JP2003155917A - Exhaust emission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control method which dispenses with a forced-heating means including an electric heater and a fuel supplying device, reduces cost, and reliably avoids any over-trapping condition of a particulate filter in a short time. SOLUTION: In the exhaust emission control method in which the particulate in the exhaust gas 3 is trapped by the catalyst regeneration type particulate filter 6 equipped in the middle of an exhaust pipe 4 with the exhaust gas 3 distributed therein, and burned and removed, an injection pattern is employed, in which the post injection is performed at the non-ignition timing behind the top dead center of compression continuous to the main injection in an operational range of low exhaust temperature in which the natural combustion of the particulate is difficult. The fuel added in the exhaust gas 3 in an unburned state by the post injection is oxidized on an oxidation catalyst of the particulate filter 6, and the catalyst floor temperature rises by the reaction heat to burn the trapped particulate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification method.

[0002]

2. Description of the Related Art Particulate Matter (Particulate Matter) emitted from a diesel engine is
Soot composed of carbonaceous matter and SO composed of high boiling hydrocarbon components
It is composed of F component (Soluble Organic Fraction) as a main component and further contains a trace amount of sulfate (mist-like sulfuric acid component), but as a measure for reducing this type of particulates, exhaust gas is used. It has been conventionally practiced to equip a particulate filter in the middle of an exhaust pipe through which gas flows.

This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow passages partitioned in a grid pattern are alternately plugged, and the inlets are plugged. The outlets of the non-flow passages are configured to be plugged so that only the exhaust gas that has permeated the porous thin wall defining each flow passage is discharged to the downstream side.

Since the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate the particulate filter, but in normal diesel engine operating conditions, there are few opportunities to obtain a high exhaust gas temperature that allows particulates to self-combust.
For example, a catalyst regeneration type particulate filter in which an oxidation catalyst formed by adding an appropriate amount of a rare earth element such as cerium to alumina supported by platinum is integrally supported is being put into practical use.

That is, if such a catalyst regeneration type particulate filter is adopted, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible to do it.

However, even when such a catalyst regenerating type particulate filter is adopted, the oxidation catalyst carried by the particulate filter has an active temperature range, which is lower than the active lower limit temperature. If the operating condition at the exhaust temperature continues (generally, the region where the exhaust temperature is low spreads to the operating region of light load), the oxidation catalyst will not be activated and the particulates will not be burned and removed well. For this reason, it is being studied to attach an electric heater, a fuel addition device, or the like to perform forced heating.

[0007]

However, when an electric heater, a fuel addition device or the like is attached, an electric system for energizing the electric heater or a fuel system for supplying fuel to the fuel addition device. Etc. must be newly laid, which complicates the system for regenerating the particulate filter and raises the cost. On the other hand, the forced heating by an electric heater or a fuel addition device is required. If not performed, the particulate filter will fall into the over-capture state in a short period of time, adversely affecting the engine performance due to an increase in exhaust pressure, or a large amount of accumulated particulates will burn rapidly and the particulate filter will melt. There was a risk of loss.

The present invention has been made in view of the above-mentioned circumstances, and the cost of the particulate filter is reduced in a short period of time while the forced heating means such as the electric heater and the fuel addition device is unnecessary. The purpose is to be able to surely avoid falling into an over-collection state.

[0009]

According to the present invention, there is provided an exhaust gas purification method for collecting and burning off particulates in exhaust gas by means of a catalyst regeneration type particulate filter installed in the middle of an exhaust pipe through which exhaust gas flows. In a low exhaust temperature operating region where it is difficult to spontaneously burn particulates, an injection pattern is adopted in which post injection is performed at a non-ignition timing later than the compression top dead center following the main injection. It is characterized in that the fuel added unburned in the gas undergoes an oxidation reaction on the oxidation catalyst of the particulate filter, and the heat of the reaction raises the catalyst bed temperature to burn the collected particulates. .

Thus, in this way, even in an operating region where the exhaust temperature is low, where it is difficult to spontaneously burn particulates, the fuel added unburned in the exhaust gas by post injection is particulated. Oxidation reaction occurs on the oxidation catalyst of the filter to generate reaction heat, and as a result of the reaction heat maintaining the catalyst bed temperature at or above the activity lower limit temperature of the oxidation catalyst, the particulates trapped in the particulate filter become the fuel. Due to the oxidation reaction of oxygen, oxygen will be slowly burned spontaneously in an oxygen-deficient atmosphere, and the particulate filter will be well regenerated while avoiding the erosion of the particulate filter due to the rapid high temperature combustion of the particulate. Can be achieved.

Further, according to the present invention, after injection is performed at a combustible timing immediately after the main injection in an operating region where the exhaust temperature is extremely low where the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter is difficult, and Adopts an injection pattern that performs post injection at a non-ignition timing later than compression top dead center following after injection, burning fuel at a timing when it is difficult to convert to output by after injection to raise the exhaust temperature, while exhausting by post injection It is also possible to oxidize the fuel added to the gas in an unburned state on the oxidation catalyst of the particulate filter and raise the catalyst bed temperature by the heat of reaction to burn the collected particulates.

Further, according to the present invention, the injection pattern for performing the after injection at a combustible timing immediately after the main injection in an operating region where the exhaust temperature is extremely low, in which the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter is difficult. After burning the fuel at a timing that is difficult to be converted to output by the after injection, the exhaust temperature is raised, and after the exhaust temperature rises, the catalyst bed temperature reaches a temperature at which the oxidation reaction of the fuel is possible, and then the after injection is performed. Following this, the injection pattern is switched to post-injection at the timing of non-ignition later than the compression top dead center, and the fuel added as unburned in the exhaust gas by the post-injection is oxidized on the oxidation catalyst of the particulate filter. It is also possible to raise the catalyst bed temperature by the reaction heat and burn the collected particulates.

The post injection start timing is preferably set within a crank angle range of 70 to 150 °, and the after injection start timing is set within a crank angle range of 0 to 30 °. Preferably.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 show an example of an embodiment for carrying out the present invention. In the exhaust gas purification method of the present embodiment, as shown in FIG. 1, from a diesel engine 1 (internal combustion engine) of an automobile to an exhaust manifold. An example is shown in which a catalyst regeneration type particulate filter 6 having an oxidation catalyst integrally supported therein is housed in a muffler 5 of an exhaust pipe 4 in which exhaust gas 3 discharged via 2 flows. The filter case 7 holding the particulate filter 6 forms an outer cylinder of the muffler 5.

That is, the front and rear inlet pipes 8 and outlet pipes 9 are provided.
A particulate filter 6 as shown in an enlarged scale in FIG. 2 is housed inside a filter case 7 provided with, and this particulate filter 6 has a porous honeycomb structure made of ceramics and has a lattice structure. The inlets of the respective flow paths 6a which are partitioned in a circular pattern are alternately plugged, and for the flow paths 6a whose inlets are not plugged, the outlets thereof are plugged, and the respective flow paths 6a are partitioned. Only the exhaust gas 3 that has permeated through the porous thin wall 6b is discharged to the downstream side.

The inlet pipe 8 of the filter case 7
Is equipped with a pressure sensor 10 for measuring the inlet gas pressure as an excessive collection determination means, and a detection signal 10a of the pressure sensor 10 is supplied to an engine control computer (ECU: Electron).
ic control unit), and the fuel injection timing is directed to the fuel injection device 12 that injects fuel into each cylinder of the diesel engine 1 in the control device 11. And a fuel injection signal 12a for instructing the injection amount.

Here, the fuel injection device 12 is composed of a plurality of injectors (not shown) provided for each cylinder, and the solenoid valves of these injectors are appropriately valve-opened controlled by the fuel injection signal 12a. The fuel injection timing (injection start timing and injection end timing) and the injection amount (valve opening time) are controlled appropriately.

Further, the accelerator in the driver's seat (not shown)
An accelerator sensor 13 (load sensor) for detecting the accelerator opening as a load of the diesel engine 1 is provided, and a rotation sensor 14 for detecting the rotation speed is provided at an appropriate position of the diesel engine 1, The accelerator opening signal 13a and the rotation speed signal 14a from the accelerator sensor 13 and the rotation sensor 14 are also input to the control device 11.

In the control device 11, the fuel injection signal 12a in the normal mode is determined based on the accelerator opening signal 13a and the rotation speed signal 14a, while the detection signal 10a from the pressure sensor 10 is used. When an abnormal rise in the inlet gas pressure was confirmed, the normal mode was switched to the forced regeneration mode, and as shown in FIG. 3, following the main injection of fuel performed near the compression top dead center (crank angle 0 °). The fuel injection signal 12a for performing the post injection at the timing of non-ignition later than the compression top dead center is determined. The start timing of the post injection may be set within the range of the crank angle of 70 to 150 °.

That is, when the post injection is performed at the non-ignition timing later than the compression top dead center following the main injection, unburned fuel (mainly HC: hydrocarbons) in the exhaust gas 3 is generated by the post injection. ) Is added, the unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 6, and the catalyst bed temperature rises due to the heat of reaction, so that the particulates in the particulate filter 6 become natural. Will be burned.

A supplementary explanation of the switching of the control unit 11 from the normal mode to the forced regeneration mode will be given below. In this embodiment, the detection signal 10a from the pressure sensor 10 is used to control the inlet gas pressure. While monitoring the measured pressure value, the predicted value of the inlet gas pressure in the current operating state based on the accelerator opening signal 13a and the rotation speed signal 14a is estimated, and the deviation between the predicted value and the measured pressure value is normal. Whether or not it is within the range is determined in the control device 11, and when the residual amount of the particulates collected by the particulate filter 6 (the unburned residue) is large, the particulate filter 6 Since the inlet gas pressure rises beyond the normal range, it is judged that the particulate filter 6 is in the over-capture state, and forced regeneration from the normal mode. Switching to over soil are then to be performed.

FIG. 4 shows an example of a post injection control map in the forced regeneration mode, in which a three-step injection amount is set in accordance with the magnitude of the load in the light load region of a predetermined number of revolutions or more. There is. The unit of the injection amount of post-injection is indicated by the volume of fuel injected by one injection of the injector per cylinder.

Thus, when the operation is performed in the operation region where the exhaust gas temperature is low in which it is difficult to spontaneously burn particulates, the controller 11 switches the combustion injection pattern from the normal mode to the forced regeneration mode, and If an injection pattern is adopted in which post injection is performed at a non-ignition timing later than the compression top dead center subsequent to the injection, the fuel added as unburned in the exhaust gas 3 by the post injection is on the oxidation catalyst of the particulate filter 6. As a result of the reaction heat maintaining the catalyst bed temperature at or above the lower limit of the activity of the oxidation catalyst, the particulates trapped in the particulate filter 6 are oxidized by the oxidation reaction of the fuel. In the oxygen-deficient atmosphere in which oxygen is consumed, it will be slowly combusted spontaneously, and the particulates due to the rapid high temperature combustion of the particulates will While avoiding erosion of Tofiruta 6 it is possible to achieve a good reproduction of the particulate filter 6.

Therefore, according to the above embodiment, only by controlling the fuel injection by the control device 11 as described above, the catalyst bed temperature is appropriately raised and the oxidation catalyst of the particulate filter 6 is maintained in a stable active state. Therefore, it is possible to eliminate the conventional forced heating means such as an electric heater and a fuel addition device to reduce the cost, and the particulate filter 6 may fall into an over-collection state within a short period of time. Can be reliably avoided.

In particular, in the present embodiment, the start timing of post injection is set within the crank angle range of 70 to 150 °. Therefore, by starting the post injection at such a timing, the particulate matter The atmosphere at the time of natural combustion can be surely made into an oxygen-deficient atmosphere, the rapid high temperature combustion of particulates can be suppressed, and the melting loss of the particulate filter 6 can be avoided more reliably.

In addition, an operating region where the exhaust gas temperature is extremely low to such an extent that the fuel thus added by post injection cannot undergo an oxidation reaction on the oxidation catalyst of the particulate filter 6 (for example, an exhaust gas temperature of about 200 ° C. or less is operated). region)
When the operation is performed at 1, it is preferable to use after-injection as described in detail below.

That is, regarding the forced regeneration mode by the controller 11, as shown in FIG. 5, the compression top dead center (crank angle 0
A fuel injection signal 12a is determined such that after-injection is performed at a combustible timing immediately after the main injection of fuel performed in the vicinity of ()) and post-injection is performed at a non-ignition timing later than the compression top dead center subsequent to the after-injection. The after injection may be started at a crank angle in the range of 0 to 30 °.

As a control map for this type of after injection, for example, the one shown in FIG. 6 may be adopted. In the example shown here, the load is applied in a light load region of a predetermined number of revolutions or more. The two-stage injection amount is set according to the size of the.

In short, when the after-injection is performed at a combustible timing immediately after the main injection in this way, the fuel of the after-injection is burned at a timing at which it is difficult to convert the output to the output, thereby lowering the thermal efficiency of the diesel engine 1 and The amount of heat that is not used for power of the heat value of the exhaust gas increases, and the exhaust gas temperature rises. As a result, the temperature required for the fuel added in the subsequent post injection to oxidize on the oxidation catalyst of the particulate filter 6 is increased. Will be secured.

If after-injection is also used in this manner, after-injection is appropriately performed even in an operating region where the exhaust gas temperature is extremely low, in which the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter 6 is difficult. Since the exhaust gas temperature can be raised to satisfactorily cause the post-injection fuel to oxidize on the oxidation catalyst of the particulate filter 6, as in the case of the embodiment of FIGS. It is possible to reliably avoid the possibility that the filter 6 falls into an over-collection state within a short period of time.

Further, in an operating region where the exhaust gas temperature is extremely low, in which the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter 6 is difficult, in addition to the method of using after injection as shown in FIG. As shown in the figure, the exhaust temperature raising mode of the injection pattern that performs only after-injection at the timing when combustion is possible immediately after the main injection is set separately, and the exhaust temperature is raised in this exhaust temperature raising mode to allow the catalyst bed temperature to oxidize fuel After reaching the leveling temperature, the injection pattern is switched to the injection pattern of FIG. 3 in which after injection is performed, post-injection is performed at a timing of non-ignition later than the compression top dead center. The collected fuel is oxidized on the oxidation catalyst of the particulate filter 6, and the catalyst bed temperature is raised by the heat of reaction to burn the collected particulates. It is also possible.

The exhaust gas purifying method of the present invention is not limited to the above-described embodiment, but is not equipped with an excessive trapping determination means such as a pressure sensor, and is used in a light load operation region where the exhaust gas temperature is low. A mode setting that always switches to the forced regeneration mode may be adopted, and when equipped with an excessive collection determination means, the measured value of the inlet gas pressure by the pressure sensor as described above and the current value In addition to the means to determine by comparing with the predicted value in the operating state, the over-collection state is determined by arranging pressure sensors before and after sandwiching the particulate filter and obtaining the differential pressure between the inlet side and the outlet side. Or
It is of course possible to employ means for estimating the excessively trapped state of the particulate filter based on the traveling distance, the driving time, etc., and of course, various changes can be made without departing from the scope of the present invention. Is.

[0034]

According to the above-described exhaust gas purification method of the present invention, various excellent effects as described below can be obtained.

(I) According to the first aspect of the present invention, only by controlling the fuel injection by the control device, the catalyst bed temperature is appropriately raised to stabilize the oxidation catalyst of the particulate filter in a stable active state. Since it can be maintained at a low level, the particulate filter falls into an over-collection state within a short period of time while reducing cost by eliminating the conventional forced heating means such as an electric heater and a fuel addition device. It is possible to surely avoid the fear.

(II) According to the second and third aspects of the present invention, even in an operating region where the exhaust gas temperature is extremely low, in which the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter is difficult, Since the fuel can be burned and the exhaust gas temperature can be raised at a timing when it is difficult to be converted to the output by the after injection, the fuel added by the post injection can be favorably oxidized on the oxidation catalyst of the particulate filter.

(III) According to the invention described in claim 4 of the present invention, by starting the post-injection in the range of the crank angle of 70 to 150 °, the atmosphere during the spontaneous combustion of the particulates is surely deficient in oxygen. The atmosphere can be created, and the rapid high temperature combustion of the particulates can be suppressed to more reliably avoid the melting loss of the particulate filter.

(IV) According to the invention described in claim 5 of the present invention, by starting the after injection in the range of the crank angle of 0 to 30 °, the exhaust gas temperature can be raised more effectively.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.

FIG. 2 is a cross-sectional view showing details of the particulate filter of FIG.

FIG. 3 is a graph showing an example of an injection pattern in which post injection is performed following main injection.

FIG. 4 is a graph showing an example of a post injection control map.

FIG. 5 is a graph showing an example of an injection pattern that also uses after injection.

FIG. 6 is a graph showing an example of a control map for after injection.

FIG. 7 is a graph showing an example of an injection pattern in which only after injection is performed after main injection.

[Explanation of symbols]

3 exhaust gas 4 exhaust pipe 6 Particulate filter 11 Control device 12 Fuel injection device 12a Fuel injection signal

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/24 F01N 3/24 R 3/36 C 3/36 F02D 41/38 B F02D 41/38 41 / 40D 41/40 B01D 53/36 103C (72) Inventor Takashi Takakura 3-1-1 Hinodai, Hino-shi, Tokyo Inside Hino Motors Ltd. (72) Inventor Satoshi Makita 3-1-1 Hinodai, Hino-shi, Tokyo 1 Hino Motors Ltd. F term (reference) 3G090 AA03 CA04 DA03 DA18 DA20 DB07 EA04 3G091 AA02 AA18 AA28 AB02 BA00 BA03 BA04 BA08 BA15 BA19 BA21 CB02 CB03 DA01 DA02 DA04 DB06 DB10 EA01 FB01 FA02 FA02 FA02 FA02 FA02 FA04 FA02 FA04 FA02 FA04 FA02 FA04 FA02 FA02 FA04 FA02 FA02 FA02 FA02 FA02 FA04 FA02 FA02 FA04 FA02 FA04 FC02 GA06 GA20 GA24 GB01X GB10X GB17X HA05 HA14 HA36 HA37 HA42 3G301 HA02 JA24 KA08 MA18 MA23 MA26 NC02 PD14Z PE01Z PF03Z 4D048 AA14 AB01 BA10X BB02 BB14 BD02 DA01 DA02 D A03 DA06 DA07 DA08 DA13 DA20

Claims (5)

[Claims] 1. An exhaust gas purification method for collecting and burning off particulates in exhaust gas by means of a catalyst regeneration type particulate filter installed in the middle of an exhaust pipe through which the exhaust gas flows, the method comprising: In an operating region where the exhaust temperature is low, where combustion is difficult, the injection pattern is adopted in which the post injection is performed at the timing of non-ignition later than the compression top dead center following the main injection. An exhaust gas purification method comprising: oxidizing the collected fuel on an oxidation catalyst of a particulate filter, raising the catalyst bed temperature by the reaction heat, and burning the collected particulates. 2. An after-injection is performed at a combustible timing immediately after the main injection in the operation region where the exhaust gas temperature is extremely low where the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter is difficult, and the compression is performed subsequent to the after-injection. Adopts an injection pattern that performs post injection at a non-ignition timing later than top dead center, and burns fuel at a timing that is difficult to convert to output by after injection to raise the exhaust temperature, while post injection does not burn the exhaust gas into the exhaust gas. The fuel added as is is oxidized on the oxidation catalyst of the particulate filter,
An exhaust gas purification method characterized by raising the catalyst bed temperature by the reaction heat to burn the collected particulates. 3. An injection pattern is adopted in which after injection is performed at a combustible timing immediately after main injection in an operating region where the exhaust gas temperature is extremely low, in which the oxidation reaction of fuel on the oxidation catalyst of the particulate filter is difficult. The fuel is burned at a timing when it is difficult to be converted to the output by the after-injection, and the exhaust temperature is raised, and after this exhaust temperature rise reaches the temperature at which the catalyst bed temperature enables the oxidation reaction of the fuel, compression top death follows the after-injection. Switching to an injection pattern that performs post injection at a timing of non-ignition later than the point, causes the fuel added as unburned in the exhaust gas by the post injection to oxidize on the oxidation catalyst of the particulate filter, and by the reaction heat An exhaust gas purification method characterized by raising the catalyst bed temperature to burn the collected particulates. 4. The crank angle is 7 when the post injection is started.
The exhaust gas purification method according to claim 1, 2 or 3, wherein the exhaust gas purification method is set in a range of 0 to 150 °. 5. The crank angle is set to 0 at the start timing of after injection.
3. A range of up to 30 degrees is set.
The exhaust gas purification method as described in 3 or 4.