JP2011214561A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, high in purifying efficiency with ozone.SOLUTION: The exhaust emission control device for the internal combustion engine includes an NOcatalyst, a DPF (Diesel Particulate Filter), an ozone supply means, an exhaust gas temperature detecting means and an ozone supply control means, and controls the ozone supply means to supply ozone to the NOcatalyst but not to the particle filter when an exhaust gas temperature is lower than 200°C, to supply ozone to the NOcatalyst and the particle filter when the exhaust gas temperature is in a range of 200°C or higher and 250°C or lower, to supply ozone to the particle filter but not to the NOcatalyst when the exhaust gas temperature is higher than 250°C and equal to or lower than 300°C, and to supply ozone to neither the NOcatalyst nor the particle filer when the exhaust gas temperature is higher than 300°C.

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly, to an exhaust gas purification device for an internal combustion engine that can achieve high ozone purification efficiency in purification of NO _x and particulate matter in exhaust gas discharged from the internal combustion engine. About.

  In general, exhaust gas from diesel engines contains particulate matter mainly composed of carbon (hereinafter abbreviated as PM; PM: Particulate Matter), which causes air pollution. Devices have been proposed for collecting and removing. As one of them, there is a method in which the collected PM is oxidized and burned by forcibly supplying fuel to raise the temperature of a particle filter (also referred to as a diesel particulate filter, hereinafter abbreviated as DPF). Are known.

However, this method of forcibly supplying fuel has a problem of DPF breakage due to deterioration of fuel consumption or rapid combustion of PM. Therefore, recently, a technique for oxidizing and treating PM using ozone (O ₃ ) having strong oxidizing power has been proposed.
For example, Patent Document 1 discloses an oxidation catalyst that is disposed in an exhaust passage and oxidizes unburned components in exhaust gas, and a particle filter that collects particulate matter installed in the exhaust passage on the downstream side thereof. An internal combustion engine comprising a NO _X catalyst installed downstream thereof, an ozone supply means between the particle filter and the NO _X catalyst, and a control means for controlling the ozone supply means based on the temperature in the exhaust passage Exhaust gas purification devices are described. Then, in the purifier is supplied with ozone to the NO _X catalyst from the ozone supply means, the particle filter ozone is not supplied.

Patent Document 2 discloses a particulate matter collection device that is installed in an exhaust gas passage and collects particulate matter in exhaust gas, and ozone that can supply ozone to the upstream particulate matter collection device. Supply means, NO _X oxidation catalyst disposed further upstream thereof, exhaust gas temperature detection means for measuring the temperature of exhaust gas passing through the particulate matter collection device, and particulate matter collection device based on the detected temperature An exhaust gas purifying apparatus including ozone supply control means for controlling ozone supply means for supplying ozone is described. Then, in the purification device, ozone is supplied from the ozone supply means to the particle filter, is the NO _X catalyst ozone is not supplied.

JP 2007-289844 A JP 2007-327460 A

However, even with these known exhaust gas purification devices, the purification efficiency by ozone is not sufficient, and further improvement is required.
Accordingly, an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine having high purification efficiency by ozone.

The present invention includes a particulate filter for collecting the NO _X catalyst for purifying NO _X in the exhaust gas flow path arranged in the exhaust gas of an internal combustion engine, the particulate matter in the exhaust gas, the NO _X catalyst and particles Ozone supply means capable of supplying ozone to the filter; exhaust gas temperature detection means; ozone supply control means for controlling the two ozone supply means based on the exhaust gas temperature detected by the exhaust gas temperature detection means; When the exhaust gas temperature is less than 200 ° C., ozone is supplied to the NO _X catalyst, but not supplied to the particle filter. When the exhaust gas temperature is in the range of 200 ° C. or more and 250 ° C. or less, ozone is supplied to the nO _X catalyst and particulate filter, when the exhaust gas temperature is in the range of 300 ° C. or less higher than 250 ° C. is ozone, but not supplied to the nO _X catalyst Supplying the particulate filter, when the exhaust gas temperature is higher than 300 ° C. is ozone, NO _X catalyst, the internal combustion engine and controls the ozone supply means either to not also supplied, as in the particle filter The present invention relates to an exhaust purification device.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, high purification efficiency by ozone can be achieved.

FIG. 1 is a schematic view showing an embodiment of the exhaust gas purifying apparatus of the present invention. FIG. 2 is a flowchart showing an example of processing in the ozone supply control means of the embodiment of the present invention. Figure 3 is a graph showing the relationship between the NO _X oxidation rate by ozone with the exhaust gas temperature at the simulation test of the exhaust gas purifying apparatus of the present invention. FIG. 4 is a graph showing the relationship between the PM oxidation rate by ozone and the exhaust gas temperature in the simulation test of the exhaust gas purification apparatus of the present invention.

In an embodiment of the present invention, an exhaust gas purification device for an internal combustion engine is disposed in an exhaust gas passage 2 of an internal combustion engine as shown in FIG. 1 for purifying NO _X in the exhaust gas, the exhaust gas flow direction NO _X catalyst 3 located upstream, particulate filter (DPF) 4 located downstream in the exhaust gas flow direction for collecting particulate matter (PM) in the exhaust gas, NO _X catalyst 3 and Ozone supply means 5, 15 capable of supplying ozone to the particle filter 4, exhaust gas temperature detection means 6, and the two ozone supply means based on the exhaust gas temperature T detected by the exhaust gas temperature detection means 6. And ozone supply control means 7 which is an electronic control unit (ECU) for controlling the ozone, and when the exhaust gas temperature is less than 200 ° C., ozone is supplied to the NO _X catalyst 3 but not to the DPF 4 , When the exhaust gas temperature is in the range of 200 ° C. or higher 250 ° C. or less, the ozone is supplied to the NO _X catalyst 3 and DPF 4, when the exhaust gas temperature is in the range of 300 ° C. or less higher than 250 ° C. is ozone Is not supplied to the NO _X catalyst 3, but is supplied to the DPF 4. When the exhaust gas temperature is higher than 300 ° C., ozone is not supplied to either the NO _X catalyst 3 or the particle filter 4 The ozone supply means 7 is controlled.

In the exhaust gas purifying apparatus of the present invention, the exhaust gas detected by the exhaust gas temperature detecting means 6 and the above-described configuration capable of supplying ozone to both the NO _X catalyst 3 and the DPF 4 by the ozone supplying means 5 and 15, respectively. In combination with the ozone supply control means 7 for controlling the ozone supply means based on the gas temperature T, and the control of the ozone supply means for supplying ozone by the flow in the ozone supply control means is important. High purification efficiency by ozone can be achieved.
The positional relationship between the NO _X catalyst 3 and the DPF 4 is preferably such that the NO _X catalyst 3 is located upstream of the particle filter 4 in the exhaust gas flow direction as shown in FIG.

In the present invention, ozone is supplied by controlling the exhaust temperature T detected by the exhaust gas temperature detection means 6 at a lower temperature, equal temperature, or higher temperature than the set temperatures of 200 ° C., 250 ° C. and 300 ° C. determines the whether or is for controlling by not supplying either deliver ozone to the nO _X catalyst 3 and the particulate filter 4 based on the flow shown in FIG.
Exhaust gas temperature detected in step S10 (T) is compared whether less than 200 ° C., and supplies the process proceeds to step S40 if it i.e. a Y T <200 ° C., ozone, the NO _X catalyst 3 However, it returns to exhaust gas temperature detection without supplying to DPF4.
If T ≧ 200 ° C., that is, N, the process proceeds to step S20, and whether or not the exhaust gas temperature (T) is less than 250 ° C. is compared. If T <250 ° C., that is, Y, the process proceeds to step 50. the ozone was supplied to the NO _X catalyst 3 and DPF 4, it returns to the exhaust gas temperature sensing.
If T ≧ 250 ° C., that is, if N, the process proceeds to step S30 to compare whether the exhaust gas temperature (T) is less than 300 ° C. If T <300 ° C., that is, if Y, the process proceeds to step S60. , Ozone is not supplied to the NO _X catalyst 3, but is supplied to the DPF 4, and the process returns to the exhaust gas temperature detection.
Proceeds to it if the step 70 is a is namely N T ≧ 300 ° C., ozone, NO _X catalyst 3, not also supplied to any of the particle filter 4, the flow returns to the exhaust gas temperature sensing, continued flow until the engine stops.

In the ozone supply control of the present invention, it is necessary that the exhaust gas temperature T, as shown in the flow of supplying ozone to the NO _X catalyst 3 in a temperature range of ambient temperature to 250 DEG ° C. (less than 250 ° C.). Although rationale for high purification efficiency by ozone is obtained is not clear by supplying ozone to the NO _X catalyst 3 in this temperature range, the outside air temperature to 250 DEG ° C. As shown in FIG. 3 (below 250 ° C.) It is understood to be particularly high NO _X oxidation ratio by the exhaust gas purification test performed on the basis of the experimental method described in detail in the column below examples within the range of ambient temperature to 225 ° C. is obtained.
This is because if NO ₃ is added to the NO _X catalyst within the above temperature range, NO and O ₃ react preferentially, and O radicals generated by thermal decomposition of O ₃ and NO _X do not react. It is thought to be due to being suppressed.

Furthermore, in the ozone supply control of the present invention, it is necessary to supply ozone to the DPF 4 in the exhaust gas temperature range of 200 ° C. (above) to 300 ° C. (less than) as shown in the above flow. Although the theoretical basis for obtaining high purification efficiency by ozone by supplying ozone to the DPF 4 in this temperature range has not been clarified, as shown in FIG. 4, it is preferably 200 ° C. (above) to 300 ° C. (less than). In the range of 225 to 300 ° C. (less than), particularly in the range of 225 to 275 ° C. (less than), a high PM oxidation rate is obtained by an exhaust purification test carried out based on an experimental method described in detail in the section of the examples below. It is understood that it is obtained.
This, the addition of O ₃ in the DPF at the temperature range, when the O radical and O ₃ that O ₃ is generated by thermal decomposition coexist PM is believed to be due to burn efficiently.
The set temperatures of the ozone supply control in the present invention, 200 ° C., 250 ° C. and 300 ° C., can be set to 225 ° C., 250 ° C. and 275 ° C. in order to define a more preferable temperature range.

The NO _X catalyst in the present invention is not particularly limited, and examples thereof include an occlusion reduction type NO _X catalyst (NSR: NO _X Storage Reduction) or a selective reduction type NO _X catalyst (SCR: Selective Catalytic Reduction).
As the storage reduction NO _X catalyst, on a substrate surface made of oxide such as alumina Al ₂ O _3, and a noble metal such as platinum Pt as a catalyst component, and the NO _X absorbing component is composed it is carried Yes. Examples of the NO _X absorbing component include alkali metals such as K, Na, Li and Cs, alkaline earths such as Ba and Ca, and rare earths such as La and Y.

When the NO _X catalyst is a NOx storage reduction catalyst, when the air-fuel ratio of the exhaust gas flowing into the NO _X catalyst is leaner than a predetermined value (typically the theoretical air-fuel ratio), NO _X is absorbed and flows into this. that the oxygen concentration in the exhaust gas to release NO _X absorbed to decrease, perform absorption and release action of NO _X. In this embodiment, since a diesel engine is used, the exhaust air-fuel ratio at normal times is lean, and the NO _X catalyst 3 absorbs NO _{X in} the exhaust. The reducing agent is supplied at the NO _X catalyst 3, the air-fuel ratio of the inflowing exhaust gas becomes rich, NO _X catalyst 3 may perform the release of the absorbed NO _X. The released NO _X can be reduced and purified by reacting with the reducing agent.

In addition, the selective reduction type NO _X catalyst is a catalyst in which a noble metal such as Pt is supported on the surface of a base material such as zeolite or alumina, or a transition metal such as Cu is supported on the surface of the base material by ion exchange. And those having a titania / vanadium catalyst (V ₂ O ₅ / WO ₃ / TiO ₂ ) supported on the surface of the substrate.
In this selective reduction type NO _X catalyst, hydrocarbon (HC) and NO _X in the exhaust gas are reacted to generate N ₂ , CO ₂ , and H ₂ O under the condition that the air-fuel ratio of the inflowing exhaust gas is lean. To be purified. However, NO _x purification requires the presence of HC, and even if the air-fuel ratio is lean, exhaust gas always contains unburned HC, so this can be used to reduce and purify NO _x. It is. Further, by carrying out the rich spike may be supplied reducing agent as the occlusion reduction type NO _X catalyst. In this case, ammonia or urea can be used as the reducing agent in addition to those exemplified above.

The particle filter 4 in the present invention is not particularly limited, and may be a so-called wall flow type having a honeycomb structure made of a porous ceramic, for example, and the honeycomb structure is made of a ceramic material such as cordierite, silica, or alumina. Can be formed. Exhaust gas flows from left to right in FIG. 1 as indicated by arrows in FIG.
Usually, the honeycomb structure is formed into a honeycomb shape by alternately forming a passage called a cell, a passage having a plug on the upstream side, and another passage having a plug on the downstream side. ing. The exhaust gas passes through the wall surface of the porous ceramic and flows into the passage and flows downstream. At this time, PM in the exhaust gas is collected by the porous ceramics, and release of PM into the atmosphere is prevented. A filter type in which exhaust gas passes through the wall surface of the flow path and collects PM at that time is called a wall flow type.

Examples of the ozone supply means 5 and 15 in the present invention include an ozone supply nozzle (not shown). An ozone generator (not shown) as an ozone supply source is connected to the ozone supply nozzle. Ozone generated by the ozone generator is supplied to the ozone supply nozzle via the ozone supply passage 51, 52, each downstream of the NO _X catalyst 3 and the exhaust gas passage toward DPF4 from the ozone supply nozzle It is supplied by injection.
The ozone supply nozzle, each disposed immediately upstream position of the NO _X catalyst 3 and DPF 4, it is preferable to supply ozone therefrom toward the NO _X catalyst 3 and DPF 4.
Or, ozone supply nozzle may be respectively provided in the apparatus of the NO _X catalyst 3 and DPF 4.

  There is no restriction | limiting in particular as said ozone generator, For example, the form which generate | occur | produces ozone, flowing dry air or oxygen used as a raw material in the discharge tube which can apply a high voltage, and the thing of other arbitrary forms are used. be able to. Here, the dry air or oxygen used as a raw material is preferably a gas taken from outside the exhaust passage 2, for example, a gas contained in the outside air.

The exhaust gas temperature detection means 6 in the present invention includes a means for detecting the temperature in the exhaust gas passage, for example, a temperature sensor, and is an electronic control unit (ECU) based on the exhaust gas temperature detected by the temperature sensor. The ozone supply control means 7 is electrically connected.
Further, the exhaust gas temperature detection means in the present invention is not limited to the temperature sensor, and the exhaust gas temperature is estimated using engine characteristic map data stored in the ozone supply control means based on the operating condition of the engine or the like. It may be a means.

The exhaust gas purification apparatus of the present invention can achieve high purification efficiency by ozone by having the above-described configuration. However, as long as the effect is not reduced, a member having any other function that can be applied to the exhaust gas purification apparatus for an internal combustion engine can be added. For example, HC and CO in the exhaust gas are oxidized at an arbitrary position. An oxidation catalyst that can be purified can be added.
According to the exhaust gas purifying apparatus of the present invention, all of the internal combustion engine capable of generating NO _X and PM as well diesel engines, for example, also applicable to a lean-burn gasoline engine is a fire-ignition internal combustion engine of direct injection .

Hereinafter, the present invention will be described based on examples. The present invention is not limited to the following examples.
The following experiment is for confirming the action and effect of the configuration of the present invention.

Experimental condition 1
Using a simulation gas (including ozone), which will be described later, the NO _X oxidation catalyst disposed in the quartz tube was passed through and discharged to the outside from the exhaust gas duct. An electric heater was installed on the outer periphery of the quartz tube, and the temperature of the NO _x oxidation catalyst was raised at a constant rate from room temperature (around 20 ° C.) to 400 ° C. A temperature sensor for measuring the temperature immediately upstream of the NO _X oxidation catalyst was provided. The NO _X concentration in the exhaust gas discharged was continuously measured with a FID gas analyzer (Horiba, MEXA-7100) to determine the NO _X oxidation rate.
The simulated gas conditions are shown below.
Flow rate: 15L / min
NO: 200ppm
O _3: 400-500ppm
O ₂ : 7%
CO ₂ : 10%
N ₂ : balance

Experimental condition 2
Using a simulation gas (including ozone) described later, a small-capacity DPF with PM attached disposed in the quartz tube was passed through and discharged to the outside from the exhaust gas duct. Install an electric heater on the outer periphery of the quartz tube, set the temperature of the DPF from 50 ° C to 400 ° C in steps of 50 ° C, and compare the mass of the DPF with PM before and after the circulation of the gas containing O ₃ Thus, the PM oxidation rate (PM mass reduction rate) was obtained.
The simulated gas conditions are shown below.
Flow rate: 10L / min
O ₃ : 1000 ppm
O ₂ : 8%
CO ₂ : 10%
N ₂ : balance

Example 1 and Comparative Example 1
Experiments were conducted using the following DPF.

1. DPF
A cordierite DPF having a diameter of 35 mm, a length of 50 mm, a cell wall thickness of 4 mil, and a cell number of 400 and having PM adhered thereto was used. For adhesion of PM, an actual gas sampling pump corresponding to the DPF was used for the exhaust gas pipe of the diesel engine, and sampling was performed at a flow rate of 10 L / min until about 0.3 g of PM was collected. The DPF with PM attached in this way was placed in a quartz tube with the surface on which the PM was attached upstream, and an experiment was conducted.
The relationship between each temperature and the NO _X oxidation ratio obtained by the temperature sensor in Fig. 3 shows the relationship between each temperature and the PM oxidation in FIG.

According to the results of FIG. 3 and FIG. 4, the outside air temperature to 250 DEG ° C. (less than 250 ° C.), in particular a high NO _X oxidation ratio in the range of ambient temperature to 225 ° C. (less than 225 ° C.), 200 ° C. (or higher) 300 A high PM oxidation rate is obtained in the range of ° C (less), particularly in the range of 225 ° C (above) to 275 ° C (less than).
The above results show that NO _X purification and PM oxidation purification can be achieved in combination by combining the results of FIG. 3 and the results of FIG.

  The exhaust gas purification apparatus of the present invention can achieve high purification efficiency by ozone, and can realize exhaust gas purification of an internal combustion engine and improvement of ozone use efficiency.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus of internal combustion engine 2 Exhaust gas flow path 3 NO _X catalyst 4 Particle filter (DPF)
5, 15 Ozone supply means 6 Exhaust gas temperature detection means 7 Ozone supply control means 51, 52 Ozone supply passage

Claims (2)

And NO _X catalyst for purifying NO _X in the exhaust gas is arranged in an exhaust gas passage of an internal combustion engine, a particulate filter for collecting particulate matter in the exhaust gas, each ozone to the NO _X catalyst and the particle filter An ozone supply means capable of supplying; an exhaust gas temperature detection means; and an ozone supply control means for controlling the two ozone supply means based on the exhaust gas temperature detected by the exhaust gas temperature detection means. when the temperature is lower than 200 ° C. is ozone, supplied to the nO _X catalyst is not supplied to the particulate filter, when the exhaust gas temperature is in the range of 200 ° C. or higher 250 ° C. or less, ozone, nO _X catalyst and supplied to the particulate filter, when the exhaust gas temperature is in the range of 300 ° C. or less higher than 250 ° C. is ozone, but not supplied to the nO _X catalyst, particle filter Supplies, when the exhaust gas temperature is higher than 300 ° C. is ozone, NO _X catalyst and does not supply to any of the particle filter so that the exhaust gas of an internal combustion engine and controls the ozone supply means Purification equipment. The NO _X catalyst, the exhaust gas purifying apparatus according to claim 1 which is located upstream of the exhaust gas flow direction with respect to the particulate filter.

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