JP2005002817A - Exhaust emission control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize calculation of a particulate collecting amount to a filter regardless of an aromatic hydrocarbon content in fuel. <P>SOLUTION: The exhaust emission control device for a diesel engine is equipped with a filter (42) for collecting particulate during exhaust. When the particulate collecting amount to filter (42) is calculated based on the particulate generation amount and the calculation value of the particulate collecting amount reaches the predetermined value, the filter regeneration is executed. The exhaust emission control device is provided with an aromatic hydrocarbon content correlation value detecting means (21) for detecting a correlation value of the aromatic hydrocarbon content in fuel and a particulate generation amount predicting means (21) for predicting the particulate generation amount on the basis of the correlation value of the aromatic hydrocarbon generation amount. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for a diesel engine.
[0002]
[Prior art]
A filter that collects particulates discharged from the engine is provided in the exhaust passage, and the amount of particulates generated per unit time in the exhaust gas is calculated based on the intake pressure, intake air temperature, engine rotation speed, and fuel injection amount, There is a method of calculating the particulate collection amount to the filter by accumulating the calculated particulate generation amount per unit time, and determining whether or not the regeneration time of the filter is reached based on this collection amount ( Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-13455
[0004]
[Problems to be solved by the invention]
By the way, when market research was conducted on diesel oil, which is the fuel for diesel engines, the results shown in FIGS. 18 to 21 were obtained. That is, as shown in FIG. 18, the cetane number decreases in inverse proportion to the standard fuel specific gravity, and as shown in FIG. 19, the lower the standard fuel specific gravity, the higher the 10% distillation point representing evaporability (the lower the distillation temperature). It has become. This is because, as shown in FIG. 20, the higher the standard fuel specific gravity, the lower the cetane number (the higher the octane number), the lower the evaporation property, and the higher the aromatic hydrocarbon content having a benzene ring structure. It seems to be because. Since the viscosity is proportional to the standard fuel specific gravity, the cetane number tends to decrease in inverse proportion to the viscosity as shown in FIG.
[0005]
In view of such market research, when the aromatic hydrocarbon content in the fuel was varied and an experiment was conducted on how the amount of particulates generated in the exhaust gas changes, the aromatic hydrocarbon content It has been found that the amount of particulates generated per unit time increases as the amount of fuel increases. Therefore, when calculating the amount of particulates generated per unit time in the exhaust gas, it is necessary to consider the content of aromatic hydrocarbons in the fuel.
[0006]
However, since the above-mentioned conventional apparatus does not consider the aromatic hydrocarbon content in the fuel, the determination accuracy as to whether or not it is time to regenerate the filter is lowered. For example, it is assumed that the calculation of the amount of particulates generated per unit time by the above-described conventional apparatus is optimal with respect to a reference fuel having a predetermined aromatic hydrocarbon content in the fuel. In this case, when a fuel having a higher aromatic hydrocarbon content than the above-mentioned reference fuel is used, the amount of particulates generated per unit time is larger than when the reference fuel is used. For example, even when a fuel having a higher aromatic hydrocarbon content than the reference fuel is used, the amount of particulates generated per unit time of the same amount as when the reference fuel is used is calculated. That is, in the conventional device, when a fuel having a higher aromatic hydrocarbon content than the reference fuel is used, the amount of particulates generated per unit time is overestimated, and it is determined that it is time to regenerate the filter. Be late. As a result, the amount of particulates collected in the filter becomes larger than that for the reference fuel, the combustion temperature in the filter after the regeneration process starts becomes high, and the filter is overheated.
[0007]
On the other hand, when a fuel having a lower aromatic hydrocarbon content than the reference fuel is used, according to the conventional device, the amount of particulates per unit time is overestimated and it is time to regenerate the filter. Judgment of is accelerated. Since, for example, post-injection is performed in order to increase the temperature of the filter during the regeneration process of the filter, the earlier regeneration time increases the opportunity for post-injection, resulting in poor fuel consumption.
[0008]
Accordingly, an object of the present invention is to optimally calculate the amount of particulates collected in the filter regardless of the aromatic hydrocarbon content in the fuel.
[0009]
[Means for Solving the Problems]
The present invention includes a filter that collects particulates in exhaust gas, calculates the amount of particulates collected in the filter based on the amount of generated particulates, and the calculated value of the amount of particulates collected is calculated. When the predetermined value is reached, the exhaust gas purification device of the diesel engine that performs the filter regeneration process detects the correlation value of the aromatic hydrocarbon content in the fuel, and the correlation value of the aromatic hydrocarbon content is detected. Based on this, the generation amount of the particulates is predicted.
[0010]
The present invention also includes a filter that collects particulates in the exhaust gas, predicts the amount of particulates generated, and determines the amount of particulates collected in the filter based on the predicted value of the amount of particulates generated. When the calculated value of the particulate collection amount reaches a predetermined value, in the exhaust gas purification device of the diesel engine that performs the regeneration process of the filter, calculate the amount of particulate generation relative to the reference fuel, A value obtained by detecting the correlation value of the aromatic hydrocarbon content in the fuel and correcting the calculated value of the amount of particulates generated relative to the reference fuel based on the detected correlation value of the aromatic hydrocarbon content in the fuel. Is set as a predicted value of the amount of generated particulates.
[0011]
【The invention's effect】
According to the experimental results, as the content of aromatic hydrocarbons in the fuel increases, the amount of particulates generated in the exhaust tends to increase, and the amount of particulates collected in the filter tends to increase. According to the present invention, based on the detected correlation value of the aromatic hydrocarbon content of the fuel, the correlation value of the aromatic hydrocarbon content indicates that the aromatic hydrocarbon content increases. Therefore, the amount of particulates collected in the filter can be accurately calculated regardless of the aromatic hydrocarbon content in the fuel used. Thus, if the amount of particulates collected in the filter can be calculated with high accuracy, the determination accuracy of the regeneration time of the filter is improved.
[0012]
As the aromatic hydrocarbon content in the fuel increases compared to the reference fuel, the amount of particulates generated in the exhaust tends to increase, and the amount of particulates collected in the filter tends to increase. According to the present invention, the amount of particulates generated relative to the reference fuel is calculated, the correlation value of the aromatic hydrocarbon content in the fuel is detected, and the detected correlation value of the aromatic hydrocarbon content in the fuel is detected. On the basis of this, the value obtained by correcting the calculated value of the particulate generation amount with respect to the reference fuel is used as the predicted value of the particulate generation amount. Therefore, even if a fuel different from the aromatic hydrocarbon content in the reference fuel is used. Thus, it is possible to accurately calculate the amount of particulates collected in the filter by the fuel. Thus, if the amount of particulates collected in the filter can be calculated with high accuracy, the determination accuracy of the regeneration time of the filter is improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the configuration of an embodiment.
[0014]
In FIG. 1, a diaphragm type EGR valve 6 that responds to a control pressure from a pressure control valve 5 is provided in an EGR passage 4 that connects the exhaust passage 2 and the collector portion 3 a of the intake passage 3. The pressure control valve 5 is driven by a duty control signal from the control unit 21 and thereby obtains a predetermined EGR rate corresponding to the operating conditions. This is because NOx increases as the combustion temperature rises. Therefore, in order to suppress the combustion temperature, a part of the exhaust gas is recirculated to the intake passage to lower the combustion temperature, thereby reducing the generation of NOx.
[0015]
The engine includes a common rail fuel injection device 11 as a fuel supply device. The fuel injection device 11 mainly includes a fuel tank (not shown), a supply pump 12, a pressure accumulating chamber 13, and a nozzle 14 provided for each cylinder. The fuel pressurized by the supply pump 12 is temporarily stored in the pressure accumulating chamber 13. After that, the high pressure fuel in the pressure accumulating chamber 13 is distributed to the nozzles 14 corresponding to the number of cylinders.
[0016]
The nozzle 14 includes a needle valve, a nozzle chamber, a fuel supply passage to the nozzle chamber, a retainer, a hydraulic piston, a return spring, and the like, and a three-way valve (solenoid valve) 15 interposed in the fuel supply passage to the hydraulic piston is interposed therebetween. It is disguised. When the three-way valve 15 is turned off, the needle valve is in a seated state. However, when the three-way valve 15 is turned on, the needle valve is raised and fuel is injected from the nozzle hole at the tip of the nozzle. That is, if the three-way valve 15 is switched from OFF to ON, the fuel injection start timing is adjusted by the ON time, and the fuel injection amount is adjusted by the ON time. The amount increases.
[0017]
The accelerator opening sensor 24, the sensor 22 for detecting the engine speed and the crank angle, and the control unit 21 to which signals from the water temperature sensor 31 are input calculate the fuel injection amount in accordance with the engine speed and the accelerator opening. In addition to controlling the ON time of the three-way valve 15 in accordance with the calculated fuel injection amount, by controlling the switching time of the three-way valve 15 to ON, a predetermined injection start time (injection time) corresponding to the operating conditions is set. Trying to get.
[0018]
A variable capacity turbocharger 31 is provided in the exhaust passage 2 downstream of the opening of the EGR passage 4. This is a variable nozzle 33 driven by an actuator 34 at the scroll inlet of the exhaust turbine 32 so that the control unit 21 can obtain a predetermined supercharging pressure from a low rotational speed range by the control unit 21. On the low rotational speed side, the nozzle opening degree is increased to increase the flow rate of the exhaust gas introduced into the exhaust turbine 32, and on the high rotational speed side, exhaust gas is introduced into the exhaust turbine 32 without resistance and controlled to the nozzle opening degree.
[0019]
The actuator 34 includes a diaphragm actuator that drives the variable nozzle 33 in response to the control pressure, and a pressure control valve 36 that adjusts the control pressure to the diaphragm actuator. The actual opening of the variable nozzle 33 is the target nozzle. A duty control signal is generated so as to have an opening, and this duty control signal is output to the pressure control valve 36.
[0020]
When the turbocharger 31 is provided in this way, a part of the exhaust energy is recovered by the exhaust turbine 32 and the engine output is increased.
[0021]
A filter 42 is provided in the exhaust passage 2 downstream of the exhaust turbine 32. For example, as described in Japanese Patent Application Laid-Open No. 2001-73743, the substantially cylindrical filter 42 as a whole has a large number of cells substantially parallel to the exhaust flow due to honeycomb-shaped partition walls made of a porous member such as ceramic. The inlet and outlet of each cell are alternately sealed with a sealing material. Specifically, the particulates contained in the exhaust gas are composites composed of soot and a soluble organic substance (SOF), and most of them are soot (particulates). For this reason, when the exhaust gas flows into the adjacent cells via the partition walls at normal exhaust temperature, soot is collected by the partition walls. On the other hand, when the exhaust time is increased when the regeneration time of the filter 42 is reached, the soot is self-ignited and CO 2 ₂ As discharged. Reference numeral 41 denotes an oxidation catalyst carrying a noble metal.
[0022]
The exhaust passage 2 is also provided with a NOx trap catalyst 43 upstream of the filter 42 (or downstream of the filter 42). The NOx trap catalyst 43 traps NOx (nitrogen oxide) in the exhaust during lean combustion when the excess air ratio is greater than 1.0, and during rich combustion where the excess air ratio becomes 1.0 or less (or At the time of combustion at the stoichiometric air-fuel ratio, the trapped NOx is reduced and purified using HC and CO in the exhaust as a reducing agent.
[0023]
When the control unit 21 determines that the particulates in the exhaust gas have been collected by the filter 42 to the limit of the allowable range, the exhaust gas temperature is increased to around the temperature at which the collected particulates can be combusted. Set the excess air ratio to be slightly lean. Further, when the NOx trapped by the NOx trap catalyst 43 at the time of lean combustion reaches the limit of the allowable range, the control unit 21 reduces and purifies the trapped NOx. The excess air ratio is controlled so that Further, since the NOx trap catalyst 43 is poisoned by SOx (sulfur oxide) contained in a trace amount in the exhaust gas, when it is determined that SOx has accumulated to the limit of the allowable range, this SOx is desorbed from the NOx trap catalyst 43. In order to raise the exhaust temperature to a possible temperature, the excess air ratio is controlled so that combustion is performed at the stoichiometric air-fuel ratio.
[0024]
As described above, the combustion of the particulates collected by the filter 42 (regeneration of the filter 42), the reduction of NOx trapped by the NOx trap catalyst 43 (regeneration of the NOx trap catalyst 43), and the SOx to the NOx and lap catalyst. It is necessary to control the excess air ratio for detoxication (sulfur detoxication),
(1) When there is a regeneration request for the filter 42, from lean combustion to combustion slightly leaner than the stoichiometric air-fuel ratio,
(2) When there is a request for releasing sulfur poisoning of the NOx trap catalyst 43, from lean combustion to stoichiometric combustion,
(3) When there is a regeneration request for the NOx trap catalyst 43, the lean combustion is switched to the rich combustion.
[0025]
In this case, rich combustion or stoichiometric air-fuel ratio combustion may not be obtained with the supercharger 31 alone, so that a diaphragm that responds to the control pressure from the pressure control valve 20 is provided in the intake passage 3 immediately upstream of the collector 3a. An intake throttle valve 18 driven by an actuator 19 is provided. The configuration of the actuator 19 is the same as that of the EGR valve 6, and the pressure control valve 20 for the intake throttle valve is also driven by a duty control signal from the control unit 21.
[0026]
On the premise of an engine that performs such an excess air ratio control, in this embodiment, (4) a value correlated with the aromatic hydrocarbon content in the fuel is further detected, and the detected aromatic hydrocarbon content in the fuel is detected. Based on the correlation value, the calculated value of the particulate generation amount relative to the reference fuel is corrected, and the particulate collection amount to the filter 42 is calculated based on the corrected value (predicted value of the particulate generation amount). When the calculated value of the particulate collection amount reaches a predetermined value, the regeneration process of the filter 42 is performed.
[0027]
Explaining this, FIGS. 18 to 21 show the results of market research on diesel oil, which is the fuel for diesel engines. That is, as shown in FIG. 18, the cetane number decreases in inverse proportion to the standard fuel specific gravity, and as shown in FIG. 19, the 10% distillation point representing evaporability is higher as the standard fuel specific gravity is lower (the distillation temperature is lower). It has become. This is because, as shown in FIG. 20, the higher the standard fuel specific gravity, the lower the cetane number (the higher the octane number), the lower the evaporation property, and the higher the aromatic hydrocarbon content having a benzene ring structure. It seems to be because. Since the viscosity is proportional to the standard fuel specific gravity, the cetane number tends to decrease in inverse proportion to the viscosity as shown in FIG.
[0028]
In view of such market research, when the amount of generated particulates in the exhaust gas was changed by varying the aromatic hydrocarbon content in the fuel, an experiment was conducted to determine how the aromatic carbonization in the fuel changes. It has been found that fuel with a higher hydrogen content increases the amount of particulates generated per unit time. Therefore, when calculating the amount of particulates generated per unit time in the exhaust, it is necessary to consider the aromatic hydrocarbon content in the fuel. In this embodiment, the correlation of the aromatic hydrocarbon content in the fuel Fuel specific gravity is adopted as a value.
[0029]
For this reason, the control unit 21 includes an output of an air flow meter 23, a fuel temperature TF from a temperature sensor 25 installed in the fuel pipe, an output of an air-fuel ratio sensor 26 disposed downstream of the filter 42, and an intake pressure sensor 27. , The intake air temperature Pa from the intake air temperature sensor 28, the temperature of the filter 42 from the temperature sensor 29, and the temperature of the NOx trap catalyst 43 from the temperature sensor 30 are input.
[0030]
The contents of this control executed by the control unit 21 will be described based on a flowchart.
[0031]
2 to 6 are main routines for performing the regeneration process for the filter 2, the regeneration process for the NOx trap catalyst 43, and the sulfur poisoning release process.
[0032]
In FIG. 2, in Step 1, the rotational speed Ne detected by the crank angle sensor 22 and the standard fuel specific gravity Gstd are read.
[0033]
Here, the calculation of the standard fuel specific gravity Gstd will be described with reference to FIG.
[0034]
FIG. 7 is executed at regular intervals. In FIG. 7, in step 501, the output of the air flow meter (AFM) 23, the engine speed Ne, the accelerator opening detected by the accelerator sensor 24, the fuel temperature TF detected by the temperature sensor 25, and the output of the air-fuel ratio sensor 26 are read. .
[0035]
In step 502, the intake air flow rate Qair is calculated by searching a predetermined table from the output of the air flow meter 23.
[0036]
In step 503, a fuel injection amount (volume flow rate) Qmain is calculated by searching a predetermined map from the engine speed Ne and the accelerator opening.
[0037]
The fuel injection amount Qmain is calculated by calculating a fuel injection period Mperiod by searching a predetermined map from the engine speed Ne and the accelerator opening, and the common rail detected by the fuel injection period Mperiod and a pressure sensor (not shown). The fuel injection amount Qmain may be calculated by searching a predetermined map from the fuel pressure in 13.
[0038]
In step 504, the actual air-fuel ratio AFreal is calculated by searching a predetermined table from the output of the air-fuel ratio sensor 26.
[0039]
In step 505, it is checked whether or not the conditions are suitable for detecting the fuel specific gravity. Normally, EGR for reducing NOx is generally performed in the engine. When EGR is performed, the air-fuel ratio of the exhaust gas is shifted to the rich side. In order to obtain the air-fuel ratio, correction by EGR is required. However, since there is a concern that the detection accuracy of the actual air-fuel ratio deteriorates due to the correction, it is desirable that the actual air-fuel ratio detection command be issued in a region where the EGR operation is stopped. For this reason, in the present embodiment, the fuel specific gravity detection condition is satisfied when the EGR operation is stopped.
[0040]
When the detection condition is not satisfied, the current specific processing is terminated without performing detection (calculation) of the fuel specific gravity.
[0041]
If the detection condition is satisfied, the process proceeds from step 505 to step 506, and the actual fuel amount (weight flow rate) Gmain is obtained from the intake air flow rate Qair and the actual air-fuel ratio AFreal by the following equation.
[0042]
Gmain = Qair / AFreal (1)
In step 507, the actual fuel specific gravity Gfuel is calculated from the actual fuel amount (weight flow rate) Gmain and the fuel injection amount (volume flow rate) Qmain by the following equation.
[0043]
Gfuel = Gmain / Qmain (2)
In step 508, a specific map is retrieved from the actual fuel specific gravity Gfuel and the fuel temperature TF to calculate the fuel specific gravity in the standard state (atmospheric pressure, 20 ° C.), that is, the standard fuel specific gravity Gstd. That is, when the fuel temperature TF is higher than the fuel temperature (20 ° C.) in the standard state, a value corrected to increase the actual fuel specific gravity Gfuel, and the fuel temperature TF is lower than the fuel temperature (20 ° C.) in the standard state. In some cases, the standard fuel specific gravity Gstd is a value obtained by correcting the actual fuel specific gravity Gfuel to be smaller.
[0044]
Returning to FIG. 2, in step 2, the content of aromatic hydrocarbons in the fuel is calculated by searching a table having the contents shown in FIG. 8 from the standard fuel specific gravity Gstd. The relationship between the standard fuel specific gravity Gstd and the aromatic hydrocarbon content needs to be matched to the commercial fuel. That is, the characteristics shown in FIG. 8 are determined based on the results of the market research shown in FIG. 20, and the aromatic hydrocarbon content increases as the standard fuel specific gravity Gstd of the fuel used increases.
[0045]
In step 3 of FIG. 2, the particulate collection amount SUMPM to the filter 42 is calculated. Here, the intake pressure, the intake air temperature, the engine speed and the fuel injection amount are detected, the amount of particulate generation per unit time is calculated based on these, and the integrated value is used as the particulate collection of the filter 42. Since a calculation method for obtaining the amount is described in Japanese Patent Application Laid-Open No. 11-13455, in this embodiment, correction according to the aromatic hydrocarbon content in the fuel is applied to the calculation method.
[0046]
The calculation of the particulate collection amount SUMPM will be described with reference to FIG. In FIG. 9 (subroutine of step 3 in FIG. 2), in step 601, the engine speed Ne, the fuel injection amount Qmain, the intake pressure Pa detected by the intake pressure sensor 27, the intake air temperature Ta detected by the temperature sensor 28, Aromatic hydrocarbon content (calculated in step 2 of FIG. 2) is read.
[0047]
In step 602 of FIG. 9, a map having the contents shown in FIG. 10 is searched from the engine speed Ne and the fuel injection amount Qmain to calculate the particulate generation amount ΔPM0 per unit time for the reference fuel in the standard state. Although characteristics are not shown in FIG. 10, as described in Japanese Patent Application Laid-Open No. 11-13455, the operation region using the engine speed Ne and the fuel injection amount Qmain as parameters is divided into several small regions. The amount of particulates generated per unit time with respect to the reference fuel may be measured in advance by a bench test for each small region under the state.
[0048]
In step 603 of FIG. 9, the atmospheric correction coefficient K1 is obtained by searching a map containing the content of FIG. 11 from the intake pressure Pa and intake air temperature Ta, and in step 604 of FIG. 9, the content is calculated from the aromatic hydrocarbon content in the fuel. The fuel property correction coefficient K2 in the standard state is calculated by searching the map having the content of 12, and the particulate generation amount ΔPM per unit time of the used fuel is calculated by the following equation in Step 605 of FIG.
[0049]
ΔPM = ΔPM0 × K1 × K2 (3)
Here, the characteristics of FIG. 11 are described in JP-A-11-13455. That is, the atmospheric correction coefficient K1 is a value that increases as the intake air temperature increases as the intake pressure is the same as shown in FIG. 11, and increases as the intake pressure decreases as the intake air temperature is the same. This is a correction for obtaining a value when the intake pressure or the intake air temperature deviates from the standard state because the particulate generation amount per unit time changes from the value in the standard state. For example, when the intake air temperature is high, the density of the intake air, that is, the air becomes low, resulting in a decrease in the amount of oxygen and an increase in the amount of particulates generated. Further, when the intake pressure is high, the density of intake air, that is, air, increases, the amount of oxygen increases, the combustion becomes active, and the generation amount of particulates decreases.
[0050]
On the other hand, the fuel property correction coefficient K2 in the standard state is as shown in FIG. Here, a fuel having the lowest aromatic hydrocarbon content is selected from among commercially available fuels as a reference fuel. For this reason, K2 becomes the lowest 1.0 when the aromatic hydrocarbon content A is relative to the reference fuel, and becomes larger than 1.0 as the aromatic hydrocarbon content increases from the reference fuel. That is, the above expression (3) is an expression that corrects the particulate generation amount per unit time (ΔPM0 × K1) with respect to the reference fuel so that it increases as the aromatic hydrocarbon content in the fuel increases from the reference fuel. is there. This corresponds to an increase in the amount of particulates generated per unit time in the exhaust gas as the aromatic hydrocarbon content in the fuel is higher than that of the reference fuel.
[0051]
The method for selecting the reference fuel is not limited to this, and a fuel having an intermediate aromatic hydrocarbon content can be selected from commercially available fuels. At this time, when the aromatic hydrocarbon content in the fuel is higher than that of the reference fuel, K2 becomes a value exceeding 1.0, whereas when the aromatic hydrocarbon content in the fuel is lower than that of the reference fuel, K2 is a value less than 1.0.
[0052]
In step 606 of FIG. 9, the particulate collection amount SUMPM of the filter 42 is calculated by the following equation using the particulate generation amount ΔPM per unit time of the used fuel.
[0053]
SUMPM = SUMMPM (previous) + ΔPM (4)
However, SUMPM (previous): previous value of SUMPM,
Equation (4) integrates the particulate generation amount ΔPM per unit time of the fuel used. When the particulate collection amount SUMPM is calculated in this way, returning to FIG. 2, the NOx accumulation amount and the sulfur accumulation amount of the NOx trap catalyst 43 are calculated in steps 4 and 5. These may be estimated from the integrated value of the engine rotational speed Ne as described in, for example, Japanese Patent Publication No. 2600492.
[0054]
Steps 6 to 9 in FIG. 2 look at the filter regeneration processing flag (reg flag), the sulfur poisoning release processing flag (desul flag), the enrichment processing flag (sp flag), and the filter erosion prevention processing flag (rec flag).
[0055]
If all these four flags are zero, the process proceeds to step 10 in FIG. 2 to compare the particulate collection amount SUMPM with the predetermined amount PM1. When the particulate collection amount SUMPM exceeds the predetermined amount PM1, it is determined that the regeneration time of the filter 42 is reached, and the routine proceeds to step 13 in FIG. 2 to set the filter regeneration processing flag (reg flag) = 1 and terminate the current processing. .
[0056]
When the particulate collection amount SUMPM is equal to or less than the predetermined amount PM1, the process proceeds to step 11 in FIG. 2, and the sulfur accumulation amount is compared with the predetermined amount SM1. When the sulfur accumulation amount exceeds the predetermined amount SM1, it is determined that the sulfur poisoning cancellation is necessary, and the routine proceeds to step 14 in FIG. 2, and the sulfur poisoning cancellation processing flag (desul flag) = 1 is set and the current processing is ended. .
[0057]
When the sulfur accumulation amount is equal to or less than the predetermined amount SM1, the process proceeds to step 12 in FIG. 2, and the NOx accumulation amount is compared with the predetermined amount NOx1. When the NOx accumulation amount exceeds the predetermined amount NOx1, it is determined that the regeneration timing of the NOx trap catalyst 43 has come, and the routine proceeds to step 15 in FIG. 2 to set the enrichment processing flag (sp flag) = 1 and terminate the current processing.
[0058]
When the particulate collection amount SUMPM, the sulfur accumulation amount, and the NOx accumulation amount are equal to or less than the predetermined amounts PM1, SM1, and NOx1, respectively, the current process is terminated.
[0059]
When the filter regeneration process flag (reg flag) = 1 in step 13 in FIG. 2, the process proceeds from step 6 in FIG. 2 to the filter regeneration process shown in FIG. 3 from the next time, and in step 14 in FIG. 2) from step 7 in FIG. 2 to the regeneration process of the NOx trap catalyst 43 shown in FIG. 4, and when the enrichment flag (sp flag) = 1 in step 15 in FIG. From the next time, the process proceeds from step 8 in FIG. 2 to the enrichment process shown in FIG.
[0060]
Hereinafter, description will be made in the order of FIG. 3, FIG. 4, and FIG.
[0061]
The flow of FIG. 3 is for performing the regeneration process of the filter 42. However, FIG. 3 shows the flow of control, and unlike FIG. 2, it is not executed at regular intervals.
[0062]
In step 101 in FIG. 3, the target excess air ratio λm during the filter regeneration process is determined by searching a table having the contents shown in FIG. 13 from the aromatic hydrocarbon content in the fuel (calculated in step 2 in FIG. 2). calculate. The target excess air ratio λm during the filter regeneration process is basically a value slightly larger than 1.0 (that is, a value slightly leaner than the theoretical air-fuel ratio). In this embodiment, as shown in FIG. The larger the content of the group hydrocarbon, the higher the value so that the value becomes leaner. This is to avoid an increase in the amount of particulate generation during the filter regeneration process by increasing the excess air ratio (making the air-fuel ratio lean) as the aromatic hydrocarbon content increases.
[0063]
In step 102 in FIG. 3, control is performed so that the actual excess air ratio λ of the exhaust gas becomes the target value λm. For example, a target intake air amount (see FIG. 14) is calculated from the target value λm and the fuel injection amount Qmain, and the opening of the intake throttle valve 18 is controlled so that this target intake air amount is obtained.
[0064]
Here, the actual excess air ratio λ may be obtained from the actual air-fuel ratio AFreal (obtained in step 504 in FIG. 7) and the theoretical air-fuel ratio (= 14.7) by the following equation.
[0065]
λ = AFreal / 14.7 (5)
In steps 103 and 104 of FIG. 3, the filter temperature detected by the temperature sensor 29 is compared with a predetermined filter temperature upper limit value T1 and filter temperature lower limit value T2 during filter regeneration processing. Here, T1 and T2 may be constant values. The filter regeneration processing time can be shortened by setting T1 and T2 higher as the aromatic hydrocarbon content increases.
[0066]
When the filter temperature is equal to or higher than the upper limit value T1, in order to return the filter temperature to less than the upper limit value T1, the routine proceeds to step 111 in FIG. 3 to decrease the post injection amount by a predetermined amount, whereas the filter temperature is lower than the lower limit value T2. In order to set the filter temperature to a value exceeding the lower limit value T2, the routine proceeds to step 112 in FIG. 3 to increase the post injection amount by a predetermined amount. For example, the unit post injection amount shown in FIG. 15 is increased or decreased according to the operating state (engine rotation speed, fuel injection amount).
[0067]
Since the actual excess air ratio λ of the exhaust gas deviates from the target value λm due to the increase or decrease of the post injection amount, the actual excess air ratio λ is adjusted by controlling the opening degree of the intake throttle valve 18, and the change to the filter temperature is suppressed to achieve the target. The value λm is achieved.
[0068]
When the filter temperature is less than the upper limit value T1 and exceeds the lower limit value T2, the process proceeds to step 105 in FIG. 3 to maintain the current post injection.
[0069]
In step 106 of FIG. 3, the elapsed time t1 from when the filter regeneration processing flag (reg flag) = 1 is compared with the reference time t dpf reg. The reference time is for determining whether or not the regeneration of the filter 42 has been completed. The reference time may be a constant value. When t1 has not reached the reference time, the current process is terminated. At this time, the particulates collected by the filter 42 are burned and removed.
[0070]
At the timing when t1 reaches the reference time, it is determined that the regeneration of the filter 42 is completed, and the process proceeds to step 107 in FIG. 3 to stop the post injection and stop the heating of the filter 42 further.
[0071]
In steps 108 and 109 of FIG. 3, in order to prepare for the next regeneration process of the filter 42, the filter regeneration process flag (reg flag) = 0 and the particulate collection amount SUMPM = 0.
[0072]
In this way, although the regeneration process of the filter 42 is completed, the excess air ratio of the exhaust when the particulate unburned residue in the filter 42 is present is set to a value at the time of normal lean combustion (for example, a value exceeding 1.4). If the value is suddenly increased to (), the unburned particulates burn at once, and the filter 42 may be melted. For this reason, in step 110 of FIG. 3, in order to perform the melting prevention process of the filter 42, the melting prevention process flag (rec flag) = 1 is set.
[0073]
The flow of FIG. 4 is for performing the sulfur poisoning release processing of the NOx trap catalyst 43. This flow also shows the flow of control, and unlike FIG. 2, it is not executed at regular intervals.
[0074]
In FIG. 4, in step 201, the actual excess air ratio λ of the exhaust gas is controlled so as to be 1.0 corresponding to the theoretical air-fuel ratio (abbreviated as “stoichi” in the figure). For example, a target intake air amount is calculated by searching a map (see FIG. 16) of a target intake air amount from which the theoretical air-fuel ratio is obtained from the fuel injection amount Qmain and the engine speed Ne so that the target intake air amount can be obtained. Then, the opening degree of the intake throttle valve 18 is controlled.
[0075]
In step 202 of FIG. 4, the temperature of the NOx trap catalyst 43 detected by the temperature sensor 30 is compared with a predetermined value T3. T3 is a lower limit value of the temperature required for desorbing sulfur from the NOx trap catalyst 43. For example, when a Ba-based NOx trap catalyst is used, it is necessary to set the temperature to 600 ° C. or higher in the atmosphere from the stoichiometric air-fuel ratio to the rich air-fuel ratio, so T3 is set to 600 ° C. or higher.
[0076]
When the temperature of the NOx trap catalyst 43 is less than the predetermined value T3, the routine proceeds to step 209 in FIG. 4 and post injection is performed to raise the temperature of the NOx trap catalyst 43 to T3 or higher. Although the actual excess air ratio λ of the exhaust gas fluctuates due to the post injection, the target excess air ratio λm and the target catalyst temperature (600 ° C. or more) are adjusted by adjusting the intake air amount again using the intake throttle valve 18 in step 201. Realize.
[0077]
On the other hand, when the temperature of the NOx trap catalyst 43 is equal to or higher than the predetermined value T3, the routine proceeds from step 202 of FIG. 4 to step 203, and the elapsed time t2 and the reference time after the sulfur poisoning release processing flag (desul flag) = 1. Compare t desul. The reference time is for determining whether or not the sulfur poisoning release is completed. The reference time may be a constant value. If t2 has not reached the reference time, the current process is terminated.
[0078]
When t2 reaches the reference time, it is determined that the sulfur poisoning release has been completed at the target excess air ratio and the target catalyst temperature, and the routine proceeds to steps 204, 205, and 206 in FIG. The sulfur poisoning release processing flag (desul flag) = 0 and the sulfur accumulation amount = 0.
[0079]
In steps 207 and 208 of FIG. 4, even if the enrichment process flag (sp flag) = 1, the enrichment process flag = 0 and the NOx accumulation amount = 0. This is because the NOx trap catalyst 43 is regenerated when the NOx trap catalyst 43 is exposed to an atmosphere having a stoichiometric air-fuel ratio for a long time in order to release sulfur poisoning. That is, when the request for regenerating the NOx trap catalyst 43 has been issued, if the sulfur poisoning release is performed, the regeneration of the NOx trap catalyst 43 is also performed at the same time.
[0080]
However, although the sulfur poisoning release processing is completed, if the filter 42 has unburned particulates under such a high temperature condition, the excess air ratio of the exhaust is set to a value during normal lean combustion (for example, 1. If the value is suddenly increased to a value exceeding 4), the unburned particulates may burn at once and the filter 42 may be melted. Therefore, in this case, the step of FIG. In step S209, the melting prevention processing flag (rec flag) is set to 1.
[0081]
FIG. 5 is for performing the enrichment process. In FIG. 5, at step 301, the target excess air ratio λm (a value slightly richer than the theoretical air-fuel ratio) during regeneration of the NOx trap catalyst 43 is set. Control is performed using the intake throttle valve 18 so that λ coincides with the target value λm.
[0082]
In step 302 of FIG. 5, the elapsed time t3 from when the enrichment process flag (sp flag) = 1 is compared with the reference time t spike. The reference time is for determining whether or not the regeneration end time of the NOx trap catalyst 43 has come. The reference time may be a constant value. If t3 has not reached the reference time, the current process is terminated.
[0083]
When t3 reaches the reference time, it is determined that the regeneration of the NOx trap catalyst 43 has ended, and in order to cancel the enrichment process, the process proceeds to Steps 303 and 304 in FIG. 5 to set the enrichment process flag (sp flag) = 0. In order to prepare for the next enrichment process, NOx accumulation amount = 0.
[0084]
In step 110 of FIG. 3 or step 209 of FIG. 4, when the melt damage prevention process flag (rec flag) = 1 of the filter 42 is set, the process proceeds from step 9 to FIG. 6 in FIG.
[0085]
The flow in FIG. 6 is for performing a filter melting prevention process. This flow also shows the flow of control, and unlike FIG. 2, it is not executed at regular intervals.
[0086]
In FIG. 6, in step 401, the filter temperature detected by the temperature sensor 29 is read.
[0087]
When the melting prevention flag (rec flag) = 1, since the filter 42 or the NOx trap catalyst 43 is immediately after the regeneration process or immediately after the high load operation, the temperature of the filter 42 is very high. . In this state, the unburned or collected particulates burn at once, and the actual excess air ratio λ of the exhaust gas is set to the target excess air ratio λm (for example, λm ≦ 1.4) so that the filter 42 does not melt. Control. For example, the target intake air amount (see FIG. 17) is calculated from the target excess air ratio λm and the fuel injection amount Qmain, and the opening of the intake throttle valve 18 is controlled so that this target intake air amount is obtained.
[0088]
In step 403 of FIG. 6, the filter temperature is compared with a predetermined value T4. T4 is a temperature at which there is no risk of sudden combustion (oxidation) of the particulates in the filter 42. T4 is a constant value. While the filter temperature exceeds T4, the current process is terminated.
[0089]
When the filter temperature is equal to or lower than T4, even if the oxygen concentration in the exhaust gas flowing through the filter 42 is equivalent to the atmosphere, the filter 42 can be prevented from being melted. Therefore, the process proceeds to Steps 404 and 405 in FIG. The control of the rate is stopped and the melting prevention processing flag (rec flag) = 0 is set.
[0090]
Here, the operation of the present embodiment will be described.
[0091]
As the aromatic hydrocarbon content in the fuel increases from the reference fuel, the amount of particulates generated per unit time in the exhaust gas increases, and the amount of particulates collected in the filter 42 tends to increase. In accordance with this trend, according to this embodiment (the invention described in claim 2), the amount of particulates generated per unit time with respect to the reference fuel is calculated, and the correlation value of the aromatic hydrocarbon content in the fuel is calculated. A value (ΔPM0 × K1 × K2) obtained by correcting the calculated value (ΔPM0 × K1) of the particulate generation amount per unit time with respect to the reference fuel is used as the predicted value of the particulate generation amount. Therefore, even if a fuel different from the aromatic hydrocarbon content in the reference fuel is used, the amount of particulates collected in the filter 42 by the fuel is calculated. Can be performed with high accuracy. In this way, when the amount of particulates collected in the filter can be calculated with high accuracy, the determination accuracy of the regeneration timing of the filter 42 is improved.
[0092]
There is a fuel specific gravity in the correlation value of the aromatic hydrocarbon content in the fuel, and according to this embodiment (the invention described in claim 4), the particulate matter per unit time with respect to the reference fuel is based on this fuel specific gravity. Since the calculated value of the generated amount is corrected as the predicted value of the generated amount of particulates, it is not necessary to directly determine the aromatic hydrocarbon content in the fuel, which results in the generated amount of particulates per unit time. Can be obtained easily.
[0093]
In the present embodiment (the invention described in claim 5), three detection means (an air flow meter 23 as an intake air amount detection means, a control unit 21 as a fuel supply amount detection means, and an air-fuel ratio as an actual air-fuel ratio detection means) The actual fuel specific gravity Gfuel is calculated based on the sensor 26), and the actual fuel specific gravity Gfuel is used as the fuel specific gravity used when correcting the amount of particulates generated per unit time with respect to the reference fuel. When the engine is already provided, it is not necessary to provide a new detecting means, and the fuel specific gravity can be calculated without increasing the cost.
[0094]
The fuel specific gravity is greatly influenced by the fuel temperature, and the fuel specific gravity decreases as the fuel temperature increases. For this reason, when the calculated value of the particulate generation amount per unit time with respect to the reference fuel is corrected based on the actual fuel specific gravity Gfuel, the corrected value differs depending on the fuel temperature. For this reason, if the calculated value of the amount of particulates generated per unit time with respect to the reference fuel is corrected correctly when the fuel temperature is in the standard state (atmospheric pressure, 20 ° C.), the fuel temperature deviating from the standard state Sometimes, the calculated value of the amount of particulates generated per unit time with respect to the reference fuel cannot be corrected correctly, but according to the present embodiment (the invention according to claim 6), the detected intake air amount Qair, fuel injection The actual fuel specific gravity Gfuel is calculated based on the amount (fuel supply amount) Qmain and the actual air-fuel ratio AFreal, and the standard fuel specific gravity Gstd which is the fuel specific gravity in the standard state is calculated from the actual fuel temperature TF and the actual fuel specific gravity Gfuel. This standard fuel specific gravity Gstd is used to correct the calculated value of the amount of particulates generated per unit time with respect to the reference fuel. Since the specific gravity, the calculated value of the amount of generated particulates per unit time irrespective of the fuel temperature can be accurately corrected.
[0095]
According to the present embodiment (the invention described in claim 8), the calculated value of the amount of particulates generated per unit time with respect to the reference fuel is increased so as to indicate that the aromatic hydrocarbon content in the fuel increases. Therefore, even if the aromatic hydrocarbon content in the fuel increases, the calculated value of the particulate generation amount per unit time with respect to the reference fuel can be accurately corrected.
[0096]
According to the present embodiment (the invention described in claim 10), the filter temperature (specifically, the filter temperature upper limit value T1 and the filter temperature lower limit value T2) when performing the regeneration process of the filter 42 is changed to the fragrance in the fuel. By increasing the content of the group hydrocarbon when the content of the group hydrocarbon is higher than that of the reference fuel, it is possible to avoid an increase in the time required for the regeneration process of the filter 42.
[0097]
According to the present embodiment (invention of claim 12), the temperature of the filter 42 is raised to the target temperature when the regeneration process of the filter 42 is performed, and then the target value λm of the excess air ratio is changed to the aromatic hydrocarbon in the fuel. As the content is higher than the reference fuel, the leaner side is set (see FIG. 13). Therefore, when the filter 42 is regenerated, the temperature of the filter 42 is raised to the target temperature λm, and then the amount of particulate generated in the exhaust gas is increased. You can avoid increasing.
[0098]
Next, what can be considered as another embodiment will be described.
1. The higher the content of aromatic hydrocarbons in the fuel, the earlier the amount of particulates collected by the filter 42 reaches a predetermined value. Therefore, even when the aromatic hydrocarbon content in the fuel is high, if the interval at which the filter 42 is regenerated is the same as when the aromatic hydrocarbon content in the fuel is low, the filter 42 The amount of curate collected becomes too large, and the filter 42 may be overheated when the filter regeneration process is performed thereafter. By shortening as the hydrogen content increases (the invention according to claim 9), overheating of the filter 42 can be avoided.
2. When the temperature of the filter 42 is raised during the regeneration process of the filter 42, the target value λm of the excess air ratio is made leaner as the aromatic hydrocarbon content in the fuel is larger than that of the reference fuel (invoicing). (Invention of Item 11) When the temperature of the filter 42 is raised during the regeneration process of the filter 42, it is possible to avoid an increase in the amount of particulates generated in the exhaust gas.
3. In the embodiment, the case where the sulfur poisoning of the NOx trap catalyst 43 is released by performing combustion at the stoichiometric air-fuel ratio has been described. However, the present invention is not limited to this. For example, by periodically repeating the excess air ratio between combustion at the stoichiometric air-fuel ratio (or rich combustion) and combustion at the lean air-fuel ratio, the sulfur poisoning release of the NOx trap catalyst 43 and the regeneration of the filter 42 are simultaneously performed. It is known that it can be done. In this case, as the aromatic hydrocarbon content is higher than that of the reference fuel, the ratio of combustion at the lean air-fuel ratio is set to be larger than a predetermined reference value for the reference fuel (claim 13). In the case of a fuel having a higher aromatic hydrocarbon content than the reference fuel, an increase in the amount of particulates generated in the exhaust can be avoided.
4). In the embodiment, the correlation value of the aromatic hydrocarbon content in the fuel is detected, and the amount of particulates generated per unit time with respect to the reference fuel based on the detected correlation value of the aromatic hydrocarbon content in the fuel. In the above description, the value obtained by correcting the calculated value is used as the predicted value of the amount of particulates generated per unit time for the fuel used. However, the correlation value of the aromatic hydrocarbon content in the fuel is detected, and this aromatic value is detected. The amount of particulates generated per unit time for the fuel used may be predicted based on the correlation value of the group hydrocarbon content (the invention according to claim 1).
5. In the embodiment, the case where the correlation value of the aromatic hydrocarbon content in the fuel is the fuel specific gravity has been described. However, the relationship shown in FIG. 18 between the fuel specific gravity and the cetane number, and the cetane number and the viscosity Since there is a relationship shown in FIG. 21, the cetane number or the viscosity can be used as the correlation value of the aromatic hydrocarbon content in the fuel (the invention according to claim 16).
[0099]
Finally, the function of the particulate generation amount calculation means according to claim 2 is based on steps 602, 603 and 605 in FIG. 9, and the function of the aromatic hydrocarbon content correlation value detection means is based on FIG. The function of the prediction means is performed by steps 604 and 605 in FIG.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a flowchart for explaining a main routine.
FIG. 3 is a flowchart for explaining filter regeneration processing;
FIG. 4 is a flowchart for explaining sulfur poisoning release processing;
FIG. 5 is a flowchart for explaining enrichment processing;
FIG. 6 is a flowchart for explaining filter melting prevention processing;
FIG. 7 is a flowchart for explaining calculation of fuel specific gravity.
FIG. 8 is a characteristic diagram showing the relationship between standard fuel specific gravity and aromatic hydrocarbon content.
FIG. 9 is a flowchart for explaining calculation of a particulate collection amount.
FIG. 10 is a characteristic diagram of particulate generation amount per unit time with respect to a reference fuel in a standard state.
FIG. 11 is a characteristic diagram of atmospheric correction coefficients.
FIG. 12 is a characteristic diagram of a fuel property correction coefficient.
FIG. 13 is a characteristic diagram showing the relationship between the aromatic hydrocarbon content and the target excess air ratio during the filter regeneration process.
FIG. 14 is a characteristic diagram of a target intake air amount for operation at a target excess air ratio during filter regeneration processing.
FIG. 15 is a characteristic diagram of a unit post injection amount.
FIG. 16 is a characteristic diagram of a target intake air amount for operation at a target excess air ratio during sulfur poisoning release processing.
FIG. 17 is a characteristic diagram of a target intake air amount for operation at a target excess air ratio at the time of filter melting prevention processing.
FIG. 18 is a characteristic diagram showing the relationship between the standard fuel specific gravity of light oil and the cetane number.
FIG. 19 is a characteristic diagram showing the relationship between standard fuel specific gravity and evaporability (10% distillation point) of light oil.
FIG. 20 is a characteristic diagram showing the relationship between the standard fuel specific gravity of light oil and the aromatic hydrocarbon component content.
FIG. 21 is a characteristic diagram showing the relationship between the viscosity of light oil and the cetane number.
[Explanation of symbols]
15 Three-way valve (solenoid valve)
18 Inlet throttle valve
21 Control unit
23 Air flow meter (intake air volume detection means)
25 Temperature sensor (Fuel temperature detection means)
26 Air-fuel ratio sensor (actual air-fuel ratio detection means)
29 Temperature sensor
42 Filter

Claims (16)

It has a filter that collects particulates in the exhaust,
A diesel engine that calculates the amount of particulates collected in the filter based on the amount of particulates generated, and performs filter regeneration processing when the calculated value of the amount of particulates collected reaches a predetermined value. In the exhaust purification device of
An aromatic hydrocarbon content correlation value detecting means for detecting a correlation value of the aromatic hydrocarbon content in the fuel;
An exhaust emission control device for a diesel engine, comprising: particulate generation amount predicting means for predicting the generation amount of the particulates based on the correlation value of the aromatic hydrocarbon content. It has a filter that collects particulates in the exhaust,
The amount of particulates generated is predicted, the amount of particulates collected in the filter is calculated based on the predicted value of the amount of particulates generated, and the calculated value of the amount of particulate collected becomes a predetermined value. In the exhaust gas purification device for a diesel engine that performs the regeneration process of the filter,
Particulate generation amount calculating means for calculating the amount of particulate generation with respect to the reference fuel;
An aromatic hydrocarbon content correlation value detecting means for detecting a correlation value of the aromatic hydrocarbon content in the fuel;
Particulate generation amount using a value obtained by correcting the calculated value of the particulate generation amount relative to the reference fuel based on the detected correlation value of the aromatic hydrocarbon content in the fuel as a predicted value of the particulate generation amount An exhaust emission control device for a diesel engine, comprising: a predicting unit. The exhaust gas purification apparatus for a diesel engine according to claim 1, wherein the correlation value of the aromatic hydrocarbon content in the fuel is fuel specific gravity. The exhaust gas purification apparatus for a diesel engine according to claim 2, wherein the correlation value of the aromatic hydrocarbon content in the fuel is a fuel specific gravity. The fuel specific gravity detecting means for detecting the fuel specific gravity,
An intake air amount detection means for detecting an intake air amount;
Fuel supply amount detection means for detecting the fuel supply amount;
An actual air-fuel ratio detecting means for detecting the actual air-fuel ratio of the exhaust;
An actual fuel specific gravity calculating means for calculating an actual fuel specific gravity based on the detected intake air amount, fuel supply amount, and actual air-fuel ratio, and using the actual fuel specific gravity as it is as the fuel specific gravity. The exhaust emission control device for a diesel engine according to claim 4, A fuel temperature detecting means for detecting the fuel temperature;
The fuel specific gravity detecting means for detecting the fuel specific gravity,
An intake air amount detection means for detecting an intake air amount;
Fuel supply amount detection means for detecting the fuel supply amount;
An actual air-fuel ratio detecting means for detecting the actual air-fuel ratio of the exhaust;
Actual fuel specific gravity calculating means for calculating the actual fuel specific gravity based on the detected intake air amount, fuel supply amount and actual air-fuel ratio;
A standard fuel specific gravity calculating means for calculating a standard fuel specific gravity, which is a fuel specific gravity in a standard state, from the fuel temperature and the actual fuel specific gravity, and using the standard fuel specific gravity as the fuel specific gravity is provided. Item 5. An exhaust emission control device for a diesel engine according to Item 4. Means for detecting the fuel injection period; and means for detecting the fuel injection pressure;
The exhaust purification device for a diesel engine according to claim 6, wherein the fuel supply amount is calculated from the detected fuel injection period and fuel injection pressure. The exhaust emission control device for a diesel engine according to claim 2, wherein the calculated value of the amount of particulates generated relative to the reference fuel is corrected so as to increase as the aromatic hydrocarbon content in the fuel increases. . The exhaust purification device for a diesel engine according to claim 2, wherein the interval for performing the regeneration processing of the filter is shortened as the content of the aromatic hydrocarbon in the fuel increases. 3. The exhaust purification device for a diesel engine according to claim 2, wherein the filter temperature at the time of performing the regeneration process of the filter is increased as the aromatic hydrocarbon content in the fuel is higher than that of the reference fuel. . When the temperature of the filter is raised when performing the regeneration process of the filter, the target value of the excess air ratio is made leaner as the aromatic hydrocarbon content in the fuel is larger than the reference fuel. The exhaust emission control device for a diesel engine according to claim 2. After the temperature of the filter is raised to the target temperature when performing the regeneration process of the filter, the target value of the excess air ratio is made leaner as the aromatic hydrocarbon content in the fuel is larger than the reference fuel. The exhaust emission control device for a diesel engine according to claim 2. A filter that collects particulates in the exhaust;
While trapping NOx in the exhaust during lean combustion, the trapped NOx is desorbed at the time of combustion at the stoichiometric air-fuel ratio or rich combustion, and the desorbed NOx is reduced and purified using a reducing component in the exhaust NOx trap catalyst
In the exhaust gas purification apparatus for a diesel engine, the sulfur poisoning release process of the NOx trap catalyst and the regeneration process of the filter are simultaneously performed by repeating lean combustion and combustion at a stoichiometric air-fuel ratio.
An aromatic hydrocarbon content correlation value detecting means for detecting a correlation value of the aromatic hydrocarbon content in the fuel;
Providing a ratio increasing means for increasing the lean combustion ratio such that the correlation value of the aromatic hydrocarbon content in the fuel indicates that the aromatic hydrocarbon content in the fuel is higher than that of the reference fuel. An exhaust emission control device for diesel engines. The exhaust gas purification apparatus for a diesel engine according to claim 13, wherein the correlation value of the aromatic hydrocarbon content in the fuel is fuel specific gravity. The exhaust purification device for a diesel engine according to claim 1 or 2, wherein the amount of generated particulates is an amount per unit time. The diesel engine exhaust gas purification apparatus according to any one of claims 1, 2, and 13, wherein the correlation value of the aromatic hydrocarbon content in the fuel is a cetane number or a viscosity.

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