JP2011149769A - Sulfur component detecting device - Google Patents

Abstract

Provided is a sulfur component detecting device for estimating the stored SO _X amount held in the stored SO _X unit, relatively accurately to enable estimates stored SO _X amount.
And A stored SO _X amount capable to retain possible holding portion 32 SO _X in the exhaust gas passing through the exhaust passage when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, measure the temperature of the holding portion The temperature sensor 31 and an oxidation catalyst arranged around the holding unit, and when estimating the current SO _X holding amount of the holding unit, the air-fuel ratio of the exhaust gas is determined from the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. made rich, the temperature rise value of the holding portion by the temperature sensor by reducing the stored SO _X amount capable and reducing substance to release NO _X held in response to the difference between the current stored SO _X amount from the holding portion To detect.
[Selection] Figure 2

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 unit that holds SO _X contained in the exhaust gas when the oxygen concentration in the exhaust gas is high, and is constant based on the SO _X holding amount held in the SO _X holding unit. and to detect the cumulative amount of sO _X passing through the exhaust passage during the period.

JP2008-175623 JP2007-183243

In the foregoing sulfur component detecting device, stored SO _X portion can hold the SO _X as the sulphate to stored SO _X amount capable corresponds to the difference between the stored SO _X amount capable and the current stored SO _X amount Thus, NO _x in the exhaust gas is retained as nitrate. Nitrate is an unstable substance compared to sulfate, and if the air-fuel ratio of the exhaust gas is made rich to lower the oxygen concentration in the exhaust gas, only NO _X held in the SO _X holding part is SO. _X can be released from the holding part and reduced by CO in the exhaust gas.

SO thereby estimate the _the NO _X holding amount held in the stored SO _X unit based on the amount of heat generated during the reduction of NO _X, based on the stored SO _X amount capable of stored SO _X portion and _the NO _X holding amount It is conceivable to estimate the current SO _X holding amount of the _X holding unit. However, the exhaust gas contains not only CO but also HC as a reducing substance, and when a part of NO _x is reduced by HC, the amount of heat generated during the reduction of NO _x differs between CO and HC. Therefore, if the NO _X retention amount is estimated based on the calorific value assuming that all NO _X is reduced by CO, it is difficult to estimate the NO _X retention amount accurately, and the SO _X retention amount is accurately estimated. May not be possible.

Accordingly, an object of the present invention is to make it possible to estimate the SO _X retention amount relatively accurately in the sulfur component detection device that estimates the SO _X retention amount retained in the SO _X retention portion.

Sulfur component detecting device as claimed in claim 1 according to the invention, capable of holding the SO _X in the exhaust gas air-fuel ratio of the exhaust gas passes through the exhaust passage when a leaner than the stoichiometric air-fuel ratio to the stored SO _X amount capable A holding unit, a temperature sensor for measuring the temperature of the holding unit, and an oxidation catalyst arranged around the holding unit, and when estimating the current SO _X holding amount of the holding unit, the air-fuel ratio is richer than the stoichiometric air-fuel ratio or stoichiometric air-fuel ratio, by the stored SO _X amount capable and reducing substance to release NO _X held in response to the difference between the current stored SO _X amount from the holding portion The temperature rise value of the holding part is detected by the temperature sensor after reduction.

A sulfur component detection device according to a second aspect of the present invention is the sulfur component detection device according to the first aspect, further comprising a heater for heating the oxidation catalyst, wherein the current SO _{X of the} holding unit. When estimating the holding amount, when the temperature of the oxidation catalyst is lower than a set temperature, the heater is operated to raise the temperature of the oxidation catalyst to the set temperature or higher.

According to the sulfur component detection device of the first aspect of the present invention, the oxidation catalyst is disposed around the holding unit, and when estimating the current SO _X holding amount of the holding unit, the exhaust gas empty space is estimated. ratio to richer than the stoichiometric air-fuel ratio or stoichiometric air-fuel ratio, by reduced by a reducing agent by stored SO _X amount capable and releasing NO _X held in response to the difference between the current stored SO _X amount from the holding portion The temperature rise value of the holding unit is detected by the temperature sensor, and HC contained in the exhaust gas having the stoichiometric air-fuel ratio or the air-fuel ratio richer than the stoichiometric air-fuel ratio is a small amount of oxygen in the exhaust gas in the oxidation catalyst. The amount of HC that is oxidized and reaches the holding part can be considerably reduced. Thereby, NO _X most released from the holding portion is reduced by CO in the exhaust gas, estimating the current of the NO _X holding of the holding portions based on the temperature rise value of the holding portion relatively accurately As a result, it is possible to relatively accurately estimate the current SO _X holding amount of the holding unit.

According to the sulfur component detection device of the second aspect of the present invention, in the sulfur component detection device of the first aspect, the sulfur component detection device further includes a heater for heating the oxidation catalyst, and the current SO _{X of the} holding unit. When the temperature of the oxidation catalyst is lower than the set temperature when estimating the holding amount, the heater is operated to raise the temperature of the oxidation catalyst to the set temperature or higher. As a result, most of the HC contained in the exhaust gas having a stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio is obtained by using a slight amount of oxygen in the exhaust gas in a fully activated oxidation catalyst that is equal to or higher than the set temperature. It can be oxidized so that almost no HC reaches the holding part. In this way, most of the NO _x released from the holding unit is reduced by CO in the exhaust gas, and the current NO _x holding amount of the holding unit can be estimated more accurately based on the temperature rise value of the holding unit, As a result, it is possible to more accurately estimate the current SO _X holding amount of the holding unit.

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 selected from alkali metals such as potassium K, sodium Na, 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. One.

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 stored decreases (S poisoning). Accordingly, if an S trap device (not shown) that stores SO _x in the exhaust gas is disposed upstream of the NO _x catalyst device 2 in the exhaust passage 1, S poisoning of the NO _x catalyst device 2 is suppressed. can do. Even if it is not arranged also such S trap device is arranged, to the integrated value of the SO _X amount flowing into NO _X catalyst device 2 corresponds to the order of the S poisoning of the NO _X catalyst device, NO _X catalyst A sulfur component detection device 3 capable of detecting the integrated value of the amount of SO _X flowing into the device 2 is arranged upstream of the NO _X catalyst device 2.

  FIG. 2 is a schematic cross-sectional view showing an embodiment of the sulfur component detection device 3 according to the present invention. In the figure, reference numeral 10 denotes an outer wall of the exhaust passage 1. Reference numeral 31 denotes a temperature sensor such as a thermocouple constituting the sulfur component detection device 3. Reference numeral 32 denotes a holding unit disposed so as to cover the temperature sensing unit of the temperature sensor 31. Reference numeral 33 denotes a cylindrical case surrounding the holding portion 31.

  The case 33 is formed of, for example, a metal plate, and a large number of opening holes 33a are formed on the cylindrical side surface. The outside of the cylindrical side surface of the case 33 is covered with a porous material 34 that supports an oxidation catalyst such as platinum Pt. In addition, several elongated electric heaters 35 extending in the axial direction of the case 33 are arranged inside the cylindrical side surface of the case 33.

The holding part 32 holds SO _X in the exhaust gas, and is formed, for example, by applying the above-described NO _X holding material and a noble metal catalyst such as platinum Pt to the temperature sensor 31. be able to.

The sulfur component detection device 3 configured as described above has been configured so far by inputting the temperature of the holding unit 32 detected by the temperature sensor 31 before and after setting the air-fuel ratio of the exhaust gas to a rich air-fuel ratio to the electronic control device. The SO _x retention amount retained in the sulfur component detection device 3 can be estimated, and based on the estimated SO _x retention amount, for example, an integrated value of the SO _x amount flowing into the NO _x catalyst device 2 is estimated. be able to.

The holding part 32 formed of the NO _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. Thus, the sulfate can be retained up to the SO _x retention capacity. Further, in response 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 32, 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.

If it is detected _the NO _X holding volume held in the holding unit 32, based on the stored SO _X amount capable and _the NO _X holding of the holding portion 32 can estimate the current stored SO _X amount. Thus, if the estimated current stored SO _X amount of sulfur component detecting device 3, the current stored SO _X amount, when the SO _X is not held in the sulfur component detecting device 3, i.e., stored SO _X amount Passes through the exhaust passage at the position of the sulfur component detection device 3 from when it is zero (when the sulfur component detection device 3 is new or when SO _x is completely released from the sulfur component detection device 3) to the present time. It can be considered that a predetermined ratio of the amount of SO _x in the exhaust gas passed through the vicinity of the sulfur component detection device 3 and held in the holding unit 32, and the SO _x holding amount is based on the current SO _x holding amount. The integrated value of the SO _X amount in the exhaust gas that has passed through the exhaust passage at the position of the sulfur component detection device 3 from the time of being zero to the present, that is, the amount of SO _X flowing into the NO _X holding catalyst device 2 The integrated value can be estimated.

In this way, the integrated value of the SO _X amount in the exhaust gas that has passed through the exhaust passage at the position of the sulfur component detection device 3 from the time when the SO _X retention amount is zero to the present is estimated relatively accurately. For this purpose, it is necessary to securely hold SO _X passing through the vicinity of the sulfur component detection device 3 in the holding unit 32. For this purpose, it must HC and CO contained in the exhaust gas of a lean air-fuel ratio during normal operation is attached to the noble metal catalyst of the holding portion 32 so as not to reduce the oxidation function of the SO _X of a noble metal catalyst, In the sulfur component detection device 3 shown in FIG. 2, the outside of the side surface of the case 33 surrounding the holding unit 32 is covered with the porous material 34, and contains SO _X that passes through the porous material 34 and reaches the vicinity of the holding unit 32. HC and CO in the exhaust gas are oxidized and removed by the oxidation catalyst supported on the porous material 34 using a large amount of oxygen contained in the exhaust gas. Adherence of HC and CO can be sufficiently suppressed.

  When the temperature of the oxidation catalyst supported on the porous material 34 is low, the temperature of the oxidation catalyst is set to the activation temperature (for example, 200 ° C. or higher) by operating the electric heater 35 disposed inside the side surface of the case 33. It is preferable that HC and CO in the exhaust gas can be sufficiently removed by oxidation.

Meanwhile, in order to detect _the NO _X holding volume held in the holding unit 32, the air-fuel ratio of the exhaust gas reduces the oxygen concentration as a rich (or stoichiometric) than the stoichiometric air-fuel ratio, from the holding portion 32 NO _X Is released and reduced by CO in the exhaust gas.
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 NO. Accordingly, the temperature rise value of the holding unit 32 before and after the exhaust gas air-fuel ratio is made rich, that is, the maximum temperature of the holding unit 32 after the exhaust gas air-fuel ratio is made rich and the exhaust gas empty The temperature sensor 31 detects the difference from the temperature of the holding unit 32 before the rich air-fuel ratio is made rich, thereby detecting the total NO _X amount released from the holding unit 32 as the current NO _X holding amount of the holding unit 32. can do. Next, based on the detected NO _X holding amount and the SO _X holdable amount of the holding unit 32, the current SO _X holding amount of the holding unit 32 can be estimated.

In order to set the air-fuel ratio of the exhaust gas to a rich air-fuel ratio, it is preferable to inject additional fuel into the cylinder at the beginning of the expansion stroke and to make the air-fuel ratio of the exhaust gas discharged from the cylinder the rich air-fuel ratio. As a result, the additional fuel is incompletely burned in the cylinder, and the exhaust gas discharged from the cylinder contains a sufficient amount of CO for reducing NO _x released from the holding portion 32. can do.

However, HC is also contained in the exhaust gas, and when a part of NO _x released from the holding part 32 is reduced by HC (for example, ethylene), heat is generated as shown below.
1 / 2Ba (NO ₃ ) ₂ → 1 / 2BaO + NO + 3 / 4O ₂ -309.6kJ / mol
NO + 2 / 14C ₂ H ₄ + 2 / 14CO → 1 / 2N ₂ + 6 / 14CO ₂ + 4 / 14H ₂ O + 319.8kJ / mol
3 / 4O ₂ + 3 / 14C ₂ H ₄ + 3 / 14CO → 9 / 14CO ₂ + 6 / 14H ₂ O + 344.2kJ / mol
Thus, when reduced by ethylene C ₂ H ₄ , about 354 kJ exotherm occurs for 1 mol of NO, and when reduced by the aforementioned CO (about 490 kJ exotherm for 1 mol of NO) The calorific value per mole of NO is different.

Accordingly, if the NO _X retention amount is estimated based on the calorific value assuming that all the NO _X released from the retention portion 32 has been reduced by CO, the accurate NO _X retention amount cannot be estimated, and the subsequent NO _X retention amount cannot be estimated. Since the estimation of the SO _X retention amount is inaccurate, the HC in the exhaust gas hardly reaches the retention portion 32 and is almost discharged from the retention portion 32 when estimating the current SO _X retention amount. it is preferred that of the NO _X to be reduced by CO.

Therefore, in the sulfur component detection device 3 of the present embodiment, the temperature of the oxidation catalyst supported on the porous material 34 disposed on the outer side of the side surface of the case 33 when estimating the current SO _X retention amount of the retention portion 32. Is estimated to be lower than the set temperature, the electric heater 35 disposed inside the side surface of the case 33 is operated to raise the temperature of the oxidation catalyst to a set temperature or higher, and thus the oxidation catalyst of the porous material 34. Is sufficiently activated, and HC contained in the exhaust gas is surely oxidized and removed using a slight amount of oxygen contained in the exhaust gas having a rich air-fuel ratio. At this time, CO in the exhaust gas is also oxidized by the oxidation catalyst, but oxygen for that purpose is only slightly contained in the exhaust gas with a rich air-fuel ratio, and a sufficient amount of CO reaches the holding unit 32. Can be made.

Thus, most NO _X released from the holding unit 32 is reduced by CO in the exhaust gas, and the current NO _X holding amount of the holding unit is estimated relatively accurately based on the temperature rise value of the holding unit 32. As a result, it is possible to relatively accurately estimate the current SO _X holding amount of the holding unit.

The electric heater 35 disposed inside the side surface of the case 33 is not necessarily required. Even when the temperature of the oxidation catalyst is not raised when estimating the current SO _x retention amount of the holding portion 32, the oxidation catalyst is contained in the exhaust gas. At least a part of the HC can be oxidized and removed so that the amount of HC reaching the holding unit 32 can be reduced. If the amount of NO _x released from the holding unit 32 and reduced by the HC decreases, the holding unit even 32 all released NO _X from is reduced by CO in the exhaust gas accurately estimated by comparing the current of the NO _X holding of the holding portions based on the temperature rise value of the holding portion 32 in a conventional Will be able to. Further, when the exhaust gas temperature is in an operation state where the exhaust gas temperature is sufficiently high, the HC reaching the holding unit 32 can be sufficiently reduced by estimating the current SO _X holding amount of the holding unit 32.

  The temperature of the oxidation catalyst can be estimated based on the current exhaust gas temperature, for example, or may be directly measured by a temperature sensor. The current exhaust gas temperature can be estimated based on the current engine operating state (engine speed and engine load), or may be directly measured by a temperature sensor.

1 exhaust passage 2 NO _X catalyst device 3 sulfur component detecting device 31 temperature sensor 32 holding unit 33 casing 34 porous material

Claims (2)

A temperature sensor for air-fuel ratio of the exhaust gas is measured SO _X in the exhaust gas passing through the exhaust passage and capable of holding the holding portion to the stored SO _X amount capable when a leaner than the stoichiometric air-fuel ratio, the temperature of the holding portion And having an oxidation catalyst disposed around the holding unit, and estimating the current SO _X holding amount of the holding unit, the air-fuel ratio of the exhaust gas is made richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, the temperature rise value of the holding portion by the temperature sensor by reduced by the stored SO _X amount capable and reducing substance to release NO _X held in response to the difference between the current stored SO _X amount from the holding portion A sulfur component detection device that detects the sulfur component. Furthermore, it has a heater for heating the oxidation catalyst, and when the temperature of the oxidation catalyst is lower than a set temperature when estimating the current SO _X retention amount of the holding unit, the heater is operated to The sulfur component detection apparatus according to claim 1, wherein the temperature of the oxidation catalyst is raised to the set temperature or higher.

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