JP2008164419A - Particle number measuring system, and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent back flow from a particle number measuring instrument with simple structure, in a particle number measuring system. <P>SOLUTION: This particle number measuring system is provided with an exhaust gas introducing port PT1 for introducing an exhaust gas from an engine, a main flow line TL with a base end connected to the exhaust gas introducing port PT1, the first suction pump VP1 connected to the main flow line TL to introduce the exhaust gas into the main flow line TL, a measuring flow line ML extended from the main flow line TL, a particle number measuring instrument 3 provided in the measuring flow line ML, and the second suction pump VP2 provided in series in a downstream of the particle number measuring instrument 3, and is constituted to measure the number of particles in the exhaust gas by the particle number measuring instrument 3. In the particle number measuring system, a dummy flow line DL having a fluid resistance part DL1 in its midway is provided in parallel to the measuring flow line ML between the main flow line TL and the second suction pump VP2, and a switching valve 7 for switching-connecting the main flow line TL is provided in either of the measuring flow line ML or the dummy flow line DL. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a particle number measurement system for measuring the number of solid particles such as PM contained in engine exhaust gas.

  As a method for measuring particulate matter (PM), which is one of exhaust substances from the engine, a filter mass method is known in which PM is collected using a filter and the PM mass is measured. By the way, the amount of PM emission is very small, and the filter weight method has become severe in terms of accuracy. Under such circumstances, a method developed as an alternative to the filter weight method is a method for measuring the number of PM in exhaust gas. As a specific system configuration, for example, a dilution unit for diluting the exhaust gas of the engine with air or the like is provided in the front stage of the particle number measuring device, and a part of the diluted exhaust gas is led to the particle number measuring device. In addition, there is known one that counts the number of particles contained therein (see Patent Document 1).

  One of such particle number measuring apparatuses is known as a CPC (Condensation Particle Counter). In this CPC, a particulate material is passed through a supersaturated alcohol (butanol, etc.) atmosphere to grow to a large diameter, and then discharged from the slit, and the emitted particles are counted with a laser beam. .

An example of a system configuration using this CPC will be briefly described. As shown in FIG. 4, this system has a main flow that communicates with an exhaust pipe of an engine directly or through a full flow dilution tunnel or a diversion dilution tunnel. A passage X7 is provided, and exhaust gas from the engine is introduced into the main passage X7 by operating the first suction pump X4 provided at the end of the main passage X7. Yes. In the main flow path X7, one to a plurality of dilution units X3 are arranged in the middle, and the exhaust gas is diluted with air in the dilution unit X3. A part of the exhaust gas diluted in this way is guided to the particle number measuring device X5 via the measurement channel X8 branched from the main channel X7, and used for particle number measurement. The second suction pump X6 provided downstream of the particle number measuring device X5 is for gas suction into the measurement channel X8, and the suction flow rate is determined by the capacity of the particle number measuring device X5.
JP 2006-194726 A

  However, the first suction pump X4 that sucks the entire exhaust gas normally has an order of magnitude of suction performance compared to the second suction pump that only needs to suck a small amount of gas. For example, in the situation where the pressure and flow rate in each part are not stable and the situation where the pump operation is not stable, for example, the suction effect by the first suction pump X4 is exerted strongly, and the upstream side of the particle number measuring device X5 is the downstream side. There is a possibility that the pressure in the particle number measuring device X5 may flow back to the main flow path side. When such a backflow occurs, not only the measurement start timing is stabilized, but also when the particle number measuring device X5 is CPC, it is discharged to the flow path like butanol that causes a nuclear agglutination reaction with the measured particles. Something that requires attention may be used, and such a backflow phenomenon must be avoided.

  The present invention has been made in view of such problems, and in the particle number measurement system, the main intended problem is to prevent backflow from the particle number measurement device with a simple structure. It is.

  That is, the particle number measurement system according to the present invention includes an exhaust gas introduction port for introducing engine exhaust gas, a main flow path having a base end connected to the exhaust gas introduction port, and a discharge to the main flow path. A first suction pump connected to the main channel for introducing gas, a measurement channel extending from the main channel, a particle number measuring device provided on the measurement channel, and a particle number measurement A second suction pump provided in series downstream of the device, and configured to measure the number of particles in the exhaust gas by the particle number measuring device, wherein the main flow path and the second suction A dummy channel provided between the pump and in parallel with the measurement channel, and a switching valve that switches and connects the main channel to either the measurement channel or the dummy channel. It is characterized by being .

  If this is the case, under conditions where the fluid environment is not stable, such as when the system is started, the switching valve is controlled to close the fluid flow to the particle number measuring device, and this is provided in parallel. By allowing the gas to flow into the dummy flow path, it is possible to prevent backflow from the particle number measuring apparatus.

  After that, after establishing a stable state of the fluid environment that does not cause a reverse flow phenomenon in the dummy flow path, the switching valve is driven so that the exhaust gas flows into the particle number measuring device. Thus, the particle number measurement can be started smoothly without any backflow from the nozzle.

  In order to maintain the stability of the fluid environment at the time of switching between the dummy flow channel and the measurement flow channel and to more reliably prevent the back flow, the dummy flow channel has a fluid resistance part on the way, It is desirable that the characteristics of the fluid resistance portion with respect to the fluid be configured to approximate the characteristics of the particle number measuring device with respect to the fluid.

  As a more specific configuration for automatically performing switching, the switching valve is capable of being remotely driven by an external switching signal, while a predetermined condition regarding the fluid environment of the main flow path is satisfied. Is provided with a valve control unit for controlling the switching valve so that the main flow path and the measurement flow path are communicated, and the predetermined flow condition is not satisfied, and the main flow path and the dummy flow path are communicated with each other. Can be mentioned.

  In order to be able to easily determine whether or not the predetermined condition is satisfied, for example, the predetermined condition may be determined as that a certain time has elapsed from the start of the introduction of the exhaust gas.

  In order to be able to prevent backflow more reliably for any system, it is desirable that the predetermined condition is that the fluid environment of the main flow path is stable within a predetermined range.

  It is not always necessary to automatically perform valve switching and determination at the time of switching, and when a predetermined condition regarding the fluid environment of the main flow path is satisfied, an operator or a computer communicates the main flow path with the measurement flow path. When the predetermined condition is not satisfied, the switching valve may be controlled so as to communicate with the main flow path and the dummy flow path.

  According to the present invention configured as described above, the switching valve and the dummy flow path are provided, and the switching valve and the dummy flow path are simply configured so as to be appropriately controlled. The backflow phenomenon from the obtained particle number measuring apparatus can be avoided, and the leakage of the substance in the particle number measuring apparatus and the resulting contamination of the measurement flow path, the main flow path, etc. can be reliably prevented.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an overall outline of a particle number measurement system 100 according to the present embodiment. This particle number measurement system 100 introduces engine exhaust gas from an exhaust gas introduction port PT1 to a main flow path TL provided therein, and performs dilution, vaporization, etc., and then the final end of the main flow path TL. The PM, which is a solid particle in the exhaust gas, is measured by the particle number measuring device 3 provided in the above.

  The particle number measuring system 100 will be described in detail below.

  The exhaust gas introduction port PT1 is connected to an exhaust line from an engine (not shown). The exhaust gas introduction port PT1 is diluted with, for example, a direct exhaust gas from the engine or a full-flow dilution tunnel or a diversion dilution tunnel. The exhaust gas is guided. In the following description, the exhaust gas is used to include the diluted exhaust gas as described above.

  The exhaust gas introduced into the inside from the exhaust gas introduction port PT1 is partly exhausted from the bypass passage BL via the dust remover CL, and the remainder is a multi-stage (two-stage) dilution unit provided in series. It is led to 21 and 22 and diluted with air which is a dilution gas. The air is temporarily accumulated in the accumulator AC from the dilution gas introduction port PT2 via the regulator RG, and is supplied from this accumulator AC to the various locations of the main flow path TL via the internal air flow path AL. is there.

  Each of the dilution units 21 and 22 is a connection point between the flow splitters FS1 and FS2 for flowing a part of the exhaust gas flowing in from upstream to the bypass passages BL1 and BL2, and the main flow path TL and the internal air flow path AL. Alternatively, mixers MX1 and MX2 provided in the vicinity thereof, flow rate measuring mechanisms 211 and 221 for measuring the mass flow rate of the exhaust gas that is the dilution gas introduced into the mixers MX1 and MX2, and the mixer MX1 In addition, air flow control units MFC1 and MFC2 that control the mass flow rate of air that is also introduced into MX2, and exhaust gas flow rate control units MFC3 and MFC4 that change the mass flow rate of the exhaust gas that is to be diluted are provided. . The flow rate of the exhaust gas flowing into the dilution units 21 and 22 is measured by the flow rate measuring units 211 and 221 and controlled by the exhaust gas flow rate control units MFC3 and MFC4 so as to realize a desired dilution ratio. It is configured.

  The flow rate measuring mechanisms 211 and 221 include orifices O1 and O2 that are fluid resistances, pressure sensors P12 and P22 that measure a differential pressure between the orifices O1 and O2, and pressures that measure an upstream absolute pressure. Sensors P11 and P21 and temperature controllers TC1 and TC2 for adjusting the temperature of the fluid are provided. Based on pressure information on the upstream and downstream of the orifices O1 and O2 and temperature information from the temperature controllers TC1 and TC2, The information processing apparatus 5 (see FIG. 2 in particular) provided separately is configured to be able to calculate the mass flow rate of the exhaust gas introduced into the mixers MX1 and MX2. The information processing apparatus 5 is a general-purpose or dedicated so-called computer that includes a CPU, a memory, input means, a display, and the like, and in which the CPU and peripheral devices operate in cooperation according to a predetermined program stored in the memory.

  When each of the flow rate control units MFC1 to MFC4 is provided with target flow rate data from the information processing device 5, the actual flow rate measured by a flow sensor (not shown) provided therein is the value of the target flow rate data (hereinafter referred to as target flow rate data). The flow rate is controlled locally by adjusting an internal valve (not shown) so that the flow rate is also referred to. This target flow rate is calculated from the dilution ratio by the information processing device 5.

  Now, part of the exhaust gas diluted by the two-stage dilution units 21 and 22 described above is guided to the particle number measuring device 3. The particle number measuring device 3 in this embodiment is of a type in which organic gas such as alcohol or butanol is mixed in a supersaturated state to grow PM in exhaust gas to a large diameter, and the grown PM is counted by laser light. It is. Therefore, a large amount of gas exceeding a predetermined flow rate cannot be flowed. Count data measured by the particle number measuring device 3 is output to the information processing device 5 and appropriately processed.

  In FIG. 1, the symbol EU is an evaporation unit provided in the rear dilution unit 22. Reference sign VPm is a main vacuum pump for making the bypass passages BL, BL1, BL2 and the like have a negative pressure, and reference sign VC is a vacuum chamber provided in the preceding stage. Reference numerals CO1 to CO3 provided in the bypass paths BL, BL1, and BL2 are constant flow devices such as critical orifices that keep the flow rate flowing therethrough constant. Reference numeral VPs provided at the subsequent stage of the particle number measuring device 3 is a local vacuum pump for introducing exhaust gas into the particle number measuring device 3. The symbol FM provided in parallel with the particle number measuring device 3 is a flow meter, and is configured so that PM can be removed by a filter provided in the subsequent stage and air can be guided to the measuring device by switching the valve. is there. The symbol HT is a temperature controller having a heating means such as a heater, and is provided in order to prevent the PM from adhering to or agglomerating on the inner wall of the pipe by increasing the temperature to some extent, thereby suppressing the counting error. is there.

  However, in this embodiment, as shown in FIG. 1, a backflow prevention mechanism 6 for preventing the gas in the particle number measuring device 3 from flowing back to the upstream side is provided.

  The backflow prevention mechanism 6 includes a dummy flow path DL provided in parallel with the measurement flow path ML between the main flow path RM and the second suction pump VP2, and the main flow path TL to the measurement flow path ML. A switching valve 7 that is provided near the branch point and selectively switches and connects the main channel to either the measurement channel ML or the dummy channel DL, and a control unit (not shown) that controls the switching valve 7 Not).

  The dummy flow path DL has a fluid resistance portion DL1 at an intermediate portion thereof, and the fluid resistance portion DL1 is composed of, for example, an orifice or a choke. And the flow path resistance which is the characteristic with respect to the fluid of this fluid resistance part DL1 is set so that the flow path resistance of the particle number measuring apparatus 3 may be approximated.

  The switching valve 7 is, for example, an electromagnetically driven three-way valve that can be remotely driven by a switching signal from the outside.

  The control unit causes the main channel TL and the measurement channel ML to communicate with each other when a predetermined condition regarding the fluid environment of the main channel TL is satisfied, and when the predetermined condition is not satisfied, the main channel TL. The switching valve 7 is controlled by outputting a valve driving signal so as to communicate with the dummy flow path DL (see FIG. 2). In this embodiment, a program that exhibits the function as the control unit is installed in the information processing apparatus 5 so that the information processing apparatus 5 also has the function as the control unit.

  By the way, the fluid environment here refers to the dilution ratio, flow rate, pressure, and the like of the exhaust gas flowing through the main flow path TL, and satisfying the predetermined condition is stable within a certain range of the fluid environment. It means that. In this embodiment, it is not directly determined whether the fluid environment is stable, and at the initial stage of system operation, that is, at the initial stage of introduction of exhaust gas, due to instability of pump operation, environmental change, etc. It is assumed that the fluid environment is unstable and the predetermined condition is not satisfied.

  Next, a specific switching valve control method will be described.

  First, the information processing apparatus 5 controls the switching valve 7 in the default state, that is, in a state where the system is not operated, and maintains the main flow path TL and the dummy flow path DL in communication (step S1).

  On the other hand, the information processing apparatus 5 monitors whether or not the system 100 has started operating (step S2), and when it detects that the system 100 has started operating, the dilution of the main flow path TL is started from that starting time. It is determined whether a predetermined time for stabilizing the ratio, flow rate, pressure, etc. has elapsed (step S3). Then, after a predetermined time has elapsed, the switching valve is controlled so that the main channel TL communicates with the measurement channel ML (step S4).

  The predetermined time is a predetermined period here, but the information processing device 5 automatically monitors the dilution ratio, flow rate, pressure, etc. of the main channel TL, and these are within a predetermined predetermined range. The switching valve 7 may be switched on the condition that it is stable.

  According to such a configuration, under conditions where the fluid environment is not stable, such as when the system is started, the fluid flow to the particle number measuring device 3 is closed, and the dummy flow path DL provided in parallel with this is closed. Gas flows in. Then, after the reverse flow phenomenon in the dummy flow path DL is solved and a stable state of the fluid environment is established, the switching valve 7 is driven, and the exhaust gas flows into the particle number measuring device 3 this time. . Since the flow characteristics of the particle number measuring device 3 and the fluid resistance portion DL1 provided in the dummy channel DL are similar, the fluid environment is hardly disturbed by the switching at this time. The particle number measurement can be started smoothly without a stable state, that is, without backflow from the particle number measuring device 3.

  The present invention is not limited to the above embodiment.

  For example, in the above-described embodiment, the information processing apparatus automatically controls the switching valve. However, the operator may manually operate the switching valve after determining the fluid environment.

  In addition, the configuration of the flow path system and the like is not limited to the illustrated example, and the present invention can be variously modified without departing from the spirit thereof.

1 is a schematic overall view showing a particle number measurement system according to an embodiment of the present invention. The information transmission figure which shows the flow of the information in the embodiment. The flowchart which shows the backflow prevention procedure in the embodiment. The typical schematic whole figure which shows the conventional particle number measurement system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Particle number measuring system 3 ... Particle number measuring device 5 ... Control part (information processing apparatus)
7 ... Switching valve PT1 ... Exhaust gas introduction port PT2 ... Dilution gas introduction port TL ... Main passage ML ... Measurement passage DL ... Dummy passage DL1 ... Fluid resistance section

Claims (6)

An exhaust gas introduction port for introducing engine exhaust gas, a main passage connected to the exhaust gas introduction port at the base end, and a main passage connected to the main passage for introducing exhaust gas into the main passage A first suction pump, a measurement channel extending from the main channel, a particle number measuring device provided on the measurement channel, and a second suction provided in series downstream of the particle number measuring device A pump, and configured to measure the number of particles in the exhaust gas by the particle number measuring device,
A dummy channel provided between the main channel and the second suction pump and in parallel with the measurement channel;
A particle number measurement system comprising: a switching valve that switches and connects the main channel to either the measurement channel or the dummy channel.   2. The particle number measurement according to claim 1, wherein the dummy channel has a fluid resistance part in the middle, and the characteristic of the fluid resistance part with respect to the fluid approximates to the characteristic of the particle number measuring device with respect to the fluid. system. The switching valve can be remotely driven by a switching signal from the outside, and further includes a valve control unit that controls the switching valve,
When the predetermined condition regarding the fluid environment of the main flow path is satisfied, the control unit communicates the main flow path with the measurement flow path. When the predetermined condition is not satisfied, the control section communicates with the main flow path and the dummy flow path. The particle number measuring system according to claim 1 or 2, wherein the switching valve is controlled so as to communicate with a road.   The particle number measuring system according to claim 3, wherein the predetermined condition is that a predetermined time has elapsed from the start of introduction of exhaust gas.   The particle number measurement system according to claim 3, wherein the predetermined condition is that a fluid environment of the main channel is stable within a predetermined range. A control method applied to the particle number measurement system according to claim 1 or 2, wherein when a predetermined condition relating to a fluid environment of the main flow path is satisfied, the main flow path and the measurement flow path are communicated with each other. A control method of a particle number measurement system that controls the switching valve so that a main channel and a dummy channel communicate with each other when a condition is not satisfied.