JP2020084907A - Exhaust system - Google Patents

Abstract

To provide an exhaust system capable of efficiently removing particulate substances.SOLUTION: An exhaust system 1 for exhausting an engine 101 is provided with a plasma reactor 3, a power supply device 5, and a control device 6. A frequency of voltage applied on the plasma reactor 3 is determined so that the number of discharges per time that particulate substances in exhaust gas pass through the plasma reactor 3 is two or more, and voltage is applied on the plasma reactor 3 at that frequency.SELECTED DRAWING: Figure 2

Description

The present invention relates to exhaust systems.

BACKGROUND ART Conventionally, as an exhaust gas purifying device that purifies exhaust gas of an internal combustion engine, an exhaust gas purifying device including a plasma generator is known (see Patent Document 1 below).

In this exhaust gas purification device, a voltage having a waveform including a burst period composed of a discharge period in which a predetermined basic waveform is periodically repeated and an undischarged period in which no discharge is performed is applied to the plasma generator. ing. Then, by adjusting the amplitude of the basic waveform, the cycle, the number of continuous repetitions, and the length of the burst cycle, the purification efficiency is improved while suppressing the increase in power consumption.

JP, 2007-23861, A

In the exhaust gas purification device as described in Patent Document 1 described above, it is required to further improve the efficiency of removing particulate matter.

Then, the objective of this invention is providing the exhaust system which can remove a particulate matter efficiently.

The present invention [1] is an exhaust system for exhausting gas from an engine, comprising a plasma reactor provided with an electrode panel and an ON state in which a voltage is applied to the electrode panel, or an OFF state in which a voltage is not applied to the electrode panel. And a control device that controls the power supply device. The control device is configured so that the number of discharges per time during which particulate matter in the exhaust gas passes through the plasma reactor is 2 or more. A frequency determining process for determining a frequency of a voltage applied to the electrode panel, and a voltage applying process for controlling the power supply device to apply a voltage to the electrode panel at the frequency determined in the frequency determining process. Includes exhaust system.

With such a configuration, the frequency of the voltage applied to the electrode panel is adjusted so that the number of discharges of the particulate matter in the exhaust gas passing through the plasma reactor per time is two or more.

Therefore, pulse discharge can be generated twice or more in the plasma reactor before the particulate matter in the exhaust gas passes through the plasma reactor.

As a result, 90% or more of the particulate matter contained in the exhaust gas can be adsorbed on the surface of the electrode panel, and the particulate matter can be decomposed while adsorbed on the electrode panel.

As a result, the particulate matter can be removed efficiently.

Further, the present invention [2] includes the exhaust system according to the above [1], wherein the control device determines the frequency so that the number of discharges is 2 or more and 4 or less in the frequency determining process.

According to such a configuration, preferably, the frequency of the voltage applied to the electrode panel is set so that the number of discharges of the particulate matter in the exhaust gas per time passing through the plasma reactor is 2 or more and 4 or less. Adjust.

As a result, pulse discharge can be generated in the plasma reactor twice or more and four times or less before the particulate matter in the exhaust gas passes through the plasma reactor.

If the number of pulse discharges is 2 times or more and 4 times or less, the particulate matter contained in the exhaust gas can be adsorbed onto a wide range of the surface of the electrode panel.

Since the particulate matter is adsorbed on a wide range of the surface of the electrode panel, the particulate matter adsorbed on the surface of the electrode panel can be efficiently decomposed.

Further, the present invention [3] further comprises a thermometer for measuring the temperature of the exhaust gas entering the plasma reactor, wherein the control device, in the frequency determination process, based on the temperature measured by the thermometer, The exhaust system according to the above [1] or [2], which corrects the frequency, is included.

With such a configuration, the control device corrects the frequency based on the temperature of the exhaust gas.

Therefore, even if the flow rate of the exhaust gas changes due to the change in the temperature of the exhaust gas, the particulate matter can be reliably captured by the electrode panel.

According to the present invention, particulate matter can be removed efficiently.

FIG. 1 is a schematic configuration diagram of a vehicle including an embodiment of an exhaust system of the present invention. FIG. 2 is a flow chart for explaining control of the exhaust system shown in FIG. FIG. 3 is a flow chart of the frequency determination processing shown in FIG. FIG. 4 is a graph showing the adsorption rate of particulate matter in each example and comparative example. FIG. 5 is a photograph showing the adsorption state of the particulate matter on the electrode panel in each example. 5A is an electrode panel of Example 1, FIG. 5B is an electrode panel of Example 2, and FIG. 5C is an electrode panel of Example 3. FIG. 6 is a graph showing the decomposition performance of the particulate matter in each example.

1. Configuration of Exhaust System As shown in FIG. 1, the exhaust system 1 is mounted on, for example, a vehicle 100.

The vehicle 100 includes an engine 101, an electric system including a battery 102, an intake system (not shown) for intake air to the engine 101, a fuel injection system (not shown) for supplying fuel to the engine 101, and exhaust from the engine 101. And an exhaust system 1 for

The exhaust system 1 includes an exhaust pipe 2, a plasma reactor 3, a thermometer 4, a power supply device 5, and a control device 6.

(1) Exhaust Pipe The exhaust pipe 2 is connected to the engine 101. Exhaust gas discharged from the engine 101 passes through the exhaust pipe 2 and is discharged outside the vehicle.

(2) Plasma Reactor The plasma reactor 3 is interposed in the middle of the exhaust pipe 2. The plasma reactor 3 decomposes harmful components (hydrocarbons (HC), nitrogen oxides (NOx), carbon monoxide (CO), particulate matter (PM)) contained in the exhaust gas.

The plasma reactor 3 has an inlet 3A and an outlet 3B. The exhaust gas discharged from the engine 101 flows into the plasma reactor 3 through the exhaust pipe 2 and the inlet 3A. The exhaust gas that has passed through the inside of the plasma reactor 3 flows out from the outlet 3B.

The plasma reactor 3 has a plurality of electrode panels 7. The plurality of electrode panels 7 are provided inside the plasma reactor 3. Each electrode panel 7 extends from the inlet 3A toward the outlet 3B. Each electrode panel 7 has a flat plate shape. The plurality of electrode panels 7 are arranged at intervals in the direction orthogonal to the direction from the inlet 3A to the outlet 3B.

Each electrode panel 7 has a conductor layer and a dielectric layer that covers the conductor layer. The conductor layer is made of, for example, a metal (conductor) such as tungsten. The dielectric layer is made of, for example, ceramics (dielectric) such as aluminum oxide.

When a voltage is applied to each electrode panel 7, a discharge occurs between the electrode panels 7. As a result, the gas between the electrode panels 7 becomes a plasma state. That is, plasma is generated in the plasma reactor 3.

Then, the harmful components contained in the exhaust gas flowing into the plasma reactor 3 are decomposed by the plasma inside the plasma reactor 3. The exhaust gas that has passed through the plasma reactor 3 is exhausted to the outside of the vehicle via the exhaust pipe 2.

(3) Thermometer The thermometer 4 measures the temperature of the exhaust gas entering the plasma reactor 3. The thermometer 4 is electrically connected to the control device 6 via the signal wiring 9A. The thermometer 4 emits an electric signal according to the temperature of the exhaust gas. The electric signal from the thermometer 4 is transmitted to the control device 6 through the signal wiring 9A.

(4) Power Supply Device The power supply device 5 can supply the power from the battery 102 to each electrode panel 7 of the plasma reactor 3. The power supply device 5 is electrically connected to the battery 102 via the power supply wiring 8A. The power supply device 5 is electrically connected to each electrode panel 7 via the power supply wiring 8B. The power supply device 5 can be switched to an on state or an off state. When the power supply device 5 is in the ON state, the power supply device 5 applies a voltage to the electrode panel 7. Further, when the power supply device 5 is in the off state, the power supply device 5 does not apply a voltage to the electrode panel 7.

(5) Control Device The control device 6 is an ECU (Electronic Control Unit) that executes electrical control in the vehicle 100, and includes a CPU, a ROM, a RAM, and the like. The control device 6 is connected to the battery 102 via the power supply wiring 10. The control device 6 is activated when power is supplied from the battery 102 via the power supply wiring 10 when the ignition switch of the vehicle 100 is turned on.

The control device 6 is electrically connected to the power supply device 5 via the signal wiring 9B. The control device 6 switches the power supply device 5 to the on state or the off state by sending a predetermined electric signal to the power supply device 5 via the signal wiring 9B. That is, the control device 6 controls the power supply device 5.

2. Control of Exhaust System Next, control of the exhaust system 1 will be described.

As shown in FIG. 2, the control device 6 executes a frequency determination process (S1) and a voltage application process (S2).

(1) Frequency determination process In the frequency determination process (S1), the control device 6 controls the electrode panel 7 so that the number of discharges per time that the particulate matter in the exhaust gas passes through the plasma reactor 3 is 2 or more. Determine the frequency of the applied voltage. The number of discharges is preferably 2 or more and 4 or less, more preferably 2.

Specifically, as shown in FIG. 3, the control device 6 first acquires the flow rate Ga of the exhaust gas in the frequency determination process (S1) (S11).

The flow rate Ga of the exhaust gas can be calculated, for example, from the intake flow rate Gw measured by an air flow meter provided in an intake system (not shown). Specifically, first, the intake air flow rate Gw (g/s) is converted by the following equation (1) to obtain the exhaust gas flow rate Ga (m ³ /s) before correction.

Formula (1): Ga=Gw/ρ
In the formula (1), ρ is the density of air and is 1.293 kg/m ³ at 0° C. and 1 atm.

Next, the control device 6 acquires the temperature T (° C.) of the exhaust gas entering the plasma reactor 3 (S12), and based on the acquired temperature T of the exhaust gas, the flow rate Ga of the exhaust gas obtained by the equation (1) Is corrected by the following equation (2) (S13). The temperature T (° C.) of the exhaust gas entering the plasma reactor 3 is measured by the thermometer 4.

Formula (2): Ga′=(273.15+T)/273.15×Ga
Next, the control device 6 calculates the frequency f of the voltage applied to the electrode panel 7 (S14).

At this time, the control device 6 determines the frequency f so that the number of discharges n per time t during which the particulate matter in the exhaust gas passes through the plasma reactor 3 becomes a desired value. In the following description, the time taken for the particulate matter in the exhaust gas to pass through the plasma reactor 3 is defined as the PM passage time.

Specifically, the frequency f is calculated by the following formula (3).

Formula (3): f=n/t
For example, when the desired number of discharges n is 2 and the PM passage time t is 0.02 seconds, the frequency f is 100 Hz.

The PM passage time t is calculated by the following equation (4) from the corrected exhaust gas flow rate Ga′ and the volume V of the portion of the plasma reactor 3 through which the exhaust gas passes.

Formula (4): t=V/Ga′
By substituting the equation (4) into the equation (3), the frequency f becomes the corrected flow rate Ga′ of the exhaust gas, the volume V of the portion of the plasma reactor 3 through which the exhaust gas passes, and the desired discharge frequency n. It is calculated from the following equation (5).

Formula (5): f=n×Ga′/V
That is, the controller 6 corrects the frequency f by correcting the exhaust gas flow rate Ga based on the temperature T measured by the thermometer 4.

(2) Voltage Application Process Next, in the voltage application process (S2) shown in FIG. 2, the control device 6 controls the power supply device 5 so that the electrode panel 7 has the frequency f determined in the frequency determination process (S1). Apply voltage.

Then, pulse discharge of a desired discharge number n occurs between the electrode panels 7 in the plasma reactor 3 before the particulate matter in the exhaust gas passes through the plasma reactor 3. That is, when the desired number of discharges n is 2 or more, the number of discharges between the electrode panels 7 in the plasma reactor 3 is 2 or more times before the particulate matter in the exhaust gas passes through the plasma reactor 3. A pulse discharge occurs.

As a result, 90% or more of the particulate matter contained in the exhaust gas is adsorbed on the surface of the electrode panel 7 so that the particulate matter adsorbed on the electrode panel 7 is decomposed, as shown in Examples described later.

3. Effect According to the exhaust system 1, the frequency f of the voltage applied to the electrode panel 7 is adjusted so that the number of discharges n per PM passage time t is 2 or more.

Therefore, the pulse discharge can be generated twice or more between the electrode panels 7 in the plasma reactor 3 before the particulate matter in the exhaust gas passes through the plasma reactor 3.

As a result, 90% or more of the particulate matter contained in the exhaust gas can be adsorbed on the surface of the electrode panel 7, and the particulate matter can be decomposed while being adsorbed on the electrode panel 7.

As a result, the particulate matter can be removed efficiently.

Further, according to the exhaust system 1, preferably, the frequency f of the voltage applied to the electrode panel 7 is adjusted so that the number of discharges n per PM passage time t is 2 or more and 4 or less.

As a result, it is possible to generate a pulse discharge of 2 times or more and 4 times or less between the electrode panels 7 in the plasma reactor 3 before the particulate matter in the exhaust gas passes through the plasma reactor 3. it can.

If the number of pulse discharges is 2 times or more and 4 times or less, the particulate matter contained in the exhaust gas can be adsorbed onto a wide range of the surface of the electrode panel 7.

Since the particulate matter is adsorbed on a wide range of the surface of the electrode panel 7, the particulate matter adsorbed on the surface of the electrode panel 7 can be efficiently decomposed.

Further, according to the exhaust system 1, the control device 6 corrects the frequency f based on the temperature T of the exhaust gas.

Therefore, even if the flow rate Ga of the exhaust gas changes due to the change of the temperature T of the exhaust gas even though the intake air flow rate Gw measured by the air flow meter is constant, the particulate matter can be reliably transferred to the electrode panel. It can be captured with 7.

Next, the present invention will be described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Examples and Comparative Examples>
Example 1
An experiment was conducted to purify exhaust gas in a plasma reactor.

The volume of the portion of the plasma reactor through which the exhaust gas passes is 0.0025 m ³ , and the flow rate of the exhaust gas that can be calculated from the intake flow rate measured by the air flow meter is 0.125 m ³ /s. The temperature was 25°C. Further, the frequency of the voltage applied to the plasma reactor was adjusted to 100 Hz so that the number of pulse discharges per PM passage time was twice.

Example 2
Example 1 was performed in the same manner as in Example 1 except that the frequency was adjusted to 250 Hz so that the number of pulse discharges per PM passage time was 4.

Example 3
Example 1 was repeated except that the frequency was adjusted to 1000 Hz so that the number of pulse discharges per PM passage time was 17.

Comparative Example The same as Example 1 except that the frequency was adjusted to 50 Hz so that the number of pulse discharges per PM passage time was 1.

<Evaluation>
(1) PM Adsorption Rate Measurement For each of the examples and comparative examples, the PM adsorption rate was calculated by the following formula.

PM adsorption rate=(1-PM amount when discharging/PM amount when not discharging)×100
The results are shown in Fig. 4.

By comparing each example with the comparative example, if the number of pulse discharges per PM passage time is two or more, 90% or more of the particulate matter contained in the exhaust gas is transferred to the surface of the electrode panel. It can be understood that it can be adsorbed.

(2) PM Decomposition Performance Measurement The PM decomposition performance was calculated for each example. Specifically, the mass of PM decomposed per unit time (PM decomposition performance) was calculated from the mass of carbon dioxide generated when PM was decomposed (integrated mass of carbon dioxide) by the following formula.

PM decomposition performance (mg/min) = cumulative mass of carbon dioxide (mg) / 44 (molecular weight of carbon dioxide) x 12 (atomic mass of carbon) / cumulative time (min)
FIG. 5 shows the adsorbed state of PM, and FIG. 6 shows the PM decomposition performance in each example. 5A is an electrode panel of Example 1, FIG. 5B is an electrode panel of Example 2, and FIG. 5C is an electrode panel of Example 3.

By comparing the examples, it can be understood that the smaller the number of pulse discharges, the more the particulate matter contained in the exhaust gas can be adsorbed onto a wide range of the surface of the electrode panel, and the more efficient the decomposition.

1 Exhaust System 3 Plasma Reactor 4 Thermometer 5 Power Supply Device 6 Control Device 7 Electrode Panel 101 Engine S1 Frequency Determination Processing S2 Voltage Application Processing

Claims (3)

An exhaust system for exhausting from the engine,
A plasma reactor equipped with an electrode panel,
A power supply device that can be switched to an ON state in which a voltage is applied to the electrode panel, or an OFF state in which a voltage is not applied to the electrode panel,
A control device for controlling the power supply device,
The control device is
A frequency determining process for determining the frequency of the voltage applied to the electrode panel so that the number of discharges of the particulate matter in the exhaust gas passing through the plasma reactor per time is 2 or more;
An exhaust system comprising: controlling the power supply device to perform a voltage application process of applying a voltage to the electrode panel at the frequency determined by the frequency determination process. The control device is
The exhaust system according to claim 1, wherein in the frequency determination process, the frequency is determined such that the number of discharges is 2 or more and 4 or less. Further comprising a thermometer for measuring the temperature of the exhaust gas entering the plasma reactor,
The control device is
The exhaust system according to claim 1 or 2, wherein in the frequency determination process, the frequency is corrected based on the temperature measured by the thermometer.

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