by the collection system  72  via water tank filling passage  76 . Collection system  72  may be coupled to one or more components  74  that refill the water storage tank with condensate collected from various engine or vehicle systems. In one example, collection system  72  may be coupled with an EGR system to collect water condensed from exhaust passing through the EGR system. In another example, collection system  72  may be coupled with an air conditioning system (not shown). Manual filling passage  69  may be fluidically coupled to a filter  68 , which may remove small impurities contained in the water that could potentially damage engine components. 
       FIG. 1  further shows a control system  28 . Control system  28  may be communicatively coupled to various components of engine system  100  to carry out the control routines and actions described herein. For example, as shown in  FIG. 1 , control system  28  may include an electronic digital controller  12 . Controller  12  may be a microcomputer, including a microprocessor unit, input/output ports, an electronic storage medium for executable programs and calibration values, random access memory, keep alive memory, and a data bus. As depicted, controller  12  may receive input from a plurality of sensors  30 , which may include user inputs and/or sensors (such as transmission gear position, gas pedal input (e.g., pedal position), brake input, transmission selector position, vehicle speed, engine speed, mass airflow through the engine, boost pressure, ambient temperature, ambient humidity, intake air temperature, fan speed, etc.), cooling system sensors (such as ECT sensor, fan speed, passenger compartment temperature, ambient humidity, etc.), CAC  18  sensors (such as CAC inlet air temperature, ACT sensor  125  and pressure, CAC outlet air temperature, MCT sensor  23 , and pressure, etc.), knock sensors  183  for determining ignition of end gases and/or water distribution among cylinders, and others. Furthermore, controller  12  may communicate with various actuators  32 , which may include engine actuators (such as fuel injectors, an electronically controlled intake air throttle plate, spark plugs, water injectors, etc.). In some examples, the storage medium may be programmed with computer readable data representing instructions executable by the processor for performing the methods described below as well as other variants that are anticipated but not specifically listed. 
     The controller  12  receives signals from the various sensors of  FIG. 1  and employs the various actuators of  FIG. 1  to adjust engine operation based on the received signals and instructions stored on a memory of the controller. For example, injecting water to the engine may include adjusting an actuator of injector  45 , injector  46 , injector  47 , and/or injector  48  to inject water and adjusting water injection may include adjusting an amount or timing of water injected via the injector. In another example, adjusting spark timing based on water injection estimates (as described further below) may include adjusting an actuator of a spark plug  184 . 
       FIGS. 2-4  show different embodiments of an engine and example placements of water injectors within the engine. The engines  200 ,  300 , and  400  shown in  FIGS. 2-4  may have similar elements to engine  10  shown in  FIG. 1  and may be included in an engine system, such as engine system  100  shown in  FIG. 1 . As such, similar components in  FIGS. 2-4  to those of  FIG. 1  are not re-described below for the sake of brevity. 
     A first embodiment of a water injector arrangement for an engine  200  is depicted in  FIG. 2  in which water injectors  233  and  234  are positioned downstream of where an intake passage  221  branches to different cylinder groups. Specifically, engine  200  is a V-engine with a first cylinder bank  261  including a first group of cylinders  281  and a second cylinder bank  260  including a second group of cylinders  280 . The intake passage branches from a common intake manifold  222  to a first manifold  245  coupled to intake runners  265  of the first group of cylinders  281  and to a second manifold  246  coupled to intake runners  264  of the second group of cylinders  280 . Thus, intake manifold  222  is located upstream of all the cylinders  281  and cylinders  280 . Further, throttle valve  220  is coupled to intake manifold  222 . Manifold charge temperature (MCT) sensors  224  and  225  may be included downstream of the branch point in the first manifold  245  and second manifold  246 , respectively, to measure the temperature of intake air at their respective manifolds. For example, as shown in  FIG. 2 , MCT sensor  224  is positioned within first manifold  245 , proximate to water injector  233 , and MCT sensor  225  is positioned within second manifold  246 , proximate to water injector  234 . 
     Each of cylinders  281  and cylinders  280  include a fuel injector  279  (as shown in  FIG. 2  coupled to one representative cylinder). Each of cylinders  281  and cylinders  280  may further include a knock sensor  283  for identifying abnormal combustion events. Additionally, as described further below, comparing the outputs of each knock sensor in a cylinder group may enable a determination of maldistribution of water between cylinders of that cylinder group. For example, comparing outputs of knock sensors  283  coupled to each of cylinders  281  may allow a controller of the engine to determine how much water from injector  233  was received by each of cylinders  281 . Due to the intake runners  265  being arranged at different lengths to the injector  233  and different conditions of each intake runner (e.g., airflow levels and pressure), water may not be evenly distributed to each of the cylinders  281  following an injection from injector  233 . 
     Water may be delivered to water injectors  233  and  234  by a water injection system (not shown), like water injection system  60  described above with reference to  FIG. 1 . Furthermore, a controller, such as controller  12  of  FIG. 1 , may control injection of water into injectors  233  and  234  individually based on operating conditions of the individual manifolds that the injectors are coupled to. For example, in some examples, MCT sensor  224  may also include a pressure and/or airflow sensor for estimating an airflow rate (or amount) of airflow at the first manifold  245  and a pressure in the first manifold  245 . Similarly, MCT sensor  225  may also include a pressure and/or airflow sensor for estimating an airflow rate and/or pressure at the second manifold  246 . In this way, each injector  233  and  234  may be actuated to inject a different amount of water based on conditions of the manifold and/or cylinder group the injector is coupled to. A method for determining a water injection amount is discussed further below with reference to  FIG. 7 . 
     In  FIG. 3 , a second embodiment of a water injector arrangement for an engine  300  is shown. Engine  300  is an in-line engine where a common intake manifold  322 , coupled downstream of a throttle valve  320  of a common intake passage, branches into a first manifold  345  of a first group of cylinders including cylinders  380  and  381  and a second manifold  346  of a second group of cylinders including cylinders  390  and  391 . The first manifold  345  is coupled to intake runners  365  of a first cylinder  380  and third cylinder  381 . The second manifold  346  is coupled to intake runners  364  of a second cylinder  390  and fourth cylinder  391 . A first water injector  333  is coupled in the first manifold  345 , upstream of cylinders  380  and  381 . A second water injector  334  is coupled in the second manifold  346 , upstream of cylinder  390  and  391 . As such, water injectors  333  and  334  are positioned downstream of the branch point from the intake manifold  322 . Manifold charge temperature (MCT) sensors  324  and  325  may be included in first manifold  345  and second manifold  346 , proximate to the first water injector  333  and second water injector  334 , respectively. 
     Each of the cylinders includes a fuel injector  379  (one representative fuel injector shown in  FIG. 2 ). Each cylinder may further include a knock sensor  383  for identifying abnormal combustion events and/or a distribution of water among the cylinders in a cylinder group. Water injectors  333  and  334  may be coupled to a water injection system (not shown), like water injection system  60  described in  FIG. 1 . 
     In this way,  FIGS. 2 and 3  shows examples of an engine where multiple water injectors are used to inject water to different groups of cylinders of the engine. For example, a first water injector may inject water upstream of a first group of cylinders and a second water injector may inject water upstream of a different, second group of cylinders. As discussed further below, different water injection parameters (such as water injection amount, timing, pulsing rate, etc.) may be selected for each water injector based on operating conditions of the group of cylinders the injector is coupled upstream from (such as airflow amount, pressure, firing order, etc.). 
     A third embodiment of a water injector arrangement for an engine  400  is depicted in  FIG. 4 . As in the previous embodiments, in the embodiment of  FIG. 4 , intake manifold  422  is configured to supply intake air or an air-fuel mixture to plurality of cylinders  480  through a series of intake valves (not shown) and intake runners  465  Each of cylinders  480  includes a fuel injector  479  coupled thereto. Each cylinder  480  may further include a knock sensor  483  for identifying abnormal combustion events and/or determining a distribution of water injected upstream of the cylinders. In the depicted embodiment, water injectors  433  are directly coupled to the cylinders  480  and thus are configured to inject water directly into the cylinders. As shown in  FIG. 4 , one water injector  433  is coupled to each cylinder  480 . In another embodiment, water injectors may be additionally or alternatively positioned upstream of the cylinders  480  in the intake runners  465  and not coupled to each cylinder. Water may be delivered to water injectors  433  by a water injection system (not shown), like water injection system  60  described in  FIG. 1 . 
     In this way, the systems of  FIGS. 1-4  present example systems that may be used to inject water into one or more locations in an engine intake or cylinders of an engine. As introduced above, water injection may be used to reduce a temperature of the intake air entering engine cylinders and thereby reduce knock and increase volumetric efficiency of the engine. Injecting water may also be used to increase engine dilution and thereby reduce engine pumping losses. As explained above, water may be injected into the engine at different locations, including the intake manifold (upstream of all engine cylinders), manifolds of groups of cylinders (upstream of a group of cylinders, such as in a V-engine), intake runners or ports of engine cylinders; or directly into engine cylinders. While direct and port injection may provide increased cooling to the engine cylinders and ports, intake manifold injection may increase cooling, of the charge air without needing high pressure injectors and pumps (such as those that may be needed for port or direct cylinder injection). However, due to the lower temperature of the intake manifold (as it is further away from the cylinders), not all the water injected at the intake manifold may atomize (e.g., vaporize) properly. In some examples, as shown in  FIG. 1  engines may include injectors at multiple locations within the engine intake or engine cylinders. Under different engine load and/or speed conditions it may be advantageous to inject water at one location over another to achieve increased charge air cooling (intake manifold) or dilution (cylinder intake ports/runners). In this way selecting a location for water injection based on engine operating conditions (as shown in the methods presented at  FIGS. 5-6  and described further below) may increase the water injection benefits described above, thereby increasing engine efficiency, increasing fuel economy, and decreasing emissions. 
     In some cases, after injecting water, a first portion of the injected water may vaporize and a remaining, second portion may condense (or stay liquid within the intake manifold or injector location). Condensed water from water injection may accumulate within the intake manifold and result in unstable combustion if ingested by the engine. Additionally, the ratio of vaporized to condensed water may change the amount of charge air cooling provided. Thus, as explained further below with reference to  FIG. 7-8 , subsequent water injection parameters (e.g., injection amounts and/or timing) and/or engine operating conditions (such as airflow amount/rate to the engine and spark timing) may be adjusted in response to an estimate of the vaporized and condensed portions of water injected. For example, engine operating parameter adjustments may compensate for increased amounts of injected water that remains liquid instead of vaporizing. 
     Additionally, as introduced above, an engine may include multiple water injectors, where each water injector injects water upstream of a different group of cylinders. In this case, water injection parameters for each injector may be individually determined based on conditions of the group of cylinders that the injector is coupled to (e.g., airflow to the group of cylinders, pressure upstream of the group of cylinders, etc.). Further, manifold water injection upstream of a group of cylinders (e.g., two or more cylinders) may result in uneven water distribution amongst the cylinders of the group due to differences in architecture or conditions (e.g., pressure, temperature, airflow, etc.) of the individual cylinders in the group. As a result, uneven cooling may be provided to the engine cylinders. In some examples, as explained further below with reference to  FIG. 8 , maldistribution of water injected upstream of a group of cylinders may be detected and compensated for in response to a comparison of outputs of knock sensors coupled to each cylinder of the group. 
     Turning to  FIG. 5 , an example method  500  for injecting water into an engine is depicted. Injecting water may include injecting water via one or more water injectors of a water injection system, such as the water injection system  60  shown in  FIG. 1 . Instructions for carrying out method  500  and the rest of the methods included herein may be executed by a controller (such as controller  12  shown in  FIG. 1 ) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference to  FIG. 1, 2, 3 , or  4 . The controller may employ engine actuators of the engine system to adjust engine operation, according to the methods described below. In one example, water may be injected via one or more water injectors using a water injection system (such as water injection system  60  shown in  FIG. 1 ). 
     The method  500  begins at  502  by estimating and/or measuring engine operating conditions. Engine operating conditions may include manifold pressure (MAP), air-fuel ratio (A/F), spark timing, fuel injection amount or timing, an exhaust gas recirculation (EGR) rate, mass air flow (MAF), manifold charge temperature (MCT), engine speed and/or load, etc. Next, at  504 , the method includes determining whether water injection has been requested. In one example, water injection may be requested in response to a manifold temperature being greater than a threshold level. Additionally, water injection may be requested when a threshold engine speed or load is reached. In yet another example, water injection may be requested based on an engine knock level being above a threshold. Further, water injection may be requested in response to an exhaust gas temperature above a threshold temperature, where the threshold temperature is a temperature above which degradation of engine components downstream of cylinders may occur. In addition, water may be injected when the inferred octane number of used fuel is below a threshold. 
     If water injection has not been requested, engine operation continues at  506  without injecting water. Alternatively, if water injection has been requested the method continues at  508  to estimate and/or measure water availability for injection. Water availability for injection may be determined based on the output of a plurality of sensors, such as water level sensor and/or water temperature sensor disposed in a water storage tank of a water injection system of the engine (such as water level sensor  65  and water temperature sensor  67  shown in  FIG. 1 ). For example, water in the water storage tank may be unavailable for injection in freezing conditions (e.g., when the water temperature in the tank is below a threshold level, where the threshold level is at or near a freezing temperature). In another example, the level of water in the water storage tank may be below a threshold level, where the threshold level is based on an amount of water required for an injection event or a period of injection cycles. In response to the water level of the water storage tank being below the threshold level, refilling of the tank may be indicated. If water is not available for injection, the method continues at  512  to adjust engine operating parameters without injecting water. For example, if water injection has been requested to reduce knock, engine operation adjustments may include enriching the air-fuel ratio, reducing an amount of throttle opening to decrease manifold pressure, retarding spark timing, etc. However, if water is available for injection, the method continues at  514  to determine whether the engine includes multiple injector locations. Multiple injector locations may include water injectors being positioned at more than one type of location in an engine. For example, an engine may include two types of water injectors: an intake manifold water injector and port water injectors in the intake runners/ports of each cylinder. If the engine does not have multiple water injector locations, the method continues at  518  to inject water via one or more water injectors. For example, the method at  518  may include injecting water via the single type of water injectors of the engine (e.g., via a single intake manifold water injector, manifold water injectors of a manifold for each group of cylinders, port water injectors, or direct cylinder water injectors). Additionally, at  518 , subsequent water injection and engine operating conditions are adjusted in response to the estimated amount of injected water that has condensed, as described below in reference to  FIG. 7 . However, if multiple types of injectors are present in the engine, the method first continues at  516  to select the type of water injectors for water injection, as discussed further below with reference to  FIG. 6 , before continuing to  518  to inject water and adjust engine operation. 
       FIG. 6  depicts a method  600  for selecting a location for water injection based on engine operating conditions. As explained above, an engine may include water injectors positioned in one or more locations including: an intake manifold (either upstream or downstream of an intake throttle), an intake port of each engine cylinder, and/or in each cylinder. Method  600  may be executed by a controller of an engine including water injectors in each of the intake manifold, cylinder intake ports (e.g., intake runners), and the cylinders themselves (e.g., in the combustion chambers).  FIG. 1  shows an example engine including such a combination of injector locations. Method  600  may continue from the method at  516  of method  500 . 
     The method  600  starts at  602  by determining whether engine speed and/or load is greater than a threshold. In one example, the threshold may be indicative of a relatively high load and/or engine speed at which engine knock may be more likely to occur. If engine speed and/or load are greater than the respective thresholds, the method continues at  604  where the intake manifold injector(s) are selected for water injection. In one example, the engine may include a single intake manifold and thus a single intake manifold water injector (such as injector  45  or  46  shown in  FIG. 1 ). In another example, the engine may include multiple manifolds, each upstream of different group of cylinders, and thus include multiple manifold water injectors (such as injectors  233  and  234  shown in  FIG. 2  or injectors  333  and  334  shown in  FIG. 3 ). Next, at  606 , the method includes assessing whether an upper threshold for manifold injection has been reached. In one example, the upper threshold for manifold injection may include a maximum amount of water that may be injected at the manifold for the current engine operating conditions (e.g., current humidity, pressure, temperature). For example, only a certain amount of water may be able to vaporize and become entrained in the airflow in the intake manifold. Thus, additional water injected above this upper threshold may not provide any additional benefits (e.g., such as additional charge air cooling). If manifold injection is at or above the upper threshold, direct injectors (adapted to inject water directly into engine cylinders) are additionally selected at  610  and water is injected at  612  using both the manifold injector(s) and the cylinder direct injectors. If manifold injection is not at the upper threshold, then water is injected at  612  using the manifold injector(s) only. Returning to  602 , if engine speed and/or load is less than the threshold, then at  608  the port water injectors are selected and water is injected into the intake ports of the cylinders at  612 . The method at  612  may return to  518  of method  500  to inject water and then adjust engine operation based on estimates of vaporized and condensed portions of the injected water, as shown at  FIG. 7 . 
       FIG. 7  illustrates a method  700  for estimating the amount of water vaporized and condensed following water injection. Method  700  continues from and may be part of the method at  518  of  FIG. 5 . It should be noted that method  700  may be repeated for each injector that injects water (e.g., each manifold, port, or direct injector). In this way, the estimated amount of water that vaporized and condensed from water injection at each injector may be determined for each individual injector. 
     The method  700  starts at  702  by determining the amount of water to inject at the selected water injectors following a water injection request. The amount of water for injection may be based on feedback from a plurality of sensors, which provide information about various engine operating parameters. These parameters may include engine speed and load, spark timing, ambient conditions (e.g. ambient temperature and humidity), a fuel injection amount and/or knock history (based on the output of knock sensors coupled to or near the engine cylinders). In one example, the water injection amount may increase as engine load increases. Additionally, at  702  the method includes measuring a manifold charge temperature of an intake manifold (e.g., monitoring an output of a MCT sensor, such as MCT  23  shown in  FIG. 1 ). In another example, if the water injectors are not located in the intake manifold, the method at  702  may include measuring the charge air temperature proximate to the selected water injector (such as sensor  324  proximate to injector  333  in  FIG. 3  or sensor  25  proximate to injector  48  in  FIG. 1 ). In yet another example, the temperature of the charge air proximate to the water injectors (such as direct injectors at the engine cylinders) may be estimated based on one or more engine operating conditions (such as measured intake and exhaust air temperatures, engine load, knock intensity signal, etc.). 
     At  704 , water is injected at selected injectors as described above with reference to method  600  shown in  FIG. 6 . Following water injection, at  706 , the method includes measuring the manifold charge temperature again after a duration. In another embodiment, the method at  706  may additionally or alternatively include measuring or estimating the temperature proximate to the selected injector following the water injection event at  704 . The duration between a water injection event and measuring manifold charge temperature may be based on an amount of time for the injected amount of water to vaporize and/or condense. Thus, this duration may be adjusted relative to the amount of water injected. In one example, the duration may increase as the amount of water injected at the injector increases. In another example, the duration may be adjusted base on the measured or estimated manifold charge temperature. Based on the change in manifold charge temperature measured from before water injection, at  702 , and after, at  706 , the amount of the injected water that vaporized may be estimated at  708 . Said another way, a vaporized portion of the injected water may be determined at  708  based on the change in manifold (or other location of the injector) charge air temperature from before to after the water injection event. 
     Next, at  710 , the method includes estimating the amount (e.g., portion) of the injected water that condensed (e.g., remained liquid) based on the amount of water injected via the selected injector and the estimated amount of water that vaporized, as determined at  708 . For example, the amount of water of the injected water that condensed may be a remaining portion of water from the vaporized portion. Then, at  712 , the method includes determining whether the vaporized portion of water is greater than a threshold. The threshold vaporized portion may be a non-zero value and may also be less than 100% of the water injected. In one example, the threshold may be 90% of the amount of water injected. However, in other examples the threshold value may be 100% or some value between 60 and 100%. If the vaporized portion following water injection is above the threshold, at  716  the method includes continuing engine operation at the current operating parameters. For example, the method at  716  may include continuing to inject the previously injected amount of water at the selected injector(s), without adjusting the amount of water for injection. 
     However, if the vaporized portion is not greater than the threshold, at  714  the method may include adjusting engine operating parameters based on the determined vaporized and/or condensed portions. In one example, when the engine includes multiple groups of cylinders with one injector coupled to and upstream of each group, engine operation may also be adjusted based on the vaporized and condensed portions of other groups, as well as a determined distribution of injected water to cylinders within a group, as described further below in reference to  FIG. 8 . In one example, at  713 , the method may include adjusting one or more engine operating parameters based on the determined condensed portion of injected water. As one example, adjusting one or more engine operating parameters at  713  may include adjusting spark timing to compensate for the condensed portion of the injected water. For example, adjusting spark timing may include increasing an amount of spark advance, where the amount of spark advance increases as the condensed portion decreases (or the vaporized portion increases). In another example at  713 , the method may include adjusting a fuel injection amount based on the determined vaporized and/or condensed portions. In yet another example, the method at  713  may include adjusting one or more engine operating parameters to increase airflow to the engine cylinders to purge the condensed portion of injected water from the intake manifold (or intake runners if that&#39;s where the selected injector is located). Adjusting one or more engine operating parameters to increase airflow to the engine cylinders may include increasing an opening of a throttle valve and/or adjusting a transmission gear to increase engine speed. The amount of increase in airflow at  713  may be based on the determined condensed portion (e.g., the amount of airflow increase may increase further as the condensed portion increases). In some examples, purging the condensed portion in this way may only proceed when the engine is able to handle the water (e.g., during deceleration fuel shut-off conditions). In yet another example, the method at  714  may include advancing spark at the same time as increasing airflow to purge the condensed portion. In one example, at  715 , the method includes adjusting the amount of water and/or timing delivered by the selected water injector(s) for subsequent injections based on the vaporized portion. For example, at  715  the method may include decreasing the amount of water for the next injection in response to an increased amount of condensate present (e.g., as the condensed portion increases and the vaporized portion decreases). Adjusting water injection at  715  may differ depending on the injectors present in an embodiment, as well as which injectors are selected for water injection. For example, where multiple injectors are present, with a single water injector coupled to or upstream of each cylinder, water injection amount may be adjusted for each water injector. In another embodiment, where one or more injectors are located upstream of multiple cylinders or a group of cylinders, injection timing of the selected water injector may be synced with intake valve opening timing of that cylinder to adjust water injection to particular cylinders, as described further below with reference to  FIG. 8 . 
     In  FIG. 8 , a method  800  for injecting water at different groups of cylinders of an engine and adjusting water injection parameters based on a distribution of water injected upstream of a group of cylinders is shown. In one embodiment, an engine may include multiple groups of cylinders with one injector coupled to and upstream of each group (such as in engine  200  shown in  FIG. 2  and engine  300  shown in  FIG. 3 ). As introduced above and discussed further below, water injected upstream of a first cylinder group may influence the amount of water or vapor received at the second cylinder group. Additionally, due to differences in architecture of the intake runners of cylinders within a cylinder group, maldistribution of water amongst the cylinders of one group may occur. 
     The method  800  starts at  801  by determining injection parameters for each injector of each cylinder group. Injection parameters may include an amount of water and timing of each injection event. For example, the method at  801  may include determining a first injection amount to inject at a first injector upstream of a first group of cylinders and determining a second injection amount to inject at a second injector upstream of a second group of cylinders. The first and second amounts may be individually determined based on operating conditions of the first and second groups of cylinders (e.g., airflow level or mass air flow to the corresponding group of cylinders, pressure at the corresponding group of cylinders, temperature of the corresponding group of cylinders, a knock level at the corresponding group of cylinders, a fuel injection amount at the corresponding group of cylinders, etc.). In one example, the injector may deliver the amount of water as a single pulse per engine cycle (for all intake valve opening events for all cylinders of the group). In another example, the injector may deliver the amount of water as a series of pulses timed to the intake valve opening of each cylinder within the cylinder group. In this example, the method at  801  may include determining the amount of water to deliver during each pulse for each cylinder within the group (or determining a total water injection amount for all cylinders and dividing by the number of cylinders within the group) and determining the timing of each pulse based on the intake valve opening timing of each cylinder within the group. In some embodiments, the initial amount and timing of the water injection pulses may be determined based on engine mapping of the cylinders. For example, each engine may have a different cylinder and intake runner architecture (e.g., geometry) that results in a difference in water distribution to each cylinder of a group from a same water injector. For example, each cylinder of the group of cylinders may be a different distance away from the water injector coupled to the group of cylinders and/or each intake runner may have a different shape or curvature that affects how the injected water is delivered to the corresponding cylinder. Further, the angle of the injector relative to each cylinder may be different within the group of cylinders. Thus, an initial pulsed injection timing and amount of water delivered for each pulse (which may be different for different cylinders within the group) may be determined based on a known architecture of the engine. This pulse timing may then be adjusted during engine operation based on operating conditions of the cylinders, as discussed further below. 
     The method continues at  802  by determining the vaporized and condensed portions of water injected by each injector for each cylinder or cylinder group. This may include measuring manifold charge temperature before and after an injection event, as previously described for method  700  in  FIG. 7 , and using the change in temperature to estimate the vaporized and condensed portions of injected water. Then, at  804  the method includes adjusting the estimated vaporized and condensed portions for the cylinders downstream of each injector based on the estimates from the other groups. For example, a first injector may inject a first amount of water upstream of a first group of cylinders and a second injector may inject a second amount of water upstream of a different, second group of cylinders. The estimated vaporized and condensed portions of the first amount may be adjusted based on the estimated vaporized and condensed portions of the second amount (and vice versa). For example, as the condensed portion of the first amount increases, the controller may increase the estimate of the condensed portion of the second amount. This may be due to a predicted amount of cross-talk or puddle communication/sharing between the cylinder groups (e.g., due to proximity of the branch points between the cylinder groups and airflow amounts to each cylinder group. Thus, an expected amount of condensed water sharing may occur between the cylinder groups under certain conditions. 
     Next, at  806 , the method includes obtaining knock sensor outputs from each cylinder in a cylinder group (such as from knock sensors  283 ,  383 , or  483  shown in  FIGS. 2-4 ) and determining maldistribution of water to the cylinders within each cylinder group based on the outputs. For example, as introduced above, intake manifold runner architecture may inherently result in uneven distribution of water from an injector to cylinders in a group. In another example, maldistribution of water may occur due to differences in the angle of the water injector upstream of the group of cylinders relative to each runner. 
     Based on the assessed water maldistribution at  806 , at  808  the method includes determining whether a water imbalance is detected for a group of cylinders. As one example, water maldistribution (e.g., water imbalance) among a group of cylinders coupled to a water injector may be determined based on a comparison of knock outputs of knock sensors coupled to each cylinder in the group. For example, the knock output may be used to determine differences in knock intensity in individual cylinders relative to other cylinders in the group. If the change in knock intensity following water injection is different for one or more cylinders in a group compared to the others, this may indicate differences in water distribution. For example, a standard deviation in knock outputs corresponding to different cylinders may be determined and if the standard deviation is greater than a threshold standard deviation value, water imbalance may be indicated. In yet another example, if a knock output corresponding to an individual cylinder differs from an average value of all knock outputs corresponding to all cylinders of the group, by a threshold amount, the individual cylinder may be indicated as receiving more or less water than the other cylinders in the group. In another example, water maldistribution among a group of cylinders coupled to a water injector may be determined based on differences in spark retard in individual cylinders from an expected amount, the expected amount based on engine mapping. If water imbalance is not detected, then the method proceeds to  810  where a subsequent water injection amount for the cylinder groups is adjusted based on the adjusted vaporized and condensed portions (and not the knock sensor outputs) determined at  804  of the method. However, if a water imbalance is detected, the method continues at  812  to adjust the injection amount, pulse rate, and/or timing of water injected by the water injector of the group of cylinders based on the determined maldistribution (e.g., knock sensor outputs) and/or the adjusted vaporized and condensed portions. In one example of the method at  812 , the controller may increase the amount of water injected for a pulse that corresponds to the intake valve opening of a cylinder to compensate for less water detected at that cylinder than others. The lower amount of water detected at the one cylinder relative to the others in the group may be based on the knock sensor output from that cylinder being higher than the other cylinders. In another example of the method at  812 , the controller may decrease water injection to a group of cylinders based on determining that the vaporized portion of water injected is less than a threshold. Next, the method continues at  814  to adjust engine operation for each group of cylinders in response to the detected water imbalance at  808  and/or the adjusted vaporized and condensed portions determined at  804 . The method at  814  may be similar to the method at  714 , as described above. Additionally, in one example, the method at  814  may include, if spark timing is retarded, advancing spark timing differently amongst a group of cylinders based on the detected water imbalance. 
     In  FIG. 9 , graph  900  illustrates adjustments to engine operation based on estimated vaporized and condensed portions of water injected via a water injector. For example, graph  900  illustrates adjustments to an amount of water injected from a water injector of a water injection system (such as water injection system  60  shown in  FIG. 1 ), based on manifold charge temperature sensor output, as well as adjustments to engine operating conditions, such as spark timing following a water injection. Specifically, the operating parameters illustrated in graph  900  show an amount of water injected via a water injector at  902 , changes in an output of a manifold charge temperature sensor at plot  904 , an estimated portion of injected water that evaporated at plot  906 , an estimated portion of injected water that condensed at plot  908 , and changes in spark timing at plot  910 . For each operating parameter, time is depicted along the horizontal axis and values of each respective operating parameter are depicted along the vertical axis. In one example, the manifold charge temperature sensor may be positioned proximate to the water injector, such as within the intake manifold if the water injector is positioned in the intake manifold. 
     Prior to time t 1 , manifold temperature increases (plot  904 ) and water injection may be requested based on engine operation. For example, water injection may be requested due to engine load being greater than a threshold. In another example, water injection may be requested in response to an indication of knock. At time t 1 , in response to an indication of knock the controller may initially retard spark timing from MBT (plot  910 ). 
     In response to the injection request, the manifold charge temperature may be measured and the controller commands an amount of water to be injected (plot  902 ) from the water injection system at time t 1 . As a result, manifold charge temperature decreases from time t 1  to t 2  (plot  904 ). After a duration following injection at t 2 , manifold charge temperature is measured again. The duration between a water injection and measuring manifold charge temperature may be adjusted in response to the amount of water injected or other engine operating conditions. From the measured change in manifold charge temperature and the amount of water injected, a vaporized, first portion of the injected water (plot  906 ) and a condensed, second portion that remains in the manifold (plot  908 ) are estimated at time t 2 . For example, spark timing from MBT (plot  910 ) may advance in response to the vaporized portion of the injected water, and then, in response determining that the vaporized portion of water is greater than the threshold, the controller may maintain spark timing from MBT at time t 2 . 
     At a later time t 3 , water injection is requested and the controller commands an adjusted amount of water to be injected based on a previous injection. For example, in response to a vaporized portion above a threshold from a previous injection at time t 2 , the amount of water injected at time t 3  may be increased from the amount injected at time t 1 . Following the water injection at time t 3 , at time t 4 , the vaporized portion is less than the threshold (plot  906 ). At time t 4 , in response to determining that the vaporized portion of water is less than a non-zero threshold, the controller may adjust engine operating parameters, such as spark timing from MBT (plot  910 ) based on the condensed portion (plot  908 ). For example, spark may be advanced in response to a vaporized portion; however, the amount of spark advance at time t 4  may be less than at time t 2  to compensate for an increased amount of liquid water from the water injection and an increased knock tendency. In this way, the amount of spark advance following a water injection event decreases with a decreased vaporized portion and increased condensed portion. 
     At time t 5 , water injection is again requested. The amount of water injected (plot  902 ) at time t 5  may be determined based on the vaporized and condensed portions from the previous water injection. Between time t 5  and t 6 , the vaporized portion of injected water is above the threshold. In response to the vaporized portion above the threshold at time t 6 , the controller may maintain current operating conditions and advance spark timing. 
     In  FIG. 10 , graph  1000  illustrates adjustments to a water injector injection amount and timing in response to uneven distribution of injected water across a group of cylinders coupled to the injector. The operating parameters illustrated in graph  1000  include water injection at plot  1002 , cylinder valve lift for each of four cylinders at  1004 - 1010 , and knock signals (e.g., knock output of a knock sensor) for each of four cylinders at  1012 - 1015 . (A dashed line corresponds to the knock output of a knock sensor coupled to cylinder  1  (plot  1012 ); a dotted line corresponds to the knock output of a knock sensor coupled to cylinder  2  (plot  1013 ); a dash-dot line corresponds to the knock output of a knock sensor coupled to cylinder  3  (plot  1014 ), and a solid line corresponds to the knock output of a knock sensor coupled to cylinder  4  (plot  1015 )). In the depicted example, water injection pulses are synced with the valve lift for each cylinder. Additionally, in this example, water may be injected upstream of all of cylinders  1 - 4  (such as via a manifold injector positioned in an intake manifold upstream of all of cylinders  1 - 4 ). For each operating parameter, time is depicted along the horizontal axis and values of each respective operating parameter are depicted along the vertical axis. 
     Prior to time t 1 , water is injected upstream of each cylinder (e.g., in the intake manifold) in response to a water injection request and knock signal intensity is monitored. As explained above. The water may be injected by pulsing the injector at times synced to the intake valve opening of each cylinder. In this way, multiple pulses of water may be delivered by a single injector positioned upstream of cylinders  1 - 4 . Knock signal intensity increases prior to time t 1  due to engine operating conditions. In response to feedback about engine operation from a plurality of sensors, including knock sensors, the controller may increase the amount of water injected for each pulse at time t 1 . Between time t 1  and t 2 , knock intensity signal may decrease due to increased water injection. Thus, the controller may continue current engine operation and water injection amount and pulsing. At a later time t 2 , knock intensity signal increases for cylinder  3 . This may occur as a result of uneven water distribution from the water injector to cylinder  3  relative to the other cylinders in the group (e.g., cylinders  1 ,  2 , and  4 ). In response to detecting that cylinder  3  has an increased knock signal and may have received less water (relative to the other cylinders in the group), the controller may increase the water injected to cylinder  3  at time t 3 . By increasing the amount of water injected for a pulse that corresponds to valve lift for cylinder three, more water can be delivered to a particular cylinder even though an injector may be upstream of a group of cylinders. After time t 3 , the controller may continue water injection pulses responsive to engine operating conditions and previous injections. 
     In this way, water injection at an intake manifold may be adjusted in response to uneven water distribution amongst cylinders coupled to an intake manifold. As one example, a first water injection amount upstream of a first group of cylinders may be based on operating conditions of the first group and a second amount of water upstream of a second group of cylinders may be based on operating conditions of the second group. In another example, an amount and/or timing of water injected at a first group of cylinder may be adjusted based on determining uneven distribution of water. For example, output from knock sensors may be used to determine if water distribution among cylinders in the group was uneven by comparing a change in knock intensity between cylinders in the group. If uneven water distribution is detected, the amount of water delivered to a cylinder in the group may be adjusted to compensate. During manifold water injection, this may include synchronizing water injection pulsing of the adjusted amount of water based on the detected maldistribution to an intake valve opening timing of each cylinder of the group of cylinders. The technical effect of comparing a change in knock signal intensity before and after a water injection event amongst cylinders in a cylinder group is to identify uneven water distribution. The technical effect of then adjusting water injection in response to uneven water distribution is to compensate for variation in water injection amounts between cylinders. As a result, the desired benefits of water injection may be provided, such as decreased knock tendency and increased engine efficiency. 
     As one embodiment, a method includes injecting a first amount of water upstream of a first group of cylinders and a different, second amount of water upstream of a second group of cylinders, the first amount determined based on operating conditions of the first group and the second amount determined based on operating conditions of the second group. In a first example of the method, the method further comprises determining a first portion of the first amount of water that vaporized based on a change in temperature upstream of the first group of cylinders following the injecting the first amount of water and determining a second portion of the first amount of water that remained liquid based on the injected first amount of water and the determined first portion of the first amount of water. A second example of the method optionally includes the first example and further comprises determining a first portion of the second amount of water that vaporized based on a change in temperature upstream of the second group of cylinders following the injecting the second amount of water and determining a second portion of the second amount of water that remained liquid based on the injected second amount of water and the determined first portion of the second amount of water. A third example of the method optionally includes one or more of the first and second examples, and further comprises adjusting the determined first portion and second portion of the first amount of water based on the determined first portion and second portion of the second amount of water and adjusting the determined first portion and second portion of the second amount of water based on the determined first portion and second portion of the first amount of water. A fourth example of the method optionally includes one or more of the first through third examples, and further comprises adjusting the first amount of water based on the adjusted first portion and second portion of the first amount of water and adjusting the second amount of water based on the adjusted first portion and second portion of the second amount and during a subsequent water injection event, injecting the adjusted first amount of water upstream of the first group of cylinders and injecting the adjusted second amount of water upstream of the second group of cylinders. A fifth example of the method optionally includes the first through fourth examples, and further includes wherein injecting the first amount of water upstream of the first group of cylinders includes pulsing a first water injector disposed upstream of the first group of cylinders to deliver the first amount of water, where the pulsing is synchronized to an intake valve opening timing of each cylinder of the first group of cylinders. A sixth example of the method optionally includes the first through fifth examples, and further includes wherein an initial amount of water delivered by and a timing of each pulse is based on an engine mapping of cylinders within the first cylinder group and further comprising adjusting the initial amount of water delivered by and timing of each pulse based on outputs of knock sensors coupled to each cylinder of the first cylinder group following the injecting. A seventh example of the method optionally includes the first through sixth examples, and further includes wherein the operating conditions of the first group includes one or more of mass air flow to the first group of cylinders, a pressure at the first group of cylinders, a fuel injection amount injected into the first group of cylinders, a temperature of the first group of cylinders, and a knock level indicated by a knock sensor coupled to each cylinder of the first group of cylinders. An eighth example of the method optionally includes the first through seventh examples, and further includes wherein the operating conditions of the second group includes one or more of mass air flow to the second group of cylinders, a pressure at the second group of cylinders, a fuel injection amount injected into the second group of cylinders, a temperature of the second group of cylinders, and a knock level indicated by a knock sensor coupled to each cylinder of the second group of cylinders. 
     As another embodiment, a method comprises injecting a first amount of water upstream of a first group of cylinders and injecting a second amount of water upstream of a second group of cylinders, where the first amount is based on a first operating condition of the first group of cylinders and the second amount is based on a first operating condition of the second group of cylinders; adjusting the first amount based on a different, second operating condition of the second group of cylinders; and adjusting the second amount based on a different, second operating condition of the first group of cylinders. In a first example of the method, the method further includes wherein the first operating condition of the first group of cylinders includes one or more of mass air flow to the first group of cylinders, a pressure at the first group of cylinders, a fuel injection amount injected into the first group of cylinders, a temperature of the first group of cylinders, and a knock level indicated by a knock sensor coupled to each cylinder of the first group of cylinders and wherein the first operating condition of the second group of cylinders includes one or more of mass air flow to the second group of cylinders, a pressure at the second group of cylinders, a fuel injection amount injected into the second group of cylinders, a temperature of the second group of cylinders, and a knock level indicated by a knock sensor coupled to each cylinder of the second group of cylinders. A second example of the method optionally includes the first example and further includes wherein the second operating condition of the first group of cylinders includes a determined first portion of the first amount of water that vaporized and a determined second portion of the first amount of water that remained liquid and wherein the second operating condition of the second group of cylinders includes a determined first portion of the second amount of water that vaporized and a determined second portion of the second amount of water that remained liquid. A third example of the method optionally includes one or more of the first and second examples, and further comprises adjusting the first amount based on both the second operating condition of the first group and the second group of cylinders and adjusting the second amount based on both the second operating condition of the first group and the second group of cylinders. A fourth example of the method optionally includes the first through third examples, and further comprises adjusting an operating parameter of the first group of cylinders based on the determined first portion and second portion of the first amount of water and the determined first portion and second portion of the second amount of water, where the operating parameter is one or more of spark timing, a fuel injection amount, and an airflow level to the engine. A fifth example of the method optionally includes the first through fourth examples, and further includes wherein adjusting the operating parameter further includes individually adjusting the operating parameter for each cylinder of the first group of cylinders based on a difference in output of knock sensors coupled to each cylinder of the first group of cylinders. A sixth example of the method optionally includes the first through fifth examples, and further comprises adjusting a pulse width and timing of injection of the first amount based on outputs of knock sensors coupled to each cylinder of the first group of cylinders and adjusting a pulse width and timing of injection of the second amount based on outputs of knock sensors coupled to each cylinder of the second group of cylinders. A seventh example of the method optionally includes the first through sixth examples, and further includes wherein the first amount of water is different than the second amount of water. 
     As yet another embodiment, a system includes a first water injector coupled to a common intake manifold of a first group of cylinders; a second water injector coupled to a common intake manifold of a second group of cylinders; and a controller including non-transitory memory with computer readable instructions for: determining a first amount of water to inject via the first water injector based on a first operating condition of the first group of cylinders and a second amount of water to inject via the second water injector based on a second operating condition of the second group of cylinders. In a first example of the system, the system further comprises a first plurality of knock sensors coupled to the first group of cylinders, where each cylinder of the first group has one knock sensor of the first plurality of knock sensors coupled thereto and wherein the computer readable instructions further include instructions for adjusting one or more of an injection amount and pulse timing of the first water injector in response to a difference between outputs of the first plurality of knock sensors. A second example of the system optionally includes the first example and further includes wherein the computer readable instructions further include instructions for determining the first amount of water based on engine mapping of the first group of cylinders and the second amount of water based on engine mapping of the second group of cylinders, where the engine mapping of the first group and second group includes a known geometry of intake runners of the first group and second group relative to the first water injector and second water injector, respectively. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.