JP2016006311A - Diesel engine exhaust emission control system and diesel engine exhaust emission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the recovery of the function of an exhaust emission control system provided in the exhaust passage of a diesel engine despite irregularities in fuel properties.SOLUTION: An exhaust emission control system of a diesel engine, which is the exhaust emission control system provided in an exhaust passage of the engine, comprises: an oxidation catalyst provided upstream of the exhaust emission control system in the exhaust passage; and reducer supply means supplying a reducer to the oxidation catalyst. The exhaust emission control system further comprises: a fuel tank 51 storing a fuel to supply the fuel to the engine; a fuel supply passage 52 supplying the fuel in the fuel tank 51 to the engine; a fuel pump 54 provided in the fuel supply passage 52; and a switching device 57 provided between the fuel tank 51 and the fuel pump 54 in the fuel supply passage 52, switching over between the fuel from the fuel tank 51 and a fuel from another fuel supply source 55 supplying the fuel lower in sulfur content than the fuel in the fuel tank 51, and supplying one of the fuels to the engine.

Description

  The present invention relates to an exhaust gas purification device and an exhaust gas purification method for a diesel engine, and more particularly to an exhaust gas purification device for a diesel engine in a construction machine that reproduces deterioration of an exhaust gas purification catalyst.

  For example, a work vehicle such as a hydraulic excavator as a construction machine is equipped with a diesel engine as a driving source, and the amount of particulate matter (hereinafter also referred to as PM) discharged from the diesel engine is nitrogen. Regulations have been strengthened year by year along with oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and the like.

  In response to such regulations, a selective catalytic reduction (hereinafter referred to as SCR catalyst) is provided in the engine exhaust pipe as an exhaust purification device for purifying NOx contained in the exhaust of a diesel engine. Exhaust gas purification devices are known. A liquid reducing agent (urea water) or a precursor thereof is injected and supplied upstream of the exhaust of the SCR catalyst in accordance with the operating state of the engine, and NOx is selectively reduced on the SCR catalyst, so that NOx is harmless. To purify.

Further, in order to remove the particulate matter (PM) contained in the exhaust of the engine, a DPF (Diesel Particulate Filter) that collects the PM and burns and removes the PM is provided in the engine exhaust pipe. .
In many cases, a pre-stage catalyst (pre-stage oxidation catalyst) having an oxidation function is provided upstream of an exhaust purification device such as the SCR catalyst or the DPF in the exhaust passage of the diesel engine.

  For example, when PM accumulates on the DPF, the differential pressure before and after the DPF (the differential pressure between the upstream side and the downstream side) increases, and when the differential pressure exceeds a predetermined value, it is necessary to regenerate the DPF. is there. At the time of regeneration, it is necessary to increase the temperature of the DPF. For this reason, a reducing agent (such as fuel) is supplied upstream of the upstream oxidation catalyst, and the supplied reducing agent is oxidized by the upstream oxidation catalyst, The DPF is heated by oxidation heat generated at that time. By raising the temperature of the DPF, the PM collected and deposited in the DPF is burned and removed. The reducing agent is supplied by, for example, post-injecting fuel.

  Further, even when the SCR catalyst is provided as the exhaust purification device, the SCR catalyst is heated by oxidation heat generated in the upstream oxidation catalyst by supplying a reducing agent upstream of the upstream oxidation catalyst. As a result, the SCR catalyst is activated and NOx contained in the engine exhaust can be purified.

As a response to the exhaust gas regulations currently being promoted in various countries, regulations on fuel properties (regulations on the content of impurities such as sulfur and phosphorus) are being promoted simultaneously. However, there is a large variation in fuel properties depending on the country or region.Therefore, in regions and countries where high-quality fuel with good properties can be used, there will be no hindrance to the operation of construction machinery such as excavators and trucks. When construction machinery is operated in countries or regions where it is difficult to obtain fuel or there is a problem in management to maintain good fuel properties, the use of fuel with poor properties causes exhaust emissions. The purification device may be deteriorated.
When the exhaust gas purification device deteriorates, there is a problem in that exhaust gas purification performance is lowered, and exhaust gas that is not purified or not sufficiently purified is released to the atmosphere.

  Japanese Patent No. 4665924 (Patent Document 1) includes an exhaust purification device in an exhaust passage of an internal combustion engine, and a pre-stage catalyst having an oxidation function provided in an exhaust passage upstream of the exhaust purification device, An exhaust purification system for an internal combustion engine having a reducing agent supply means for supplying a reducing agent to the upstream catalyst is described. The reducing agent supply means performs recovery control for increasing the temperature of the exhaust purification device by supplying the reducing agent to the pre-stage catalyst, thereby recovering the function of the exhaust purification device.

  And a prohibition region setting means for detecting a deterioration degree of the front catalyst and setting a recovery control prohibition region, which is an operation region of the internal combustion engine in which execution of the recovery control is prohibited, based on the deterioration degree, The prohibition region setting means describes a configuration in which the maximum values of the engine torque and the engine speed in the recovery control prohibition region are set to higher values as the degree of deterioration of the preceding catalyst is higher.

  Japanese Patent Application Laid-Open No. 2011-169161 (Patent Document 2) discloses a particulate filter (DPF) for collecting particulate matter (PM) in an exhaust passage and an oxidation provided on the upstream side of the DPF. When the clogging of the DPF is detected by the differential pressure sensor, the fuel supplied to the engine is switched from biodiesel fuel (BDF) to light oil having a boiling point lower than this BDF, and the light oil is post-posted. There is described an invention in which unburned gas oil of light oil is oxidized by the oxidation catalyst, the exhaust temperature is raised by the reaction heat at that time, and PM accumulated in the DPF is burned and removed.

Japanese Patent No. 4665924 JP 2011-169161 A

  In the thing of the said patent document 1, the maximum value of the engine torque and engine speed of a recovery control prohibition area | region is set to a higher value, so that the deterioration degree of a front | former stage catalyst is high, ie, based on the deterioration degree of a front | former stage catalyst. Since the exhaust temperature is set high by controlling the torque and the rotational speed of the engine (engine), the function of the exhaust purification device can be recovered to some extent. However, since the thing of the cited reference 1 did not consider the influence of the property of the fuel to be used, the function recovery effect of the exhaust emission control device is not necessarily high.

  Moreover, in the thing of the said patent document 2, when using biodiesel fuel as a diesel fuel, when burning and removing PM deposited on DPF, the fuel is switched to light oil and the light oil is post-posted. Since it is configured to inject, it is possible to reliably raise the exhaust gas temperature and regenerate the DPF.

  However, in addition to the main fuel tank that stores the main fuel (biodiesel fuel), there is a sub fuel tank that stores the sub fuel (light oil), and related piping for supplying the fuel, such as a hydraulic excavator Since it is necessary to additionally install in the vehicle, the fuel supply system becomes large, and it is necessary to secure a space for installing the sub fuel tank and related piping. For this reason, there is a problem of cost increase.

  In addition, since the fuel in the sub fuel tank is only used when the PM accumulated in the DPF is burned and removed, the fuel in the sub fuel tank may not be used for a long time. When the fuel is not used for a long time and stored in the fuel tank, the oxidative deterioration of the light oil in the sub fuel tank proceeds. When this oxidized and deteriorated fuel is used, there is a risk of deteriorating members (rubber, metal, etc.) of the fuel system. When oxidized, diesel oil used as a fuel for diesel engines is discolored to generate a precipitated polymer (sludge) or increase in viscosity. Further, the peroxide (peroxide) generated by oxidation has a problem of deteriorating members (rubber and metal) of the fuel system.

An object of the present invention is to provide an exhaust of a diesel engine that can reliably recover the function of an exhaust purification device provided in an exhaust passage of the engine even when there are variations in fuel properties used in the diesel engine depending on countries and regions. It is to obtain a purification device and an exhaust purification method.
Another object of the present invention is to obtain a diesel engine exhaust gas purification device and an exhaust gas purification method capable of recovering the function of the exhaust gas purification device at a low cost without significantly changing the layout of the fuel supply system. .

  To achieve the above object, the present invention provides an exhaust purification device provided in an exhaust passage of a diesel engine, an oxidation catalyst provided in an exhaust passage upstream of the exhaust purification device, and a reducing agent in the oxidation catalyst. An exhaust emission control device for a diesel engine comprising a reducing agent supply means for supplying fuel, a fuel tank for storing fuel for supplying fuel to the diesel engine, and for supplying fuel in the fuel tank to the diesel engine A fuel supply passage, a fuel pump provided in the fuel supply passage, a fuel supply passage between the fuel tank and the fuel pump, and fuel from the fuel tank and fuel in the fuel tank A switching device that supplies fuel to the diesel engine by switching fuel from another fuel supply source that supplies fuel with low sulfur content. Characterized in that it comprises and.

  In the above, the apparatus further comprises a control device for performing regeneration control of the exhaust purification device, and an external input means for commanding execution of the regeneration control, and the other fuel supply source is connected to the switching device. In this state, when a command for executing the regeneration control of the purification device is issued from the external input means to the control device, the switching device causes the fuel from the other fuel supply source to flow to the fuel pump. It is preferable that the switching is automatically controlled as described above.

  In addition, after the switching device is switched so that the low-sulfur fuel from the other fuel supply source flows to the fuel pump, the control device performs regeneration control of the exhaust purification device after a set time has elapsed. It is good to control so that it may carry out.

  Note that the set time is the surplus of the supplied low-sulfur fuel after the supply of the low-sulfur fuel from the other fuel supply source is started after the switching device is switched. The time until all the fuel is recovered in the main fuel tank 51 or the time until it reaches the fuel return passage to the fuel tank may be used.

  Another feature of the present invention is an exhaust gas purification method for a diesel engine provided with an exhaust gas purification device provided in an exhaust passage of the diesel engine. The diesel engine supplies fuel normally used during normal operation to the diesel engine. When exhaust gas from the exhaust gas is purified by the exhaust gas purification device and regeneration control of the exhaust gas purification device is performed, the fuel is switched to a fuel having less sulfur content than the normally used fuel and supplied to the diesel engine, The object is to implement regeneration control of the exhaust purification device.

ADVANTAGE OF THE INVENTION According to this invention, even if the fuel property used for a diesel engine changes with countries or regions, the function of the exhaust gas purification device provided in the exhaust passage of the engine can be reliably recovered. There is an effect that an apparatus and an exhaust purification method can be obtained.
Further, according to the present invention, it is possible to obtain an exhaust gas purification device and an exhaust gas purification method for a diesel engine that can recover the function of the exhaust gas purification device at a low cost without significantly changing the layout of the fuel supply system. .

It is a schematic block diagram which shows Example 1 of the exhaust gas purification apparatus of the diesel engine of this invention. It is a circuit diagram explaining the fuel supply system of the conventional diesel engine. It is a diagram explaining the influence of the fuel property in the deterioration regeneration of the deteriorated catalyst in the exhaust gas purification apparatus. It is a circuit diagram explaining the fuel supply system of the diesel engine in Example 1 of this invention. It is explanatory drawing explaining the structure of the switching device part shown in FIG. 4 in detail. It is a diagram explaining the temperature increase rate according to the deterioration degree of the front | former stage oxidation catalyst shown in FIG. It is a flowchart explaining the catalyst reproduction | regeneration control in Example 1 of this invention.

  Hereinafter, specific embodiments of an exhaust emission control device and an exhaust emission purification method for a diesel engine according to the present invention will be described with reference to the drawings. In each figure, the part which attached | subjected the same code | symbol has shown the part which is the same or it corresponds.

Embodiment 1 of the present invention will be described below with reference to FIGS.
FIG. 1 is a schematic configuration diagram showing a first embodiment of an exhaust emission control device for a diesel engine according to the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine (engine), 2 denotes an exhaust passage of the engine 1, and 3 denotes an exhaust purification device connected to the exhaust passage 2. The engine 1 includes a common rail 4 common to each cylinder. The high-pressure fuel (light oil) stored in the common rail 4 is supplied to the injectors 5 provided in each cylinder, and is injected from the injectors 5 into the respective cylinders.
In addition, re-engine oil is supplied and lubricated to each sliding portion such as an engine piston, a crankshaft, and a connecting rod by an engine oil lubrication mechanism (not shown).

  The intake passage 6 is equipped with a turbocharger 7. The intake air drawn from an air cleaner (not shown) flows into the compressor 7a of the turbocharger 7 from the intake passage 6 and is supercharged by the compressor 7a. Is introduced into the intake manifold 10 via the intercooler 8 and the intake control valve 9.

  On the other hand, the exhaust from the engine 1 flows into the exhaust passage 2 via the exhaust manifold 11 and the turbine 7 b of the turbocharger 7. Between the exhaust manifold 11 and the intake manifold 10, there is provided an EGR passage 13 that communicates via an EGR valve 12. One end side of the exhaust passage 2 is connected to the discharge side of the turbine 7 b of the turbocharger 7, and the other end side of the exhaust passage 2 is connected to one end side of the exhaust purification device 3.

  The rotating shaft of the turbine 7b is connected to the rotating shaft of the compressor 7a. Exhaust gas flowing into the exhaust passage 2 collides with turbine blades (not shown) of the turbine 7b to rotate the turbine 7b, thereby driving the compressor 7a.

  In the present embodiment, the exhaust purification device 3 includes a front-stage oxidation catalyst (front-stage oxidation catalyst) 30, an SCR catalyst 31, a rear-stage oxidation catalyst (rear-stage oxidation catalyst) 32, and a silencer 33 in order from the upstream side of the exhaust passage. Yes. A DPF that collects PM contained in the exhaust gas may be provided between the upstream oxidation catalyst 30 and the SCR catalyst 31.

The oxidation catalyst 30 of the preceding stage, the NO in the exhaust is oxidized to generate NO _2, and supplies the NO ₂ in the SCR catalyst 31. Further, the oxidation catalyst 30 in the previous stage is for oxidizing CO (carbon monoxide) or HC (hydrocarbon) contained in the unburned gas in the exhaust gas by reacting with oxygen in the exhaust gas.

  Furthermore, by supplying a relatively large amount of unburned gas (reducing agent) to the preceding oxidation catalyst 30 by means such as post-injection (additional injection of fuel from the end of the combustion stroke to the exhaust stroke). The exhaust gas is heated with the reaction heat (oxidation heat) when the unburned gas is oxidized, and the SCR catalyst 31 is heated with the heated exhaust gas heat. As a result, the SCR catalyst 31 is activated, and NOx contained in the engine exhaust can be purified.

  The preceding oxidation catalyst 30 is not particularly limited as long as it is a catalyst capable of oxidizing CO, HC, NO. For example, at least one kind of noble metal such as platinum, palladium, iridium, rhodium, titania, zirconia, A catalyst in which a catalyst component carried on alumina or the like is carried on a cordierite honeycomb structure or the like is suitable.

  An exhaust temperature sensor 42 for detecting the exhaust temperature on the SCR catalyst inlet side and an injection nozzle (not shown) for injecting and supplying an aqueous urea solution are provided upstream of the SCR catalyst 31. The urea aqueous solution injected from the injection nozzle is thermally decomposed or hydrolyzed by exhaust heat to become ammonia, and is supplied to the SCR catalyst 31.

The SCR catalyst 31 adsorbs the supplied ammonia and promotes a denitration reaction between the adsorbed ammonia and NOx in the exhaust, thereby purifying NOx to be harmless N ₂ .

  The SCR catalyst 31 is not particularly limited as long as it is a catalyst normally used for denitration. For example, a catalyst in which titanium oxide is loaded with a denitration active component such as vanadium or tungsten, or a transition metal such as copper, iron, or cerium. A catalyst or the like in which a zeolite obtained by ion-exchanging zeolite is supported on a cordierite honeycomb structure or the like is suitable.

The downstream oxidation catalyst 32 is provided on the downstream side of the SCR catalyst 31. The post-stage oxidation catalyst 32 oxidizes and decomposes ammonia (ammonia slip) flowing out from the SCR catalyst 31 without reacting with NOx due to excessive supply of a reducing agent (ammonia) to the SCR catalyst 31 or rapid temperature change, it is intended to discharge a harmless N _2.
The latter stage oxidation catalyst 32 may be the same as the preceding stage oxidation catalyst 30.
The exhaust gas thus purified is configured to be released into the atmosphere through the silencer 33.

  In the exhaust passage 2, a first exhaust temperature sensor 41 that detects the temperature of the exhaust before (upstream) the oxidation catalyst 30 in the previous stage, and the temperature of the exhaust before (upstream) of the SCR catalyst 31 is detected. A second exhaust temperature sensor 42 that detects the concentration of nitrogen oxides (NOx) in front of the SCR catalyst 31, and an exhaust temperature in front (upstream) of the downstream oxidation catalyst 32 that detects the concentration of nitrogen oxide (NOx). A third exhaust temperature sensor 46 and an SCR downstream NOx sensor 47 that detects the downstream (downstream) NOx concentration of the downstream oxidation catalyst 32 are provided.

Thus in order from the upstream side of the exhaust passage 2, front of the oxidation catalyst 30, by placing the SCR catalyst 31, a part of the NO is oxidized by the oxidation catalyst 30 of the preceding stage is converted to NO ₂ . Further, in the pre-stage oxidation catalyst 30, if there is unburned fuel (hydrocarbon HC), CO or the like in the exhaust gas, it is oxidized, and the exhaust gas is heated by the reaction heat at the time of oxidation, The temperature of the SCR catalyst 31 disposed on the downstream side can be raised to activate the SCR catalyst 31. Thereby, NOx contained in the engine exhaust can be reacted with ammonia supplied to the SCR catalyst 31 to be harmless N ₂ and can be purified.

In order to supply unburned fuel to the oxidation catalyst 30 in the previous stage, for example, the post injection described above is performed. That is, after the main injection of fuel into the engine cylinder, additional injection of fuel (post injection) is again performed in the cylinder, thereby greatly delaying the injection timing. As a result, the injected fuel does not burn, becomes a large amount of unburned fuel (unburned gas), is discharged outside the cylinder, and is supplied to the oxidation catalyst 30 in the preceding stage.
The post injection corresponds to a reducing agent (unburned fuel) supply means.

  50 is a fuel supply system for supplying high-pressure fuel (light oil) to the common rail 4, a fuel tank (main fuel tank) 51, a fuel supply passage 52, a fuel filter 53 provided in the fuel supply passage 52, and the A fuel pump (supply pump) for supplying fuel to the common rail 4 is configured.

In the present embodiment, a switching device 57 for switching the fuel supply source is provided in the fuel supply passage 52 between the fuel filter 53 and the fuel pump 54. The sub fuel supply passage 52b from the fuel tank (sub fuel tank; another fuel supply source) 55 (see FIG. 4) can be connected via a connection joint 58.
Therefore, in this embodiment, the fuel from the main fuel tank 51 and the fuel from the sub fuel tank 55 can be switched and supplied to the common rail 4.

  Reference numeral 60 denotes an engine control unit (ECU; electronic control unit). The ECU 60 is a control unit for performing comprehensive control including operation control of the engine 1, and includes a calculation unit (CPU) that executes various procedures. A storage unit (memory) that stores various setting values in advance, an input / output device, and the like are provided, and various control amounts are calculated and various devices are controlled based on the control amounts.

  In addition to the above-described first to third exhaust temperature sensors 41, 42, 46, the SCR upstream NOx sensor 45, the SCR wake NOx sensor 47, the ECU 60 collects information necessary for various controls on the input side. Various sensors such as a rotational speed sensor for detecting the engine rotational speed are connected. Further, various devices such as the injector 5 of each cylinder, the intake control valve 9 and the EGR control valve 12 which are controlled based on the calculated control amount are connected to the output side of the ECU 60.

  Further, in this embodiment, a multi-function multi-monitor 90 is connected to the ECU 60, and an hour for displaying the accumulated operating time of the engine cooling thermometer 91, the engine fuel gauge 92, the warning lamp 93, the engine, the equipment, and the like. An operation information display area such as a meter (hour meter) is provided. Display control of the multi-function multi-monitor 90 is performed by the ECU 60.

Next, the fuel supply system 50 will be described in detail.
First, a conventional fuel supply system will be described with reference to FIG. As shown in FIG. 2, a conventional fuel supply system 50 includes a fuel tank 51, a fuel supply passage 52, a fuel filter 53 that removes impurities in the fuel that passes through the fuel supply passage 52, a fuel pump 54, a common rail 4, and an injector. 5 etc. The fuel tank 51 stores fuel (light oil) to be used. The fuel in the fuel tank 51 is used not only for burning in a cylinder of a diesel engine to generate driving force, but also during post-injection for supplying unburned fuel to the exhaust gas purification device 3. It has come to be used.

  Reference numeral 56 denotes a fuel return passage which returns excess fuel that has not been supplied into the cylinders of the engine to the fuel tank 51, and is connected to the return side of the common rail 4, the injector 5, and the fuel pump 54. Yes.

  FIG. 3 is a diagram for explaining the influence of the fuel property in the deterioration regeneration of the catalyst in the exhaust gas purification apparatus. When the SCR catalyst 31 in the exhaust purification device 3 deteriorates, it needs to be regenerated. At the time of regeneration, the post-injection described above is performed to supply unburned fuel to the preceding oxidation catalyst 30 to oxidize, and the temperature of the exhaust gas is raised by the reaction heat to raise the temperature of the SCR catalyst 31. Thus, the SCR catalyst 31 can be activated and regenerated.

FIG. 3 shows the SCR catalyst purification rate (NOx purification rate) with respect to the inlet temperature (exhaust temperature) of the SCR catalyst. Up to a certain temperature, the purification rate increases as the catalyst inlet temperature increases. It shows that the purification rate decreases as the temperature decreases.
Further, the dotted broken line A in FIG. 3 indicates the purification with respect to the catalyst inlet temperature when the new SCR catalyst is used for the purification of exhaust gas using a fuel having a good property free from sulfur (S) and phosphorus (P). It shows the change in rate.

  The solid broken line B (broken line indicated by a black triangle) shows the change in the purification rate with respect to the catalyst inlet temperature when the SCR catalyst is poisoned, that is, when the SCR catalyst whose performance has deteriorated due to poisoning is used for exhaust purification. Show.

The solid broken lines C and D indicate purification with respect to the catalyst inlet temperature when the SCR catalyst 31 is used for exhaust purification using the SCR catalyst that has been regenerated by heating the SCR catalyst 31 and activating the SCR catalyst 31. It shows the change in rate.
In addition, the broken line C indicated by the white square is in an environment where SO ₂ is contained in the exhaust gas because the regeneration process and the operation after the regeneration process are continued using the fuel having poor properties including S (or further including P). The change of the purification rate with respect to the catalyst inlet temperature when the SCR catalyst is used for exhaust purification is shown.
A broken line D indicated by a white circle indicates a change in the purification rate with respect to the catalyst inlet temperature when the SCR catalyst regeneration process and the operation after the regeneration process are continued using a high-quality fuel having no property of S and P. .

  From FIG. 3, when operating using fuel with poor properties including S as the supplied fuel, the performance of the SCR catalyst has not recovered as shown by the broken line C even if the exhaust temperature is increased and regeneration is performed. I understand that. The reason for this is considered to be that if the fuel contains a large amount of S or the like, the exhaust gas contains SOx and the recovered fuel is poisoned again.

  In addition, when the regeneration process of the SCR catalyst is performed using a fuel having a good property free from S or P, it may be used by switching to a normally used fuel whose property is not necessarily good during operation after the regeneration process. It was also found that almost the same performance (purification rate) as that of a new SCR catalyst was obtained. Therefore, by using a fuel having good properties that does not contain S or the like at least during the regeneration process, and has almost the same properties as a new SCR catalyst, it can be obtained.

  FIG. 4 is a circuit diagram illustrating a fuel supply system for a diesel engine in Embodiment 1 of the present invention. In FIG. 4, 50 is a fuel supply system for supplying high-pressure fuel (light oil) to the common rail 4, and includes a fuel tank (main fuel tank) 51, a fuel supply passage 52, a main fuel supply passage 52a, and this fuel supply passage 52a. And a fuel pump 54 for supplying fuel to the common rail 4 and the like.

  The fuel supply passage 52 between the fuel filter 53a and the fuel pump 54 is provided with a switching device 57 for switching the fuel supply source. The switching device 57 includes a sub fuel tank ( The secondary fuel supply passage 52b from another fuel supply source) 55 can be connected via the connection joint 58. The secondary fuel tank 55 stores a fuel having a good property with little or no S. A fuel filter 53b is provided in the middle of the secondary fuel supply passage 52b.

  By configuring the fuel supply system 50 in this way, the fuel from the main fuel tank 51 and the fuel from the sub fuel tank 55 can be switched by the switching device 57 and supplied to the common rail 4 side. . Therefore, even if it is unavoidable to use fuel with a large amount of S and poor properties as a normal fuel depending on the country or region, when the catalyst is regenerated, the amount of S or S Regeneration can be performed by supplying a fuel having no good properties, and the operation can be continued by regenerating the SCR catalyst so that the performance of the SCR catalyst is almost equal to that of a new catalyst. Therefore, the life of the catalyst can be extended, and the period of catalyst replacement can be extended.

  In this embodiment, the fuel return passage 56 is composed of only one, and even when operating using fuel with good properties from the sub fuel tank 55, it was not supplied into the cylinder of the engine. Excess fuel is returned to the main fuel tank 51. As a result, the structure can be simplified and the fuel property in the sub fuel tank 55 is always kept in a good state by preventing the fuel having deteriorated properties from returning to the sub fuel tank 55.

  The switching device 57 is normally open on the A side (main fuel tank 51 side) and closed on the B side (sub fuel tank 55 side), and normally supplies fuel from the main fuel tank 51 to the C side ( The fuel pump 54, the common rail 4, and the injector 5 are supplied from a port on the fuel pump 54 side.

  When performing the catalyst regeneration processing operation, first, the secondary fuel supply passage 52b is connected to the connection joint 58, and then the A side of the switching device 57 is closed and the B side is opened. As a result, fuel with good properties from the sub fuel tank 55 can be supplied from the port on the C side to the fuel pump 54, the common rail 4 and the injector 5, and catalyst regeneration is performed using the fuel with good properties. be able to.

  The switching operation of the switching device 57 can be automatically performed by the control from the ECU 60 described above. That is, the ECU 60 is a control device for performing regeneration control of the exhaust gas purification device, and includes an external input means for instructing the multi-function multi-monitor 90 and the like to perform the regeneration control.

  Further, the sub fuel tank (another fuel supply source) 55 is connected to the switching device 57. As a result, when a command to execute the regeneration control of the purification device is issued from the external input means to the control device (ECU 60), the switching device 57 causes the fuel from the sub fuel tank 55 to flow to the fuel pump. It can be configured to be automatically controlled so as to flow to 54.

  Further, the secondary fuel tank 55 and the secondary fuel supply passage 52b are not usually installed in a work vehicle such as a hydraulic excavator, and are connected to the connection joint 58 of the work vehicle only when a catalyst regeneration processing operation is performed. If the regenerating process is performed by operating the switching device 57, the structure of the work vehicle can be simplified, and it is necessary to secure an installation space for the sub fuel tank 55 and the sub fuel supply passage 57 in the work vehicle. Therefore, the present invention can be implemented at a low cost.

  Further, the sub fuel tank 55 and the sub fuel supply passage 52b may be installed in a work vehicle, and the fuel tank 55 may be always connected according to the switching device 57. The regeneration process is configured to be able to detect the deterioration of the catalyst periodically or when the deterioration is detected, and as described above, the switching device 57 is automatically switched by the ECU 60 as described above. It is possible to always automatically perform the regeneration operation.

  FIG. 5 is an explanatory diagram for explaining in detail an example of the structure of the portion of the switching device 57 shown in FIG. As shown in FIG. 5, the switching device 57 can use a three-port single-acting solenoid valve. That is, normally, the solenoid valve is not energized, the solenoid valve is demagnetized, and the port A and the port C are in communication. Therefore, as shown in FIG. 4, the fuel from the main fuel tank 51 is supplied to the fuel pump 54 side.

  Further, during the regeneration processing operation of the SCR catalyst, the solenoid valve is excited by energizing the solenoid valve, and the port B and the port C are in communication with each other. As a result, as shown in FIG. 4, fuel with good properties from the sub fuel tank 55 can be supplied to the fuel pump 54 side.

  FIG. 6 is a diagram illustrating the rate of temperature increase corresponding to the degree of deterioration of the pre-stage oxidation catalyst 30 shown in FIG. The horizontal axis represents time, and the vertical axis represents the temperature of the oxidation catalyst. A new article indicates that the catalyst is a new article. Degrees of deterioration 1 and 2 indicate a catalyst that has been deteriorated. Deterioration degree 2 is a further deterioration of the catalyst than deterioration degree 1.

As shown in FIG. 6, when the oxidation catalyst 30 is new, the temperature increase rate is high, and the temperature increase rate decreases as the degree of deterioration of the catalyst progresses.
FIG. 6 is obtained in advance by experiments and stored in the ECU 60 shown in FIG. 1 as a deterioration degree map. Therefore, if the temperature rise rate of the oxidation catalyst 30 is obtained, the degree of deterioration of the oxidation catalyst can be known.

FIG. 7 is a flowchart for explaining the catalyst regeneration control (purge control) in the first embodiment of the present invention. With reference to FIG. 7, the control for the regeneration process of the deteriorated catalyst executed by the ECU 60 described above will be explained. .
When the diesel engine is started, first, in step S1, it is determined whether or not the engine operating region is in the active region of the preceding oxidation catalyst 30. This determination is made based on, for example, whether or not the exhaust temperature detected by the first exhaust temperature sensor 41 provided in front of the pre-stage oxidation catalyst 30 is equal to or higher than a predetermined temperature. When it is determined that the engine operating region is not in the active region of the oxidation catalyst 30 (in the case of NO), the processing is terminated as it is or step S1 is executed again after the control time has elapsed.

If it is determined in step S1 that the engine operating region is in the active region of the pre-oxidation catalyst 30, the process proceeds to step S2, and the pre-oxidation detected by the first exhaust temperature sensor 41 and the second exhaust temperature sensor 42 is performed. From the exhaust temperatures on the inlet side and the outlet side of the catalyst 30, the rate of increase of the exhaust temperature in the pre-stage oxidation catalyst 30, that is, the catalyst temperature increase rate ΔTd is obtained by the following equation.
ΔTd = (Inlet temperature−Outlet temperature) / hour

  In step S3, the catalyst temperature increase rate ΔTd obtained in step S2 is compared with a determination threshold value ΔTs. As a result of the comparison, if the catalyst temperature increase rate ΔTd is greater than or equal to the determination threshold value ΔTs (ΔTd ≧ ΔTs), it is determined that the oxidation catalyst 30 is normal, and the process ends. On the other hand, if the catalyst temperature increase rate ΔTd is less than the determination threshold value ΔTs (ΔTd <ΔTs), it is determined that catalyst deterioration has occurred in the pre-oxidation catalyst 30, and the process proceeds to step S4.

  In step S4, the inlet side of the fuel switching device 57 is switched from the main fuel tank 51 side (A port) to the sub fuel tank 55 side (B port), and the inlet side of the fuel switching device 57 is switched to the sub fuel tank 55 side. . That is, the main fuel supply passage 52a is shut off, and the supply of fuel stored in the main fuel tank 51 is shut off. On the other hand, since the secondary fuel supply passage 52 b is communicated, the high-quality fuel stored in the secondary fuel tank 55 is sucked into the fuel pump 54.

  Then, it progresses to step S5. In step S5, an elapsed time tim after switching to the sub fuel supply passage 52b is measured, and control is performed to wait until the elapsed time tim passes the first set time t1. During the first set time tl, after the fuel supply passage 52 is switched from the main fuel tank 51 to the sub fuel tank 55, the fuel in the sub fuel tank 55 (good quality fuel) is injected from the injector 5. The time until all the surplus fuel is collected in the main fuel tank 51 or the time until the fuel return passage 56 to the main fuel tank 51 is reached is taken. That is, the first set time tl is a time until switching to the high-quality fuel, and is determined and set in advance from an experiment or the like.

In step S5, after the elapsed time tim reaches the first set time t1 (tim ≧ t1), the process proceeds to step S6, and in this step S6, exhaust temperature increase control for increasing the exhaust temperature of the engine 10 is executed. .
As the exhaust gas temperature raising control, for example, during the expansion stroke in the engine 1, it is possible to perform control by executing sub fuel injection (post injection), control for reducing the opening of the intake control valve 11, or the like. It can also be executed by increasing the opening of the EGR valve 12 and increasing the amount of exhaust gas (EGR gas) introduced into the intake passage. That is, fuel or the like injected by post-injection that does not contribute to combustion is supplied to the pre-stage oxidation catalyst 30 in the state of unburned fuel (unburned gas) and is oxidized here, so that the exhaust heat is exhausted by the reaction heat at that time. The temperature can be raised.

Thereafter, the process proceeds to step S7, where the exhaust temperature Tg downstream of the pre-stage oxidation catalyst 30 is detected by the second exhaust temperature sensor 42, and it is determined whether or not the exhaust temperature Tg has risen to a target temperature Tgs or higher. In step S7, when the condition is satisfied (in the case of YES), the process proceeds to step S8, and when the condition is not satisfied (in the case of NO), step S7 is repeated.
The target temperature Tgs is set based on the degree of deterioration of the pre-stage oxidation catalyst 30 described with reference to FIG. That is, the relationship between the degree of deterioration of the oxidation catalyst and the catalyst temperature increase rate ΔTd is obtained in advance by experiments or the like, and the degree of deterioration of the preceding oxidation catalyst 30 is determined based on the value of the catalyst temperature increase rate ΔTd obtained in step S2. The target temperature Tgs is determined according to the degree of deterioration.

  In step S8, since the exhaust gas temperature Tg has risen to the target temperature Tgs or more by the exhaust gas temperature raising control, the temperature of the SCR catalyst 31 provided on the downstream side of the pre-stage oxidation catalyst 30 rises to increase the SCR catalyst 31. Is activated and its regeneration control is executed. Thereafter, the process proceeds to step S9, where an elapsed time tim during which the regeneration control of the SCR catalyst 31 is executed is obtained, and the regeneration control of the SCR catalyst 31 is executed until the elapsed time tim reaches the set time t2. When the elapsed time tim becomes equal to or longer than the set time t2, the process proceeds to step S10, and the inlet side of the fuel switching device 57 is switched from the sub fuel tank 55 side (B port) to the main fuel tank 51 side (A port). The catalyst regeneration control ends.

  Thus, according to the present embodiment, when performing catalyst regeneration control, the sulfur (S) content stored in the sub fuel tank 55 is changed from the normal fuel stored in the main fuel tank 51 to the fuel for operating the engine. By switching to less high-quality fuel and performing post-injection that does not contribute to combustion in the engine cylinders, the unburned fuel is supplied to the pre-stage oxidation catalyst 30 for oxidation, and the exhaust heat is increased by the reaction heat at that time. The SCR catalyst 31 on the downstream side is regenerated by heating. Therefore, even if the nature of the fuel used in the diesel engine changes depending on the country or region, it can be operated by switching to a good quality fuel with low sulfur content during catalyst regeneration control. The function of the exhaust emission control device can be reliably restored.

  In addition, according to the present embodiment, the switching device 57 for switching the fuel is provided, and the connection joint 58 for connecting to a sub fuel tank (another fuel supply source) that stores high-quality fuel is provided. Therefore, since it is not necessary to install the sub fuel tank 55 and its fuel supply passage 52b in a work vehicle such as a hydraulic excavator, the exhaust gas purification is inexpensively performed without significantly changing the layout of the fuel supply system 50. It can be configured to restore the functionality of the device.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, in each of the above-described embodiments, an example in which the present invention is applied to a work vehicle such as a hydraulic excavator as a construction machine has been described. However, the present invention is similarly applied to a vehicle equipped with a diesel engine such as a work vehicle such as a dump truck. The invention can be applied.

In the above embodiment, the SCR catalyst 31 and the rear-stage oxidation catalyst 32 are provided as the exhaust purification device downstream of the front-stage oxidation catalyst 30. However, the present invention is not limited to this, and instead of the SCR catalyst 31. In addition, the present invention can be implemented in the same manner even if a DPF that collects PM and combusts and removes it together with the SCR catalyst 31 is provided.
Further, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.

1: diesel engine (engine), 2: engine exhaust passage, 3: exhaust purification device,
4: common rail, 5: injector, 6: intake passage,
7: Turbocharger, 7a: Compressor, 7b: Turbine,
8: Intercooler, 9: Intake control valve,
10: intake manifold, 11: exhaust manifold,
12: EGR control valve, 13: EGR passage,
30, 32: Oxidation catalyst (30: pre-stage oxidation catalyst, 32: post-stage oxidation catalyst)
31: SCR catalyst,
41, 42, 46: exhaust temperature sensor,
45: SCR upstream NOx sensor, 47: SCR wake NOx sensor,
50: Fuel supply system, 51: Fuel tank (main fuel tank),
52: Fuel supply passage, 52a: Main fuel supply passage, 52b: Sub fuel supply passage,
53: Fuel filter, 53a: Main fuel filter, 53b: Secondary fuel filter,
54: Fuel pump (supply pump),
55: Secondary fuel tank (another fuel supply source), 56: Fuel return passage,
57: Switching device (fuel switching valve), 58: Connection joint,
60: ECU (engine control unit; control device),
90: Multi-function multi-monitor,
91: Engine cooling thermometer, 92: Engine fuel gauge, 93: Warning lamp.

Claims (4)

Diesel comprising an exhaust purification device provided in an exhaust passage of a diesel engine, an oxidation catalyst provided in an exhaust passage upstream of the exhaust purification device, and a reducing agent supply means for supplying a reducing agent to the oxidation catalyst In an engine exhaust purification system,
A fuel tank for storing fuel for supplying fuel to the diesel engine;
A fuel supply passage for supplying fuel in the fuel tank to the diesel engine;
A fuel pump provided in the fuel supply passage;
Provided in a fuel supply passage between the fuel tank and the fuel pump; fuel from the fuel tank; and fuel from another fuel supply source that supplies fuel having a lower sulfur content than fuel in the fuel tank; A diesel engine exhaust gas purification apparatus, comprising: a switching device configured to switch between and supply to the diesel engine.   The exhaust emission control device for a diesel engine according to claim 1, comprising a control device for performing regeneration control of the exhaust gas purification device, and an external input means for commanding execution of the regeneration control, When the control device is instructed to perform regeneration control of the purification device from the external input means with the other fuel supply source connected to the switching device, the switching device An exhaust emission control device for a diesel engine, which is automatically switched and controlled so that fuel from a source flows to the fuel pump.   3. The exhaust gas purification apparatus for a diesel engine according to claim 2, wherein after the switching device is switched so that fuel with a small amount of sulfur from the another fuel supply source flows to the fuel pump, after a set time has elapsed. The diesel engine exhaust gas purification device is characterized in that the control device controls the exhaust gas purification device to perform regeneration control. An exhaust purification method for a diesel engine comprising an exhaust purification device provided in an exhaust passage of the diesel engine,
During normal operation, normally used fuel is supplied to the diesel engine, and exhaust from the diesel engine is purified by the exhaust gas purification device.
When performing regeneration control of the exhaust purification device, switching to a fuel having a lower sulfur content than the normally used fuel is supplied to the diesel engine, and regeneration control of the exhaust purification device is performed. Diesel engine exhaust purification method.

Images