Abstract:
The present invention relates to a method and to a device for sampling gaseous compounds contained in a gas stream, notably in diluted exhaust gases from an internal-combustion engine.  
     According to the invention, the method consists in providing passage of the gas stream through at least one sampling channel ( 26, 26   a;    80, 80   a ) containing an adsorbent that traps the polycyclic aromatic hydrocarbons in gaseous form.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and to a device for sampling gaseous compounds contained in a gas stream, notably polycyclic aromatic hydrocarbons contained in diluted exhaust gases from an engine, in particular an internal-combustion engine.  
         [0002]     More particularly, it is aimed at a method and a device for sampling from internal-combustion engines used within the context of test cells, roller type test dynamometers or engine test benches.  
       BACKGROUND OF THE INVENTION  
       [0003]     Some Polycyclic Aromatic Hydrocarbons (PAHs) are generally considered to be toxic pollutants harmful to man&#39;s health and all possible means to identify, quantify and process them if necessary are sought.  
         [0004]     These PAHs are notably present in the exhaust gases of engines, in gaseous form for PAHs whose molecular structure is less than four rings or in condensed form in the particle phase of these gases for PAHs having a molecular structure greater than four rings.  
         [0005]     It is already well-known to sample, identify and quantify PAHs condensed in the particle phase and contained in exhaust gases from an internal-combustion engine, notably for motor vehicles.  
         [0006]     To carry out these operations, the exhaust gases are first diluted in a tunnel, then the particles contained in these gases are recovered by means of a generally Teflon-coated filter. The particles retained by this filter are then extracted by means of an organic solvent and a representative part of the soluble fraction collected is analysed by any means, such as chromatography.  
         [0007]     In some types of internal-combustion engines, notably gasoline engines, the PAHs present in the particle phase are practically nonexistent in the exhaust gases and the major part of the PAHs is in the gaseous form. In this case, the sampling operation performed is not representative of the PAHs present in the exhaust gases.  
         [0008]     A method allowing indirect characterization of the PAHs in gaseous form present in exhaust gases by trapping the hydrocarbons higher than C14 is also well known. From these trapped hydrocarbons, the PAHs in gaseous form are extracted according to long protocols, then identified and quantified by means of complex analysis equipments. These various operations can entail considerable PAH loss or contamination risks.  
         [0009]     The present invention aims to overcome the aforementioned drawbacks by means of a method and of a device allowing simple and efficient sampling of the PAHs in gaseous form and quantification thereof by means of commonly used extraction and analysis equipments.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention thus relates to a method for sampling gaseous compounds contained in a gas stream, notably in diluted exhaust gases from an internal-combustion engine, characterized in that it consists in providing passage of the gas stream through at least one sampling channel containing an adsorbent intended to trap the polycyclic aromatic hydrocarbons in gaseous form.  
         [0011]     Advantageously, the method can consist in carrying out filtration of the gas stream before passage thereof through the adsorbent.  
         [0012]     It can consist in providing passage of the gas stream through a first sampling channel, in stopping passage of the gas stream through the first sampling channel and in providing passage of the gas stream through a second sampling channel.  
         [0013]     In the case where the gas stream is first diluted by a dilution air, the method can consist in providing passage of the dilution air through at least one sampling channel containing an adsorbent trapping the polycyclic aromatic hydrocarbons in gaseous form.  
         [0014]     It can also consist in providing passage of the dilution air through a first sampling channel, in stopping passage of the dilution air through said first sampling channel and in providing passage of this air through a second sampling channel.  
         [0015]     Preferably, it can consist in filtering the dilution air prior to its passage through the adsorbent.  
         [0016]     An adsorbent containing a resin based on porous polymers can be used.  
         [0017]     This resin can be a resin with a matrix of polyaromatic styrene/divinylbenzene type.  
         [0018]     The invention also relates to a device for sampling gaseous compounds contained in a gas stream, notably in diluted exhaust gases from an internal-combustion engine, characterized in that it comprises a sampling unit provided with at least one sampling circuit comprising at least one sampling means containing an adsorbent that traps the polycyclic aromatic hydrocarbons in gaseous form contained in said stream.  
         [0019]     The sampling circuit can comprise a means for filtering the dilution air before it is mixed with the gas stream, when said gas stream contains such a dilution air.  
         [0020]     The sampling circuit can comprise at least one sampling means containing an adsorbent that traps the polycyclic aromatic hydrocarbons in gaseous form contained in said dilution air.  
         [0021]     The sampling means can comprise at least one cartridge containing the adsorbent.  
         [0022]     The adsorbent can comprise a resin based on porous polymers.  
         [0023]     The sampling circuit can comprise a gas stream filtration means.  
         [0024]     The sampling unit can comprise two sampling circuits and throttling means to actuate one or other of the sampling circuits.  
         [0025]     The device can comprise a control unit controlling the sampling unit. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0026]     Other features and advantages of the invention will be clear from reading the description hereafter, given by way of non limitative example, with reference to the accompanying drawings wherein:  
         [0027]      FIG. 1  is a diagrammatic view of a sampling device according to the invention in a first configuration,  
         [0028]      FIG. 2  is a cross-sectional view of a cartridge used in the device of  FIG. 1 , and  
         [0029]      FIG. 3  is a diagrammatic view of the sampling device according to the invention in another configuration.  
     
    
     DETAILED DESCRIPTION  
       [0030]     In  FIG. 1 , the device for sampling the Polycyclic Aromatic Hydrocarbons (PAHs) in gaseous form contained in a gas stream, such as diluted exhaust gases from an internal-combustion engine placed on a roller type test dynamometer, comprises a sampling unit  10  and a control unit  12  controlling unit  10 .  
         [0031]     This sampling device is associated with a sampling tunnel  14  which, in the roller type test dynamometer configuration, is a full-flow dilution tunnel in which exhaust gases  16  from the internal-combustion engine circulate. This tunnel is supplied with dilution air, generally treated ambient air, through a line  18  so as to obtain, at sampling head  20  located close to the tunnel outlet, diluted exhaust gases meeting the current sampling criteria (temperature, water content, . . . ).  
         [0032]     Sampling unit  10  comprises at least one circuit  22  for sampling the PAHs in gaseous form, two in the present case, comprising each two sampling channels, a channel  24  for sampling the PAHs contained in the dilution air and a channel  26  for the PAHs contained in the diluted exhaust gases, as well as a dilution air filtration channel  28 .  
         [0033]     Channel  24  for sampling the PAHs contained in the dilution air comprises a collection unit  30  including a support  32  in which a removable sampling cartridge  34  is arranged. Dilution air filtered beforehand by filtration channel  28  and fed through a line  36  flows through cartridge  34 . A line  38  allows the dilution air to be discharged after collection of the PAHs and sent to any known devices.  
         [0034]     Filtration channel  28  comprises a filtration unit  40  with at least one filter  42  intended to collect all the impurities contained in the dilution air that flows through this filter. The inlet of filtration unit  40  is connected by a line  44  to dilution air line  18  and the outlet of this unit is connected by an outlet line  46  to line  36  leading to the inlet of collection unit  30 .  
         [0035]     Channel  26  for sampling the PAHs contained in the diluted exhaust gases collected by sampling head  20  comprises a collection unit  48  with a support  50  in which a removable sampling cartridge  52  is arranged. The inlet of collection unit  48  is connected by a line  54  to diluted gas sampling head  20  and the outlet of this unit is connected by a line  56  to any known means allowing the exhaust gases to be discharged and treated. As it is known in the art, the exhaust gases circulating in line  54  are already filtered, advantageously downstream from head  20 , which allows to eliminate the impurities likely to clog sampling cartridge  50 .  
         [0036]     Advantageously, supports  32 ,  50  and cartridges  34 ,  52  can be identical for both sampling channels.  
         [0037]     As shown in  FIG. 1 , sampling unit  10  comprises a second circuit  22   a  for sampling the PAHs in gaseous form, comprising two sampling channels  24   a ,  26   a  with the same components as described for circuit  22 . Of course, for device simplification reasons, the same filtration channel  28  is used for circuit  22   a . This allows two successive distinct sampling operations to be carried out without having to stop the PAH sampling procedure or the engine. A throttling means  58  such as a three-way valve is therefore provided on outlet line  46  of filtration unit  40 , which allows to alternately communicate either line  36  or line  36   a . Similarly, lines  56  and  56   a  are each fitted with a throttling means  60  and  60   a , such as a two-way valve of rotary or other type, allowing to provide or to stop the supply of diluted exhaust gases to collection units  48  and  48   a . Valves  60  and  60   a  are controlled in such a way that they are never simultaneously in open or closed position. Thus, when sampling circuit  22  is operational, line  36  communicates with line  46  through the action of valve  58 , valve  60  is in open position to allow passage of the exhaust gases into sampling channel  26  and valve  60   a  is in closed position to prevent circulation of these gases in sampling channel  26   a.    
         [0038]     Control unit  12  allows, as it is known in the art, to parametrize, to permanently control and/or check the sampling conditions, such as the flow rate, the pressure and the temperature of the exhaust gases and/or of the dilution air admitted at the inlet of the collection units, the sampling time, the actuation of the other sampling circuit  22   a  in the case of a two-circuit sampling unit, by actuating throttling means  58 ,  60  and  60   a . This unit also controls all the devices linked with the operation of this sampling unit, such as the pumps allowing circulation of the gas stream in the dilution air filtration  26 ,  28  and sampling  24  channels.  
         [0039]     It also comprises sound and/or visual alarms allowing to detect a possible malfunction or failure to respect a programmed parameter.  
         [0040]     During the sampling process in the configuration of  FIG. 1  corresponding to a vehicle used on a roller type test dynamometer, only sampling circuit  22  is used. In this configuration, valve  60  is in open position, valve  58  is actuated so as to communicate outlet line  46  of filtration channel  28  with inlet line  36  of sampling channel  24 , and valve  60   a  is in closed position.  
         [0041]     The exhaust gases  16  from the internal-combustion engine of this vehicle are mixed in tunnel  14  with dilution air carried by line  18 . Part of this dilution air is sent, prior to being fed into tunnel  14 , through line  44  into filtration channel  28  in order to be freed of the impurities it contains, such as dusts. This filtered dilution air is then sent into unit  30  for collecting the PAHs in gaseous form and flows through sampling cartridge  34 . The PAHs in gaseous form are collected by the adsorbent contained in this cartridge and the dilution air freed of a large part of the PAHs is discharged at the outlet of unit  30  through line  38  and sent to any known means. Simultaneously, the diluted exhaust gases, that have been filtered beforehand, are sampled close to the outlet of this tunnel  14  by head  20  and sent through line  54  into unit  48  for collecting the PAHs in gaseous form. These gases flow through cartridge  52  and the PAHs in gaseous form present in these gases are retained by the adsorbent contained in this cartridge. The PAH-freed exhaust gases are then discharged through line  56  and sent to any known means in order to be treated prior to being discharged to the atmosphere.  
         [0042]     Thus, during this process, the PAHs contained both in the dilution air and in the diluted exhaust gases are recovered by two sampling cartridges arranged in parallel.  
         [0043]     As mentioned above, it is possible to carry out two successive PAH sampling operations without stopping the engine of the vehicle and the sampling device. After a first PAH sampling carried out in sampling circuit  22  by the cartridges of collection units  30  and  48 , this sampling operation is stopped just by actuating throttling means  58  and  60  so as to break the circulation of the dilution air and of the diluted exhaust gases through the various filtration and sampling channels. After this stop, a second sampling of the PAHs contained in the dilution air and in the diluted exhaust gases can be carried out in sampling circuit  22   a  by collection units  30   a  and  48   a , by acting on the opening of throttling means  58 ,  60   a . In this configuration, filtration channel  28  used for the first sampling operation is advantageously used also for the second sampling operation.  
         [0044]     Once the PAH sampling operation is over, cartridges  34 ,  52  are taken off from their supports  32 ,  50 . These cartridges are then treated so as to extract the PAHs therefrom by means of a solvent such as dichloromethane or toluene. Advantageously, this extraction is carried out using an accelerated solvent extraction (ASE) system which has the advantage of using a very small amount of solvent, which saves an adsorbent reconcentration. Furthermore, the extraction system is suited to the configuration of the cartridges so as to avoid dismantling of their constituent elements or transfer of the adsorbent they contain.  
         [0045]     The PAHs extracted for each cartridge are analysed by any means, in particular by coupling chromatography with mass spectrometry or by high-performance liquid chromatography, so as to identify and to quantify the PAHs contained in the dilution air and in the diluted exhaust gases.  
         [0046]     After these analyses, identification and quantification of the PAHs in gaseous form finally contained in the exhaust gases are determined after deduction of the PAHs identified and quantified in the dilution air.  
         [0047]     Advantageously, this sampling device is associated with any known means allowing to sample, to identify and to quantify the PAHs condensed in the particle phase of the exhaust gases.  
         [0048]     Thus, the present invention allows to complete knowledge of the PAHs condensed in the particle phase contained in the exhaust gases by identification and quantification of the PAHs in gaseous form.  
         [0049]      FIG. 2  shows an example of embodiment of sampling cartridge  52  used in unit  48  intended for collection of the PAHs contained in the exhaust gases. Advantageously, the same type of cartridge can be used in unit  30  intended for collection of the PAHs of the dilution air, and in collection units  30   a  and  48   a . As mentioned above, these types of cartridge allow fast and simple adjustment, without any adsorbent handling by the extraction system used.  
         [0050]     This cartridge  52  comprises a substantially cylindrical tubular body  62  closed at both ends by two removable covers  64 ,  66 . Each cover is provided with a bore  68 ,  70  allowing to communicate the inside of body  62  with the exhaust gas inlet of line  54  and the exhaust gas outlet of line  56  respectively. The covers are tightly fastened to body  62  by any known means, by screwing for example. The body contains in its hollow volume an adsorbent  72  consisting of resin based on porous polymers, known as Amberlite. By way of example, the adsorbent is of the type marketed under the trade name XAD2 Supelpak and comprises a resin with a matrix of polyaromatic styrene/divinylbenzene type. A quartz wool bed  74 ,  76  is arranged between each cover  64 ,  66  and adsorbent  72  so as to immobilize this adsorbent inside body  62  without hindering circulation of the exhaust gases through these beds.  
         [0051]     Advantageously, bores  68 ,  70  are designed in such a way that they can be shut off by any known means, such as O-ring caps, after removal of the cartridge from its support.  
         [0052]      FIG. 3  shows the sampling device in another configuration referred to as engine test bench configuration.  
         [0053]     In this configuration, sampling unit  10  also comprises two sampling circuits  22  and  22   a  and it is associated with a microtunnel  14  which contains a dilution air that is already purified and filtered.  
         [0054]     Each sampling circuit comprises an exhaust gas filtration channel  78  connected to a sampling channel  80  intended for the PAHs in gaseous form contained in the filtered exhaust gases.  
         [0055]     Filtration channel  78  comprises a filtration unit  40  similar to the unit described above, with at least one filter  42  for collecting all the impurities contained in the diluted exhaust gases that flow through this filter, an exhaust gas inlet line  82  leading these gases from head  20  to the inlet of unit  40  and an outlet line  84  for the filtered exhaust gases. The inlet line is provided with a throttling means  86 , in form of a valve, allowing to provide or to prevent inflow of the diluted exhaust gases into this filtration unit  40 .  
         [0056]     Sampling channel  80  also comprises a collection unit  48  similar to the collection unit of  FIG. 1 , with a support  50  carrying a removable sampling cartridge  52 . The inlet of collection unit  48  is connected to filtered gas outlet line  84  and the outlet of this unit is connected to a line  88  for discharging the PAH-free diluted exhaust gases.  
         [0057]     Preferably, line  84  can comprise a bypass line  90  allowing to discharge part of the diluted and filtered exhaust gases, notably towards the microtunnel control system (not shown). In this case, a throttling means  92  such as a three-way valve allows to selectively communicate line  90  or line  90   a  with the microtunnel control system.  
         [0058]     During operation, as illustrated by way of example in  FIG. 3 , only sampling circuit  22  is used. In this configuration, valve  86  is in open position so as to communicate, by means of line  82 , the gases collected by sampling head  20  with filtration unit  40  and valve  92  is in a position allowing line  90  to discharge part of the exhaust gases after filtration. These diluted gases flow through filtration unit  40  so as to be freed of the impurities they contain. These filtered exhaust gases are then sent into unit  48  intended for collection of the PAHs in gaseous form through line  84  after flowing through sampling cartridge  52  and line  90 . The PAHs in gaseous form are collected by the adsorbent contained in this cartridge, the PAH-free exhaust gases are discharged through line  88  and sent to any known means.  
         [0059]     As already mentioned above in the configuration of  FIG. 1 , it is possible to carry out two successive PAH sampling operations without having to stop the engine of the vehicle and the sampling device. Thus, after the first PAH sampling operation carried out in sampling circuit  22  by collection unit  48 , circulation of the exhaust gases in the filtration channel is stopped just by closing valve  86 . Once this valve is closed, valve  92  is actuated to allow circulation of the filtered gases in valve  90   a  and valve  86   a  can be opened to allow circulation of the diluted exhaust gases in filtration channel  78   a  and in sampling channel  80   a.    
         [0060]     Once the PAH sampling operations are over, cartridge  52  is removed from its support  50  to be treated in order to extract therefrom, to identify and to quantify the PAHs as described for  FIG. 1 .  
         [0061]     This sampling device will also be associated with any known devices allowing to sample, identify and quantify the PAHs present in condensed form in the particle phase of these gases.