Power device

Abstract

To early activate a catalyst of a three-way catalyst device for purifying exhaust gas of an internal combustion engine, in a power device including the internal combustion engine using ammonia and ignition fuel as fuel.SOLUTION: A power plant 10 comprises a turbocharger 26 that turbocharges intake air of an internal combustion engine 12 to increase an intake pressure, and a throttle valve 24 that narrows a flow path of an intake pipe 22. When a catalyst in a three-way catalytic device 44 is inactive, a wastegate valve 50 of the turbocharger 26 is opened, or in addition, an intake flow path is narrowed by the throttle valve 24, to lower the intake pressure compared to that in normal time. The lowering of the intake pressure reduces a heat capacity of materials in a cylinder, increases a combustion temperature, and increases an exhaust temperature. High-temperature exhaust gas increases a temperature of the catalyst early, to accelerate activation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power plant that uses ammonia as its primary fuel. [Background technology]

[0002] In recent years, internal combustion engines that use ammonia as fuel have been considered from the perspective of reducing greenhouse gas emissions. Even when ammonia is burned, carbon dioxide, a greenhouse gas, is not produced. The following Patent Document 1 describes an engine that supplies liquid fuel for ignition and mixes and burns the ammonia. The engine purifies exhaust gas using a selective catalytic reduction (SCR). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-155927 Summary of the Invention [Problem to be solved by the invention]

[0004] When an oxidation catalyst is used to purify exhaust gas in an internal combustion engine that burns a mixture of ammonia and liquid fuel, in an excess air state, unburned ammonia, nitrogen oxides (NOx), and excess oxygen react in the oxidation catalyst to produce nitrous oxide (N2O), a greenhouse gas. In addition, since the ammonia fuel contains nitrogen, there is a lot of nitrogen oxide in the exhaust gas, and when a selective reduction catalyst is used to break it down, a large amount of reducing agent is required.

[0005] The use of an exhaust purification device equipped with a three-way catalyst (hereinafter referred to as a three-way catalyst device) can suppress the generation of nitrous oxide and can also reduce the amount of reducing agent used in the selective reduction catalyst. However, three-way catalysts are inactive when the temperature is low, and cannot sufficiently purify exhaust gas.

[0006] An object of the present invention is to quickly raise the temperature of a catalyst in a three-way catalytic converter. [Means for solving the problem]

[0007] The power plant of the present invention includes an internal combustion engine that injects ignition fuel for igniting ammonia into an air-fuel mixture containing ammonia compressed inside a cylinder, and obtains power by burning the ammonia and the ignition fuel, an intake pressure regulating device that adjusts the pressure of the intake air taken in by the internal combustion engine, a three-way catalyst device that purifies exhaust gas from the internal combustion engine, and a catalyst activity detection device that detects whether the catalyst of the three-way catalyst device is active or inactive, and when the catalyst is inactive, the intake pressure regulating device lowers the intake pressure compared to when the catalyst is active.

[0008] Lowering the intake pressure increases the exhaust temperature and speeds up catalyst activation.

[0009] The power plant may include an exhaust gas recirculation device that introduces a portion of the exhaust gas from the internal combustion engine into the intake air as recirculated exhaust gas, and when the catalyst is inactive, the exhaust gas recirculation device may reduce the recirculated exhaust gas in response to a reduction in the intake pressure by the intake pressure regulator, so that the composition of the substances in the cylinder is stoichiometric. By adjusting the amount of the recirculated exhaust gas, the composition of the substances in the cylinder can be maintained at the stoichiometric composition.

[0010] In the power plant described above, the intake pressure regulating device may include a turbocharger, and a wastegate valve of the turbocharger may be opened when the intake pressure is reduced.

[0011] In the power plant, the intake pressure regulating device may further include a throttle valve disposed in the intake passage that guides the intake air to the cylinder, and the intake pressure may be adjusted by the opening degree of the throttle valve. The intake pressure may be set to a value lower than that when supercharging by the turbocharger is stopped.

[0012] In the power plant, the catalyst activity detection device may detect whether the catalyst is activated or inactivated based on the exhaust gas temperatures before and after passing through the three-way catalyst device.

[0013] In the above power plant, the catalyst activity detection device may detect the activation / inactivation of the catalyst based on the concentration of nitrogen oxides in the exhaust gas before and after passing through the three-way catalyst device.

[0014] In the above-mentioned power plant, the turbocharger may be equipped with a variable nozzle that changes the cross-sectional area of ​​the exhaust flow passage in the exhaust turbine housing, and when the catalyst is activated, the variable nozzle may adjust the cross-sectional area of ​​the exhaust flow passage so as to optimize fuel efficiency.

[0015] The above power plant may be provided with an unstable operation detection device that detects an unstable operating state of the internal combustion engine based on at least one of torque fluctuations and misfires of the internal combustion engine, and if an unstable operating state is detected when the intake pressure is low because the catalyst is inactive, the amount of ignition fuel may be increased, and if a stable operating state is detected when the catalyst is activated and the intake pressure is high, the amount of ignition fuel may be decreased. Effect of the Invention

[0016] When the catalyst in the three-way catalytic converter is inactive, the intake pressure is lowered compared to when it is active, thereby increasing the temperature of the exhaust gas from the internal combustion engine. This increases the temperature of the catalyst in the three-way catalytic converter, and activates it more quickly. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a power plant according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram showing a structure of a turbine of a turbocharger. [Diagram 3] FIG. 4 is a diagram showing a comparison of the performance of an internal combustion engine when a high intake pressure is applied and when a low intake pressure is applied. [Figure 4] FIG. 4 is a graph showing a heat release rate versus crank angle. [Diagram 5] FIG. 4 is a graph showing the internal cylinder pressure versus crank angle. [Figure 6]4 is a chart showing a control flow relating to early activation of a catalyst. [Figure 7] 4 is a chart showing a control flow for a process of transitioning from control related to early activation of a catalyst to normal control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a power unit 10 that drives a vehicle of this embodiment. The power unit 10 includes a reciprocating internal combustion engine 12. The internal combustion engine 12 may be a compression ignition engine. The internal combustion engine 12 has a plurality of cylinders 14. The internal combustion engine 12 shown in the figure has four cylinders arranged in series, but the number of cylinders is not limited to this, and the cylinder arrangement is not limited to this either. The power unit 10 further includes an intake system device 16 related to the supply of intake air to the internal combustion engine 12, an exhaust system device 18 related to the discharge of exhaust from the internal combustion engine 12, and an exhaust gas recirculation device 20 that circulates a part of the exhaust of the internal combustion engine 12 back to the intake air.

[0019] The intake system 16 includes an intake pipe 22 through which intake air to the internal combustion engine 12 flows, a throttle valve 24, a turbocharger 26, and an intercooler 28 arranged along the intake pipe 22. The intake air flowing through the intake pipe 22 passes through the throttle valve 24, a compressor 30 of the turbocharger 26, and the intercooler 28 in this order. The throttle valve 24 is, for example, a butterfly valve, and the flow passage cross-sectional area of ​​the intake pipe 22 can be changed by the operation of the throttle valve 24. By reducing the flow passage cross-sectional area, i.e., by narrowing it, the pressure of the intake air in the intake pipe 22 downstream of the throttle valve 24 can be reduced. The turbocharger 26 compresses the intake air using exhaust energy from the internal combustion engine 12. A turbine wheel arranged in a turbine 32 of the turbocharger 26 is rotated by the exhaust. A compressor wheel that rotates integrally with the turbine wheel is arranged in a compressor 30 of the turbocharger 26. The compressor 30 functions as a centrifugal compressor to compress the intake air. The intake air, which has become hot as a result of compression, is cooled in the intercooler 28 by outside air or the cooling water of the internal combustion engine 12.

[0020] An ammonia injector 34 that injects ammonia, which is a fuel, into the intake pipe 22 is provided downstream of the intercooler 28 of the intake pipe 22. Here, the intake air sent through the intake pipe 22 becomes an air-fuel mixture containing the injected ammonia. The air-fuel mixture is distributed and supplied to each cylinder 14 via an intake manifold 36.

[0021] An ignition fuel injection valve 38 is provided for each cylinder 14, which directly injects ignition fuel into the cylinder 14 at a predetermined timing. The ignition fuel is burned by the high-temperature air-fuel mixture compressed in the cylinder 14, and the ammonia is further burned. The exhaust gases from each cylinder 14 after combustion are joined together by an exhaust manifold 40 and sent to the turbocharger 26.

[0022] The exhaust system 18 includes an exhaust pipe 42, a turbocharger 26, a three-way catalytic converter 44, and a reduction type catalytic converter 46 arranged along the exhaust pipe 42. The three-way catalytic converter 44 and the reduction type catalytic converter 46 are exhaust purification devices that purify the exhaust gas from the internal combustion engine 12. As described above, the turbocharger 26 has a turbine wheel that is rotated by the exhaust gas, and the rotation of the turbine wheel is transmitted to the compressor wheel. The exhaust gas that has passed through the turbine 32 of the turbocharger 26 is sent to the three-way catalytic converter 44 and the reduction type catalytic converter 46 in this order by the exhaust pipe 42, and then discharged. Furthermore, the turbocharger 26 has an exhaust bypass pipe 48 that sends the exhaust gas to the exhaust pipe 42, bypassing the turbine 32. The exhaust bypass pipe 48 is provided with a wastegate valve 50 that can be opened and closed. When the wastegate valve 50 is opened, a part of the exhaust gas flows into the exhaust bypass pipe 48 and is sent to the exhaust pipe 42 without passing through the turbine 32. The wastegate valve 50 opens when the rotation speed of the internal combustion engine 12 is high and the exhaust flow rate is large, suppressing an increase in the exhaust gas flowing to the turbine 32 and suppressing an excessive increase in intake pressure.

[0023] The three-way catalytic converter 44 purifies the exhaust gas of the internal combustion engine 12 when the internal combustion engine 12 is operated with a mixture of air and ammonia and a composition of the ignition fuel injected into the cylinder 14, i.e., the composition of the substances in the cylinder, being stoichiometric. Nitrogen oxides, nitrous oxides, unburned fuel, etc. are efficiently purified by the catalyst of the three-way catalytic converter 44. The reduction type catalytic converter 46 uses a reducing agent to decompose nitrogen oxides in the exhaust gas when the catalyst of the three-way catalytic converter 44 is inactive due to low temperature, and when the internal combustion engine 12 is operated with a composition of the substances in the cylinder 14 not being stoichiometric. Ammonia stored as fuel can be used as the reducing agent.

[0024] The exhaust gas recirculation system 20 includes a recirculation pipe 52 that guides the exhaust gas of the internal combustion engine 12 from the exhaust manifold 40 or the exhaust pipe 42 to the intake pipe 22, and a recirculation valve 54 that adjusts the flow rate of the exhaust gas flowing through the recirculation pipe 52. By adjusting the opening degree of the recirculation valve 54, the amount of exhaust gas mixed into the intake air is adjusted.

[0025] The throttle valve 24 and turbocharger 26 function as an intake pressure regulator that adjusts the pressure of the intake air. As described above, the throttle valve 24 can adjust the pressure of the intake air by narrowing the flow path of the intake pipe 22 and adjusting the amount of narrowing. The turbocharger 26 can suppress the pressure of the intake air (supercharging pressure) by opening the wastegate valve 50. By opening the wastegate valve 50 when the rotation speed of the internal combustion engine 12 is low and the exhaust flow rate is small, a state of almost no supercharging can be achieved.

[0026] The operation of the power plant 10 is controlled based on a plurality of physical quantities indicating the operating state of the power plant 10. The power plant 10 includes a control device 56, which controls each operating part of the power plant 10 based on the input physical quantities to control the operation of the power plant 10. For example, the control device 56 receives inputs of the driver's operation amount of the accelerator pedal 58, the engine speed, the vehicle speed, the cooling water temperature, the intake air flow rate, the intake air temperature, the exhaust temperature, and the like, and controls the injection amounts of ammonia and ignition fuel from the ammonia injector 34 and the ignition fuel injector 38 so as to obtain an output according to the driver's request. The control device 56 also controls the operation of the throttle valve 24, the wastegate valve 50, and the recirculation valve 54.

[0027] FIG. 2 is a schematic cross-sectional view of the turbocharger 26, particularly the turbine 32. The turbine 32 includes a turbine wheel 60, which is an impeller, and a turbine housing 62 that surrounds the turbine wheel 60 and defines a vortex chamber around the turbine wheel 60. Furthermore, a plurality of variable nozzles 64 are arranged in the vortex chamber. The plurality of variable nozzles 64 are arranged circumferentially along the outer periphery of the turbine wheel 60. The variable nozzles 64 can rotate within a predetermined angle range, and in FIG. 2(a), the variable nozzles 64 are arranged at a small angle with respect to the circumferential direction of the turbine wheel 60, and in FIG. 2(b), the variable nozzles 64 are arranged at a large angle. When the variable nozzles 64 are arranged at a small angle, the cross-sectional area of ​​the flow path of the exhaust gas from the vortex chamber toward the turbine wheel 60 becomes small. Therefore, even if the flow rate of the exhaust gas flowing into the turbine 32 is small, the speed of the exhaust gas colliding with the turbine wheel 60 can be increased. Therefore, the rotation speed of the turbine wheel and the compressor wheel can be increased to increase the supercharging pressure. On the other hand, when the variable nozzle 64 is disposed at a large angle, the cross-sectional area of ​​the flow passage becomes large, and exhaust resistance is reduced when the exhaust flow rate is large. The rotation amount of the variable nozzle 64 is controlled by the control device 56.

[0028] FIG. 3 shows the performance of the internal combustion engine 12 when ammonia and ignition fuel are mixed and burned. The performance is compared depending on the intake pressure (boost pressure) at the same output torque. The left column shows the performance when the intake pressure is 0.15 MPa (absolute pressure), and the right column shows the performance when the intake pressure is 0.10 MPa (absolute pressure). In addition, the ratio of exhaust gas introduced by exhaust gas recirculation is determined so that the equivalence ratio is 1 at both high and low intake pressures, that is, so that the composition of the substances in the cylinder is stoichiometric. Since the output torque is the same at high and low intake pressures, the amount of fuel supplied is the same, but since the intake pressures are different, the amount of air (oxygen) supplied differs. In other words, if the amount of exhaust gas introduced is the same, at low intake pressure, the amount of air is reduced compared to at high intake pressure, and the equivalence ratio becomes rich. In order to maintain the equivalence ratio, at low intake pressure, the amount of exhaust gas introduced is reduced and the amount of new air supplied is increased. In the example shown in FIG. 3, the ratio of exhaust to the entire mixture is 49.7% at high intake pressure (0.15 MPa) and 24.0% at low intake pressure (0.10 MPa), so that the equivalence ratio is 1 in both cases.

[0029] FIG. 4 is a diagram showing the heat generation rate at the high intake pressure and the low intake pressure shown in FIG. 3. FIG. 5 is a diagram showing the change in the cylinder pressure at the high intake pressure and the low intake pressure shown in FIG. 3. In FIG. 4 and FIG. 5, 0 on the horizontal axis is the compression top dead center. The rise in the heat generation rate is faster at high intake pressure, so the risk of misfire is low. This is because the rate coefficient of the third body reaction depends on the pressure, and the rate coefficient increases as the pressure increases. At low intake pressure, the heat capacity of the gas in the cylinder is small, so once ignition occurs, the temperature rises rapidly and the maximum temperature also becomes higher. For this reason, as shown in FIG. 3, the heat loss is larger at low intake pressure, and the amount of nitrogen oxide emissions is also larger. In addition, the exhaust temperature is higher at low intake pressure. By utilizing this, the temperature of the three-way catalytic device 44 can be increased early and the catalyst can be activated early. In other words, when the catalyst of the three-way catalytic device 44 is inactive, the catalyst can be activated early by lowering the intake pressure.

[0030] The inactivation / activation of the catalyst can be detected based on the exhaust gas temperature before and after passing through the three-way catalyst device 44. For example, the activity of the catalyst can be determined by comparing the exhaust gas temperature immediately before flowing into the three-way catalyst device 44 with the exhaust gas temperature immediately after flowing out of the three-way catalyst device 44. An upstream temperature sensor 66 and a downstream temperature sensor 68 are disposed on the upstream side and downstream side of the three-way catalyst device 44, respectively, to detect the exhaust gas temperature. The control device 56 determines the activity of the catalyst based on the detection values ​​of these temperature sensors 66, 68. Specifically, when the exhaust gas temperature on the downstream side becomes higher than the exhaust gas temperature on the upstream side, the control device 56 determines that the catalyst is activated. When the catalyst is activated, the exhaust gas is heated by the heat of reaction, and the exhaust gas temperature on the downstream side becomes higher. In this case, the upstream temperature sensor 66, the downstream temperature sensor 68, and the control device 56 function as a catalyst activation detection device.

[0031] Alternatively, the inactivation / activation of the catalyst may be determined by directly or indirectly detecting the temperature of the catalyst carrier of the three-way catalytic device 44. Specifically, the control device 56 determines that the catalyst is activated when the temperature of the catalyst carrier reaches or exceeds a predetermined value. The sensor that detects the temperature of the catalyst carrier and the control device 56 function as a catalyst activation detection device.

[0032] The inactivity / activation of the catalyst can also be detected based on the concentration of nitrogen oxides. The activity of the catalyst can be determined by comparing the nitrogen oxide concentration of the exhaust gas just before it flows into the three-way catalyst device 44 with the nitrogen oxide concentration of the exhaust gas just after it flows out. An upstream nitrogen oxide sensor 70 and a downstream nitrogen oxide sensor 72 are disposed on the upstream and downstream sides of the three-way catalyst device 44, respectively, to detect the nitrogen oxide concentrations. The control device 56 determines the activity of the catalyst based on the detection values ​​of these nitrogen oxide concentration sensors 70, 72. Specifically, the catalyst is determined to be activated when the ratio of the nitrogen oxide concentration on the downstream side to that on the upstream side falls below a predetermined value. In this case, the upstream nitrogen oxide sensor 70, the downstream nitrogen oxide sensor 72, and the control device 56 function as a catalyst activation detection device.

[0033] Alternatively, instead of providing the upstream nitrogen oxide sensor 70, the nitrogen oxide concentration in the exhaust immediately before it flows into the three-way catalyst device 44 may be estimated from the operating conditions of the internal combustion engine 12 at that time. Specifically, a correspondence table that associates the operating conditions of the internal combustion engine 12 with the nitrogen oxide concentration in the exhaust at that time is stored in advance, and the nitrogen oxide concentration is estimated based on the correspondence table. This correspondence table can be stored in the control device 56. In this case, the downstream nitrogen oxide sensor 72 and the control device 56 function as a catalyst activation detection device.

[0034] To lower the intake pressure, the turbocharger 26, particularly the wastegate valve 50, is used. When it is detected that the catalyst in the three-way catalytic converter 44 is inactive, the control device 56 controls the wastegate valve 50 to open. By opening the wastegate valve 50, the exhaust gas sent to the turbine 32 is reduced, the capacity of the compressor 30 is reduced, and the intake pressure, which was high due to supercharging, is reduced. In addition to this, the throttle valve 24 may be used. The intake flow path in the intake pipe 22 is narrowed by the throttle valve 24, and the intake pressure can be lowered. The throttle valve 24 is also controlled by the control device 56. As described above, the lower the intake pressure, the higher the exhaust gas temperature, so the catalyst temperature can be raised earlier and the catalyst is activated sooner.

[0035] Since a sudden reduction in intake pressure may cause the operation of the internal combustion engine 12 to become unstable, the throttle valve 24 may be configured to gradually narrow the flow passage.

[0036] Even if the catalyst of the three-way catalytic converter 44 is inactive, a certain degree of exhaust purification function can be expected, so it is desirable to maintain the composition of the substances in the cylinder 14 at a stoichiometric composition. In addition, since the driver feels uncomfortable when the output torque of the internal combustion engine 12 changes, it is necessary to maintain the output torque even if the intake pressure is lowered to activate the catalyst. Therefore, it is necessary to maintain the amount of fuel (ammonia, ignition fuel) supplied to the cylinder 14. On the other hand, if the volume of the intake air introduced into the cylinder 14 is the same, when the intake pressure is lowered, the amount of new air (oxygen) decreases, so the equivalence ratio becomes rich. In order to maintain the stoichiometric composition, it is necessary to increase the intake air amount. This is done by adjusting the amount of exhaust gas introduced by exhaust gas recirculation. In other words, when the intake pressure is lowered, the amount of exhaust gas introduced is made smaller than before the intake pressure was lowered to maintain the stoichiometric composition. The amount of exhaust gas introduced by exhaust gas recirculation is controlled by the control device 56 by adjusting the opening of the recirculation valve 54. Exhaust gas recirculation is effective in suppressing nitrogen oxides in the exhaust gas. Moreover, if there is too much exhaust gas recirculated, the intake air becomes rich, and the thermal efficiency deteriorates. For these reasons, it is advantageous to make the composition of materials in the cylinder stoichiometric, even if the catalyst in the three-way catalytic device 44 is inactive. The amount or rate of exhaust gas introduced by the exhaust gas recirculation is controlled by the control device 56 based on the detection value of the air-fuel ratio sensor or oxygen sensor installed in the exhaust pipe 42.

[0037] When the intake pressure is low, the ignition timing is delayed compared to when the intake pressure is high. FIG. 4 shows that the rise of the heat release rate at low intake pressure is slower than that at high intake pressure. When the ignition timing is delayed, misfire and torque fluctuations occur, that is, the operation of the internal combustion engine 12 may become unstable. When a misfire or torque fluctuation occurs, the control device 56 increases the amount of ignition fuel to stabilize combustion. At this time, the amount of ammonia, which is the main fuel, is reduced in accordance with the increase in the amount of ignition fuel to maintain the total heat generation amount. The amount of ignition fuel can be gradually increased until ignition is stable. The torque fluctuation can be detected using a torque sensor that detects the output torque of the internal combustion engine 12, a sensor (e.g., a crank angle sensor) that detects the rotation speed of the output shaft of the internal combustion engine 12, a combustion pressure sensor that directly detects the pressure inside the cylinder, or the like. In addition, misfire can be determined by, for example, estimating the ignition timing from the oxygen concentration or fuel concentration in the exhaust gas, or the temperature inside the cylinder, and comparing it with the appropriate ignition timing.

[0038] After the catalyst of the three-way catalytic device 44 is activated, the wastegate valve 50 is opened. Also, if the intake flow passage is narrowed by the throttle valve 24, the throttle valve 24 is opened. If the turbocharger 26 is equipped with a variable nozzle 64, the rotation amount of the variable nozzle 64 is adjusted to set the flow passage cross-sectional area and intake pressure to values ​​that optimize fuel efficiency. Furthermore, as the intake pressure increases, the amount of exhaust gas recirculated is increased so that the composition of materials in the cylinder maintains a stoichiometric composition. The amount of ignition fuel is reduced to the extent that misfire and torque fluctuation do not occur. The amount of ammonia is increased in accordance with the reduction in ignition fuel.

[0039] 6 and 7 are charts showing a control flow related to the early activation of the catalyst of the three-way catalytic converter 44. The control device 56 sets the rotation speed and output torque of the internal combustion engine 12 based on the driver's request based on the accelerator operation amount, the operating state of the internal combustion engine 12, the running state of the vehicle, the environmental conditions, etc. (S100). Furthermore, the control device 56 sets the intake pressure, the ratio of exhaust gas returned to the intake side by exhaust gas recirculation (hereinafter referred to as EGR rate), the injection amount of ignition fuel, and the injection amount of ammonia, which is the main fuel, in the normal state, i.e., when the catalyst is activated, corresponding to the above rotation speed and output torque. These are previously associated with the rotation speed and output torque, and information showing the association is stored in the control device 56 as, for example, a correspondence table. The intake pressure, EGR rate, and injection amount of fuel are set based on this correspondence table (S102). In the normal state, the internal combustion engine 12 is supercharged by the turbocharger 26 and operated at a high intake pressure.

[0040] Next, the control device 56 judges whether the catalyst of the three-way catalytic converter 44 is in an active state (S104). If the catalyst is not in an active state, the control device 56 next judges whether the EGR rate exceeds 0 (S106). If the EGR rate is 0, the process returns to step S104, and steps S104 and S106 are repeated until the catalyst is in an active state. If the EGR rate exceeds 0 in step S106, there is room to lower the intake pressure while maintaining the stoichiometric composition, and the control device 56 controls the wastegate valve 50 to open (S108). This reduces the intake pressure that was supercharged by the turbocharger 26. In addition, the control device 56 may rotate the throttle valve 24 by a predetermined amount in a direction that narrows the intake passage, thereby reducing the intake pressure (S108). At this time, the control device 56 reduces the EGR rate in response to the reduction in fresh air due to the reduction in intake pressure, so that the composition of the substances in the cylinder becomes stoichiometric (S108).

[0041] Next, the control device 56 judges whether misfire or torque fluctuation has occurred (S110). If misfire or torque fluctuation has occurred, the control device 56 increases the amount of ignition fuel by a predetermined amount and decreases the amount of ammonia by the amount of the increase in the amount of ignition fuel so that the output torque is maintained (S112). At this time, the EGR rate is controlled to maintain the stoichiometric composition in the cylinder (S112). Until the misfire or torque fluctuation subsides, the control device 56 repeats the process of step 112, gradually increasing the ratio of ignition fuel. When the misfire or torque fluctuation disappears (S110), the process proceeds to step S104. If the catalyst is not yet in an active state, the control device 56 executes the processes of steps S106 and S108 again. In step S108, the throttle valve 24 further narrows the intake passage, and the intake pressure further decreases. When it is judged in step S104 that the catalyst has become active, the internal combustion engine 12 is shifted to normal control, that is, control when the catalyst is in an active state.

[0042] FIG. 7 is a chart showing a control flow of a process of shifting the control of the internal combustion engine 12 to normal control. When it is determined that the catalyst is activated, the control device 56 closes the wastegate valve 50 and fully opens the throttle valve 24 (S114). By closing the wastegate valve 50, the intake air is supercharged by the turbocharger 26, and the intake pressure increases. If the turbocharger 26 is equipped with a variable nozzle 64, the control device 56 controls the variable nozzle 64 so as to optimize fuel economy (S116). The control device 56 associates the driver's request (accelerator operation amount), driving conditions, the rotation angle of the variable nozzle 64, etc. with fuel economy, and stores information indicating the correspondence, for example, as a correspondence table. Based on this correspondence table, the control device 56 controls the rotation angle of the variable nozzle 64.

[0043] Closing the wastegate valve 50 and opening the throttle valve 24 increases the intake pressure, and in response to this increase, the control device 56 adjusts the EGR rate so that the composition of the substances in the cylinder becomes stoichiometric (S118). Next, the control device 56 reduces the injection amount of the ignition fuel by a predetermined amount, increases the injection amount of the ammonia by a predetermined amount (S120), and sets the counter n to 1 (n=1) (S122). The control device 56 determines whether a misfire or torque fluctuation has occurred (S124), and if a misfire or the like has not occurred, reduces the injection amount of the ignition fuel by a predetermined amount again, and increases the injection amount of the ammonia by a predetermined amount (S126). Then, the counter n is increased (n=n+1) (S128), and the process proceeds to step S124. By repeating the processes from step S124 to step S128, the injection amount of the ignition fuel gradually decreases.

[0044] If it is determined in step S124 that a misfire or torque fluctuation has occurred, the control device 56 returns the injection amounts of ignition fuel and ammonia to the values ​​set in the previous steps S124 to S128, that is, the values ​​when the counter n was n-1 (S130), and ends the control of the transition process to normal control. [Explanation of symbols]

[0045] 10 power unit, 12 internal combustion engine, 14 cylinder, 16 intake system, 18 exhaust system, 20 exhaust gas recirculation system, 22 intake pipe, 24 throttle valve (intake pressure adjustment device), 26 turbocharger (intake pressure adjustment device), 28 intercooler, 30 compressor, 32 turbine, 34 ammonia injector, 38 ignition fuel injector, 42 exhaust pipe, 44 three-way catalytic device (exhaust gas purification device), 46 reduction type catalytic device (exhaust gas purification device), 48 exhaust bypass pipe, 50 wastegate valve, 52 recirculation pipe, 54 recirculation valve, 56 control device, 60 turbine wheel, 62 turbine housing, 64 variable nozzle.

Claims

1. an internal combustion engine that injects ignition fuel for igniting ammonia into an air-fuel mixture containing ammonia compressed in a cylinder, and burns the ammonia and the ignition fuel to obtain power; an intake pressure regulating device for regulating the pressure of intake air taken into the internal combustion engine; a three-way catalytic converter for purifying exhaust gas from the internal combustion engine; a catalyst activity detection device for detecting whether a catalyst in the three-way catalyst device is activated or deactivated; Equipped with When the catalyst is inactive, the intake pressure regulating device lowers the intake pressure compared to when the catalyst is active. Power plant.

2. 2. The power plant of claim 1, an exhaust gas recirculation device that introduces a portion of the exhaust gas from the internal combustion engine into an intake air as recirculated exhaust gas; When the catalyst is inactive, the exhaust gas recirculation device reduces the recirculated exhaust gas in response to a reduction in intake pressure by the intake pressure regulator, thereby making the composition of substances in the cylinder a stoichiometric composition. Power plant.

3. 3. The power plant according to claim 2, wherein the intake pressure regulating device includes a turbocharger, and a wastegate valve of the turbocharger is opened when the intake pressure is reduced.

4. 4. The power plant according to claim 3, wherein the intake pressure regulating device further includes a throttle valve disposed in an intake flow path that guides intake air to the cylinder, and adjusts the intake pressure by an opening degree of the throttle valve.

5. 5. The power plant according to claim 1, wherein the catalyst activity detection device detects whether the catalyst is activated or inactivated based on exhaust gas temperatures before and after passing through the three-way catalyst device.

6. 5. The power plant according to claim 1, wherein the catalyst activity detection device detects whether the catalyst is activated or not based on a concentration of nitrogen oxides in exhaust gas before and after passing through the three-way catalyst device.

7. 4. The power plant according to claim 3, wherein the turbocharger is provided with a variable nozzle that changes a cross-sectional area of ​​an exhaust flow passage in an exhaust turbine housing, and when the catalyst is activated, the cross-sectional area of ​​the exhaust flow passage is adjusted by the variable nozzle so as to optimize fuel efficiency.

8. 2. The power plant of claim 1, an unstable operation detection device that detects whether the internal combustion engine is in an unstable operating state based on at least one of a torque fluctuation and a misfire of the internal combustion engine, When an unstable operating condition is detected while the intake pressure is low because the catalyst is inactive, the amount of ignition fuel is increased, When the catalyst is activated and the intake pressure is increased, if a stable operating state is detected, the amount of the ignition fuel is reduced. Power plant.

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