JP2019044757A - Exhaust emission control device and internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control device capable of controlling the form of ashes, and to provide an internal combustion engine.SOLUTION: The exhaust emission control device includes a filter for trapping particulate matters included in exhaust gas from the internal combustion engine, the filter being adapted to be regenerated with the trapped particulate matters burnt, and a transfer part for transferring reductant to the exhaust upstream side of the filter so that the reductant is used to push away ashes accumulated on the filter when regenerated to the exhaust downstream side of the filter. For example, the exhaust emission control device includes a urea SCR catalyst for eliminating nitrogen oxide included in the exhaust gas, and the transfer part for transferring the reductant to the exhaust upstream side of the urea SCR catalyst when eliminating the nitrogen oxide.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an exhaust purification system and an internal combustion engine.

  Conventionally, as a filter for collecting particulate matter (hereinafter referred to as PM) contained in exhaust gas from an internal combustion engine, for example, a diesel particulate filter (DPF) is known.

  After the causative substance such as Ca contained in the additive of the oil is deposited on the DPF together with the PM, it is burned off by the regeneration of the DPF and is deposited in the DPF. The unburned component may be called ash.

  The ash includes what is called wall ash deposited on the DPF, and what is called plug ash deposited on the exhaust downstream side of the DPF.

JP, 2011-202573, A

  By the way, it is known that wall ash is transported to the exhaust downstream side of the DPF by high temperature gas to change the form of ash into plug ash.

  In addition, it is known that the influence of ash deposition on the pressure drop of DPF is greater for wall ash than for plug ash.

  In order to reduce the effect of DPF on pressure loss, it is desirable to change the form of ash from wall ash to plug ash. However, among conventional DPF regeneration methods, there is no way to control the form of ash.

  An object of the present disclosure is to provide an exhaust gas purification device and an internal combustion engine capable of controlling the form of ash.

The exhaust purification system of the present disclosure
A filter that collects particulate matter in exhaust gas from an internal combustion engine and is regenerated by burning the collected particulate matter;
A transfer unit for transferring the reducing agent to the exhaust upstream side of the filter so that the ash deposited on the filter by the regeneration is flushed with the reducing agent to the exhaust downstream side of the filter;
Equipped with

  An internal combustion engine of the present disclosure includes the above-described exhaust gas purification device.

  According to the present disclosure, the form of ash can be controlled.

A schematic configuration diagram partially showing an example of an exhaust system of an engine according to an embodiment of the present disclosure Partial longitudinal cross-sectional view of DPF before diluted urea water is cut along the exhaust direction Partial longitudinal cross-sectional view of DPF after diluted urea water is cut along the exhaust direction Flow chart showing an example of urea aqueous solution transfer processing

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
The present embodiment describes the case where the present invention is applied to a diesel engine (internal combustion engine) mounted on a vehicle.

  First, a schematic structure of a diesel engine (hereinafter simply referred to as an engine) according to the present embodiment will be described. FIG. 1 is a schematic configuration view showing an example of an exhaust system of an engine according to the embodiment. Note that the X axis is depicted in FIGS. 1 to 3. In the following description, the left and right direction in FIGS. 1 to 3 is referred to as the X direction or the exhaust direction, the right direction is the “+ X direction”, the “exhaust downstream direction” or the “exhaust downstream side”, and the left direction is the “−X direction”. , "Exhaust upstream direction" or "exhaust upstream side".

  As shown in FIG. 1, an exhaust pipe 10 is connected to an exhaust manifold (not shown) of the engine. Exhaust gas from the engine flows into the exhaust pipe 10. In the exhaust pipe 10, an oxidation catalyst (Diesel Oxidation Catalyst: DOC) 11, a DPF 12, and a urea SCR catalyst 13 are provided in this order from the exhaust upstream side (-X direction).

  When the fuel is supplied, the DOC 11 oxidizes it to raise the temperature of the exhaust gas.

  The urea SCR catalyst 13 purifies nitrogen oxides contained in the exhaust gas using a reducing agent. The reducing agent used here is, for example, urea water.

  2 and 3 are partial longitudinal cross-sectional views of the DPF 12 taken along the exhaust direction (X direction).

  The DPF 12 has a large number of cells 121 partitioned by porous partition walls 122. The cells 121 are disposed along the exhaust direction (X direction). The inlet on the exhaust upstream side (-X direction) of the cell 121 and the outlet on the exhaust downstream side (+ X direction) are alternately plugged. The DPF 12 collects PM contained in the exhaust gas on the pores and the surface of the partition wall 122. By burning the PM collected in the partition wall 122 of the DPF 12, the DPF 12 is regenerated. The regeneration of the DPF 12 is performed by supplying fuel to the DOC 11 on the exhaust upstream side of the DPF 12 and raising the temperature of the exhaust gas to the PM combustion temperature.

  Among the PMs discharged from the engine, there are unburned components called ash produced from metal components contained in oil and fuel additives (hereinafter, oil etc.). Ash remains in the DPF 12 and occupies the volume of the DPF 12. Since the area which filters PM in DPF12 decreases by this, pressure loss rises with distance.

  The effect of ash deposition on pressure drop depends on where in the DPF 12 the ash is deposited. The wall ash 3a deposited on the partition wall 122 of the DPF 12 is shown in FIG. Further, FIG. 3 shows the plug ash 3 b deposited on the exhaust downstream side (the outlet side of the cell) of the DPF 12.

  It is known that wall ash 3a is larger than plug ash 3b in the influence of ash deposition on pressure loss.

  The exhaust gas purification apparatus 1 according to the present embodiment, as shown in FIG. 1, includes tanks 20A and 20B and a transfer unit 30 in addition to the DPF 12 described above.

  The tank 20 </ b> A stores the urea water 2.

  The tank 20 B stores the water 3.

  The water 3 is, for example, condensed water generated in an exhaust system of the engine. Specifically, the exhaust gas discharged from the engine contains not only the water vapor originally contained in the intake air but also the water vapor generated as a result of the combustion of fuel or PM. While the exhaust gas containing water vapor flows through the exhaust system, its temperature is lowered, and when the temperature of the exhaust gas falls below the dew point, the water vapor condenses to generate condensed water in the exhaust gas. The generated condensed water is stored in the tank 20B.

  Further, the water 3 is, for example, one in which water in the EGR gas is condensed. Specifically, when the EGR gas cooled by the EGR cooler is cooled to the dew point or lower, the water in the EGR gas is condensed to generate condensed water. The generated condensed water is stored in the tank 20B.

  As shown in FIG. 1, the transfer unit 30 includes a pump 31, nozzles 32A and 32B, water channels 33A and 33B, a control valve 34, and a flow control valve 35.

  The pump 31 is connected to the nozzles 32A and 32B via the control valve 34, respectively. The pump 31 is connected to the tanks 20A and 20B via the flow rate adjustment valve 35, respectively.

  The nozzle 32A is disposed on the exhaust upstream side (-X direction) of the DPF 12.

  The nozzle 32 </ b> B is disposed on the exhaust upstream side (−X direction) of the urea SCR catalyst 13.

  The control valve 34 has a state in which the diluted urea water 4 flows through the water channel 33A communicating with the nozzle 32A, a state in which the urea water 2 flows through the water channel 33B communicating with the nozzle 32B, and a diluted urea water 4 in any of the water channels 33A and 33B. , And the urea water 2 is not circulated.

  The flow rate adjustment valve 35 adjusts the flow rate of the urea water 2 sent from the tank 20A to the pump 31 and the flow rate of the water 3 sent from the tank 20B to the pump 31. The flow rate adjustment valve 35 is controlled so that, for example, only urea water 2 is fed to the pump 31. Further, the flow rate adjustment valve 35 is controlled so that, for example, diluted urea water 4 obtained by diluting urea water 2 with water 3 is sent to the pump 31. The water 3 becomes more viscous by being mixed with the urea water 2. Further, by diluting the urea water 2 with the water 3, the diffusivity of the urea water 2 is improved.

  The ECU 40 controls the flow rate adjusting valve 35 so that only the urea water 2 is sent to the pump 31 when purifying nitrogen oxides in the exhaust gas, and controls the urea water 2 to flow through the water passage 33B. Control the valve 34.

  The nozzle 32 B releases (injects) the urea water 2 to the exhaust upstream side of the urea SCR catalyst 13. Ammonia gas obtained from the urea water 2 reduces nitrogen oxides in the exhaust gas and decomposes it into water and nitrogen. That is, the urea water 2 according to the present embodiment is also used as urea water for purifying nitrogen oxides in the exhaust gas.

  The ECU 40 controls the flow control valve 35 so that diluted urea water 4 obtained by diluting urea water 2 with water 3 is sent to the pump 31 at cold start of the engine, and the diluted urea water 4 flows through the water passage 33A. Control valve 34 so that

  The transfer unit 30 transfers the diluted urea water 4 having a viscosity higher than that of the exhaust gas to the nozzle 32A. The nozzle 32A releases (injects) the diluted urea water 4 toward the exhaust upstream side (the inlet side of the cell) of the DPF 12. The diluted urea water 4 flows from the exhaust upstream side (−X direction) of the DPF 12 to the exhaust downstream side (+ X direction) by the flow of the exhaust gas. In FIG. 2, the flow direction of the diluted urea water 4 is indicated by a white arrow.

  The diluted urea water 4 flows from the exhaust upstream side to the exhaust downstream side of the DPF 12 so that the highly viscous liquid, the diluted urea water 4 deposits on the partition wall 122 of the cell 121 as the exhaust downstream side (+ X Push away in the direction). The direction in which the wall ash 3a is pushed away is indicated by arrows in FIG.

  The form of the wall ash 3a is transformed into the form of the plug ash 3b (see FIG. 3) as the wall ash 3a is pushed away to the exhaust downstream side by the diluted urea water 4 (see FIG. 2). Further, the amount of wall ash 3 a deposited on the partition wall 122 is reduced by dissolving the ash component in the diluted urea water 4 and flowing out of the cell 121 together with the diluted urea water 4.

  The release of the diluted urea water 4 is performed based on the oil consumption and the respective water amounts of the urea water 2 and the water 3. The specific release method (for example, the amount of water, time, etc.) of the diluted urea water 4 is set based on simulation or an experimental result.

  Next, urea aqueous solution transfer processing will be described with reference to FIG. FIG. 4 is a flowchart showing an example of the urea aqueous solution transfer process. This process is started by starting the engine.

  In step S100, the ECU 40 determines whether to purify nitrogen oxides in the exhaust gas.

  When purifying nitrogen oxides (step S100: YES), the ECU 40 controls the pump 31, the control valve 34 and the flow rate adjustment valve 35 to transfer the urea water 2 to the exhaust upstream side of the urea SCR catalyst 13 (step S100) S110). If the nitrogen oxide is not purified (step S100: NO), the process proceeds to step S120.

  In step S120, the ECU 40 determines whether it is at the cold start of the engine.

  When it is at cold start of the engine (step S120: YES), the ECU 40 controls the pump 31, the control valve 34 and the flow rate adjustment valve 35 to transfer the diluted urea water 4 to the exhaust upstream side of the DPF 12 (step S130). The process returns to step S120 after a predetermined time.

  In the case other than cold start of the engine (step S120: NO), the process ends.

<Effect of this embodiment>
As described above, the exhaust gas purification apparatus 1 according to the present embodiment collects the PM in the exhaust gas from the engine, and the DPF 12 regenerated by burning the collected PM; Diluted urea water so that the ash deposited on the DPF 12 by the tank 20A for storing water, the tank 20B for storing water 3, and the regeneration can be flushed out with the diluted urea water 4 (urea water 2 and water 3) toward the exhaust downstream of the DPF 12 And 4, a transfer unit 30 for transferring the pressure 4 to the exhaust upstream side of the DPF 12. By pushing the wall ash 3a to the exhaust downstream side, it is possible to accelerate the change of the form from the wall ash 3a to the plug ash 3b. As a result, the effect of the wall ash 3a on the pressure loss can be suppressed.

  Further, according to the exhaust gas purification device 1 according to the present embodiment, the transfer unit 30 transfers the diluted urea water 4 to the exhaust upstream side of the DPF 12 at the time of cold start of the engine. As a result, at the time of cold start, the amount of PM contained in the exhaust gas is large, and accordingly, even when a large amount of wall ash 3a is deposited on the DPF 12, the diluted urea water 4 is transferred to the exhaust upstream side of the DPF 12. By doing this, the form of the wall ash 3a can be changed to the form of the plug ash 3b, so the influence of pressure loss can be suppressed.

  Although the conditions for transferring the diluted urea water 4 to the exhaust upstream side of the DPF 12 in the exhaust gas purification device 1 are at the time of cold start of the engine, the present invention is not limited to this. It may be a temperature at which the diluted urea water 4 passed through the DPF 12 does not evaporate. Further, for example, the pressure difference (differential pressure) between the pressure on the exhaust upstream side of the DPF 12 and the pressure on the exhaust downstream side may be set to exceed a predetermined value. Also, for example, the engine may be cold-started and the differential pressure may exceed a predetermined value.

  The exhaust purification system of the present disclosure is useful as an internal combustion engine that is required to control the form of ash.

1 exhaust gas purification device 2 urea water 3 water 4 dilution urea water 10 exhaust pipe 11 DOC
12 DPF
13 Urea SCR catalyst 20A, 20B Tank 30 Transfer part 31 Pump 32A, 32B Nozzle 33A, 33B Water channel 34 Control valve 35 Flow control valve 40 ECU

Claims (6)

A filter that collects particulate matter in exhaust gas from an internal combustion engine and is regenerated by burning the collected particulate matter;
A transfer unit for transferring the reducing agent to the exhaust upstream side of the filter so that the ash deposited on the filter by the regeneration is flushed with the reducing agent to the exhaust downstream side of the filter;
, An exhaust purification device. A urea SCR catalyst that purifies nitrogen oxides contained in the exhaust gas;
The exhaust gas purification apparatus according to claim 1, wherein the transfer unit transfers the reducing agent to the exhaust upstream side of the urea SCR catalyst when purifying the nitrogen oxide.   The exhaust gas purification apparatus according to claim 2, wherein the transfer unit transfers the reducing agent diluted with water to the exhaust upstream side of the filter. The transfer unit includes a flow control valve, a pump, a first water passage, a second water passage, and a control valve.
The flow control valve adjusts the flow rate of the reducing agent sent to the pump and the flow rate of the water;
The first water passage extends from the control valve to the exhaust upstream side of the filter,
The second water passage extends from the control valve to the exhaust upstream side of the urea SCR catalyst,
The control valve is switched such that the reducing agent diluted with the water sent from the pump flows through the first water channel, and the reducing agent sent from the pump flows through the second water channel The exhaust gas purification device according to claim 3, wherein the exhaust gas purification device is switched.   The exhaust gas purification apparatus according to any one of claims 1 to 4, wherein the transfer unit transfers the reducing agent to the exhaust upstream side of the filter at cold start of the internal combustion engine.   An internal combustion engine comprising the exhaust gas purification device according to any one of claims 1 to 5.

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