Abstract:
An engine emissions test system according to the principles of the present disclosure includes a sampling conduit, at least one sample bag, a read circuit, and a fill circuit. The sampling conduit is configured to receive exhaust from an engine. The at least one sample bag is configured to store a sample of exhaust. The read circuit is configured to communicate the stored sample of exhaust between the at least one sample bag and an analyzer. The fill circuit includes a fill gas line configured to provide a fill gas to be mixed with the sample of exhaust. The fill gas line extends between a fill gas source and the read circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure is a divisional of U.S. patent application Ser. No. 13/463,226 (now U.S. Pat. No. 9,097,623), filed on May 12, 2012, which is a continuation of U.S. patent application Ser. No. 12/501,767 (now U.S. Pat. No. 8,181,543), filed on Jul. 13, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/855,246 (now U.S. Pat. No. 7,559,262), filed on Sep. 14, 2007, which claims the benefits of U.S. Provisional Application No. 60/845,271, filed on Sep. 15, 2006. The entire disclosures of the applications referenced above are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    With traditional constant volume samplers (CVS), engine exhaust is diluted with ambient air, and a small sample of the diluted exhaust is proportionally extracted and stored in one or more sample bags. Depending upon the engine size, drive cycle and ambient conditions, the CVS total flow rate, which includes both ambient air and engine exhaust, is selected to ensure the sample collected does not condense water when stored in the bags, or during subsequent analysis. This flow rate is determined by calculating the average dew point in the bag sample. 
         [0003]    It is desirable to avoid water condensation within the sample bag for several reasons. First, condensation of water impacts the accuracy of the exhaust analysis. Some substances in the exhaust become soluble in water. These substances can be effectively “pulled out” of the exhaust so that they are not measured at the conclusion of the test. Also, the water vapor that becomes condensed is not measured and included in the test results. Second, the condensation can cause the collection of substances on the inside of the bag as the water subsequently evaporates thereby leaving an undesirable residue that will be present during future tests. Finally, new legislation requires no condensation in the sample bags. 
         [0004]    There are several factors that make it difficult to avoid condensation of the sample within the bags. For example, use of alternative fuels, new test cycles and larger displacement engines all can lead to condensation within the sample bags. For example, if an aggressive test cycle is performed and the traditional optimal flow CVS flow rate is selected, then condensation will form. This is particularly true for test cycles where the maximum exhaust comes very early in the collection of the sample. The dew point of the sample may be higher than ambient conditions even though the average water concentration in the bag is less than ambient at the end of the cycle. CVS optimal flow rate is selected to ensure the average water concentration in the bags has a dew point less than ambient temperature. 
         [0005]    One potentially problematic test is the newly proposed US06 drive cycle. The cycle is 600 seconds long and the second sample bag used in the test will start filling 133 seconds into the drive cycle. The traditional desired flow rate is 1050 scfm when diluting a gas with a dew point of 18° C. For vehicles running on ethanol fuel, the ending dew point in the bag will be just above 23° C., with a peak dew point at the beginning of the second bag fill of 27° C. This is often higher than ambient conditions in a test cell. In this scenario, the CVS flow rate would typically be selected to dilute for the average bag dew point of 23° C., which would result in the sample condensing in the second sample bag due to the initial high peak. 
         [0006]    In order to avoid condensation in the bag, the CVS flow rate would have to be raised to 2000 scfm to avoid the initial peak, which is undesirable. Increasing the CVS flow rate would reduce the already low concentration of exhaust within the sample making it more difficult to analyze. One approach that can be used to avoid condensation is to heat the bags, which would maintain the sample gas temperature above the maximum dew point and avoid the initial dew point peak. However, additional equipment must be employed for such an approach leading to a higher cost CVS 
         [0007]    Hybrid vehicles pose unique problems when trying to determine mass emissions rates during emission test sequences. Current test procedures require bag sampling using either a CVS method or a bag mini-diluter (BMD) method. Hybrid vehicles that produce exhaust gas from internal combustion engines may not be in operation or may operate for a brief period of time over the test cycle. When using the CVS method the CVS bag sample is overdiluted and determination of mass emissions is difficult since the dilution factor from the CVS method is very high. When using the BMD method the bag sample is diluted at a fixed rate so the dilution factor issue is resolved but the sample is collected proportional to the exhaust flow. Since there are periods of operation where either no exhaust flow is expelled out of the hybrid vehicle or the vehicle exhaust is expelled intermittently very little exhaust may be emitted during the sample phase. Therefore, very little sample will be collected in the sample bag making accurate analysis more difficult. 
       SUMMARY 
       [0008]    A disclosed method of collecting an exhaust gas sample includes pre-filling a sample bag with a pre-fill gas. An exhaust sample is collected in the sample bag with the pre-fill gas remaining in the sample bag. 
         [0009]    An exhaust sampling system is disclosed that includes a pre-fill gas source having a pre-fill gas. A sampling conduit is configured to collect exhaust gas and make-up gas. A sample bag is fluidly connected to the sampling conduit and the pre-fill gas source. A controller is programmed to run a test procedure in which a sample of exhaust gas and make-up gas is collected in the sample bag. The controller is configured to send a command that fills the sample bag with pre-fill gas prior to the test procedure. The pre-fill gas remains in the sample bag during the test procedure. In one example, the amount of pre-fill gas is selected to prevent the sample from condensing in the sample bag during the test procedure. In another example, the amount of pre-fill gas is selected to provide a sufficient volume of gases for analysis during the test procedure. 
         [0010]    These and other features of the disclosure can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic view of an example CVS including an example pre-fill gas system. 
           [0012]      FIG. 2  is a flow chart depicting an example pre-fill procedure. 
           [0013]      FIG. 3  is a schematic view of an example BMD including an example pre-fill gas system. 
           [0014]      FIG. 4  is a flow chart depicting an example pre-fill procedure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A schematic view of an exhaust sampling system  10  is shown in  FIG. 1 . In this disclosure, like numerals are used to indicate like elements. The system  10  includes a make-up air inlet  12  that includes a filter  14 . The inlet  12  provides make-up air  32  to a sampling conduit that also receives exhaust from a tailpipe  16  of an engine  18 . The make-up air  32  and exhaust E pass through a mixing plate  20  to promote homogeneous mixing of the make-up air  32  and exhaust E as it flows through a tunnel  22  prior to sampling. A constant volume of the mixture is drawn through the sampling conduit by a pump  28 . A heat exchanger  24  is used, in one example, to maintain the mixture at a desired temperature. The mixture is measured by a measuring device  26 , prior to being expelled by the pump  28  through a discharge  30 , to determine the quantity of mixture flowing through the sampling conduit. It should be understood that the system  10  is only exemplary and that many modifications can be made and still fall within the scope of the claims. 
         [0016]    The engine  18  is run through a test procedure to determine the quantity of exhaust byproducts that the engine  18  produces. For the example system  10  shown, only a small portion of the exhaust E is sampled for subsequent analysis. As the amount of exhaust E produced by the engine  18  during the test procedure fluctuates, the make-up air  32  provides the remainder of the volume. The amount of byproducts in the sample is so small at times, that the components in the make-up air can impact the test results. To this end, a pump  34  draws an amount of make-up air into background bags  42  during the test procedure so that the effects of the make-up air can be taken into account. Valves  36 ,  40  regulate the flow of make-up air  32  into the background bags  42 , and the flow meter  38  measures the amount of make-up air collected within the background bags  42 . 
         [0017]    A sampler  43  collects a small sample of the mixture for collecting into sample bags  52 . One or more sample bags  52  may be used, and filling of the sample bags may be scheduled during various periods of the test procedure. A pump  44  draws the sample through a valve  46  and flow meter  48 . Valves  50  regulate the filling of the sample bags  52 . After the sample bags  52  have collected the samples, an analyzer  60  analyzes the contents of the sample bags  52  and  42  to determine the amount of various combustion byproducts. A pump  54  flows the sample through valve  56  and flow meter  58 . It should be understood that more or fewer pumps, valves and flow meters than shown could be used. 
         [0018]    A controller  70  communicates during the test procedure with the various pumps  28 ,  34 ,  54 ,  64 ,  72 , valves  36 ,  40   46 ,  50 ,  56 ,  66 ,  74  and flow meters  38 ,  48 ,  58 ,  68  to obtain readings and direct their operation. All of the connections between the controller  70  and these components are not shown for clarity. 
         [0019]    In one example of this disclosure, one or more of the sample bags  52  is pre-filled with dry gas to prevent any peaks in dew point during the test procedure that would lead to undesired condensation. A source of pre-fill gas  62  is shown schematically in  FIG. 1 . An amount of pre-fill gas is pumped into one or more of the sample bags  52  prior to the collection of the exhaust sample. The controller  70  commands the pump  64  and valve  66  to fill a desired amount of pre-fill gas to a desired sample bag  52  to prevent condensation in the sample bag  52 . The pre-fill may also incorporate other means to fill the bag such as a compressed air source. The flow meter  68  measures the amount of pre-fill gas. 
         [0020]    An example test procedure  78  according to the disclosure is shown in  FIG. 2 . The amount of pre-fill gas needed to prevent condensation is calculated at block  84  based upon one or more of the following (indicated at block  86 ): CVS test flow rate, dew point of the pre-fill gas, dew point of the make-up air, and anticipated test dew point within the sample bag  52 . Calculations are performed based upon the various factors of each test to determine the minimum amount of pre-fill gas required to avoid condensation. This approach is desirable to minimize further dilution of the sample. The bags susceptible to condensation would be filled with dry clean air prior to the sampling (filling of the bag). According to this disclosure, the initial peak of wet gas is compensated for by the dry air, thus preventing condensation. 
         [0021]    The sample bags  52  and ambient bags  42 , as well as any intervening conduits, are evacuated through vent  74  using pump  72  ( FIG. 1 ), as indicated at block  80 . The system  10  is leak checked (block  82 ), and the sample bag  52  is filled with a predetermined amount of pre-fill gas, as indicated at block  88 . The amount of pre-fill gas is measured. The exhaust sample is collected and its mass and/or volume measured in the sample bag  52  during the test procedure with the pre-fill gas remaining in the sample bag  52 , as indicated at block  92 . As the sample bag  52  is filled during the test procedure, the dew point of the predetermined amount of pre-fill gas prevents the exhaust sample from condensing within the sample bag  52 . The contents of the sample bag  52  and ambient bag  42  can then be analyzed to determine the amount of byproducts within the sample, as indicated at block  94 . 
         [0022]    In one example, the same “zero grade” or “instrument grade” air that is typically used to initially calibrate the system  10  can be used to pre-fill the sample bag  52 . As a result, the pre-fill feature can be incorporated into a traditional CVS with very little modification and expense. Alternatively, ambient air can be used to pre-fill the sample bag  52 . Using ambient air may be desirable since it makes accounting for the pre-fill air&#39;s affects at the analysis stage of the test simpler. The analytical equations set forth in the Code of Federal Regulations for test procedures are such that accounting for pre-fill ambient air is more straightforward. Using zero grade air instead of ambient air requires modifications to those equations, which may be undesired by some customers. For example, using zero air requires using dilution ratio equations similar to those used for a BMD to determine the concentration necessary to use traditional CVS equations. It should be understood that any number of suitable substances may be used to pre-fill the sample bags  52 . 
         [0023]    A schematic view of another exhaust sampling system  110  is shown in  FIG. 3 . The system  110  illustrates a BMD sampling system in which the exhaust sample is diluted at a fixed rate and the exhaust gas sample is collected in proportion to the exhaust flow from the engine  118 . In the example, the engine  118  includes an internal combustion engine  96  and another engine  98  (such as an electric motor) that together comprise the propulsion unit for a hybrid vehicle. The other engine  98  may be used to propel the vehicle in varying degrees throughout vehicle operation. As a result, there may be periods of operation when the engine  118  expels little or no exhaust through its tailpipe  116  when the other engine  98  is in use. 
         [0024]    The system  110  includes a “mini-diluter” having a probe or sampler  143 . The sampler  143  collects a small sample of exhaust gas from the tailpipe  116 . The sample exhaust gas is drawn into a sampling unit  102  by a pump  144 . The sampling unit  102  includes a mixer  104 . A diluent  112  is introduced to the sampling unit  102  at the mixer  104  where it commingles with the sample exhaust gas to produce a diluted exhaust gas that is supplied to a diluted exhaust gas outlet  108 . In one example, the diluent  112  is nitrogen or zero air. The diluent  112  is measured by a flowmeter  106 . The sample exhaust gas flow corresponds to a difference between a total exhaust gas flow measured by a flowmeter  148 , which receives the diluted exhaust gas from the outlet  108 , and the flowmeter  106 . In the example shown, the exhaust gas sample is measured directly by a flowmeter  141 . 
         [0025]    The engine  118  is run through a test procedure to determine the quantity of exhaust byproducts that the engine  118  produces. For the example system  110  shown, only a small portion of the exhaust is sampled for subsequent analysis. As the amount of exhaust produced by the engine  118  during the test procedure fluctuates, the diluent  112  provides the remainder of the volume. 
         [0026]    The sampler  143  collects a small sample of the mixture for collecting into sample bags  152 . One or more sample bags  152  may be used, and filling of the sample bags may be scheduled during various periods of the test procedure. Valves  150  regulate the filling of the sample bags  152 . After the sample bags  152  have collected the samples, an analyzer  160  analyzes the contents of the sample bags  152  to determine the amount of various combustion byproducts. A pump  154  flows the sample through valve  156  and flow meter  158 . It should be understood that more or fewer pumps, valves and flow meters than shown could be used. 
         [0027]    A controller  170  communicates during the test procedure with the various pumps  128 ,  154 ,  164 ,  172 , valves  150 ,  156 ,  174  and flow meters  106 ,  148 ,  158  to obtain readings and direct their operation. All of the connections between the controller  170  and these components are not shown for clarity. 
         [0028]    In one example of this disclosure, one or more of the sample bags  152  is pre-filled with dry gas to provide a sufficient volume of gases in the bags  152  for subsequent analysis. A source of pre-fill gas  162  is shown schematically in  FIG. 3 . A common nitrogen source can be used for both the diluent  112  and the pre-fill gas  162 . In an example, the pre-fill gas  162  is nitrogen. An amount of pre-fill gas is pumped into one or more of the sample bags  152  prior to the collection of the exhaust sample. The controller  170  commands the pump  164  to fill a desired amount of pre-fill gas to a desired sample bag  152  to sufficiently fill the sample bag  152 , discussed in more detail below. The pre-fill may also incorporate other means to fill the bag such as a compressed air source. The flow meter  106  measures the amount of pre-fill gas. Using the same flow meter  106  to measure the pre-fill gas and the diluent during the test procedure minimizes calibration error. 
         [0029]    An example test procedure  178  according to the disclosure is shown in  FIG. 4 . The amount of pre-fill gas needed to provide a sufficient volume of gases in the bags  152  is calculated at block  184  based upon one or more of the following (indicated at block  186 ): time for the sample to stabilize (time period for the sample to fully reach the analyzer  160 ), the flow rate of gases within the analytical system and the analysis time required. In regards to the analysis time required, the amount of sample collected within the bags  152  should be enough to provide the analytical system with approximately 3 minutes of analysis time. This is based upon the typical scenario in which a typical analysis by the analyzer  160  takes approximately 30 seconds to 1 minute. Typically, three or four analyses are conducted with the contents of a given bag  152  in connection with the steps described in relation to block  192 . Calculations are performed based upon the various factors of each test to determine the minimum amount of pre-fill gas required for analysis. Pre-filling one or more of the bags  152  is desirable to ensure that enough sample is available for analysis even if the hybrid vehicle produces no exhaust during the sampling period. 
         [0030]    The sample bags  152 , as well as any intervening conduits, are evacuated through vent  174  using pump  172  ( FIG. 3 ), as indicated at block  180 . The system  110  is leak checked (block  182 ), and the sample bag  152  is filled with a predetermined amount of pre-fill gas, as indicated at block  88 . The amount of pre-fill gas is measured. The exhaust sample is collected and its mass and/or volume measured in the sample bag  152  during the test procedure with the pre-fill gas remaining in the sample bag  152 , as indicated at block  192 . 
         [0031]    The collect/measure sample step in block  192  requires a sufficient volume of gases within each sample bag  152  in order to perform the measuring steps. The measuring steps first includes “sniffing” the sample bag  152  to determine the concentration of byproducts that will be analyzed. The analyzer  160  typically includes multiple analyzers, each corresponding to a different concentration range. A particular analyzer having a range corresponding to the “sniffed” range is selected for use in subsequent analysis of each byproduct in the contents of sample bag  152 . Secondly, a calibration of the analytical system is performed, including zeroing the instruments, which may be performed by flowing nitrogen through the instruments. Thirdly, an analysis of the contents of the sample bag  152  is then performed to determine the amount of byproducts collected within the bag, such as carbon dioxide, carbon monoxide, hydrocarbons, and oxides of nitrogen. Finally, a zero check is performed to ensure that none of the instruments have drifted during the analysis. Any of the measuring steps above may be repeated if the system fails the calibration check. The system  10  and method  78  shown in  FIGS. 1 and 2  also employ the above collect/measure sample step in block  92 . 
         [0032]    In a typical BMD system, the dilution ratio is measured as the ratio sample flow to total flow of the BMD and integrated over the test procedure. In the example system  110 , the dilution ratio integrates the amount of dilution gas in a given bag  152  from the pre-filled process plus the amount of diluent used during the test procedure. The dilution ratio for the system  110  is as follows (block  190 ): 
         [0000]    
       
         
           
             
               
                 
                   
                     DR 
                     = 
                     
                       
                         
                           PrefillBagVol 
                           + 
                           DillutionVol 
                         
                         SampleVol 
                       
                       + 
                       1 
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0000]    where PrefillBagVol, DilutionVol and SampleVol respectively correspond to the pre-fill gas, diluent and sample exhaust gas volumes relating to a given sample bag  152 . The contents of the sample bag  152  and ambient bag  142  can then be analyzed to determine the amount of byproducts within the sample, as indicated at block  194 . The diluent flow  112  through flow meter  106  may be set to zero, such that the exhaust sample within the bag  152  is only diluted by pre-fill gas  162  within the bag  152  (i.e., Dilution Vol=0). 
         [0033]    In one example, the same “zero grade” or “instrument grade” air that is typically used to initially calibrate the system  110  can be used to pre-fill the sample bag  152 . As a result, the pre-fill feature can be incorporated into a traditional BMD with very little modification and expense. Alternatively, ambient air can be used to pre-fill the sample bag  152 . Using ambient air may be desirable since it makes accounting for the pre-fill air&#39;s affects at the analysis stage of the test simpler. The analytical equations set forth in the Code of Federal Regulations for test procedures are such that accounting for pre-fill ambient air is more straightforward. Using zero grade air instead of ambient air requires modifications to those equations, which may be undesired by some customers. It should be understood, however, that any number of suitable substances may be used to pre-fill the sample bags  152 . 
         [0034]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.