JP2001050035A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a NOx purification ratio while reducing an amount of ammonia emitted to the atmosphere. SOLUTION: A NOx reduction catalyst 18 suitable for reducing NOx in exhaust gas by ammonia in oxygen-excessive condition is disposed in an exhaust passage of an internal combustion engine. An ammonia oxidation catalyst 21 suitable for oxidizing ammonia to nitrogen in oxygen-excessive condition is disposed in the exhaust passage downstream of the NOx reduction catalyst 18. Aqueous urea is supplied from supply means 24 in an exhaust passage 17 upstream of the NOx reduction catalyst 18. A supply quantity of the aqueous urea is controlled such that an equivalence ratio thereof with respect to a flow rate of the NOx flowing in the NOx reduction catalyst 18 is greater than 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Prior Art Oxygen excess ammonia under Place _the NO _x reduction catalyst suitable for reducing the NO _x in the exhaust gas in the engine exhaust passage, to supply the urea aqueous solution _the NO _x reduction catalyst, N seeking NO _x inflow into _the NO _x reduction catalyst
O _x inflow exhaust purification system of an internal combustion engine for controlling the supply amount of the urea aqueous solution as the equivalent ratio of the supply amount of the urea is 1 for a known (see Japanese Patent real-Open No. 3-129712).

[0003]

[SUMMARY OF THE INVENTION However, not capable of reducing all of the NO _x flowing into _the NO _x reduction catalyst also equivalent ratio as was exactly match the 1, room to increase _the NO _x reduction rate is there. On the other hand, according to the present inventor,
If the equivalent ratio is larger than 1, the NO _x reduction rate increases,
_The NO _x reduction rate was found to increase as the time to increase the equivalence ratio. In other words, if supplying an excess of aqueous urea solution relative amount of NO _x flowing into _the NO _x reduction catalyst, it is possible to obtain a very high _the NO _x reduction rate.

However, when the urea aqueous solution is excessively supplied, a large amount of ammonia is discharged from the NO _x reduction catalyst,
Therefore, in order to increase the NO _x reduction rate, it is necessary to treat the ammonia discharged from the NO _x reduction catalyst. Accordingly, an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can increase the NO _x purification rate while reducing the amount of ammonia discharged into the atmosphere.

[0005]

According Means for Solving the Problems In order to solve the problems in the first invention, the oxygen excess of the NO _x that is suitable for reducing the NO _x in the exhaust gas by ammonia under
The reducing catalyst disposed in an engine exhaust passage, the exhaust purification system of an internal combustion engine which is adapted to supply a liquid containing ammonia generating compound to _the NO _x reduction catalyst, to oxidize ammonia to nitrogen under oxygen excess a suitable ammonia oxidation catalyst disposed NO _x in reduction catalyst or _the NO _x reduction catalyst in the exhaust passage downstream of the equivalent ratio of the supply amount of the ammonia generating compound to the NO _x inflow into _the NO _x reduction catalyst than 1 The supply amount of the liquid is controlled to increase. That is, in the first invention, since the excess ammonia generating compound is supplied to the NO _x reduction catalyst, the NO _x reduction rate is maintained high, and at this time, the excess ammonia discharged from the NO _x reduction catalyst is oxidized by the ammonia oxidation catalyst. And thus are prevented from being released into the atmosphere.

According to a second aspect of the present invention, in the first aspect, it is determined whether or not the temperature of the ammonia oxidation catalyst is within an optimum temperature range. When it is determined, the supply amount of the liquid is set so that the equivalent ratio becomes 1 or less when it is determined that the temperature of the ammonia oxidation catalyst is not within the optimum temperature range so that the equivalent ratio becomes larger than 1. Controlling. That is, in the second aspect, when the temperature of the ammonia oxidation catalyst is within the optimum temperature range, the excess liquid is supplied.

According to a third aspect, in the first aspect, the supply amount of the liquid is controlled such that the equivalent ratio is greater than 1 and less than or equal to 5. According to a fourth aspect, in the first aspect, the ammonia-generating compound is urea, and the liquid containing the ammonia-generating compound is an aqueous urea solution. According to a fifth aspect, in the first aspect, the ammonia oxidation catalyst includes zeolite.

[0008]

FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can be applied to a spark ignition type engine. Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber, 3 is an electrically controlled fuel injection valve for directly injecting fuel into the combustion chamber 2, 4 is an intake valve, and 5 is an intake valve.
Denotes an intake port, 6 denotes an exhaust valve, and 7 denotes an exhaust port. The intake port 5 is connected to a surge tank 9 via a corresponding intake branch 8, and the surge tank 9 is connected to an intake duct 10.
Is connected to the air cleaner 11 via the Intake duct 1
A throttle valve 13 driven by a step motor 12 is arranged in the area 0.

On the other hand, the exhaust port 7 is connected to the exhaust manifold 14.
Is connected to an inlet of a casing 16 containing the catalyst 15, and an outlet of the casing 16 is connected to a casing 19 containing the catalyst 18 via an exhaust pipe 17. An outlet of the casing 19 is connected to an inlet of a casing 22 containing the catalyst 21 via an exhaust pipe 20, and an outlet of the casing 22 is connected to an exhaust pipe 23. Catalyst 15 in this embodiment is made of a catalyst having an oxidation function, for example, oxidation catalysts or three-way catalyst, the catalyst 18 is _the NO _x reduction suitable for reducing the NO _x in the exhaust gas by ammonia under an excess of oxygen consists catalyst, the catalyst 21 is comprised of ammonia oxidation catalyst suitable ammonia under an excess of oxygen to oxidize the nitrogen N _2.

[0010] In the embodiment shown in FIG. 1, NO _x reduction catalyst 1
A catalyst V ₈ O ₅ / TiO ₂ (hereinafter, referred to as a vanadium titania catalyst) in which titania is used as a carrier and vanadium oxide is supported on this carrier, or a catalyst in which zeolite is used as a carrier and copper Cu is supported on this carrier Cu / ZSM5
(Hereinafter, referred to as a copper zeolite catalyst). On the other hand, a copper zeolite catalyst as the ammonia oxidation catalyst 21,
Alternatively, a catalyst in which platinum Pt and copper Cu are supported on a zeolite carrier (hereinafter, referred to as a platinum-copper zeolite catalyst), or a combination of a copper zeolite catalyst and a platinum-copper zeolite catalyst is used.

Each fuel injection valve 3 is connected to an electrically controlled variable discharge fuel pump (not shown) via a fuel reservoir, a so-called common rail (not shown). A fuel pressure sensor (not shown) for detecting fuel pressure in the common rail is attached to the common rail, and a fuel pump is provided so that the fuel pressure in the common rail becomes a target fuel pressure based on an output signal of the fuel pressure sensor. Is controlled.

Further, a supply device 24 is connected to the exhaust pipe 17. The supply device 24 is a tank 2 containing a liquid containing an ammonia generating compound that generates ammonia.
5, a supply conduit 26, a supply pump 27, and an electromagnetically controlled flow control valve 28. The liquid containing the ammonia generating compound stored in the tank 25 is supplied to the supply conduit 26, the supply pump 27, and the electromagnetically controlled flow control valve 2.
The gas is supplied into the exhaust pipe 17 through the pipe 8.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a power supply connected to each other by a bidirectional bus 31. B-RAM (backup RAM) 35, an input port 36, and an output port 37. A water temperature sensor 38 for detecting the temperature of the engine cooling water is attached to the engine body 1, and this water temperature sensor 38 generates an output voltage indicating the temperature of the engine cooling water. An intake air amount sensor 39 for detecting an intake air mass flow rate is disposed in the intake duct 10 upstream of the throttle valve 13, and the intake air amount sensor 39 generates an output voltage indicating the intake air mass flow rate. A temperature sensor 4 for detecting the temperature of the exhaust gas flowing in the exhaust pipe 20 is provided in the exhaust pipe 20.
0 is disposed, and the temperature sensor 40 generates an output voltage representing the exhaust gas temperature. This exhaust gas temperature represents the temperature of the NO _x reduction catalyst 18 and is hereinafter referred to as the NO _x reduction catalyst temperature TNC. A temperature sensor 4 for detecting the temperature of the exhaust gas flowing in the exhaust pipe 23 is provided in the exhaust pipe 23.
The temperature sensor 41 generates an output voltage representing the exhaust gas temperature. This exhaust gas temperature represents the temperature of the ammonia oxidation catalyst 21 and is hereinafter referred to as ammonia oxidation catalyst temperature TAC. Further, a depression amount sensor 42 for detecting the depression amount of an accelerator pedal (not shown) is provided, and this depression amount sensor 42 generates an output voltage indicating the depression amount. These sensors 38, 3
Output signals 9, 40, 41, and 42 are input to the input port 36 via the corresponding AD converters 43, respectively. Further, a rotation speed sensor 44 for detecting the engine rotation speed is connected to the input port 36. The rotation speed sensor 44 generates an output pulse indicating the engine rotation speed. On the other hand, the output port 37 is connected to the fuel injection valve 3 via the corresponding drive circuit 45,
Step motor 12, pump 27, and flow control valve 28
Connected to.

Now, as described above, the NO _x reduction catalyst 18
A liquid containing an ammonia generating compound is supplied into the upstream exhaust pipe 17. There are various types of ammonia-generating compounds capable of generating ammonia, and thus various compounds can be used as the ammonia-generating compound. In the embodiment according to the present invention, urea (CO (NH ₂ ) ₂ ) is used as the ammonia generating compound, and an aqueous urea solution is used as the liquid containing the ammonia generating compound. Therefore the following, NO _x reducing catalyst 18 upstream of the exhaust pipe 17
The present invention will be described by taking as an example a case where an aqueous urea solution is supplied to the inside.

When an aqueous urea solution is supplied to the exhaust gas containing excess oxygen, NO contained in the exhaust gas is reduced on the NO _x reduction catalyst 18 by ammonia NH ₃ generated from urea CO (NH ₂ ) _2. (For example, 4NH ₃
+ 4NO + O ₂ → 4N ₂ + 6H ₂ O). The mechanism of ammonia generation in this case is not necessarily clarified. However, it is believed that at least the following two mechanisms exist. That is, the first is due to the thermal decomposition of urea in the exhaust passage or in the NO _x reduction catalyst 18. The second is accompanied by a change in the form of urea. Specifically, urea changes to biuret at about 132 ° C, biuret changes to cyanuric acid at about 190 ° C, and cyanuric acid changes to cyanic or isocyanic acid at about 360 ° C. It is considered that ammonia is gradually generated in the course of the form change due to such a temperature rise.

In any case, NO _x flowing into the NO _x reduction catalyst 18 is converted into ammonia NH ₃ generated from urea.
Is reduced by In this case, theoretically, it is reacted in equimolar The NO _x and ammonia as can be seen from the above described reaction formulas. Therefore, theoretically, the NO _x to the NO _x reduction catalyst 18
By controlling the supply amount of the urea aqueous solution as the equivalent ratio of the supply amount of urea against the inflow is 1, NO _x reducing catalyst 18
All the NO _x flowing into the gas can be reduced to nitrogen N ₂ .

However, even when the equivalence ratio exactly matches 1 as described at the beginning, in practice, not all N
O _x cannot be reduced. On the other hand, as shown in FIG. 2, when the equivalent ratio is larger than 1, the NO _x purification rate E
FF increases, and as the equivalent ratio increases, N
O _x purification rate EFF is increased. In other words, if supplying an excess of an aqueous urea solution with respect to NO _x inflow into _the NO _x reduction catalyst 18, it is possible to obtain a very high _the NO _x purification rate.

However, as shown in FIG. 2, when the urea aqueous solution is excessively supplied, ammonia is discharged from the NO _x reduction catalyst 18 and the ammonia discharge amount Q (NH ₃ )
Increases with increasing equivalence ratio. Therefore NO _x
In order to increase the purification rate, it is necessary to treat the ammonia discharged from the NO _x reduction catalyst 18. Therefore, in this embodiment of the present invention, the ammonia oxidation catalyst 21 provided in _the NO _x reduction catalyst 18 in the exhaust passage downstream of, and the excess ammonia in the ammonia oxidation catalyst 21 so as to remove oxide. That is, if there is an excess of oxygen in the ammonia oxidation catalyst 21, first, a part of
O is generated (4NH ₃ + 5O ₂ → 4NO + 6H
₂ O). The NO thus produced then reacts with the remaining ammonia (4NH ₃ + 4NO + O ₂ → 4N
₂ + 6H ₂ O). Such a sequential reaction completely removes ammonia and prevents its release into the atmosphere.

[0019] Thus, in the embodiment according to the present invention, to place the ammonia oxidation catalyst 21 to _the NO _x reduction catalyst 18 in the exhaust passage downstream of the equivalent ratio of the supply amount of urea for NO _x inflow into _the NO _x reduction catalyst 18 Means that the supply amount of the aqueous urea solution is controlled so that the value of urea is larger than 1.
In this way, the emission of ammonia into the atmosphere can be prevented while maintaining the NO _x purification rate at an extremely high level. In addition, since it is not necessary to precisely control the equivalent ratio, control of the supply amount of the urea aqueous solution can be simplified.

In this case, it is preferable to keep the ammonia in the ammonia oxidation catalyst 21 in order to make the successive reaction of ammonia favorably. On the other hand, zeolite has excellent ammonia retention ability. Therefore, a catalyst including zeolite as the ammonia oxidation catalyst 21 is preferable. However, since the ammonia removal ability of the ammonia oxidation catalyst 21 is also limited, the upper limit of the equivalent ratio should be set. In this case, the supply amount of the urea aqueous solution is preferably controlled so that the equivalent ratio is greater than 1 and 5 or less, and more preferably the supply amount of the urea aqueous solution is controlled such that the equivalent ratio is 2 or more and 5 or less. Is done.

However, the ammonia removing ability of the ammonia oxidation catalyst 21 also depends on the ammonia oxidation catalyst temperature TAC. FIG. 3 shows an ammonia oxidation catalyst 2 when a model gas containing ammonia and containing no NO _x is supplied.
1 represents a purification rate EAN. Here, the purification rate EAN is determined by the amount of ammonia flowing into the ammonia oxidation catalyst 21, the amount of ammonia flowing out of the ammonia oxidation catalyst 21, and NO _x
It is calculated based on the outflow amount. As shown in FIG. 3, when the ammonia oxidation catalyst temperature TAC is low, the purification rate EAN is low. It is considered that this is because the ammonia oxidation catalyst 21 is not in an active state. When the ammonia oxidation catalyst temperature TAC increases, the purification rate EAN gradually increases, and when the ammonia oxidation catalyst temperature TAC becomes higher than the lower threshold TL, the purification rate EAN becomes higher than the allowable minimum purification rate LL.

When the temperature TAC of the ammonia oxidation catalyst is further increased, the purification rate EAN is maintained at almost 100%. Further, as the ammonia oxidation catalyst temperature TAC increases, the purification rate EAN gradually decreases, and the ammonia oxidation catalyst temperature TAC increases.
Is higher than the upper threshold TU, the allowable minimum purification rate L
It becomes lower than L. This is considered to be because the former NO generation reaction becomes more active than the latter ammonia oxidation reaction in the above-described sequential reaction, and as a result, a large amount of NO is discharged.

Therefore, the purification rate EAN is equal to the allowable minimum purification rate L.
When the range of the ammonia oxidation catalyst temperature TAC that is higher than L is referred to as an optimum temperature range, in the embodiment according to the present invention,
It is determined whether or not the ammonia oxidation catalyst temperature TAC is within the optimum temperature range. When it is determined that the ammonia oxidation catalyst temperature TAC is within the optimum temperature range, the supply of the aqueous urea solution is performed so that the equivalent ratio becomes 2 or more and 5 or less. The amount is controlled, and when it is determined that the ammonia oxidation catalyst temperature TAC is not within the optimum temperature range, the supply amount of the aqueous urea solution is controlled so that the equivalent ratio becomes 1.

The high purification rate EAN of the ammonia oxidation catalyst 21 indicates that the ammonia oxidation catalyst 21 can sufficiently purify ammonia even when the equivalent ratio is increased. Therefore, in the embodiment according to the present invention, when the ammonia oxidation catalyst temperature TAC is within the optimum temperature range,
When the ammonia oxidation catalyst temperature TAC is high, the supply amount of the urea aqueous solution is controlled such that the equivalent ratio becomes larger than when the temperature is low. In other words, the supply amount of the aqueous urea solution is controlled such that the equivalent ratio is proportional to the purification rate EAN of the ammonia oxidation catalyst 21.

Next, a method of calculating the supply amount QL of the aqueous urea solution from the supply device 24 will be described in detail with reference to the routine shown in FIG. This routine is executed by interruption every predetermined set time. Referring to FIG. 4, first, at step 100, the urea equivalent QE with respect to the NO _x inflow amount into the NO _x reduction catalyst 18 per unit time is calculated from the map of FIG. N per unit time
O _x inflow is _the NO _x reduction catalyst temperature TNC representing the engine load
Increases, and increases as the intake air amount Ga increases. Therefore, the urea equivalent QE is also NO _x
It increases as the reduction catalyst temperature TNC increases, and increases as the intake air amount Ga increases. The equivalent QE of urea is stored in advance experimentally and calculated by, in advance in the ROM32 in the form of a map shown in FIG. 5 as a function of _the NO _x reduction catalyst temperature TNC and the intake air amount Ga.

In the following step 101, it is determined whether or not the ammonia oxidation catalyst temperature TAC is within the optimum temperature range (FIG. 3). When the ammonia oxidation catalyst temperature TAC is not within the optimum temperature range, the process then proceeds to step 102,
The increase coefficient KI representing the target equivalent ratio is set to 1.0. Next, the routine proceeds to step 104. On the other hand, when the ammonia oxidation catalyst temperature TAC is within the optimum temperature range, the routine proceeds to step 103, where the increase coefficient KI is calculated from the map of FIG. As described above and shown in FIG. 6, the increase coefficient KI in this case depends on the ammonia oxidation catalyst temperature TAC and is proportional to the purification rate EAN (FIG. 3). This increase coefficient KI is based on the ammonia oxidation catalyst temperature TA.
ROM as a function of C in the form of the map shown in FIG.
32. Next, the routine proceeds to step 104. In step 104, the basic supply amount QB of urea is calculated by multiplying the equivalent amount QE by the increase coefficient KI (Q
B = QE · KI). This basic supply amount QB represents the supply amount of urea necessary to make the actual equivalent ratio the target equivalent ratio.

The following steps 105 to 109 are a part for correcting the basic supply amount QB of urea necessary for the storage / release function of the NO _x reduction catalyst 18. That is,
It has been found that the NO _x reduction catalyst 18 configured as described above has a function of storing and releasing urea or ammonia. Although the mechanism of this storage and release is not clear, it is believed that it is adsorbed in the form of urea and desorbed in the form of ammonia. It is to be noted that there is also a concept that it is converted into ammonia after being adsorbed in the form of ammonia or released in the form of urea.

In the case where the NO _x reduction catalyst 18 has a storage / release function as described above, if urea is supplied by the basic supply amount QB, when urea is stored in the NO _x reduction catalyst 18, it is necessary for NO _x reduction. Ammonia shortage, NO
_When urea is released from the _x reduction catalyst 18 in the form of ammonia, the ammonia becomes excessively excessive. Therefore, in this embodiment of the present invention, _the NO _x reduction urea storage amount of the catalyst 18 and to estimate the urea release from _the NO _x reduction catalyst 18, the basic supply quantity Q based on the amount of these urea storage and urea emissions
B is corrected.

This will be described in more detail. NO_xReduction catalyst 1
8, the total amount of urea stored in the urea 8 is calculated as an integrated urea storage amount SQ,
NO per unit time for accumulated urea storage amount SQ_xReturn
The ratio of the amount of urea released from the source catalyst 18 is determined by the release coefficient KR
(<1.0), relative to the amount of urea supplied per unit time
NO per unit time_xUrea stored in the reduction catalyst 18
Assuming that the ratio of the quantity is represented by the storage coefficient KS (<1.0),
NO per unit time _xUrine released from the reduction catalyst 18
The elementary quantity is roughly represented by SQ · KR. That is, SQ
Supply amount of urea per unit time because it is excessive by KR
Q should be QB-SQ · KR. In this case, the unit
NO per hour_xThe amount of urea stored in the reduction catalyst 18 is
Roughly represented by (QB-SQ · KR) · KS,
(QB-SQ · KR) · KS is insufficient.

Therefore, the urea amount Q to be supplied per unit time is expressed by the following equation. Q = (QB−SQ · KR) + (QB−SQ · KR) · KS = (QB−SQ · KR) · (1 + KS) Next, a method of calculating the accumulated urea storage amount SQ will be described. The accumulated urea storage amount SQ and the supply amount Q of urea per unit time in the previous processing cycle are represented by SQOL, respectively.
If expressed by D and QOLD, the amount of urea stored in the NO _x reduction catalyst 18 from the previous processing cycle to the current processing cycle is roughly expressed by QOLD · KS. Further, the amount of urea released from the NO _x reduction catalyst 18 from the previous processing cycle to the current processing cycle is roughly represented by SQOLD · KR. Therefore, the accumulated urea storage amount SQ in the current processing cycle is represented by the following equation.

SQ = SQOLD + QOLD.KS-SQOLD.KR Referring again to FIG. 4, in step 105, the storage coefficient KS is calculated from the map of FIG. Storage coefficient KS is NO
It decreases as the ratio SQ / MAX integrated urea storage amount SQ to the maximum of the urea storage amount MAX possible _x reduction catalyst 18 increases, decreases as the _the NO _x reduction catalyst temperature TNC becomes higher. The storage modulus KS is stored in advance experimentally and calculated by, in the form of a map as a function of the ratio SQ / MAX and _the NO _x reduction catalyst temperature TNC shown in Figure 7 in advance in the ROM 32.

In the following step 106, the release coefficient KR is calculated from the map shown in FIG. Emission coefficient KR increases as the is _the NO _x reduction catalyst temperature TNC becomes higher, to increase as the intake air amount Ga increases. This release coefficient KR
Is stored in advance experimentally and calculated by, in advance in the ROM32 in the form of a map shown in FIG. 8 as a function of _the NO _x reduction catalyst temperature TNC and the intake air amount Ga.

In the following step 107, the accumulated urea storage amount S
Q is calculated (SQ = SQOLD + QOLD · KS−
SQUAD.KR). In the following step 108, the supply amount Q of urea per unit time is calculated (Q = (QB-S
Q · KR) · (1 + KS)). In the following step 109, the accumulated urea storage amount SQ and the supply amount Q of urea per unit time are stored as SQOLD and QOLD, respectively.

In the subsequent step 110, the supply amount QL of the aqueous urea solution per unit time is calculated by multiplying the supply amount Q of urea per unit time by the concentration correction coefficient KC (QL = Q · KC). Here, the concentration correction coefficient KC is determined according to the concentration of the aqueous urea solution supplied from the supply device 24. For example, when a 30% by weight urea aqueous solution is used as the urea aqueous solution, the value of the concentration correction coefficient KC is (100 + 30) /30=4.3. The flow control valve 28 is controlled so that the actual supply amount of the urea aqueous solution per unit time becomes QL.

In the embodiment according to the present invention, NO
The supply amount of urea is determined in consideration of the urea storage / release function of the _x reduction catalyst 18. Therefore, when the ammonia oxidation catalyst temperature TAC is within the optimum temperature range, the actual equivalent ratio may be 1 or less or may be greater than 5.
Further, when the ammonia oxidation catalyst temperature TAC is not within the optimum temperature range, the actual equivalent ratio may be larger than 1.

In the above-described embodiment, the NO _x reduction catalyst 18 and the ammonia oxidation catalyst 21 are separated from each other, and the ammonia oxidation catalyst 21 is disposed in the exhaust passage downstream of the NO _x reduction catalyst 18. However, it is also possible to arrange the _the NO _x reduction catalyst 18 and the ammonia oxidation catalyst 21 on a common carrier arranged ammonia oxidation catalyst 21 into _the NO _x reduction catalyst 18.

Further, the present invention has been described above by taking as an example the case where a urea aqueous solution is used as the liquid containing the ammonia generating compound. In this case, as described above, a compound other than urea can be used as the ammonia-generating compound, and a compound other than water can be used as the solvent. Further, ammonia water or a gas containing ammonia can be supplied into the exhaust passage together with the liquid containing the ammonia generating compound. In this case, the gas containing ammonia can be generated using solid urea.

[0038]

As described above, the NO _x purification rate can be increased while reducing the amount of ammonia discharged into the atmosphere.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a NO _x purification rate EFF of a NO _x reduction catalyst and an ammonia emission amount Q (NH ₃ ).

FIG. 3 is a diagram showing a purification rate EAN of an ammonia oxidation catalyst.

FIG. 4 Amount Q of urea aqueous solution to be supplied per unit time
9 is a flowchart illustrating a calculation routine of L.

FIG. 5 is a diagram showing the urea equivalent QE.

FIG. 6 is a diagram showing an increase coefficient KI.

FIG. 7 is a diagram showing a storage coefficient KS.

FIG. 8 is a diagram showing an emission coefficient KR.

[Explanation of symbols]

1 ... engine body 14 ... exhaust manifold 18 ... NO _x reduction catalyst 21 ... ammonia oxidation catalyst 24 ... feeder 40, 41 ... temperature sensor

Continued on the front page F term (reference) 3G091 AA02 AA17 AA18 AB02 AB03 AB05 BA04 BA14 BA32 BA39 CA16 CA17 CB02 CB07 CB08 DA01 DA02 DB06 DB10 DB13 EA00 EA01 EA05 EA07 EA16 EA17 EA18 EA31 GA16 GB10W GB01X GB06W GB01X GB06 HA GB HA42 4D048 AA06 AA08 AB01 AB02 AB07 AC04 BA07X BA11X BA23X BA30X BA35X BA41X CC47 DA01 DA02 DA06 DA10 DA13

Claims (5)

[Claims] 1. A an oxygen excess of the NO _x reduction catalyst suitable for reducing the NO _x in the exhaust gas by ammonia under placed in the engine exhaust passage, comprising the ammonia generating compound in the _the NO _x reduction catalyst In an exhaust gas purifying apparatus for an internal combustion engine adapted to supply a liquid, an ammonia oxidation catalyst suitable for oxidizing ammonia to nitrogen under an excess of oxygen is NO.
placed _x the reduction catalyst or _the NO _x reduction catalyst in the exhaust passage downstream of, NO _x equivalent ratio of the supply amount of the ammonia generating compound to the NO _x flow rate to the reducing catalyst of the liquid to be greater than 1 An exhaust gas purification device for an internal combustion engine that controls a supply amount. And determining whether or not the temperature of the ammonia oxidation catalyst is within an optimum temperature range. When it is determined that the temperature of the ammonia oxidation catalyst is within an optimum temperature range, the equivalence ratio is set to a value less than 1. 2. The internal combustion engine according to claim 1, wherein when the temperature of the ammonia oxidation catalyst is determined not to be within the optimum temperature range, the supply amount of the liquid is controlled so that the equivalent ratio becomes 1 or less. Exhaust gas purification device. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the supply amount of the liquid is controlled such that the equivalent ratio is greater than 1 and equal to or less than 5. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the ammonia generating compound is urea, and the liquid containing the ammonia generating compound is an aqueous urea solution. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said ammonia oxidation catalyst comprises zeolite.