WO2013121115A1 - Apparatus and method for flushing particle measurement device - Google Patents

Apparatus and method for flushing particle measurement device Download PDF

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Publication number
WO2013121115A1
WO2013121115A1 PCT/FI2013/050184 FI2013050184W WO2013121115A1 WO 2013121115 A1 WO2013121115 A1 WO 2013121115A1 FI 2013050184 W FI2013050184 W FI 2013050184W WO 2013121115 A1 WO2013121115 A1 WO 2013121115A1
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WO
WIPO (PCT)
Prior art keywords
flow
clean gas
sample
gas flow
particle
Prior art date
Application number
PCT/FI2013/050184
Other languages
French (fr)
Inventor
Kauko Janka
Original Assignee
Pegasor Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pegasor Oy filed Critical Pegasor Oy
Priority to CN201390000404.XU priority Critical patent/CN205049446U/en
Publication of WO2013121115A1 publication Critical patent/WO2013121115A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G01N15/0656—Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2247—Sampling from a flowing stream of gas
    • G01N1/2252—Sampling from a flowing stream of gas in a vehicle exhaust
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/24—Suction devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/38—Diluting, dispersing or mixing samples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0011—Sample conditioning
    • G01N33/0018—Sample conditioning by diluting a gas
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0029—Cleaning of the detector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G01N2001/222—Other features
    • G01N2001/2223—Other features aerosol sampling devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2247—Sampling from a flowing stream of gas
    • G01N1/2252—Sampling from a flowing stream of gas in a vehicle exhaust
    • G01N2001/2255—Sampling from a flowing stream of gas in a vehicle exhaust with dilution of the sample
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/24—Suction devices
    • G01N2001/242—Injectors or ejectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N2015/0042—Investigating dispersion of solids
    • G01N2015/0046—Investigating dispersion of solids in gas, e.g. smoke

Definitions

  • the present invention relates to an apparatus for monitoring particles and especially to an apparatus as defined in the preamble of independent claim 1.
  • the present invention also relates to a process for monitoring particles according to the preamble of independent claim 6.
  • Fine particles having diameter between 1 nanometer and 10 micrometers are formed in many combustion processes. For various reasons these fine particles are measured.
  • the fine particle measurements may be conducted because of their potential health effects and also for monitoring operation of combustion processes, such as operation of combustion engines, especially diesel engines. Due to the above reasons there is need for reliable fine particle measurement apparatus.
  • One prior art method and apparatus for measuring fine particles is described in document WO2009109688 Al.
  • clean, essentially particle free, gas is supplied into the apparatus and directed as a main flow via an inlet chamber to an ejector provided inside the apparatus.
  • the clean gas is further ionized before and during supplying it into the inlet chamber.
  • the ionized clean gas may be preferably fed to the ejector at a sonic or close to sonic speed.
  • the ionizing of the clean gas may be carried out for example using a corona charger.
  • the inlet chamber is further provided with a sample inlet arranged in fluid communication with a channel or a space comprising aerosol having fine particles.
  • the clean gas flow and the ejector together cause suction to the sample inlet such that a sample aerosol flow is formed from the duct or the space to the inlet chamber.
  • the sample aerosol flow is thus provided as a side flow to the ejector.
  • the ionized clean gas charges the particles.
  • the charged particles may be further conducted back to the duct or space containing the aerosol.
  • the fine particles of the aerosol sample are thus monitored by monitoring the electrical charge carried by the electrically charged particles. Free ions may further be removed by an ion trap.
  • the size distribution of the diesel engine exhaust particles generally shows three different modes: the nuclei mode consists of particles having a diameter of less than approximately 50 nm, the accumulation mode consists of particles having diameters between 50 nm and 1 ⁇ and in the coarse mode the particle diameter is greater than 1 ⁇ . A majority of the diesel engine exhaust particles is born after the exhaust gases escape from the exhaust pipe and these particles typically belong to the accumulation and nuclei mode.
  • fine particle monitoring apparatuses especially for onboard-diagnoses of diesel engines are small and compact construction. Furthermore, it is also preferable that these fine particle monitoring apparatuses may be operated long time periods without need for maintenance. In many applications, such as monitoring fine particles of combustion engines, it is further preferable that the monitoring apparatus may be operated continuously for conducting fine particle measurements in real-time.
  • the fine particle monitoring apparatus In order to fulfill the long operation time requirement, it is essential that the fine particle monitoring apparatus is not blocked by particle, i.e. avoidance of apparatus soiling.
  • One of the critical soiling areas is the inlet nozzle for sample flow inlet, leading to the actual measurement space.
  • US patent 4,307,061, Robert Bosch GmbH, 22.12.1981 describes a self-recovering soot detector, particularly to monitor carbon content in diesel engine exhaust gases.
  • An insulating support body for example an aluminum oxide ceramic, supports two electrodes spaced from each other by a small gap, for example 0.1 mm, which will have there between a high resistance. Upon collection of soot, the resistance between the electrodes across the gap will drop, which can be indicated by sensing current through the electrodes upon connection to a source of electrical energy.
  • the electrodes are applied over, or embedded in a layer of essentially nonconducting catalyzing material which, in the presence of oxygen, catalyzes the oxidation of soot located in the gap between the electrodes to thereby remove the soot by oxidation and restore the resistance of the path between the electrodes and hence the restore also the sensitivity of the sensor for subsequent detection of accumulation of soot in the gap.
  • the non-conductive catalyzing material is a mixture of platinum, or a platinum metal, or a platinum metal alloy and a metal oxide which is compatible with, or identical to the ceramic base, for example aluminum oxide.
  • the essentially electrically non-conductive layer can be applied by thick-film technology, and the electrodes also by thick-film
  • the electrodes may be in the form of fine platinum wires extending through the catalyzing electrically non-conductive layer.
  • the sensing element can be held in a housing or socket, similar to a spark plug socket. The described solution for soiling removal is, however, complex.
  • PCT application WO 2008/138849 Al, Robert Bosch GmbH, 20.11.2008 relates to a method for the detection of particles in a gas flow with a sensor element comprising at least two electrodes.
  • a measurement voltage is applied to the electrodes of the sensor element during a measurement phase, wherein particle paths formed by the accumulation of particles short circuit the electrodes, and the resulting current flow, voltage reduction, and/or electrical resistance is measured and is given as a measurement of the concentration and/or mass flow rate.
  • the invention is characterized in that during a regeneration phase following the measurement phase, the accumulated particles are partially or entirely removed by raising the measurement voltage applied to the electrodes to a regeneration voltage. This approach requires complex power supply design and construction.
  • the object of the present invention is to provide an apparatus so as to overcome the prior art disadvantages.
  • the objects of the present invention are achieved with an apparatus according to the characterizing portion of claim 1.
  • Another object of the present invention is to provide a process so as to overcome the prior art disadvantages, achieved with a process according to the characterizing portion of claim 6.
  • the preferred embodiments of the invention are disclosed in the dependent claims.
  • the process for fine particle measurement comprises pulling sample flow Qs into a measurement apparatus, feeding additional, essentially clean gas flow QA into the
  • additional flows which can be adjusted so that the QS/QT ratio can be varied in a large range, on the basis of the particle measurement result, is obvious for a person skilled in the art or fine particle measurements: it allows the use of the measurement apparatus at its optimal particle concentration
  • the invented process and apparatus are best suited for use with non-collecting particle measurement apparatuses, i.e. with measurement processes which do not deliberately collect particles.
  • Sample flow is beneficially pulled into measurement apparatus by using an ejector pump where essentially clean gas is used for the motive fluid flow and thus the measurement result is not erroneously affected by the particles in the motive fluid flow.
  • particle accumulation into the particle measurement apparatus can adversely affect the operation of the particle measurement apparatus. In many cases this can be seen as too small or noisy measurement signal, reduction of sample flow Qs or by some other way.
  • the inventor has found that it is possible to reduce or even completely remove the harmful particle accumulation by frequent or infrequent flushing of the particle measurement apparatus and in particularly the sample inlet of the particle measurement apparatus with essentially clean gas.
  • the suction which drives the sample flow through the inlet nozzle is generated by an ejector which is placed inside the particle monitoring apparatus.
  • Clean gas flow Qc forms the motive fluid of the ejector.
  • Gas flow Qc is ionized and the motive fluid flow is - in addition to suction generation - used to charge the particles entering the particle monitoring apparatus. This ensures that the measurement method described in WO2009109688 Al, which is hereby incorporated by reference in its entirety, can be used for particle measurement.
  • flushing can advantageously be achieved by feeding the additional flow QA to the sample inlet which allows using the additional flow as sample dilution flow during normal operation. If Qso is the sample flow without the additional flow QA, then during normal operation of the particle measurement apparatus Q A is set to be smaller than Q so .
  • the additional flow QA is set to be higher than Qso, preferably higher than 1,5 times Qso (l,5xQso) and more preferably higher than 2 times Qso (2xQso).
  • flushing can also be realized by closing the outlet fluid conduit of the measurement apparatus and letting clean air flow Qc pass upstream, through the inlet conduit of the measurement apparatus.
  • flushing when using the measurement apparatus described in WO2009109688 Al, it is often preferable to switch of the ionization during flushing.
  • the particle measurement apparatus is at high temperature, preferably higher than 300°C and more preferably higher than 400°C temperature, if oxygen containing gas is used for clean gas flow Qc, and if corona discharge is used for ionization, it may be beneficial to keep the corona voltage on, or even set the corona voltage to a value higher than during normal operation.
  • Corona discharge unit converts at least a fraction of oxygen into ozone, which improves burning off the accumulated soot particles during flushing.
  • Flushing can be triggered on by time (i.e. at frequent or infrequent periods) or it can be triggered on by some other means.
  • One way to trigger flushing on is to keep information on the total amount of particles which has passed through the particle measurement apparatus and switch flushing on after a predetermined value.
  • Another way to trigger flushing on is to switch it on after particle concentration exceeds a certain limit. This triggering process has the advantage that too high particle concentrations are not allowed to flow into the particle measurement apparatus.
  • Yet another way of triggering flushing on is to monitor the sample flow Qs and switch flushing on if sample flow drops below a certain limit. Sample flow monitoring can be realized in various ways, especially if the flow is monitored before the measurement apparatus is switched into measurement mode.
  • sample flow is monitored by a method described in applicant's currently non-public application PCT/FI2011/050730, which is hereby incorporated by reference in its entirety, where an apparatus and process for measuring particle concentration comprises a sensing element for particle concentration measurement, means for switching or modulating a parameter which affects the output of the sensing element and means for determining the volumetric flow on the basis of the response which switching or modulation creates to the sensing element output.
  • Fig. 1 shows a schematic drawing of a particle measuring apparatus with means for setting the apparatus into flush mode
  • Fig 2 shows an embodiment where the control means are situated outside the particle sensor and various ways to realize the flush mode are possible.
  • Figure 1 shows a schematic drawing of a particle measuring apparatus 1 with sample flow Qs and additional flow Qc-
  • the particle measuring apparatus 1 comprises means 7,8 for ionizing essentially clean gas flow Qc which is fed into apparatus 1 from gas conduit 4 and through channel 5 and is ionized by corona charger 7 which is electrically insulated by insulator 8 so that a high voltage can be applied to the corona charger 7.
  • Essentially clean means in this case that the particle number concentration, expressed in 1/cm , of the essentially clean gas is much lower than the particle number concentration in the sample flow F.
  • the particle number concentration in the essentially clean gas, N cg is 10 "1 ...
  • the clean gas flow Qc enters into an ejector which consists of ejector inlet 9a, ejector throat 9b and ejector outlet 9c.
  • the clean gas flow Qc forms the motive fluid flow of the ejector and generates a negative pressure (as compared to the space from which the sample flow Qs is taken) to the inlet nozzle 14, which negative pressure ensures sample flow Qs to the particle measuring apparatus 1.
  • Sensor 101 is connected to means 102,103 for triggering the flush function, i.e. setting apparatus 1 into flush mode.
  • Functional unit 102 provides information on the particle concentration.
  • the term "functional unit” means that the unit 102 is functionally an essential part of the present invention but can physically be constructed in various ways, i.e. by analogue or digital means and it can situate either inside or outside the actual measuring apparatus 1.
  • the functional unit means that the unit 102 is functionally an essential part of the present invention but can physically be constructed in various ways, i.e. by analogue or digital means and it can situate either inside or outside the actual measuring apparatus 1.
  • Functional unit 103 can physically be constructed in various ways, i.e. by analogue or digital means and it can situate either inside or outside the actual measuring apparatus 1 or it can be integrated into flow control unit 6*.
  • Essential feature of the present invention is that the flow control unit 6* can be set to flow QA which is higher than the sample flow Qso, i.e. Qs in a situation where Q A is set to zero.
  • FIG. 2 shows an embodiment of the present invention which clarifies the meaning of functional components 101, 102 and 103.
  • Apparatus 1 consists of various components and most of them are not placed inside sensor 1* which comprises the actual particle measurement sensor 101, but also comprises heater He for heating sensor 1*, thermocouple Tc for measuring temperature of sensor 1* and thermal switch TSw for preventing overheating of sensor 1*.
  • Clean gas flow Qc in this case clean pressurized air flow, is fed into sensor 1* from conduit 4 through oil separator OS, water separator WS, filter F, active carbon filter ACF and membrane dryer, which guarantee that the clean gas is particle and moisture free.
  • the clean air pressure is adjusted by pressure regulator PR and the pressures upstream and downstream of the regulator are measured by pressure meters PM.
  • the moisture level is controlled by a dew point meter DPM.
  • the clean gas flow Qc into sensor 1* can be switched ON and OFF by a solenoid valve SV.
  • the clean gas flow Qc generates suction to the sensor 1* inlet and thus sample flow Qs is drew into sensor 1*.
  • the volumetric value of sample flow Qs depends in normal operation only on the pressure set by the pressure regulator PR. Sample flow Qs is combined with additional gas flow QA which is fed from the clean gas channel via solenoid valve SC, flow controller 6* and check valve CV.
  • the diluted sample flow which is the sum of the sample flow and the additional flow, QS+QA, is further directed to sensor l*via heater He and ball valve BV.
  • Temperature of (essentially) heater He is measured by thermocouple TC and heater He is protected by thermal switch TSw, which sets heating power OFF in case of overheating.
  • Flow outlet from sensor 1* passes through ball valve BV before it is exhausted. The temperature of the outlet tubing can be monitored by a
  • thermocouple TC thermocouple
  • the ball valves are operated by pneumatic actuators PA, which are set to different positions by pressurized gas entering actuators PA through solenoid valves SV.
  • pneumatic actuators PA which are set to different positions by pressurized gas entering actuators PA through solenoid valves SV.
  • solenoid valves SV When the solenoid valves are set OFF, pneumatic actuators return to OFF position due to the spring force and pressurizing gas exits from the actuator via silencer S.
  • the output signal of sensor 6* corresponding to particle concentration in the flow passing through sensor 1*, i.e. combined flow QS+QA+QC, is fed from sensor 1* into a programmable logic which contains the functional units 102, 103. Based on the concentration result, functional units 102, 103 set the additional flow FA during normal measurement mode to a value which keeps sensor 1* working in the optimal measurement area.
  • the actual figures depend very much on the particle measurement apparatus 1 construction, but e.g. for a Pegasor ® PPS, Pegasor Oy, Finland particle sensor, the clean gas pressure PR is set to 1...
  • sample flow F is 3-10 1/min
  • clean gas flow Fc is 2- 8 1/min
  • additional flow QA is from zero to Qso- Additional flow QA is typically, but not necessarily, set by a mass flow controller based either on thermal or Coriolis measurement.
  • the selection of the flow controller 6* depends mainly on the dynamic requirements set to the controller. Generally it is beneficial for efficient control of additional flow QA that the response time of the flow controller 6* is less than the response time of sensor 1*. Typically the response time of the flow controller 6* has to be less than 100 ms.
  • the apparatus shown in Figure 2 can be set to flush mode by various embodiments. For each of these embodiments it is common that apparatus 1 comprises means for triggering the apparatus into flush mode.
  • Such means may comprise timers, means for detecting particle concentration 1*, means 102, 103 for triggering apparatus 1 on flush mode based on particle concentration or on total amount of particulate material passed through sensor 1*. It is also common to all embodiments that apparatus 1 comprises means for adjusting the gas flows in such a way that at least part of apparatus 1* is flushed with essentially clean air.
  • flush mode triggering means 102,103 set the additional gas flow QA to a value which is higher than Q SO and thus clean gas flows into sensor 1* as well as upwards through inlet channel 2, i.e. out from the inlet tube. This prevents sample flow into apparatus 1.
  • sample flow Qs inlet into sensor is prevented by closing inlet ball valve BV. All additional flow QA now flows out from inlet channel 2 and the inlet is effectively flushed.
  • the outlet valve BV of sensor 1* is closed and clean air flow Qc passes then upwards through sensor 1* inlet channel 2 and prevents sample flow Qs into sensor 1*. If sensor 1* is similar to the one described in WO2009109688 Al, it is often preferable to switch of the ionization during flushing.
  • the particle measurement apparatus is at high temperature, preferably higher than 300°C and more preferably higher than 400°C temperature, if oxygen containing gas is used for clean gas flow Qc, and if corona discharge is used for ionization, it may be beneficial to keep the corona voltage on, or even set the corona voltage to a value higher than during normal operation.
  • Corona discharge unit converts at least a fraction of oxygen into ozone, which improves burning off the accumulated soot particles during flushing.
  • Such high temperature may arise from the environment of sensor 1*, or sensor 1* may be heated to such high temperature using heater He of sensor 1*.
  • flush mode triggering means 102,103 set the additional gas flow QA to a value which is higher than Q so and thus clean gas flows into sensor 1* as well as upwards through inlet channel 2, i.e. out from the inlet tube. This prevents sample flow into apparatus 1.
  • the flush flow (part of Q A ) entering sensor 1* is heated using heater He around the inlet fluid conduit and the voltage of the corona discharge unit in sensor 1* is set to a value which is higher than during normal operation and thus ozone production is enhanced.

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Abstract

Apparatus (1) for particle measurement, comprising means (9a-9c) for sucking sample flow (QS) into apparatus (1), means for triggering (102,103) apparatus (1) into flush mode, in which mode sample flow (QS) into apparatus (1) is essentially zero and means for adjusting gas flows in such a way that at least part of apparatus (1) is flushed with essentially clean gas, where apparatus (1) further comprises means (5) for feeding essentially clean gas flow (QC) into apparatus (1), the clean gas flow (QC) forming the motive fluid flow of the ejector (9a-9c) which pulls sample flow (QS) into apparatus (1) during the normal measurement mode of apparatus (1) and means for triggering (102,103) the apparatus (1) into flush mode by closing the outlet valve (BV) of apparatus (1), which forces clean gas flow (QC) upwards the sample inlet channel (2).

Description

APPARATUS AND METHOD FOR FLUSHING PARTICLE MEASUREMENT
DEVICE
Field of invention
The present invention relates to an apparatus for monitoring particles and especially to an apparatus as defined in the preamble of independent claim 1. The present invention also relates to a process for monitoring particles according to the preamble of independent claim 6.
Description of the state of the art
Fine particles having diameter between 1 nanometer and 10 micrometers are formed in many combustion processes. For various reasons these fine particles are measured. The fine particle measurements may be conducted because of their potential health effects and also for monitoring operation of combustion processes, such as operation of combustion engines, especially diesel engines. Due to the above reasons there is need for reliable fine particle measurement apparatus.
One prior art method and apparatus for measuring fine particles is described in document WO2009109688 Al. In this prior art method clean, essentially particle free, gas is supplied into the apparatus and directed as a main flow via an inlet chamber to an ejector provided inside the apparatus. The clean gas is further ionized before and during supplying it into the inlet chamber. The ionized clean gas may be preferably fed to the ejector at a sonic or close to sonic speed. The ionizing of the clean gas may be carried out for example using a corona charger. The inlet chamber is further provided with a sample inlet arranged in fluid communication with a channel or a space comprising aerosol having fine particles. The clean gas flow and the ejector together cause suction to the sample inlet such that a sample aerosol flow is formed from the duct or the space to the inlet chamber. The sample aerosol flow is thus provided as a side flow to the ejector. The ionized clean gas charges the particles. The charged particles may be further conducted back to the duct or space containing the aerosol. The fine particles of the aerosol sample are thus monitored by monitoring the electrical charge carried by the electrically charged particles. Free ions may further be removed by an ion trap.
In addition to the above mentioned fine particles, industrial processes and combustion processes form usually also particles having particle diameter greater than 1 μιη, or greater than 2 μιη, 3 μιη, 5 μιη or even greater. These coarse particles having particle diameter greater than 1 μιη may be formed in small amounts in normal operation conditions, but especially in special operation conditions such as during startups, shutdowns, malfunction conditions. The size distribution of the diesel engine exhaust particles generally shows three different modes: the nuclei mode consists of particles having a diameter of less than approximately 50 nm, the accumulation mode consists of particles having diameters between 50 nm and 1 μιη and in the coarse mode the particle diameter is greater than 1 μιη. A majority of the diesel engine exhaust particles is born after the exhaust gases escape from the exhaust pipe and these particles typically belong to the accumulation and nuclei mode.
One important demand for the fine particle monitoring apparatuses especially for onboard-diagnoses of diesel engines is small and compact construction. Furthermore, it is also preferable that these fine particle monitoring apparatuses may be operated long time periods without need for maintenance. In many applications, such as monitoring fine particles of combustion engines, it is further preferable that the monitoring apparatus may be operated continuously for conducting fine particle measurements in real-time.
In order to fulfill the long operation time requirement, it is essential that the fine particle monitoring apparatus is not blocked by particle, i.e. avoidance of apparatus soiling. One of the critical soiling areas is the inlet nozzle for sample flow inlet, leading to the actual measurement space.
US patent 4,307,061, Robert Bosch GmbH, 22.12.1981 describes a self-recovering soot detector, particularly to monitor carbon content in diesel engine exhaust gases. An insulating support body, for example an aluminum oxide ceramic, supports two electrodes spaced from each other by a small gap, for example 0.1 mm, which will have there between a high resistance. Upon collection of soot, the resistance between the electrodes across the gap will drop, which can be indicated by sensing current through the electrodes upon connection to a source of electrical energy. To remove soot upon termination of smoking, or soot contents in the gases, the electrodes are applied over, or embedded in a layer of essentially nonconducting catalyzing material which, in the presence of oxygen, catalyzes the oxidation of soot located in the gap between the electrodes to thereby remove the soot by oxidation and restore the resistance of the path between the electrodes and hence the restore also the sensitivity of the sensor for subsequent detection of accumulation of soot in the gap.
Preferably, the non-conductive catalyzing material is a mixture of platinum, or a platinum metal, or a platinum metal alloy and a metal oxide which is compatible with, or identical to the ceramic base, for example aluminum oxide. The essentially electrically non-conductive layer can be applied by thick-film technology, and the electrodes also by thick-film
technology there over, or the electrodes may be in the form of fine platinum wires extending through the catalyzing electrically non-conductive layer. The sensing element can be held in a housing or socket, similar to a spark plug socket. The described solution for soiling removal is, however, complex.
PCT application WO 2008/138849 Al, Robert Bosch GmbH, 20.11.2008, relates to a method for the detection of particles in a gas flow with a sensor element comprising at least two electrodes. A measurement voltage is applied to the electrodes of the sensor element during a measurement phase, wherein particle paths formed by the accumulation of particles short circuit the electrodes, and the resulting current flow, voltage reduction, and/or electrical resistance is measured and is given as a measurement of the concentration and/or mass flow rate. The invention is characterized in that during a regeneration phase following the measurement phase, the accumulated particles are partially or entirely removed by raising the measurement voltage applied to the electrodes to a regeneration voltage. This approach requires complex power supply design and construction.
There is a need for an improved particle measurement apparatus and process where soiling of the particle measurement apparatus, especially soiling of the inlet nozzle, can be avoided.
Summary of the invention
The object of the present invention is to provide an apparatus so as to overcome the prior art disadvantages. The objects of the present invention are achieved with an apparatus according to the characterizing portion of claim 1. Another object of the present invention is to provide a process so as to overcome the prior art disadvantages, achieved with a process according to the characterizing portion of claim 6. The preferred embodiments of the invention are disclosed in the dependent claims.
The process for fine particle measurement comprises pulling sample flow Qs into a measurement apparatus, feeding additional, essentially clean gas flow QA into the
measurement apparatus, preferably mixing the sample flow Qs with additional flow QA and with another clean gas flow Qc, measuring particle concentration from the total flow QT=QS+QA+QC and preferably adjusting additional flows on the basis of the particle concentration measurement result. The advantage of adjusting the additional flows, which can be adjusted so that the QS/QT ratio can be varied in a large range, on the basis of the particle measurement result, is obvious for a person skilled in the art or fine particle measurements: it allows the use of the measurement apparatus at its optimal particle concentration
measurement range and greatly reduces or even completely hinders soiling of the inlet nozzle.
As the use of the measurement apparatus at its optimal particle concentration measurement range, and preventing apparatus soiling has greatest effect in long-term measurements, the invented process and apparatus are best suited for use with non-collecting particle measurement apparatuses, i.e. with measurement processes which do not deliberately collect particles.
Sample flow is beneficially pulled into measurement apparatus by using an ejector pump where essentially clean gas is used for the motive fluid flow and thus the measurement result is not erroneously affected by the particles in the motive fluid flow.
Especially in long-term measurements particle accumulation into the particle measurement apparatus, particularly into the sample inlet channel can adversely affect the operation of the particle measurement apparatus. In many cases this can be seen as too small or noisy measurement signal, reduction of sample flow Qs or by some other way.
The inventor has found that it is possible to reduce or even completely remove the harmful particle accumulation by frequent or infrequent flushing of the particle measurement apparatus and in particularly the sample inlet of the particle measurement apparatus with essentially clean gas.
In one embodiment of the present invention, the suction which drives the sample flow through the inlet nozzle is generated by an ejector which is placed inside the particle monitoring apparatus. Clean gas flow Qc forms the motive fluid of the ejector. Gas flow Qc is ionized and the motive fluid flow is - in addition to suction generation - used to charge the particles entering the particle monitoring apparatus. This ensures that the measurement method described in WO2009109688 Al, which is hereby incorporated by reference in its entirety, can be used for particle measurement.
In the previous embodiment of the invention, flushing can advantageously be achieved by feeding the additional flow QA to the sample inlet which allows using the additional flow as sample dilution flow during normal operation. If Qso is the sample flow without the additional flow QA, then during normal operation of the particle measurement apparatus QA is set to be smaller than Qso. When the apparatus is set into flushing mode, the additional flow QA is set to be higher than Qso, preferably higher than 1,5 times Qso (l,5xQso) and more preferably higher than 2 times Qso (2xQso).
With an embodiment of the present invention where an ejector with motive fluid flow Qc is used to such sample flow Qs into the measurement apparatus, flushing can also be realized by closing the outlet fluid conduit of the measurement apparatus and letting clean air flow Qc pass upstream, through the inlet conduit of the measurement apparatus. In such cases, when using the measurement apparatus described in WO2009109688 Al, it is often preferable to switch of the ionization during flushing. However, if the particle measurement apparatus is at high temperature, preferably higher than 300°C and more preferably higher than 400°C temperature, if oxygen containing gas is used for clean gas flow Qc, and if corona discharge is used for ionization, it may be beneficial to keep the corona voltage on, or even set the corona voltage to a value higher than during normal operation. Corona discharge unit converts at least a fraction of oxygen into ozone, which improves burning off the accumulated soot particles during flushing.
Flushing can be triggered on by time (i.e. at frequent or infrequent periods) or it can be triggered on by some other means. One way to trigger flushing on is to keep information on the total amount of particles which has passed through the particle measurement apparatus and switch flushing on after a predetermined value. Another way to trigger flushing on is to switch it on after particle concentration exceeds a certain limit. This triggering process has the advantage that too high particle concentrations are not allowed to flow into the particle measurement apparatus. Yet another way of triggering flushing on is to monitor the sample flow Qs and switch flushing on if sample flow drops below a certain limit. Sample flow monitoring can be realized in various ways, especially if the flow is monitored before the measurement apparatus is switched into measurement mode. In one embodiment of the present invention, sample flow is monitored by a method described in applicant's currently non-public application PCT/FI2011/050730, which is hereby incorporated by reference in its entirety, where an apparatus and process for measuring particle concentration comprises a sensing element for particle concentration measurement, means for switching or modulating a parameter which affects the output of the sensing element and means for determining the volumetric flow on the basis of the response which switching or modulation creates to the sensing element output.
Brief description of the drawings
In the following, the invention will be described in more detail with reference to the appended schematic drawings, where
Fig. 1 shows a schematic drawing of a particle measuring apparatus with means for setting the apparatus into flush mode;
Fig 2 shows an embodiment where the control means are situated outside the particle sensor and various ways to realize the flush mode are possible.
For the sake of clarity, the figures only show the details necessary for understanding the invention. The structures and details which are not necessary for understanding the invention and which are obvious for a person skilled in the art have been omitted from the figures in order to emphasize the characteristics of the invention.
Detailed description of preferred embodiments
Figure 1 shows a schematic drawing of a particle measuring apparatus 1 with sample flow Qs and additional flow Qc- The particle measuring apparatus 1 comprises means 7,8 for ionizing essentially clean gas flow Qc which is fed into apparatus 1 from gas conduit 4 and through channel 5 and is ionized by corona charger 7 which is electrically insulated by insulator 8 so that a high voltage can be applied to the corona charger 7. "Essentially clean" means in this case that the particle number concentration, expressed in 1/cm , of the essentially clean gas is much lower than the particle number concentration in the sample flow F. Preferably the particle number concentration in the essentially clean gas, Ncg is 10"1 ... 10~6 times the particle number concentration in the sample flow, Ns and more preferably Ncg = lCΓ 3...10~6 x Ns. The clean gas flow Qc enters into an ejector which consists of ejector inlet 9a, ejector throat 9b and ejector outlet 9c. The clean gas flow Qc forms the motive fluid flow of the ejector and generates a negative pressure (as compared to the space from which the sample flow Qs is taken) to the inlet nozzle 14, which negative pressure ensures sample flow Qs to the particle measuring apparatus 1. Ionized clean gas charges particles flowing into the apparatus 1 with the sample flow Qs in the mixing chamber formed by the ejector inlet 9a and ejector throat 9b and charged particles escape the apparatus 1 through outlet channel 3. Apparatus 1 comprises a sensor 101 whose output signal corresponds to the concentration of particles flowing through apparatus 1, i.e. the concentration of particles in the sum of the sample, additional and clean gas flow (QT=QS+QA+QC). Knowing the value of the individual flows Qs, QA and Qc allows determining particle concentration in the sample flow Qs only and thus provides means for particle concentration measurement. Sensor 101 is connected to means 102,103 for triggering the flush function, i.e. setting apparatus 1 into flush mode. Functional unit 102 provides information on the particle concentration. The term "functional unit" means that the unit 102 is functionally an essential part of the present invention but can physically be constructed in various ways, i.e. by analogue or digital means and it can situate either inside or outside the actual measuring apparatus 1. The functional unit
102 is connected into another functional unit 103, which controls the additional flow QA through flow control unit 6*. Functional unit 103 can physically be constructed in various ways, i.e. by analogue or digital means and it can situate either inside or outside the actual measuring apparatus 1 or it can be integrated into flow control unit 6*. Essential feature of the present invention is that the flow control unit 6* can be set to flow QA which is higher than the sample flow Qso, i.e. Qs in a situation where QA is set to zero. Setting QA to such value, preferably to higher than 1,5 times Qso (l,5xQso) and more preferably to higher than 2 times QSo (2xQso) , ensures that no sample flow Qs is sucked into apparatus 1, but actually clean gas flows upstream through inlet channel 2. In the preferred embodiment of the present invention particle concentration measurement is based on measuring the current escaping with the charged particles as explained in prior art publication WO2009109688 Al.
Figure 2 shows an embodiment of the present invention which clarifies the meaning of functional components 101, 102 and 103. Apparatus 1 consists of various components and most of them are not placed inside sensor 1* which comprises the actual particle measurement sensor 101, but also comprises heater He for heating sensor 1*, thermocouple Tc for measuring temperature of sensor 1* and thermal switch TSw for preventing overheating of sensor 1*. Clean gas flow Qc, in this case clean pressurized air flow, is fed into sensor 1* from conduit 4 through oil separator OS, water separator WS, filter F, active carbon filter ACF and membrane dryer, which guarantee that the clean gas is particle and moisture free.
The clean air pressure is adjusted by pressure regulator PR and the pressures upstream and downstream of the regulator are measured by pressure meters PM. The moisture level is controlled by a dew point meter DPM. The clean gas flow Qc into sensor 1* can be switched ON and OFF by a solenoid valve SV. The clean gas flow Qc generates suction to the sensor 1* inlet and thus sample flow Qs is drew into sensor 1*. The volumetric value of sample flow Qs depends in normal operation only on the pressure set by the pressure regulator PR. Sample flow Qs is combined with additional gas flow QA which is fed from the clean gas channel via solenoid valve SC, flow controller 6* and check valve CV. The diluted sample flow, which is the sum of the sample flow and the additional flow, QS+QA, is further directed to sensor l*via heater He and ball valve BV. Temperature of (essentially) heater He is measured by thermocouple TC and heater He is protected by thermal switch TSw, which sets heating power OFF in case of overheating. Flow outlet from sensor 1* passes through ball valve BV before it is exhausted. The temperature of the outlet tubing can be monitored by a
thermocouple TC.
The ball valves are operated by pneumatic actuators PA, which are set to different positions by pressurized gas entering actuators PA through solenoid valves SV. When the solenoid valves are set OFF, pneumatic actuators return to OFF position due to the spring force and pressurizing gas exits from the actuator via silencer S.
The output signal of sensor 6*, corresponding to particle concentration in the flow passing through sensor 1*, i.e. combined flow QS+QA+QC, is fed from sensor 1* into a programmable logic which contains the functional units 102, 103. Based on the concentration result, functional units 102, 103 set the additional flow FA during normal measurement mode to a value which keeps sensor 1* working in the optimal measurement area. The actual figures depend very much on the particle measurement apparatus 1 construction, but e.g. for a Pegasor® PPS, Pegasor Oy, Finland particle sensor, the clean gas pressure PR is set to 1... 2 bar (as compared to ambient air pressure), sample flow F is 3-10 1/min, clean gas flow Fc is 2- 8 1/min and additional flow QA is from zero to Qso- Additional flow QA is typically, but not necessarily, set by a mass flow controller based either on thermal or Coriolis measurement. The selection of the flow controller 6* depends mainly on the dynamic requirements set to the controller. Generally it is beneficial for efficient control of additional flow QA that the response time of the flow controller 6* is less than the response time of sensor 1*. Typically the response time of the flow controller 6* has to be less than 100 ms. The apparatus shown in Figure 2 can be set to flush mode by various embodiments. For each of these embodiments it is common that apparatus 1 comprises means for triggering the apparatus into flush mode. Such means may comprise timers, means for detecting particle concentration 1*, means 102, 103 for triggering apparatus 1 on flush mode based on particle concentration or on total amount of particulate material passed through sensor 1*. It is also common to all embodiments that apparatus 1 comprises means for adjusting the gas flows in such a way that at least part of apparatus 1* is flushed with essentially clean air.
In one embodiment of the present invention, flush mode triggering means 102,103 set the additional gas flow QA to a value which is higher than QSO and thus clean gas flows into sensor 1* as well as upwards through inlet channel 2, i.e. out from the inlet tube. This prevents sample flow into apparatus 1.
In another embodiment of the present invention the sample flow Qs inlet into sensor is prevented by closing inlet ball valve BV. All additional flow QA now flows out from inlet channel 2 and the inlet is effectively flushed.
In yet another embodiment of the present invention the outlet valve BV of sensor 1* is closed and clean air flow Qc passes then upwards through sensor 1* inlet channel 2 and prevents sample flow Qs into sensor 1*. If sensor 1* is similar to the one described in WO2009109688 Al, it is often preferable to switch of the ionization during flushing.
However, if the particle measurement apparatus is at high temperature, preferably higher than 300°C and more preferably higher than 400°C temperature, if oxygen containing gas is used for clean gas flow Qc, and if corona discharge is used for ionization, it may be beneficial to keep the corona voltage on, or even set the corona voltage to a value higher than during normal operation. Corona discharge unit converts at least a fraction of oxygen into ozone, which improves burning off the accumulated soot particles during flushing. Such high temperature may arise from the environment of sensor 1*, or sensor 1* may be heated to such high temperature using heater He of sensor 1*.
In yet another embodiment of the present invention, flush mode triggering means 102,103 set the additional gas flow QA to a value which is higher than Qso and thus clean gas flows into sensor 1* as well as upwards through inlet channel 2, i.e. out from the inlet tube. This prevents sample flow into apparatus 1. The flush flow (part of QA) entering sensor 1* is heated using heater He around the inlet fluid conduit and the voltage of the corona discharge unit in sensor 1* is set to a value which is higher than during normal operation and thus ozone production is enhanced.
It is possible to produce various embodiments of the invention in accordance with the spirit of the invention. Therefore, the above-presented examples must not be interpreted as restrictive to the invention, but the embodiments of the invention can be freely varied within the scope of the inventive features presented in the claims herein below.

Claims

Apparatus (1) for particle measurement, comprising:
a. means (9a-9c) for sucking sample flow (Qs) into apparatus (1)
b. means for triggering (102,103) apparatus (1) into flush mode, in which mode sample flow (Qs) into apparatus (1) is essentially zero; and
c. means for adjusting gas flows in such a way that at least part of apparatus (1) is flushed with essentially clean gas,
c h ar ac te ri z e d in that apparatus ( 1 ) further comprises :
d. means (5) for feeding essentially clean gas flow (Qc) into apparatus (1), the clean gas flow (Qc) forming the motive fluid flow of the ejector (9a-9c) which pulls sample flow (Qs) into apparatus (1) during the normal measurement mode of apparatus (1); and
e. means for triggering (102,103) the apparatus (1) into flush mode by closing the outlet valve (BV) of apparatus (1), which forces clean gas flow (Qc) upwards the sample inlet channel (2).
Apparatus of claim 1, c h ar a c t eri z e d in comprising:
a. means (5) for feeding essentially clean, oxygen containing gas flow (Qc) into apparatus (1); and
b. corona charger (7) used to convert at least part of oxygen in clean gas flow (Qc) to ozone.
Process for flushing a particle measurement apparatus (1) which comprises means for sucking sample flow (Qs) into apparatus (1), comprising:
a. triggering apparatus (1) into flush mode, in which mode sample flow (Qs) into apparatus (1) is essentially zero; and
b. adjusting gas flows in such a way that at least part of apparatus (1) is flushed with essentially clean gas,
c h ar ac te ri z e d in that the process further comprises :
c. feeding essentially clean gas flow (Qc) into apparatus (1), the clean gas flow (Qc) forming the motive fluid flow of the ejector (9a-9c) which pulls sample flow (Qs) into apparatus (1) during the normal measurement mode of apparatus (1); and d. triggering (102,103) the apparatus (1) into flush mode by closing the outlet valve (BV) of apparatus (1), which forces clean gas flow (Qc) upwards the sample inlet channel (2).
Process for flushing particle measurement apparatus (1) as in claim 3,
c h ar ac te ri z e d in comprising:
a. feeding essentially clean, oxygen containing gas flow (Qc) into apparatus (1); and
b. converting at least part of oxygen in clean gas flow (Qc) to ozone.
PCT/FI2013/050184 2012-02-19 2013-02-18 Apparatus and method for flushing particle measurement device WO2013121115A1 (en)

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