KR101091625B1 - Exhaust system - Google Patents

Abstract

The present invention relates to an exhaust system for reducing nitrogen oxide contained in exhaust gas.

Exhaust system according to an embodiment of the present invention, the exhaust line passing through the exhaust gas is discharged to the outside, the injector for injecting fuel to the exhaust line, converting the fuel additionally injected from the injector into a reducing agent, exhaust gas Part of the nitrogen oxide contained in the fuel is reduced by using unburned fuel or hydrocarbon, and another part of the nitrogen oxide is purified by the nitrogen oxide purification catalyst installed in the exhaust line and the injector under the set conditions so as to diffuse and store the fuel therein. And a control unit for additional injection, wherein the nitrogen oxide purification catalyst desorbs and stores the stored nitrogen oxide using a reducing agent formed by the fuel additionally injected from the injector.

Injector, NOx, Fuel Decomposition Catalyst, DPF, DOC, Nitrogen Oxide, Purification Catalyst

Description

Exhaust system {EXHAUST SYSTEM}

The present invention relates to an exhaust system, and more particularly to an exhaust system for reducing nitrogen oxide contained in the exhaust gas.

In general, the exhaust gas discharged from the engine through the exhaust manifold is guided to a catalytic converter formed in the middle of the exhaust pipe and purified, and the noise is attenuated while passing through the muffler, and then released into the atmosphere through the tail pipe.

The catalytic converter treats pollutants contained in the exhaust gas. And a soot filter for trapping particulate matter (PM) contained in the exhaust gas is mounted on the exhaust pipe.

Selective Catalytic Reduction (SCR) equipment is a type of such catalytic converter. Selective Catalytic Reduction (SCR) devices are termed selective catalytic reduction in the sense that reducing agents such as urea, ammonia, carbon monoxide and hydrocarbons (HC) react better with nitrogen oxides in oxygen and nitrogen oxides. do.

In the case of internal combustion engines equipped with such a selective catalytic reduction device, fuel was continuously injected continuously according to the amount of nitrogen oxide contained in the exhaust gas. Thus, slip of hydrocarbon occurs and fuel economy deteriorates.

An object of the present invention is to store a portion of the nitrogen oxide contained in the exhaust gas, and according to the set conditions further convert the fuel injected into a reducing agent to desorb the stored nitrogen oxide using the reducing agent, the desorbed nitrogen oxide It is to provide an exhaust system for reducing by using the reducing agent.

Exhaust system according to an embodiment of the present invention for achieving this object, an exhaust line through which the burned exhaust gas is discharged to the outside, an injector for injecting fuel to the exhaust line, a fuel injected further from the injector reducing agent The nitrogen oxide purification catalyst installed in the exhaust line to convert a portion of the nitrogen oxide contained in the exhaust gas into an unburned fuel or hydrocarbon and to diffuse and store the other portion of the nitrogen oxide therein. And a control unit for controlling the injector to further inject fuel, wherein the nitrogen oxide purification catalyst desorbs and stores the stored nitrogen oxide using a reducing agent formed by the fuel additionally injected from the injector.

The nitrogen oxide purification catalyst is a fuel decomposition catalyst layer which is disposed in close proximity to the exhaust gas and splits the fuel using the catalyst component contained therein to form a highly reactive reducing agent, and is formed inside the fuel decomposition catalyst layer to form the exhaust gas. A reduction catalyst layer for reducing and removing nitrogen oxides, and a storage catalyst layer formed inside the reduction catalyst layer to store the nitrogen oxide contained in the exhaust gas.

The reduction catalyst layer reduces a portion of the nitrogen oxides contained in the exhaust gas by an oxidation-reduction reaction with unburned fuel or hydrocarbons contained in the exhaust gas, and diffuses another portion of the nitrogen oxides into the storage catalyst layer, The storage catalyst layer stores the diffused nitrogen oxide and desorbs the stored nitrogen oxide using a reducing agent formed in the fuel decomposition catalyst layer to be reduced in the reduction catalyst layer.

The fuel decomposition catalyst layer is characterized in that it comprises at least one catalyst component of Pt, Pd, Rh, Ir, Ru, W, Cr, Mn, Fe, Co, Cu, Ag, and Zn.

The fuel decomposition catalyst layer cuts the long carbon ring of the fuel to form a plurality of short hydrocarbons to improve the purification efficiency of the nitrogen oxides in the nitrogen oxide purification catalyst.

The injector includes a first injector for injecting fuel into a cylinder of an engine, and a second injector installed in the exhaust line to inject fuel.

As described above, according to the present invention, the nitrogen oxide purification catalyst includes a fuel decomposition catalyst layer for transforming fuel contained in exhaust gas into a highly reactive reducing agent, and a reduction for reducing nitrogen oxides of exhaust gas using a reducing agent formed in the fuel decomposition catalyst layer. By storing a nitrogen oxide contained in the catalyst layer and the exhaust gas, the storage catalyst layer for desorbing the stored nitrogen oxides to the reducing catalyst layer under the set conditions, thereby effectively removing the nitrogen oxide contained in the exhaust gas.

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

An exhaust system according to an embodiment of the present invention will first be described with reference to FIG. 3.

3 is a schematic structural diagram of an exhaust system according to an embodiment of the present invention.

Referring to FIG. 3, the exhaust system includes an engine 300, an exhaust line, an injector 310, and a nitrogen oxide purification catalyst 320.

The injector 310 and the nitrogen oxide purification catalyst 320 are sequentially disposed in the exhaust line.

Although not shown, the exhaust line includes a turbocharger (not shown), a catalytic filtration filter (not shown), a differential pressure sensor (not shown), a temperature sensor (not shown), and a detailed description thereof will be omitted.

Exhaust gas combusted in the cylinder of the engine 300 is discharged to the outside through the exhaust line, the turbocharger (for example, a turbine) is disposed in the exhaust line of the rear end of the engine 300, The turbocharger is connected to the intake line to charge air to the engine.

The injector 310 and the nitrogen oxide purification catalyst 320 are sequentially disposed in the exhaust line.

The ratio of the nitrogen oxide stored in the nitrogen oxide purification catalyst 320 and the HC in the exhaust gas is set in the map data, and the controller compares the ratio of HC to NOx and the value set in the map data under the actual operating conditions. When the value is less than or equal to the set value, the injector 310 is operated to further inject fuel into the exhaust line.

The structure and function of the nitrogen oxide purification catalyst will be described with reference to FIGS. 1 and 2.

1 is a cross-sectional view showing the storage mode of the nitrogen oxide purification catalyst provided in the exhaust system according to an embodiment of the present invention, Figure 2 is a regeneration mode of the nitrogen oxide purification catalyst provided in the exhaust system according to an embodiment of the present invention It is a cross-sectional view.

Referring to FIG. 1, a fuel decomposition catalyst layer 100 is formed on a carrier constituting the nitrogen oxide purification catalyst 320 and adjacent to exhaust gas, and a reducing catalyst layer 110 is formed therein. The storage catalyst layer 120 is formed inside the reduction catalyst layer 110.

The fuel decomposition catalyst layer 100 breaks the chain ring of the carbon compound contained in the fuel through a catalytic reaction as in the following reaction formula.

Steam Reforming: C16H34 + 16H2O ↔ 16CO + 33H2

* Partial Oxidation: C16H34 + 0.5O2 → 8C2H4 + H2O, C16H34 + 8O2 ↔ 16CO + 17H2

* Catalytic Cracking: C11-CH2-CH2-CH2-CH2-CH3 (long chain) → C11-CH = CH2 (olefine) + CH3-CH2-CH3 (Praffin)

In addition, the fuel decomposition catalyst layer 100 is broken by breaking the connecting ring constituting the hydrocarbon through the thermal cracking function to decompose the fuel as shown in the following reaction formula.

* C ₁₆ H ₃₄ → 2n-C ₈ H17 * → nC ₆ H ₁₃ * → nC ₄ H ₉ * → C ₂ H ₅ * → C ₂ H ₄

* C ₁₆ H ₃₄ → 8C ₂ H ₄ + H ₂ , * means a radical.

As described above, the fuel decomposition catalyst layer 100 converts some of the hydrocarbons into hydrocarbons combined with oxygen to activate fuel injected from the injector 310.

In addition, the fuel decomposition catalyst layer 100 converts the fuel evaporated and ejected into the droplet state into a highly reactive reducing agent, and also reduces the concentration of oxygen and increases the temperature of the exhaust gas by oxidation.

The catalyst component included in the fuel decomposition catalyst layer 100 may include at least one of Pt, Pd, Rh, Ir, Ru, W, Cr, Mn, Fe, Co, Cu, Zn, and Au.

A nitrogen oxide detection sensor may be provided at a rear end of the nitrogen oxide purification catalyst 320, and the nitrogen oxide detection sensor may detect an amount of nitrogen oxide in the exhaust gas and transmit a signal thereof to the controller.

On the other hand, instead of using the nitrogen oxide sensor, it is preferable to predict the storage amount from the map determined by the experimental value.

The controller removes and removes nitrogen oxide stored in the storage catalyst layer 120 of the nitrogen oxide purification catalyst 320 by controlling the additional injection amount and the additional injection timing of the fuel based on the signals and map data detected by the sensors. do.

The control unit is a ratio in which the ratio of the hydrocarbon (HC) to the nitrogen oxide (NOx) contained in the exhaust gas so that the nitrogen oxide stored in the storage catalyst layer 120 of the nitrogen oxide purification catalyst 320 is separated and easily reduced Control to be abnormal. The set ratio may be eight.

The reduction catalyst layer 110 oxidizes the nitrogen oxide contained in the exhaust gas, and reduces a portion of the oxidized nitrogen oxide by redox reaction with unburned fuel or hydrocarbon contained in the exhaust gas.

In addition, another portion of the oxidized nitrogen oxide is diffused into the storage catalyst layer 120. As shown, the reduction catalyst layer 110 may include at least one of a zeolite catalyst and a metal catalyst supported on the porous alumina.

The zeolite catalyst is a catalyst in which at least one element of copper, platinum, manganese, iron, cobalt, nickel, zinc, silver, cerium, and gallium is ion exchanged. Chemical reactions occurring in the zeolite catalyst are as follows.

Z-Cu ²⁺ O- + NO → Z-Cu ²⁺ (NO _2- ) _ads → Z-Cu ²⁺ + NO ₂

Z ⁺ O- + NO → Z ⁺ (NO _2- ) _ads → Z ⁺ + NO ₂

Z-Cu ²⁺ (NO _2- ) _ads + NO → Z-Cu ²⁺ (N ₂ O ₃ ) _-ads → Z-Cu ²⁺ O- + N ₂ + O ₂

ZH ⁺ + C _n H _2n → ZC _n H _{2n + 1} ⁺ → n (ZH) + C _n H _2n ⁺

mNO ₂ + C _n H _2n + → C _n H _2n N _m O _2m → N ₂ + CO ₂ + H ₂ O

Here, Z means zeolite and subscript ads means adsorption.

In addition, at least one metal of platinum, palladium, rhodium, iridium, ruthenium, tungsten, chromium, manganese, iron, cobalt, copper, zinc, and silver may be used as the metal catalyst supported on the porous alumina. Chemical reactions occurring in the metal catalyst supported on the porous alumina are as follows.

NO + O ₂ → (NO _x ) _ads

THC + (NO _x ) _ads → THC-ONO or THC-NO ₂

THC-NO ₂ → THC-NCO

THC-NCO + NO + O ₂ → N ₂ + CO ₂ + H ₂ O

Here, THC means hydrocarbon. As mentioned above, hydrocarbons are intended to represent compounds composed of carbon and hydrogen contained in exhaust gases and fuels.

The storage catalyst layer 120 stores a portion of the nitrogen oxide oxidized in the reduction catalyst layer 110, and desorbs the stored nitrogen oxide by fuel injected further according to a set condition so that the storage catalyst layer 120 is reduced in the reduction catalyst layer 110. do.

As mentioned above, the set condition is a case where the nitrogen oxide stored in the storage catalyst layer 120 is greater than or equal to the value set in the map data so that the reduction reaction of the nitrogen oxide in the reduction catalyst layer 110 is activated.

The storage catalyst layer 120 includes a noble metal and a nitrogen oxide storage material. Barium oxide may be used as the nitrogen oxide storage material. The precious metal promotes the storage of nitrogen oxides by the nitrogen oxide storage material. As the precious metal, various metal materials such as platinum and palladium may be used.

Hereinafter, the operating principle of the present invention will be described in detail.

NOx storage mode

When the nitrogen oxide stored in the storage catalyst layer 120 is smaller than the set value, the nitrogen oxide contained in the exhaust gas is oxidized in the reduction catalyst layer 110, and a part of the oxidized nitrogen oxide is combined with hydrocarbons contained in the exhaust gas. The oxidation-reduction reaction is reduced to nitrogen gas, and the other part is stored in the storage catalyst layer 120. In this process, the hydrocarbons contained in the exhaust gas are oxidized to carbon dioxide. The reaction occurring in the reduction catalyst layer 110 is briefly expressed as in the following equation.

NO + 1 / 2O ₂ → NO ₂

NO + HC → 1 / 2N ₂ + CO ₂

In addition, when a portion of the oxidized nitrogen oxide and nitrogen oxide contained in the exhaust gas are diffused and stored in the storage catalyst layer 120, the noble metal of the storage catalyst layer 120 is a nitrogen oxide storage material stores the nitrogen oxide. Promotes The reaction occurring in the storage catalyst layer 120 is briefly expressed as in the following equation.

BaO + 2NO ₂ + 1 / 2O ₂ → Ba (NO ₃ ) ₂

NOx Regeneration Mode

When the nitrogen oxide stored in the storage catalyst layer 120 is greater than or equal to a set value, the controller causes the injector 310 to further inject fuel.

The further injected fuel is converted into low molecular hydrocarbons in the fuel decomposition catalyst layer 100 and converted. In addition, some of the low molecular weight hydrocarbons are converted to hydrocarbons combined with oxygen.

At this time, in the storage catalyst layer 120, the nitrogen oxide is desorbed through the substitution reaction with the hydrocarbon, which is briefly expressed as follows.

Ba (NO ₃ ) ₂ + 3CO → BaCO ₃ + 2NO + 2CO ₂

In addition, in the reduction catalyst layer 110, the nitrogen oxide is reduced to nitrogen gas by a redox reaction between the nitrogen oxide desorbed from the storage catalyst layer 120 and the hydrocarbon combined with the hydrocarbon / oxygen, and the hydrocarbon combined with the hydrocarbon / oxygen is Oxidized to carbon dioxide. This is briefly expressed as follows.

NO + HC / Oxygenated HC = 1 / 2N ₂ + CO ₂

As described above, nitrogen oxides and hydrocarbons contained in the exhaust gas are purified.

In the embodiment of the present invention, instead of continuously performing further injection of fuel, the control unit performs further injection of fuel in the injector when the ratio of HC / NOx in exhaust gas is equal to or less than a preset value.

Therefore, since fuel is additionally injected under conditions optimized according to the operating conditions, slip of hydrocarbon is prevented and fuel economy is improved.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, And all changes to the scope that are deemed to be valid.

1 is a cross-sectional view illustrating an occlusion mode of a nitrogen oxide purification catalyst included in an exhaust system according to an exemplary embodiment of the present invention.

2 is a cross-sectional view showing a regeneration mode of the nitrogen oxide purification catalyst provided in the exhaust system according to the embodiment of the present invention.

3 is a schematic structural diagram of an exhaust system according to an embodiment of the present invention.

Claims (6)

An exhaust line through which the burned exhaust gas is discharged to the outside; An injector for injecting fuel into the exhaust line or the cylinder of the engine; The fuel injected further from the injector is converted into a reducing agent, and a part of the nitrogen oxide contained in the exhaust gas is reduced by using unburned fuel or hydrocarbon, and another part of the nitrogen oxide is diffused into the exhaust line so as to be stored. Installed nitrogen oxide purification catalysts; And A controller configured to control the injector under additional conditions to further inject fuel; Including, The nitrogen oxide purification catalyst is reduced by desorbing the stored nitrogen oxide using a reducing agent formed by the fuel additionally injected from the injector, A fuel decomposition catalyst layer disposed in close proximity to the exhaust gas to split a fuel using a catalyst component included therein to form a highly reactive reducing agent; A reduction catalyst layer formed inside the fuel decomposition catalyst layer to reduce and remove nitrogen oxides in the exhaust gas; And A storage catalyst layer formed inside the reduction catalyst layer to store nitrogen oxide contained in exhaust gas; Exhaust system comprising a. delete The method according to claim 1, The reduction catalyst layer reduces a portion of the nitrogen oxides contained in the exhaust gas by an oxidation-reduction reaction with unburned fuel or hydrocarbons contained in the exhaust gas, and diffuses another portion of the nitrogen oxides into the storage catalyst layer, And the storage catalyst layer stores the diffused nitrogen oxide and desorbs the stored nitrogen oxide using a reducing agent formed in the fuel decomposition catalyst layer to be reduced in the reduction catalyst layer. The method according to claim 1, The fuel cracking catalyst layer comprises at least one catalyst component of Pt, Pd, Rh, Ir, Ru, W, Cr, Mn, Fe, Co, Cu, Ag, and Zn. The method according to claim 1, The fuel decomposition catalyst layer is an exhaust system, characterized in that to cut the long carbon ring of the fuel to make a plurality of short hydrocarbons to improve the purification efficiency of the nitrogen oxide in the nitrogen oxide purification catalyst. The method according to claim 1, The injector, A first injector for injecting fuel into a cylinder of the engine; And A second injector installed in the exhaust line to inject fuel; Exhaust system comprising a.

Images