JPH0612174Y2 - Nisel oxide removal mechanism of diesel engine - Google Patents

Description

Description of the invention The present invention <relates> are nitrogen oxides contained in the exhaust gas of a diesel engine (hereinafter, referred to as NO _X) nitrogen oxides diesel engine can be effectively removed removed It is related to the mechanism.

As a method of reducing the amount of NO _X contained in the exhaust gas of <Prior Art> Diesel engine, by delaying the injection timing of the fuel, the timing retard method is known which is adapted to lower the combustion temperature. However, according to such a timing retard method, with combustion efficiency is deteriorated despite possible to suppress the generation of NO _X, it is possible that black smoke is easily generated.

By the way, since the diesel engine has a higher residual oxygen concentration in the exhaust gas than the gasoline engine, the reducing agent such as hydrogen or carbon monoxide is used as in the case of the gasoline engine to reduce the N in the exhaust gas of the diesel engine.
It is impossible to reduce the O _X.

That is, in a gasoline engine, air and fuel can be burned under a theoretical mixing ratio, so that oxygen in exhaust gas becomes almost zero. However, in the case of a diesel engine, a large amount of oxygen remains in the exhaust gas because it requires about 1.3 times the theoretical mixing ratio of air even at full load operation. Therefore, even if a reducing agent such as hydrogen or carbon monoxide is added to the exhaust gas of a diesel engine having such a high residual oxygen concentration in the presence of a catalyst, the added reducing agent first reacts with oxygen. Therefore, NO _x cannot be reduced because it is lost.

On the other hand, in recent years, NO contained in combustion gas of thermal power plants
_As a method of removing _X , it is said to be effective to add ammonia gas (hereinafter referred to as NH ₃ ) as a reducing agent in the presence of a catalyst. Thus, N as a reducing agent
When H ₃ is used, there is an advantage that NO _{X in} exhaust gas having a high residual oxygen concentration can be effectively removed. This cannot be diverted to the nitrogen oxide removing mechanism of the diesel engine as it is.

That is, in the thermal power plant, since the steady combustion is performed, the temperature and NO _X amount (concentration) of the combustion gas are substantially constant. However, in a diesel engine, the exhaust gas temperature and N
The amount of O _x generated greatly changes, and NH ₃ used as a reducing agent has a strong irritating odor and is toxic. Therefore, N
In order to remove NO _X in the exhaust gas of diesel engines using with H _3, it NH ₃ does not remain in the exhaust gas is strictly controlled amount of NH ₃ in response to generation amount of the NO _X There are various conditions, such as the need to provide an inexpensive control device with excellent reliability and durability that can withstand vibration or heat associated with engine operation. This is because.

In order to overcome these various conditions, the present applicant has
The amount of NO _x in the exhaust gas is measured, and an amount of NH ₃ corresponding to this measured value is added to the exhaust gas in the presence of the catalyst to obtain NO _x.
We have previously proposed a removal method and mechanism for reducing hydrogen (Japanese Patent Application No. 61-201321, etc.).

<Problems to be Solved by the Invention> The present invention was made in order to materialize and put into practical use the above-mentioned removal mechanism, and responds to changes in the operating state of the engine without releasing unreacted NH _3. An object of the present invention is to provide a nitrogen oxide removing mechanism of a diesel engine that can efficiently remove (reduce) NO _X in changing exhaust gas.

<Means for Solving the Problems> In order to solve the above problems, the present invention proposes to add N in exhaust gas in the presence of a titanium oxide catalyst (hereinafter referred to as TiO ₂ catalyst).
In a nitrogen oxide removing mechanism in which H ₃ is added to reduce and remove NO _{X in} exhaust gas, NH ₃ stored in a storage unit that stores NH ₃ is added to exhaust gas of a diesel engine. Addition means and N by the addition means
A catalytic converter having an adjusting means for adjusting the amount of H ₃ added and a TiO ₂ -based catalyst for reducing NO _X in the exhaust gas to which the NH ₃ has been added is provided.

Further, a load sensor for detecting the load of the diesel engine and a rotation speed sensor for detecting the rotation speed are provided, and a temperature sensor for detecting the temperature of the exhaust gas is provided. Then, while calculating the addition amount of NH ₃ corresponding to the estimated generation amount of NO _x obtained by estimating based on the outputs of the load sensor and the rotation speed sensor, the calculated addition amount is calculated based on the output of the temperature sensor. By providing a computer for correcting and correcting the corrected addition amount, when the temperature of the exhaust gas detected based on the output of the temperature sensor does not deviate from the active temperature range of the titanium oxide-based catalyst, it corresponds to the calculated addition amount. While the amount of NH ₃ is added to the exhaust gas, the addition amount of NH ₃ is set to zero when the temperature of the exhaust gas deviates from the activation temperature range of the titanium oxide-based catalyst.

<Operation> When the engine is operated, the load sensor, the rotation speed sensor, and the temperature sensor respectively supply signals corresponding to the engine load, the rotation speed, and the exhaust gas temperature to the computer. Computer generation amount of the NO _X at that time based on a signal the output from each sensor, i.e., estimates calculate the amount of the NO _X to be about to be released into the atmosphere together with the exhaust gases.

Further, the computer calculates the addition amount of NH ₃ corresponding to the estimated generation amount of NO _x obtained by the above estimation, and supplies the control means with a control signal responsive to the calculated addition amount. The adjusting means adds NH ₃ to the exhaust gas from the storage means through the adding means based on the signal supplied from the computer.

The exhaust gas thus added with NH ₃ is supplied to a catalytic converter having a TiO ₂ -based catalyst. Then, in the catalytic converter, NO _X in the exhaust gas is NH ₃
NO _x in the exhaust gas released into the atmosphere can be extremely reduced because it reacts with and is reduced and removed.

On the other hand, when the computer determines that the temperature of the exhaust gas detected based on the output of the temperature sensor deviates from the activation temperature range of the TiO ₂ -based catalyst, a signal indicating that the addition amount of NH ₃ should be zero is issued. Supply to the adjusting means.

Therefore, if the temperature of the exhaust gas deviates from the activation temperature range of the TiO ₂ -based catalyst, the addition of NH ₃ to the exhaust gas will be interrupted and the activity of the TiO ₂ -based catalyst will not be reduced. The release of reactive NH ₃ is prevented. In this way, in the temperature region where the temperature of the exhaust gas deviates from the activation temperature range of the TiO ₂ -based catalyst, the NO _x generation amount is so small as to be negligible, so that no particular problem occurs.

<Embodiment> An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows the NO of the diesel engine according to the present invention.
FIG. 3 is a block diagram showing an embodiment of an _X removal mechanism, in which an exhaust pipe 2 of a diesel engine 1 is exhausted through a switching valve 3 to an exhaust main pipe.
21 and a branch pipe 22 are branched. The exhaust main pipe 21 is provided with a catalytic converter 4 filled with a TiO ₂ -based catalyst, and is joined to a branch pipe 22 at a portion downstream of the catalytic converter 4 and connected to a muffler (not shown).

An NH ₃ injection nozzle 7 functioning as an addition means is provided in an upstream portion of the exhaust main pipe 21 of the catalytic converter 4. Further, by connecting the NH ₃ injection nozzle 7 and the NH ₃ tank 5 via a flow rate adjusting valve 6 provided as an adjusting means, NH ₃ can be added and supplied to the exhaust gas flowing into the catalytic converter 4. .

On the other hand, a load sensor 8 for detecting the load of the diesel engine 1 and a rotation speed sensor 9 for detecting the rotation speed are provided. Further, a temperature sensor 10 for detecting the temperature of the exhaust gas is provided in the exhaust main pipe 21 upstream of the catalytic converter 4 and downstream of the NH ₃ injection nozzle 7. And each sensor 8,
Computer 11 to which signals output from 9 and 10 are supplied
Is provided, the computer 11 controls the switching valve 3 and the flow rate adjusting valve 6.

The NH ₃ tank 5, NH ₃ in the NH ₃ tank 5
An NH ₃ amount sensor 12 for detecting the amount is provided. Also, N
By connecting of H ₃ amount sensor 12 to the computer 11, NH ₃ amount of NH ₃ tank 5 is to actuate the alarm means 13 when it is below a predetermined amount. In addition,
The alarm means 13 is composed of, for example, a warning lamp.

Therefore, it is sufficient to replenish the NH ₃ tank 5 with NH ₃ when the alarm means 13 is activated. Sokoroga can not replenish the NH ₃ during operation of the alarm means 13, when the NH ₃ in the NH ₃ tank 5 runs out on the fact, the diesel engine 1 by sending a signal from the computer 11 to the fuel injection pump 14 The fuel supply amount (injection amount) is reduced to suppress the generation of NO _X itself.

When the diesel engine 1 is operated in the nitrogen oxide removing mechanism of the diesel engine having the above-described configuration, the load sensor 8 and the rotation speed sensor 9 respectively output signals corresponding to the load and the rotation speed at that time to the computer 11. Is supplied to. Further, the exhaust gas discharged from the exhaust pipe 2 along with the operation of the diesel engine 1 flows into the exhaust main pipe 21 through the switching valve 3, and the NH ₃ injection nozzle 7
Catalytic converter 4 mixed with NH ₃ added and supplied from
Flow into.

Inside the catalytic converter 4, the following general formulas (1) and (2)
Accordingly, NO _X in the exhaust gas is reduced and removed.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1) 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (2) By the way, the amount of NO _X to be reduced and removed in this way,
That is, the generation amount of the NO _X in the combustion chamber, when the constant rotational speed of the engine 1 is proportionally increased with an increase in the load of the engine 1 as shown in FIG. 2, in the figure a There is a tendency for the load to decrease when the load exceeds the specified load shown. When the load on the engine 1 is constant,
The amount of NO _x generated tends to increase as the rotation speed increases. Thus, it to be grasped amount of NO _X in the exhaust gas by measuring the rotational speed and the load of the engine 1, usually a may control the amount of NH ₃ in response to a load and the rotational speed of the engine 1 become.

However, the temperatures of the exhaust gas and the catalyst depend on the engine 1.
Change with a delay due to the load change, and the delay time of such temperature change is not always constant. For this reason, N is set in correspondence with only the load and the number of revolutions of the engine 1.
When the amount of H ₃ added is determined, a large amount of NH ₃ may be supplied and unreacted NH ₃ may be released even if the temperature of the catalyst deviates from the activation temperature range.

On the other hand, the amount of NO _X in the exhaust gas increases as the combustion temperature rises due to an increase in load or rotation speed, and TiO ₂ used as a catalyst has a relatively high temperature range (200 ° C).
The activity becomes higher at ~ 500 ° C.

Focusing on such a situation, in the present invention, the amount of NH ₃ added to the exhaust gas in the presence of the catalyst is controlled in response to the load of the engine 1, the rotational speed and the temperature of the exhaust gas. It was done.

That is, the computer 11 estimates the amount of NO _X generated based on the outputs of the load sensor 8 and the rotation speed sensor 9 (load and rotation speed of the engine 1), and calculates the addition amount of NH ₃ corresponding to this estimated generation amount. To obtain the calculated addition amount. Further, the computer 11 corrects the calculated addition amount according to the output of the temperature sensor 10 (the temperature of the exhaust gas supplied to the catalytic converter 4).

When the temperature of the exhaust gas detected based on the output of the temperature sensor 10 is within the activation temperature range of the catalyst, the signal corresponding to the calculated addition amount is output to the flow rate adjusting valve 6 without correction and the engine 1 An amount of NH ₃ calculated based on the load and the number of revolutions is added to the exhaust gas. For this,
Since the amount of NH ₃ responsive to the estimated amount of NO _x generated, which is estimated based on the load and the rotation speed of the engine 1, is supplied, the NO _x in the exhaust gas is efficiently reduced / removed.

On the other hand, when the temperature of the exhaust gas detected based on the output of the temperature sensor 10 deviates from the activation temperature range of the catalyst, the addition of NH ₃ is interrupted to correct the calculated addition amount to zero.

Therefore, even if the load and the rotational speed of the engine 1 are high, the temperature of the exhaust gas is low and it is difficult to carry out the reducing action by the catalyst, or the reducing action causes the temperature of the catalyst to rise abnormally and become active. When the exhaust gas temperature may decrease, that is, when the exhaust gas temperature deviates from the activation temperature of the catalyst, the amount of NH ₃ added to the exhaust gas is made zero. For this reason, secondary problems due to the release of unreacted NH ₃ do not occur, and damage to the catalyst is also avoided. In the region where the temperature of the exhaust gas deviates from the active temperature range of the catalyst, the amount of NO _x generated is extremely small, so no particular problem occurs even if the amount of NH ₃ added is zero.

Thus, the temperature of the exhaust gas based on the output of the temperature sensor 10 is within the range of 200 ° C. to 500 ° C., which is the activation temperature of the TiO ₂ -based catalyst, and based on the outputs of the load sensor 8 and the rotation speed sensor 9, The exhaust pipe 2 is connected to the exhaust main pipe 21 via the switching valve 3 when the NO _x generation amount calculated by the above is greater than or equal to b in FIG. 2, for example. By adjusting the opening of flow control valve 6 in the signal from the computer 11 directs the NH ₃ that is stored in NH ₃ tank 5 to the NH ₃ injection nozzle 7, the estimated from the NH ₃ injection nozzle 7 The amount of NH ₃ corresponding to the amount generated is added to the exhaust gas and supplied to the catalytic converter 4. The temperature of the exhaust gas is 200 ° C
Alternatively, when the temperature is near 500 ° C., that is, near the boundary of the activation temperature range of the catalyst, the addition amount of NH ₃ is corrected to be reduced in consideration of the reduction of the reducing function of the catalyst.

Further, when the temperature of the exhaust gas detected based on the output of the temperature sensor 10 deviates from the active region of the TiO ₂ -based catalyst, NO _X
Since the generation amount of NOx is small, it is not necessary to remove NO _X in the exhaust gas, and the reduction removal efficiency by the catalytic converter is also extremely low. Therefore, when the temperature of the exhaust gas is low as described above, the flow rate adjusting valve 6 is closed and the switching valve 3 is switched by the signal from the computer 11 to switch the exhaust pipe 2 to the branch pipe 22 to connect the exhaust gas. The catalyst converter 4 is prevented from being clogged by black smoke or fine particles in the gas, and the decrease in the activity of the TiO ₂ -based catalyst due to the adhesion of the black smoke or fine particles is prevented.

On the other hand, based on the output of the quantity detection sensor 12, the NH ₃ tank 5
When it is detected that the amount of NH ₃ in the inside is less than the predetermined amount, the computer 11 activates the alarm means 13 and
Warns of lack of H ₃ content. Therefore, the driver may receive this warning and replenish the NH ₃ tank 5 with NH ₃ .

Further, there is a possibility that NH ₃ reduced NH ₃ amount in the NH ₃ tank 5 still can not be added when no supplemented with regardless NH ₃ in such a warning. Therefore, when the NH ₃ is not replenished during the operation of the alarm means 13 as described above, a signal indicating that the injection amount should be reduced is supplied from the computer 11 to the fuel injection pump 14 to change the fuel injection amount. The decrease correction is performed to suppress the generation of NO _X , the switching valve 3 is switched to guide the exhaust gas to the branch pipe 22, and the flow rate adjusting valve 6
To close the valve.

The exhaust gas flowing out from the catalytic converter 4 and the exhaust gas supplied to the branch pipe 22 are discharged into the atmosphere through a muffler (not shown). However, the NO _x contained in this exhaust gas is a negligible amount that is substantially negligible, and since the unreacted NH ₃ is not contained in this exhaust gas, a secondary problem occurs. Nothing.

In the above embodiment, the catalytic converter 4 is provided in the exhaust main pipe 21, the branch pipe 22 is connected to the exhaust main pipe 21 in parallel, and the switching valve 3 is provided in the branch portion of both pipes 21, 22 to achieve N
When H ₃ is not added, the exhaust pipe 2 is switched and connected to the branch pipe 22 to prevent clogging of the catalyst due to black smoke or fine particles contained in the exhaust, but the branch pipe 22 is not necessarily provided. There is no need.

<Effect of Device> As is apparent from the above description, according to the present invention, the amount of NO _x generated is estimated based on the engine load and engine speed, and the amount of NH ₃ added corresponding to this estimated amount is calculated. After calculation, determine whether the temperature of the exhaust gas deviates from the activation temperature range of the titanium oxide-based catalyst, and if it does not deviate from the activation temperature range, it corresponds to the addition amount calculated by the above calculation. A certain amount of NH ₃ is added to the exhaust gas, but when the temperature of the exhaust gas deviates from the activation temperature range of the titanium oxide-based catalyst, the calculated addition amount is set to zero and the addition to the exhaust gas is interrupted. Therefore, the optimum amount of NH ₃ corresponding to the reducing ability of the catalytic converter is added to the exhaust gas. Therefore, unreacted NH ₃ released into the atmosphere without impairing the removal efficiency of NO _{X in} the exhaust gas.
The amount of can be minimized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a nitrogen oxide removing mechanism of a diesel engine according to the present invention, and FIG. 2 is an engine load and NO when the engine speed is constant.
It is a graph which shows the relationship of _X generation amount. 1 ...... diesel engine, 2 ...... exhaust pipe 21 ...... exhaust main pipe, 22 ...... branch pipe 3 ...... switching valve, 4 ...... catalytic converter 5 ...... NH ₃ tank, 6 ...... flow regulating valve 7 ...... NH ₃ injection nozzle, 9-rotation speed sensor 10-temperature sensor, 11-computer 12-NH ₃ amount detection sensor, 13-alarm means 14-fuel injection pump

Claims (1)

[Scope of utility model registration request] 1. A storage means for storing ammonia gas, an addition means for adding the ammonia gas stored in the storage means to the exhaust gas of a diesel engine, and an addition amount of the ammonia gas by the addition means are adjusted. Adjusting means, a catalytic converter having a titanium oxide-based catalyst that reduces nitrogen oxides in the exhaust gas to which the ammonia gas has been added, a load sensor that detects the load of the diesel engine, and a rotational speed of the engine. A rotation sensor,
While calculating the addition amount of ammonia gas corresponding to the estimated generation amount of nitrogen oxides obtained by estimating based on the output of the temperature sensor for detecting the temperature of exhaust gas and the load sensor and the rotation speed sensor, this calculation When the temperature of the exhaust gas detected based on the output of the temperature sensor does not deviate from the activation temperature range of the titanium oxide-based catalyst by providing a computer that corrects the addition amount based on the output of the temperature sensor to obtain the corrected addition amount While adding the amount of ammonia gas corresponding to the calculated addition amount to the exhaust gas, when the temperature of the exhaust gas deviates from the activation temperature range of the titanium oxide-based catalyst, the addition amount of ammonia gas should be set to zero. The nitrogen oxide removing mechanism of the diesel engine, which is characterized by the above.