JP2003239728A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an effect of exhaust emission control by an after-treatment device from an exhaust gas temperature region lower in temperature than a prior art. <P>SOLUTION: This exhaust emission control device is provided with a particulate filter 10 (after-treatment device) of catalyst regeneration type in the middle of an exhaust pipe 9 of a diesel engine 1 (internal combustion engine). In this device, a plasma generation device 11 for generating plasma by performing discharge in an exhaust gas 8 is provided in the exhaust pipe 9 arranged a more upstream side than the particulate filter 10, and even in an operation state in which an exhaust gas temperature is low, in a light-load operation, an exhaust gas excitation component high in activity is generated in the exhaust gas 8 through discharge by the plasma generation device 11, and due to the exhaust gas excitation component, an oxidation reaction of a particulate collected in the particulate filter 10 is accelerated. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device.

[0002]

2. Description of the Related Art Particulate Matter (Particulate Matter) emitted from a diesel engine is
Soot composed of carbonaceous matter and SO composed of high boiling hydrocarbon components
It is composed of F component (Soluble Organic Fraction) as a main component and further contains a trace amount of sulfate (mist-like sulfuric acid component), but as a measure for reducing this type of particulates, exhaust gas is used. It has been conventionally practiced to equip a particulate filter in the middle of an exhaust pipe through which gas flows.

This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow passages partitioned in a grid pattern are alternately plugged, and the inlets are plugged. The outlets of the non-flow passages are configured to be plugged so that only the exhaust gas that has permeated the porous thin wall defining each flow passage is discharged to the downstream side.

Since the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate the curate filter, but in normal diesel engine operating conditions, there is little opportunity to obtain a high exhaust temperature enough to cause the particulates to self-combust. It has been studied to employ a catalyst regeneration type particulate filter in which the resulting oxidation catalyst is integrally supported on the particulate filter, or the oxidation catalyst is separately arranged before the particulate filter.

That is, if such a catalyst regeneration type particulate filter is adopted, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible to do it.

In addition to the above-mentioned particulate filter, it is also proposed to equip a selective reduction type catalyst for removing NOx in exhaust gas, a NOx occlusion reduction catalyst, etc. as an aftertreatment device in the middle of the exhaust pipe. In particular, in recent years, a post-treatment device in which a particulate filter is combined with a NOx storage reduction catalyst has also been developed.

[0007]

However, even if any of these post-treatment devices is adopted, the exhaust gas temperature above a predetermined temperature is required in order to surely remove particulates by burning and to obtain sufficient catalytic activity. As it is necessary, there is a problem that the aftertreatment device cannot be fully functioned if the operating state where the exhaust gas temperature is low (generally, the region where the exhaust gas temperature is low spreads to the operating region of light load). For vehicles that run only on congested roads such as route buses in Tokyo, for example, the operation at the required temperature or higher does not continue for a long time, so the exhaust purification effect by installing the aftertreatment device is sufficient. There was a fear that I could not get it.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purification device which can obtain the effect of exhaust gas purification by a post-treatment device from an exhaust gas temperature region lower than conventional ones.

[0009]

SUMMARY OF THE INVENTION The present invention is an exhaust gas purification device equipped with a post-treatment device for ventilating and purifying exhaust gas in the middle of an exhaust pipe of an internal combustion engine, the exhaust gas upstream of the post-treatment device. It is characterized in that the tube is provided with a plasma generator for generating plasma by discharging in the exhaust gas.

When discharge is carried out in the exhaust gas by the plasma generator, the exhaust gas is excited and unburned hydrocarbons become oxygen-containing hydrocarbons, oxygen becomes ozone, and NO becomes NO ₂ . Since these exhaust gas excitation components are in the activated state, it is possible to obtain the effect of exhaust gas purification by the aftertreatment device from the exhaust gas temperature region lower than the conventional one.

Here, in the plasma generator, discharge plates formed by arranging electrodes facing each other on a substrate are stacked in multiple layers while ensuring a flow path of exhaust gas therebetween, and a pulse is applied to the electrodes of each discharge plate. It may be configured by connecting a power supply via a generator.

Further, a catalyst regeneration type particulate filter can be adopted in the post-treatment device. In such a case, the oxidation reaction of the particulates collected by the particulate filter is activated. As a result of being promoted by the exhaust gas excitation component in the activated state, the particulates are ignited and burned and removed even at a lower exhaust temperature than before.

Further, it is possible to employ a selective reduction type catalyst having an enhanced reaction selectivity between urea and NOx in the aftertreatment device. In such a case, the exhaust gas is discharged by the discharge of the plasma generator. Since NO in the gas is oxidized to highly active NO ₂ , if a urea addition device is installed upstream of the selective reduction catalyst to add urea to the exhaust gas, this urea will act as a reducing agent on the selective reduction catalyst. As a result, NO ₂ is efficiently reduced to N _2, and as a result, the effect of reducing NOx can be obtained even at a lower exhaust temperature than before.

Further, it is possible to employ an oxidation catalyst in the post-treatment device. In such a case, the SOF component in the particulates and the oxidation catalyst for hydrocarbons and carbon monoxide in the exhaust gas are used. As a result of the above oxidation reaction being promoted by the exhaust gas excitation component in the activated state, it is possible to obtain the effect of reducing SOF content in particulates and hydrocarbons and carbon monoxide in exhaust gas even at a lower exhaust temperature than before. become.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine (internal combustion engine) equipped with a turbocharger 2, and an air cleaner 3 The intake pipe 4 that guides the intake air 4
Through a compressor 2a of the turbocharger 2 to pressurize the turbocharger 2, and pressurize the intake air 4 which has been pressurized.
It is configured to be distributed to each cylinder of the diesel engine 1 and introduced through the.

Further, the exhaust gas 8 discharged from each cylinder of the diesel engine 1 through the exhaust manifold 7 is sent to the turbine 2b of the turbocharger 2, and the exhaust gas 8 driving the turbine 2b is regenerated by a catalyst regeneration type catalyst. The particulates are collected through the curate filter 10 (post-processing device) and then discharged.

A plasma generator 11 is disposed in the exhaust pipe 9 upstream of the particulate filter 10 to generate a plasma by discharging the exhaust gas 8.

As shown in FIGS. 2 and 3, the plasma generator 11 includes a discharge plate 15 formed by disposing electrodes 13 and 14 on a substrate 12 so as to face each other, and a flow of exhaust gas 8 through a spacer 16 therebetween. Stacking in multiple stages while securing the path 17,
A power source 19 is connected to the electrodes 13 and 14 of each discharge plate 15 via a pulse generator 18.
In particular, in this embodiment, since the battery mounted on the vehicle is assumed as the power source 19, the pulse generator 18, the electrode 13,
A pressure increasing device 20 for increasing the voltage of the power source 19 to a voltage at which discharge is possible is interposed between the pressure increasing device 14 and the pressure increasing device 14.

In the example shown here, each electrode 1
Each of the electrodes 3 and 14 is formed in a comb-teeth shape, and the longitudinal portions of the comb-teeth shape are alternately inserted into the other side, but such electrodes 13 and 14 are formed. In this case, for example, a platinum paste may be printed on the substrate 12 made of alumina and sintered.

Also, the spacer 16 shown here
Have a long plate shape extending in the flow direction of the exhaust gas 8 and are arranged on both sides of each discharge plate 15 in the width direction. The upper and lower discharge plates 15 and the left and right spacers 1
A portion surrounded by 6 and 6 forms a flow path 17 for the exhaust gas 8.

The operation of the plasma generator 11 is performed by an engine control computer (ECU: Electronic C).
command signal 18 from the control device 21 which constitutes an ontrol unit)
The pulse generator 18 which has received the signal a is executed by the pulse generator 18. On the other hand, in the controller 21, a rotation speed signal 22a from a rotation sensor 22 for detecting the rotation speed of the diesel engine 1 and an operation not shown An accelerator opening signal 23a from an accelerator sensor 23 (load sensor) that detects the opening of the accelerator of the seat as the load of the diesel engine 1 is respectively input, and the rotation speed signal 22a and the accelerator opening signal are inputted. The operating state is estimated from a control map (two-dimensional map based on the number of rotations and the load) based on the current number of rotations and the load of the diesel engine 1 determined by the signal 23a, and the plasma generator in the operating region where the exhaust temperature is low. 11 is operated.

Then, in the exhaust gas 8, a voltage of about 5,000 to 100,000 V, about 50 is generated by the plasma generator 11.
When discharging at a frequency of 10,000 Hz and an output of about 0.1 to 10 kW, the exhaust gas 8 is excited, unburned hydrocarbons become oxygen-containing hydrocarbons, oxygen becomes ozone, and NO becomes NO _2.
Since these exhaust gas excitation components are in the activated state, the oxidation reaction of the particulates collected in the particulate filter 10 is promoted by the exhaust gas excitation component, and even at an exhaust temperature lower than the conventional one. The particulates are ignited and burned and removed.

In fact, according to the verification experiment by the present inventors, as shown by the solid line in the graph of FIG. 4, the combustion of particulates in the present embodiment example starts from around 120 ° C. and the combustion speed increases with the temperature rise. In contrast to this, the conventional particulate combustion shown by the chain line in the graph of FIG. 4 starts at around 200 ° C., and when the discharge by the plasma generator 11 is performed, It was confirmed that the combustion efficiency of particulates in the operating region where the exhaust temperature is low is much better.

Therefore, according to the above-described embodiment, even when the exhaust temperature is low, such as during light load operation, a highly active exhaust gas excited component is generated in the exhaust gas 8 by the discharge by the plasma generator 11. However, since the exhaust gas excitation component can accelerate the oxidation reaction of the particulates collected in the particulate filter 10, the particulates can be ignited and removed by combustion even at an exhaust temperature lower than the conventional one.

Further, in the above-described embodiments of FIGS. 1 to 3, the case where the catalyst regeneration type particulate filter 10 is adopted as the post-treatment device is illustrated, but the post-treatment device includes urea and NOx. It is also possible to employ a selective reduction type catalyst having an improved reaction selectivity with.

In this case, the NO in the exhaust gas 8 is highly active due to the discharge of the plasma generator 11.
Since it is oxidized to O ₂ , if a urea addition device is provided on the upstream side of the selective reduction catalyst and urea is added to the exhaust gas 8, NO ₂ can be efficiently converted to N ₂ on the selective reduction catalyst by using this urea as a reducing agent. As a result of being reduced to ₂ , the effect of reducing NOx can be obtained even at a lower exhaust temperature than before.

In fact, according to the verification experiments by the present inventors, as shown by the solid line in the graph of FIG. 5, the NOx reducing effect in the present embodiment starts to be obtained from around 150 ° C. While the conventional NOx reduction effect shown by the chain line in the graph of FIG. 5 begins to be obtained at around 200 ° C., discharge by the plasma generator 11 is performed. It was confirmed that the NOx reduction effect in the operating range where the exhaust gas temperature is low is much better.

It is also possible to employ an oxidation catalyst in the post-treatment device. In such a case, the SOF component in the particulates and the oxidation of hydrocarbons and carbon monoxide in the exhaust gas 8 are used. As a result of the oxidation reaction on the catalyst being promoted by the exhaust gas excitation component in the activated state, the SOF content in the particulates and the exhaust gas
The effect of reducing the content of hydrocarbons and carbon monoxide will be obtained.

In fact, according to the verification experiment focusing on hydrocarbons by the present inventors, as shown by the solid line in the graph of FIG. 6, the effect of reducing hydrocarbons in this embodiment is about 120 ° C.
While the reduction rate starts to be obtained from the vicinity and the reduction rate is remarkably increased as the temperature rises, the conventional hydrocarbon reduction effect shown by the chain line in the graph of FIG. And the plasma generator 11
It was confirmed that the effect of reducing hydrocarbons in the operating region where the exhaust gas temperature is low is much better when the discharge is performed by the method.

The exhaust gas purifying apparatus of the present invention is not limited to the above-mentioned embodiment, and a post-processing apparatus other than the catalyst regeneration type particulate filter may be adopted. Needless to say, various changes can be made without departing from the scope of the present invention.

[0032]

According to the above-described exhaust gas purification apparatus of the present invention, even when the exhaust gas temperature is low at the time of light load operation, the exhaust gas excited by the plasma generator is highly active in the exhaust gas. Since it is possible to generate a component and promote the reaction of exhaust purification in the aftertreatment device by this exhaust gas excitation component, the effect of the exhaust purification by the aftertreatment device can be obtained from a lower exhaust temperature range than before. It can produce the effect.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.

FIG. 2 is a perspective view showing details of the plasma generator shown in FIG.

FIG. 3 is a plan view showing details of the discharge plate of FIG.

FIG. 4 is a graph showing the relationship between the burning rate of particulates and the temperature of exhaust gas.

FIG. 5 is a graph showing the relationship between the NOx reduction rate and the temperature of exhaust gas.

FIG. 6 is a graph showing the relationship between the reduction rate of hydrocarbons and the temperature of exhaust gas.

[Explanation of symbols]

1 Diesel engine (internal combustion engine) 8 exhaust gas 9 exhaust pipe 10 Particulate filter (post-processing device) 11 Plasma generator 12 substrates 13 electrodes 14 electrodes 15 Discharge plate 17 channels 18 pulse generator 19 power supply

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/24 F01N 3/28 301C 3/28 301 9/00 Z 9/00 B01D 46/42 B // B01D 46 / 42 53/36 103C F Term (reference) 3G090 AA03 AA06 BA01 DA18 DA20 EA05 3G091 AA02 AA18 AA28 AB02 AB05 AB13 AB14 BA00 BA03 BA14 BA15 BA19 EA01 EA02 EA07 FA02 FA04 FA12 FA13 FB05 FA0 4A01 AB02 4A01 A02 JB02 JB22 KC01 MA41 MA42 MA44 MA51 SA08 TA01 TA06 4G075 AA27 AA37 AA57 AA61 BA05 BA06 BD01 BD14 CA02 CA15 CA47 DA02 EA05 EB21 FB01 FC06

Claims (5)

[Claims] 1. An exhaust gas purification device equipped with a post-treatment device for ventilating and purifying exhaust gas in the middle of an exhaust pipe of an internal combustion engine, wherein the exhaust pipe upstream of the post-treatment device is discharged into the exhaust gas. An exhaust emission control device is provided with a plasma generation device for generating plasma. 2. A discharge plate having electrodes arranged opposite to each other on a substrate is stacked in multiple layers while ensuring a flow path of exhaust gas between them, and a power source is connected to the electrodes of each discharge plate via a pulse generator. The exhaust emission control device according to claim 1, wherein the plasma generation device is configured by the above. 3. The exhaust emission control device according to claim 1 or 2, wherein the aftertreatment device is a catalyst regeneration type particulate filter. 4. The urea addition device in which the aftertreatment device is a selective reduction catalyst having an enhanced reaction selectivity between urea and NOx, and urea is added to the exhaust gas upstream of the selective reduction catalyst as a reducing agent. The exhaust emission control device according to claim 1 or 2, further comprising: 5. The exhaust emission control device according to claim 1, wherein the aftertreatment device is an oxidation catalyst.