JPH0422014Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an exhaust particulate treatment device for an internal combustion engine.

<Conventional technology> In internal combustion engines such as diesel engines,
Since the exhaust gas contains many exhaust particulates whose main component is carbon, in order to prevent environmental pollution, the exhaust particulates are collected in the exhaust passage and burned and removed at predetermined intervals. Such a conventional example is shown in FIG. 3 (see Japanese Patent Laid-Open No. 101523/1983).

That is, the exhaust passage 2 of the diesel engine 1
A trap 3 with a catalyst is installed to collect exhaust particulates. Furthermore, an injection valve 4 is provided in the exhaust passage 2 upstream of the catalytic trap 3 to inject and supply light oil as engine fuel.

Then, when the exhaust gas temperature is 150° C. or higher, light oil is injected and supplied from the injection valve 4 to the exhaust passage 2 for a predetermined period of time at predetermined intervals.

As a result, HC and CO are supplied into the exhaust gas and flow into the catalyst trap 3 together with the exhaust gas. and,
The HC and CO are subjected to an oxidation reaction in the catalyst-equipped trap 3, and the heat of this reaction is used to burn exhaust particulates, thereby regenerating the trap.

Note that 7 is an exhaust component analyzer for detecting exhaust components upstream of the catalyst trap 3, which was installed for the purpose of experimentation and is not used in practice.

<Problems to be solved by the invention> By the way, in such conventional exhaust particulate treatment devices, since light oil contains a large amount of sulfur, it is necessary to use a catalyst with high oxidation activity, which is used in gasoline engines, etc. Since a large amount of sulfate is produced in the catalytic trap, a catalyst with suppressed oxidation activity to some extent was used to prevent environmental pollution. For this reason, in the past, even if HC, CO, etc. were introduced into a trap with a catalyst, the temperature of the exhaust gas discharged from the engine was low (e.g. 250°C to 350°C).
℃ or below), the oxidation reaction by the catalyst is slow to proceed, and exhaust particulates are not burned well, making it difficult to regenerate the trap.

The present invention was developed in view of the above circumstances, and the purpose is to provide an exhaust particulate treatment device for an internal combustion engine that can suppress the generation of sulfate and regenerate the trap even in an operating range where the exhaust temperature is low. do.

<Means for Solving the Problems> For this reason, the present invention provides a trap with a catalyst installed in an exhaust passage to collect particulates in the exhaust gas, a determination means for determining when to regenerate the trap with a catalyst, an exhaust bypass passage that bypasses the exhaust passage on the upstream side of the trap with catalyst; a catalyst device that is interposed in the exhaust bypass passage and includes a catalyst that has higher low-temperature activity than the catalyst; and an exhaust temperature detection means that detects the exhaust temperature. and a combustible material supply device that supplies a combustible material having a higher conversion rate at low temperature than light oil to the catalyst device according to the exhaust temperature when it is determined that it is time to regenerate the trap; A switching valve device that allows the flow to flow through the bypass passage is provided.

<Function> In this way, by supplying combustibles to the catalyst device according to the exhaust temperature, the combustibles are burnt exothermically to raise the exhaust temperature, and the heated exhaust gas is collected in the catalyst trap. The trap is regenerated by burning the exhaust particulates.

<Example> An example of the present invention will be described below based on FIG. 1.

In the figure, a catalyst trap 13 is installed in an exhaust passage 12 of a diesel engine 11 to collect exhaust particulates. The trap 13 with catalyst is
It is formed from a honeycomb-shaped porous member, and the porous member is coated with an oxidation catalyst.

Exhaust passage 12 on the upstream side of trap 13 with catalyst
An exhaust bypass passage 14 is provided to bypass a portion of the exhaust gas, and a catalyst device 15 is interposed on the exhaust bypass passage 14. This catalytic device 15 is equipped with an oxidation catalyst having a higher low-temperature activity than the catalyst in the catalytic trap 13. The exhaust bypass passage 14 upstream of the catalyst device 15 includes the exhaust bypass passage 14.
An on-off valve 16 is provided to open and close the on-off valve 1.
6 is configured to be operated by a control signal from a control device 17, which will be described later.

Exhaust bypass passage 14 upstream of the catalyst device 15
An injection valve 18 is provided for injecting and supplying methanol as a combustible substance, and methanol is supplied under pressure to this injection valve 18 from a methanol tank 19 by a pump 20 . These injection valves 18 and pump 2
0 is configured to be operated by a control signal from the control device 17.

On the inlet side of the catalyst device 15, there is an exhaust temperature sensor 2 as an exhaust temperature detection means for detecting the exhaust temperature.
1 is provided, and the detection signal of the exhaust temperature sensor 21 is input to the control device 17. Exhaust pressure sensors 22 and 23 for detecting exhaust pressure are provided on the inlet and outlet sides of the catalyst trap 13, and detection signals from these exhaust pressure sensors 22 and 23 are input to the control device 17.

The control device 17 includes the exhaust pressure sensors 22 and 23.
When the differential pressure of the catalyst-equipped trap 13 exceeds a predetermined value based on the detection signal, it is determined that it is time to regenerate the trap. When the control device 17 determines that it is time to regenerate the trap, it outputs a control signal to the on-off valve 16 to close the exhaust bypass passage 14.
The circuit is configured to open the circuit. When the control device 17 determines that it is time to regenerate the trap, the control device 17 controls the injection valve 18 based on the detection signal of the exhaust temperature sensor 21.
and the pump 20. Specifically, methanol is injected and supplied to the exhaust bypass passage 14 in accordance with the exhaust temperature when the exhaust temperature is below the activation temperature of the catalyst of the catalyst trap 13 (for example, 400 to 500°C). Here, as shown in FIG. 2, the conversion rate of methanol is higher than the conversion rate of light oil even when the exhaust temperature is low.

Here, the control device 17 constitutes a trap regeneration timing determination means, the control device 17, the injection valve 18, and the pump 20 constitute a combustible material supply device, and the on-off valve 16 and the control device 17 constitute a switching valve device. Configure.

Next, the action will be explained.

When the differential pressure across the catalyst trap 13 is less than a predetermined value, the on-off valve 16 closes the exhaust bypass passage 14 in response to a control signal from the control device 17, and the operation of the injection valve 18 and pump 20 is stopped.

Exhaust particulates discharged from the diesel engine 11 flow into the catalyst trap 13 via the exhaust passage 12 and are collected. At this time, if the exhaust gas temperature is high, the exhaust particulates are collected in the catalyst-equipped trap 13 and burned by the exhaust heat, thereby regenerating the catalyst-equipped trap 13. Furthermore, since the activity of the catalyst trap 13 is low, the production of sulfate can be suppressed. Here, in a device equipped with a catalyst, combustion treatment of exhaust particulates becomes possible when the exhaust temperature is 400 to 500°C or higher.

When the differential pressure across the catalyst trap 13 exceeds a predetermined value, the control device 17 determines that it is time to regenerate the trap, and operates the on-off valve 16 to open the exhaust bypass passage 14. As a result, a part of the exhaust gas flows through the exhaust bypass passage 14 and the exhaust temperature sensor 2
1, the exhaust temperature is detected. Then, when the exhaust gas temperature is below the activation temperature of the catalyst in the catalyst trap 13 (for example, 400 to 500 degrees Celsius), the control device 17 controls the operation of the injection valve 18 and the pump 20 to change the amount of methanol according to the exhaust temperature. Then, it is injected and supplied to the exhaust bypass passage 14.

As a result, methanol is introduced into the catalyst device 15, but since the low-temperature activity of this catalyst is set higher than the low-temperature activity of the catalyst in the catalyst trap 13, the temperature of the exhaust gas discharged from the diesel engine 11 increases. Even if the temperature is relatively low, methanol undergoes an oxidation reaction due to the catalytic action in the catalyst device 15 and generates heat. The heat generated increases the temperature of the exhaust gas flowing through the catalyst device 15, so that relatively high-temperature exhaust gas is introduced from the exhaust bypass passage 14 into the exhaust passage 12 and then flows into the catalyst trap 13.

Therefore, the exhaust particles collected in the catalytic trap 13 are oxidized by the action of the catalyst activated by the heated exhaust gas, so the catalytic trap 13 can be regenerated from an operating range where the exhaust temperature is lower than before. can. In particular, methanol, which has a higher conversion rate at low temperatures than diesel oil, is
Since these two functions work together, the catalyst device 15 can raise the exhaust temperature to the regeneration temperature of the catalyst trap 13 even if the temperature of the exhaust gas discharged from the engine is significantly lower than before. Therefore, the catalytic trap 13 can be regenerated with a simple configuration without providing a heating means such as a burner in an operating range where the exhaust gas temperature is significantly lower than in the past. At this time, since the low-temperature activity of the catalyst in the catalyst trap 13 is low, the production of sulfate can be suppressed.

Here, in the case of the catalyst with high low-temperature activity, the methanol oxidation reaction proceeds at an exhaust temperature of 150 to 200°C or higher, so if the exhaust temperature is 200 to 500°C, for example.
It is preferable to inject and supply methanol to the catalyst device 15 within the range of .

Further, even if methanol is not almost completely oxidized in the catalyst device 15, the remaining methanol is oxidized in the activated catalyst trap 13,
In this case, the temperature increase rate in the catalyst trap 13 is higher than that in the case where methanol is almost completely oxidized in the catalyst device 15.

Note that the methanol injection amount may be substantially constant regardless of the exhaust gas temperature. Further, the mounting position of the exhaust gas temperature sensor 21 is not limited to the upstream side of the catalyst device 15.

<Effects of the invention> As explained above, the present invention uses a catalyst that has higher low-temperature activity than the catalyst in a trap with a catalyst to burn combustibles and raise the exhaust temperature, thereby suppressing the production of sulfate. At the same time, the catalytic trap can be activated by this heated exhaust gas. In particular, we have used a combustible material that has a higher conversion rate at low temperatures than that of light oil, so the conversion rate of combustible materials and the low-temperature activity of the catalyst device are combined, making it easy to use without the need for heating means. With this configuration, even if the temperature of the exhaust gas discharged from the engine is significantly low, the exhaust temperature can be raised to the regeneration temperature of the catalytic trap. Therefore, even if the temperature of the exhaust gas discharged from the engine is significantly low, the exhaust particulates collected in the catalytic trap can be combusted, and the trap can be regenerated.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention;
The figure is a diagram showing the relationship between exhaust temperature and conversion rate for methanol and light oil, and FIG. 3 is a configuration diagram showing a conventional example of an exhaust particulate treatment device. 12... Exhaust passage, 13... Trap with catalyst,
14...Exhaust bypass passage, 15...Catalyst device,
16... Opening/closing valve, 17... Control device, 18... Injection valve, 21... Exhaust temperature sensor.

Claims (1)

[Scope of utility model registration request] a catalytic trap that is interposed in an exhaust passage and collects particulates in the exhaust; a determining means that determines when to regenerate the catalytic trap; and an exhaust bypass passage that bypasses the exhaust passage upstream of the catalytic trap; a catalyst device which is interposed in the exhaust bypass passage and includes a catalyst having a higher low temperature activity than the catalyst of the catalyst-equipped trap; an exhaust temperature detection means for detecting the exhaust temperature; and when it is determined that it is time to regenerate the trap,
A combustible material supply device that supplies a combustible material having a higher conversion rate at low temperatures than light oil to the catalyst device according to exhaust temperature, and a switching valve device that allows exhaust gas to flow through the exhaust bypass passage when the combustible material is supplied. An exhaust particulate treatment device for an internal combustion engine, characterized in that: