JP2011032931A - Catalyst temperature raising device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst temperature raising device reducing fuel required for raising the temperature of an exhaust gas aftertreatment catalyst. <P>SOLUTION: This catalyst temperature raising device 1 for raising the temperature of the exhaust gas aftertreatment catalyst 4 provided in the exhaust pipe 3 of an engine 2 and cleaning exhaust gas from the engine 2 by endothermic reaction includes: a burner means 5 arranged in the exhaust pipe 3 provided upstream of the exhaust gas aftertreatment catalyst 4 and raising the temperature of the exhaust gas led to flow into the exhaust gas aftertreatment catalyst 4; and a waste heat recovery means 6 for performing heat exchange between the exhaust gas led to flow out of the exhaust gas aftertreatment catalyst 4 and the exhaust gas led to flow into the burner means 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a catalyst temperature raising apparatus for raising the temperature of an exhaust gas aftertreatment catalyst that purifies exhaust gas by an endothermic reaction.

  Conventionally, a burner system has been studied in order to improve the purification performance of the exhaust gas aftertreatment catalyst at an early stage. This is a device that activates the catalyst early by warming the exhaust gas by directly burning (igniting) light oil when the engout (engine-out) exhaust gas temperature is low.

  In addition, an apparatus that recovers waste heat that is discarded as exhaust gas and raises the exhaust gas temperature at the catalyst entrance has been studied. This is a device that places a heat exchanger between the catalyst inlet and outlet and recovers the amount of heat generated by the combustion of HC, CO, etc. with the catalyst to raise the inlet exhaust gas temperature (see, for example, Patent Document 1).

JP 2007-198706 A

  However, the burner device and the waste heat recovery device described above have the following problems.

  The disadvantage of the burner device is that the volume of light oil burned for warming is very large and the fuel consumption is severely deteriorated because the exhaust gas volume is very large. Since the burner device introduces air necessary for combustion from the outside, a compressor is required.

  Further, the disadvantage of the waste heat recovery device is that this device recovers the heat generated by the combustion of HC, CO, light oil, etc. with a catalyst, so a DOC (Diesel Oxidation Catalyst) or LNT catalyst (occlusion reduction type NOx catalyst). ) And the like can be effective, but a catalyst that does not generate heat by an endothermic reaction such as an SCR catalyst (selective reduction catalyst) is not effective, and the usable catalyst system is limited.

  Therefore, an object of the present invention is to provide a catalyst temperature raising apparatus that can solve the above-described problems and reduce the fuel required for raising the temperature of the exhaust gas aftertreatment catalyst.

  In order to achieve the above object, the present invention provides an exhaust gas aftertreatment catalyst for purifying exhaust gas from the engine by an endothermic reaction in an exhaust pipe of the engine, and increases the temperature of the exhaust gas aftertreatment catalyst. In the apparatus, burner means for raising the temperature of exhaust gas that is provided in an exhaust pipe upstream of the exhaust gas aftertreatment catalyst and flows into the exhaust gas aftertreatment catalyst, exhaust gas that has flowed out of the exhaust gas aftertreatment catalyst, and the burner means Waste heat recovery means for exchanging heat with the inflowing exhaust gas is provided.

  Preferably, the exhaust gas aftertreatment catalyst is a selective reduction catalyst for reducing NOx contained in the exhaust gas from the engine.

  Preferably, a filter means for collecting PM contained in the exhaust gas from the engine is provided in an exhaust pipe upstream of the exhaust gas aftertreatment catalyst, and the burner means includes the filter means and the exhaust gas aftertreatment. It is arranged in the exhaust pipe between the catalyst.

  Preferably, temperature detection means for detecting the temperature of the exhaust gas in the exhaust pipe between the exhaust gas aftertreatment catalyst and the burner means, and the temperature detected by the temperature detection means is the catalytic activity of the exhaust gas aftertreatment catalyst And control means for controlling the burner means so as to match the temperature.

  According to the present invention, the excellent effect that the fuel required for raising the temperature of the exhaust gas aftertreatment catalyst can be reduced is exhibited.

FIG. 1 is a schematic configuration diagram of a catalyst temperature raising apparatus according to an embodiment of the present invention. FIG. 2 is an example of a flowchart according to the temperature increase control of the present embodiment. FIG. 3 shows an operation example of this embodiment. FIG. 4 is a diagram for explaining the amount of heat necessary for raising the temperature of the exhaust gas aftertreatment catalyst. FIG. 5 is a diagram for explaining the temporal change of the required heat amount. FIG. 6 is a schematic configuration diagram of a catalyst temperature raising apparatus according to a modification of the present invention.

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

  The catalyst temperature raising apparatus of the present embodiment is applied to a vehicle on which a diesel engine is mounted, for example.

  A schematic structure of the catalyst temperature raising apparatus of the present embodiment will be described based on FIG.

  As shown in FIG. 1, the engine 2 is provided with an exhaust pipe 3 for discharging exhaust gas (exhaust gas). The exhaust pipe 3 is provided with an aftertreatment system 10 for purifying exhaust gas and the present embodiment. And a catalyst temperature raising device 1 of the form.

  The aftertreatment system 10 includes a filter device (filter means) 7 for removing PM in the exhaust gas, and a catalyst device 8 for removing NOx in the exhaust gas. In the illustrated example, the filter device 7 is disposed on the upstream side of the catalyst device 8.

  The filter device 7 is a so-called continuous regeneration type filter device, a filter with a catalyst (hereinafter referred to as CSF) 71 for collecting PM, and a diesel oxidation catalyst (hereinafter referred to as DOC) arranged upstream of the CSF 71. 72).

  The CSF 71 is formed, for example, by supporting a catalyst component such as platinum or vanadium on a wall flow type filter body (such as a porous plugged ceramic honeycomb). The DOC 72 is formed by, for example, supporting a catalyst component on a carrier made of a ceramic honeycomb or the like. The CSF 71 and the DOC 72 are accommodated in series in a housing 73 provided in the exhaust pipe 3.

  In the filter device 7, PM is collected by the CSF 71, and the collected PM is oxidized by the catalyst component of the CSF 71. Further, HC, CO, and the like in the exhaust gas are oxidized by the DOC 72, whereby the temperature of the exhaust gas flowing into the CSF 71 is raised and the oxidation in the CSF 71 is promoted.

  The catalyst device 8 includes an SCR catalyst (selective reduction catalyst) 4 for reducing NOx contained in the exhaust gas, and the SCR catalyst 4 serves as an exhaust gas aftertreatment catalyst that purifies the exhaust gas by an endothermic reaction.

  The SCR catalyst 4 of this embodiment is a urea SCR catalyst using ammonia as a reducing agent. The SCR catalyst 4 is formed by supporting a catalyst component (such as vanadium) on a carrier made of a ceramic honeycomb or the like. The SCR catalyst 4 has a predetermined catalyst activation temperature (about 250 ° C.) at which the function as a catalyst is activated.

  A urea water injection valve (not shown) is provided upstream of the SCR catalyst 4, and urea water (urea aqueous solution) injected from the urea water injection valve is decomposed into ammonia and supplied to the SCR catalyst 4.

  An oxidation catalyst (DOC) 41 for treating ammonia slipping (outflowing) from the SCR catalyst 4 is provided downstream of the SCR catalyst 4. The SCR catalyst 4 and the oxidation catalyst 41 are accommodated in series in a housing 42 provided in the exhaust pipe 3.

  The catalyst temperature raising apparatus 1 of the present embodiment is a combination of the burner means 5 and the heat exchanger 6 so that a catalyst that does not generate heat such as the SCR catalyst 4 can raise the temperature of the catalyst with little deterioration in fuel consumption.

  More specifically, the catalyst temperature raising device 1 includes a burner means 5 for raising the temperature of the exhaust gas flowing into the SCR catalyst 4, and the exhaust gas flowing out from the SCR catalyst 4 and the exhaust gas flowing into the burner means 5. And a heat exchanger 6 (waste heat recovery means) for performing heat exchange.

  In the following description, the exhaust pipe between the engine 2 and the heat exchanger 6 is the first exhaust pipe 31, the exhaust pipe between the heat exchanger 6 and the filter device 7 is the second exhaust pipe 32, and the filter device 7. The exhaust pipe between the catalyst device 8 is the third exhaust pipe 33, the exhaust pipe between the catalyst device 8 and the heat exchanger 6 is the fourth exhaust pipe 34, and between the heat exchanger 6 and the tail pipe (not shown). The exhaust pipe is referred to as a fifth exhaust pipe 35.

  The burner means 5 includes a burner device 51 that raises the temperature of exhaust gas by oxidizing a fuel and air, a temperature detecting means (hereinafter referred to as a T1 sensor) 52 disposed downstream of the burner device 51, and the T1 sensor. And an electronic control unit 53 for controlling the burner device 51 based on the detected temperature 52.

  The burner device 51 supplies air from an exhaust pipe injection valve 511 for injecting fuel into the exhaust pipe 3, an air supply pipe 512 for supplying air (secondary air), and fuel from the exhaust pipe injection valve 511. An oxidation catalyst (hereinafter referred to as a burner catalyst) 513 for oxidizing (combusting) with air from the pipe 512. In the illustrated example, an introduction pipe 514 extending from the exhaust pipe injection valve 511 to the third exhaust pipe 33 is provided, and an air supply pipe 512 and a burner catalyst 513 are provided on the introduction pipe 514.

  More specifically, the introduction pipe 514 has a funnel portion 515 whose one end faces the exhaust pipe injection valve 511 and whose diameter is reduced as it reaches the other end side, and the third exhaust pipe extends continuously from the funnel portion 515. 33 and a straight pipe portion 516 connected to 33.

  The exhaust pipe injection valve 511 is disposed in the funnel portion 515 of the introduction pipe 514 and is directed to the third exhaust pipe 33. The exhaust pipe injection valve 511 is connected to the fuel system of the engine 2 and is supplied with the same type of fuel as the engine 2 (light oil in this embodiment). The exhaust pipe injection valve 511 is controlled by the electronic control unit 53 for the injection amount and the injection timing.

  The air supply pipe 512 is connected to an air supply source (for example, a compressor or a tank mounted on the vehicle), and introduces air from the air supply source into the funnel portion 515. In the illustrated example, the air supply pipe 512 is attached to be inclined with respect to the side surface of the funnel portion 515 so that the air introduced into the funnel portion 515 becomes a swirl (swirl flow). The air supply pipe 512 is provided with an adjustment valve (not shown) for continuously adjusting the flow rate, and the opening degree of the adjustment valve is controlled by the electronic control unit 53.

  The burner catalyst 513 is accommodated in the straight pipe portion 516. The burner catalyst 513 has the same structure as the oxidation catalysts 41 and 72 described above, and is formed by, for example, supporting a catalyst component (platinum, vanadium, etc.) on a carrier made of a ceramic honeycomb or the like.

  In the burner device 51, the fuel from the exhaust pipe injection valve 511 and the air from the air supply pipe 512 are mixed in the funnel portion 515, and the mixed gas flows into the straight pipe portion 516 and is oxidized by the burner catalyst 513 ( Burned) and become hot. The hot gas flows into the third exhaust pipe 33 from the straight pipe portion 516, and thereby the temperature of the exhaust gas in the third exhaust pipe 33 is raised.

  The T1 sensor 52 is attached to the third exhaust pipe 33 downstream of the burner device 51. The T1 sensor 52 is for detecting the temperature of the exhaust gas flowing into the SCR catalyst 4, and outputs the detected temperature to the electronic control unit 53.

The third exhaust pipe 33 upstream of the burner device 51 is provided with a λ sensor (O ₂ sensor) 22 for detecting λ (excess air ratio) flowing into the burner device 51.

  The λ sensor 22 is used to apply an upper limit guard for the fuel supply amount (addition amount) to the burner device 51. That is, when λ becomes 1 (theoretical air-fuel ratio) or less, even if fuel is added to the burner device 51, the fuel cannot be oxidized because there is no oxygen. Therefore, λ of the burner device 51 is monitored by the λ sensor 22, and an upper limit guard is applied to the fuel supply amount to the burner device 51 so that λ> 1.

  Various sensors such as a MAF sensor 21 and a λ sensor 22 provided in an intake pipe (not shown) of the engine 2 are connected to the electronic control unit 53, and detection values from the sensors 21 and 22 are input. .

  Further, an engine ECU 23 for controlling the engine 2 is connected to the electronic control unit 53, and an injection amount (fuel amount) of fuel injected (supplied) into each cylinder of the engine 2 from the engine ECU 23 is input. .

  The heat exchanger 6 is for recovering the heat of the exhaust gas flowing out from the SCR catalyst 4 and for raising the temperature of the exhaust gas flowing into the burner device 51 in advance by the recovered heat. The heat exchanger 6 includes a low temperature side flow path that communicates the first exhaust pipe 31 and the second exhaust pipe 32, a high temperature side flow path that communicates the fourth exhaust pipe 34 and the fifth exhaust pipe 35, and the high temperature A heat transfer section for performing heat transfer between the side flow path and the low temperature side flow path (not shown). As the heat exchanger 6, various types such as a diaphragm type (through-flow type) heat exchanger that separates exhaust gas from each other by a flat plate or a tubular diaphragm and exchanges heat by passing through the diaphragm can be considered.

  Next, the operation of this embodiment will be described with reference to FIGS.

  As shown in FIG. 1, the exhaust gas (engout exhaust gas) discharged from the engine 2 passes through the filter device 7 (DOC72-CSF71) via the heat exchanger 6 (low temperature side). The exhaust gas that has passed through the filter device 7 then passes through the catalyst device 8 (SCR4-DOC41) via the burner device 51, and again from the tail pipe (not shown) via the heat exchanger 6 (high temperature side). Discharged.

  Here, when the exhaust gas temperature is low (such as when the engine 2 is cold started), the electronic control unit 53 operates the burner device 51 to increase the temperature of the SCR catalyst 4 and improve the NOx reduction efficiency.

  Waste heat from the SCR catalyst 4 is recovered by the heat exchanger 6, and the engout exhaust gas is warmed by the recovered heat. The warmed engout exhaust gas enters the burner device 51 via the filter device 7 (DOC72-CSF71).

  At this time, since the temperature of the exhaust gas entering the burner device 51 is increased by the amount of waste heat recovery, the amount of light oil necessary for achieving the target temperature (catalytic activation temperature) (the amount of light oil burned by the burner) and necessary The amount of air can be reduced by the amount of waste heat recovery. Therefore, there are merits such as prevention of fuel consumption deterioration and downsizing of the compressor.

  Next, an example of temperature rise control by the catalyst temperature raising apparatus 1 of the present embodiment will be described based on FIG. The control flow of FIG. 2 is executed by the electronic control unit 53 every predetermined control period after the engine 2 is started.

  First, in step S1, the electronic control unit 53 is supplied to the detection value of the MAF sensor 21 (air amount MAF value), the detection value of the λ sensor 22 (λ after catalyst), and the detection value of the T1 sensor 52 (T1 gas temperature). Then, the fuel flow rate of the engine 2 and the burner start threshold value are input. The burner start threshold value is stored in advance in a memory (not shown) in the electronic control unit 53. The memory also stores the catalyst activation temperature (target temperature) of the SCR catalyst 4.

  Furthermore, the electronic control unit 53 calculates the difference (target temperature−T1 gas temperature) between the target temperature (temperature increase target temperature) and the T1 gas temperature. When the calculated temperature difference is smaller than the burner start threshold, the electronic control unit 53 stops the temperature increase (burner temperature increase) by the burner device 51 and returns to step S1.

  That is, when the temperature of the exhaust gas flowing into the SCR catalyst 4 exceeds the catalyst activation temperature, or when the temperature is close to the catalyst activation temperature even when the temperature is equal to or lower than the catalyst activation temperature, the temperature can be quickly raised only by the heat exchanger 6. In this case, the temperature of the burner is not increased.

  On the other hand, when the above temperature difference exceeds the burner start threshold value in step S1, the electronic control unit 53 determines that the burner temperature needs to be increased and proceeds to step S2.

  In step S <b> 2, the electronic control unit 53 obtains the fuel injection amount (light oil amount) of the exhaust pipe injection valve 511 of the burner device 51 and the air supply amount (required air amount) of the air supply pipe 512. The amount of light oil and the amount of air supply are determined so that the T1 gas temperature matches the target temperature.

  Specifically, first, a heat generation amount (burner heat generation amount) to be generated from the burner device 51 is obtained. The amount of heat generated by the burner is calculated by the product of the temperature difference obtained in step S1, the amount of exhaust gas, and the specific heat of the exhaust gas. Here, the amount of exhaust gas is the amount of gas discharged to the exhaust pipe 3 by combustion of the engine 2 and is obtained from the air amount MAF value and the fuel flow rate.

Next, the light oil amount and the required air amount are calculated from the relational expression between the calculated burner heat generation amount (necessary heat amount), the light oil heat generation amount and the flow rate, and the light oil heat generation amount * flow rate = the required heat amount. The amount of light oil is limited so that air does not become insufficient, that is, λ (= A _mass / F _mass ÷ 14.05) does not become less than the stoichiometric air-fuel ratio (1 in terms of λ). Similarly, the required air amount is determined so that λ does not become 1 or less.

  Next, in step S3, the electronic control unit 53 operates the burner device 51 with the light oil amount and the required air amount obtained in step S2.

  Specifically, the electronic control unit 53 injects the light oil fuel of the light oil amount obtained in step S2 from the exhaust pipe injection valve 511, and supplies the injected light oil fuel with the necessary air amount obtained in step S2. As much as possible, the opening degree of the adjustment valve (not shown) of the air supply pipe 512 is adjusted.

  An operation example according to the control flow of FIG. 2 will be described based on FIG. In FIG. 3, the horizontal axis represents time, the upper vertical axis represents temperature, and the lower vertical axis represents fuel flow rate. The upper part of FIG. 3 is a graph showing the change over time of the temperature of the SCR catalyst 4, and the lower part is a graph showing the change over time of the fuel flow rate injected from the exhaust pipe injection valve 511.

  First, at time t0, the engine 2 is started. At this time, as shown in the upper part of FIG. 3, the temperature (catalyst temperature) of the SCR catalyst 4 is about 180 ° C., which is lower than the catalyst activation temperature (250 ° C. in the example).

  After the engine 2 is started, as shown in the lower part of FIG. 3, fuel injection from the exhaust pipe injection valve 511 is started by the temperature increase control of the burner device 51, and the exhaust gas flowing into the SCR catalyst 4 is increased in temperature. . Further, the exhaust gas flowing into the burner device 51 is preliminarily heated by the heat exchanger 6.

  As a result, the catalyst temperature starts to rise, and the catalyst temperature approaches the catalyst activation temperature (target temperature). Further, the fuel injection from the exhaust pipe injection valve 511 gradually decreases.

  At time t1, the catalyst temperature reaches the catalyst activation temperature (target temperature), and fuel injection from the exhaust pipe injection valve 511 stops.

  Here, comparing this embodiment with the case where there is no auxiliary means for raising the temperature of the exhaust gas, when there is no auxiliary means, the catalyst temperature reaches the catalyst activation temperature even at time t1, as shown in the upper part of FIG. Not. From this, it can be seen that in the present embodiment, the temperature of the SCR catalyst 4 can be quickly increased as compared with the case where there is no auxiliary means.

  Further, in the case where the waste heat recovery is not performed only by the burner device (that is, the heat exchanger 6 is omitted from the configuration of the catalyst temperature increasing device 1 of the present embodiment), the catalyst temperature increasing device 1 of the present embodiment is not used. If the fuel consumption is the same, there is no heat exchanger 6 and the rate of temperature rise is slow.

  In the conventional apparatus in which the temperature of exhaust gas is raised only by using a burner device that directly burns fuel, the heating speed of the catalyst temperature is faster than in the case where there is no auxiliary means. The fuel injection amount of the apparatus is increased as compared with the present embodiment.

  As described above, in the present embodiment, the above-described catalyst temperature raising device 1 uses the heat exchanger (waste heat recovery means) 6 in combination with the burner device 51 in the catalyst device 8 for endothermic reaction. Compared to using it alone, it is possible to obtain a great merit in terms of deterioration of fuel consumption.

  This point will be described in more detail with reference to FIGS. 4 and 5, the line L1 shows the present embodiment, and the line L2 shows a conventional example in which the temperature of the SCR catalyst 4 is raised only by the burner device.

  The necessary heat amount of the burner device 51 when the SCR catalyst 4 is heated from the engout exhaust gas temperature (180 ° C.) to the catalyst activation temperature (250 ° C.) will be described.

  As shown in FIG. 4, in the conventional example, the required heat amount of the burner device is a temperature difference between the engout exhaust gas temperature and the catalyst activation temperature (250 ° C.-180 ° C.) * Exhaust gas amount * specific heat.

  On the other hand, in this embodiment, the temperature of the engout exhaust gas is raised to T (> 180 ° C.) by waste heat recovery of the heat exchanger 6.

  Therefore, the required heat quantity of the burner device 51 is (250 ° C.-T) * exhaust gas quantity * specific heat. Therefore, in the present embodiment, the necessary heat amount of the burner device 51 is reduced by (T-180 ° C.) * Exhaust gas amount * specific heat as compared with the conventional example.

  Thus, in this embodiment, since the temperature of exhaust gas is raised by waste heat recovery, the necessary heat amount of the burner device 51 can be reduced.

  FIG. 5 shows a comparison of the required heat amount of the burner device 51 between this embodiment and the conventional example. As shown in FIG. 5, in the present embodiment, since the waste heat is recovered, the required heat amount of the burner device 51 starts to decrease earlier than the conventional example and becomes zero.

  As described above, in this embodiment, it was confirmed that the fuel injection amount of the burner device 51 can be reduced and deterioration of fuel consumption can be suppressed as compared with the conventional example.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, in the above-described embodiment, the burner device 51 is arranged in the third exhaust pipe 33 between the filter device 7 and the catalyst device 8, but the present invention is not limited to this, and as shown in FIG. You may arrange | position in the 2nd exhaust pipe 32 between 6 and the filter apparatus 7. FIG. In this case, the same effect as the above-described embodiment can be obtained.

  Further, for a catalyst that generates heat by combustion of HC and CO, such as DOC, LNT, and DPF with catalyst, the position of the burner device may be in front of the heat exchanger. Even in this case, there is a merit of reducing the amount of light oil required for the burner and the amount of air by the heat exchanger.

1 catalyst temperature raising device 2 engine 3 exhaust pipe 4 exhaust gas aftertreatment catalyst 5 burner means 6 heat exchanger (waste heat recovery means)

Claims (4)

In the exhaust pipe of the engine, an exhaust gas aftertreatment catalyst for purifying exhaust gas from the engine by an endothermic reaction is provided, and in a catalyst temperature raising device for raising the temperature of the exhaust gas aftertreatment catalyst,
Burner means for raising the temperature of the exhaust gas provided in the exhaust pipe upstream of the exhaust gas aftertreatment catalyst and flowing into the exhaust gas aftertreatment catalyst;
A catalyst temperature raising apparatus, comprising: waste heat recovery means for exchanging heat between the exhaust gas flowing out from the exhaust gas aftertreatment catalyst and the exhaust gas flowing into the burner means.   The catalyst temperature raising apparatus according to claim 1, wherein the exhaust gas aftertreatment catalyst is a selective reduction catalyst for reducing NOx contained in the exhaust gas from the engine. Filter means for collecting PM contained in the exhaust gas from the engine is provided in the exhaust pipe upstream of the exhaust gas aftertreatment catalyst,
The catalyst temperature raising apparatus according to claim 1 or 2, wherein the burner means is disposed in an exhaust pipe between the filter means and the exhaust gas aftertreatment catalyst. Temperature detecting means for detecting the temperature of the exhaust gas in the exhaust pipe between the exhaust gas aftertreatment catalyst and the burner means;
4. The catalyst temperature rise according to claim 1, further comprising a control unit that controls the burner unit such that the temperature detected by the temperature detection unit coincides with the catalyst activation temperature of the exhaust gas aftertreatment catalyst. apparatus.

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