Fuel and water injection system and method for controlling the same

A fuel and water injection system includes: an injector having a needle which is movable upwardly and downwardly by a solenoid coil, a nozzle orifice which is opened and closed by upward and downward movements of the needle, and a pressure chamber communicating with the nozzle orifice; a fuel pump supplying fuel to the pressure chamber; a water pump supplying water to the pressure chamber; a solenoid shut-off valve disposed on a water supply pipe connecting the water pump and the injector; an engine control unit (ECU) controlling the fuel pump and the injector; and a water supply controller controlling the water pump and the solenoid shut-off valve.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0131651, filed on Oct. 31, 2018, the entire contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a fuel and water injection system and a method for controlling the same, and more particularly, to a fuel and water injection system and a method for controlling the same.

BACKGROUND

Various techniques have been researched and developed for reducing combustion heat during combustion in an internal combustion engine of a vehicle to reduce emissions such as nitrogen oxides (NOx), and reducing a mixture ratio of air and fuel to improve fuel efficiency.

As representative techniques for reducing combustion heat and NOxemissions and improving fuel efficiency, an exhaust gas recirculation (EGR) system, a water injection system, emulsion fuel, CO2capture and injection, and the like have been researched and developed.

The EGR system may include an EGR pipe for circulating EGR gas from an exhaust system to an intake system, an EGR cooler for cooling temperature of the EGR gas, and an EGR valve for regulating the flow of the EGR gas, so that it may occupy a relatively large installation space in a narrow engine room and the assembly cost may be increased.

In addition, the EGR system may only operate in a portion of an operating range of the vehicle and operate depending on RPM of the engine, so that the range of use of the EGR gas may be very limited. For example, the operation of the EGR system may not be smoothly performed in a low RPM region and a high RPM region of the engine.

The water injection system may be configured to spray water into the incoming air or fuel-air mixture, or directly into a combustion chamber of the engine. Water injection may lower the temperature of the combustion chamber, reduce emissions of NOx, hydrocarbons, and the like, and reduce the mixture ratio of air and fuel to thereby improve fuel efficiency.

Recently, a fuel and water injection system in which fuel and water are supplied to a single injector and the injector injects the fuel and the water together into the combustion chamber of the engine has been researched and developed.

In a conventional fuel and water injection system, however, a mixture of water and fuel remaining in the injector may be collected (circulated) in a fuel tank through a return passage connected to the injector, so that the water-fuel mixture may gradually increase in the fuel tank as the operating time elapses. We have discovered that even when the injection of fuel alone is desired in a full load operating condition, or the like, the water together with the fuel may be injected, which lowers the combustion efficiency.

The above information described in this background section is provided to assist in understanding the background of the inventive concept, and may include any technical concept which is not considered as the prior art that is already known to those skilled in the art.

SUMMARY

An aspect of the present disclosure provides a fuel and water injection system and a method for controlling the same, capable of reducing NOx emissions and improving combustion performance by selectively injecting fuel alone or injecting fuel and water together according to operating conditions of an engine.

According to an aspect of the present disclosure, a fuel and water injection system may include: an injector having a needle which is movable upwardly and downwardly by a solenoid coil, a nozzle orifice which is opened and closed by upward and downward movements of the needle, and a pressure chamber communicating with the nozzle orifice; a fuel pump supplying a fuel to the pressure chamber of the injector; a water pump supplying water to the pressure chamber of the injector; a solenoid shut-off valve disposed on a water supply pipe connecting the water pump and the pressure chamber of the injector; an engine control unit (ECU) controlling the fuel pump and the injector; and a water supply controller configured to control the water pump and the solenoid shut-off valve, wherein the water supply controller is configured to selectively open and close the solenoid shut-off valve based on operating conditions of an engine, so that the fuel and water injection system may selectively operate in a fuel injection mode in which the injector injects only the fuel, or in a fuel and water injection mode in which the injector injects the fuel and the water together.

The water supply controller may be configured to supply the water to the pressure chamber when a pressure in the pressure chamber is lower than a predetermined first pressure, the predetermined first pressure is equal to a injection pressure.

The ECU may be configured to drive the solenoid coil according to a first predetermined duty cycle, and the water supply controller may be configured to drive the solenoid shut-off valve according to a second predetermined duty cycle.

The water supply controller may turn on the solenoid shut-off valve during a turn-off period of the solenoid coil.

A pulse width of the first predetermined duty cycle may be greater than a pulse width of the second predetermined duty cycle.

One injection cycle of the injector may include a first injection period in which a fuel injection rate increases, a second injection period in which the fuel injection rate is maintained at a predetermined peak fuel injection rate, and a third injection period in which the fuel injection rate decreases. When the system operates in the fuel and water injection mode, the water supply controller may open the solenoid shut-off valve in the third injection period of one injection cycle so that the water may be supplied to the pressure chamber in the third injection period of one injection cycle, and the ECU may drive the solenoid coil of the injector according to a first predetermined duty cycle so that the water supplied to the pressure chamber may be injected together with the fuel supplied to the pressure chamber through the nozzle orifice of the injector in the first injection period and the second injection period of a next injection cycle.

The system may further include a check valve inhibiting or preventing the water from flowing back from the pressure chamber to the water pump, wherein the check valve may be disposed between the pressure chamber and the water pump.

The pressure chamber may have a fuel inlet and a water inlet, and the check valve may be mounted on a portion facing the water inlet.

According to another aspect of the present disclosure, a method for controlling a fuel and water injection system, the system including an injector having a needle which is movable upwardly and downwardly by a solenoid coil, a nozzle orifice which is opened and closed by upward and downward movements of the needle, and a pressure chamber communicating with the nozzle orifice; a fuel pump supplying a fuel to the pressure chamber of the injector; a water pump supplying water to the pressure chamber of the injector; a solenoid shut-off valve disposed on a water supply pipe connecting the water pump and the injector; an ECU controlling the fuel pump and the injector; and a water supply controller controlling the water pump and the solenoid shut-off valve, may include: driving the solenoid coil of the injector in accordance with a first duty cycle, and turning on the water pump and driving the solenoid shut-off valve in accordance with a second duty cycle when an engine speed is lower than or equal to a first predetermined speed or an engine load is lower than or equal to a first predetermined load, thereby allowing the system to operate in fuel and water injection mode in which the injector injects the fuel and the water together; and driving the solenoid coil of the injector in accordance with the first duty cycle, and turning off the water pump and closing the solenoid shut-off valve when the engine speed exceeds the first predetermined speed or the engine load exceeds the first predetermined load, thereby allowing the system to operate in fuel injection mode in which the injector injects only the fuel.

The method may further include: driving the solenoid coil of the injector in accordance with the first duty cycle, and turning on the water pump and driving the solenoid shut-off valve in accordance with the second duty cycle when a coolant temperature is greater than or equal to a predetermined temperature, thereby allowing the system to operate in the fuel and water injection mode.

The method may further include: driving the solenoid coil of the injector in accordance with the first duty cycle, and turning off the water pump and closing the solenoid shut-off valve when a coolant temperature is lower than a predetermined temperature, thereby allowing the system to operate in the fuel injection mode.

The fuel and the water may be purged from the injector by turning off the water pump and closing the solenoid shut-off valve, and driving the solenoid coil of the injector in accordance with a predetermined duty cycle when an engine is stopped.

DETAILED DESCRIPTION

In addition, a detailed description of well-known techniques associated with the present disclosure will be ruled out in order not to unnecessarily obscure the gist of the present disclosure.

Referring toFIGS. 1 to 3, a fuel and water injection system1, according to an exemplary form of the present disclosure, may include an injector10mounted on an engine5, a fuel pump21supplying a fuel to the injector10, and a water pump31supplying water to the injector10.

An intake pipe6and an exhaust pipe7may be connected to the engine5. A compressor8aof a turbocharger and an intercooler8cmay be provided on the intake pipe6, and a turbine8bof the turbocharger may be provided on the exhaust pipe7. An EGR pipe9amay be connected between the exhaust pipe7and the intake pipe6, and an EGR cooler9band an EGR valve9cmay be provided on the EGR pipe9a. According to an exemplary form of the present disclosure, the EGR pipe9a, the EGR cooler9b, and the EGR valve9cmay be eliminated.

The injector10may include an injector body11, a solenoid coil12which is mounted on the injector body11, an armature13which is movable by electromagnetic force of the solenoid coil12, a control chamber14which is formed below the armature13, and a needle15which is movable between an opened position and a closed position by a fuel pressure change in the control chamber14.

The injector body11may have a nozzle orifice11a, and the nozzle orifice11amay be formed at the bottom end of the injector body11. The nozzle orifice11amay be opened and closed by upward and downward movements of the needle15. A control rod16may be connected to the top end of the needle15. As the armature13moves upwardly and downwardly, the fuel pressure in the control chamber14may change, and the control rod16may move upwardly and downwardly according to the fuel pressure change in the control chamber14. The control rod16and the needle15may move together upwardly and downwardly, and the needle15may be movable between the closed position in which the nozzle orifice11ais closed and the opened position in which the nozzle orifice11ais opened.

The injector body11may have a fuel supply port17, a fuel passage41communicating with the fuel supply port17, a water supply port18, a water passage51communicating with the water supply port18, and a pressure chamber61communicating with the fuel passage41and the water passage51.

The fuel supply port17may communicate with a common rail23, so that the fuel supply port17may receive high-pressure fuel which is supplied from the common rail23. The fuel passage41may allow the fuel supply port17and the pressure chamber61to communicate with each other, so that the high-pressure fuel may be supplied from the fuel supply port17to the pressure chamber61through the fuel passage41. A branch passage41abranching from the fuel passage41may allow the fuel supply port17and the control chamber14to communicate with each other, so that the high-pressure fuel may be supplied from the fuel supply port17to the control chamber14through the branch passage41a.

The water supply port18may communicate with the water pump31, so that the water supply port18may receive the water which is supplied by the water pump31. The water passage51may allow the water supply port18and the pressure chamber61to communicate with each other, so that the water may be supplied from the water supply port18to the pressure chamber61through the water passage51.

The pressure chamber61may be formed in a lower portion of the injector body11, and the pressure chamber61may communicate with the nozzle orifice11a. The pressure chamber61may have a fuel inlet61ato which the fuel passage41is connected, and a water inlet61bto which the water passage51is connected. The fuel may flow into the pressure chamber61through the fuel inlet61a, and the water may flow into the pressure chamber61through the water inlet61b.

According to an exemplary form of the present disclosure, the injector10may further include a check valve63inhibiting or preventing the water from flowing back from the pressure chamber61to the water pump31or a return passage65of the injector10. The check valve63may be mounted on a portion facing the water inlet61bof the pressure chamber61, so that it may inhibit or prevent the water from flowing back from the pressure chamber61to the water passage51. For example, a space for mounting the check valve63may be formed at an end portion of the water passage51facing the water inlet61bof the pressure chamber61. By mounting the check valve63on the portion facing the water inlet61bof the pressure chamber61, the backflow of the water from the pressure chamber61to the water pump31or the return passage65of the injector10may be effectively inhibited or prevented.

The needle15may move in the pressure chamber61upwardly and downwardly, so that the needle15may move to the opened position to open the nozzle orifice11aand move to the closed position to close the nozzle orifice11a. A spring15amay be disposed around the needle15, and the spring15amay urge the needle15downwardly.

The solenoid coil12may be mounted at the top end of the injector body11by a coil bobbin12a. A spring13bmay be disposed in a cavity of the coil bobbin12ato urge the armature13downwardly. The armature13may be disposed adjacent to the lower portion of the solenoid coil12, and the bottom end of the spring13bmay contact the top surface of the armature13so that the armature13may be moved downwardly by a force of the spring13b.

A valve block14cmay be mounted inside the injector body11, and the valve block14cmay be downwardly spaced apart from the solenoid coil12.

The control chamber14may be defined by the valve block14cand the control rod16, and the high-pressure fuel may flow into the control chamber14through the branch passage41aso that the control chamber14may be filled with the high-pressure fuel. A drain chamber14bmay be disposed between the control chamber14and the solenoid coil12, and the drain chamber14bmay be defined by the valve block14cand a cavity of the injector body11.

The valve block14cmay have a passage14dallowing the control chamber14and the drain chamber14bto communicate with each other, and a ball valve13amay be formed at the bottom end of the armature13, so that the movement of the armature13may allow the ball valve13ato open and close the passage14dof the valve block14c.

As the ball valve13aof the armature13opens and closes the passage14dof the valve block14c, the fuel pressure in the control chamber14may change. As the fuel pressure in the control chamber14changes, the control rod16and the needle15may move together upwardly and downwardly.

When the upward movement of the armature13allows the ball valve13aof the armature13to open the passage14dof the valve block14c, the high-pressure fuel may be discharged from the control chamber14to the drain chamber14bthrough the passage14d, so that the fuel pressure in the control chamber14may be reduced, and the control rod16and the needle15may move upwardly. When the downward movement of the armature13allows the ball valve13aof the armature13to close the passage14dof the valve block14c, the control chamber14may be filled with the high-pressure fuel, so that the fuel pressure in the control chamber14may be increased, and the control rod16and the needle15may move downwardly. As the fuel pressure in the control chamber14changes, an imbalance in the force applied to the control rod16and the needle15may occur, so that the control rod16and the needle15may move upwardly and downwardly and the needle15may open and close the nozzle orifice11a.

The return passage65may be formed at the top end of the injector body11. The return passage65may communicate with the drain chamber14b, and the return passage65may be connected to the common rail23and the fuel tank22through a return pipe66. As the armature13moves upwardly, the high-pressure fuel in the drain chamber14bmay return to the fuel tank22through the return passage65and the return pipe66.

According to an exemplary form of the present disclosure, a middle chamber19may be elongated in the middle of the injector body11. The middle chamber19may be disposed between the needle15and the control chamber14, and the control rod16may be movable in the middle chamber19upwardly and downwardly. The middle chamber19may communicate with the drain chamber14bthrough a connecting passage19a, so that the high-pressure fuel in the drain chamber14bmay be supplied to the middle chamber19through the connecting passage19a. As the high-pressure fuel received in the middle chamber19is positioned above the needle15, the high-pressure fuel in the middle chamber19may inhibit or prevent the water and/or the fuel from rising through a fine gap between the needle15and a bore. Thus, the backflow of the water and/or the fuel to the return passage65of the injector body11may be reliably prevented.

The fuel pump21may pressurize the fuel sucked from the fuel tank22to high pressure and supply the high-pressure fuel to the common rail23. The common rail23may accumulate the fuel at high pressure to maintain a relatively high target rail pressure so that the common rail23may supply the high-pressure fuel to the injector10through a fuel supply pipe25.

An electronic control unit or engine control unit (ECU)70may be configured to control the engine5, the injector10, the fuel pump21, and the common rail23. The ECU70may include inputs and outputs which are connected to a variety of sensors, the engine5, the injector10, and the common rail23, and a memory.

The ECU70may include any suitable microprocessor, microcontroller, personal computer, or the like, which has a central processing unit capable of executing a control program and data stored in the memory.

The water pump31may suck water from the water tank32and supply the water to the injector10. A water supply pipe35may connect the water pump31and the water supply port18of the injector10, and a solenoid shut-off valve33may be provided on the water supply pipe35.

A water supply controller80may control the water pump31and the solenoid shut-off valve33to adjust a water supply flow rate and a water supply time. The water supply controller80may cooperate with the ECU70.

The water supply controller80may control selective opening and closing of the solenoid shut-off valve33according to operating conditions of an engine, so that fuel injection mode and fuel and water injection mode may be selectively operated. In the fuel injection mode, the injector10may inject only the fuel at a predetermined injection pressure, and in the fuel and water injection mode, the injector10may inject the fuel and the water together at the predetermined injection pressure.

According to an exemplary form of the present disclosure, in a full load operating condition or an operating condition similar thereto in which the injection of water is not required, the water supply controller80may control the solenoid shut-off valve33to be closed so that the injector10may inject only the fuel according to an injection signal of the ECU70(the fuel injection mode), and in a partial load operating condition in which the injection of water is desired, the water supply controller80may control the solenoid shut-off valve33to be opened according to a predetermined cycle so that the injector10may inject the fuel and the water together according to an injection signal of the ECU70(the fuel and water injection mode). The ECU70may control the solenoid coil12to drive in accordance with a first duty cycle, irrespective of the fuel injection mode and the fuel and water injection mode.

The water supply controller80may include inputs and outputs which are connected to a variety of sensors, the water pump31, and the solenoid shut-off valve33, and a memory. The water supply controller80may include any suitable microprocessor, microcontroller, personal computer, or the like, which has a central processing unit capable of executing a control program and data stored in the memory.

As illustrated inFIG. 1, the water supply controller80may be a stand-alone device. Alternatively, the water supply controller80may be embedded in the ECU70.

FIG. 4illustrates a graph of relations of fuel injection voltage, fuel injection rate, pressure in pressure chamber, water supply voltage, and water supply flow rate, when the fuel and water injection system1operates in fuel and water injection mode.

Referring toFIG. 4, the ECU70may control the solenoid coil12of the injector10to be driven in accordance with a first predetermined duty cycle (see curved line A inFIG. 4). Thus, the solenoid coil12may be turned on during a first pulse width PW1of the first duty cycle. When a predetermined voltage for fuel injection is applied to the solenoid coil12, the needle15of the injector10may move upwardly to open the nozzle orifice11a, so that the high-pressure fuel supplied to the pressure chamber61of the injector10may be injected through the nozzle orifice11a. When the solenoid coil12of the injector10is turned on for a predetermined period of time (i.e., t1to t4) as illustrated by curved line A inFIG. 4, the high-pressure fuel supplied to the pressure chamber61may be injected from the pressure chamber61of the injector10through the nozzle orifice11aat a predetermined fuel injection rate for a predetermined period of time (i.e., t1to t5) as illustrated by curved line B inFIG. 4.

One injection cycle includes a first injection period91, a second injection period92, and a third injection period93. As illustrated by curved line B inFIG. 4, the first injection period91refers to a period in which the fuel injection rate gradually increases from the start of injection (SOI) to a peak fuel injection rate, the second injection period92refers to a period in which the fuel injection rate is maintained at a predetermined peak fuel injection rate, and the third injection period93refers to a period in which the fuel injection rate gradually decreases from the predetermined peak fuel injection rate to the end of injection (EOI).FIG. 4illustrates the injection cycles as a continuous process, but there may be an injection interval between the injection cycles, and the injection interval may be referred to as pre-injection and post-injection.

As illustrated by curved line C inFIG. 4, a pressure in the pressure chamber61may gradually increase to the predetermined first pressure in the first injection period91(i.e., t1to t2), gradually decrease to a predetermined second pressure that is lower than the predetermined first pressure and be kept constant at the predetermined second pressure in the second injection period92(i.e., t2to t4), and be kept constant at the predetermined second pressure in the third injection period93(i.e., t4to t5). The predetermined first pressure may correspond to the predetermined injection pressure. For example, the predetermined first pressure may be equal to or similar to the predetermined injection pressure.

Referring toFIG. 4, the water supply controller80may control the solenoid shut-off valve33to be driven in accordance with a second predetermined duty cycle (see curved line D inFIG. 4). Thus, the solenoid shut-off valve33may be turned on during a second pulse width PW2of the second duty cycle. When a predetermined voltage for water supply is applied to the solenoid shut-off valve33for a predetermined period of time (i.e., t0to t1and t4to t5), the solenoid shut-off valve33may be opened so that the water stored in the water tank32may be supplied to the pressure chamber61. In detail, when the solenoid shut-off valve33is turned on for a predetermined period of time (i.e., t0to t1and t4to t5) as illustrated by curved line D inFIG. 4, the water may be supplied to the pressure chamber61of the injector10at a predetermined water supply flow rate for a predetermined period of time (i.e., t01to t11and t41to t51) as illustrated by curved line E inFIG. 4.

As illustrated inFIG. 4, an interval T between a fuel injection start timing t1and a water supply start timing t4may be substantially the same as a turn-off period (t1to t4) of the solenoid shut-off valve33. For example, the interval T between the fuel injection start timing t1and the water supply start timing t4may be the same as or slightly different from the turn-off period of the solenoid shut-off valve33.

According to an exemplary form of the present disclosure, when the pressure in the pressure chamber61of the injector10is lower than the predetermined first pressure (i.e., t0to t1and t4to t5), in other word, the pressure in the pressure chamber61is the predetermined second pressure, the water supply controller80may be configured to supply the water to the pressure chamber61of the injector10. Thus, the water pump31may be allowed to supply the water to the pressure chamber61using a relatively lower pressure than that of the fuel pump21, so a relatively inexpensive water pump may be applied.

Referring to curved lines A, D, and E inFIG. 4, the water supply controller80may turn on the solenoid shut-off valve33in the third injection period93of one injection cycle, so that the water pump31may be operated to supply a predetermined amount of water to the pressure chamber61for a predetermined period of time (i.e., t01to t11and t41to t51). In other words, the water supply controller80may turn on the solenoid shut-off valve33(that is, the solenoid shut-off valve33is opened) during a turn-off period (i.e., t0to t1and t4to t5) of the solenoid coil12, so that the water stored in the water tank32may be supplied to the pressure chamber61by the operation of the water pump31for a predetermined period of time.

As illustrated inFIG. 4, the turn-on period (i.e., t1to t4) of the solenoid coil12of the injector10and the turn-on period (i.e., t4to t5) of the solenoid shut-off valve33may be continued to thereby determine one injection cycle.

The water may be supplied to the pressure chamber61in the third injection period93(i.e., t4to t5) of one injection cycle, so that the predetermined amount of water may be received in the pressure chamber61. The water received in the pressure chamber61may be injected together with the fuel supplied to the pressure chamber61according to the injection signal of the ECU70through the nozzle orifice11aof the injector10in the first injection period91and the second injection period92of a next injection cycle.

As described above, after the water is received in the pressure chamber61in the third injection period93of one injection cycle, the fuel supplied to the pressure chamber61may be injected together with the water through the nozzle orifice11aof the injector10in the first injection period91and the second injection period92of the next injection cycle. In other words, the supply of water and the injection of fuel and water may be performed in the third injection period93of one injection cycle, and the first injection period91and the second injection period92of the next injection cycle in a time series manner, so that the injection of fuel and water may be efficiently performed. For example, the water may be supplied to the pressure chamber61in the third injection period93of one injection cycle, and then the fuel may be accumulated or stacked on the water received in the pressure chamber61in the first injection period91and the second injection period92of the next injection cycle. As a result, a liquid column having alternate layers or a multi-layered liquid column of water and fuel is formed in the pressure chamber61, so that the injection of water and fuel may be efficiently performed.

The backflow of the water received in the pressure chamber61in the EOI period may be inhibited or prevented by the check valve63. In addition, the water received in the pressure chamber61may be injected together with the high-pressure fuel from the pressure chamber61through the nozzle orifice11aby the pressure of the high-pressure fuel supplied to the pressure chamber61in the SOI and MI periods, so that the water remaining in the pressure chamber61may be inhibited or prevented from being leaked to the return passage65through the fine gap between the needle15and the bore of the injector body11.

The first pulse width PW1of the first duty cycle may be greater than the second pulse width PW2of the second duty cycle. For example, a ratio of the first pulse width PW1of the first duty cycle and the second pulse width PW2of the second duty cycle may range from 7:3 to 9:1. In one form, the ratio of the first pulse width PW1of the first duty cycle and the second pulse width PW2of the second duty cycle may be 7:3.

FIG. 5illustrates logic for determining a water supply flow rate according to a fuel injection rate and the start of injection (SOI) of one injection cycle.

As illustrated inFIG. 5, when a fuel injection rate Q1and SOI are input from the ECU70to the memory of the water supply controller80, the water supply controller80may determine a water supply flow rate Q2and an interval T between the fuel injection start timing t1and the water supply start timing t4based on a water supply map85. The water supply map85may be stored in the memory of the water supply controller80. The water supply map85may include the water supply flow rate Q2mapped according to SOI of one injection cycle, and the interval T between the fuel injection start timing t1and the water supply start timing t4, and the water supply map85may be provided in any one of a lookup table and a graph.

FIG. 6illustrates a flowchart of a method for controlling a fuel and water injection system according to an exemplary form of the present disclosure.

The ECU70may receive various information, such as engine speed R, engine load L, and coolant temperature CT, from various sensors while the engine is operating (S1).

According to an exemplary form of the present disclosure, in a full load operating condition or an operating condition similar thereto in which the injection of water is not required, the water supply controller80may control the solenoid shut-off valve33to be closed so that the injector10may inject only the fuel according to an injection signal of the ECU70(fuel injection mode), and in a partial load operating condition in which the injection of water is desired, the water supply controller80may control the solenoid shut-off valve33to be opened according to a predetermined cycle so that the injector10may inject the fuel and the water together according to an injection signal of the ECU70(fuel and water injection mode).

The ECU70may determine whether the engine speed R is lower than or equal to a first predetermined speed R1or the engine load L is lower than or equal to a first predetermined load L1(S2). The first predetermined speed may be an upper limit for engine speed at which the injection of water is desired. For example, the first predetermined speed may be 1500 RPM. The first predetermined load may be an upper limit for engine load at which the injection of water is desired. For example, the first predetermined load may be 10 bar.

When the engine speed R is lower than or equal to the first predetermined speed R1or the engine load L is lower than or equal to the first predetermined load L1(R≤R1or L≤L1), the water supply controller80may turn on the water pump31and operate the solenoid shut-off valve33according to the second duty cycle (see curved line D inFIG. 4), and the ECU70may operate the solenoid coil12of the injector10according to the first duty cycle (see curved line A inFIG. 4). Thus, the fuel and water injection system may operate in the fuel and water injection mode (seeFIG. 7) in which the injector10injects the fuel and the water together (S3).

When the engine speed R exceeds the first predetermined speed R1or the engine load L exceeds the first predetermined load L1(R>R1and L>L1), the water supply controller80may turn off the water pump31and close the solenoid shut-off valve33so that the water stored in the water tank32may not be supplied to the injector10, and the ECU70may drive the solenoid coil12of the injector10in accordance with the first duty cycle (see curved line A inFIG. 4). Thus, the fuel and water injection system may operate in the fuel injection mode (seeFIG. 7) in which the injector10injects only the fuel according to the injection signal of the ECU70(S4).

The ECU70may determine whether the coolant temperature CT is is greater than or equal to than a predetermined temperature CT1(S5). The predetermined temperature CT1may be a lower limit for coolant temperature in order to determine an operating condition in which the injection of water is not required, such as cold start. For example, the predetermined temperature CT1may be 55° C.

When the coolant temperature CT is greater than or equal to than the predetermined temperature CT1(CT≥CT1), the water supply controller80may turn on the water pump31and drive the solenoid shut-off valve33in accordance with the second duty cycle, and the ECU70may drive the solenoid coil12of the injector10in accordance with the first duty cycle. Thus, the fuel and water injection system may operate in the fuel and water injection mode (seeFIG. 7) in which the injector10injects the fuel and the water together (S6).

When the coolant temperature CT is lower than the predetermined temperature CT1(CT<CT1), the water supply controller80may turn off the water pump31and close the solenoid shut-off valve33to thereby block the supply of water stored in the water tank32to the injector10, and the ECU70may drive the solenoid coil12of the injector10in accordance with the first duty cycle (see curved line A inFIG. 4). Thus, the fuel and water injection system may operate in the fuel injection mode (seeFIG. 7) in which the injector10injects only the fuel according to the injection signal of the ECU70(S7).

Then, the ECU70may determine whether the engine is stopped (S7).

When the engine is stopped, the water supply controller80may turn off the water pump31and close the solenoid shut-off valve33to thereby block the supply of water stored in the water tank32to the injector10, and the ECU70may drive the solenoid coil12of the injector10in accordance with the predetermined duty cycle to thereby allow the purging of fuel and water from the injector10(S8). Thus, the fuel and the water remaining in the injector10may be discharged.

As set forth above, the fuel and water injection system and the method for controlling the same, according to exemplary forms of the present disclosure, can reduce NOx emissions and improve combustion performance by selectively injecting fuel alone or injecting fuel and water together according to operating conditions.

In addition, according to exemplary forms of the present disclosure, by mounting the check valve on the portion facing the water inlet of the pressure chamber, the backflow of water from the pressure chamber to the water pump or the return passage of the injector can be effectively reduced or prevented.

Hereinabove, although the present disclosure has been described with reference to exemplary forms and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure.