US20160209300A1

US20160209300A1 - Exhaust Sampling System And Method For Water Vapor Management

Info

Publication number: US20160209300A1
Application number: US15/080,623
Authority: US
Inventors: William Martin Silvis; James Patrick Williamson; Gerald Marek; Douglas Edward Miller
Original assignee: AVL Test Systems Inc
Current assignee: AVL Test Systems Inc
Priority date: 2012-05-23
Filing date: 2016-03-25
Publication date: 2016-07-21
Also published as: EP2667175A2; KR20130131241A; US20130317757A1; JP6288947B2; EP2667175A3; EP2667175B1; CN103424286B; US9297726B2; CN103424286A; JP2013246169A

Abstract

Disclosed is an exhaust sampling system including a plurality of exhaust sampling system zones. The zones are, at least, a sampling conduit, a fill circuit, and a read circuit. A controller is programmed to predict a minimum dilution ratio to avoid condensation in one of the exhaust sampling system zones. The controller is further programmed to run a test procedure in which a sample of exhaust is diluted with a make-up gas at a selected minimum dilution ratio that is greater than or equal to the predicted minimum dilution ratio. Further disclosed are methods of predicting whether condensation occurs during a test procedure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/478,170 filed on May 23, 2012. The entire disclosure of the application referenced above is incorporated herein by reference.

BACKGROUND

In typical exhaust sampling systems, such as constant volume samplers (CVS), engine exhaust is diluted with a make-up gas, or diluent, and a 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 the make-up gas and engine exhaust, is selected to ensure the diluted exhaust sample does not condense water when stored in the bags.
In addition to determining an appropriate CVS total flow rate, some systems fill the sample bags with a gas, such as a pre-fill gas, to avoid bag condensation. Some other systems apply heat to the sample bags such that the temperature of the sample is maintained above the dew point.

SUMMARY

Disclosed is an exhaust sampling system including a plurality of exhaust sampling system zones. The zones are, at least, a sampling conduit, a fill circuit, and a read circuit. A controller is programmed to predict a minimum dilution ratio to avoid condensation in one of the exhaust sampling system zones. The controller is further programmed to run a test procedure in which a sample of exhaust is diluted with a make-up gas at a selected minimum dilution ratio that is greater than or equal to the predicted minimum dilution ratio. Further disclosed are methods of predicting whether condensation occurs during a test procedure.
These and other features of the present disclosure can be best understood from the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings can be briefly described as follows:

FIG. 1 is a schematic view of an example exhaust sampling system.

FIG. 2 is a schematic view of another example exhaust sampling system.

FIG. 3 is a flow chart illustrating example steps for selecting a minimum dilution ratio for a test procedure.

FIG. 4 is a flow chart illustrating example steps for determining whether a test procedure has been compromised.

FIG. 5 is an example of the engine performance considered in the flow chart of FIG. 4.

FIG. 6 is another flow chart illustrating example steps for determining whether a test has been compromised.

FIG. 7 is an example of the running average considered in the flow chart of FIG. 6.

DETAILED DESCRIPTION

A schematic view of an example exhaust sampling system 10 is shown in FIG. 1. In particular, the illustrated system 10 is a CVS. An example CVS is present in U.S. Pat. No. 7,559,262, the entirety of which is herein incorporated by reference. It should be understood, however, that this application extends to other types of exhaust sampling systems, and is not limited to the particularities of the illustrated system 10.
The example system 10 includes a sampling conduit 12 configured to receive a make-up air 14 and exhaust 16 from an engine 18. The make-up air 14 is directed to the sampling conduit 12 by way of an inlet 20 formed in one end of the sampling conduit. The inlet 20 is provided with a filter 22 in this example. A pump 24 is positioned opposite the inlet 20 to draw a desired amount of make-up air into the sampling conduit 12. Exhaust 16 is directed into the sampling conduit 12 by way of a tail pipe 26.
As used herein, the term exhaust refers to the various fluids emitted from an engine (including gasses and vapors), as well as the particulate matter (PM) suspended therein. PM is commonly emitted from engines and typically includes carbonaceous matter in elemental form (or, soot) and carbonaceous matter in the form of volatile and semi-volatile hydrocarbon compounds (which may be SOF, or soluble organic fraction), and other organic and inorganic compounds (such as sulfates). The make-up air discussed above can be any type of diluent, such as ambient air, whose water concentration is known or readily determinable.
As illustrated, the sampling conduit 12 further includes a mixer 28, a tunnel 30, a heat exchanger 32, and a measuring device 34. A detailed discussion of these components is present in U.S. Pat. No. 7,559,262. While the sampling conduit includes these components 28, 30, 32, 34 in this example, this application extends to other types of sampling conduits, including conduits without these components.
Downstream of the inlet 20 and the tail pipe 26 is a sampler 36 for extracting a sample of the mixture of the makeup gas 14 and the exhaust 16. The mixture of the makeup gas 14 and the exhaust 16 is referred to herein as the diluted exhaust. The sample, sampled by sampler 36, is referred to as the diluted exhaust sample.
Downstream of the sampler 36, the diluted exhaust sample is directed through a fill circuit 38. In this example, the fill circuit includes a valve 40, pump 42, and a flow meter 44. The fill circuit 38 further includes independently adjustable valves 46 leading to a respective sample bag 48. While the fill circuit 38 is shown including the valve 40, pump 42 and flow meter 44, the fill circuit could include any combination of components, as desired. As used herein, use of the term fill circuit 38 refers to the portion of the sampling system 10 downstream of the sampling conduit 12 and upstream of the sample bags 48. The term fill circuit can be inclusive of the sampler 36, in some examples.
As illustrated, the fill circuit 38 directs the diluted exhaust sample to two sample bags 48, however this application extends to disclosures which include any number of bags, including only one sample bag. Depending on the number of sample bags 48, the number of valves 46 can be adjusted accordingly.
Downstream of the bags 48 is a read circuit 50, which includes independently adjustable valves 52, a pump 54, a flow meter 55, and an emissions analyzer 56, which may be a bench-type analysis unit. Like the fill circuit 38, the read circuit 50 may include any combination of desired components. As used herein, the term read circuit 50 refers to the portion of the sampling system 10 downstream of the bags 48.
A controller 58, which may be any type of known computer including a computer readable medium with the capability of storing instructions executable by the controller. The controller 58 is further in communication with each of the disclosed system components. For example, the controller is operable to control and monitor the engine 18, and is further capable of independently operating the various pumps 24, 42, 54 and valves 40, 46, 52.
Variations of the system 10 come within the scope of this disclosure. For example, in one variation the system 10 fills the sample bags 48 with a gas, such as a pre-fill gas from a source 60, before filling the bags with the diluted exhaust sample to ensure an accurate measurement at the analyzer 56. Such a system is disclosed in U.S. Pat. No. 7,559,262. This disclosure extends to systems that do not include a pre-filling feature. This disclosure further extends to systems that include a post-filling feature either alone, or in combination with, a pre-filling feature.
In another example, the system 10 includes a mini-diluter 62, such as the one illustrated in FIG. 2. Between FIGS. 1 and 2, like reference numerals are used to indicate like elements. In FIG. 2 the exhaust 16 from the engine 18 is directed into the sampling conduit 12 and is sampled by the sampler 36. The exhaust sample is diluted with a make-up gas from the mini-diluter 62, at the mixer 64. An example system including a mini-diluter is U.S. Patent Application Publication No. 2010/0000339, the entirety of which is herein incorporated by reference.
With reference back to FIG. 1, an exemplary emissions test procedure is conducted by directing exhaust 16 from the engine 18 into the sampling conduit 12, and diluting the exhaust 16 with the make-up air 14 at a minimum dilution ratio, DR_CVS-MIN, selected in advance of the procedure, as explained below. To dilute the exhaust 16 at the selected minimum dilution ratio, the controller 58 is programmed to instruct the pump 24 to draw an appropriate amount of make-up air 14 into the sampling conduit. In the example of FIG. 2, dilution would take place at the mixer 64, by way of instructions from the controller 58 to the mini-diluter 62.
The diluted exhaust sample is directed from the sampling conduit 12 to the sample bags 48, by way of the fill circuit 38. The diluted exhaust sample is collected in the sample bags 48 during the test procedure. Following the test procedure, the diluted exhaust sample is directed from sample bags 48 downstream to the read circuit 50, and ultimately to an analyzer 56.
During test procedures such as the example procedure described above, the formation of condensation in the diluted exhaust sample not only leads to inaccurate test results, but certain legislation prohibits condensation from being permitted inside the sample bags. New legislation is even more restrictive, and prohibits condensation from forming in more than just the sample bags 48. In other words, if condensation occurs at any point in the sampling system 10 during a test procedure, the new legislation effectively renders that test procedure compromised, and a new test procedure would be required.
Accordingly, this disclosure considers not only the sample bags 48, but alternatively, or in addition, considers at least one of the read circuit 38, the fill circuit 50, and the sampling conduit 12, when selecting a minimum dilution ratio DR_CVS-MINfor the exhaust 16.
In general, the dilution ratio DR_CVSis defined in accordance with the following:
$D R_{CVS} = \frac{Q_{m} + Q_{ex}}{Q_{ex}}$
where Q_Mis the make-up gas 14 flow rate and Q_EXis an exhaust 16 flow rate. Once DR_CVS-MINis selected (e.g., DR_CVSis set to DR_CVS-MIN), as discussed below, then the flow rate in the sampling conduit Q_CVSis provided in accordance with:
Q _CVS=DR_CVS-MIN ·Q _ex-ave
where Q_ex-aveis an average expected exhaust 16 flow rate during a test procedure. Alternatively, Q_ex-avecould be a running average of exhaust 16 flow rate during the procedure. Given DR_CVS-MIN, the controller 58 is operable to provide an appropriate Q_CVS.
As generally mentioned above, the problem of condensation could be avoided by excessively diluting the exhaust 16 with the make-up gas 14. However, this would lead to an exhaust sample that would be extremely difficult to analyze, due to the high content of make-up gas 14 in the diluted exhaust sample. Accordingly, in one example of this disclosure the minimum dilution ratio DR_CVS-MINis selected such that it is as low as possible, while still being high enough to avoid condensation within the various components of the exhaust sampling system 10. To find this optimum DR_CVS-MIN, dilution ratios to avoid condensation in the fill circuit 38, the bags 48, the read circuit 50, and the sampling conduit 12 are separately determined, and the minimum dilution ratio of the exhaust 16 is set such that it is greater than or equal to a maximum of the predicted dilution ratios.
In particular, and with reference to FIG. 3, a minimum dilution ratio to avoid condensation in the fill circuit 38 DR_fill-minis predicted at 68, and is defined as follows:
$D R_{fill - \min} \geq \frac{W_{ex - \max}}{W_{fill - sat} - W_{m}}$
where W_ex-maxis a maximum expected water concentration in the exhaust during the test procedure, W_fill-satis an expected saturated water concentration to be associated with the fill circuit 38 during the test procedure, and W_mis an expected water concentration in the make-up gas during the test procedure. In one example, W_fill-satis determined from the following equation:
$W_{fill - sat} = \frac{P_{H 20 - vap} (T_{fill})}{P_{fill}}$
where P_H20-vapis a saturation vapor pressure that is identified using a known method (for example, a look-up table). In another example, P_H20-vapis identified using certain federal regulations as a guide. In this example, the input temperature T_fillis an expected average temperature of the diluted exhaust sample in the fill circuit 38 during a given test procedure. P_fillis an expected average pressure of the diluted exhaust sample in the fill circuit 38 during the test procedure. T_filland P_fillcan be determined by considering ambient conditions, for example, as well as the T_filland P_fillpresent during prior, similar tests. In one example, T_fill, is selected such that it is above the dew point of the mixture of the make-up gas 14 and the exhaust 16 at the minimum dilution ratio expected during testing, thus providing a built-in safety factor.
The remaining variables in the DR_fill-minequation, W_ex-maxand W_m, are predicted based on inputs from the engine and the surrounding system. For example, the composition of the fuel combusted by the engine, as well as the properties and composition of the engine intake air will impact the water concentration in the exhaust, W_ex-max. In the example where the make-up gas 14 is ambient air, the water concentration in the make-up gas 14 is determined based on parameters such as the temperature and pressure of the surroundings of the system 10. Various pressure and temperature sensors can be positioned relative to the system 10, and these sensors are capable of communicating with the controller 58.
At 70, a minimum dilution ratio to avoid condensation in the read circuit, DR_read-min, is predicted. Similar to DR_fill-min, DR_read-minis predicted in accordance with:
$D R_{read - \min} \geq \frac{W_{ex - ave} - W_{m}}{W_{read - sat} - W_{m}}$
where W_mis defined above, W_ex-aveis an is a average expected water concentration in the exhaust during the test procedure, and W_read-satis an expected saturated water concentration to be associated with the read circuit 50 during the test procedure. W_read-satis determined in a manner similar to W_fill-sat, above, and is based on T_readand P_read, an expected average temperature and pressure of the diluted exhaust sample in the read circuit 50 during a given test procedure. In particular, in the example, T_readis set above the dew point that corresponds to the water content in the diluted exhaust sample, and P_readis above a pressure to which the diluted exhaust sample is raised when pumping (e.g., with pump 54) to the analyzer 56.
Likewise, a predicted minimum dilution ratio is determined for the bags at 72. DR_bag-minis predicted in accordance with:
$D R_{bag - \min} \geq \frac{W_{ex - ave} - W_{m}}{W_{bag - sat} - W_{m}}$
where W_bag-satis an expected saturated water concentration to be associated with the at least one sample bag 48 during the test procedure. W_bag-satis determined in a manner similar to W_read-satand W_fill-sat, above, and is based on and P_bag, an expected average temperature and pressure of the diluted exhaust sample within the bags 48 during a test procedure. T_bagwill need to be above the dew point of the diluted exhaust sample in some examples. When computing DR_bag-min, some examples could substitute W_ex-avewith a maximum integrated value for the concentration of water in the exhaust gas, to protect for peak exhaust. That is, while the actual W_ex-avecould be used some examples would substitute the value for W_ex-avewith the average plus a test-dependent margin.
Further, a predicted minimum dilution ratio is determined for the sampling conduit 12, at 73. DR_tun-minis predicted in accordance with:
$D R_{samp - cond - \min} \geq \frac{W_{ex - \max} - W_{m}}{W_{tun - sat} - W_{m}}$
where W_ex-maxand W_mare defined above, and W_tun-satis an expected saturated water concentration to be associated with the sampling conduit 12 during the test procedure. W_{samp-cond-sat}is determined in a manner similar to W_fill-sat, above, and is based on T_samp-condand P_samp-cond, an expected average temperature and pressure of the diluted exhaust sample in the sampling conduit 12 during a given test procedure. In particular, in the example, T_samp-condis set above the dew point that corresponds to the water content in the diluted exhaust sample, and P_samp-condis assumed to be equal to atmospheric pressure.
In one example, during the test, the actual temperature of bags is higher by roughly 4-5° C. than the T_bagused in the calculations, to give some safety factor. P_bagmay vary between the calculations and actual test conditions to provide a safety factor. Likewise, DR_fill-minand DR_read-mincan be provided with built-in safety factors.
Once these minimum dilution ratios are predicted at steps 68, 70 and 72, the controller 58 selects an exhaust minimum dilution ratio, DR_CVS-MIN, that is greater than or equal to a maximum of the predicted minimum dilution ratios, DR_fill-min, DR_bag-min, DR_read-min, and DR_{samp-cond-min}·DR_CVS-MINis selected, at 74, as follows:
DR_CVS-MIN≧max(DR_fill-min, DR_read-min, DR_bag-min, DR_{samp-cond-min})
In one example test procedure, exhaust 16 is diluted with the make-up gas 14 at a ratio equal to DR_CVS-MIN. It is possible in some examples to dilute the exhaust at a ratio above the maximum of the predicted ratios for an added safety factor. However, as mentioned above, more accurate test results are possible with a lower dilution ratio. In one example, DR_CVS-MINis selected such that the make-up gas 14 is mixed with the exhaust 16 at a ratio within a range of 1:1 and 10:1.
The ratios DR_fill-min, DR_bag-min, DR_read-min, DR_{samp-cond-min}, and DR_CVS-MINare absolute minimums, such that the minimum dilution ratio should not drop below DR_CVS-MINat any point during the test procedure. In another example, the overall average dilution ratio over the course of a test would not drop below DR_CVS-MIN. In yet another example, the ratios are running averages, such that a running average of the dilution should not drop below DR_CVS-MIN.
In another example, the controller 58 dilutes the exhaust 18 at a ratio DR_CVS-MINdetermined based on at least one test parameter, which can include parameters from an engine or vehicle performance model 78 and parameters 80 of the system 10, as illustrated in FIG. 4. In this example, the engine performance model 78 is a known model associated with the particular type of engine involved in the test procedure. The at least one test parameter can further include coefficients from a dynamometer, such as settings for resistive load, which may relate to peak exhaust expected during a test cycle.
Regardless of how DR_CVS-MINis selected, average and maximum exhaust flow rate from the engine or vehicle over the course of the test procedure Q_ex-aveand Q_ex-max, can be estimated by given values, or, for example, can be predicted based on an estimated engine horsepower throughout the test procedure. Then the minimum Q_CVS-minused throughout the test procedure can be provided as follows:
Q _CVS-min≧max(Q _ex-max·DR_fill-min , Q _ex-ave·DR_read-min , Q _ex-max·DR_bag-min , Q _ex-max·DR_{samp-cond-min})
In one example, the at least one test parameter includes such parameters as resistive load (e.g., dyno coefficients), engine RPM, fuel type, fuel composition, engine or vehicle intake air properties and composition, and combustion efficiency. Certain exhaust sampling system parameters would also be relevant in determining a minimum dilution ratio, as generally mentioned above, and would impact the engine performance model 78. These parameters 80 include T_filland P_fill, T_readand P_read, T_bagand P_bag, T_samp-condand P_samp-condand the composition properties of the make-up gas 14 (e.g., portions attributable to N₂, O₂, etc). For these parameters, a known engine performance model is determinable, and the controller can select a flow rate Q_CVSfor a required minimum dilution ratio DR_CVS-MIN.
Alternatively, the minimum dilution ratio selected for the test of FIG. 4 could be determined based on the method of FIG. 3. Regardless of how DR_CVSis selected, an emissions test procedure begins as illustrated at 76 in FIG. 4. As mentioned, the test procedure could dilute exhaust either at a minimum ratio selected in step 74, or at a minimum ratio determined based on at least one of the test parameters. In either case, once DR_CVS-MINis selected, the controller can suggest an optimized flow rate Q_CVS.
During the test, at 82, the controller 58 will monitor the actual performance of the test parameters relative to the model to determine whether the difference between the two indicates a possible condensation in the exhaust sampling system 10, at 84. If such an indication is present such that the tests may be compromised by potential condensation, the test procedure is ended at 86.
A graphical representation of a scenario indicating a possible compromise in the test procedure is shown in FIG. 5. In the illustrated example, an engine 18 or system 10 parameters exceeds a value predicted by the model for an amount of time, as indicated by the shaded-in area between the actual value of the parameter and the value predicted by the model.
In one example, during the test procedure, the controller 58 monitors RPM of the engine 18 relative to a model relating engine RPM to minimum dilution ratio. If the engine RPM exceeds the value associated with the model such that the minimum dilution ratio DR_CVS-MINis not sufficient to avoid condensation, as represented in the shaded area of FIG. 5, the controller 58 ends the test. In another example, when ambient air is used as the make-up gas 14, the controller 58 monitors the relative humidity of the ambient air. An unexpected peak in the relative humidity can indicate a compromised test.
Another feature of this disclosure is represented in the flowchart of FIG. 6. During a test procedure, which begins at 88, an integral of the saturated water concentration within the sample bags, W_bag-sat-int, is calculated at 90. That is, W_bag-satis monitored as a function of time during the test procedure, and the integral of W_bag-satfrom time zero to “t” is used to determine whether there is concentration in bags at time “t.” The integral is calculated at set intervals, for example (e.g., t is 1 second, 2 seconds, 3 seconds, etc). From this integral, W_bag-sat-int, the controller 58 determines, at 92, whether a possible condensation in the sample bags 48 is indicated, by comparing W_bag-sat-intwith a model, for example. If a possible compromise in the test is identified, the test is ended, at 94.
FIG. 7 represents an example where a possible compromise occurs during the test procedure. In this example, W_bag-sat-intexceeds an average W_bag-satexpected over the test procedure, as illustrated in the shaded area. Thus, the bags may be over-saturated and condensation may be present.
This disclosure can be used to avoid condensation in more than just the sample bags of an exhaust system. As noted, there are several reasons to avoid condensation in more than just the sample bags, including more accurate testing, and compliance with new regulations.
This disclosure can be used to interrupt a compromised test procedure by monitoring for condensation during the test, rather than determining, after a completed test, that condensation had occurred. Interrupting a compromised test leads to time and cost savings relative to the alternative.
Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.
One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.

Claims

What is claimed is:

1. A method of predicting whether condensation occurs during a test procedure comprising:

providing an exhaust sampling system including at least one sample bag;

diluting exhaust from an engine with a make-up gas;

filling the at least one sample bag with a sample of the diluted exhaust; and

determining, during a test procedure, whether condensation occurs in the at least one sample bag based on an integral of water concentration in the at least one sample bag.

2. The method of claim 1, wherein the integral of the water concentration in the at least one sample bag is continually calculated, by a controller, during the test procedure.

3. The method of claim 1, further comprising continuously calculating the integral of the water concentration in the at least one sample bag during the test procedure.

4. The method of claim 1, further comprising monitoring the water concentration as a function of time during the test procedure.

5. The method of claim 4, further comprising determining the integral of the water concentration in the at least one sample bag from a first time at the start of the test procedure to a second time during the test procedure.

6. The method of claim 5, further comprising determining whether there is condensation in the at least one sample bag at the second time based on the integral of the water concentration in the at least one sample bag from the first time to the second time.

7. The method of claim 1, further comprising calculating the integral of the water concentration in the at least one sample bag at set intervals during the test procedure.

8. The method of claim 1, further comprising determining whether condensation is present in the at least one sample bag based on a comparison of the integral of water concentration in the at least one sample bag and a model.

9. The method of claim 1, further comprising determining that condensation in the at least one sample bag is possible when the integral of water concentration in the at least one sample bag is greater than an average water concentration expected during the test procedure.

10. The method of claim 1, further comprising diluting exhaust from the engine with the make-up gas in at least one of a sampling conduit and a mixer disposed downstream from the sampling conduit and upstream from the at least one sample bag.

11. A method comprising:

filling at least one sample bag with a sample of exhaust from an engine during a test procedure;

monitoring a water concentration in the at least one sample bag over a period of the test procedure; and

determining a likelihood that condensation is present in the at least one sample bag based on the water concentration in the at least one sample bag over the period.

12. The method of claim 11, wherein the period is at least one second.

13. The method of claim 11, wherein the period is from a first time at a start of the test procedure to a second time during the test procedure.

14. The method of claim 11, further comprising:

determining an integral of the water concentration in the at least one sample bag over the period; and

determining the likelihood that condensation is present in the at least one sample bag based on the integral of the water concentration in the at least one sample bag over the period.

15. The method of claim 11, further comprising:

diluting exhaust from the engine with a make-up gas; and

filling the at least one sample bag with a sample of the diluted exhaust during the test procedure.

16. An exhaust sampling system, comprising:

at least one sample bag;

a sampling conduit configured to receive exhaust gas from an engine;

a fill circuit configured to direct a sample of exhaust gas from the sampling conduit to the at least one sample bag during a test procedure; and

a controller that:

monitors a water concentration in the at least one sample bag over a period of the test procedure; and

determines a likelihood that condensation is present in the at least one sample bag based on the water concentration in the at least one sample bag over the period.

17. The exhaust sampling system of claim 16, wherein the period is at least one second.

18. The exhaust sampling system of claim 16, wherein the period is from a first time at a start of the test procedure to a second time during the test procedure.

19. The exhaust sampling system of claim 16, wherein the controller:

determines an integral of the water concentration in the at least one sample bag over the period; and

determines the likelihood that condensation is present in the at least one sample bag based on the integral of the water concentration in the at least one sample bag over the period.

20. The exhaust sampling system of claim 16, further comprising at least one of:

a pump disposed at an outlet of the sampling conduit; and

a mini-diluter in fluid communication with the fill circuit at a location downstream from the sampling conduit and upstream from the at least one sample bag, wherein the controller:

controls at least one of the pump and the mini-diluter to dilute exhaust from the engine with a make-up gas; and

controls the fill circuit to fill the at least one sample bag with a sample of the diluted exhaust during the test procedure.