JP2006233837A - Exhaust gas purification system of hydrogen-used internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification system of a hydrogen-used internal combustion engine, enabling reduction treatment of NOx and temperature rising control of an NOx catalyst at the same time. <P>SOLUTION: In the exhaust gas purification system, it is determined whether or not an NOx occluded amount of the calculated NOx catalyst is less than a predetermined value (S102). When the NOx occluded amount is not less than the predetermined value, it is determined whether or not an NOx catalyst floor temperature is lower than the predetermined value (S106). When the NOx catalyst floor temperature is lower than the predetermined value, the catalyst floor temperature is raised by reacting part of hydrogen supplied into the NOx catalyst with unburned oxygen, while the NOx occluded capacity of the NOx catalyst is restored by reducing NOx with hydrogen (S108). When the NOx catalyst floor temperature is not lower than the predetermined value, the NOx occluded capacity of the NOx catalyst is controlled only to restore by reducing NOx with hydrogen (S110). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification apparatus for a hydrogen-using internal combustion engine that purifies exhaust gas discharged from a hydrogen-using internal combustion engine.

  In order to improve fuel efficiency, a lean burn engine is known in which fuel is burned at an air / fuel ratio that is leaner than the stoichiometric air / fuel ratio. The lean burn engine is provided with a NOx catalyst for storing NOx discharged during lean combustion.

  However, the NOx storage capacity of this NOx catalyst has a limit. For this reason, when the NOx storage limit is approached, rich spike control is performed in which a larger amount of fuel than the stoichiometric combustion is supplied so that the air-fuel ratio of the exhaust gas becomes rich. Thereby, the unburned fuel contained in the exhaust gas serves as a reducing agent, and NOx stored in the NOx catalyst is reduced. As a result, the storage capacity of the NOx catalyst is recovered.

  In addition, an exhaust purification device that supplies hydrogen as a reducing agent upstream of the NOx catalyst in order to recover the storage capacity of the NOx catalyst has been disclosed (see, for example, Patent Document 1). However, it is necessary to separately provide a device for supplying hydrogen upstream of the catalyst. By the way, a hydrogen-based internal combustion engine that adds hydrogen as a combustion accelerator to gasoline is known. It is conceivable to supply hydrogen upstream of the NOx catalyst by diverting the hydrogen supply system of this hydrogen-utilizing internal combustion engine.

JP 2000-186528 A

  However, even if the above-described hydrogen-utilizing internal combustion engine is used, there is a possibility that hydrogen may be wasted in the combustion chamber. The amount of hydrogen loaded in the vehicle is limited by the size of the hydrogen tank. In addition, hydrogen can be generated on the vehicle by a fuel reforming reaction or dehydrogenation reaction, but in this case as well, it is difficult to generate a large amount of hydrogen. Therefore, it is necessary to suppress the consumption of hydrogen as a NOx reducing agent as much as possible.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an exhaust purification device for a hydrogen-using internal combustion engine that can suppress the consumption of hydrogen as a NOx reducing agent. Another object of the present invention is to provide an exhaust purification device for a hydrogen-using internal combustion engine that can simultaneously perform NOx reduction processing and NOx catalyst temperature increase control.

In order to achieve the above object, a first invention is an exhaust purification device for a hydrogen-using internal combustion engine that can be operated using non-hydrogen fuel and hydrogen as fuel,
Non-hydrogen fuel supply means for supplying non-hydrogen fuel to the combustion chamber;
A NOx catalyst provided in an exhaust passage communicating with the combustion chamber and storing NOx in the exhaust gas;
Hydrogen supply means for directly supplying hydrogen into the combustion chamber for reducing NOx stored in the NOx catalyst;
In the expansion stroke or exhaust stroke after the non-hydrogen fuel is burned in the combustion chamber, the hydrogen supply means supplies hydrogen so that the air-fuel ratio of the exhaust gas discharged from the combustion chamber becomes rich. And a control means for performing.

  Further, according to a second aspect, in the first aspect, the control means uses the non-hydrogen fuel supply means to remove the non-hydrogen from the non-hydrogen fuel supply means so that the ratio of the non-hydrogen fuel to the intake air amount is equal to or higher than the ratio required for stoichiometric combustion. It is characterized by performing control for supplying fuel.

The third invention further comprises catalyst temperature detecting means for detecting the temperature of the NOx catalyst in the first invention,
The non-hydrogen fuel supply means controls the non-hydrogen fuel supply means so that when the NOx catalyst temperature is lower than a predetermined value, the ratio of the non-hydrogen fuel to the intake air amount is smaller than the ratio required for stoichiometric combustion. It is characterized by carrying out control to supply.

Further, a fourth invention further comprises a storage amount calculating means for calculating a NOx storage amount stored in the NOx catalyst in the first to third inventions,
The control means performs the control when the calculated NOx occlusion amount is a predetermined value or more.

  According to the first aspect of the present invention, hydrogen having high NOx reducing ability can be supplied to the NOx catalyst without providing new equipment. Furthermore, by supplying hydrogen for NOx reduction in the expansion stroke or exhaust stroke, hydrogen can be supplied to the NOx catalyst without burning in the combustion chamber. Therefore, the consumption of hydrogen as a NOx reducing agent can be suppressed.

  According to the second invention, by making the supply ratio of the non-hydrogen fuel to the intake air amount stoichiometric or rich, the generation of unburned oxygen can be prevented, and the supply of unburned oxygen to the NOx catalyst can be prevented. Can do. Therefore, all hydrogen in the NOx catalyst can be used for NOx reduction, and hydrogen consumption can be suppressed.

  According to the third invention, when the NOx catalyst temperature is low, unburned oxygen can be supplied to the NOx catalyst by making the supply ratio of the non-hydrogen fuel to the intake air amount lean. Furthermore, hydrogen can be supplied to the NOx catalyst without burning in the combustion chamber. Therefore, the temperature of the NOx catalyst can be raised by reacting a part of hydrogen with unburned oxygen in the NOx catalyst. The remaining hydrogen that does not contribute to the temperature rise of the NOx catalyst can be used as a NOx reducing agent. Therefore, NOx reduction processing and NOx catalyst temperature increase control can be executed simultaneously.

  According to the fourth invention, it is possible to efficiently perform the NOx reduction process according to the NOx occlusion amount.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to an embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10. The internal combustion engine 10 includes a fuel injection valve 36 that injects gasoline as non-hydrogen fuel into the combustion chamber 11, and a hydrogen injection valve 44 that injects hydrogen into the combustion chamber 11. The fuel injection valve 36 communicates with the fuel tank 30 through the fuel passage 32. A pump 34 is provided in the middle of the fuel passage 32. The hydrogen injection valve 44 communicates with the hydrogen tank 40 via the hydrogen passage 42. The hydrogen tank 40 stores compressed hydrogen. The internal combustion engine 10 includes a spark plug 18 for igniting the air-fuel mixture in the combustion chamber 11.

  An intake passage 12 communicates with the combustion chamber 11 via an intake valve 16. A throttle valve 14 is provided midway in the intake passage 12. An air flow meter 15 is provided upstream of the throttle valve 14 in the intake passage 12. The air flow meter 15 is configured to detect an intake air amount Ga flowing into the internal combustion engine 10.

  An exhaust passage 22 communicates with the combustion chamber 11 via an exhaust valve 20. A three-way catalyst 24 is provided in the exhaust passage 22, and a NOx catalyst 26 is provided downstream of the three-way catalyst 24.

  An air-fuel ratio sensor 23 is provided upstream of the three-way catalyst 24. The air-fuel ratio sensor 23 is configured to detect the exhaust air-fuel ratio. An oxygen sensor 25 is provided between the three-way catalyst 24 and the NOx catalyst 26. The oxygen sensor 25 is configured to emit a signal depending on whether the air-fuel ratio is rich or lean.

  The NOx catalyst 26 is provided with a NOx catalyst temperature sensor 27 that detects the temperature of the NOx catalyst 26. A NOx sensor 28 that detects the NOx concentration in the exhaust gas is provided downstream of the NOx catalyst 26.

The system shown in FIG. 1 includes an ECU (Electronic Control Unit) 50. The above-described throttle valve 14, air flow meter 15, intake valve 16, exhaust valve 20, spark plug 18, air-fuel ratio sensor 23, oxygen sensor 25, NOx catalyst temperature sensor 27, NOx sensor 28, pump 34, fuel injection valve 36, and hydrogen The injection valve 44 and the like are connected to the ECU 50 and controlled by the ECU 50, respectively. The ECU 50 performs overall control of the internal combustion engine 10 such as fuel injection control and ignition timing control.
Further, the ECU 50 can calculate the engine speed NE based on a detection signal of a crank angle sensor 19 provided on a crankshaft (not shown).
Further, the ECU 50 can calculate the NOx occlusion amount of the NOx catalyst 26 by a known method. For example, the ECU 50 calculates the amount of NOx discharged from the internal combustion engine 10 based on the operating state of the vehicle (for example, engine speed NE, exhaust air-fuel ratio, etc.), and accumulates the calculated NOx amount to store NOx. The amount can be calculated.

[Features of the embodiment]
Next, the operation of the system in this embodiment will be described.
In the above system, hydrogen can be injected into the combustion chamber 11 from the hydrogen injection valve 44, and gasoline can be injected into the combustion chamber 11 from the combustion injection valve 36. Therefore, according to the above system, the hydrogen addition lean combustion operation can be executed.
Moreover, according to the said system, the lean combustion operation by stratified combustion and the lean combustion operation by uniform combustion can be performed. During these lean combustion operations, NOx contained in the exhaust gas discharged from the internal combustion engine 10 cannot be efficiently purified by the three-way catalyst 24. Therefore, NOx that has passed through the three-way catalyst 24 is captured by the NOx catalyst 26. However, the NOx storage capacity of the NOx catalyst 26 is finite. Therefore, when the amount of NOx stored in the NOx catalyst 26 approaches the NOx storage capacity, it is necessary to reduce the storage capacity of the NOx catalyst 26 by reducing NOx.

  In the present embodiment, hydrogen having high reducibility is used as the NOx reducing agent. That is, the storage capacity of the NOx catalyst 26 is recovered by executing rich spike control using hydrogen as a reducing agent. However, the amount of hydrogen that can be mounted on the vehicle is limited, and it is difficult to generate a large amount of hydrogen on the vehicle. Therefore, it is necessary to suppress the amount of hydrogen used for NOx reduction as much as possible. However, hydrogen is more easily combusted than non-hydrogen fuel such as gasoline. Therefore, even if hydrogen is supplied at the same time as gasoline, the hydrogen burns.

In the present embodiment, hydrogen is efficiently supplied to the NOx catalyst 26 without burning. Specifically, stoichiometric combustion is performed only with gasoline, and hydrogen is injected into the combustion chamber 11 from the hydrogen injection valve 44 during the exhaust stroke after the combustion. The hydrogen injected into the combustion chamber 11 is sent to the exhaust passage 22 without being burned, and is efficiently supplied to the NOx catalyst 26. In the NOx catalyst 26, NOx is reduced to N ₂ by the supplied hydrogen and released. As a result, the storage capacity of the NOx catalyst 26 is recovered.

  By the way, it is known that the temperature of the exhaust gas during the lean combustion operation is generally low. For this reason, the temperature of the NOx catalyst 26 may decrease during the lean combustion operation. In addition, the temperature of the NOx catalyst 26 may decrease due to other factors. Since the NOx catalyst 26 becomes inactive when the temperature decreases, it becomes impossible to efficiently capture NOx. Therefore, when the temperature of the NOx catalyst 26 decreases, it is necessary to raise the catalyst temperature early.

  Therefore, in the present embodiment, when the temperature of the NOx catalyst 26 decreases, unburned oxygen discharged without burning in the combustion chamber 11 in the NOx catalyst 26 (hereinafter referred to as “unburned oxygen”). Reacts with hydrogen. Since this reaction is an exothermic reaction, the temperature of the NOx catalyst 26 can be raised. Specifically, by making the ratio of the gasoline injection amount to the intake air amount smaller than the ratio required for stoichiometric combustion (hereinafter referred to as “stoichiometric level”), unburned oxygen is transferred from the combustion chamber 11 to the NOx catalyst 26. To be supplied. Further, an amount of hydrogen that reacts with the unburned oxygen and contributes to raising the catalyst temperature is injected together with an amount of hydrogen necessary for the NOx reduction.

  That is, when the temperature of the NOx catalyst 26 decreases, unburned oxygen is generated by reducing the ratio of the gasoline injection amount, and extra hydrogen is injected for the amount of reaction with the unburned oxygen. Thereby, the storage capacity of the NOx catalyst 26 can be recovered, and the temperature of the NOx catalyst 26 can be raised.

[Specific processing in the embodiment]
FIG. 2 is a flowchart of a routine executed by ECU 50 in the present embodiment. According to the routine shown in FIG. 2, during the lean combustion operation, first, the amount of NOx stored in the NOx catalyst 26 is calculated (step 100).

  Next, it is determined whether or not the calculated NOx occlusion amount is smaller than a predetermined value (step 102). If it is determined in step 102 that the NOx storage amount is smaller than the predetermined value, it is determined that it is not necessary to restore the storage capacity of the NOx catalyst 26. That is, it is determined that it is not necessary to execute a rich spike using hydrogen. In this case, the ECU 50 continues the lean combustion operation (step 104).

  On the other hand, if it is determined in step 102 that the NOx storage amount is equal to or greater than the predetermined value, it is determined that the storage capacity of the NOx catalyst 26 needs to be recovered. In this case, as described below, the hydrogen rich spike is executed according to the NOx catalyst temperature.

First, it is determined whether or not the temperature of the NOx catalyst 26 is lower than a predetermined value (step 106). If it is determined in step 106 that the NOx catalyst temperature is lower than the predetermined value, it is determined that the catalyst temperature needs to be raised in order to activate the NOx catalyst 26. In this case, the ECU 50 simultaneously performs NOx reduction and NOx catalyst temperature raising processing (step 108).
Specifically, as shown in FIG. 3, gasoline is injected into the combustion chamber 11 from the fuel injection valve 36 at a rate smaller than the stoichiometric level (ie, lean). Thus, unburned oxygen is discharged from the combustion chamber 11 and supplied to the NOx catalyst 26 during the exhaust stroke after gasoline is combusted. Further, during this exhaust stroke, hydrogen is injected from the hydrogen injection valve 44 into the combustion chamber 11. Here, as shown in FIG. 3, the hydrogen injection amount includes an amount necessary to react with the unburned oxygen and contribute to the temperature rise of the NOx catalyst 26, and an amount necessary to reduce NOx. Is the sum of
As a result, the temperature of the NOx catalyst 26 rises due to an exothermic reaction between unburned oxygen and hydrogen in the NOx catalyst 26, and NOx is reduced by hydrogen, so that the storage capacity of the NOx catalyst 26 is restored.

  On the other hand, when it is determined in step 106 that the NOx catalyst temperature is equal to or higher than the predetermined value, the ECU 50 executes only NOx reduction (step 110). Specifically, as shown in FIG. 4, gasoline is injected into the combustion chamber 11 from the fuel injection valve 36 at a ratio equal to or higher than the stoichiometric level (that is, stoichiometric or rich). At this time, since all the oxygen in the air-fuel mixture is used for combustion, unburned oxygen is not discharged from the combustion chamber 11 during the exhaust stroke after gasoline is burned. During this exhaust stroke, hydrogen is injected into the combustion chamber 11 from the hydrogen injection valve 44. Here, as shown in FIG. 4, the hydrogen injection amount is sufficient for reducing NOx. That is, since unburned oxygen is not supplied to the NOx catalyst 26, hydrogen is not consumed for raising the catalyst bed temperature. Thereby, NOx is reduced by hydrogen and the storage capacity of the NOx catalyst 26 is recovered.

  When this routine is started after the next time, when the NOx occlusion amount is equal to or greater than a predetermined value and the NOx catalyst temperature is lower than the predetermined value, the catalyst temperature is increased simultaneously with the NOx reduction. Further, when the NOx occlusion amount is not less than a predetermined value and the NOx catalyst temperature is not less than the predetermined value, NOx reduction is executed.

As described above, according to the routine shown in FIG. 2, hydrogen is injected into the combustion chamber 11 during the exhaust stroke after gasoline combustion, thereby supplying the NOx catalyst 26 without burning hydrogen in the combustion chamber 11. can do. Therefore, useless combustion of hydrogen can be prevented, so that hydrogen consumption can be suppressed.
Further, when the temperature of the NOx catalyst 26 is low, the NOx catalyst temperature can be raised by supplying unburned oxygen to the NOx catalyst 26 and reacting the unburned oxygen with a part of hydrogen. Therefore, the recovery of the storage capacity of the NOx catalyst 26 and the temperature increase of the NOx catalyst 26 can be executed simultaneously.

  In the present embodiment, the system for directly injecting gasoline into the combustion chamber 11 from the fuel injection valve 36 has been described. However, a system for injecting gasoline into the intake port of the intake passage 12 may be used. Further, a system capable of port injection and in-cylinder injection of gasoline may be used. Also in this case, the same effect as in the first embodiment can be obtained.

  In the present embodiment, the system for supplying hydrogen from the hydrogen tank 40 has been described. However, a system for generating hydrogen by performing a reforming reaction or a dehydrogenation reaction of fuel on a vehicle may be used.

  In the present embodiment, a system for injecting hydrogen as a NOx reducing agent in the exhaust stroke after gasoline is burned in the combustion chamber 11 has been described. However, a system for injecting hydrogen in the expansion stroke may be used. .

  Further, in the present embodiment, the system that executes rich spike control according to the calculated NOx occlusion amount has been described. However, the system that executes rich spike control according to the NOx concentration detected by the NOx sensor 28 is used. Also good.

In the present embodiment, a system in which the three-way catalyst 24 and the NOx catalyst 26 are provided in series has been described. However, a system in which the three-way catalyst 24 is not provided may be used.
Alternatively, a system in which the NOx catalyst 26 and the three-way catalyst 24 are provided in parallel by a manifold provided in the exhaust passage 22 may be used. In this case, if the NOx catalyst 26 is used instead of the three-way catalyst 24 by operating a valve or the like, the same system configuration as that of the system in which the three-way catalyst 24 is omitted can be achieved.

  In the present embodiment, the ECU 50 executes the process of step 108 or step 110, so that the “control means” in the first invention executes the process of step 110, and “ The "control means" executes the processing of step 106 and step 108, the "control means" in the third invention performs the processing of step 100, and the "occlusion amount calculation means" in the fourth invention results in Each is realized.

It is a figure for demonstrating the system configuration | structure of embodiment of this invention. It is a flowchart of the routine which ECU50 performs in embodiment of this invention. It is a figure which shows the fuel quantity at the time of NOx reduction | restoration and catalyst temperature rising in the flowchart shown in FIG. It is a figure which shows the fuel quantity at the time of NOx reduction | restoration in the flowchart shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Combustion chamber 12 Intake passage 14 Throttle valve 15 Air flow meter 16 Intake valve 18 Spark plug 19 Crank angle sensor 20 Exhaust valve 22 Exhaust passage 23 Air-fuel ratio sensor 24 Three-way catalyst 25 Oxygen sensor 26 NOx catalyst 27 NOx catalyst temperature sensor 28 NOx sensor 30 Fuel tank 32 Passage 34 Pump 36 Combustion injection valve 40 Hydrogen tank 42 Passage 44 Hydrogen injection valve 50 ECU (Electronic Control Unit)

Claims (4)

An exhaust purification device for a hydrogen-utilizing internal combustion engine that can be operated using non-hydrogen fuel and hydrogen as fuel,
Non-hydrogen fuel supply means for supplying non-hydrogen fuel to the combustion chamber;
A NOx catalyst provided in an exhaust passage communicating with the combustion chamber and storing NOx in the exhaust gas;
Hydrogen supply means for directly supplying hydrogen into the combustion chamber for reducing NOx stored in the NOx catalyst;
In the expansion stroke or exhaust stroke after the non-hydrogen fuel is burned in the combustion chamber, control is performed to supply hydrogen by the hydrogen supply means so that the air-fuel ratio of the exhaust gas discharged from the combustion chamber becomes rich. And an exhaust emission control device for a hydrogen-utilizing internal combustion engine, comprising: The exhaust gas purification apparatus for a hydrogen-utilizing internal combustion engine according to claim 1,
The control means controls the supply of non-hydrogen fuel by the non-hydrogen fuel supply means so that the ratio of the non-hydrogen fuel to the intake air amount is equal to or higher than the ratio required for stoichiometric combustion. An exhaust purification device for a hydrogen-using internal combustion engine. The exhaust gas purification apparatus for a hydrogen-utilizing internal combustion engine according to claim 1,
A catalyst temperature detecting means for detecting the temperature of the NOx catalyst;
The non-hydrogen fuel supply means controls the non-hydrogen fuel supply means so that when the NOx catalyst temperature is lower than a predetermined value, the ratio of the non-hydrogen fuel to the intake air amount is smaller than the ratio required for stoichiometric combustion. An exhaust emission control device for a hydrogen-utilizing internal combustion engine characterized by performing control for supplying the hydrogen. The exhaust gas purification apparatus for a hydrogen-utilizing internal combustion engine according to any one of claims 1 to 3,
A storage amount calculating means for calculating a storage amount of NOx stored in the NOx catalyst;
The exhaust purification device of a hydrogen-utilizing internal combustion engine, wherein the control means performs the control when the calculated NOx occlusion amount is a predetermined value or more.

Images