JP2011242236A - Sulfur component detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sulfur component detecting device for estimating a retaining amount of SOretained in a SOretaining portion, which can detect an integrated amount of SOhaving passed through an exhaust passage during a relatively-long period even if a sulfur poisoning recovery process of a NOcatalytic device arranged at a downstream side is performed.SOLUTION: A sulfur component detecting device 4 includes a retaining portion capable of retaining SOin exhaust gas passing through an exhaust passage 1 and estimates a retaining amount of SOretained in the SOretaining portion. A NOcatalytic device 2 for retaining NOand SOin the exhaust gas is arranged in the exhaust passage such that the retained SOis not released from the retaining portion during a recovery process of the NOcatalytic device which releases the retained SOfrom the NOcatalytic device by heating up the NOcatalytic device to be a preset temperature.

Description

  The present invention relates to a sulfur component detection device.

An SO _X concentration sensor for detecting the SO _X concentration in exhaust gas is known. A general SO _X concentration sensor measures the electromotive force generated when SO _X changes to sulfate ions in a solid electrolyte, and detects the SO _X concentration in the exhaust gas. However, the SO _X concentration sensor for detecting the SO _X concentration in such instant, when the low SO _X concentration in the exhaust gas, it is difficult to detect an accurate SO _X concentration.

Although such an instantaneous SO _X concentration in the exhaust gas cannot be detected, even if the SO _X concentration in the exhaust gas is low, the cumulative amount of SO _X that has passed through the exhaust passage during a certain period is relatively large. A sulfur component detection device that can be detected accurately has been proposed (see Patent Document 1).

This sulfur component detection device has a SO _X holding part that holds SO _X in the exhaust gas as a sulfate, and passes through the exhaust passage for a certain period based on the SO _X holding amount held in the SO _X holding part. Thus, the integrated amount of SO _X is detected.

By the way, an NO _x catalyst device for holding NO _x in the exhaust gas as nitrate is arranged in the exhaust passage. Such NO _X catalyst device can not be held indefinitely NO _X, has _the NO _X holding possible amount. Before _the NO _X holding amount of the NO _X catalyst device reaches the NO _X holdable amount, regeneration process is performed to make the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or a rich air-fuel ratio, holding thereby the NO _X catalyst device The released NO _x can be released and reduced and purified. The NO _x catalyst device retains SO _x in the exhaust gas as sulfate by the same mechanism as NO _x . Since sulfate is a stable substance compared to nitrate, SO _x is released depending on regeneration treatment. Therefore, the amount of SO _X retained increases while the amount of NO _X retained decreases as the amount of SO _X retained increases (S poisoning).

The aforementioned sulfur component detecting device disposed on the upstream side of the NO _X catalyst device, by detecting the cumulative amount of SO _X passing through the exhaust passage during a predetermined period, detects the stored SO _X amount of the NO _X catalyst device can do. Thus, when the stored SO _X amount of the NO _X catalyst device reaches a set amount, S as poisoning recovery process, the NO _X catalyst device was raised to a set temperature by increasing the temperature of exhaust gas flowing into the NO _X catalyst device Immediately after that, by making the air-fuel ratio of the exhaust gas flowing into the NO _x catalyst device rich, the SO _x held as sulfate is released to the NO _x catalyst device to recover the NO _x holdable amount. be able to.

JP2008-175623 JP2010-019092A

However, when such an SOX poisoning recovery process of the NO _x catalyst device is carried out, SO _x may be unintentionally released from the SO _x holding part of the sulfur component detection device. it becomes impossible to detect the cumulative amount of SO _X passing through the exhaust passage between the target long period.

Accordingly, an object of the present invention, the sulfur component detecting device for estimating the stored SO _X amount held in the stored SO _X unit, and the S-poisoning recovery process of the NO _X catalyst device disposed downstream is performed Also, it is possible to detect the integrated amount of SO _X that has passed through the exhaust passage during a relatively long period.

According to a first aspect of the present invention, there is provided a sulfur component detection device comprising a holding portion capable of holding SO _{X in} exhaust gas passing through an exhaust passage, and the SO _X holding amount held in the SO _X holding portion. a sulfur component detecting device for estimating the exhaust passage, NO _X catalyst device for holding the NO _X and SO _X in the exhaust gas is arranged, by elevating the temperature of the NO _X catalyst device to the set temperature the nO _X sO _X held from the holding portion during the recovery process of the catalyst device to release sO _X held from the nO _X catalyst device is characterized in that so as not to be released.

Sulfur component detecting device as claimed in claim 2 of the present invention, in the sulfur component detecting device as claimed in claim 1, and stored SO _X material for holding the SO _X are supported on the holding portion, the NO _X catalyst device The NO _X holding material that is supported on the NO _X and SO _X and is different from the NO _X holding material, and the SO _X holding material of the holding portion is at a temperature higher than the set temperature of the recovery process of the NO _X catalyst device. It is characterized by not releasing the retained SO _x unless the temperature is raised.

According to the sulfur component detecting device as claimed in claim 1 according to the present invention, the SO _X in the exhaust gas passing through the exhaust passage comprising a holding portion configured to hold, SO held in the stored SO _X part _X holding a sulfur component detecting device for estimating the amount in the exhaust passage, NO _X catalyst device for holding the NO _X and SO _X in the exhaust gas is arranged, by elevating the temperature of the NO _X catalyst device to the set temperature NO for sO _X held from the holding portion during the recovery process of the nO _X catalyst device for releasing sO _X held from _X catalyst device is prevented is released, and the recovery process of the nO _X catalyst device is performed also, never integrated amount of SO _X in the holding portion of the sulfur component detecting device is reset, is possible to detect the cumulative amount of SO _X passing through the exhaust passage during a relatively long period of time by a sulfur component detecting device it can.

According to the sulfur component detecting device as claimed in claim 2 according to the present invention, the sulfur component detecting device as claimed in claim 1, and stored SO _X material carried on the holding portion for holding the SO _X, NO _X catalyst device As long as the temperature of the SO _X holding material of the holding portion is not raised to a temperature higher than the set temperature of the recovery process of the NO _X catalyst device, the NO _X holding material is different from the NO _X holding material that holds NO _X and SO _X. The retained SO _x is not released, so that the accumulated amount of SO _{x in} the holding portion of the sulfur component detection device is not easily reset even when the recovery process of the NO _x catalyst device is performed. It is possible to detect the integrated amount of SO _x that has passed through the exhaust passage during a relatively long period by the sulfur component detection device.

It is the schematic which shows the engine exhaust system by which the sulfur component detection apparatus by this invention is arrange | positioned. It is a schematic sectional drawing which shows embodiment of the sulfur component detection apparatus by this invention.

FIG. 1 is a schematic view showing an engine exhaust system in which a NO _x detecting device according to the present invention is arranged. In FIG. 1, 1 is an exhaust passage of an internal combustion engine. The internal combustion engine is an internal combustion engine that performs lean combustion, such as a diesel engine or a direct injection spark ignition internal combustion engine. The exhaust gas of such an internal combustion engine, in order to contain a relatively large amount of NO _X, in the exhaust passage 1, NO _X catalyst device 2 for purifying NO _X is arranged.

The NO _X catalyst device 2 carries a NO _X holding material and a noble metal catalyst such as platinum Pt. The NO _x holding material is at least one selected from alkali metals, alkaline earth metals, or rare earths such as lanthanum La and yttrium Y.

When the exhaust gas has a lean air-fuel ratio, that is, when the oxygen concentration in the exhaust gas is high, the NO _x catalyst device 2 holds NO _x in the exhaust gas well, that is, absorbs it well as nitrate. , NO ₂ adsorbs well. However, it is not possible to hold an unlimited number of NO _X, before _the NO _X holding amount becomes impossible to retain the more NO _X reached the NO _X holdable amount, as the reproduction process, the air-fuel ratio of the exhaust gas The stoichiometric air-fuel ratio or rich air-fuel ratio is set, that is, the oxygen concentration in the exhaust gas is reduced. As a result, the retained NO _x is desorbed, that is, the absorbed NO _x is released, and the adsorbed NO ₂ is desorbed, and these desorbed NO _x is reduced and purified to N ₂ by the reducing substance in the exhaust gas.

When such NO _X catalyst device 2 occludes SO _X in the exhaust gas as sulfate, since sulfate is a stable substance compared to nitrate, it cannot be released in the regeneration process. The amount of NO _{x that} can be retained is reduced (S poisoning). Thus, when the stored SO _X amount of the NO _X catalyst device 2 has reached the set amount, for example, by increasing the temperature of the exhaust gas flowing into the NO _X catalyst device 2 to the set temperature NO _X catalyst device 2 to the set temperature The temperature is raised, and then the recovery process for reducing the oxygen concentration in the exhaust gas is performed by setting the air-fuel ratio of the exhaust gas to the stoichiometric or rich air-fuel ratio, so that SO _X is released from the NO _X catalyst device 2. It has become.

By disposing the sulfur component detecting device 4, capable of detecting the cumulative amount of SO _X passing through the exhaust passage 1 in a period of time on the upstream side of the NO _X catalyst device 2, NO _X catalyst device 2 of stored SO _X As an amount, the integrated value of the amount of SO _x flowing into the NO _x catalyst device 2 can be detected.

3 is a catalyst device (an oxidation catalyst device or a three-way catalyst device) having an oxidation function, which is disposed upstream of the sulfur component detection device 4. When exhaust gas containing a large amount of oxygen and fuel at the time of lean combustion of the internal combustion engine are caused to flow into the catalyst device 4 (lean as the air-fuel ratio of the exhaust gas), the fuel uses oxygen in the exhaust gas in the catalyst device 4. Te satisfactorily burned, thereby raising the temperature of exhaust gas flowing through the combustion heat to the NO _X catalyst device 2 to the set temperature. The fuel burned in the catalyst device 4 may be supplied to the exhaust passage 1 upstream of the catalyst device 4 or may be supplied into the cylinder in the expansion stroke or the exhaust stroke.

FIG. 2 is a schematic longitudinal sectional view showing an embodiment of the sulfur component detection device 4 according to the present invention. In the figure, reference numeral 10 denotes an outer wall of the exhaust gas passage 1. 41 is a substrate of the sulfur component detection device 4. A temperature sensor 42 such as a thermocouple is disposed on one side of the substrate 1 (preferably on the exhaust upstream side). An electric heater 43 is arranged on the other side of the substrate 1. Reference numeral 44 denotes a holding portion for NO _x and SO _x arranged so as to cover the temperature sensing portion of the temperature sensor 42. Reference numeral 45 denotes a cylindrical case that surrounds the sulfur component detection device 4 thus configured and penetrates the outer wall 10 of the exhaust gas passage 1.

  A plurality of opening holes 45 a are formed in the case 45, and exhaust gas that passes through the exhaust passage 1 flows into the case 45 through the opening holes 45 a. Reference numeral 46 denotes an oxygen pump for supplying oxygen (for example, oxygen in the atmosphere) to the vicinity of the holding portion 44 in the case 45. The oxygen pump 46 is positioned around the integrated temperature sensor 42, the substrate 41, and the electric heater 43. The space around the holding portion 44 in 45 is separated from the atmospheric chamber. The oxygen pump 46 is formed of zirconia or the like, and is capable of moving oxygen in the atmosphere to the vicinity of the holding portion 44 in the case 45 by applying a voltage contrary to the zirconia oxygen concentration sensor.

Holding unit 44 is for holding the SO _X in the exhaust gas, for example, and _the NO _X holding material described above as the stored SO _X material, the temperature sensitive portion of the temperature sensor 42 and a noble metal catalyst such as platinum Pt It can be formed by coating.

The holding unit 44 supporting the SO _X holding material oxidizes SO _X in the exhaust gas by the noble metal catalyst when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, that is, when the oxygen concentration of the exhaust gas is high. As a sulfate, it can be retained up to the SO _x retention capacity. The amount of SO _{X that} can be held by the holding portion 44 can be determined in accordance with the amount of SO _X holding material that is carried. The holding portion 44, corresponding to the difference between the stored SO _X amount capable and the current stored SO _X amount for holding the NO _X in the exhaust gas as nitrate was oxidized by the noble metal catalyst. In the holding unit 44, sulfate is a substance that is more stable than nitrate, and the sulfate is increased by replacing the nitrate, and the retention of SO _x proceeds.

Thus, by detecting the current of the NO _X holding of the holding portion 44, SO based on _X holdable amount, so far it is possible to estimate the current stored SO _X amount held in the sulfur component detecting device 4, The estimated SO _X retention amount can be considered as a constant ratio of the integrated amount of SO _X that has passed through the exhaust passage 1 at the position of the sulfur component detection device 4 during a certain period.

In order to detect the current NO _x retention amount in the holding unit 44, the air-fuel ratio of the exhaust gas may be richer than the stoichiometric air-fuel ratio (or the stoichiometric air-fuel ratio), and the oxygen concentration in the exhaust gas may be reduced. only NO _X from the holding portion 44 is brought into reduced by a reducing agent in the exhaust gas is discharged.
1 / 2Ba (NO ₃ ) ₂ → 1 / 2BaO + NO + 3 / 4O ₂ -309.6kJ / mol
CO + NO → 1 / 2N ₂ + 2CO ₂ + 373.2kJ / mol
3 / 2CO + 3 / 4O ₂ → 3 / 2CO ₂ + 424.5kJ / mol

In this way, about 490 kJ is generated for 1 mol of released NO. Accordingly, the temperature rise value of the holding unit 44 before and after the exhaust gas air-fuel ratio is made rich, that is, the maximum temperature of the holding unit 44 after the exhaust gas air-fuel ratio is made rich, and the exhaust gas The temperature sensor 42 detects the difference (temperature rise value) from the temperature of the holding unit 44 before the rich air-fuel ratio is made to be the air-fuel ratio, so that the total NO _x amount released from the holding unit 44 is It can be detected as the NO _x retention amount.

  In order to make the air-fuel ratio of the exhaust gas rich, the additional fuel is supplied to the exhaust passage 1 upstream of the catalyst device 3 even if the additional fuel is injected into the cylinder in the expansion stroke or the exhaust stroke. Also good.

Meanwhile, the stored SO _X material carried on the holding portion 44 of the sulfur component detecting device, NO _X catalyst in the case of a supported _the NO _X holding material was the same material in the apparatus, NO _X catalyst device 2 from SO _X to carry out the recovery process for releasing, by increasing the temperature of the exhaust gas flowing into the NO _X catalyst device 2 to the set temperature, then, when the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or a rich air-fuel ratio, the sulfur component Since the holding unit 44 of the detection device is also raised to the set temperature (recovery processing temperature) and the surrounding oxygen concentration is lowered, SO _X is also released from the holding unit 44. As a result, the accumulated amount of SO _x in the holding unit 44 is unintentionally reset, and thus the accumulated amount of SO _x that has passed through the exhaust passage during a relatively long period is detected by the sulfur component detection device 4. I can't do that.

In the present embodiment, the stored SO _X material carried on the holding portion 44 of the sulfur component detecting device, NO _X catalyst device has the _the NO _X holding material and a different material carried on, stored SO _X of the holding portion 44 The material does not release the retained SO _x unless the temperature is raised to a temperature higher than the set temperature of the recovery process of the NO _x catalyst device.

For example, the SO _x holding material carried on the holding unit 44 of the sulfur component detection device is potassium K having a particularly high basicity among alkali metals, and the NO _x holding material carried on the NO _x catalyst device is sodium Na At least one selected from alkali metals such as lithium Li and cesium Cs, alkaline earth metals such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y.

As a result, when the NO _x holding material carried on the NO _x catalyst device is set to about 650 ° C. as the set temperature for the recovery process and the surrounding oxygen concentration is lowered, the held SO _x is released. Potassium K as the SO _X holding material carried on the holding unit 44 of the sulfur component detection device does not release the held SO _X unless the ambient oxygen concentration is lowered by about 700 ° C.

Thus, even if the S poison recovery process of the NO _x catalyst device 2 arranged on the downstream side is performed, the integrated amount of SO _x in the holding unit 44 is not reset, and the sulfur component detection device 4 relatively it is possible to detect the cumulative amount of SO _X passing through the exhaust passage during a long period.

Further, the SO _X holding material carried on the holding unit 44 of the sulfur component detection device is made an alkali metal having a recovery processing set temperature of 650 ° C. or more, and the NO _X holding material carried on the NO _X catalyst device is recovered. It is good also as an alkaline-earth metal whose processing preset temperature is about 600 degreeC.

Further, if the NO _x catalyst device is a cordierite or metal base, and the NO _x holding material is a layer of zeolite, alumina, zirconia, titania, etc., iron Fe or silver Ag is supported. NO _X catalyst device as, if it is about 500 ° C as a setting temperature of the recovery process, in order to release the sO _X held, sO _X held carried on the holding portion 44 of the sulfur component detecting device The materials are alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earth metals such as barium Ba, calcium Ca, lanthanum La, yttrium Y, and the like. Or at least one selected from rare earths such as

In addition, the holding unit 44 of the sulfur component detection device 4 holds the NO _X catalyst device 2 during the recovery process of the NO _X catalyst device that raises the NO _X catalyst device 2 to a set temperature and releases the SO _X held from the NO _X catalyst device 2. it suffices so sO _X is not released to the holding example, the stored sO _X material carried on the holding portion 44 for holding the sO _X, the are carried in the nO _X catalyst device 2 nO _X and sO _X Even if the NO _x holding material to be used is the same substance, if the cooling means (air blowing means or cooling water circulation means) for cooling the holding portion 44 is provided during the recovery process of the NO _X catalyst device, the holding portion The temperature 44 can be prevented from being raised to the set temperature for the recovery process, and SO _x can be prevented from being released even when the surrounding oxygen concentration is lowered.

Thus, even if the recovery process of the NO _x catalyst device 2 is performed, if SO _x is not released from the holding unit 44 of the sulfur component detection device 4, the SO _x holding amount of the holding unit 44 of the sulfur component detection device 4 is in order to not correspond to the stored SO _X amount of the NO _X catalyst device 2, is no longer possible to stored SO _X amount also NO _X catalyst device 2 is multiplied by a set factor stored SO _X amount of holding portion 44 .

However, when the recovery process of the NO _x catalyst device 2 is performed and all the SO _x is released from the NO _x catalyst device 2, if the SO _x retention amount M 0 of the holding unit 44 of the sulfur component detection device 4 is detected, by multiplying the set coefficients from stored SO _X amount M1 of the current holding section 44 to a value obtained by subtracting the M0, it may be the current stored SO _X amount of the NO _X catalyst device 2.

If it is necessary to reset the SO _X retention amount of the holding unit 44 of the sulfur component detection device 4, the temperature of the holding unit 44 is raised to the set temperature of the recovery process for the holding unit 44, and the surrounding oxygen concentration By reducing the above, SO _x can be released from the holding portion 44.

By the way, when the holding part 44 of the sulfur component detection device 4 holds NO _x in the exhaust gas as nitrate, when oxygen is supplied in the vicinity of the holding part 44, the NO in the exhaust gas is supplied to the supplied oxygen. Thus, it is oxidized to NO ₂ and then easily held in the holding unit 44 as nitrate. Depending on the engine operating state, the oxygen concentration of the exhaust gas flowing into the case 45 may be relatively low, so the air-fuel ratio of the exhaust gas is intentionally different, such as the NO _x release process from the holding unit 44. It is preferable that the oxygen pump 46 is operated to supply oxygen to the vicinity of the holding unit 44 so that NO in the exhaust gas is easily held by the holding unit 44, particularly during the period when the gas is made rich. It is preferable to set the air-fuel ratio of the exhaust gas near 44 to about 40 or more. Also, because the holding portion 44 does not sufficiently retain the SO _X in the exhaust gas is cold, it is preferred to warm up the holding portion 44 by the electric heater 43 immediately after engine startup.

1 exhaust passage 2 NO _X catalyst device 3 catalyst device 4 sulfur component detecting device

Claims (2)

A sulfur component detection device comprising a holding part capable of holding SO _X in exhaust gas passing through an exhaust passage and estimating the amount of SO _X held in the SO _X holding part, is, NO _X catalyst device for holding the NO _X and SO _X in the exhaust gas is arranged, the NO _X catalyst device was heated to the set temperature the NO _X catalyst device the NO for releasing SO _X held from _The sulfur component detection device, wherein the held SO _x is not released from the holding portion during the recovery process of the _X catalyst device. A stored SO _X material for holding the SO _X are supported on the holding portion, said being carried in the NO _X catalyst device and _the NO _X holding material for holding the NO _X and SO _X is different materials, the holding portion 2. The sulfur component according to claim 1, wherein the SO _X holding material does not release the held SO _X unless the temperature is raised to a temperature higher than the set temperature of the recovery process of the NO _X catalyst device. Detection device.

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