KR20050118762A - Exhaust gas purifying system using diesel reformer - Google Patents

Abstract

The present invention relates to an automobile exhaust gas purification system using a diesel reformer, wherein a CPF system in which DOC and CPF are sequentially arranged in series on an exhaust line is installed in front, and NOx storage catalyst and DOC are disposed in series in the rear. And a diesel reformer for supplying diesel fuel and air to autothermal reforming reaction to generate a synthesis gas including hydrogen and carbon monoxide, and receiving the synthesis gas generated from the diesel reformer and spraying the NOx storage catalyst front end. The present invention relates to an automobile exhaust gas purification system using a diesel reformer provided with an engine injector and an engine ECU outputting a control signal for injection operation of the injector in a rich spike control mode.

According to the present invention, compared to the conventional method of directly injecting diesel fuel in liquid phase, problems such as catalyst deactivation or catalyst breakdown due to abnormal combustion in the catalyst can be solved, and NOx and PM can be simultaneously reduced. Since the amount of post-injected fuel can be reduced, fuel economy can be improved.

Description

Exhaust gas purifying system using diesel reformer

The present invention relates to an automobile exhaust gas purification system using a diesel reformer, wherein a CPF system in which DOC and CPF are sequentially arranged in series on an exhaust line is installed in front, and NOx storage catalyst and DOC are disposed in series in the rear. And a diesel reformer for supplying diesel fuel and air to autothermal reforming reaction to generate a synthesis gas including hydrogen and carbon monoxide, and receiving the synthesis gas generated from the diesel reformer and spraying the NOx storage catalyst front end. The present invention relates to an automobile exhaust gas purification system using a diesel reformer provided with an engine injector, and configured to output a control signal for injection operation of the injector along with fuel after injection.

Generally, automobiles are classified into passenger cars, buses, and trucks according to their type, but even vehicles of the same type may be used as gasoline vehicles using gasoline, diesel vehicles using diesel, LPG vehicles using LPG, etc., depending on fuel used. Can be classified.

Due to its low fuel consumption and excellent reliability, dual diesel engines have various uses across industries such as automobiles, ships, and general industries, and are capable of high power and high load operation, and demand thereof continues to increase.

In addition, the adoption of diesel engines in the 3L automotive program or supercar project, which is being promoted for low fuel consumption vehicles, is being actualized, and an increase in diesel engine vehicles is expected.

However, in advanced countries, such diesel vehicles occupy a very high proportion of total air pollution and are recognized as a major cause of air pollution, and in order to cope with this, countries are gradually tightening emission regulations of diesel engines.

Air pollution in diesel vehicles is mainly caused by nitrogen oxides (NOx) and particulate matter (PM) called soot.

In the United States, the federal regulations that are in force are expected to be strengthened since 2004. The European Union is also applying or planning to apply EURO III in 2000 and EURO IV in 2005. EURO V is 50% of EURO IV. Regulation of particulate matter is expected to be tightened.

Therefore, the main targets of diesel vehicle exhaust regulation are nitrogen oxides and particulate matters. The countermeasures include the delay of fuel injection timing, the reduction of nitrogen oxide concentration by the exhaust gas recirculation (EGR) device, and the reduction of particulate matters. In order to improve and improve the combustion performance of the engine, the research has been focused on the after-treatment technology.

The specific countermeasures of diesel vehicle exhaust regulation are classified into engine improvement and aftertreatment technology. First, engine improvement technology of diesel vehicle is improved fuel chamber, intake system (turbo charger + intercooler), and fuel injection system ( Electronically controlled high-pressure fuel injection device) and exhaust gas recirculation device are being applied or under development.

In addition, post-treatment technologies developed so far include diesel oxidation catalyst (DOC) for oxidizing and purifying SOF among gaseous HC, CO, and particulate matter, and diesel for physically purifying particulate matter by filtration. Diesel Particulate Filter (DPF) or catalyst coated diesel particulate filter (CPF), DeNOx catalyst that decomposes or reduces nitrogen oxides in lean oxygen atmosphere, and other DeNOx in diesel oxidation catalyst. 4Way catalyst with added functions.

In order to cope with the EURO IV emission regulations, the world's leading automakers use diesel oxidation catalyst (DOC) and diesel particulate filter (CPF) to reduce particulate matter and EGR to reduce NOx. The method is adopted.

However, in the case of particulate matter, the diesel particulate catalyst filtration filter installed in the diesel passenger car can sufficiently cope with the EURO V emission regulation to cope with the EURO IV emission regulation. It is not enough to meet EURO V emission regulations.

Therefore, a separate NOx post-treatment device must be attached, and the NOx post-treatment device under research and development for EURO V response is based on lean NOx trap, NOx absorber, and urea. Selective Catalytic Reduction (SCR) systems.

The NOx conversion rate of the NOx storage catalyst is very high, about 70-90% or more, and the activity of the NOx storage catalyst is over a relatively wide range of the catalyst active temperature window, which ranges from about 200 ° C. It reaches 500 degreeC.

The active temperature window of the NOx storage catalyst has a very good correlation between the load and the exhaust temperature range of the diesel engine in which most of the diesel NOx are generated, and thus the conversion efficiency of the NOx is very high.

Therefore, the adoption of the NOx storage catalyst system has become mainstream in terms of cost and efficiency.

The NOx storage catalyst absorbs NOx in the catalyst's washcoat when the vehicle is in lean driving conditions and releases it when it is in a rich driving zone.The catalyst layer is composed of precious metals such as platinum (Pt) and barium oxide ( It consists of an adsorber such as Barium Oxide (BaO).

The reaction of adsorption occurs in the lean operating zone of the engine, and the reaction is as follows.

NO + 1 / 2O ₂ = NO ₂ (1)

BaO + NO ₂ + 1 / 2O ₂ = Ba (NO ₂ ) ₂ (2)

In addition, when the engine is in a rich operating condition, the following reaction occurs.

Ba (NO ₃ ) ₂ = BaO + 2NO + 3 / 2O ₂ (3a)

Ba (NO ₃ ) ₂ = BaO + 2NO ₂ + 1 / 2O ₂ (3b)

NO + CO = 1 / 2N ₂ + CO ₂ (4)

As the adsorption capacity of NOx becomes more saturated, the stored NOx must be discharged and reduced by the catalyst. This process is called regeneration.

Since a diesel engine is always operated in a lean driving region, it is necessary to artificially form a rich mixer, and in a rich spike method, with fuel post injection in the engine, shown in FIG. 3. As such, a separate secondary injection system must be installed in the exhaust system to provide secondary fuel injection.

However, such a system has the following problems, which will be described with reference to FIG. 3.

In FIG. 3, reference numeral 1 denotes a fuel cracking catalyst, reference numeral 2 denotes a NOx storage catalyst, and reference numeral 3 denotes a catalyzed particulate filter (CPF).

First, the diesel fuel is injected into the secondary injection nozzle 4 to form a rich mixer, wherein the diesel fuel is injected into the liquid phase and decomposed through the fuel decomposition catalyst 1.

However, as much decomposition as desired does not occur, and some of the undecomposed fuel components are attached to the NOx storage catalyst (2) to reduce the activity of the catalyst, and high temperature exhaust as in the regeneration or desulfurization process of the NOx storage catalyst (2). Passage of gas can cause abnormal combustion, which can lead to catalyst failure.

In particular, since fuel is injected from the injection nozzle 4 into the liquid phase, the combustion of the liquid phase adheres to the catalyst and causes abnormal combustion, which causes a problem that the catalyst is broken or melted, and a large amount of hydrocarbon (HC) is purified. Problem occurs.

The NOx storage catalyst 2 also produces some undesirable reactants, due to the sulfur content in the diesel fuel, which produces sulfur compounds as follows.

SO ₂ + 1 / 2O ₂ = SO ₃ (5)

BaO + SO ₃ = BaSO ₄ (6)

As the barium sulfate (Barium Sulfate, BaSO ₄ ) continues to produce as described above, the barium active point is gradually saturated with sulfur, and loses activity for nitrogen oxides (NOx).

Therefore, a desulfation process is required to remove the sulfate, which requires a very high temperature of 600 ° C. or higher.

Therefore, the present invention is invented to solve the above problems,

On the exhaust line, install a CPF system in which DOC and CPF are arranged in series, and install a catalytic purifier in which NOx storage catalyst and DOC are arranged in series in the rear. A diesel reformer that reacts to generate a synthesis gas including hydrogen and carbon monoxide, and an injector that receives the synthesis gas generated from the diesel reformer and injects it into the front of the NOx storage catalyst, while the engine ECU is combined with the fuel post-injection. By outputting a control signal for the injection operation of the injector, problems such as catalyst inactivation or catalyst damage due to abnormal combustion in the catalyst can be solved as compared to the conventional method of directly injecting diesel fuel of liquid phase, and NOx And PM can be reduced at the same time, and the amount of post-injection fuel can be reduced to improve fuel economy. The object is to provide a vehicle exhaust purification system using a gel reformer.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention, in the vehicle exhaust gas purification system,

A catalytic purifier having a NOx storage catalyst is installed, and a diesel reformer is provided with diesel fuel and air to generate a synthesis gas including hydrogen and carbon monoxide by autothermal reforming reaction, and receives the synthesis gas generated from the diesel reformer. It is characterized in that the injector is injected to the front end of the catalyst, the engine ECU is provided to output a control signal for the injection operation of the injector in the rich spike (Rich Spike) control mode.

In particular, a CPF system in which a diesel oxidation catalyst (DOC) and a diesel particulate catalyst filtration filter (CPF) are arranged in series on an exhaust line is installed in front of the catalyst purifier in which the NOx storage catalyst is embedded.

In addition, the engine ECU is characterized in that it is provided to periodically output a control signal for the injection operation of the injector with the fuel after injection.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The present invention relates to an exhaust gas purification system for a passenger diesel vehicle, and more particularly, to a diesel exhaust system for reducing nitrogen oxides (NOx) and particulate matter (PM) using a diesel reformer.

Hereinafter, the configuration of the present invention will be described.

1 is a block diagram showing a purification system of the present invention, Figure 2 is a schematic diagram showing a diesel reformer.

First, a catalytic apparatus 11 installed in close proximity to the exhaust manifold of the engine 100, that is, a catalytic apparatus 11 using a diesel oxidation catalyst (DOC) as a warm-up catalytic converter (WCC), is installed, and then forward on the exhaust line. CPF filtration system (CPF system; 'Diesel Oxidation Catalyst (DOC) + Diesel Soot Catalyst Filtration Filter (CPF)' system) (12), and NOx absorber (15) and diesel oxidation behind it. A catalyst device using the catalyst 16 is installed.

The CPF filtration device 12 has a configuration in which a diesel oxidation catalyst (DOC) 13 and a diesel particulate catalyst filtration filter (CPF) are arranged in series in a can of a catalyst purifier. In the case of the catalytic apparatus at the rear, the NOx storage catalyst 15 and the diesel oxidation catalyst 16 are arranged in series in the can.

In particular, in the present invention, the injector 19 is installed so that the product gas of the diesel reformer 18, which will be described later, can be injected to the front of the NOx storage catalyst 15, and the injector 19 is provided in a can of the catalytic purifier. It is inserted and installed at a position where gas injection can be made toward the front end of the NOx storage catalyst 15.

On the other hand, the injector 19 is injection controlled by the engine ECU 20 to inject the gas generated from the diesel reformer 18, the engine ECU 20 is provided to operate the injector 19 periodically. .

Preferably, the engine ECU 20 is provided to operate the injector 19 in time for regeneration and desulfurization of the NOx storage catalyst 15 in which fuel post injection is performed.

That is, the injector 19 is injected by the control signal output from the engine ECU 20, the engine ECU 20 injects a control signal for injection of the generated gas during the rich spike control such as after-fuel injection Will print (19).

In addition, the diesel reformer 18 is connected to the fuel line to receive diesel fuel from the fuel tank 17, and at the same time, the air is supplied to the diesel reformer by receiving the diesel fuel and the air. The reaction generates hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (CO ₂ ), and hydrocarbons (HC) having four carbons (C).

Looking at the composition of the main components, hydrogen is at least 21%, carbon monoxide at least 20%, carbon dioxide and hydrocarbons at 5% or less, respectively, the chemical reaction in the diesel reformer 18 is exothermic (autothermal reaction), the temperature of the generated gas Is about 600 to 800 ° C.

In the case of using the diesel reformer 18 as described above, compared with the conventional method of directly injecting the diesel fuel in liquid phase, since all of the products are gaseous, there is no fear of attachment to the catalyst, and the reaction rate in the catalyst is also very fast. There is an advantage.

That is, the injection of the generated gas does not cause problems such as deactivation of the catalyst and catalyst breakdown due to abnormal combustion in the catalyst, which occurred when the fuel decomposition catalyst is used.

As mentioned above, the product gas temperature of the diesel reformer 18 is approximately 600 to 800 ° C., and when this is introduced through the injector 19, the NOx storage catalyst 15 and its rear diesel oxidation catalyst (DOC) 16 are introduced. Increases the low temperature activity of

Since the temperature of a typical diesel exhaust gas is about 150 to 400 ° C. and the start-up temperature is 100 ° C. or lower, the temperature in the exhaust system can be quickly changed by generating heat through the heat of the reformed gas itself and oxidation of the catalyst. You can increase it.

In general, vehicle testing in the NEDC mode (European fuel economy and emissions reference test mode) takes some time to activate the catalyst from the beginning of the startup, which releases a significant amount of harmful emissions.

Therefore, in the present invention, since the catalyst can be heated by the heat of the generated gas by using a diesel reformer, the exhaust gas at the start of the start can be mostly purified by a harmless gas.

In order to optimally operate the NOx storage catalyst, a rich spike must be periodically generated (richly controlled by fuel injection, etc.), and a high temperature of 650 ° C. or higher is required for desulfurization.

To this end, in the prior art, since fuel injection in the engine requires secondary fuel injection into the exhaust pipe, fuel economy loss naturally occurred.

However, the use of the diesel reformer 18 can reduce fuel consumption loss.

That is, in the regeneration process of the NOx storage catalyst (15), when rich spikes are applied, NOx is discharged to N ₂ through the reactions of the reaction formulas (3a), (3b) and (4). It is most effective when hydrogen and carbon monoxide are present together as a reductant, and thus the NOx conversion efficiency is also increased because the temperature required for regeneration can be reduced when regeneration using the product gas of the diesel reformer.

Therefore, the amount of fuel injected after injection can be reduced, and fuel economy can be improved eventually.

In addition, it is most effective in the desulfurization process of the NOx storage catalyst 15 when hydrogen and carbon monoxide are present together, and the amount of post-injection fuel can be greatly reduced compared to the method without using the diesel reformer 18 due to the reducing agent of the reforming gas. .

In particular, as shown in FIG. 1, by placing the diesel particulate catalyst filtration filter (CPF) 14 in front of the NOx storage catalyst 15, fuel efficiency loss can be minimized. As the PM burns, the exhaust gas temperature at the rear end of the CPF 14 rises by about 700 ° C. or more, and the oxygen concentration drops rapidly (the lower the oxygen concentration at the time of desulfurization of the NOx storage catalyst), the more the CPF 14 Regeneration and desulfurization of the NOx occlusion catalyst 15 may be simultaneously performed, and by using this, there is no need for additional measures such as post-injection of fuel for desulfurization of the NOx occlusion catalyst 15, and thus, fuel loss may be minimized.

Of course, in this case, the engine ECU 20 should be provided to output a control signal for the injection operation of the injector 19 at the time when CPF regeneration is performed, wherein the reaction gas generated in the diesel reformer 18 serves as a reducing agent. The amount of injected fuel can be greatly reduced.

In addition, by linking the regeneration of the CPF 14 and the desulfurization of the NOx storage catalyst 15, the volume of the CPF system ('DOC 13 + CPF 14') 12 can be reduced.

In addition, a diesel oxidation catalyst (DOC) 16 is positioned behind the NOx storage catalyst 15 to completely purify the carbon monoxide (CO) and the hydrocarbon (HC) passed through the NOx storage catalyst 15 and the CPF 14. give.

As described above, according to the automobile exhaust gas purification system using the diesel reformer according to the present invention, a CPF system in which DOC and CPF are arranged in series in front of the exhaust line is installed, and the NOx storage catalyst and DOC is installed in a series of catalyst purifiers in series, but the diesel reformer that receives the diesel fuel and air, and generates a synthesis gas of hydrogen and carbon monoxide, carbon dioxide, hydrocarbon by the autothermal reforming reaction by the catalyst is installed by connecting the fuel tank In addition, by providing an injector for receiving the synthesis gas generated from the diesel reformer and injecting the NOx storage catalyst in front, the following effects are obtained.

1) Compared with the conventional method of directly injecting the diesel fuel of liquid phase, since all of the products are gaseous, there is no possibility of attaching to the catalyst, and the reaction speed in the catalyst is also very fast. Problems such as catalyst deactivation due to deactivation of catalyst or abnormal combustion in the catalyst do not occur.

2) Since the product gas temperature of diesel reformer is about 600 ~ 800 ℃ high temperature, if injected through the injector, it will increase the low-temperature activity of the NOx storage catalyst and the DOC of the rear end there is an effect of reducing the exhaust gas.

3) NOx and PM can be reduced at the same time, the amount of post-injected fuel can be reduced, and fuel economy can be improved.

4) By placing the CPF in front of the NOx storage catalyst, regeneration of the CPF and desulfurization of the NOx storage catalyst can proceed at the same time.Therefore, there is no need for additional measures such as post-injection of fuel for desulfurization of the NOx storage catalyst, and thus fuel efficiency. Can minimize the loss.

1 is a block diagram showing a purification system of the present invention,

2 is a schematic view showing a diesel reformer in the present invention,

Figure 3 is a schematic diagram showing a conventional NOx aftertreatment device.

<Explanation of symbols for the main parts of the drawings>

12: CPF filtration device 13: diesel oxidation catalyst (DOC)

14: Diesel particulate catalyst filtration filter (CPF) 15: NOx storage catalyst

16: diesel oxidation catalyst (DOC) 17: fuel tank

18: diesel reformer 19: injector

20: ECU

Claims (3)

In the automobile exhaust purification system, A catalytic purifier having a NOx storage catalyst is installed, and a diesel reformer is provided with diesel fuel and air to generate a synthesis gas including hydrogen and carbon monoxide by autothermal reforming reaction, and receives the synthesis gas generated from the diesel reformer. Injector for injecting to the front end of the catalyst, and the engine ECU is a vehicle exhaust gas purification system using a diesel reformer characterized in that it is provided to output a control signal for the injection operation of the injector in the rich spike (Rich Spike) control mode . The method according to claim 1, A diesel reformer using a diesel reformer characterized in that a CPF system in which a diesel oxidation catalyst (DOC) and a diesel particulate catalyst filtration filter (CPF) are arranged in series on an exhaust line is installed in front of the catalytic purifier with the NOx storage catalyst. Exhaust gas purification system. The method according to claim 1, The engine ECU is a vehicle exhaust gas purification system using a diesel reformer characterized in that it is provided to periodically output a control signal for the injection operation of the injector with the fuel after injection.