JP2005113832A - Method for controlling engine emission gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling engine emission gas in which a fuel as a reducing-agent is injected in a cylinder after a piston has reached the top dead center in the exhaust stroke, so that exhaust-gas containing thermally decomposed fuel reducing-agent is brought into contact with a denitration catalyst to efficiently remove NOx, and an un-reacted light-oil reducing agent, and HC, PM and CO are removed by an oxidation catalyst to attain simultaneous removal of NOx, PM, HC and CO in the exhaust gas of an diesel engine. <P>SOLUTION: By the method for controlling emission gas, nitrogen oxides (NOx) particulate matters (PM), hydrocarbons (HC), and carbon monoxide (CO) in the engine emission-gas are removed. The denitration catalyst and the oxidation catalyst are arranged in series in the exhaust-gas passage of the engine. Engine exhaust-gas is brought into contact with the denitration catalyst in the presence of fuel reducing-agent derived from a part of the fuel, subsequently is brought into contact with the oxidation catalyst to purify the exhaust gas. In this case, the fuel reducing-agent is injected in the cylinder after the piston having reached the top-dead center, so that the engine emission-gas containing the injected fuel reducing-agent is brought into contact with the denitration catalyst to purify the nitrogen oxides. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for purifying exhaust gas from a diesel engine or a lean combustion engine.

  In lean combustion such as diesel engines, nitrogen oxides (NOx) are not decomposed even if they come into contact with the three-way catalyst in the presence of reducing components of carbon monoxide (CO) and hydrocarbons (HC) due to excess oxygen exhaust gas. In recent years, however, small diesel engines have become possible to operate lean combustion and rich combustion alternately by adopting an electronically controlled fuel injection system. NOx is absorbed by the absorbent during lean combustion, and from the NOx absorbent during rich combustion. A NOx occlusion reduction method in which NOx is released and NOx decomposed with a three-way catalyst has been proposed (see Non-Patent Document 1). However, in large diesel engines, alternate operation of lean combustion and rich combustion is possible, but fuel consumption is greatly deteriorated, and catalyst deterioration due to sulfur in the fuel is also large, and the NOx occlusion reduction method has not been put into practical use (non-patent) Reference 2).

  In addition, as a NOx purification method for large diesel engines, practical use of the urea selective reduction method has been studied, and high purification performance has been obtained, but it is practical due to problems such as downsizing of the removal equipment and development of urea supply infrastructure It has not led to.

  Patent Document 1 discloses a NOx reduction system that combines exhaust gas recirculation (EGR) and a denitration catalyst. This method can achieve a certain level of effect by bringing the exhaust gas with a predetermined amount of diesel oil reducing agent into contact with the NOx removal catalyst in the engine exhaust passage, but this method is also becoming more stringent every year. It's not enough.

Furthermore, the exhaust temperature of the next-generation diesel engine with a cold supercharger and cold EGR is 180-400 ° C, especially in urban areas, which is lower than 300 ° C. The NOx selective reduction method that adds light oil fuel directly to the exhaust path is It will be disadvantageous.
JP-A-9-122447 Hirota et al., Diesel PM, NOx simultaneous reduction catalyst system, Automobile Engineering Society Annual Conference No.68-01 (2001) T. Tanaka, After-Treatment System and Fuel Properties for Controlling Engine Emissions, Proceedings of the International Workshop on Next Generation Power Systems for Automobiles (Proceedings of the International Workshop on Next Generation Power System for Automobiles). (IWPS2000) p58-67 (2000)

  An object of the present invention is to inject a fuel reducing agent into a cylinder after exhaust top dead center and efficiently remove nitrogen oxides (NOx) by contacting the exhaust gas containing the thermally decomposed fuel reducing agent with a denitration catalyst. NOx, PM, HC and CO in diesel engine exhaust gas that removes unreacted diesel oil reducing agent and removes hydrocarbon (HC), particulate matter (PM), and carbon monoxide (CO) with an oxidation catalyst It is to provide a method for purifying engine exhaust gas.

The above object is achieved by the present invention described below.
(1) A method for purifying engine exhaust gas that removes nitrogen oxides (NOx), particulate matter (PM), hydrocarbons (HC), and carbon monoxide (CO) in engine exhaust gas, the engine exhaust gas A denitration catalyst and an oxidation catalyst are arranged in series in the exhaust passage of the engine, and the engine exhaust gas is brought into contact with the denitration catalyst in the presence of a fuel reducing agent from which a part of the fuel has been taken out, and then brought into contact with the oxidation catalyst. When purifying exhaust gas,
An electronically controlled fuel injection device injects a fuel reducing agent into the cylinder after the top dead center of the piston position, and contacts the engine exhaust gas containing the injected fuel reducing agent with a denitration catalyst to purify nitrogen oxides, Thereafter, the engine exhaust gas purification method is brought into contact with the oxidation catalyst.
(2) The denitration catalyst is a granular or monolithic catalyst with titanium and silver supported on γ-alumina, using light oil as a fuel reducing agent, with an engine speed ratio of 50% or more and an engine load ratio of 40% or more. When it reaches, the diesel fuel is injected into the cylinder after the top dead center of the piston position by an electronically controlled fuel injection device so that the ratio of light oil / nitrogen oxide (NO conversion amount) ratio is 0.5-4 by mass ratio. The engine exhaust gas purification method according to (1), wherein the engine exhaust gas containing the injected light oil is brought into contact with a denitration catalyst and nitrogen oxide is purified by a nitrogen oxide (NOx) selective reduction method.
(3) The denitration catalyst has a titanium layer in which titanium is supported on a γ-alumina carrier and calcined to form anatase-type titanium oxide. Further, silver is supported on the titanium layer and calcined. (2) The method for purifying engine exhaust gas according to (2) above, comprising a silver layer on which silver oxide is formed.
(4) A diesel engine equipped with an electronically controlled fuel injection device, which uses diesel fuel as a reducing agent, and the electronically controlled fuel injection device allows the diesel oil / nitrogen oxide to be added to the cylinder after the top dead center of the piston position. (2) or (3) for purifying exhaust gas from a diesel engine equipped with an electronically controlled fuel injection device by injecting light oil so that the (NO equivalent) ratio is a mass ratio of 2 to 3 A method for purifying engine exhaust gas.
(5) Any one of the above (1) to (4), in which a fuel reducing agent is injected into a cylinder after the top dead center of the piston position by an electronically controlled fuel injection device to obtain a low molecular weight fuel reducing agent by thermal decomposition How to clean the engine exhaust.
(6) The method for purifying engine exhaust gas according to any one of the above (1) to (5), wherein the oxidation catalyst is a catalyst in which at least one metal selected from platinum and palladium is supported on γ-alumina.
(7) The engine exhaust gas purification method according to any one of (1) to (6), wherein a catalyst reactor having a catalyst layer having a denitration catalyst layer as a first layer and an oxidation catalyst layer as a second layer is disposed.
(8) The exhaust gas recirculation (EGR) system is combined, the EGR system is operated when the engine is under a low load, and the engine exhaust gas is brought into contact with the denitration catalyst and the oxidation catalyst when the engine is under a high load. ) Any method for purifying engine exhaust gas.

  According to the present invention, preferably, γ-alumina is used as a carrier, titanium is supported on this carrier and calcined, and further, the silver supported on this titanium carrier and calcined is used as a denitration catalyst. Nitrogen oxide (NOx) in diesel engine exhaust gas is removed by contacting the catalyst with a fuel reducing agent partially added to the exhaust gas. In the present invention, preferably, light oil is used as a fuel reducing agent, and NOx can be removed by contacting the exhaust gas containing light oil with a denitration catalyst. However, light oil is a high-boiling point saturated hydrocarbon. It is easy to suppress the denitration reaction because it is a mixture of alcohols and aromatic compounds. When light oil is pyrolyzed, it can be converted into low-molecular hydrocarbons. By using this as a reducing agent, NOx can be removed with high efficiency.

  In this thermal decomposition of the fuel reducing agent, in the present invention, since the fuel reducing agent is injected into the cylinder after the top dead center of the piston position, the thermal reduction of the fuel reducing agent proceeds very efficiently, which is advantageous for NOx removal. Conversion to a low molecular weight hydrocarbon is sufficient. Further, since NOx generated in each cylinder can be removed, the efficiency is higher than injecting the fuel reducing agent into the exhaust passage.

  Furthermore, since an electronically controlled fuel injection device is used as the reducing agent addition device, a new supply pump, control device and piping are not required, which is advantageous from the viewpoint of safety and economy.

Hereinafter, the present invention will be described in detail.
In the present invention, exhaust gas purification of a diesel engine is performed by arranging a denitration catalyst (NOx reduction catalyst) and an oxidation catalyst in series in the exhaust gas exhaust passage. In this case, the exhaust gas is brought into contact with the denitration catalyst, and then the oxidation catalyst is brought into contact. However, when contacting with the denitration catalyst, the electronically controlled fuel injection device uses a fuel to the cylinder after the top dead center of the piston position. Is injected and contacted in the presence of a pyrolyzed fuel reducing agent.

  The electronically controlled fuel injection device is a high-pressure fuel injection system with a fuel injection pressure of 180 MPa, and includes a supply pump, a common rail (pressure accumulation chamber), a common rail pressure sensor, a solenoid injector, an injector drive control unit, and an engine control unit. It is configured. The high-pressure fuel sent from the supply pump is stored in the common rail, and injected from the solenoid injector into the combustion chamber. The feature of this injection device is that high-pressure fuel stored in the common rail can be injected not only at high-pressure injection of fuel but also at low engine speeds. It is said that PM can be reduced. In addition, fuel injection from the solenoid injector can be controlled at intervals of 1/2000 second, so multistage injection is possible. In the near future, pilot injection, pre-injection, main injection, after-injection, and post-injection five-stage injection It is said that you can also.

  In the present invention, since light oil is specifically preferably used as the fuel, the method for thermally decomposing light oil fuel of the present invention is carried out by carrying out the pyrolysis reaction of the fuel reducing agent using this fuel injection device. . Specifically, the exhaust process is used among the piston movements of the intake process → the compression process → the explosion process → the exhaust process. If you look at this piston process corresponding to the opening and closing of the piston valve, it will vary depending on the presence or absence of the engine addition device and the fuel type, but in general, the intake air opens at a position of 5 to 20 ° before the top dead center of the piston, and the air flows into the cylinder. Then, after the intake valve closes at 30-40 ° after bottom dead center, the compression process shifts to the explosion process. The explosion process ends at 50 to 55 ° before the bottom dead center, the exhaust valve opens immediately, the process proceeds to the exhaust process, and the exhaust valve closes at 5 to 20 ° after the top dead center. At this time, in the range of ± 20 ° before and after the piston top dead center, the intake and exhaust valves are open, but the combustion exhaust gas is released to the outside because the pressure in the cylinder is higher than the atmosphere.

  When the exhaust manifold temperature reaches 300 ° C or higher, the engine speed ratio is 50% or higher, and the engine load ratio is 40% or higher, the piston exhaust process, that is, the piston position is dead. From the time when the point is reached until the exhaust valve is closed (specifically, in the range of 5 to 20 ° after the top dead center when the exhaust valve is closed), the NOx amount (NO conversion amount) is preferably 0.5 to 4 times the amount (mass), more preferably 0.5 to 3 times the amount (mass), even more preferably 1 to 3 times the amount (mass), particularly preferably 2 to 3 times the amount (mass) Dispersed and injected to prepare a pyrolytic fuel reducing agent.

  By injecting the fuel reducing agent in this way, the temperature of the fuel reducing agent varies depending on conditions such as the engine speed ratio and engine load ratio, but is exposed to a high temperature atmosphere of 400 to 800 ° C. It is thermally decomposed and becomes a low molecular hydrocarbon preferable for the progress of the denitration reaction. In addition, since the injection is in the cylinder, NOx generated in each cylinder can be removed. For this reason, extremely high efficiency NOx removal can be realized. Further, since the fuel reducing agent is injected by the electronically controlled fuel injection device, there is no need to newly install a fuel reducing agent injection device. Moreover, in diesel engines, light oil is used as fuel, and light oil can be used as a reducing agent as it is, and it is not necessary to add new components together with the use of an electronically controlled fuel injection device.

  In diesel engines equipped with an electronically controlled fuel injection device, the installation of the electronically controlled fuel injection device tends to improve fuel combustion efficiency and reduce the generation of particulate matter (PM). NOx generation tended to increase. In the present invention, since NOx removal can be performed efficiently, the effect can be sufficiently exerted in a diesel engine equipped with an electronically controlled fuel injection device.

  First, depending on the contact between the exhaust gas containing the pyrolytic fuel reducing agent obtained under the above conditions and the denitration catalyst, in particular, the exhaust temperature is 250 ° C. or more, which is the operating temperature of the denitration reaction by the denitration catalyst When the engine speed ratio is 50% or more and the engine load ratio is 40% or more, the denitration reaction starts and nitrogen oxides (NOx) are removed. In particular, light oil fuel can be converted into low molecular weight hydrocarbons by pyrolysis, and by using this as a reducing agent, the effect of the NOx purification rate is enhanced. The denitration catalyst exhibits activity at 250 ° C. or higher, further 300 ° C. or higher, particularly 350 to 550 ° C.

  On the other hand, depending on the contact with the oxidation catalyst, combustion of particulate matter (PM), hydrocarbon (HC) and carbon monoxide (CO) starts when the exhaust gas temperature reaches 250 ° C or higher. The material is removed. At the same time, the unreacted substance (surplus) of the fuel reducing agent used in the denitration reaction is removed by combustion. The oxidation catalyst exhibits activity at 250 ° C. or higher, particularly 250 to 500 ° C.

  In this manner, by arranging the denitration catalyst and the oxidation catalyst in series in order, it is possible to efficiently remove all NOx, PM, HC and CO in the exhaust gas. Moreover, since the reducing agent remaining without being used in the denitration reaction can be removed, the removal of harmful substances in the exhaust gas further proceeds.

  Such a removal effect cannot be obtained only by arranging one of the catalysts, and if the arrangement order is changed, the above harmful substances are increased, or once detoxified ones are made harmful substances. The catalyst acts in such a direction as to return, and again such a removal effect cannot be obtained.

  The denitration catalyst used in the present invention is preferably one in which γ-alumina is used as a carrier and titanium and silver are carried on this carrier, while the oxidation catalyst is at least one metal selected from platinum and palladium using γ-alumina as a carrier. It is preferable to carry one.

  The carrier of the denitration catalyst and the oxidation catalyst may be primary particles of γ-alumina (particle size: 0.9 to 20 μm, preferably 2 to 10 μm), or may be used after being formed into secondary particles. May be granular or monolithic such as honeycomb.

As the γ-alumina particles, it is preferable to use particles having a specific surface area of 100 m ² / g or more by a nitrogen adsorption method (BET method). In addition, although there is no restriction | limiting in particular about the upper limit of a specific surface area, Usually, it is about 1000 m < ² > / g.

The γ-alumina support preferably contains γ-alumina in the alumina component at 50% (mass percentage) or more, particularly preferably 90% (mass percentage) or more. This content can be determined from a fluorescent X-ray chart. In the γ-alumina carrier, the Al ₂ O ₃ component is preferably 90% (mass percentage) or more, SiO ₂ is preferably 10% (mass percentage) or less, and Na ₂ O, Fe ₂ O _{3 and the} like. It is preferable that the content of impurities is 1% (mass percentage) or less. γ-alumina is a thermal decomposition method of crystalline alumina hydrate, a method in which sodium aluminate is neutralized with aluminum sulfate and calcined (“Catalyst Course” “Catalyst Design” Kodansha 1985), hydrolysis of aluminum metal alkoxide You may obtain by any methods, such as the method of preparing by, and may use what is marketed.

  The denitration catalyst is preferably one in which titanium is first supported on a γ-alumina carrier, then dried and air calcined, and then silver is supported and then dried and air calcined, and has a silver layer on the titanium layer. Is preferred. The catalyst at this time may be granular or powder. Alternatively, the powder catalyst may be a monolith that is wash-coated.

In addition to the catalyst supported in the order of titanium and silver, the catalyst supported on the opposite side, or the catalyst supported by mixing both components may be used. However, when moisture and sulfur oxide (SO ₂ ) coexist in the exhaust gas In the former, the catalyst supported in the order of titanium and silver has a lower denitration activity reduction and a longer catalyst life. Further, the combined use of titanium and silver makes it possible to obtain denitration activity from a relatively low temperature (for example, 250 ° C. or higher, and further 300 ° C. or higher).

  The supported amount of titanium and silver in the denitration catalyst is, in terms of metal, preferably 0.1 to 2% (mass percentage) of titanium, more preferably 0.2 to 0.8% (mass percentage). The content is preferably 0.1 to 2.5% (mass percentage), more preferably 0.3 to 1.2% (mass percentage). Thus, the denitration activity is improved by adjusting the metal loading.

  In addition, when forming a titanium layer and a silver layer, it may be in the state which diffused and mixed, for example, silver into the titanium layer or titanium into the silver layer in the vicinity of the contact surface of adjacent layers. Further, a metal such as titanium may be diffused in the carrier, and components in the carrier may be diffused into a metal layer such as a titanium layer. Titanium and silver are usually present as oxides, but some or all of them may be in a metallic state. Titanium produces anatase-type titanium oxide by firing.

  The oxidation catalyst is preferably one in which palladium is supported on a γ-alumina carrier, then dried and air calcined, and the catalyst in this case may be granular or powder. Moreover, the powder catalyst may be a monolith that is wash-coated. Thus, it is preferable to use palladium, but platinum may be used instead of palladium, or both may be used in combination. When both are used in combination, they may be supported in a layered form or mixed and supported, or diffusion of components may occur between layers or between a layer and a carrier. These are usually present as oxides, but may be present as metals.

  The supported amount of palladium and / or platinum in the oxidation catalyst is preferably 0.03 to 0.5% (mass percentage) in terms of metal, more preferably 0.05 to 0.1% (mass percentage).

  The use of a catalyst with a low palladium / platinum catalyst, particularly in a diesel engine equipped with an electronically controlled fuel injection device, improves combustion efficiency, and sulfuric acid tends to be generated by sulfur components in the fuel, but this is prevented. For this reason, sulfuric acid production can be further suppressed by using the above metal loading.

  In the above, as a method of supporting a metal on a carrier, a method of adding a carrier to an aqueous solution of a metal compound such as a metal salt and carrying the mixture while stirring is common. The carrier at this time may be granular or monolithic. Thereafter, drying may be performed at a temperature of about 120 ° C. for about 10 to 20 hours, and baking may be performed at about 400 to 700 ° C. for about 1 to 4 hours. Examples of the metal compound used at this time include titanium trichloride, titanium tetrachloride, titanium sulfate, titanium alkoxide (for example, titanium butoxide) as the titanium compound, and silver compounds such as silver nitrate and silver acetate as the palladium compound, and palladium compound. Examples thereof include metal salts and complex salts such as palladium chloride, palladium nitrate, and palladium acetate, and examples of platinum compounds include chloroplatinic acids, tetraamineplatinic acid, and hexahydroxoplatinic acid Na. At this time, the concentration of the aqueous solution of the metal compound to be used is about 0.005 to 0.2 mol / L.

  The denitration catalyst and the oxidation catalyst are preferably used as a catalyst reactor in which each catalyst is packed in layers in the container, the denitration catalyst is the first layer and the oxidation catalyst layer is the second layer from the exhaust gas introduction side. . This facilitates installation and replacement of the catalyst.

The present invention is applied to exhaust gas purification of diesel engines and lean combustion engines. Exhaust gas current emission compliance diesel engine (1998) is, NOx: 100~700ppm, HC: 50~400ppm , CO: 60~300ppm, CO 2: 1~10 vol%, SO _2: 5~20ppm about Contains ingredients.

  Moreover, in this invention, you may combine with another emission reduction technique in combination with a catalyst reactor and an electronically controlled fuel injection apparatus. As such a thing, there exist a combination with emission reduction technologies, such as a supercharger, EGR (exhaust gas recirculation), and a diesel particulate filter (DPF: Diesel Particulate Filter).

  In particular, depending on the combination with EGR, the NOx reduction effect is further improved.

  The EGR system has an EGR passage for recirculating exhaust gas to the intake passage, and an EGR control valve for opening and closing the EGR passage. The EGR system lowers the oxygen temperature in the intake air and generates NOx. It is to suppress. The operation control of the EGR system, that is, the adjustment of the EGR rate is performed by adjusting the carbon dioxide concentration in the exhaust gas and the intake gas, the oxygen concentration in the intake passage, the pressure in the intake passage, the engine speed, the coolant temperature, the fuel injection amount, and the exhaust gas. It is preferable to detect at least one type of parameters selected from the gas temperature and perform based on these parameters.

  The operation control of the EGR system is preferably performed as follows. The EGR system is operated when the engine load is low and the exhaust gas temperature is low. The timing for fully closing the EGR control valve is when the engine load ratio is preferably 20 to 60%, more preferably 30 to 50%, and the exhaust gas temperature is preferably 300 to 500 ° C, more preferably. Is when it becomes 350-450 degreeC. The timing for opening the EGR adjustment valve when the engine load decreases is the same.

  Note that the EGR operation timing is not always constant, and varies depending on the operation pattern even in the same engine. That is, even if the load ratio is the same, the exhaust gas temperature at that time varies depending on the operation pattern. Therefore, it is preferable to comprehensively determine the operation timing based on the load ratio and the exhaust gas temperature. The operation timing also varies depending on the engine displacement and the like. For this reason, the preferred operation timing has a width as described above.

  The EGR rate when the EGR control valve is open is preferably 50% or less, more preferably 10 to 40%. The EGR rate may be constant, but it is preferable to variably operate the EGR control valve so that the EGR rate changes within the above range. In this case, it is preferable that the variable operation is performed so that the EGR rate decreases as the load increases. In low load areas such as idling, NOx can be reduced by increasing the EGR rate, but as the load increases, CO and HC increase and particulate matter (PM) emissions also increase. In order to prevent this, it is preferable to lower the EGR rate.

The EGR rate is defined as V ₀ when the amount of intake air when the EGR is not operating and V _S when the amount of intake air when the EGR is operated.
EGR rate = 100 (V ₀ −V _S ) / V ₀ [%]
It is.

  EGR improves the NOx reduction effect. In particular, the EGR operation is performed at a low load, and the EGR operation is stopped at a high load and the purification by the catalytic reactor of the present invention is performed. Is obtained.

  The engine load is determined by the engine speed, load, and torque. Since the engine output necessary for maintaining a constant rotational speed changes according to the load at that time, the load ratio is calculated from the engine output necessary for maintaining the constant rotational speed. Specifically, the load is changed while maintaining the rotational speed of 60% of the rated engine rotational speed (= maximum torque generating rotational speed), and the maximum output value Pmax required to maintain the rotational speed is obtained. The load ratio at this time is 100%. The ratio of the output to Pmax when a certain load is applied and maintained at 60% of the rated engine speed is the load ratio at that time.

  Hereinafter, the present invention will be specifically described by way of examples.

<Thermal decomposition of light oil fuel>
In order to investigate the thermal decomposition of light oil fuel as a fuel reducing agent was injected into the cylinder after the top dead center of the piston position with an electronically controlled fuel injection device, the following simulation test was conducted. The pyrolysis temperatures were 700 ° C and 800 ° C, which are considered to be realized as described above.

  The amount of gas produced by a simulated pyrolysis device with a stainless steel tube (φ2 mm and φ3 mm diameter, length 500 mm, spiral shape) in the electric furnace, a micro metering pump on the inlet side, and a gas-liquid separator on the outlet side The product was confirmed by gas chromatography.

The light oil cracking test uses the above simulated pyrolysis device, cracking temperature: 700 ° C or 800 ° C, reaction tube φ2mm diameter and φ3mm diameter, light oil flow rate per cross section of reaction tube: 5.3kg / m ² · s or 11.9kg / The gasification rate (%) was determined by combining as shown in Table 1 from the conditions of m ² · s and contact time of 2 seconds or 3 seconds. The gasification rate (%) was calculated from [(light oil supply amount) − (light oil amount after gas-liquid separation)] × 100 / (light oil supply amount). The results are shown in Table 1. As shown in Table 1, the gasification rate was high when the light oil flow rate per cross-sectional area was fast and the contact time was long even at the same decomposition temperature.

  Similarly, decomposition when the contact time is changed as shown in Table 2 between 0.6 and 3.0 seconds under the conditions of decomposition temperature: 700 ° C. or 800 ° C., reaction tube φ3 mm diameter, and light oil addition amount: 130 to 280 g / h. The product was examined. The results are shown in Table 2. As shown in Table 2, the production of saturated hydrocarbons and unsaturated hydrocarbons from C1 to C4 was confirmed, and the production amounts were in the order of ethane + ethylene> methane> propylene. In particular, reducing agents containing ethane / ethylene and propylene are effective reducing agents for removing NOx.

In order to confirm the denitration effect by thermal decomposition of light oil, the following test was conducted.
The catalyst performance test uses a direct fuel injection, 2290cc (2290ml) 4-cylinder diesel engine with a load AC generator installed. The composition of the engine exhaust gas is NOx: 900-1250ppm in mass display, CO: 90 ppm, CO ₂ : 8.9%, SO ₂ : 9.6 ppm, and moisture: 7.6%.

  A reaction tube was charged with 40 cc (40 ml) of a denitration catalyst prepared as described below, SV = 20,000 / h, and the catalyst temperature was changed in every 50 ° C. within the range of 350 to 500 ° C. For the diesel oil reducing agent, a simulated pyrolysis device is installed in front of the catalyst reaction tube to supply 2 to 3 times the mass (mass) of diesel oil to the pyrolysis device. Aerated. The NOx after the reaction was analyzed with an atmospheric pressure chemiluminescence NOx meter.

(Preparation of denitration catalyst)
A catalyst having titanium and silver supported on γ-alumina was prepared.
A granular carrier of γ-alumina (manufactured by Mizusawa Chemical Co., Ltd.) was used, and this carrier was added to a 0.08 mol / L titanium trichloride solution so that the solid / solution = 1: 2 (volume ratio), and 50 ° C. for 1 hour. Soaking with stirring, washing with 2 times the amount of ion exchange water (repeat 3 times), solid-liquid separation, solid / solution = 1: 2 (volume ratio) again with ion exchange water, and holding at 50 ° C. While stirring, the solution was neutralized with 1 mol / L ammonia hydroxide and kept in that state for 1 hour. After solid-liquid separation, it was washed with twice the amount of ion-exchanged water, dried at 120 ° C. for 12 hours, and then fired in air at 550 ° C. for 2 hours to carry titanium.

  Subsequently, the titanium-supported one was immersed in a 0.1 mol / L silver nitrate solution (solid / liquid = 1: 2 (volume ratio)) and left for 30 minutes while maintaining and stirring at 30 ° C. After solid-liquid separation, it was dried at 120 ° C. and calcined in air at 500 ° C. for 2 hours to prepare a denitration catalyst (NOx reduction catalyst).

  As a result of measuring the metal loading of the prepared denitration catalyst by fluorescent X-ray analysis, titanium was 0.4% (mass percentage) and silver was 0.8% (mass percentage).

  Table 3 shows the denitration rate when a pyrolysis gas oil reducing agent, a gas oil reducing agent (no thermal decomposition) or a propane reducing agent is used at a pyrolysis temperature of 700 ° C or 800 ° C. The denitration rate when using a light oil reducing agent and a propane reducing agent is taken as a comparative example.

  Looking at the temperature dependence of the denitration rate at decomposition temperatures of 700 ° C and 800 ° C, the denitration rate of both decomposition temperatures is almost the same, and compared with the light oil reducing agent of the comparative example, the denitration rate is high at any catalyst temperature, When compared with the propane reducing agent, the denitration rate was higher at catalyst temperatures below 400 ° C. From this, it can be seen that the denitration rate of 400 ° C or less is lower than that of the low-molecular hydrocarbons of ethane + ethylene, which is the pyrolysis product, and propane and propylene produced above 450 ° C. It can be improved.

  From the above, rather than adding light oil fuel directly to the exhaust passage, the decomposition effect of nitrogen oxides is better when the light oil fuel is pyrolyzed in the engine cylinder and converted to low molecular hydrocarbons and brought into contact with the denitration catalyst. growing.

  Thus, the NOx removal effect can be improved by thermal decomposition of the fuel reducing agent (light oil) of the present invention, and PM, HC, CO, etc. can be removed by using an oxidation catalyst according to the present invention. .

  Moreover, since actual embodiment of this invention becomes light oil injection by an electronically controlled fuel injection apparatus, it is not necessary to newly install an injection apparatus. Further, when an electronically controlled fuel injection device is used, PM and the like can be reduced, but there is a problem that NOx tends to increase. The present invention is an effective method for improving this point. For NOx removal, combined use with EGR is also effective.

In addition, when light oil is injected into the exhaust passage, even if the temperature is high, it is around 500 ° C. If the conditions such as the engine speed ratio and engine load ratio are the same, the temperature is higher than the temperature in the cylinder. The temperature is lowered by about 200 to 300 ° C., and the thermal decomposition of the light oil is not sufficient as compared with the present invention, and the efficiency is deteriorated as compared with the case where the light oil is injected into each cylinder as in the present invention.

Claims (8)

A method for purifying engine exhaust gas that removes nitrogen oxides (NOx), particulate matter (PM), hydrocarbons (HC), and carbon monoxide (CO) in engine exhaust gas, the engine exhaust gas exhaust path The NOx removal catalyst and the oxidation catalyst are arranged in series, and the engine exhaust gas is brought into contact with the NOx removal catalyst in the presence of the fuel reducing agent from which a part of the fuel is taken out, and then the engine exhaust gas is brought into contact with the oxidation catalyst. In purifying,
An electronically controlled fuel injection device injects a fuel reducing agent into the cylinder after the top dead center of the piston position, and contacts the engine exhaust gas containing the injected fuel reducing agent with a denitration catalyst to purify nitrogen oxides, Thereafter, the engine exhaust gas purification method is brought into contact with the oxidation catalyst. When the denitration catalyst is a granular or monolithic catalyst with titanium and silver supported on γ-alumina, light oil is used as the fuel reducing agent, the engine speed ratio is 50% or more, and the engine load ratio is 40% or more By using an electronically controlled fuel injection device, light oil is injected into the cylinder after the top dead center of the piston so that the light oil / nitrogen oxide (NO equivalent) ratio is 0.5 to 4 in terms of mass ratio. 2. The engine exhaust gas purification method according to claim 1, wherein engine exhaust gas containing injected light oil is brought into contact with a denitration catalyst and nitrogen oxide is purified by a nitrogen oxide (NOx) selective reduction method. The denitration catalyst has a titanium layer in which titanium is supported on a γ-alumina carrier and baked to form anatase-type titanium oxide. Further, silver is supported on the titanium layer and baked to oxidize silver. The method for purifying engine exhaust gas according to claim 2, further comprising a silver layer on which an object is formed. It is a diesel engine equipped with an electronically controlled fuel injection device. Light oil / nitrogen oxide (NO conversion) is added to the cylinder after the top dead center of the piston position by the electronically controlled fuel injection device using diesel fuel as the reducing agent. The method for purifying engine exhaust gas according to claim 2 or 3, wherein light oil is injected so that the ratio is 2 to 3 in terms of mass ratio, and exhaust gas of a diesel engine equipped with an electronically controlled fuel injection device is purified. . 5. The engine exhaust gas according to claim 1, wherein a fuel reducing agent is injected into a cylinder after top dead center of the piston position by an electronically controlled fuel injection device to obtain a low molecular weight fuel reducing agent by thermal decomposition. Purification method. The method for purifying engine exhaust gas according to any one of claims 1 to 5, wherein the oxidation catalyst is a catalyst in which at least one metal selected from platinum and palladium is supported on γ-alumina. The method for purifying engine exhaust gas according to any one of claims 1 to 6, wherein a catalyst reactor having a catalyst layer having a denitration catalyst layer as a first layer and an oxidation catalyst layer as a second layer is disposed. The engine according to any one of claims 1 to 7, wherein an exhaust gas recirculation (EGR) system is combined, the EGR system is operated when the engine is under a low load, and the engine exhaust gas is brought into contact with the denitration catalyst and the oxidation catalyst when the engine is under a high load. Exhaust gas purification method.