JP2013174203A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reduction efficiency of NOx in exhaust gas in a high-temperature zone of the exhaust gas.SOLUTION: A selective reduction type catalyst 19 capable of reducing NOx in exhaust gas into Nis disposed in an exhaust pipe 16; and a particulate filter 22 having a ceria-containing oxidation catalyst layer formed therein is disposed on the exhaust pipe 16 at the upstream side of an exhaust gas flow from the selective reduction type catalyst 19. A liquid spray nozzle 26 capable of spraying a hydrocarbon liquid 24 toward the particulate filter 22 is disposed on the exhaust pipe 16 at the upstream side of the exhaust gas flow from the particulate filter 22, and the hydrocarbon liquid 24 is supplied by a liquid supply means 28 to the liquid spray nozzle 26. A controller 43 is configured to control the liquid supply means 28 based on the detection output of a temperature sensor 38 that detects an exhaust gas temperature relating to the particulate filter 22.

Description

  The present invention relates to an apparatus for purifying exhaust gas by reducing nitrogen oxide (hereinafter referred to as NOx) contained in exhaust gas of a diesel engine.

  2. Description of the Related Art Conventionally, an internal combustion engine in which an exhaust passage of an internal combustion engine is provided with a first addition valve, a filter carrying an oxidation catalyst, a second addition valve, an ammonia generation catalyst, and a NOx catalyst in order from the internal combustion engine side (exhaust gas upstream side). (For example, refer to Patent Document 1). In this exhaust purification apparatus, the ammonia generation catalyst is a catalyst that generates ammonia by adding HC excessively, and is, for example, a three-way catalyst. The NOx catalyst is a NOx catalyst provided integrally with an adsorption layer such as zeolite on the upper layer of the lower storage-reduction type NOx catalyst. When HC is added from the second addition valve, ammonia is produced by the ammonia production catalyst, and this ammonia is adsorbed on the adsorption layer of the NOx catalyst. This ammonia selectively acts on NOx in the exhaust gas to reduce NOx. Furthermore, since NOx is occluded in the lower layer of the NOx catalyst, NOx occluded in the lower layer of the NOx catalyst is reduced by addition of HC from the second addition valve.

  In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when ammonia is generated by the ammonia generation catalyst and when NOx stored in the NOx storage reduction catalyst is reduced, HC is supplied from the second addition valve. It is necessary to add. Here, although there is a request to add HC from the second addition valve, the degree of reduction in the exhaust gas purification function increases unless HC is added from the second addition valve. In other words, it is difficult to purify NOx unless HC is added from the second addition valve. On the other hand, the particulates hardly flow out from the filter without adding fuel from the first addition valve. For this reason, HC addition to the NOx catalyst or ammonia generation catalyst is preferentially performed, assuming that HC addition to the NOx catalyst or ammonia generation catalyst has a higher priority than the HC addition to the filter. That is, when the filter regeneration request and the NOx reduction request overlap, priority is given to adding HC to the NOx catalyst or the ammonia generation catalyst.

  An oxidation catalyst that oxidizes and purifies hydrocarbons in the exhaust gas is provided in the exhaust passage of the internal combustion engine, and an index value relating to the adsorption ability of specific components other than hydrocarbons in the oxidation catalyst is measured by the measuring means. An oxidation catalyst deterioration diagnosis device is disclosed in which the deterioration determination means is configured to determine the deterioration of the oxidation catalyst based on the index value measured by the means (see, for example, Patent Document 2). In this oxidation catalyst deterioration diagnosis apparatus, an oxidation catalyst that oxidizes and purifies hydrocarbon (HC) and carbon monoxide (CO), which are unburned components in exhaust gas, in order from the upstream side of exhaust gas, and exhaust gas in an exhaust passage. A NOx catalyst for reducing and purifying NOx therein is provided in series. The NOx catalyst is a selective reduction type NOx catalyst, and is configured such that NOx can be continuously reduced when the catalyst temperature is in the active temperature range and the reducing agent is added. On the other hand, a urea addition valve for adding urea as a reducing agent to the NOx catalyst is provided in the exhaust passage between the oxidation catalyst and the NOx catalyst. Urea is used in the form of an aqueous urea solution, and is injected and supplied into the exhaust passage from the urea addition valve toward the NOx catalyst on the exhaust gas downstream side. A supply device for supplying a urea aqueous solution is connected to the urea addition valve, and a tank for storing the urea aqueous solution is connected to the supply device. Also, a fuel addition valve is provided upstream of the oxidation catalyst from the exhaust gas, and fuel, particularly HC in the fuel, is added to the oxidation catalyst.

The oxidation catalyst is a catalyst that purifies by reacting unburned components such as HC and CO in exhaust gas with oxygen (O ₂ ), and forms a coating material on the surface of a carrier made of cordierite or the like. A large number of noble metal fine particles such as Pt forming active points are dispersedly arranged. In particular, the coating material includes a material having an adsorption ability for a specific component other than HC, and the material is zeolite, and the specific component other than HC is NOx. Supplying HC to the oxidation catalyst mainly for heat generation in the oxidation catalyst, that is, increasing the amount of HC contained in the exhaust gas flowing into the oxidation catalyst is called rich spike. Due to this rich spike, the air-fuel ratio of the exhaust gas is usually the stoichiometric air-fuel ratio or richer than that. A rich spike is executed when the temperature of the oxidation catalyst is in a predetermined activation temperature range (for example, 250 ° C. or higher) and the temperature of the NOx catalyst is lower than the predetermined activation temperature range (for example, 200 to 600 ° C.). . The exhaust gas is heated by the rich spike, and the temperature of the NOx catalyst reaches the activation temperature range. Thus, the temperature of the NOx catalyst is maintained in the activation temperature range, and NOx can be continuously reduced and purified by supplying urea.

  On the other hand, since the oxidation catalyst contains zeolite having NOx adsorption capacity in its coating material, NOx is used as a specific component, and deterioration of the oxidation catalyst is judged by looking at the change in this NOx adsorption capacity. Here, the principle of NOx adsorption by the oxidation catalyst is considered to be due to the fact that the zeolite includes pores having dimensions of molecular order, and NOx molecules are mainly physically adsorbed in the pores. When the oxidation catalyst deteriorates with time (mainly heat deterioration), the noble metal fine particles forming the active site are in a sintered state and the HC purification ability is reduced. At the same time, the NOx adsorption ability of the zeolite is also reduced. That is, since there is a correlation between the deterioration degree of the oxidation catalyst and the NOx adsorption capacity, an index value related to the NOx adsorption capacity of the oxidation catalyst is measured, and the measured index value is compared with a predetermined deterioration determination value. The presence or absence of deterioration of the oxidation catalyst is determined.

  Specifically, the presence or absence of deterioration of the oxidation catalyst is determined as follows. The oxidation catalyst gradually adsorbs NOx during normal engine operation. This adsorbed NOx is desorbed when fuel is added by the fuel addition valve, that is, when rich spike is executed. This is because the rich spike causes an oxidation reaction of HC in the oxidation catalyst, the reaction heat increases the catalyst temperature, and the adsorbed NOx is desorbed. This amount of desorbed NOx serves as an index value regarding the NOx adsorption ability of the oxidation catalyst. On the other hand, the adsorbed NOx is desorbed by a short rich spike of about 1 second. This is a much shorter time than the prior art, and the amount of HC is small. Therefore, deterioration of fuel consumption and exhaust emission is suppressed to a minimum. As a result, in addition to shortening the diagnosis time, the temperature range of the catalyst that can be diagnosed is wide (for example, 250 ° C. or higher), and diagnosis is possible even at a relatively high temperature, so that more diagnosis opportunities can be secured. As a result, if the catalyst temperature is such that the added HC reacts with the catalyst and the adsorbed NOx is desorbed, the diagnosis can be made basically even in the high temperature range.

JP 2009-36084 A (paragraphs [0136] to [0138], FIG. 9) JP 2008-240577 (Claim 1, paragraphs [0026] [0027], [0030] to [0032], [0034], [0041] to [0043], FIG. 1)

  However, in the exhaust gas purification apparatus for an internal combustion engine disclosed in Patent Document 1 above, the NOx catalyst is an NOx storage reduction catalyst, and this catalyst usually carries a highly basic metal such as barium. For this reason, the NOx catalyst has a phenomenon in which sulfur in the exhaust gas is occluded from NOx in the exhaust gas, that is, a sulfur poisoning phenomenon of the supported metal, resulting in a reduction in the purification rate of NOx in the exhaust gas. In order to eliminate the sulfur poisoning phenomenon of the supported metal, it is necessary to regenerate the NOx catalyst by continuously exposing the NOx catalyst to a rich atmosphere at a high temperature of 650 ° C. or more. In this case, a relatively large amount of fuel is consumed. There was a problem to do. Further, in the conventional oxidation catalyst deterioration diagnosis device disclosed in Patent Document 2, the oxidation catalyst coating material contains zeolite having NOx adsorption ability, and the NOx adsorbed on the oxidation catalyst is added to the fuel (rich spike). ), But the amount of NOx adsorbed by the zeolite is relatively small, and even if NOx is desorbed from the oxidation catalyst during the rich spike, this NOx is not reformed into ammonia, and the oxidation catalyst deteriorates. Since it is only used for diagnosis, in order to purify NOx with the NOx catalyst, it is necessary to add urea as a reducing agent to the NOx catalyst, and a urea water tank must be mounted separately from the fuel tank, There was a problem with low convenience.

  The first object of the present invention is to prevent the occurrence of sulfur poisoning by using a selective catalytic reduction catalyst, thereby reducing the NOx purification rate in the exhaust gas, and increasing the NOx catalyst to a high temperature of 650 ° C. or higher. It is therefore an object of the present invention to provide an exhaust gas purifying apparatus that does not need to regenerate the NOx catalyst by continuously exposing it to a fuel-rich atmosphere. A second object of the present invention is to provide an exhaust gas purifying apparatus that can generate ammonia gas using only fuel without using urea water, thereby eliminating the need to mount a urea water tank and improving convenience. There is. The third object of the present invention is to provide an exhaust gas purifying apparatus capable of improving the NOx reduction efficiency in the exhaust gas in the high temperature range of the exhaust gas.

As shown in FIGS. 1 and 2, the first aspect of the present invention is a selective reduction that is provided in the exhaust pipe 16 and can reduce NOx in the exhaust gas to N ₂ in the exhaust gas purification device that purifies the exhaust gas of the engine 11. And a ceria-containing oxidation catalyst layer 22h that is provided in the exhaust pipe 16 upstream of the exhaust gas from the selective reduction catalyst 19 and is formed to be porous so that the exhaust gas can pass therethrough and to prevent the passage of the exhaust gas. Further, the particulate filter 22 capable of collecting particulates in the exhaust gas, and the liquid injection capable of injecting the hydrocarbon-based liquid 24 toward the particulate filter 22 provided in the exhaust pipe 16 on the upstream side of the exhaust gas from the particulate filter 22. The nozzle 26, the liquid supply means 28 for supplying the liquid 24 to the liquid jet nozzle 26, and the particulate filter 22. A temperature sensor 38 for detecting the temperature of the exhaust gas, characterized by comprising a controller 43 for controlling the liquid supply means 28 on the basis of the detection output of the temperature sensor 38.

As shown in FIG. 5, the second aspect of the present invention is a selective reduction catalyst 19 provided in the exhaust pipe 16 and capable of reducing NOx in the exhaust gas to N ₂ in the exhaust gas purification device that purifies the exhaust gas of the engine 11. An oxidation catalyst 61 that is provided in the exhaust pipe 16 upstream of the selective reduction catalyst 19 and contains ceria and oxidizes at least unburned fuel in the exhaust gas to increase the exhaust gas temperature; The liquid injection nozzle 26 is provided in the exhaust pipe 16 and can inject the hydrocarbon-based liquid 24 toward the oxidation catalyst 61, the liquid supply means 28 for supplying the liquid 24 to the liquid injection nozzle 26, and the oxidation catalyst 61. And a controller 43 for controlling the liquid supply means 28 based on the detection output of the temperature sensor 38.

  A third aspect of the present invention is an invention based on the first aspect, and further, as shown in FIG. 6, an exhaust pipe on the exhaust gas upstream side of the particulate filter 22 and on the exhaust gas downstream side of the liquid injection nozzle 26. 16 further includes an oxidation catalyst 61 that contains ceria and oxidizes at least unburned fuel in the exhaust gas to raise the exhaust gas temperature, and the temperature sensor 38 detects the temperature related to the oxidation catalyst 61 and the particulate filter 22. It was configured as described above.

  A fourth aspect of the present invention is an invention based on the first or third aspect, and further, as shown in FIG. 1 or FIG. 6, the exhaust pipe 16 between the particulate filter 22 and the selective reduction catalyst 19. And an auxiliary liquid injection nozzle 27 that can inject the hydrocarbon-based liquid 24 toward the selective catalytic reduction catalyst 19 and an auxiliary temperature sensor 39 that detects the temperature of the exhaust gas related to the selective catalytic reduction catalyst 19. The liquid supply means 28 is configured to supply the hydrocarbon-based liquid 24 to the liquid injection nozzle 26 and the auxiliary liquid injection nozzle 27, and the controller 43 is configured to supply the liquid supply means based on the detection outputs of the temperature sensor 38 and the auxiliary temperature sensor 39. 28 is configured to be controlled.

  The fifth aspect of the present invention is an invention based on the second aspect, and is further provided as shown in FIG. 5 in the selective reduction catalyst provided in the exhaust pipe 16 between the oxidation catalyst 61 and the selective reduction catalyst 19. The auxiliary liquid injection nozzle 27 capable of injecting the hydrocarbon-based liquid 24 toward the apparatus 19 and the auxiliary temperature sensor 39 for detecting the temperature of the exhaust gas related to the selective catalytic reduction catalyst 19 are further provided. The hydrocarbon liquid 24 is supplied to the nozzle 26 and the auxiliary liquid injection nozzle 27, and the controller 43 is configured to control the liquid supply means 28 based on the detection outputs of the temperature sensor 38 and the auxiliary temperature sensor 39. It is characterized by that.

  A sixth aspect of the present invention is an invention based on the first or third aspect, and further, as shown in FIG. 2, the particulate filter 22 is divided into through holes 22b partitioned by a porous partition wall 22a. An inflow hole 22d and an outflow hole 22e are formed by alternately sealing adjacent outlet portions and inlet portions of the plurality of through-holes 22b. The oxidation catalyst layer 22h supporting one or more kinds of noble metals selected from the group consisting of platinum, palladium and rhodium and containing ceria is formed so as not to prevent passage of exhaust gas. To do.

  A seventh aspect of the present invention is the invention based on the second or third aspect, wherein the oxidation catalyst 61 further includes a plurality of through-holes partitioned by a porous partition wall in parallel to each other, and both ends are opened. The support is configured to carry one or more kinds of noble metals selected from the group consisting of platinum, palladium and rhodium and contain ceria.

  An eighth aspect of the present invention is an invention based on any one of the first to third aspects, and as shown in FIG. 1 or FIG. 5, the controller 43 includes a liquid ejecting nozzle 26 for the liquid 24. A liquid injection nozzle that injects at an injection interval of a predetermined injection interval in the range of 100 to 500 milliseconds and that the excess air ratio λ of the exhaust gas before flowing into the particulate filter 22 or the oxidation catalyst 61 is less than 1. The amount of liquid injection from one time is controlled so that the inside of the exhaust pipe 16 before flowing into the particulate filter 22 or the oxidation catalyst 61 becomes intermittently a fuel-rich atmosphere. And

In the exhaust gas purifying apparatus according to the first aspect of the present invention, when the temperature sensor detects that the temperature related to the particulate filter has become equal to or higher than a predetermined temperature, the controller performs liquid ejection based on the detection output of the temperature sensor. A hydrocarbon-based liquid is injected from the nozzle at a predetermined interval. Part of the NOx in the exhaust gas is adsorbed by the oxidation catalyst layer of the particulate filter immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle and immediately before the injection of the next liquid at a predetermined interval. When the hydrocarbon-based liquid is injected from the liquid injection nozzle in this state, the NOx adsorbed on the oxidation catalyst layer reacts with the mist-like hydrocarbon-based liquid to generate ammonia gas. This ammonia gas exhibits a selective reduction function of reacting with NOx in the exhaust gas and reducing NOx to N ₂ on the selective catalytic reduction catalyst. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature range of the exhaust gas can be improved.

  Further, the sulfur poisoning phenomenon of the metal supported on the NOx storage reduction catalyst occurs, and the purification rate of NOx in the exhaust gas is lowered. In order to eliminate this sulfur poisoning phenomenon, the NOx catalyst is heated to a high temperature of 650 ° C. or more. In comparison with the conventional exhaust gas purification apparatus for an internal combustion engine, which has a problem that a NOx catalyst needs to be regenerated by continuously exposing it to a fuel-rich atmosphere and consumes a relatively large amount of fuel, Since selective reduction catalyst is used and sulfur poisoning phenomenon does not occur, the NOx purification rate in exhaust gas does not decrease, and the NOx catalyst is continuously exposed to a fuel-rich atmosphere at a high temperature of 650 ° C. or higher. There is no need to regenerate the NOx catalyst. Furthermore, the amount of NOx adsorbed by zeolite is relatively small, and even if NOx is released from the oxidation catalyst during a rich spike, this NOx is not reformed into ammonia but only used for diagnosing deterioration of the oxidation catalyst. In order to purify NOx with a NOx catalyst, it is necessary to add urea as a reducing agent to the NOx catalyst, and a urea water tank must be mounted separately from the fuel tank, which has a problem of low convenience. Compared with the conventional oxidation catalyst deterioration diagnosis device, in the present invention, ammonia gas can be generated using only a hydrocarbon-based liquid (fuel) without using urea water, and thus it is necessary to mount a urea water tank. And convenience can be improved.

In the exhaust gas purifying apparatus according to the second aspect of the present invention, when the temperature sensor detects that the temperature related to the oxidation catalyst has become equal to or higher than the predetermined temperature, the controller uses the liquid injection nozzle based on the detection output of the temperature sensor. The hydrocarbon-based liquid is jetted at a predetermined interval. Part of the NOx in the exhaust gas is adsorbed by the oxidation catalyst immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle to immediately before the injection of the next liquid at a predetermined interval. When the hydrocarbon-based liquid is injected from the liquid injection nozzle in this state, NOx adsorbed on the oxidation catalyst reacts with the mist-like hydrocarbon-based liquid to generate a relatively large amount of ammonia gas. This ammonia gas exhibits a selective reduction function of reacting with NOx in the exhaust gas and reducing NOx to N ₂ on the selective catalytic reduction catalyst. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature range of the exhaust gas can be further improved.

In the exhaust gas purifying apparatus according to the third aspect of the present invention, when the temperature sensor detects that the temperature related to the oxidation catalyst and the particulate filter has become equal to or higher than a predetermined temperature, the controller is based on the detection output of the temperature sensor. The hydrocarbon-based liquid is ejected from the liquid ejection nozzle at a predetermined interval. Part of the NOx in the exhaust gas is adsorbed by the oxidation catalyst and the oxidation catalyst layer immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle and immediately before the injection of the next liquid at a predetermined interval. When the hydrocarbon-based liquid is injected from the liquid injection nozzle in this state, the NOx adsorbed on the oxidation catalyst and the oxidation catalyst layer reacts with the atomized hydrocarbon-based liquid to generate a relatively large amount of ammonia gas. This ammonia gas exhibits a selective reduction function of reacting with NOx in the exhaust gas and reducing NOx to N ₂ on the selective catalytic reduction catalyst. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature range of the exhaust gas can be further improved.

In the exhaust gas purifying apparatus according to the fourth aspect of the present invention, the temperature sensor detects that the temperature related to the particulate filter has become equal to or higher than the predetermined temperature when the particulate filter having the oxidation catalyst layer is provided although the oxidation catalyst is not provided. When the auxiliary temperature sensor detects that the temperature related to the selective catalytic reduction catalyst has become equal to or higher than the predetermined temperature, the controller detects whether the temperature of the liquid injection nozzle and the auxiliary liquid injection nozzle is on the basis of the detection outputs of these temperature sensors. The hydrocarbon-based liquid is injected at predetermined intervals. Part of the NOx in the exhaust gas is adsorbed by the oxidation catalyst layer of the particulate filter immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle and immediately before the injection of the next liquid at a predetermined interval. When the hydrocarbon-based liquid is injected from the liquid injection nozzle in this state, the NOx adsorbed on the oxidation catalyst layer reacts with the mist-like hydrocarbon-based liquid to generate ammonia gas. On the other hand, the hydrocarbon-based liquid injected from the auxiliary liquid injection nozzle reacts with NOx in the exhaust gas on the selective reduction catalyst to exhibit a selective reduction function of reducing NOx to N _2, and the ammonia gas is selectively reduced. reacts with NOx in the exhaust gas on the type catalysts exert selective reduction function of reducing NOx in N _2. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature region of the exhaust gas can be further improved.

In addition, in the case of having an oxidation catalyst and a particulate filter with an oxidation catalyst layer, the temperature sensor detects that the temperature related to the oxidation catalyst and the particulate filter has exceeded a predetermined temperature, and is related to the selective reduction catalyst. When the auxiliary temperature sensor detects that the temperature to be discharged is equal to or higher than the predetermined temperature, the controller, based on the detection outputs of these temperature sensors, distributes the hydrocarbon-based liquid from the liquid injection nozzle and the auxiliary liquid injection nozzle at a predetermined interval. Open each and inject each. Part of the NOx in the exhaust gas is adsorbed by the oxidation catalyst and the oxidation catalyst layer immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle and immediately before the injection of the next liquid at a predetermined interval. When the hydrocarbon-based liquid is injected from the liquid injection nozzle in this state, the NOx adsorbed on the oxidation catalyst and the oxidation catalyst layer reacts with the atomized hydrocarbon-based liquid to generate ammonia gas. On the other hand, the hydrocarbon-based liquid injected from the auxiliary liquid injection nozzle reacts with NOx in the exhaust gas on the selective reduction catalyst to exhibit a selective reduction function of reducing NOx to N _2, and the ammonia gas is selectively reduced. reacts with NOx in the exhaust gas on the type catalysts exert selective reduction function of reducing NOx in N _2. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature region of the exhaust gas can be further improved.

In the exhaust gas purifying apparatus according to the fifth aspect of the present invention, the temperature sensor detects that the temperature related to the oxidation catalyst is equal to or higher than the predetermined temperature, and the temperature related to the selective catalytic reduction catalyst is equal to or higher than the predetermined temperature. Is detected by the auxiliary temperature sensor, the controller injects the hydrocarbon-based liquid from the liquid injection nozzle and the auxiliary liquid injection nozzle at predetermined intervals based on the detection outputs of these temperature sensors. Part of the NOx in the exhaust gas is adsorbed by the oxidation catalyst immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle to immediately before the injection of the next liquid at a predetermined interval. When the hydrocarbon-based liquid is injected from the liquid injection nozzle in this state, NOx adsorbed on the oxidation catalyst reacts with the mist-like hydrocarbon-based liquid to generate ammonia gas. On the other hand, the hydrocarbon-based liquid injected from the auxiliary liquid injection nozzle reacts with NOx in the exhaust gas on the selective reduction catalyst to exhibit a selective reduction function of reducing NOx to N _2, and the ammonia gas is selectively reduced. reacts with NOx in the exhaust gas on the type catalysts exert selective reduction function of reducing NOx in N _2. As a result, similarly to the above, the NOx reduction efficiency in the exhaust gas in the high temperature region of the exhaust gas can be further improved.

  In the exhaust gas purifying apparatus according to the eighth aspect of the present invention, the controller causes the liquid injection nozzle to inject the liquid injection interval at a predetermined injection interval within a range of 100 to 500 milliseconds, and to the particulate filter or the oxidation catalyst. Since the amount of one liquid injection from the liquid injection nozzle is controlled so that the excess air ratio λ of the exhaust gas before flowing becomes less than 1, the inside of the exhaust pipe before flowing into the particulate filter or the oxidation catalyst is intermittently A fuel rich atmosphere. As a result, the NOx adsorbed on the oxidation catalyst or the oxidation catalyst layer is injected from the liquid injection nozzle immediately after the injection of the hydrocarbon-based liquid from the liquid injection nozzle to immediately before the injection of the next liquid at a predetermined interval. It reacts quickly with the produced mist-like hydrocarbon liquid and can produce a relatively large amount of ammonia gas.

It is a block diagram which shows the exhaust gas purification apparatus of 1st Embodiment of this invention. It is a section lineblock diagram of the particulate filter of the exhaust gas purification device. Is a diagram illustrating an example of a hydrocarbon injection interval of the liquid from the liquid injection nozzle during reduction to N ₂ of NOx during playback or selective reduction catalyst of the particulate filter. It is a figure which shows an example of the injection space | interval of the hydrocarbon-type liquid from a liquid injection nozzle when making the fuel injected from the liquid injection nozzle and NOx adsorb | sucking to the oxidation catalyst layer react, and producing | generating ammonia gas. It is a block diagram which shows the exhaust gas purification apparatus of 2nd Embodiment of this invention. It is a block diagram which shows the exhaust gas purification apparatus of 3rd Embodiment of this invention. It is a figure which shows the change of the NOx reduction rate with respect to the change of the exhaust gas temperature in the selective reduction catalyst inlet_port | entrance of Example 1 and Comparative Example 1. FIG. It is a figure which shows the change of the ammonia gas production rate with respect to the change of the exhaust gas temperature in the particulate filter exit of Example 1, and the change of the ammonia gas production rate with respect to the change of the exhaust gas temperature in the particulate filter outlet of the comparative example 1.

  Next, an embodiment for carrying out the present invention will be described based on the drawings.

<First Embodiment>
As shown in FIG. 1, an intake pipe 13 is connected to an intake port of a diesel engine 11 via an intake manifold 12, and an exhaust pipe 16 is connected to an exhaust port via an exhaust manifold 14. The intake pipe 13 is provided with a compressor housing 17a of the turbocharger 17 and an intercooler 18 for cooling the intake air compressed by the turbocharger 17, and the exhaust pipe 16 is provided with a turbine of the turbocharger 17. A housing 17b is provided. Compressor rotor blades (not shown) are rotatably accommodated in the compressor housing 17a, and turbine rotor blades (not shown) are rotatably accommodated in the turbine housing 17b. The compressor rotor blades and the turbine rotor blades are connected by a shaft (not shown), and the compressor rotor blades are rotated via the turbine rotor blades and the shaft by the energy of the exhaust gas discharged from the engine 11, and the compressor rotor blades are rotated. Thus, the intake air in the intake pipe 13 is compressed.

A selective reduction catalyst 19 capable of reducing NOx in the exhaust gas to N ₂ is provided in the middle of the exhaust pipe 16. The selective catalytic reduction catalyst 19 is accommodated in a downstream case 21 having a larger diameter than the exhaust pipe 16. The selective reduction catalyst 19 is a monolithic catalyst, and is formed by coating a honeycomb carrier made of cordierite with copper zeolite or iron zeolite, and then drying and firing. Specifically, the selective reduction catalyst 19 made of copper zeolite is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of copper. The selective reduction catalyst 19 made of iron zeolite is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of iron, followed by drying and firing. Although not shown, both ends of the honeycomb carrier (both ends of the through hole) are open.

  On the other hand, a particulate filter 22 capable of collecting particulates in the exhaust gas is provided in the exhaust pipe 16 upstream of the selective reduction catalyst 19 (FIG. 1). The particulate filter 22 is accommodated in an upstream case 23 having a larger diameter than the exhaust pipe 16. As shown in FIG. 2, the particulate filter 22 is a honeycomb-shaped carrier in which a plurality of through holes 22b partitioned by porous partition walls 22a made of ceramic such as cordierite and silicon carbide are formed in parallel to each other. 22c. The inflow holes 22d and the outflow holes 22e are formed by alternately sealing the outlet portions and the inlet portions adjacent to each other of the plurality of through holes 22b. That is, an inflow hole 22d is formed by sealing the outlet side of the plurality of through holes 22b with the sealing member 22f and opening the inlet side, and the inlet side of the plurality of through holes 22b is formed by the sealing member 22f. The outflow hole 22e is formed by sealing and opening the outlet side. Further, the porous partition wall 22a is formed with a plurality of pores 22g that connect the inflow hole 22d and the outflow hole 22e. In the particulate filter 22, when the exhaust gas of the engine 11 introduced from the inflow hole 22d passes through the pores 22g of the partition wall 22a, the particulates contained in the exhaust gas are collected and discharged from the outflow hole 22e. It is like that.

Furthermore, an oxidation catalyst layer 22h is formed on a part of the inner surfaces of the inflow holes 22d and the outflow holes 22e of the particulate filter 22 and a part of the inner surfaces of the plurality of pores 22g so as not to inhibit the passage of the exhaust gas. The oxidation catalyst layer 22h is made of alumina (Al ₂ O ₃ ) containing ceria (CeO ₂ ) and supporting a predetermined noble metal. Here, the predetermined noble metal refers to one or more noble metals selected from the group consisting of platinum, palladium and rhodium. The oxidation catalyst layer 22h is formed by the following method. After impregnating the above-mentioned noble metal solution with the alumina powder and supporting the noble metal on the alumina powder, the ceria powder is mixed with the alumina powder supported on the noble metal to prepare a mixed powder, and the slurry of the mixed powder is filtered. The oxidation catalyst layer 22 h can be formed on the filter 22 by coating the carrier 22 c, drying and firing. A slurry of mixed powder of ceria powder and alumina powder is prepared, and this slurry is coated on the carrier 22c of the filter 22, and then the carrier 22c of the filter 22 coated with this mixed powder is immersed in the above-mentioned noble metal solution and dried. The oxidation catalyst layer 22h may be formed on the filter 22 by firing.

  Returning to FIG. 1, the exhaust pipe 16 on the exhaust gas upstream side of the particulate filter 22 is provided with a liquid injection nozzle 26 capable of injecting a hydrocarbon-based liquid 24 toward the particulate filter 22. An auxiliary liquid injection nozzle 27 that can inject the hydrocarbon-based liquid 24 toward the selective reduction catalyst 19 is provided in the exhaust pipe 16 between the selective reduction catalyst 19. A liquid supply means 28 is connected to the liquid ejection nozzle 26 and the auxiliary liquid ejection nozzle 27. The liquid supply means 28 is provided at the base end of the tank 29 for storing the hydrocarbon-based liquid 24, the open / close valve 31 provided at the base end of the liquid injection nozzle 26 and capable of opening and closing the nozzle 26, and the auxiliary liquid injection nozzle 27. An auxiliary on-off valve 32 that can open and close the nozzle 27, a liquid supply pipe 33 that connects the tank 29 to the on-off valve 31 and the auxiliary on-off valve 32, and a hydrocarbon system provided in the liquid supply pipe 33 in the tank 29. And a pump 34 capable of supplying the liquid 24 to the liquid jet nozzle 26 and the auxiliary liquid jet nozzle 27.

  The liquid supply pipe 33 has a main pipe line 33a having one end connected to the tank 29, a first branch pipe line 33b having one end connected to the other end of the main pipe line 33a and the other end connected to the on-off valve 31, and one end connected to the open / close valve 31. The second branch pipe 33 c is connected to the other end of the main pipe 33 a and the other end is connected to the auxiliary opening / closing valve 32. In this embodiment, the hydrocarbon-based liquid 24 is a fuel such as light oil, the pump 34 is driven by a pump drive motor (not shown), and the tank 29 can also be used as a fuel tank of the engine 11. Further, one end of a return pipe 36 is connected to the main pipe line 33 a downstream of the pump 34, and the other end of the return pipe 36 is connected to the tank 29, so that the return pipe 36 bypasses the pump 34. The Further, the return pipe 36 is provided with a flow rate adjusting valve 37. The flow rate and pressure of the hydrocarbon-based liquid 24 discharged from the pump 34 can be adjusted by changing the rotational speed of the pump drive motor continuously or stepwise, or by adjusting the opening of the flow rate adjustment valve 37. It has become.

  In the exhaust pipe 16 between the liquid jet nozzle 26 and the particulate filter 22, the temperature of the exhaust gas related to the particulate filter 22, in this embodiment, the temperature of the exhaust gas immediately before flowing through the particulate filter 22 is detected. A temperature sensor 38 is provided. Further, in the exhaust pipe 16 between the auxiliary liquid injection nozzle 27 and the selective catalytic reduction catalyst 19, the temperature of the exhaust gas related to the selective catalytic reduction catalyst 19, in this embodiment, the exhaust gas immediately before flowing through the selective catalytic reduction catalyst 19. An auxiliary temperature sensor 39 is provided for detecting the temperature. Further, the rotation speed of the engine 11 is detected by a rotation sensor 41, and the load of the engine 11 is detected by a load sensor 42. The detection outputs of the temperature sensor 38, the auxiliary temperature sensor 39, the rotation sensor 41, and the load sensor 42 are connected to the control input of the controller 43. The control output of the controller 43 is the on-off valve 31, the auxiliary on-off valve 32, the pump drive motor, and the flow rate. Each is connected to a regulating valve 37.

The controller 43 is provided with a memory 44. In this memory 44, changes in the NOx flow rate in the exhaust gas according to changes in the engine speed and engine load are stored in advance as a map. Further, the memory 44 stores the exhaust gas temperature at the inlet of the particulate filter 22 (immediately before flowing through the particulate filter 22), the exhaust gas temperature at the inlet of the selective catalytic reduction catalyst 19 (immediately before flowing through the selective catalytic reduction catalyst 19), the engine speed, and the engine load. The open / close interval of the open / close valve 31 according to the above, the open / close interval of the auxiliary open / close valve 32, the rotational speed of the pump drive motor, and the opening degree of the flow rate adjusting valve 37 are stored in advance as a map. For example, when the particulate filter 22 is regenerated, that is, the particulate matter deposited on the particulate filter 22 is increased by oxidizing the hydrocarbon liquid 24 injected from the liquid injection nozzle 26 with the oxidation catalyst layer 22h to raise the exhaust gas temperature. When the filter 22 is regenerated by incineration, the ejection interval T ₁ of the liquid 24 from the liquid ejection nozzle 26 is set within a range of 10 to 30 milliseconds (for example, in the case of T ₁ = 10 milliseconds in FIG. 3). Is shown.) Further, when ammonia gas is generated, that is, when ammonia gas is generated by reacting the hydrocarbon-based liquid 24 injected from the liquid injection nozzle 26 with NOx adsorbed on the oxidation catalyst layer 22h, the liquid 24 from the liquid injection nozzle 26 is used. injection interval T ₂ are 100 to 500 ms, preferably in the range of 100 to 200 ms (for example, Figure 4 shows the case of T ₂ = 100 msec.). Further, when the selective reduction catalyst 19 reduces NOx to N ₂ , that is, the hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27, the ammonia gas, and NOx in the exhaust gas are reacted on the selective reduction catalyst 19. When NOx is reduced to N ₂ , the ejection interval T ₃ of the liquid 24 from the auxiliary liquid ejection nozzle 27 is set within a range of 10 to 30 milliseconds (for example, T ₁ = 10 milliseconds in FIG. 3). Shows the case.)

A single liquid injection amount Q ₂ at the time of generation of ammonia gas for _one liquid injection amount Q ₁ at the time of regeneration of the filter 22 is a generation of ammonia gas at an injection interval T ₁ of the liquid 24 at the time of regeneration of the filter 22. It is set to increase in proportion to the ejection interval T ₂ of the liquid 24 at the time. Specifically, the amount of liquid injection once from the liquid injection nozzle 26 when ammonia gas is generated is such that the excess air ratio λ of the exhaust gas before flowing into the filter 22 is less than 1, preferably less than 0.9. It is set as follows. Here, the reason for limiting the injection interval of the liquid 24 from the liquid injection nozzle 26 during the generation of ammonia gas to the range of 100 to 500 milliseconds is that between the liquid injection and the next liquid injection in less than 100 milliseconds. NOx in the exhaust gas cannot be sufficiently adsorbed, and the amount of liquid injection at one time is small, and the exhaust pipe 16 does not become a fuel-rich atmosphere, so ammonia gas cannot be generated. If it exceeds 500 milliseconds, ammonia gas is generated. This is because the surplus hydrocarbon-based liquid 24 is discharged into the atmosphere although it can. In addition, the amount of liquid ejected from the liquid ejection nozzle 26 is limited so that the excess air ratio λ of the exhaust gas before flowing into the filter 22 is less than 1 when the excess air ratio λ is 1 or more. This is because ammonia gas cannot be generated because the inside of the pipe 16 does not become a fuel-rich atmosphere. A reference numeral 46 in FIG. 1 is an EGR pipe that connects the exhaust manifold 14 and the intake pipe 13 to bypass the engine 11. The EGR pipe 46 branches off from the branch pipe portion of the exhaust manifold 14 and merges with the intake pipe 13 on the intake downstream side of the intercooler 18. Reference numeral 47 in FIG. 1 is an EGR valve that is provided in the EGR pipe 46 and adjusts the flow rate of exhaust gas (EGR gas) recirculated from the EGR pipe 46 to the intake pipe 13. Further, reference numeral 48 in FIG. 1 is an EGR cooler that cools exhaust gas (EGR gas) passing through the EGR pipe 46.

The operation of the exhaust gas purification apparatus configured as described above will be described. The temperature sensor 38 detects that the temperature related to the particulate filter 22 is in a high temperature range (for example, 250 to 500 ° C.), and the temperature related to the selective catalytic reduction catalyst 19 is a high temperature range (for example, 250 to 500 ° C.). Is detected by the auxiliary temperature sensor 39, the controller 43 operates the pump drive motor based on the detection outputs of the temperature sensor 38, auxiliary temperature sensor 39, rotation sensor 41 and load sensor 42, and sets the flow rate adjustment valve 37. It opens at a predetermined opening, opens and closes the on-off valve 31 at a predetermined interval (for example, every 100 milliseconds), and opens and closes the auxiliary on-off valve 32 at a predetermined interval (for example, every 10 milliseconds). At this time, immediately after the hydrocarbon-based liquid 24 is injected from the liquid injection nozzle 26, immediately before the next liquid 24 is injected at a predetermined interval, the oxidation catalyst layer 22h of the particulate filter 22 has an Part of NOx is adsorbed. Further, the controller 43 controls the amount of liquid ejected from the liquid ejecting nozzle 26 once so that the excess air ratio λ of the exhaust gas before flowing into the filter 22 is less than 1. As a result, a relatively large amount of liquid 24 is injected from the liquid injection nozzle 26 and the exhaust gas becomes a fuel-rich atmosphere. Therefore, NOx (NO ₂ , NO, etc.) adsorbed on the oxidation catalyst layer 22h is a mist-like hydrocarbon system. It reacts with the liquid 24 to produce ammonia gas and carbon dioxide. The ammonia gas is mixed with the mist-like hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27, and then flows into the selective reduction catalyst 19. The mist-like hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27 reacts with NOx in the exhaust gas on the selective catalytic reduction catalyst 19, thereby reducing NOx in the exhaust gas to N ₂ and purifying it. Is done. Also the ammonia gas exerts a selective reduction function for reducing reacts with NOx in the exhaust gas on the selective reduction catalyst 19 NOx into N _2. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature range of the exhaust gas can be improved.

<Second Embodiment>
FIG. 5 shows a second embodiment of the present invention. 5, the same reference numerals as those in FIG. 1 denote the same components. In this embodiment, an oxidation catalyst 61 and a particulate filter 62 on which no oxidation catalyst layer is formed are accommodated in the upstream case 23 in order from the exhaust gas upstream side. The oxidation catalyst 61 is a monolithic catalyst, and is formed by coating a honeycomb carrier made of cordierite with alumina (Al ₂ O ₃ ) containing ceria (CeO ₂ ) and supporting a predetermined noble metal, followed by drying and firing. Is done. Here, the predetermined noble metal refers to one or more noble metals selected from the group consisting of platinum, palladium and rhodium. The oxidation catalyst is formed by the following method. After impregnating the alumina powder with the above-mentioned noble metal solution and supporting the noble metal on the alumina powder, the ceria powder is mixed with the alumina powder supported on the noble metal to prepare a mixed powder, and the slurry of the mixed powder is added to the honeycomb carrier. The oxidation catalyst 61 can be formed by coating, drying and baking. In addition, a slurry of mixed powder of ceria powder and alumina powder was prepared, and this slurry was coated on a honeycomb carrier, and then the honeycomb carrier coated with this mixed powder was immersed in the above precious metal solution and dried and fired to oxidize. A catalyst 61 may be formed. Although not shown, both ends of the honeycomb carrier (both ends of the through hole) are opened. Further, the temperature sensor 38 is provided in the upstream case 23 between the liquid jet nozzle 26 and the oxidation catalyst 61 and detects a temperature related to the oxidation catalyst 61. Specifically, the temperature of the exhaust gas immediately before flowing through the oxidation catalyst 61 is detected by the temperature sensor 38. The configuration other than the above is the same as that of the first embodiment.

The operation of the exhaust gas purification apparatus configured as described above will be described. The temperature sensor 38 detects that the temperature related to the oxidation catalyst 61 is in a high temperature range (for example, 250 to 500 ° C.), and the temperature related to the selective catalytic reduction catalyst 19 is in the high temperature range (for example, 250 to 500 ° C.). When the auxiliary temperature sensor 39 detects that there is, the controller 43 operates the pump drive motor based on the detection outputs of the temperature sensor 38, the auxiliary temperature sensor 39, the rotation sensor 41, and the load sensor 42, and sets the flow rate adjustment valve 37 to a predetermined value. The opening / closing valve 31 is opened and closed at a predetermined interval (for example, every 100 milliseconds), and the auxiliary opening / closing valve 32 is opened and closed at a predetermined interval (for example, every 10 milliseconds). At this time, a portion of NOx in the exhaust gas is adsorbed by the oxidation catalyst 61 immediately after the hydrocarbon-based liquid 24 is injected from the liquid injection nozzle 26 until immediately before the next liquid 24 is injected at a predetermined interval. Is done. Further, the controller 43 controls the amount of liquid ejected from the liquid ejecting nozzle 26 once so that the excess air ratio λ of the exhaust gas before flowing into the oxidation catalyst 61 is less than 1. As a result, a relatively large amount of liquid 24 is injected from the liquid injection nozzle 26 and the exhaust gas becomes a fuel-rich atmosphere. Therefore, the NOx (NO ₂ , NO, etc.) adsorbed on the oxidation catalyst 61 is a mist-like hydrocarbon liquid. Reaction with 24 produces ammonia gas and carbon dioxide. Since the NOx adsorption amount by the oxidation catalyst 61 is larger than the NOx adsorption amount by the oxidation catalyst layer in the first embodiment, more ammonia gas is generated than in the first embodiment. The ammonia gas is mixed with the mist-like hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27, and then flows into the selective reduction catalyst 19. The mist-like hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27 reacts with NOx in the exhaust gas on the selective catalytic reduction catalyst 19, thereby reducing NOx in the exhaust gas to N ₂ and purifying it. Is done. Also the ammonia gas exerts a selective reduction function for reducing reacts with NOx in the exhaust gas on the selective reduction catalyst 19 NOx into N _2. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature range of the exhaust gas is improved as compared with the first embodiment.

<Third Embodiment>
FIG. 6 shows a third embodiment of the present invention. 6, the same reference numerals as those in FIGS. 1 and 5 denote the same components. In this embodiment, an oxidation catalyst 61 and a particulate filter 22 on which an oxidation catalyst layer is formed are accommodated in the upstream case 23 in order from the exhaust gas upstream side. Similar to the second embodiment, the oxidation catalyst 61 is a monolithic catalyst, and includes alumina (Al ₂ O ₃ ) containing ceria (CeO ₂ ) and supporting a predetermined noble metal on a cordierite honeycomb carrier. ) And then dried and fired. The oxidation catalyst layer formed on the filter 22 is made of alumina (Al ₂ O ₃ ) containing ceria (CeO ₂ ) and supporting a predetermined noble metal, as in the first embodiment. Further, the temperature sensor 38 is provided in the upstream case 23 between the liquid jet nozzle 26 and the oxidation catalyst 61 and detects a temperature related to the oxidation catalyst 61 and the filter 22. Specifically, the temperature of the exhaust gas immediately before flowing through the oxidation catalyst 61 is detected by the temperature sensor 38. The configuration other than the above is the same as that of the first embodiment.

The operation of the exhaust gas purification apparatus configured as described above will be described. The temperature sensor 38 detects that the temperature related to the oxidation catalyst 61 is in a high temperature range (for example, 250 to 500 ° C.), and the temperature related to the selective catalytic reduction catalyst 19 is in the high temperature range (for example, 250 to 500 ° C.). When the auxiliary temperature sensor 27 detects that there is, the controller 43 operates the pump drive motor based on the detection outputs of the temperature sensor 38, the auxiliary temperature sensor 39, the rotation sensor 41, and the load sensor 42, and sets the flow rate adjustment valve 37 to a predetermined value. The opening / closing valve 31 is opened and closed at a predetermined interval (for example, every 100 milliseconds), and the auxiliary opening / closing valve 32 is opened and closed at a predetermined interval (for example, every 10 milliseconds). At this time, immediately after the hydrocarbon-based liquid 24 is injected from the liquid injection nozzle 26 until immediately before the next liquid 24 is injected at a predetermined interval, the oxidation catalyst 61 and the oxidation catalyst layer receive NOx in the exhaust gas. Part is adsorbed. Further, the controller 43 controls the amount of liquid ejected from the liquid ejecting nozzle 26 once so that the excess air ratio λ of the exhaust gas before flowing into the oxidation catalyst 61 is less than 1. Thereby relatively much liquid 24 from the liquid injection nozzle 26 is injected, since the exhaust gas is the atmosphere of the fuel-rich, adsorbed NOx to the oxidation catalyst 61 and the oxidation catalyst layer (NO _2, NO, etc.) mist It reacts with the hydrocarbon liquid 24 to produce ammonia gas and carbon dioxide. Since the NOx adsorption amount by the oxidation catalyst 61 and the oxidation catalyst layer is larger than the NOx adsorption amount by the oxidation catalyst 61 in the second embodiment, the ammonia gas is generated more than in the second embodiment. The ammonia gas is mixed with the mist-like hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27, and then flows into the selective reduction catalyst 19. The mist-like hydrocarbon liquid 24 injected from the auxiliary liquid injection nozzle 27 reacts with NOx in the exhaust gas on the selective catalytic reduction catalyst 19, thereby reducing NOx in the exhaust gas to N ₂ and purifying it. Is done. Also the ammonia gas exerts a selective reduction function for reducing reacts with NOx in the exhaust gas on the selective reduction catalyst 19 NOx into N _2. As a result, the NOx reduction efficiency in the exhaust gas in the high temperature region of the exhaust gas is improved as compared with the second embodiment.

In the first to third embodiments, the exhaust gas purifying apparatus of the present invention is applied to a diesel engine. However, the exhaust gas purifying apparatus of the present invention may be applied to a gasoline engine. In the first to third embodiments, the exhaust gas purifying apparatus of the present invention is applied to a turbocharged diesel engine. However, the exhaust gas purifying apparatus of the present invention is a naturally aspirated diesel engine or a naturally aspirated gasoline. It may be applied to the engine. In the first to third embodiments, the hydrocarbon-based liquid is not injected from the auxiliary liquid injection nozzle, and only the ammonia gas generated in the oxidation catalyst or the oxidation catalyst layer is used for the selective reduction catalyst. If the NOx in the exhaust gas can be reduced to N ₂ and purified, the auxiliary liquid injection nozzle becomes unnecessary, and the temperature related to the selective reduction catalyst is substantially the same as the temperature related to the oxidation catalyst or particulate filter. This eliminates the need for an auxiliary temperature sensor.

  In the first embodiment, the temperature sensor is provided in the upstream case between the liquid jet nozzle and the particulate filter. However, if the temperature related to the filter can be detected, the temperature sensor is provided between the filter and the auxiliary liquid jet nozzle. Or the upstream case between the liquid jet nozzle and the filter and the upstream case between the filter and the auxiliary liquid jet nozzle. Here, when the temperature sensors are provided at the two locations on the upstream case, the average value of the detected temperatures of the two temperature sensors is set as a temperature related to the filter. In the second embodiment, the temperature sensor is provided in the upstream case between the liquid injection nozzle and the oxidation catalyst. However, if the temperature related to the oxidation catalyst can be detected, the temperature sensor is used as the oxidation catalyst and the auxiliary liquid injection nozzle. It may be provided in the upstream case between the two, or the upstream case between the liquid injection nozzle and the oxidation catalyst and the upstream case between the oxidation catalyst and the auxiliary liquid injection nozzle. Here, when the temperature sensors are provided at the two locations on the upstream case, the average value of the detected temperatures of the two temperature sensors is set as the temperature related to the oxidation catalyst.

  In the third embodiment, the temperature sensor is provided in the upstream case between the liquid jet nozzle and the oxidation catalyst. However, if the temperature related to the oxidation catalyst and the filter can be detected, the temperature sensor is provided between the oxidation catalyst and the filter. Of the upstream case between the filter and the auxiliary liquid jet nozzle, or the upstream case between the liquid jet nozzle and the oxidation catalyst and the upstream case between the filter and the auxiliary liquid jet nozzle. Alternatively, it may be provided at three locations, that is, an upstream case between the liquid injection nozzle and the oxidation catalyst, an upstream case between the oxidation catalyst and the filter, and an upstream case between the filter and the auxiliary liquid injection nozzle. Here, when the temperature sensors are provided in the two places on the upstream case, the average value of the detected temperatures of the two temperature sensors is set as the temperature related to the oxidation catalyst and the filter, and the temperature sensors are arranged in the three places on the upstream case. In this case, the average value of the detected temperatures of the three temperature sensors is set as the temperature related to the oxidation catalyst and the filter. Furthermore, in the first to third embodiments, the auxiliary temperature sensor is provided in the downstream case between the auxiliary liquid injection nozzle and the selective catalytic reduction catalyst. However, if the temperature related to the selective catalytic reduction catalyst can be detected, the auxiliary temperature sensor is provided. Two temperature sensors are installed in the downstream case downstream of the selective reduction catalyst or in the downstream case between the auxiliary liquid injection nozzle and the selective reduction catalyst and the downstream case downstream of the selective reduction catalyst. May be provided. Here, when the auxiliary temperature sensors are provided in the two places on the downstream case, the average value of the detected temperatures of these auxiliary temperature sensors is set as the temperature related to the selective catalytic reduction catalyst.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
As shown in FIG. 6, the selective reduction catalyst 19 is provided in the exhaust pipe 16 of the in-line 6-cylinder turbocharger-equipped diesel engine 11 whose displacement is 8000 cc. This selective reduction catalyst 19 was a catalyst produced by coating a honeycomb carrier with a slurry containing copper ion-exchanged zeolite powder, followed by drying and firing. Further, an oxidation catalyst 61 and a particulate filter 22 on which an oxidation catalyst layer is formed are provided in order from the exhaust gas upstream side to the exhaust pipe 16 on the exhaust gas upstream side of the selective catalytic reduction catalyst 19. The oxidation catalyst 61 was a catalyst produced by coating a honeycomb carrier with alumina (Al ₂ O ₃ ) containing ceria (CeO ₂ ) and carrying platinum, followed by drying and firing. The oxidation catalyst layer is formed on a part of the inner surface of the inflow hole and the outflow hole of the particulate filter 22 and a part of the inner surface of the plurality of pores so as not to inhibit the passage of the exhaust gas, and ceria (CeO _2). ) And platinum-supported alumina (Al ₂ O ₃ ).

  On the other hand, a liquid injection nozzle 26 capable of injecting a hydrocarbon liquid (light oil) 24 toward the oxidation catalyst 61 is provided in the exhaust pipe 16 upstream of the oxidation catalyst 61. An opening / closing valve 31 is provided at the base end of the liquid jet nozzle 26, and the opening / closing valve 31 is connected to the tank 29 via the first branch pipe 33b and the main pipe 33a. The main pipe 33a is provided with a pump 34 driven by a pump drive motor. Further, the main line 33 a and the tank 29 are connected by a return pipe 36 so as to bypass the pump 34, and the return pipe 36 is provided with a flow rate adjusting valve 37 for adjusting the opening degree of the return pipe 36. Note that the auxiliary liquid ejection nozzle 27 and the auxiliary temperature sensor 39 in FIG. 6 were not used. This exhaust gas purification apparatus was designated as Example 1.

<Comparative Example 1>
In FIG. 6, although the liquid injection nozzle 26 was not used, the configuration was the same as that of Example 1 except that the auxiliary liquid injection nozzle 27 that injects light oil toward the selective reduction catalyst 19 was used. This exhaust gas purification apparatus was designated as Comparative Example 1.

<Comparative test 1 and evaluation>
NOx reduction by the exhaust gas purification apparatuses of Example 1 and Comparative Example 1 when the engine speed and load are changed to gradually increase the temperature of exhaust gas discharged from the exhaust pipe of the engine from 100 ° C. to 500 ° C. While measuring each rate, the amount of ammonia gas in the exhaust gas at the particulate filter outlet of Example 1 and Comparative Example 1 was measured. The results are shown in FIGS. In the exhaust gas purification apparatus of Example 1, the hydrocarbon-based liquid was injected from the liquid injection nozzle every 100 milliseconds when the exhaust gas temperature at the selective catalytic reduction catalyst inlet was in the range of 170 to 420 ° C. In the exhaust gas purifying apparatus of Comparative Example 1, the hydrocarbon-based liquid was injected from the auxiliary liquid injection nozzle every 10 milliseconds in the range where the exhaust gas temperature at the selective catalytic reduction catalyst inlet was 170 to 420 ° C. Further, the single liquid injection amount from the liquid injection nozzle of Example 1 with respect to the single liquid injection amount from the auxiliary liquid injection nozzle of Comparative Example 1 is set to the liquid injection interval from the liquid injection nozzle of Example 1. It was set so as to increase in proportion to the liquid ejection interval from the auxiliary liquid ejection nozzle. That is, the amount of one liquid injection from the liquid injection nozzle of Example 1 was set so that the excess air ratio λ of the exhaust gas before flowing into the oxidation catalyst was less than 1.

  As is clear from FIG. 7, in the exhaust gas purification apparatus of Comparative Example 1, the NOx reduction rate began to increase after the exhaust gas temperature exceeded about 350 ° C., whereas in the exhaust gas purification apparatus of Example 1, the exhaust gas temperature The NOx reduction rate began to rise after the temperature exceeded about 250 ° C. In the exhaust gas purification apparatus of Comparative Example 1, the maximum NOx reduction rate was as low as about 18%, whereas in the exhaust gas purification apparatus of Example 1, the maximum NOx reduction rate was as high as about 42%. Thus, the exhaust gas purification apparatus of Example 1 can exhibit NOx reduction performance from a relatively low temperature even in a high temperature range of the exhaust gas, and greatly reduces the NOx reduction rate in the exhaust gas, as compared with the exhaust gas purification apparatus of Comparative Example 1. It was found that it can be improved.

  On the other hand, as is clear from FIG. 8, in the exhaust gas purification apparatus of Comparative Example 1, even when the exhaust gas temperature rose, ammonia gas was hardly contained in the exhaust gas, whereas in the exhaust gas purification apparatus of Example 1, When the exhaust gas temperature reaches about 250 ° C., ammonia gas begins to be contained in the exhaust gas, and as the exhaust gas temperature rises, the ammonia gas in the exhaust gas gradually increases. When the exhaust gas temperature exceeds 400 ° C., the ammonia gas amount exceeds 80 ppm. It was.

DESCRIPTION OF SYMBOLS 11 Diesel engine 16 Exhaust pipe 19 Selective reduction type catalyst 22 Particulate filter 22a Partition 22b Through hole 22c Carrier 22d Inflow hole 22e Outflow hole 22h Oxidation catalyst layer 24 Hydrocarbon liquid 26 Liquid injection nozzle 27 Auxiliary liquid injection nozzle 28 Liquid supply means 38 Temperature sensor 39 Auxiliary temperature sensor 43 Controller 61 Oxidation catalyst

Claims (8)

In the exhaust gas purification device that purifies the exhaust gas of the engine (11),
A selective reduction catalyst (19) provided in the exhaust pipe (16) and capable of reducing NOx in the exhaust gas to N ₂ ;
A ceria-containing oxidation catalyst layer provided in the exhaust pipe (16) on the exhaust gas upstream side of the selective catalytic reduction catalyst (19) and formed in a porous material through which the exhaust gas can pass and so as not to block the passage of the exhaust gas ( And a particulate filter (22) capable of collecting particulates in the exhaust gas,
A liquid injection nozzle (26) provided in the exhaust pipe (16) on the exhaust gas upstream side of the particulate filter (22) and capable of injecting a hydrocarbon-based liquid (24) toward the particulate filter (22);
Liquid supply means (28) for supplying the liquid (24) to the liquid jet nozzle (26);
A temperature sensor (38) for detecting the temperature of the exhaust gas related to the particulate filter (22);
An exhaust gas purification apparatus comprising: a controller (43) that controls the liquid supply means (28) based on a detection output of the temperature sensor (38). In the exhaust gas purification device that purifies the exhaust gas of the engine (11),
A selective reduction catalyst (19) provided in the exhaust pipe (16) and capable of reducing NOx in the exhaust gas to N ₂ ;
An oxidation catalyst (61) that is provided in the exhaust pipe (16) upstream of the exhaust gas from the selective catalytic reduction catalyst (19) and contains ceria and oxidizes at least unburned fuel in the exhaust gas to raise the exhaust gas temperature;
A liquid injection nozzle (26) provided in the exhaust pipe (16) on the exhaust gas upstream side of the oxidation catalyst (61) and capable of injecting a hydrocarbon-based liquid (24) toward the oxidation catalyst (61);
Liquid supply means (28) for supplying the liquid (24) to the liquid jet nozzle (26);
A temperature sensor (38) for detecting the temperature of the exhaust gas related to the oxidation catalyst (61);
An exhaust gas purification apparatus comprising: a controller (43) that controls the liquid supply means (28) based on a detection output of the temperature sensor (38).   Provided in the exhaust pipe (16) on the exhaust gas upstream side of the particulate filter (22) and on the exhaust gas downstream side of the liquid injection nozzle (26), contains ceria and oxidizes at least unburned fuel in the exhaust gas. An oxidation catalyst (61) for raising the exhaust gas temperature is further provided, and the temperature sensor (38) is configured to detect a temperature related to the oxidation catalyst (61) and the particulate filter (22). The exhaust gas purification apparatus according to 1.   It is provided in the exhaust pipe (16) between the particulate filter (22) and the selective catalytic reduction catalyst (19) and can inject the hydrocarbon-based liquid (24) toward the selective catalytic reduction catalyst (19). An auxiliary liquid injection nozzle (27), and an auxiliary temperature sensor (39) for detecting the temperature of the exhaust gas related to the selective catalytic reduction catalyst (19), and the liquid supply means (28) includes the liquid injection nozzle ( 26) and the auxiliary liquid injection nozzle (27) are configured to supply the hydrocarbon-based liquid (24), and the controller (43) includes each of the temperature sensor (38) and the auxiliary temperature sensor (39). The exhaust gas purifying apparatus according to claim 1 or 3, wherein the liquid supply means (28) is controlled based on a detection output.   An auxiliary provided in the exhaust pipe (16) between the oxidation catalyst (61) and the selective reduction catalyst (19) and capable of injecting a hydrocarbon-based liquid (24) toward the selective reduction catalyst (19) The liquid injection nozzle (27) and an auxiliary temperature sensor (39) for detecting the temperature of the exhaust gas related to the selective reduction catalyst (19) are further provided, and the liquid supply means (28) includes the liquid injection nozzle (26 ) And the auxiliary liquid injection nozzle (27) to supply the hydrocarbon-based liquid (24), and the controller (43) detects each of the temperature sensor (38) and the auxiliary temperature sensor (39). The exhaust gas purifying apparatus according to claim 2, wherein the liquid supply means (28) is controlled based on an output.   The particulate filter (22) has a carrier (22c) in which a plurality of through-holes (22b) partitioned by a porous partition wall (22a) are formed in parallel to each other, and adjacent to the plurality of through-holes (22b) Inlet holes (22d) and outflow holes (22e) are formed by alternately sealing the outlet portion and the inlet portion, and a part of the through hole (22b) is selected from the group consisting of platinum, palladium and rhodium The exhaust gas purification apparatus according to claim 1 or 3, wherein the oxidation catalyst layer (22h) supporting the one or more kinds of noble metals and containing the ceria is formed so as not to prevent the passage of the exhaust gas.   The oxidation catalyst (61) has one or two selected from the group consisting of platinum, palladium and rhodium on a support in which a plurality of through-holes partitioned by a porous partition wall are formed in parallel and both ends are open. The exhaust gas purifying apparatus according to claim 2 or 3, wherein the exhaust gas purifying apparatus is configured to carry the above precious metal and contain the ceria.   The controller (43) ejects the liquid ejection nozzle (26) at a predetermined ejection interval within a range of 100 to 500 milliseconds, and the particulate filter (22) or the liquid ejection nozzle (26). The amount of one liquid injection from the liquid injection nozzle (26) is controlled so that the excess air ratio (λ) of the exhaust gas before flowing into the oxidation catalyst (61) is less than 1, thereby the particulates. The inside of the exhaust pipe (16) before flowing into the filter (22) or the oxidation catalyst (61) is configured to intermittently become a fuel-rich atmosphere. Exhaust gas purification device.

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