Abstract:
A system for extracting samples from a stream in a conduit utilizing a probe, placed in the stream and having a channel for passing samples from the conduit stream. First and second pressure taps measure the pressure inside and outside the probe. A feedback signal, based on a pressure differential relative to the probe, is generated and controls a valve regulating sample velocity flow through the probe channel, that bears a fixed proportion to the velocity of flow in the conduit. The constant of proportionality between flow velocities in the conduit and the probe may be 1.0, resulting in an isokinetic sampling condition.

Description:
This application is a division of application Ser. No. 09/150,632, filed Sep. 9, 1998, now U.S. Pat. No. 6,062,092. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a system for extracting samples from a stream flowing in a conduit, which is portable and operates on either an isokinetic or a constant volume sampling basis. 
   Constant volume sampling (CVS) has been recognized as the most accurate way of measuring pollutant emissions under conditions of varying flow rate, example, exhaust emissions of a vehicle driven at varying speeds. In a CVS system, the exhaust stream containing the pollutants is diluted with clean air such that the combined flow rate of the mixed exhaust gases and clean air is substantially constant. As a result, the pollutant concentration in the diluted mixture is proportional to the mass flow rate of pollutants in the exhaust stream. Moreover, particulate components are condensed and measured. However, such CVS sampling systems in existence are relatively large and expensive. As a practicality, these systems do not accurately measure exhaust streams from large engines, such as those used in locomotives and heavy trucks. In addition, such systems are not portable. 
   Portable emission sampling systems have also been developed. However, such systems are generally not CVS systems. Instead, prior portable emissions sampling systems rely on measurements of pollutant concentration in the undiluted exhaust and are combined or compared to a direct or indirect measurement of exhaust flow rate. Unfortunately, these portable pollutant concentration systems are inaccurate, since the measuring or estimating of exhaust flow rates varies from vehicle to vehicle. In addition, present pollutant concentration measurement systems are unable to determine particulate emissions accurately. 
   U.S. Pat. No. 5,090,253 describes a flow meter which is used to measure fluid from an exhaust conduit. 
   U.S. Pat. No. 5,333,511 shows a batch exhaust analyzer which is programmed to obtain samples at certain times. 
   U.S. Pat. Nos. 4,586,367, 4,633,706, 4,654,058, and 4,747,297 describe apparatuses for measuring particulate matter in exhaust streams, with or without the use of dilution tubes. 
   U.S. Pat. Nos. 5,058,440, 5,101,670, 5,218,857, and 5,410,907 show pollutant concentration sampling devices which use dilution tunnels. U.S. Pat. Nos. 5,184,501 and 5,337,595 employ pollutant concentration type samplers which also measure bulk stream flow rates. 
   A paper entitled “The Measurement of Gases and Particulate Emissions from Light-Duty and Heavy-Duty Motor Vehicles Under Road Driving Conditions” by Potter, C. J. et al describes an emission sampling system which operates on a CVS principle. This system employs a passive cap for the end of the vehicle exhaust pipe to divide the exhaust flow among a large number of identical parallel small pipes. One of the pipes leads to a dilution tunnel. To maintain proportional flow through all of the pipes, the system requires that the pressure drop across the cap be much greater than the pressure drop between the cap and the dilution tunnel. Changing the pressure in the exhaust system affects the generation of pollutant emissions. Inaccurate measurements ensue, especially in turbocharged engines. In addition, the system is unwieldy for mounting to a vehicle. 
   In measuring particulate emissions from exhaust streams, such as chimney outflows, having particles larger than a few microns, it is important to maintain isokinetic sampling conditions. In other words, the velocity of the gas entering a sample probe must possess substantially the same velocity as the gas in the exhaust stream. If such condition is not achieved, the inertia of particles in the exhaust stream may result in a sample being enriched or depleted in particles, relative to the concentration of particles in the exhaust stream. U.S. E.P.A. Method 5—“Determination of Particulate Emissions from Stationary Sources” documents a standard procedure for measuring particulate emissions in stationary exhaust stacks, using isokinetic sampling. The method requires the use of a separate pitot tube and orifice meter. Manual adjustments and calculations achieve isokinetic sampling only under steady state conditions. 
   A system which is capable of automatically extracting a proportional or isokinetic sample of gas and/or particulate emissions from an exhaust stream under varying flow rates, which is portable, accurate, and does not interfere with the exhaust stream would be a notable advance in the field emission measurements. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention a novel and useful system for extracting samples from a stream is herein provided. 
   The portable emission system of the present invention utilizes a probe which may be located in the exhaust conduit of an internal combustion engine such as those found in a vehicle. The probe includes a channel for gathering and passing emission from the exhaust conduit for analysis. The probe may take the form of a tube which extends a certain distance into the exhaust conduit with its long axis parallel to the direction of flow of emissions or constituents in the exhaust conduit. The probe is intended to extract a fixed proportion of the total exhaust gas flow, i.e. isokinetic sampling conditions. 
   To maintain constant volume and isokinetic conditions at the probe inlet within the exhaust conduit, means is employed for controlling the velocity of flow through the probe channel to correspond to the velocity of flow through the exhaust conduit. To achieve this result, means is provided for generating a feedback signal representing the relative velocities of flow through the exhaust conduit and flow through the probe channel. In this regard, first pressure measuring means determines the pressure within the probe channel and second pressure measuring means determines the pressure in the exhaust conduit. Both pressure measurements are sent to comparator means where the pressure differential is transduced into an electrical signal representing such pressure differential. 
   The present CVS system also includes a dilution conduit carrying ambient air, or other diluent fluid, from a source by the use of a blower or pump. Ambient air, or other diluent fluid, from the source is also filtered in this regard. The probe channel delivers emissions through an exhaust line to the dilution conduit at a place of entry downstream from the ambient air source. Valve means is provided in the dilution conduit to regulate the flow rate of ambient air. The valve means utilizes the signal from the comparator means and provides throttling of the flow of ambient air in response to the same. In other words, to increase the flow rate of emissions from the probe channel, the flow of ambient air through the dilution tube is reduced and vice versa. In any case, the velocity of the sample flowing through the probe channel and the velocity of constituents flowing through the exhaust conduit are maintained correspondent to one another, i.e., essentially equal. 
   A sample is tapped from the dilution tunnel downstream of the place of entry of the emissions exhaust line from the probe channel. Such sample tap is then sent to an instrument which continuously measures the concentration of emissions, or to a batch type measuring device. The latter is particularly useful in measuring particulate emissions from an internal combustion engine. Both the batch and continuous measurement determine emission concentrations proportional to the mass flow of emissions in the vehicle exhaust conduit. A background sample may also be taken upstream of the place of entry of the emissions exhaust line. 
   In an isokinetic version of the system of the present invention, the feedback signal regulates a pump which forces exhaust particulates into a filter. Particulate-free gas is then sent to a condenser and gas meter. Measurements of the metered gas, condensate, and filter particulates determines particulate concentration. 
   It may be apparent that a novel and useful system for sampling emissions from an exhaust conduit has been described. 
   It is therefore an object of the present invention to provide a system for sampling emissions from an exhaust conduit of a pollution source which extracts particulate samples on an isokinetic basis. 
   Another object of the present invention is to provide a system for sampling emissions from an internal engine by which a probe in an exhaust conduit of the internal combustion engine extracts a fixed proportion of the total exhaust gas flow. 
   A further object of the present invention is to provide a system for sampling emissions from an exhaust conduit of an internal combustion engine which may be used to measure such emissions as a fraction of the total exhaust flow without changing the exhaust back pressure or otherwise affecting the operation of the internal combustion engine. 
   Yet another object of the present invention is to provide a system for sampling emissions from an exhaust conduit of an internal combustion engine which is capable of measuring gaseous pollutants and particulate matter pollutants. 
   A further object of the present invention is to provide a system for sampling components in a conduit stream which is portable and does not require extensive adaption to engines of various sizes. 
   Another object of the present invention is to provide a system for sampling emissions from an exhaust conduit of an internal combustion engine which is accurate and does not require the independent measurement of the exhaust mass flow rate from the exhaust conduit of the internal combustion engine. 
   Another object of the present invention is to provide a system for sampling emissions from an exhaust conduit of an internal combustion engine which is capable of determining measurements of particulate matter in the exhaust conduit and provides necessary cooling without additional equipment required in the prior art. 
   Another object of the present invention is to provide a system which is capable of measuring pollutant emissions from motor vehicles on a portable constant volume sampling basis, and is capable of measuring particulate emissions from chimneys on an isokinetic sampling basis. 
   A further object of the present invention is to provide a system for extracting and diluting a continuous proportional sample of the exhaust flow from a source that obviates the need for using a special cap on the exhaust conduit, which creates a detrimental backpressure on the exhaust conduit. 
   The invention possesses other objects and advantages especially as concerns particular characteristics and features thereof which will become apparent as the specification continues. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a flow diagram of the system of the present invention demonstrating constant volume sampling. 
       FIG. 2  is a sectional view of the probe of the present invention. 
       FIG. 3  is a sectional view taken along line  3 — 3  of  FIG. 2 . 
       FIG. 4  is a flow diagram of the system demonstrating isokinetic sampling. 
   

   For a better understanding of the invention references made to the following detailed description of the preferred embodiments which should be taken in conjunction with the hereinabove described drawings. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Various aspects of the present invention will evolve from the following detailed description of the preferred embodiments thereof, which should be referenced to the previously described drawings. 
   The invention as a whole is shown in the drawings by reference character  10 ,  FIG. 1 . Generally system  10  may be used to extract samples from a stream flowing in a conduit. In the present embodiment, system  10  is employed to obtain accurate emission samples from exhaust conduit  12  which may lead from any internal combustion engine such as that found in an automobile, truck, train, boat, and the like. Typically, the emissions measured from exhaust conduit  12  include oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO 2 ), and particulate matter such as unburned hydrocarbons. System  10  of the present invention is deemed to be a portable type system, one that can be mounted on and “ride along” with the vehicle to measure emissions while such vehicles are operating in a normal fashion. The present system obviates the need for an expensive chassis dynamometer system of the prior art. Also, the system  10  of the present invention is responsive to rapid changes in exhaust flow rates which are the result of differences in engine speed. 
   System  10  includes as one of its elements a probe  14  which is located within chamber  16  of exhaust conduit  12 . Probe  14  directly connects to an exhaust line or channel  18  which passes exhaust gas from exhaust chamber  16  of conduit  12 . Referring now to  FIG. 2 , it may be observed that probe  14  is in the form of a tube  20  having a mitred edge  22 . The long axis  24  of probe  14  is positioned essentially parallel to the directional flow of gases through exhaust conduit  12 , represented by multiplicity of directional arrows  26 . The probe  14  is held in that position by any suitable fastening means such as a bracket (not shown). Thus, a portion of the exhaust gas from the engine associated with exhaust conduit  12  flows through chamber  28  of probe  14 . 
   Means  30  is also provided for controlling the velocity of the exhaust gas stream through chamber  28  of the probe  14 . Again, referring to  FIG. 2 , means  30  utilizes a quartet of tubes  32  which are mounted to the exterior of probe tube  22  by any suitable means such as high temperature vacuum brazing. For example, probe tube  22  may possess a central diameter of approximately 8 mm while each of the plurality of tubes  32  might possess a diameter of approximately 2 mm. Referring to  FIG. 3 , it may be observed that tubes  34  and  36  include static pressure taps or openings or ports  38  and  40 , respectively, to chamber  28  of tube  20 . Directional arrows  42  indicate that chamber  42  and  44  of tubes  34  and  36  communicate with chamber  28  of tube  20 . Tubes  46  and  48 , on the other hand, include pressure taps or ports  50  and  52  which communicate with chamber  16  of exhaust conduit  12 . The external pressure taps  50  and  52  are formed into an enclosed path on and that extends to the end of the probe  20  and adjacent to the internal pressure taps  38  and  40 , respectively. Directional arrows  54  and  56  indicate this communication. Thus, tubes  34  and  36  are capable of measuring the static pressure within chamber  28  of probe tube  20 , while tubes  46  and  48  are capable of measuring the static pressure within exhaust conduit  12 . Dual tubes are employed to eliminate disparate measurements of probe  12 , due to the effect of small misalignments between the long axis  24  of probe  14  and the direction of flow, direction arrows  26 , of the exhaust gas in exhaust conduit  12 . 
   Turning again to  FIG. 1 , pairs of tubes  34  and  36  and pairs of tubes  46  and  48 , each pair combined to a single tube, pass to differential pressure sensor or comparator  58 . Sensor  58  produces an electrical signal which is sent through electrical leg  60  to automatic controller  62 . An electrical feedback signal is then sent to stepping motor  64  via electrical conduits  66 . Stepping motor  64  is capable of rotating throttle valve  68  according to directional arrow  70 , the purpose of which will be discussed hereinafter. 
   System  10  further includes a dilution conduit or tunnel  72 ,  FIG. 1 , which is of sufficient length and provides sufficient flow to assure turbulent mixing within chamber  74  of the same. Channel  18  communicates with dilution conduit  72 . Neck  76  of dilution conduit connects to a filter  78 . Ambient air, or other diluent fluid, from a source (usually the external atmosphere) flows through filter  78  by the motivating power of pump  80 , which may be a blower. Blower  80  is used in conjunction with a critical flow venturi  82 . Thus, throttle  68  is rotated by stepping motor  64  to control the flow of air through dilution tunnel  72 . Differential pressure sensor  58  may detect a static pressure inside probe chamber  28  which is higher than the static pressure within chamber  16  of exhaust conduit  12 . In such a case, throttle  68  will close slightly. The terminus  84  of exhaust line  18 , located downstream of ambient air filter  78 , senses a slight decrease in pressure. This causes the rate of flow through the exhaust line  18  to increase. This, in turn, increases the velocity of exhaust gases within chamber  28  of tube  20  and lowers the pressure differential between chamber  28  of tube  20  and chamber  16  of exhaust conduit  12 . Conversely, throttle  68  will open slightly when a higher pressure is detected in chamber  16  of conduit  12  than in chamber  28  of tube  20 . This, in turn, reduces the flow of exhaust sample through exhaust line  18 . Thus, a proportional sampling condition exists between tube  20  and exhaust conduit  12  due to the zeroing-out of the pressure differential between chambers  28  and  16 , respectively. It should be noted that temperature sensor  86  may be employed in certain cases within chamber  74  of dilution conduit  72 . 
   The sample tap  88  within chamber  74  downstream of terminus  84  of exhaust sample line  18  directs a properly diluted sample of constituents therein, such as gaseous and particulate pollutants, for analysis. For example, pump  90  and sample bag  92  are capable of gathering gaseous pollutants in a batch process for analysis. On the other hand, pump  92  and continuous gas monitor  94  are capable of analyzing pollutants on a continuous level. Continuous gas monitor  94  may take the form of a California Analytical Instruments Model ZRH, for measuring CO and CO 2 , and a Thermo Electron Model 42 analyzer for measuring NO x . Filter  96 , flow meter  98 , and pump  100  continually withdraw sample, containing constituents, from sample tap  88  and send the same to the ambient atmosphere. It should be noted that filter  96  may be used to collect particulate matter in many cases. Background sample tap  102  is employed to monitor the gaseous chemicals in the ambient air upstream at exhaust line terminal  84 . 
   Referring now to  FIG. 4 , an isokinetic application of the system of the system of the present invention is shown in which probe  14  is placed within chamber  16  of exhaust conduit  12 . Pairs of tubes  34 ,  36  and  46 ,  48  lead from probe  14  in the same manner as the embodiment depicted in  FIG. 1 . Differential pressure sensor or comparator  58  produces an electrical signal, again, to controller  62 . Electrical output leg  104  of controller  62  sends a signal to variable speed pump  106  which pulls a gas sample containing particulate matter through conduit  108  and to filter  110 . Exhaust material, generally in gaseous form, then passes to condenser  112  where liquids are formed. In most cases, such liquids take the form of water body  114 . Gases from condenser pass from condenser  112  through conduit  116 , to dry gas meter  118 . Arrow  120  represents the exhaust stream from dry gas meter  118 . 
   In operation,  FIG. 1 , probe  14  is placed within exhaust gas conduit  12  in axial position. Pollutant samples pass through probe  14  and exhaust line  18 , exiting the same at terminus  84  within dilution conduit  72 . Means  30  for controlling the velocity through probe  14  includes pairs of tubes  34  and  36  and  46  and  48  to determine the differential pressure between chamber  16  of exhaust conduit  12  and interior chamber  28  of probe tube  20 . An isokinetic condition may be maintained between probe  14  and exhaust conduit  12  by means  30 . Thus, a gaseous sample exiting terminus  84  is properly diluted resulting in pollutant quantities proportional to those in exhaust conduit  12 . This result is achieved by pairs of tubes  34  and  36 , as well as,  46  and  48  which measure the pressure differential between probe  14  and exhaust conduit  12 . Differential pressure sensor  58 , controller  62 , stepping motor  64 , and throttle  68  adjusts the flow of ambient air through dilution tube  72 . Sample tap  88  passes properly diluted emission samples to a batch analysis at sample bag  92  or to continuous sampler  94 . Particulate matter may be collected for later analysis at filter  96  adjacent flow meter  98  in the pump  100 . Background sample tap  102  is used to analyze the ambient air prior to the injection of the exhaust gas sample through terminus  84  of exhaust line  18  within dilution conduit  72 . 
   Turning to  FIG. 4 , the isokinetic operation is illustrated in which probe  14  produces a feedback signal through electrical leg  104  in the same manner as shown in  FIG. 1 , via differential pressure sensor  58  and controller  62 . Feedback signal  104  regulates the speed of pump  106  according to the velocity of the exhaust stream within chamber, 16 represented by directional arrow  122 . Thus, particulates passing through conduit  108  and are captured by filter  110 . The particulate matter found in filter  110  under such isokinetic sampling conditions represent a fixed proportion of the total particulates in the exhaust flow  122  within chamber  116  of exhaust conduit  12 . In other words, filter  110  has captured or acquired a fixed fraction of the total exhaust flow  122  without changing the exhaust back pressure within conduit  12 , or otherwise affecting the operation of the vehicle to which exhaust conduit  12  is connected. Weighing the particulates in filter  110 , water body  114  in condenser  112 , and the quantity of air detected by meter  118  results in a measurements of particulate concentration within conduit  12 . Thus, the instantaneous mass emission rate is determined. 
   While in the foregoing, embodiments of the present invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, it may be apparent to those of skill in the art that numerous changes may be made in such detail without departing from the spirit and principles of the invention.