Diesel engine and control method thereof

Abstract

To provide a diesel engine capable of injecting an appropriate amount of water even during a transient operation in which the state of the engine changes.SOLUTION: A control device 50 estimates a spray temperature Tmax from a mass fraction Y of intake oxygen in accordance with predetermined relation between state amount indicating the amount of oxygen included in intake gas to be supplied into a combustion chamber (mass fraction of intake oxygen) and a spray temperature of fuel injected into the combustion chamber. From a temperature difference ΔT between the estimated spray temperature Tmax and a target spray temperature Tmax0, the control device 50 determines water injection amount Qw of each water injection valve 63A-63D.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a diesel engine and a control method thereof. [Background technology]

[0002] In diesel engines, the amount of NOx in the exhaust gas increases as the combustion temperature increases, so it is known that the generation of NOx can be suppressed by injecting water into the combustion chamber to lower the combustion temperature in the combustion chamber.

[0003] For example, Japanese Utility Model Application Publication No. 5-10761 (Patent Document 1) discloses setting the amount of water injection to obtain the combustion temperature required to reduce the amount of NOx depending on the engine speed and load (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 5-10761 Summary of the Invention [Problem to be solved by the invention]

[0005] The engine speed and load may not adequately reflect changes in engine conditions during transient operation, which may result in an inability to adequately control NOx emissions or a drop in power output due to an excessive drop in combustion temperature.

[0006] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide a diesel engine and a control method thereof that can inject an appropriate amount of water even during transient operation when the engine state changes. [Means for solving the problem]

[0007] The diesel engine of the present disclosure includes an engine body having a combustion chamber, a fuel injection device configured to inject fuel into the combustion chamber, a water injection device configured to inject water into the combustion chamber, a control device for controlling the water injection device, and an acquisition unit that acquires a state quantity that indicates the amount of oxygen contained in intake gas supplied to the combustion chamber. The control device estimates the spray temperature from the state quantity acquired by the acquisition unit in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber, and determines the amount of water injection by the water injection device from the temperature difference between the estimated spray temperature and a target spray temperature.

[0008] The control method disclosed herein is a control method for a diesel engine equipped with a fuel injection device that injects fuel into a combustion chamber and a water injection device that injects water into the combustion chamber, and includes the steps of: acquiring a state quantity that indicates the amount of oxygen contained in the intake gas supplied to the combustion chamber; estimating the spray temperature from the acquired state quantity in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber; and determining the amount of water injected by the water injection device from the temperature difference between the estimated spray temperature and a target spray temperature.

[0009] In the diesel engine and control method described above, the water injection amount is determined from the state variables directly related to the combustion state in the combustion chamber, so an appropriate water injection amount can be determined based on the combustion state even during transient operation. Therefore, with this diesel engine and control method, an appropriate amount of water can be injected even during transient operation. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in output due to an excessive decrease in combustion temperature can be suppressed.

[0010] The diesel engine may further include an EGR device. The EGR device connects the exhaust passage to the intake passage without passing through the engine body and is configured to recirculate a portion of the exhaust gas to the intake passage. The control device may determine the water injection amount based on the temperature difference when changing the amount of exhaust gas recirculated by the EGR device.

[0011] By using an EGR device to recirculate a portion of the exhaust gas back into the combustion chamber, the combustion temperature can be suppressed, thereby reducing the amount of NOx generated. However, for example, during transient operation when the required amount of EGR gas increases, there is a delay in the increase in the actual amount of EGR gas. In this case, if the water injection amount is set according to the engine speed and load, the amount of water may be insufficient until the actual amount of EGR gas reaches the required amount, and as a result, the amount of NOx may not be sufficiently suppressed. In the above-mentioned diesel engine, the temperature difference and the amount of water injection are determined from the above-mentioned state variables directly related to the combustion state in the combustion chamber, so the above-mentioned water shortage during transient operation can be suppressed. Therefore, the amount of NOx can be sufficiently suppressed.

[0012] The control device may determine the amount of water injection from the temperature difference during a cold start of the engine body when operation of the EGR device is restricted.

[0013] During a cold start of the engine, the operation of the EGR device may be restricted because condensed water is generated when the EGR device is operated. Restricting the operation of the EGR device may increase the combustion temperature and the amount of NOx. In this diesel engine, the amount of water injection is determined from the above state quantities as described above, so the combustion temperature can be appropriately suppressed. Therefore, the amount of NOx can be sufficiently suppressed.

[0014] The target spray temperature may be determined based on the engine speed and load. This allows the spray temperature to approach the target spray temperature determined based on the engine speed and load, thereby making it possible to appropriately suppress the amount of NOx.

[0015] The predetermined relationship may be a relationship between the state quantity and a maximum value of the spray temperature in one stroke of the engine body. The control device may then estimate the maximum value of the spray temperature from the state quantity acquired by the acquisition unit in accordance with the relationship, and determine the water injection amount from the temperature difference between the estimated maximum value of the spray temperature and a target maximum value of the spray temperature.

[0016] By using the maximum value of the spray temperature in this manner, the spray temperature can be sufficiently and appropriately suppressed.

[0017] The control device may calculate the amount of water injection by multiplying the mass of spray gas in the combustion chamber, which is determined depending on the operating state of the engine body, the constant pressure specific heat of the spray gas, and the above-mentioned temperature difference, and dividing the result by the latent heat of vaporization value of water.

[0018] This allows the water injection amount to be calculated appropriately. [Effects of the Invention]

[0019] The diesel engine and control method of the present disclosure can inject an appropriate amount of water even during transient operation when the engine state changes, thereby sufficiently suppressing the amount of NOx and preventing a decrease in output due to an excessive drop in combustion temperature. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an overall configuration diagram of a diesel engine according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an example of the arrangement of fuel injection valves and water injection valves in a cylinder. [Figure 3] FIG. 10 is a diagram showing an example of the transition of the NOx amount during transient operation of the engine, as a reference example. [Figure 4] FIG. 10 is a diagram showing an example of transition of the maximum value of the average spray temperature in the combustion chamber. [Figure 5] FIG. 10 is a diagram showing an example of the relationship between the temperature difference of the spray temperature from the base condition and the amount of water injection. [Figure 6] 4 is a flowchart illustrating a process for calculating the amount of water injection from the water injection valve, which is executed by the control device. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0022] 1 is an overall configuration diagram of a diesel engine according to an embodiment of the present disclosure. Referring to FIG. 1, diesel engine 1 includes engine body 10, intake pipes 11A and 11B, an intake manifold 11C, an exhaust manifold 12A, exhaust pipes 12B and 12C, a turbocharger 30, an EGR device 13, and a control device 50.

[0023] The diesel engine 1 further includes an intake air flow sensor 21, an intercooler 16, a throttle device 47, and a pressure sensor 24.

[0024] The intake pipe 11A is connected to the inlet side of a compressor 35 of the turbocharger 30, and the intake pipe 11B is connected to the outlet side of the compressor 35. An intake manifold 11C is provided on the intake side of the engine body 10, and the intake pipe 11B is connected to the intake manifold 11C.

[0025] The intake air flow rate sensor 21 is provided in the intake pipe 11A and detects the flow rate of air introduced into the intake pipe 11A. The turbocharger 30 includes a compressor 35 having a compressor impeller 35A and a turbine 36 having a turbine impeller 36A. The compressor impeller 35A is rotationally driven by the turbine impeller 36A, which is rotationally driven by exhaust gas, and supercharges the air taken in through the intake pipe 11A and supplies it to the intake pipe 11B.

[0026] The intercooler 16 is provided in the intake pipe 11B and is an air-cooled or water-cooled heat exchanger that cools the air supercharged by the compressor 35. The throttle device 47 is provided in the intake pipe 11B downstream of the intercooler 16 and adjusts the intake air flow rate by driving a throttle valve 47A based on a control signal from the control device 50. The pressure sensor 24 is provided in the intake pipe 11B downstream of the throttle device 47 and detects the pressure of the intake gas supplied to the intake manifold 11C and outputs the detected pressure to the control device 50.

[0027] The diesel engine 1 further includes a common rail 41, fuel pipes 42A to 42D, fuel injection valves 43A to 43D, a water supply common rail 61, water pipes 62A to 62D, water injection valves 63A to 63D, a supply pipe 65, a pump 66, and a water tank 67.

[0028] A plurality of cylinders 45A to 45D are provided in the engine body 10. Although four cylinders 45A to 45D are shown in this example, the number of cylinders is not limited to this.

[0029] Fuel injection valves 43A to 43D are provided in cylinders 45A to 45D, respectively. Fuel is supplied to fuel injection valves 43A to 43D from common rail 41 through fuel pipes 42A to 42D, respectively. Fuel injection valves 43A to 43D are driven by control signals from control device 50, and inject fuel into cylinders 45A to 45D, respectively.

[0030] Water injection valves 63A to 63D are also provided in the cylinders 45A to 45D, respectively. Water (non-flammable liquid) is supplied to the water injection valves 63A to 63D from the water supply common rail 61 through water pipes 62A to 62D, respectively. The water injection valves 63A to 63D are driven by control signals from the control device 50, and inject water into the cylinders 45A to 45D, respectively.

[0031] The water supply common rail 61 is connected to a water tank 67 through a supply pipe 65. A pump 66 is provided in the supply pipe 65, and the pump 66 supplies water from the water tank 67 through the supply pipe 65 to the water supply common rail 61.

[0032] An exhaust manifold 12A is provided on the exhaust side of the engine body 10, and an exhaust pipe 12B is connected to the exhaust manifold 12A. The outlet side of the exhaust pipe 12B is connected to the inlet side of the turbine 36 of the turbocharger 30, and an exhaust pipe 12C is connected to the outlet side of the turbine 36.

[0033] The diesel engine 1 further includes a temperature sensor 29 and a pressure sensor 26. The temperature sensor 29 is provided in the exhaust pipe 12B and detects the temperature of the exhaust gas discharged from the engine body 10. The pressure sensor 26 is provided in the exhaust pipe 12B and detects the pressure of the exhaust gas in the exhaust pipe 12B and outputs the detected pressure to the control device 50.

[0034] Although not shown in Fig. 1, the exhaust pipe 12C is provided with an exhaust gas purification device. The exhaust gas purification device includes, for example, an oxidation catalyst, a particulate filter, a selective reduction catalyst, and the like.

[0035] The EGR device 13 includes EGR pipes 13A and 13B, a path switching device 14A, an EGR valve 14B, an EGR cooler 15, and a bypass pipe 13C. The EGR pipe 13A is connected to the exhaust pipe 12B, and the EGR pipe 13B is connected to the intake pipe 11B. The exhaust pipe 12B and the intake pipe 11B are connected to each other by the EGR pipes 13A and 13B, and a portion of the exhaust gas (EGR gas) in the exhaust pipe 12B can be recirculated to the intake side of the engine body 10.

[0036] The path switching device 14A is a path switching valve that switches between an EGR cooler path that returns the EGR gas recirculated through the EGR piping 13A to the intake pipe 11B via the EGR cooler 15, and a bypass path that bypasses the EGR cooler 15 via the bypass piping 13C and returns the EGR gas to the intake pipe 11B.

[0037] The EGR valve 14B is provided in the EGR pipe 13B, downstream of the junction with the bypass pipe 13C. The EGR valve 14B adjusts the flow rate of the EGR gas flowing through the EGR pipe 13B (i.e., the flow rate of the EGR gas recirculated to the intake pipe 11B) based on a control signal from the control device 50.

[0038] The EGR cooler 15 is a heat exchanger that is provided between the EGR pipe 13A and the EGR pipe 13B and cools the EGR gas. The EGR cooler 15 cools the EGR gas that flows in from the EGR pipe 13A and discharges the cooled EGR gas into the EGR pipe 13B.

[0039] The control device 50 is configured to include at least a processor 51 and a storage device 53. The processor 51 is configured to include a CPU (Central Processing Unit), an MPU (Micro Processing Unit), etc. The storage device 53 is configured to include a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The ROM stores a processing program to be executed by the processor 51, and the processor 51 loads the processing program stored in the ROM into the RAM and executes it.

[0040] The control device 50 detects the operating state of the diesel engine 1 based on detection signals from various sensors, and controls various actuators including the fuel injection valves 43A to 43D, the water injection valves 63A to 63D, the EGR valve 14B, and the like.

[0041] The diesel engine 1 further includes a rotation angle sensor 22, an atmospheric pressure sensor 23, an accelerator pedal sensor 25, and a vehicle speed sensor 27. The rotation angle sensor 22 detects the rotation angle (crank angle) of the crankshaft of the engine main body 10. The atmospheric pressure sensor 23 detects the ambient atmospheric pressure. The accelerator pedal sensor 25 detects the amount of depression of the accelerator pedal by the driver. The vehicle speed sensor 27 detects the rotation speed of the wheels of the vehicle on which the diesel engine 1 is mounted.

[0042] In the above-mentioned diesel engine 1, the amount of NOx in the exhaust gas increases as the combustion temperature in the combustion chambers formed in the cylinders 45A to 45D increases, so water injection valves 63A to 63D are provided to inject water into the cylinders 45A to 45D (combustion chambers) to lower the combustion temperature.

[0043] 2 is a diagram showing an example of the arrangement of the fuel injector 43A and the water injector 63A in the cylinder 45A. The arrangement of the fuel injector 43B to 43D and the water injector 63B to 63D in the other cylinders 45B to 45D is similar to the arrangement of the fuel injector 43A and the water injector 63A in the cylinder 45A.

[0044] 2, engine body 10 includes a cylinder block 71 in which cylinder 45A is formed, and a cylinder head 72. A piston 73 that reciprocates within cylinder 45A is provided within cylinder 45A. A combustion chamber 75 in which an air-fuel mixture is burned is formed within cylinder 45A between piston 73 and cylinder head 72. A concave cavity 76 is formed in the top surface of piston 73.

[0045] The fuel injection valve 43A is disposed at the center of the upper wall surface of the combustion chamber 75, and is configured to inject fuel F directly toward the peripheral portion of a cavity 76 formed in the piston 73 (see the lower diagram in FIG. 2). The water injection valve 63A is disposed at an angle relative to the fuel injection valve 43A, on the peripheral portion of the upper wall surface of the combustion chamber 75. The water injection valve 63A is configured to inject (supply) water 68 to a predetermined region FL around a plurality (e.g., eight) of fuel injection ports (not shown) of the fuel injection valve 43A (see the upper diagram in FIG. 2). As a result, the predetermined region FL is cooled to a temperature lower than the ignition temperature of the fuel F by the heat of vaporization of the water 68.

[0046] While water injection into the combustion chamber by the water injection valves 63A-63D can suppress the combustion temperature and reduce the amount of NOx in the exhaust gas, excessive water injection can result in a decrease in output due to an excessive drop in combustion temperature, so an appropriate amount of water must be injected by the water injection valves 63A-63D. Therefore, it is conceivable to set the amount of water injection that can reduce the amount of NOx without excessively lowering the combustion temperature, for example, depending on the engine speed and load.

[0047] However, setting the water injection amount according to the engine speed and load may not be able to sufficiently suppress the amount of NOx during transient operation when the engine state changes. Specifically, during transient operation when the required amount of EGR gas increases, there is a delay in the increase in the actual amount of EGR gas. Therefore, setting the water injection amount according to the engine speed and load may result in an insufficient amount of water until the actual amount of EGR gas reaches the required amount, and as a result, the amount of NOx may not be sufficiently suppressed.

[0048] FIG. 3 is a diagram showing, as a reference example, an example of the transition of the NOx amount during transient operation of an engine. In FIG. 3, the EGR rate indicates the proportion of the EGR gas amount in the intake gas supplied to the engine body. Line L1 (dotted line) is the target value of the EGR rate (target EGR rate), which in this example is determined from the engine speed and load (fuel injection amount, etc.). Line L2 (solid line) is the actual value of the EGR rate (actual EGR rate). Line L3 indicates the transition of the NOx amount.

[0049] 3, the change in the actual EGR rate (line L2) lags behind the change in the target EGR rate (line L1). Specifically, the target EGR rate peaks at time t1, whereas the actual EGR rate peaks at time t2, which is later than time t1. This is because there is a time lag between when the opening of the EGR valve increases in response to an increase in the target EGR rate and when this change in opening is reflected in a change in the EGR rate of the intake gas supplied to the combustion chamber. Due to this delay, the actual EGR rate is lower than the target EGR rate between time t1 and time t2.

[0050] In this reference example, the target EGR rate is determined based on the engine speed and load, and accordingly, the water injection amount is also determined based on the engine speed and load. Therefore, between time t1 and time t2, the water injection amount is small for an actual EGR rate that is lower than the target EGR rate, and as a result, the combustion temperature cannot be sufficiently suppressed, and the amount of NOx increases (line L3). The same is true for times t3 and t4, where the amount of NOx increases due to the EGR delay between time t3 and time t4.

[0051] Therefore, in the diesel engine 1 according to this embodiment, the water injection amount is determined based on the rotation speed and load of the engine body 10, and also based on the amount of intake oxygen, which is a state quantity directly related to the combustion state. Intake oxygen is oxygen contained in the intake gas supplied to the combustion chamber, and in this embodiment, the mass fraction of intake oxygen in the intake gas is used as the state quantity. By determining the water injection amount from such a state quantity directly related to the combustion state in the combustion chamber, an appropriate water injection amount can be determined based on the combustion state even during transient operation.

[0052] Fig. 4 is a diagram showing an example of the transition of the maximum value of the average spray temperature in the combustion chamber. In Fig. 4, line L4 indicates the maximum value of the average spray temperature (hereinafter sometimes simply referred to as the "spray temperature") Tmax, and line L5 indicates the target value of the spray temperature Tmax (hereinafter simply referred to as the "target spray temperature") Tmax0. In Fig. 4, as a reference example, line L4 shows the transition of temperature when the water injection amount according to this embodiment is not set as described above.

[0053] The mean spray temperature indicates the spatial average value of the combustion temperature in the combustion chamber, and the maximum mean spray temperature indicates the maximum mean spray temperature in one stroke of the engine. The target spray temperature Tmax0 is the spray temperature Tmax required to obtain a target NOx amount, and in this embodiment, is determined based on the rotation speed and load of the engine body 10. The target spray temperature Tmax0 is determined in advance by experiment, simulation, etc., and is stored in the storage device 53 as a map using the rotation speed and load of the engine body 10 as parameters.

[0054] 4, due to a change in the state of engine body 10 (for example, the transient change described in FIG. 3), spray temperature Tmax (line L4) rises relative to target spray temperature Tmax0 (line L5) at times t11 and t12. In this example, at time t11, a temperature difference ΔT(1) occurs between spray temperature Tmax and target spray temperature Tmax0, and at time t12, a temperature difference ΔT(2) occurs between spray temperature Tmax and target spray temperature Tmax0. Such an increase in spray temperature Tmax leads to an increase in the amount of NOx.

[0055] In this embodiment, this temperature difference ΔT is estimated from the intake oxygen amount (mass fraction of intake oxygen). Then, based on the estimated temperature difference ΔT, the water injection amount of the water injection valves 63A to 63D is determined so as to suppress the temperature difference ΔT. This makes it possible to inject an appropriate amount of water even during transient operation. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in engine output due to an excessive decrease in spray temperature can be suppressed. Below, the above temperature difference ΔT and a method for calculating the water injection amount based thereon will be described.

[0056] In diesel engine 1 according to the present embodiment, the fuel spray temperature Tmax(K) is calculated using the following empirical formula (1) derived from a prior experiment, simulation, or the like.

[0057]

number

[0058] This equation (1) assumes that the Arrhenius equation holds between the amount of NOx generated and the spray temperature, and employs an Arrhenius model that has a temperature parameter in the exponential term of e (Napier's number). In equation (1), Y represents the mass fraction of intake oxygen, and Y0 represents the mass fraction of intake oxygen under base conditions.

[0059] The mass fraction Y of intake oxygen can be calculated using a known method from the intake air amount detected by the intake air flow sensor 21 and the EGR amount (rate). The EGR amount (rate) can be estimated using a known method from the intake air amount detected by the intake air flow sensor 21 and the detection value of the pressure sensor 24.

[0060] The base conditions are conditions based on the engine speed and engine load at the time of calculation under steady-state operation of the diesel engine 1. Specifically, Y0 is the mass fraction of intake oxygen at the speed and load of the engine body 10 at the time of calculation, and Tmax0 is the spray temperature (maximum value of the injection average temperature) at the speed and load of the engine body 10 at the time of calculation. The intake oxygen mass fraction Y0 and spray temperature Tmax0 under these base conditions correspond to the target values of the intake oxygen mass fraction Y and spray temperature Tmax, respectively. The intake oxygen mass fraction Y0 and spray temperature Tmax0 are obtained in advance by experiments, simulations, etc. using the engine speed and load of the engine body 10 as parameters, and are stored in the storage device 53 as a map.

[0061] The mass fraction Y0 of intake oxygen and the spray temperature Tmax0 under the base conditions are obtained from the map based on the rotation speed and load of the engine body 10 at the time of calculation, and the spray temperature Tmax can be calculated from the mass fraction Y of intake oxygen using equation (1). The rotation speed of the engine body 10 can be calculated from the detection value of the rotation angle sensor 22. The load of the engine body 10 is calculated from, for example, the fuel injection amount from the fuel injection valves 43A to 43D and / or the depression amount of the accelerator pedal detected by the accelerator pedal sensor 25.

[0062] Then, the temperature difference ΔT between the calculated spray temperature Tmax and the spray temperature Tmax0 under the base conditions is calculated using the following equation (2).

[0063] ΔT=Tmax-Tmax0 …(2) In this embodiment, the water injection amount Qw(g) of each water injector 63A to 63D is calculated from this temperature difference ΔT. The water injection amount Qw is calculated by the following equation as the amount required to lower the spray temperature Tmax by the temperature difference ΔT.

[0064] Qw = Ms × Cp × ΔT / Hw … (3) Ms is the mass (g) of the spray gas (a mixture of intake gas and fuel) generated when fuel is sprayed into the combustion chamber, Cp is the constant pressure specific heat (kJ / (kg K)) of the gas in the spray, and Hw is the latent heat of vaporization of water (kJ / kg).

[0065] The spray gas mass Ms is a parameter that depends on the amount or injection pressure of fuel injected from each of the fuel injection valves 43B to 43D and changes depending on the operating conditions of the engine body 10. The spray gas mass Ms is obtained in advance by experiment, simulation, or the like using the rotation speed and load (fuel injection amount, etc.) of the engine body 10 as parameters, for example, and is stored in the storage device 53 as a map.

[0066] Fig. 5 is a diagram showing an example of the relationship between the temperature difference ΔT in the spray temperature from the base condition and the water injection amount Qw. In Fig. 5, the horizontal axis represents the temperature difference ΔT between the spray temperature Tmax and the spray temperature Tmax0 under the base condition, and the vertical axis represents the water injection amount Qw.

[0067] Referring to FIG. 5, the line L11 indicates the engine speed of 1200 rpm and the fuel injection amount of 20 qv (mm 3 / st) ("st" indicates stroke). Line L12 indicates the relationship when the engine speed is 1600 rpm and the fuel injection amount is 30 qv, and line L13 indicates the relationship when the engine speed is 2000 rpm and the fuel injection amount is 50 qv.

[0068] In this way, in the diesel engine 1 according to this embodiment, the fuel spray temperature Tmax is calculated from the intake oxygen amount (mass fraction Y of intake oxygen) using equation (1), and the water injection amount Qw of each water injection valve 63A to 63D is determined based on the temperature difference ΔT of the spray temperature from the base condition.

[0069] 6 is a flowchart illustrating the process of calculating the water injection amount of the water injection valves 63A to 63D executed by the control device 50. The series of processes shown in this flowchart are repeatedly executed at predetermined time intervals or whenever predetermined conditions are met while the diesel engine 1 is in operation.

[0070] 6, the control device 50 first calculates the mass fraction Y of intake oxygen, which indicates the amount of intake oxygen, which is a state quantity directly related to the combustion state in the combustion chamber (step S10). The mass fraction Y of intake oxygen can be calculated using a known method from the intake air amount detected by the intake flow sensor 21 and the EGR amount (rate).

[0071] Next, the control device 50 detects the rotation speed and load of the engine body 10 (step S20). The rotation speed is calculated from the detection value of the rotation angle sensor 22. The load of the engine body 10 is calculated from the fuel injection amount from the fuel injection valves 43A to 43D and / or the depression amount of the accelerator pedal detected by the accelerator pedal sensor 25.

[0072] Furthermore, the control device 50 uses a map showing the relationship between the engine speed and engine load under steady operation and the mass fraction of intake oxygen and spray temperature, respectively, to obtain the mass fraction Y0 of intake oxygen and the spray temperature Tmax0 under base conditions based on the speed and load detected in step S20 (step S30). This spray temperature Tmax0 under the base conditions corresponds to the target value of the spray temperature Tmax (the target spray temperature required for NOx reduction).

[0073] Then, the control device 50 uses the above-mentioned formula (1), which is an empirical formula obtained in advance, to calculate the spray temperature Tmax at the time of calculation from the intake oxygen mass fraction Y calculated in step S10, and the intake oxygen mass fraction Y0 and spray temperature Tmax0 under the base conditions acquired in step S30 (step S40).

[0074] Next, the control device 50 calculates the temperature difference ΔT (=Tmax−Tmax0) between the spray temperature Tmax calculated in step S40 and the spray temperature Tmax0 (target spray temperature necessary for NOx reduction) under the base conditions (step S50).

[0075] Next, the control device 50 calculates the spray gas mass Ms under the operating condition of the engine body 10 at the time of calculation (step S60). Specifically, the control device 50 calculates the spray gas mass Ms based on the rotation speed and load detected in step S20, using a map showing the relationship between the rotation speed and load (fuel injection amount, etc.) of the engine body 10 and the spray gas mass Ms.

[0076] Then, the control device 50 calculates the water injection amount Qw by each of the water injectors 63A to 63D from the temperature difference ΔT calculated in step S50 (step S70). Specifically, using the above-mentioned formula (3), the water injection amount Qw is calculated from the temperature difference ΔT calculated in step S50 and the spray gas mass Ms calculated in step S60.

[0077] As described above, in this embodiment, the spray temperature Tmax is estimated from the intake oxygen mass fraction Y in accordance with the predetermined relationship (Equation (1)) between the intake oxygen mass fraction (fuel oxygen amount), which is a state quantity directly related to the combustion state in the combustion chamber, and the spray temperature of the fuel injected into the combustion chamber. Then, the water injection amount Qw of each fuel injection valve 43A to 43D is determined from the temperature difference ΔT between the estimated spray temperature Tmax and the spray temperature Tmax0 (target spray temperature) under the base conditions.

[0078] This allows an appropriate water injection amount Qw to be determined based on the combustion state even during transient operation. Therefore, according to this embodiment, an appropriate amount of water can be injected even during transient operation. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in output due to an excessive decrease in combustion temperature can be suppressed.

[0079] Furthermore, in the above embodiment, the EGR device 13 is provided, and when the amount of exhaust gas recirculated by the EGR device 13 is changed, the water injection amount Qw is determined from the mass fraction of intake oxygen (amount of intake oxygen). This prevents the problem of insufficient water injection due to a delayed response of EGR gas during transient operation. Therefore, according to this embodiment, the amount of NOx can be sufficiently suppressed.

[0080] During a cold start of the engine body 10, the operation of the EGR device 13 may be restricted because condensed water is generated when the EGR device 13 is operated. If the operation of the EGR device 13 is restricted, the combustion temperature may rise, possibly increasing the amount of NOx. In this embodiment, the water injection amount Qw is determined from the intake oxygen amount (mass fraction Y of intake oxygen), which is a state quantity directly related to the combustion state. Therefore, the amount of NOx can be sufficiently suppressed even during a cold start of the engine body 10.

[0081] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The technical scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0082] 1 diesel engine, 10 engine body, 11A, 11B intake pipe, 11C intake manifold, 12A exhaust manifold, 12B, 12C exhaust pipe, 13 EGR device, 13A, 13B EGR piping, 13C bypass piping, 14A path switching device, 14B EGR valve, 15 EGR cooler, 16 intercooler, 21 intake air flow sensor, 22 rotation angle sensor, 23 atmospheric pressure sensor, 24, 26 pressure sensor, 25 accelerator pedal sensor, 27 vehicle speed sensor, 29 temperature sensor, 30 turbocharger, 35 compressor, 35A compressor impeller, 36 turbine, 36A turbine impeller, 41 common rail, 42A to 42D fuel piping, 43A to 43D fuel injection valve, 45A to 45D cylinder, 47 throttle device, 47A Throttle valve, 50 control device, 51 processor, 53 storage device, 61 water supply common rail, 62A-62D water piping, 63A-63D water injection valve, 65 supply pipe, 66 pump, 67 water tank, 71 cylinder block, 72 cylinder head, 73 piston, 75 combustion chamber, 76 cavity.

Claims

1. an engine body having a combustion chamber; a fuel injector configured to inject fuel into the combustion chamber; a water injection device configured to inject water into the combustion chamber; a control device for controlling the water injection device; an acquisition unit that acquires a state quantity indicating an amount of oxygen contained in intake gas supplied into the combustion chamber, The control device estimating the spray temperature from the state quantity acquired by the acquisition unit in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber; a water injection amount by the water injection device is determined based on a temperature difference between the estimated spray temperature and the target spray temperature.

2. an EGR device configured to connect an exhaust passage to an intake passage without passing through the engine body and to recirculate a portion of the exhaust gas to the intake passage; 2. The diesel engine according to claim 1, wherein the control device determines the amount of water injection based on the temperature difference when the amount of exhaust gas recirculated by the EGR device is changed.

3. 3. The diesel engine according to claim 2, wherein the control device determines the amount of water injection from the temperature difference during a cold start of the engine body in which operation of the EGR device is restricted.

4. 4. The diesel engine according to claim 1, wherein the target spray temperature is determined based on a rotation speed and a load of the engine body.

5. the relationship is a relationship between the state quantity and a maximum value of the spray temperature in one stroke of the engine body, The control device estimating a maximum value of the spray temperature from the state quantity acquired by the acquisition unit in accordance with the relationship; 5. The diesel engine according to claim 1, wherein the water injection amount is determined from a temperature difference between the estimated maximum value of the spray temperature and a target maximum value of the spray temperature.

6. 6. The diesel engine according to claim 1, wherein the control device calculates the water injection amount by multiplying a mass of the spray gas in the combustion chamber, a spray gas constant pressure specific heat, and the temperature difference, which are determined depending on an operating state of the engine body, and dividing the product by a latent heat of vaporization value of water.

7. 1. A control method for a diesel engine equipped with a fuel injection device that injects fuel into a combustion chamber and a water injection device that injects water into the combustion chamber, comprising: acquiring a state quantity indicating the amount of oxygen contained in the intake gas supplied into the combustion chamber; a step of estimating the spray temperature from the acquired state quantity in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber; determining an amount of water injection by the water injection device from a temperature difference between the estimated spray temperature and a target spray temperature.

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