JP2005232975A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of obtaining a high NOx reduction ratio notwithstanding the operating conditions. <P>SOLUTION: The exhaust emission control device is provided with an NOx occlusion reduction catalyst 5 midway along an exhaust pipe 4, and formed to reduce and purify NOx by adding a reducing agent (light oil 13) upstream of the NOx occlusion reduction catalyst 5. A burner means (an injection nozzle 17, a spark plug 26, a burner chamber 7) to ignite and burn by injecting an appropriate amount of fuel (light oil) into the upstream side of the NOx occlusion reduction catalyst 5 is installed upstream of the NOx occlusion reduction chamber 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device.

Conventionally, exhaust purification is carried out with an exhaust purification catalyst installed in the middle of the exhaust pipe. As this type of exhaust purification catalyst, NOx in exhaust gas is oxidized when the exhaust air-fuel ratio is lean. Thus, a NOx occlusion reduction catalyst having the property of temporarily storing in the form of nitrate and decomposing and releasing NOx through the intervention of unburned HC, CO, etc. when the O ₂ concentration in the exhaust gas decreases is reduced and purified. Are known.

  As this type of NOx occlusion reduction catalyst, platinum / barium / alumina catalyst, iridium / platinum / barium / alumina catalyst and the like are already known as having the above-mentioned properties.

In the NOx occlusion reduction catalyst, when the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded, and therefore, O _{2 of} the exhaust gas flowing into the NOx occlusion reduction catalyst periodically. It is necessary to decompose and release NOx by reducing the concentration.

For example, when used in a gasoline engine, the operating air-fuel ratio of the engine is reduced (the engine is operated at a rich air-fuel ratio), thereby reducing the O ₂ concentration in the exhaust gas and unburned HC in the exhaust gas. It is possible to promote the decomposition and release of NOx by increasing reducing components such as CO and CO. However, when the NOx storage reduction catalyst is used as an exhaust purification device of a diesel engine, it is difficult to operate the engine at a rich air-fuel ratio. is there.

For this reason, by adding fuel (HC) to the exhaust gas upstream of the NOx storage reduction catalyst, the added fuel is used as a reducing agent to react with O ₂ on the NOx storage reduction catalyst. ₂ It is necessary to reduce the concentration (see, for example, Patent Document 1).
JP 2000-356127 A

However, in the method of adding fuel upstream of the NOx storage reduction catalyst in this way, a part of HC generated by evaporation of the added fuel reacts with O ₂ in the exhaust gas on the surface of the NOx storage reduction catalyst. (Combustion), and NOx decomposition and release is started after the O ₂ concentration in the atmosphere around the NOx storage reduction catalyst becomes almost zero, so that HC is O ₂ on the surface of the NOx storage reduction catalyst. NOx is efficiently removed from the NOx occlusion reduction catalyst under operating conditions where the combustion temperature (about 220-250 ° C) required for reaction (combustion) with NOx cannot be obtained (for example, slow driving in cities with heavy traffic). There was a problem that the NOx occlusion reduction catalyst could not be decomposed and released, and the regeneration of the NOx occlusion reduction catalyst did not proceed efficiently, so that the recovery rate of the NOx occlusion site in the catalyst volume was reduced and the occlusion capacity was lowered.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust purification device that can always ensure a high NOx reduction rate regardless of operating conditions.

  The present invention relates to an exhaust purification device that is equipped with a NOx occlusion reduction catalyst in the middle of an exhaust pipe and is configured to reduce and purify NOx by adding a reducing agent upstream of the NOx occlusion reduction catalyst. A burner means for injecting an appropriate amount of fuel and igniting and burning it is provided upstream of the reduction catalyst.

Thus, in this way, the operating conditions are such that the combustion temperature (about 220 to 250 ° C.) necessary for the reducing agent to react (combust) with O ₂ on the surface of the NOx storage reduction catalyst cannot be obtained. However, if an appropriate amount of fuel is injected upstream of the NOx storage reduction catalyst by the burner means and ignited and combusted, the exhaust gas heated to this temperature is introduced into the NOx storage reduction catalyst, and the catalyst bed temperature is As a result of forcibly raising the temperature to the temperature required for the reaction, the combustion temperature necessary for the reducing agent to react (combust) with O ₂ on the surface of the NOx storage reduction catalyst is ensured regardless of the current operating conditions. can get.

  The burner means of the present invention includes a fuel injection nozzle for injecting an appropriate amount of fuel upstream of the NOx storage reduction catalyst, an ignition device provided in the vicinity of the injection port of the fuel injection nozzle, the fuel injection nozzle and the ignition It is possible to configure the apparatus with a burner chamber that encloses the required combustion space.

  Further, in carrying out the present invention more specifically, for example, a temperature sensor for detecting the catalyst bed temperature of the NOx storage reduction catalyst, and the catalyst bed temperature of the NOx storage reduction catalyst based on a detection signal from the temperature sensor, It is preferable to include a control device that ignites and burns the burner means until the temperature is exceeded under a condition that is equal to or lower than a predetermined temperature.

According to the exhaust gas purification apparatus of the present invention described above, the combustion necessary for the NOx storage reduction catalyst to be appropriately heated by the burner means and the reducing agent to react (combust) with O ₂ on the surface of the NOx storage reduction catalyst. Since the temperature can be reliably obtained, a high NOx reduction rate can always be ensured regardless of the operating conditions, and the practicality of the exhaust purification apparatus using the NOx storage reduction catalyst can be greatly improved. The effects can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 and FIG. 2 show an example of an embodiment for carrying out the present invention. As shown in FIG. 1, in the exhaust purification apparatus of this embodiment, the exhaust gas discharged from the diesel engine 1 through the exhaust manifold 2 is shown. A NOx occlusion reduction catalyst 5 having a flow-through type honeycomb structure is provided in the middle of the exhaust pipe 4 through which the gas flow 3 circulates and is mounted on the casing 6. A burner chamber 7 is formed.

  Further, a reducing agent injection nozzle 8 is provided through the exhaust pipe 4 upstream of the burner chamber 7, and a light oil supply pipe 10 is provided between the reducing agent injection nozzle 8 and a light oil tank 9 provided at a required location. And the casing of the light oil tank 9 through the reducing agent injection nozzle 8 using the light oil 13 in the light oil tank 9 as a reducing agent by driving the supply pump 11 provided in the middle of the light oil supply pipe 10 and opening the light oil injection valve 12. 6 can be added to the inlet side.

  Further, the diesel engine 1 is equipped with a rotation sensor 14 for detecting the engine rotation speed, and a rotation speed signal 14a from the rotation sensor 14 and an accelerator sensor 15 (a sensor for detecting the depression angle of the accelerator pedal). ) Is input to the control device 16.

  On the other hand, in the control device 16, the amount of NOx generated is estimated based on the current operating state determined from the rotation speed signal 14a from the rotation sensor 14 and the load signal 15a from the accelerator sensor 15, and The addition amount of the light oil 13 corresponding to the estimated NOx generation amount is further calculated, and the drive command signal 11a and the light oil injection from the control device 16 to the supply pump 11 are executed so that the required amount of the light oil 13 is added. A valve opening command signal 12a to the valve 12 is output.

  Further, a fuel injection nozzle 17 for injecting an appropriate amount of light oil 13 is provided through the burner chamber 7 upstream of the NOx storage reduction catalyst 5, and the fuel injection nozzle 17, the supply pump 11, Are connected by a branch pipe 18, and the light oil 13 in the light oil tank 9 is used as fuel for the burner by opening the light oil metering valve 19 provided in the middle of the branch pipe 18 and driving the supply pump 11. The fuel can be injected from the fuel injection nozzle 17.

  Further, in the vicinity of the injection port of the fuel injection nozzle 17, a spark plug 26 that generates a discharge by a high voltage signal 26a output from the ignition coil 20 serves as an ignition device for igniting the light oil 13 injected from the injection port. The spark plug 26, the fuel injection nozzle 17, and the burner chamber 7 that encloses the spark plug 26 while securing a required combustion space are configured.

  On the other hand, the casing 6 of the NOx storage reduction catalyst 5 is equipped with a temperature sensor 21 for detecting the inlet exhaust temperature of the NOx storage reduction catalyst 5 and a temperature sensor 22 for detecting the outlet exhaust temperature of the NOx storage reduction catalyst 5. The detection signals 21 a and 22 a from these temperature sensors 21 and 22 are input to the control device 16.

  The control device 16 obtains the temperature difference between the inlet exhaust temperature and the outlet exhaust temperature of the NOx storage reduction catalyst 5 based on the detection signals 21a and 22a from the temperature sensors 21 and 22 described above. Based on the temperature difference, the catalyst bed temperature of the NOx occlusion reduction catalyst 5 is estimated (indirectly detected), and burner combustion is performed until the estimated catalyst bed temperature exceeds the predetermined temperature under the condition that the estimated catalyst bed temperature is below a predetermined temperature. In order to achieve this, a valve opening command signal 19a to the light oil metering valve 19 and an energization command signal 20a to the ignition coil 20 are output.

  However, in the example shown here, it is technically difficult to directly detect the temperature of the catalyst bed by inserting the temperature sensor of the temperature sensor inside the NOx storage reduction catalyst 5. However, the temperature sensor 21 and 22 are arranged to indirectly detect (estimate) the catalyst bed temperature. If possible, a temperature sensor of the temperature sensor is inserted into the NOx storage reduction catalyst 5. The catalyst bed temperature may be directly measured.

  In FIG. 1, reference numeral 23 denotes a turbocharger, 24 denotes an intake pipe, and 25 denotes an intercooler.

Thus, if the exhaust gas purification apparatus is configured in this way, a combustion temperature (about 220 to 250 ° C.) necessary for HC to react (combust) with O ₂ on the surface of the NOx storage reduction catalyst 5 can be obtained. Even under non-operating conditions, based on the detection signals 21a and 22a from the temperature sensors 21 and 22, the valve opening command signal 19a from the control device 16 to the light oil metering valve 19 and the energization command signal to the ignition coil 20 are provided. 20a is output and an appropriate amount of light oil 13 is injected from the fuel injection nozzle 17 constituting the burner means to the upstream side of the NOx storage reduction catalyst 5 and ignited and combusted by the spark plug 26. The converted exhaust gas 3 is introduced into the NOx occlusion reduction catalyst 5, and the temperature of the catalyst bed is forcibly raised to the temperature required for the reaction.

As a result, it is possible to reliably obtain the combustion temperature necessary for HC to react (combust) with O ₂ on the surface of the NOx storage reduction catalyst 5 regardless of the current operating conditions. The supply pump 11 is driven by 11a, and the light oil injection valve 12 is opened by the valve opening command signal 12a, so that the addition amount of light oil 13 corresponding to the amount of NOx estimated from the current operation state is reduced. HC generated from the light oil 13 added as a reducing agent reacts (combusts) with O ₂ in the exhaust gas 3 on the surface of the NOx storage reduction catalyst 5, and thereby the surroundings of the NOx storage reduction catalyst 5. this O ₂ concentration in the atmosphere is started substantially zero and becomes an exploded release of NOx, the NOx by residual HC is reduced processed efficiently N ₂ as it on the surface of the NOx storage reduction catalyst 5 To become.

Therefore, according to the embodiment as described above, the NOx storage reduction catalyst 5 is appropriately heated by the burner means including the fuel injection nozzle 17, the spark plug 26, and the burner chamber 7, so that the NOx storage reduction catalyst 5 Since the combustion temperature necessary for HC to react (combust) with O ₂ on the surface can be reliably obtained, a high NOx reduction rate can always be ensured regardless of the operating conditions, and the NOx storage reduction catalyst 5 The practicality of the exhaust gas purification apparatus using can be greatly improved.

  In fact, according to the results of experiments conducted by the present inventors, as shown in the graph of FIG. 2, the case X in which the heating support by the burner means is implemented in the apparatus configuration of the present embodiment described above and the burner means are provided. In comparison with the case Y equipped only with the NOx occlusion reduction catalyst 5, the case X can obtain a higher NOx reduction rate than the case Y from the low load region (the operation region where the exhaust temperature is low). Proven.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. For fuel added as a reducing agent, in addition to using light oil that is a general diesel engine fuel, kerosene or the like. Of course, different types of fuels may be used, and various modifications can be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is a graph which shows the relationship between a NOx reduction rate and load with a comparative example.

Explanation of symbols

3 Exhaust gas 4 Exhaust pipe 5 NOx storage reduction catalyst 7 Burner chamber (burner means)
8 Reducing agent injection nozzle 13 Light oil (Reducing agent: Fuel for burner)
16 Control device 17 Fuel injection nozzle (burner means)
21 temperature sensor 21a detection signal 22 temperature sensor 22a detection signal 26 spark plug (ignition device: burner means)

Claims (3)

  An exhaust gas purification apparatus equipped with a NOx storage reduction catalyst in the middle of an exhaust pipe and configured to reduce and purify NOx by adding a reducing agent upstream of the NOx storage reduction catalyst, upstream of the NOx storage reduction catalyst An exhaust emission control device comprising burner means for injecting and burning an appropriate amount of fuel on the side.   A fuel injection nozzle that injects an appropriate amount of fuel upstream of the NOx storage reduction catalyst, an ignition device provided in the vicinity of the injection port of the fuel injection nozzle, and the fuel injection nozzle and the ignition device to ensure a required combustion space. 2. The exhaust emission control device according to claim 1, wherein a burner means is constituted by the burner chamber to be encapsulated.   A temperature sensor for detecting the catalyst bed temperature of the NOx storage reduction catalyst, and a burner means based on a detection signal from the temperature sensor until the catalyst bed temperature of the NOx storage reduction catalyst is lower than a predetermined temperature until the temperature exceeds the temperature. The exhaust emission control device according to claim 1, further comprising a control device that performs ignition and combustion.

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