JP7393999B2 - Plasma reactor device for exhaust gas purification - Google Patents

Description

The present invention relates to a plasma reactor device installed in an engine for an automobile or the like and used for purifying exhaust gas.

Exhaust gas from gasoline and diesel engines contains harmful components such as CO (carbon monoxide), HC (hydrocarbons), NOx (nitrogen oxides), and PM (particulate matter).

Therefore, as a means to purify exhaust gas, gasoline engines generally use a catalytic exhaust gas purification device using a three-way catalyst, while diesel engines use a DPF, which removes PM. There are many problems, such as the problem of requiring fuel injection control for combustion and the problem of increased pressure loss due to PM and ash (unburned ash due to sulfur components in the fuel) accumulated in the DPF.

On the other hand, since gasoline engines emit less PM than diesel engines, they have traditionally been dealt with using catalytic exhaust gas purification devices, but with the shift to particle control (PN) regulations regarding PM, even gasoline engines PM treatment has emerged as an important issue.

As described above, detoxifying PM is an urgent issue for engines, and plasma reactors are attracting attention as a PM treatment technology. A plasma reactor has a structure in which multiple discharge panels are arranged side by side with discharge gaps in a casing through which exhaust gas flows, and a current is applied between the electrodes of the facing (adjacent) discharge panels. By generating plasma (non-equilibrium plasma), PM contained in the exhaust gas is oxidized and rendered harmless.

Plasma reactors can make PM harmless, but because they use electric power, it is necessary to secure the necessary PM processing capacity while suppressing power consumption as much as possible. However, when the amount of PM contained in the exhaust gas is large, the PM may not be completely removed from the exhaust gas, and the PM may adhere to and accumulate on the surface of the discharge panel.

If PM accumulates on the discharge panel, the discharge between the electrodes becomes weaker and the PM removal performance deteriorates, the power supply may be damaged due to overcurrent due to current leakage, or the discharge There are problems such as increased pressure loss due to a decrease in the gap.

Therefore, if it is possible to detect whether or not PM is deposited on the discharge panel, it is possible to take measures such as strengthening or suppressing the discharge power or extending or shortening the discharge time, thereby allowing effective use of electric power. Therefore, it has been proposed to control the discharge of the plasma reactor by detecting the accumulation of PM on the discharge panels.As an example, Patent Document 1 describes that when PM accumulates, the flow of negative current between the discharge panels is reduced. It has been disclosed that the presence or absence of PM deposition is detected by focusing on the change and using the integrated value of negative current as a parameter.

Japanese Patent Application Publication No. 2018-123711

Now, as a means of detecting PM accumulation, there is a method that uses the pressure difference before and after the plasma reactor, but this method requires two pressure gauges, which increases the cost, and the pressure loss due to PM accumulation is small, so it is not accurate. However, the method of Patent Document 1 can reduce costs by using the ammeter built into the control device, and has high detection accuracy because there is a strong relationship between PM deposition and negative current. There are advantages.

However, when the inventors of the present application subsequently considered this in combination with the driving mode of a car, a problem that needed to be overcome emerged. In other words, Figure 2 shows the changes in the negative current integrated value and the temperature of the exhaust gas entering the plasma reactor in the operation mode in which the engine is warmed up and runs/stops for 1500 seconds (25 minutes) after starting the engine. The graph shows that the temperature of the exhaust gas entering the plasma reactor tends to increase with the passage of operating time, and in response to this, the negative current integrated value (absolute value) increases as the PM It showed a tendency to increase both in the absence of deposition and in the presence of PM.

From this, it can be understood that when controlling the plasma reactor using (the absolute value of) the negative current integrated value as a parameter, it is necessary to correct the negative current integrated value in accordance with the temperature of the exhaust gas. If a temperature sensor is provided in the device, the cost will increase accordingly.

The present invention has been made based on such knowledge, and while it is common to Patent Document 1 that the negative current integrated value is used as a parameter to control the plasma reactor, it is possible to detect the presence or absence of PM deposition without using a temperature sensor. The aim is to make it detectable.

As described in Patent Document 1, when PM is deposited on the surface of the discharge panel, the discharge between the electrodes becomes weaker compared to the initial state where no PM is deposited, and the power is applied between the electrodes from the power supply device. The integrated value of the negative current flowing through the electrode in the opposite direction to the direction of the current flowing through the electrode becomes smaller due to the voltage. This tendency itself is consistent regardless of the exhaust gas temperature, but as mentioned above, the negative current integrated value differs depending on the exhaust gas temperature. Therefore, if the exhaust gas temperature differs, the same negative current Even if it is an integrated value, the presence or absence of PM accumulation will make a difference.

On the other hand, the inventors studied how the maximum current value and the integrated negative current value change under a specific discharge voltage, but there is no clear difference between the maximum current value and the integrated negative current value. There is a correlation, and the negative current integrated value in the absence of PM and the negative current integrated value in the state where PM is deposited appear as different values, and these negative current integrated values are the maximum current. It was clarified that it changes in proportion to the change in value.

The inventors of the present application have completed the present invention based on such knowledge.

The plasma reactor device of the present invention includes:
``Equipped with a plasma reactor main body in which a large number of discharge panels are arranged in parallel through a discharge gap in a casing through which exhaust gas flows, and a control device that controls discharge between the discharge panels,
Discharge control by the control device is performed based on a negative current integrated value, which is a value obtained by integrating the value of a negative current flowing between the electrodes in the opposite direction to the direction in which the discharge current is applied over a predetermined period of time.
In the configuration,
``Under the preset reference conditions of maximum voltage and current, the reference value of the negative current cumulative value when no PM is deposited , or the standard value of the negative current cumulative value when PM is deposited. is set in advance, and the negative current integrated value actually detected under the above reference conditions is compared with any of the above reference values, and if the actual detected value is larger than any of the above reference values, PM is determined. If there is no accumulation but it is small, it is determined that there is PM accumulation, and the control device performs discharge control based on the determination result.
It has the following characteristics.

According to the present invention, by controlling the voltage and current and measuring the negative current integrated value, the presence or absence of PM deposition and the degree of PM deposition can be detected regardless of the temperature of the exhaust gas. Therefore, it is possible to control the plasma reactor with high precision based on the negative current integrated value at low cost without using a temperature sensor or a pressure sensor.

In particular, a feature of the present invention is that the presence or absence of PM deposition can be determined while operating the plasma reactor, thereby further reducing costs and improving control responsiveness.

(A) is an overall block diagram, and (B) is a partial longitudinal sectional side view of the inside of the plasma reactor. (A) is a graph showing the operation mode, (B) is a graph showing the exhaust gas temperature in the plasma reactor, and (C) is a graph showing the change in the absolute value of the negative current integrated value. (A) is a graph showing changes in the maximum current value in the operation mode, and (B) is a graph (similar to FIG. 2(C)) showing changes in the absolute value of the negative current integrated value. It is a graph showing the relationship between the presence or absence of PM deposition and the waveform of current. It is a graph showing the relationship between the maximum current value and the absolute value of the negative current integrated value. It is a flow chart showing an example of detection and control.

Next, an embodiment in which the present invention is applied to a plasma reactor device for an automobile engine will be described based on the accompanying drawings.

(1).Overview An overview of the plasma reactor device is shown in Figure 1. The plasma reactor device is for removing PM contained in the exhaust gas of an automobile, and a plasma reactor main body 1 as a core device is interposed in the middle of an exhaust pipe 2. The plasma reactor main body 1 is composed of a rectangular casing 3 made of a metal plate such as a stainless steel plate, and a large number of discharge panels 4 and 5 arranged inside the casing 3.

The discharge panel is composed of a negative discharge panel 4 and a positive discharge panel 5, and the negative discharge panel 4 and the positive discharge panel 5 are arranged alternately in a direction perpendicular to the flow direction of exhaust gas with a discharge gap 6 interposed therebetween. ing. The discharge panels 4 and 5 have a structure in which electrodes 7 and 8 made of tungsten or the like are embedded inside a ceramic plate made of alumina or the like. ) is held inside the casing 3.

One of the pair of side electrode plates described above is electrically connected to the negative electrode 7 of each negative electrode discharge panel 4, and the other side electrode plate is electrically connected to the positive electrode 8 of each positive electrode discharge panel 5. . The side electrode plate is connected to a power supply section 9, and the power supply section 9 is supplied with power from a battery 10 of the automobile.

The power supply section 9 is equipped with a high voltage generation means such as a booster coil, and the high-voltage high-frequency current (pulse current) is applied to the negative electrode 7 of the negative discharge panel 4, and the electron flow is changed from the negative electrode 7 to the positive electrode. Plasma is generated in the discharge gap 6 by flowing toward the electrode 8, and the plasma oxidizes (burns) PM to render it harmless.

A control unit 11 is inserted in a circuit connecting the power supply unit 9 and the negative electrode 7, and the control unit 11 controls the power supply to the plasma reactor main body 1 and the strength of current and voltage. If PM adheres to the surfaces of the discharge panels 4 and 5, problems such as poor plasma generation will occur as described above. Therefore, if PM accumulation is detected, the voltage can be increased to promote PM removal, while if no PM is observed, the voltage can be lowered or discharge stopped to save power. can. Note that the control section 11 may be created as an independent part, or may be incorporated into an ECU (engine control unit) as a part thereof.

A PM detection section 12 is connected to the control section 11 . The PM detection unit 12 is equipped with a storage means, an arithmetic circuit, etc., and includes a current sensor 13 that detects the strength of the current (positive current strength, negative current strength) applied to the plasma reactor main body 1. , a voltage sensor 14 that detects the strength of voltage (potential difference) applied between the negative electrode 7 and the positive electrode 8 is connected. Sensors 13 and 14 are built into the circuit.

Since the control of the plasma reactor main body 1 is closely related to the operating state of the engine, the control unit 11 includes, as auxiliary data acquisition means, a rotation sensor 15 that detects the engine rotation speed and acceleration, and a rotation sensor 15 for starting and stopping the engine. An ignition switch 16 that detects the temperature of the cooling water, a water temperature sensor 17 that detects the temperature of the cooling water, a throttle sensor 18 that detects the opening of the throttle valve, and the like are connected.

(2) Prerequisites for detection As already mentioned in Figure 2, it shows how the temperature of the exhaust gas flowing into the plasma reactor main body 1 and the negative current integrated value change in a driving mode that resembles actual driving. it's shown. In FIG. 2(A), the dotted line bar graph indicates a state in which PM is deposited, while the solid line bar graph indicates a state in which no PM is deposited (initial state), which is related to the temperature of the exhaust gas. However, if there is PM accumulation, the negative current integrated value decreases.

FIG. 3 shows the relationship between the maximum current value applied to the plasma reactor main body 1 and the negative current integrated value, and shows that the maximum current value is high when PM is not present, and when PM is present. The maximum current value is low. Although FIG. 3(B) is basically the same as FIG. 2(C), it differs from FIG. 2(A) because the measurement conditions are slightly different.

FIG. 4 shows the current waveform when the discharge voltage is 4.5 kV. From this Figure 4, in the region where the current is negative, when PM is deposited, the minimum value of the current (discharge current) is larger than in the initial state where no PM is deposited (the absolute value is It is possible to understand that This is because the discharge between electrodes 7 and 8 becomes weaker when PM is deposited (note that even in the region where the current is positive, if PM is deposited, the maximum value of the current is tend to be lower).

(3). Control Example Next, an example of detecting the presence of PM and controlling based on the detection will be described based on the flowchart shown in FIG. 6. In this example, as a premise, a reference map corresponding to one or more discharge voltages has been created, and the reference map includes a maximum current value E set as a specific reference value, as shown in FIG. Corresponding to this, a lower limit value Y1 of the negative current integrated value when there is no PM deposition is stored.

Since generation of PM becomes a problem especially during warm-up operation, control of the plasma reactor main body 1 starts at the same time as the engine starts. Then, a discharge voltage is applied between the electrodes 7 and 8 using a current and voltage of a preset intensity based on a map created in advance based on FIG. 2(C) and FIG. 3(B). Step 1). That is, the plasma reactor main body 1 is in a normal operating state.

Then, in the detection mode, the maximum current value E is detected (measured) (step 2), and from the maximum current value E, a threshold value (reference value) Y1 (A.s. ) is obtained (step 3). Thereafter, the current negative current integrated value Y(A·s) is detected (step 4). Furthermore, in order to determine whether PM is deposited or not, it is determined whether Y is smaller than Y1 (step 5).

In step 5, if Y is larger than Y1, it is determined that there is no PM accumulation, the process returns to normal operation, and the process returns to step 1.

On the other hand, if Y is smaller than Y1, it is determined that there is PM accumulation, and PM removal measures are taken such as increasing the voltage or increasing the current value (step 6). After a predetermined time has elapsed since taking PM removal measures (step 7), the process returns to normal operation (step 1).

If the vehicle is traveling at a substantially constant speed and Y is greater than Y1, it is determined that the vehicle is in a driving state where less PM is generated, and it is possible to suppress the current or voltage. Since it is considered that PM is likely to occur when the engine load is large, it is possible to forcibly enter the detection mode when the throttle opening becomes larger than a set value.

In the above control example, the negative current integrated value Y1, which is the threshold value, was calculated from the maximum current value, but since the positive current integrated value is also correlated with the maximum current value and the negative current integrated value, the negative current integrated value is calculated from the positive current integrated value. It is also possible to determine the threshold value Y1 of the integrated value. Further, in the above control example, the threshold value (reference value) Y1 is set from the lower limit value when there is no PM accumulation , but it is also possible to set the threshold value Y1 from the upper limit value when there is PM accumulation. In any case, if Y is smaller than Y1, it is determined that there is PM accumulation, and PM removal measures such as increasing the voltage or increasing the current value are taken (step 6).

Moreover, as a means for measuring the voltage, the voltage does not have to be actually measured by a sensor, but it is also possible to estimate the voltage from, for example, the time during which the primary voltage is applied to the boost power source. Since sensors that measure voltages of several kilovolts are expensive, replacing detected voltage values with estimated values has the advantage of eliminating the need for expensive voltage sensors and reducing costs.

The present invention can be embodied in a plasma reactor device for exhaust gas purification. Therefore, it can be used industrially.

1 Plasma reactor main body 2 Exhaust pipe 3 Casing 4, 5 Discharge panel 6 Discharge gap 7, 8 Electrode 9 Power supply section 11 Control section 12 Detection section 13 Current sensor 14 Voltage sensor

Claims (1)

It includes a plasma reactor main body in which a large number of discharge panels are arranged in parallel through a discharge gap in a casing through which exhaust gas flows, and a control device that controls discharge between the discharge panels,
A configuration in which the discharge control by the control device is performed based on a negative current integrated value that is a value obtained by integrating the value of a negative current flowing between the electrodes in a direction opposite to the direction in which the discharge current is applied over a preset predetermined time,
Under preset reference conditions of maximum voltage and current, set the reference value of the negative current cumulative value when no PM is deposited , or the standard value of the negative current cumulative value when PM is deposited. Set in advance and compare the negative current integrated value actually detected under the above reference conditions with any of the above reference values, and if the actual detected value is larger than any of the above reference values, PM deposition is detected. If there is no PM deposit but it is small, it is determined that there is PM accumulation, and discharge control is performed by the control device based on the determination result.
Plasma reactor device for exhaust gas purification.

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