JP4554894B2 - Exhaust gas purification method and exhaust gas purification system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification system that includes a continuously regenerating diesel particulate filter and purifies engine exhaust gas.
[0002]
[Prior art]
The amount of particulate matter (PM: particulate matter: hereinafter referred to as PM) emitted from diesel engines, together with nitrogen oxide (hereinafter referred to as NOx), carbon monoxide (hereinafter referred to as CO), hydrocarbon (HC), etc. Regulations have been strengthened year by year, and with the strengthening regulations, it has become impossible to respond only by improving the engine. Therefore, a technology has been developed that collects PM discharged from the engine with a filter called a diesel particulate filter (DPF) and reduces the amount of PM discharged to the outside. Yes.
[0003]
The DPF that directly collects PM includes ceramic monolith honeycomb wall flow type filters and fiber type filters made of ceramic or metal fibers. Exhaust gas purification using these DPFs Similar to other exhaust gas purification systems, the system is installed in the middle of the exhaust passage of the engine and purifies exhaust gas generated by the engine.
[0004]
When the filter collects PM, the exhaust pressure (exhaust gas pressure) rises in proportion to the amount collected, so it is necessary to regenerate the DPF by removing the collected PM by burning or the like. Various methods have been proposed for this regeneration method, including an electric heater heating type, a burner heating type, and a backwash type.
[0005]
However, when these regeneration methods are used, PM is burned by receiving energy supply from the outside, which leads to deterioration of fuel consumption, and control during regeneration is difficult, and PM collection, PM combustion (DPF) There is a problem that the system becomes large and complicated, such as requiring a two-system DPF system that alternately performs (regeneration).
[0006]
In order to solve this problem, a technique has been proposed in which a catalyst is used to lower the oxidation temperature of PM, and the DPF is regenerated by oxidizing the PM with exhaust heat from the engine without receiving energy from the outside. In this case, since DPF regeneration is basically continuous, it is called a continuous regeneration type DPF system. However, these systems become a simpler one-system DPF system, and regeneration control is also simplified. There is an advantage that
[0007]
NO shown as an example in FIG.₂Regenerative DPF system 1X is NO₂This system oxidizes PM with (nitrogen dioxide) to regenerate DPF. An oxidation catalyst 3Aa is disposed upstream of a normal wall flow filter 3Ab to oxidize NO (nitrogen monoxide) in the exhaust gas. Therefore, most of the NOx in the exhaust gas downstream of the oxidation catalyst 3Aa is NO.₂become. This NO₂Then, the PM collected by the downstream filter 3Ab is oxidized to produce CO.₂(Carbon dioxide) and PM is removed. This NO₂Is O₂Since the energy barrier is smaller, the PM oxidation temperature (DPF regeneration temperature) is lowered, so that PM combustion is continuously generated by the thermal energy in the exhaust gas without supplying energy from the outside.
[0008]
In FIG. 11, E is a diesel engine, 2 is an exhaust passage, 4 is a fuel pump system, 5 is an electronic control box, 7 is a battery, 8 is a silencer, and 9 is a fuel tank.
[0009]
Further, FIG. 12 shows NO in FIG.₂An improved system 1Y of a regenerative DPF system is shown. In this improved system 1Y, the porous catalyst coat layer 31 of the oxidation catalyst 32A is applied to the porous wall surface 30 of the wall flow filter 3B to oxidize NO and generate NO.₂PM is oxidized on the wall surface of the wall flow filter 3B to simplify the system.
[0010]
Then, in FIG. 13, a porous catalyst coat layer 31 of an oxidation catalyst 32A and a PM oxidation catalyst 32B such as an oxide is applied to the porous wall surface 30 of the wall flow filter 3C, and the PM accumulated in the filter 3C is reduced at a low temperature. 1 shows a system 1Z that burns and continuously regenerates.
[0011]
These DPF systems with a catalyst are composed of a catalyst and NO.₂This is a system that realizes continuous regeneration of PM by lowering the PM oxidation start exhaust temperature than the normal filter by the oxidation reaction of PM.
[0012]
However, even if the PM oxidation start exhaust temperature is lowered, an exhaust temperature of about 350 ° C. is still necessary, so the exhaust temperature is low under idling and low-load engine operating conditions, so PM oxidation and DPF self-regeneration Does not occur.
[0013]
Therefore, if engine operating conditions with low exhaust temperature such as idling or low load continue, PM will not be oxidized even if PM accumulates, resulting in increased exhaust pressure, worse fuel consumption, and engine stop Troubles such as this may occur.
[0014]
Therefore, in these continuous regeneration type DPF systems, it is necessary to regenerate the DPF by calculating the PM accumulation amount in the filter from the engine operating conditions or estimating the PM accumulation amount from the filter pressure loss corresponding to the PM accumulation amount. When the conditions are set and this DPF regeneration requirement is satisfied, the exhaust gas temperature is forcibly raised, and the accumulated PM is forcibly burned and removed to perform DPF regeneration control.
[0015]
In this DPF regeneration control, even under engine operating conditions such as idle and low load, an electronically controlled fuel injection system such as a common rail is used to increase the exhaust temperature by delaying injection timing, multistage injection, etc. Then, the exhaust temperature is increased by combustion of fuel supplied by post injection or in-pipe injection to the oxidation catalyst in the front stage of the DPF, and the collected PM is burned and removed to regenerate the DPF. ing.
[0016]
For example, in an exhaust gas purifying apparatus for an engine having an upstream oxidation catalyst, a downstream DPF, and an electronically controlled accumulator, when the pressure sensor detects that the amount of collected PM exceeds a predetermined amount, the cylinder Immediately before the exhaust valve of the (cylinder) is closed, control is performed to inject fuel into the cylinder, and the injected unburned fuel is oxidized and burned by the upstream oxidation catalyst, and the exhaust gas temperature is raised to a high temperature. It is proposed to regenerate the DPF by incinerating PM collected in the downstream DPF with the exhaust gas (see Patent Document 1).
[0017]
[Patent Document 1]
JP 08-42326 A (page 2)
[0018]
[Problems to be solved by the invention]
However, since an exhaust temperature of about 350 ° C. is necessary for regeneration of the DPF, the temperature rise range of the exhaust gas becomes large under idling and low-load engine operating conditions, and a large amount of exhaust gas is heated to a high temperature. Therefore, there is a problem that the fuel consumption is greatly deteriorated.
[0019]
The present invention has been made to solve the above-described problems, and its purpose is to perform carbonization by, for example, post-injection of a main injection device or injection from a hydrocarbon addition device installed in an exhaust pipe in a continuous regeneration type DPF. Provided is an exhaust gas purification method and an exhaust gas purification system capable of performing PM regeneration combustion even at a low exhaust temperature by utilizing hydrogen at a low temperature oxidation reaction by a catalyst of a hydrocarbon by supplying hydrogen to a DPF with a catalyst. There is.
[0020]
[Means for Solving the Problems]
  An exhaust gas purification method for achieving the above object is provided in an exhaust passage of an internal combustion engine.Oxidation catalyst or oxidation catalyst and PM oxidation catalyst supportedA method of burning and removing PM collected in a DPF with a catalyst,A first step of adding an integrated value of the superheat time when the exhaust temperature is equal to or higher than the hydrocarbon oxidation combustion temperature, and maintaining an integrated value of the superheat time when the exhaust temperature is lower than the hydrocarbon oxidation combustion temperature; A second step of determining whether the exhaust temperature is equal to or lower than a balance point temperature, which is a lower limit value at which PM is burned and removed, when the integrated value of the superheat time in the first step is equal to or greater than a predetermined time; Is below the balance point temperature, hydrocarbons are added to the exhaust gas upstream of the DPF with catalyst, and the PM collected in the DPF with catalyst is burned using a low temperature oxidation reaction of hydrocarbons Perform the third step to removeIt is characterized by that.
[0021]
This hydrocarbon is a fuel used for an internal combustion engine or the like, and is a general hydrocarbon such as gasoline, light oil, kerosene, A heavy oil or the like.
[0022]
According to this exhaust gas purification method, hydrocarbons added to the exhaust gas are adsorbed in the vicinity of the catalyst of the catalyst-attached DPF, and this gas-adsorbed hydrocarbon has a very large catalytic activity and is in a low temperature range (for example, about 200 Since it reacts with the catalyst from about (° C.), the PM collected in the DPF with catalyst can be burned and removed from the low temperature region using the reaction heat as an ignition source.
[0023]
Therefore, the combustion start temperature for PM regeneration can be lowered, PM can be burned and removed even at a low exhaust temperature, the number of forced exhaust temperature increases performed for DPF regeneration is reduced, and the exhaust temperature increase Since the temperature range can be remarkably lowered, fuel can be saved and fuel consumption deterioration due to DPF regeneration can be prevented.
[0025]
  With this configuration, on the upstream side of the DPF with catalystProvide an oxidation catalystProvide hydrocarbon addition means just before the DPF with catalystIn caseBy setting the predetermined temperature as the balance point temperature, the hydrocarbons are supplied only when the supplied hydrocarbons can contribute to the oxidative combustion of the collected PM. Therefore, it is possible to avoid supplying unnecessary hydrocarbons.
[0028]
  In the above exhaust gas purification method,The hydrocarbon addition means includes the catalyst-attached DPF.It comprises means for adding hydrocarbons into the exhaust gas by injection into the exhaust passage from a hydrocarbon addition device provided on the upstream side. Thereby, hydrocarbons can be easily supplied to the upstream side of the DPF with catalyst.
[0029]
  thisIn the means for injecting into the exhaust passage from the hydrocarbon addition device, the fuel supplied to the engine may be used, or the hydrocarbon may be prepared in a separate tank.
[0030]
  An exhaust gas purification system is also provided in the exhaust pipe of an internal combustion engine.An exhaust gas purification system comprising an oxidation catalyst or a DPF with a catalyst carrying an oxidation catalyst and a PM oxidation catalyst, and comprising a hydrocarbon addition control means for controlling the amount of hydrocarbons supplied to the DPF with a catalyst. When the temperature is higher than the hydrocarbon oxidation combustion temperature, an integrated value of the super warm time is added, and when the temperature is lower than the hydrocarbon oxidation combustion temperature, a first step of maintaining the integrated value of the super warm time; A second step of determining whether the exhaust temperature is equal to or lower than a balance point temperature, which is a lower limit value at which PM is burned and removed, when the integrated value of the superheat time in the process reaches a predetermined time or more; When the hydrocarbon is added to the exhaust gas upstream of the DPF with catalyst when the temperature is lower than the point temperature, the PM collected in the DPF with catalyst using the low-temperature oxidation reaction of hydrocarbons Performing a third step of burning and removingIt is configured to perform control.
[0031]
According to this exhaust gas purification system, the hydrocarbon added to the exhaust gas is adsorbed in the vicinity of the catalyst of the DPF with catalyst and reacts with the catalyst from a low temperature range. Since PM collected in the DPF can be burned and removed from the low temperature region, fuel consumption deterioration due to DPF regeneration can be prevented.
[0032]
  In addition, as this predetermined temperature,There is a balance point temperature,Further, as the DPF with a catalyst, there are a DPF which is used in a continuous regeneration type DPF, and which supports an oxidation catalyst, a DPF which supports an oxidation catalyst and a PM oxidation catalyst, and the like. Oxidation catalyst)Provide.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, regarding an exhaust gas purification method and an exhaust gas purification system according to an embodiment of the present invention, a continuous regeneration type DPF (diesel particulate filter) composed of a combination of an oxidation catalyst (DOC) and a filter with catalyst (CSF) is provided. The exhaust gas purification system provided will be described as an example with reference to the drawings.
[0034]
  In FIG.Of reference form1 shows a configuration of an exhaust gas purification system 1. In this exhaust gas purification system 1, a continuous regeneration type DPF 3 is provided in an exhaust passage (exhaust pipe) 2 connected to an exhaust manifold of a diesel engine E. The continuous regeneration type DPF 3 includes an oxidation catalyst 3Aa on the upstream side and a filter with a catalyst 3Ab on the downstream side.
[0035]
The oxidation catalyst 3Aa is formed by supporting an oxidation catalyst such as platinum (Pt) on a carrier such as a porous ceramic honeycomb structure, and the catalyst-attached filter 3Ab is formed at the inlet of the channel of the porous ceramic honeycomb. And a monolith honeycomb wall flow type filter in which the outlets are alternately sealed. A catalyst such as platinum or cerium oxide is supported on the filter. In this filter with catalyst 3Ab, PM (particulate matter) in the exhaust gas G is collected (trapped) by a porous ceramic wall.
[0036]
FIG. 4 shows the external shape of the filter with catalyst 3Ab, FIG. 5 shows an enlarged view of the inlet portion where the state of sealing can be seen, and FIG. 6 shows the detailed structure of the wall cross section of the filter. As shown in FIG. 6, a coat layer 31 carrying an oxidation catalyst 32A such as platinum or a PM oxidation catalyst 32B such as a metal oxide is provided on the wall surface of a catalyst carrier 30 such as alumina, and these oxidation catalyst 32A and PM oxidation are provided. The catalyst 32B is highly dispersed and supported on the surface of the catalyst carrier 30.
[0037]
In order to estimate the amount of PM deposited on the filter with catalyst 3Ab, as shown in FIG. 1, the DPF inlet exhaust pressure sensor 51, the DPF outlet exhaust pressure sensor 52, and the DPF inlet exhaust temperature are placed before and after the continuous regeneration type DPF 3. A sensor 53 and a DPF outlet exhaust temperature sensor 54 are provided.
[0038]
The output values of these sensors, together with the output values of load sensors, rotation sensors, etc., are control devices (electronic control box: ECU: engine control unit) that perform general control of the operation of the engine E and regeneration control of the filter 3Ab with catalyst. ) 5 and the control signal output from the control device 5 controls the electronically controlled fuel injection system 41 such as the common rail of the engine E, the exhaust gas purification system 1 and the like.
[0039]
This control device 5 also has information such as ON / OFF of the PTO switch, ON / OFF of the neutral switch, vehicle speed, coolant temperature, engine speed, load (accelerator opening), etc. for engine operation. Entered.
[0040]
  Also,Another helpfulIn the embodiment, as shown in FIG. 2, a fuel injection valve 42, which is a hydrocarbon addition device, is installed in the exhaust passage 2 upstream of the oxidation catalyst 3Aa. Also,According to the present inventionIn the embodiment, the fuel injection valve 43 which is a hydrocarbon addition device is installed on the downstream side of the oxidation catalyst 3Aa and on the upstream side of the filter with catalyst 3Ab. The fuel injection valves 42 and 43 may use the fuel in the fuel tank of the engine E, but may supply hydrocarbons from a separate tank.
[0041]
Next, combustion removal of PM collected by the filter with catalyst 3Ab in the present invention will be described.
[0042]
As shown in FIG. 9 (a), when hydrocarbon (HC) F is not adsorbed in the vicinity of the catalysts 32A and 32B, the solid PM approaches a distance that causes a catalytic reaction with the solid catalytic metal 32A. And oxidation reaction hardly occurs. Therefore, the PM regeneration combustion start temperature is almost the same as the DPF that does not carry the catalysts 32A and 32B.
[0043]
On the other hand, as shown in FIG. 9B, when hydrocarbon (HC) F is adsorbed in the vicinity of the catalysts 32A and 32B, the gaseous hydrocarbon F reacts with the catalyst metal 32A from the low temperature range. The oxidation of PM can be started using the reaction heat as an ignition source, and the PM regeneration combustion start temperature can be greatly reduced.
[0044]
FIG. 10 shows the simulated gas test results showing the PM combustion rate (g / s) with respect to the exhaust temperature (° C.) when hydrocarbons are adsorbed (solid line) A and when hydrocarbons are not adsorbed (dashed line). . In the case of adsorbing hydrocarbons (solid line) A, it can be seen that the PM regeneration combustion rate increases from the low temperature range, and the regeneration start temperature is lowered.
[0045]
Therefore, if the exhaust gas is supplied in a low exhaust temperature state where hydrocarbons do not burn, and the hydrocarbon F is adsorbed to the filter with catalyst 3Ab, when the exhaust temperature Tg becomes higher than the hydrocarbon oxidation combustion temperature T1, PM can be removed by combustion. Further, when the exhaust gas temperature Tg is higher than the hydrocarbon oxidation combustion temperature T1, PM can be burned and removed by supplying hydrocarbon F to the filter with catalyst 3Ab.
[0046]
In the present invention, by utilizing the fact that the start temperature of PM oxidation removal decreases when this hydrocarbon is adsorbed in the vicinity of the catalyst, the PM trapped in the filter with catalyst 3Ab is burned even at a low exhaust temperature. While removing, the exhaust gas can be purified.
[0047]
Next, an exhaust gas purification method in these exhaust gas purification systems will be described.
[0048]
  Be helpfulIn the exhaust gas purification system 1 of the present embodiment, the electronically controlled fuel injection is performed when the DPF inlet exhaust temperature Tg is lower than the activation temperature of the oxidation catalyst 3Aa (oxidation catalyst light-off temperature: about 200 ° C.) T2. The system 41 performs post-injection to supply hydrocarbon F into the exhaust gas in the exhaust passage 2 and adsorb it to the filter with catalyst 3Ab and the PM accumulated in the filter with catalyst 3Ab.
[0049]
  Also,Another helpfulIn the embodiment, when the engine operating condition is that the DPF inlet exhaust temperature Tg is lower than the activation temperature T2 of the oxidation catalyst 3Aa, the hydrocarbon F is injected from the fuel injection valve 42, and the hydrocarbon is discharged into the exhaust gas in the exhaust passage 2. Supply F with catalystfilterAfter passing the oxidation catalyst 3Aa arranged on the upstream side of 3Ab, it is adsorbed by the filter 3Ab with catalyst and the PM accumulated in the filter 3Ab with catalyst.
[0050]
  In this reference form,When the DPF inlet exhaust temperature Tg is higher than the activation temperature T2 of the oxidation catalyst 3Aa, the hydrocarbon F supplied in the exhaust gas is oxidized by the oxidation catalyst 3Aa and is not supplied to the catalyst-equipped filter 3Ab. In order to avoid this, hydrocarbon F is supplied when the DPF inlet exhaust temperature Tg is lower than the activation temperature T2 of the oxidation catalyst 3Aa.
[0051]
  AndAccording to the present inventionIn the embodiment, when the engine operating condition is that the DPF inlet exhaust temperature Tg is lower than the balance point temperature (about 350 ° C.) T3, the hydrocarbon F is injected from the fuel injection valve 43 to enter the hydrocarbon into the exhaust passage 2. Supply F with catalystfilterWithout passing through the oxidation catalyst 3Aa disposed upstream of the 3Ab, the catalyst-attached filter 3Ab and the PM accumulated in the catalyst-attached filter 3Ab are adsorbed.
[0052]
  thisAccording to the present inventionIn the case of the embodiment, since the hydrocarbon addition device 43 is disposed downstream of the oxidation catalyst 3Aa, there is no fear of being consumed by the oxidation catalyst 3Aa. However, when the balance point temperature is equal to or higher than T3, the PM is oxidized and burned away without using the hydrocarbon F as a combustion aid, so the hydrocarbon F is not supplied.
[0054]
Next, a method for supplying these hydrocarbons will be described in more detail.
[0055]
  Be helpfulFIG. 7 shows a control flow of the hydrocarbon supply in the form. When this HC supply control starts with the start of the engine, in step S11, normal operation is performed for a predetermined time (a time related to the time interval for determining regeneration start) ΔTa, and in this normal operation, in step S12. It is determined whether or not the exhaust gas temperature Tg is lower than the hydrocarbon oxidation combustion temperature (HC oxidation combustion temperature: about 200 ° C.) T1, and if it is equal to or higher than the hydrocarbon oxidation combustion temperature T1, the super warm time ta is counted in step S13. If it is small, the super warm time ta is not counted.
[0056]
Then, in the next step S14, it is checked whether or not the counted superheat time ta has passed the predetermined time t1, and if not, the process returns to step S11, and until it has elapsed, step S11 to step S14. repeat.
[0057]
This is because, when the time ta when the exhaust gas temperature Tg is equal to or higher than the hydrocarbon oxidation combustion temperature T1 becomes equal to or higher than the predetermined time t1, HC adhering to the PM is carbonized and becomes dry soot and is not oxidized at a low temperature. This is because it is necessary to attach new hydrocarbon F to PM. The predetermined time t1 is obtained in advance by experiments.
[0058]
If it is determined in step S14 that the superheat time ta is equal to or longer than the predetermined time t1, whether or not the exhaust temperature Tg is equal to or lower than the activation temperature (about 200 ° C.) T2 of the oxidation catalyst 3Aa in the next step S15. Judgment is made. If it is not below in this determination, the process returns to step S11. That is, if the exhaust temperature Tg is higher than the activation temperature T2 of the oxidation catalyst 3Aa, the hydrocarbon F supplied by the oxidation catalyst 3Aa is oxidized.
If it is determined in step S15 that the exhaust gas temperature Tg is equal to or lower than the activation temperature T2 of the oxidation catalyst 3Aa, the process goes to step S16 to calculate and set the addition set time t2. The setting of the addition setting time t2 is performed in order to control the control for supplying a predetermined hydrocarbon addition amount into the exhaust pipe 2 with the addition time tc on the assumption that the injection amount per time is constant. In step S16, the super warm time ta is reset (ta = 0).
[0059]
The addition time tc is calculated from map data using the engine speed and the load as variables because the amount of hydrocarbons discharged from the engine varies depending on the engine speed and the load. That is, since the hydrocarbon concentration is generally high at a low load, the addition set time t2 is short, and at high load, the hydrocarbon concentration is generally low and the addition set time t2 is long.
[0060]
In the next step S17, it is determined whether or not the exhaust gas temperature Tg is equal to or lower than the activation temperature T2 of the oxidation catalyst 3Aa. If this determination is not below, the operation without adding the hydrocarbon F in step S19 is performed until the following is reached, and the process returns to step S17. If the determination is negative in step S17, the exhaust pipe is determined in step S18. The operation of adding hydrocarbon F in 2 is performed, and the addition time tc is counted.
[0061]
  In step S20, this addition timetcDetermines whether or not the set addition time t2 has been exceeded. If not, the process goes to step S17, and steps S17 to S20 are repeated until the set time is exceeded. If the addition time tc exceeds the set addition time t2 in step S20, the addition time is determined in step S21.tcReset (tc= 0) and the like, and the process returns to step S11.
[0062]
By the control according to the control flow of FIG. 7 described above, the process returns to step S11 through any one of steps S11 to S14, steps S11 to S15, and steps S11 to S21, and interrupts step S22 by turning off the engine key. Repeat until this occurs. Then, upon occurrence of an interrupt, an end operation such as storage of the state at the time of occurrence of the interrupt is performed in step S23, and this control flow is terminated.
[0063]
  Also,Implementation of the present inventionFIG. 8 shows a control flow of the hydrocarbon supply in the form. In the control flow of FIG. 8, the determination value T2 in the determination of the exhaust temperature in steps S15 and S17 of the control flow of FIG. 7 is changed from the activation temperature T2 of the oxidation catalyst 3Aa to the balance point temperature (about 350 ° C.) T3. Is.
[0064]
  AndBe helpfulIn the embodiment, when the exhaust temperature Tg is equal to or lower than the activation temperature T2 of the oxidation catalyst 3Aa, the hydrocarbon F is supplied to the filter 3Ab with catalyst and adsorbed, so that the exhaust temperature Tg becomes the hydrocarbon oxidation combustion temperature T1. At this time, the hydrocarbon F starts to be oxidized by the catalytic action of the oxidation catalyst 32A, and the PM is also oxidized by the catalytic action of the oxidation catalyst 32A and the PM oxidation catalyst 32B by the reaction heat, so that the combustion can be removed.
[0065]
When the exhaust temperature Tg is equal to or lower than the activation temperature T2 of the oxidation catalyst 3Aa and equal to or higher than the hydrocarbon oxidation combustion temperature T1, the hydrocarbon F is attached to the catalyst by supplying the hydrocarbon F to the catalyst-equipped filter 3Ab. Since oxidation is performed by the oxidation catalyst 32A of the filter 3Ab, PM is also oxidized by the catalytic action by this reaction heat, and is removed by combustion.
[0066]
  Also,According to the present inventionIn the case of the embodiment, when the exhaust gas temperature Tg is equal to or lower than the balance point temperature T3, the hydrocarbon F is supplied to the filter with catalyst 3Ab, whereby the hydrocarbon F starts to be oxidized by the oxidation catalyst 32A of the filter with catalyst 3Ab. Since PM is also oxidized by the catalytic action by this reaction heat, it can be removed by combustion.
[0067]
The control flow in FIGS. 7 and 8 is a hydrocarbon supply control, and this control is a control for lowering the combustion start temperature of the PM collected in the filter with catalyst 3Ab. This is shown as being performed in parallel with the reproduction control.
[0068]
Therefore, in these controls, hydrocarbons are supplied according to the control flow of FIG. 7 or FIG. 8, and the amount of PM accumulated in the DPF is determined according to the regeneration control flow of DPF different from these control flows. When it is detected by the differential pressure before and after the DPF or the calculated PM accumulation amount that it exceeds the predetermined value, forced exhaust temperature rise control is performed by post injection, multistage injection, intake throttling, EGR control, etc. , DPF regeneration is performed.
[0069]
In the present invention, the PM collected in the DPF can be burned and removed even at a low exhaust temperature by supplying hydrocarbons to the filter with catalyst. Therefore, the number of forced exhaust temperature increase controls and the temperature increase range at that time are As a result, the deterioration of fuel consumption accompanying DPF regeneration can be suppressed.
[0070]
【The invention's effect】
As described above, according to the exhaust gas purification method and the exhaust gas purification system of the present invention, the gas-adsorbed hydrocarbon has a very large catalytic activity, and the catalyst is removed from a low temperature range (for example, about 200 ° C.). Utilizing the reaction, hydrocarbon is added to the exhaust gas and adsorbed in the vicinity of the catalyst of the DPF with catalyst, and the reaction heat of the hydrocarbon that starts combustion at a low exhaust temperature is used as an ignition source. PM collected by the DPF with catalyst can be burned and removed.
[0071]
Accordingly, the exhaust temperature at the start of PM combustion for DPF regeneration can be lowered, PM regeneration combustion can be performed from a low exhaust temperature, and PM is combusted and removed even at a low exhaust temperature. The increase in temperature can be avoided, the interval of DPF regeneration control is extended, the number of forced exhaust temperature increase control performed for DPF regeneration is decreased, and the temperature increase range in this exhaust temperature increase control is significantly reduced. Therefore, fuel consumption can be reduced.
[0072]
And when supplying hydrocarbons directly to the DPF with catalyst without passing through an oxidation catalyst, when the exhaust temperature is equal to or higher than the balance point temperature, the supplied hydrocarbons are oxidized and burned without being supplied. By supplying hydrocarbons only when they can contribute to the above, it is possible to avoid unnecessary hydrocarbon supply.
[Brief description of the drawings]
[Figure 1]Be helpfulIt is a block diagram of the exhaust gas purification system of a form.
[Figure 2]Another helpfulIt is a figure which shows arrangement | positioning of the hydrocarbon supply apparatus of the exhaust gas purification system of a form.
[Fig. 3]According to the present inventionIt is a figure which shows arrangement | positioning of the hydrocarbon supply apparatus of the exhaust-gas purification system of embodiment.
FIG. 4 is a view showing the outer shape of a monolith honeycomb wall flow type filter with a catalyst.
FIG. 5 is an enlarged view of the inlet portion of FIG. 4;
FIG. 6 is a view showing a wall cross section of a filter with a catalyst.
[Fig. 7]Be helpfulIt is a figure which shows an example of the control flow of the supply of the hydrocarbon in a form.
[Fig. 8]According to the present inventionIt is a figure which shows an example of the control flow of the supply of the hydrocarbon in embodiment.
FIG. 9 is an explanatory view of PM combustion removal temperature decrease due to hydrocarbon adsorption in the present invention, (a) is a diagram schematically showing the state of the wall surface when hydrocarbons are not adsorbed; (A) is a figure which shows typically the state of the wall surface at the time of adsorb | sucking a hydrocarbon.
FIG. 10 is a graph showing the relationship between PM combustion speed and exhaust temperature when hydrocarbons are supplied and when hydrocarbons are not supplied.
FIG. 11 is a system configuration diagram showing an example of a conventional exhaust gas purification system.
FIG. 12 is a system configuration diagram showing another example of a conventional exhaust gas purification system.
FIG. 13 is a system configuration diagram showing another example of a conventional exhaust gas purification system.
[Explanation of symbols]
    1 Exhaust gas purification system
    2 Exhaust passage
    3 Continuous regeneration type DPF
    3Aa oxidation catalyst
    Filter with 3Ab catalyst
    E Diesel engine
    G exhaust gas
    Gc Purified exhaust gas
    Tg Exhaust temperature
    T1 Hydrocarbon oxidation combustion temperature
    T2 oxidation catalyst activation temperature (predetermined temperature)
    T3 Balance point temperature (predetermined temperature)

Claims (2)

A method of burning and removing PM collected in an oxidation catalyst provided in an exhaust passage of an internal combustion engine or a DPF with a catalyst carrying an oxidation catalyst and a PM oxidation catalyst ,
A first step of adding an integrated value of the superheat time when the exhaust temperature is equal to or higher than the hydrocarbon oxidation combustion temperature, and maintaining an integrated value of the superheat time when the exhaust temperature is lower than the hydrocarbon oxidation combustion temperature; A second step of determining whether the exhaust temperature is equal to or lower than a balance point temperature, which is a lower limit value at which PM is burned and removed, when the integrated value of the superheat time in the first step is equal to or greater than a predetermined time;
When the exhaust gas temperature is equal to or lower than the balance point temperature, the hydrocarbons are added to the exhaust gas upstream of the catalyzed DPF, and the PM trapped in the catalyzed DPF using the low temperature oxidation reaction of hydrocarbons An exhaust gas purification method characterized by performing a third step of burning and removing the gas. Exhaust gas purification comprising an oxidation catalyst or a DPF with a catalyst carrying an oxidation catalyst and a PM oxidation catalyst in an exhaust pipe of an internal combustion engine , and a hydrocarbon addition control means for controlling the amount of hydrocarbons supplied to the DPF with a catalyst In the system,
The hydrocarbon addition control means is
A first step of adding an integrated value of the superheat time when the exhaust temperature is equal to or higher than the hydrocarbon oxidation combustion temperature, and maintaining an integrated value of the superheat time when the exhaust temperature is lower than the hydrocarbon oxidation combustion temperature; A second step of determining whether the exhaust temperature is equal to or lower than a balance point temperature that is a lower limit value at which PM is burned and removed when the integrated value of the superheat time in the first step is equal to or greater than a predetermined time;
When the exhaust gas temperature is equal to or lower than the balance point temperature, the hydrocarbons are added to the exhaust gas upstream of the catalyzed DPF, and the PM trapped in the catalyzed DPF using the low temperature oxidation reaction of hydrocarbons An exhaust gas purification system that performs control to perform a third step of burning and removing gas.

Images