40 CFR § 1065.341 - CVS and PFD flow verification (propane check).
This section describes two optional methods, using propane as a tracer gas, to verify CVS and PFD flow streams. You may use good engineering judgment and safe practices to use other tracer gases, such as CO2 or CO. The first method, described in paragraphs (a) through (e) of this section, applies for the CVS diluted exhaust flow measurement system. The first method may also apply for other single-flow measurement systems as described in Table 2 of § 1065.307. Paragraph (g) of this section describes a second method you may use to verify flow measurements in a PFD for determining the PFD dilution ratio.
(a) A propane check uses either a reference mass or a reference flow rate of C3H8 as a tracer gas in a CVS. Note that if you use a reference flow rate, account for any non-ideal gas behavior of C3H8 in the reference flow meter. Refer to §§ 1065.640 and 1065.642, which describe how to calibrate and use certain flow meters. Do not use any ideal gas assumptions in §§ 1065.640 and 1065.642. The propane check compares the calculated mass of injected C3H8 using HC measurements and CVS flow rate measurements with the reference value.
(b) Prepare for the propane check as follows:
(1) If you use a reference mass of C3H8 instead of a reference flow rate, obtain a cylinder charged with C3H8. Determine the reference cylinder's mass of C3H8 within ±0.5% of the amount of C3H8 that you expect to use. You may substitute a C3H8 analytical gas mixture (i.e., a prediluted tracer gas) for pure C3H8. This would be most appropriate for lower flow rates. The analytical gas mixture must meet the specifications in § 1065.750(a)(3).
(2) Select appropriate flow rates for the CVS and C3H8.
(3) Select a C3H8 injection port in the CVS. Select the port location to be as close as practical to the location where you introduce engine exhaust into the CVS, or at some point in the laboratory exhaust tubing upstream of this location. Connect the C3H8 cylinder to the injection system.
(4) Operate and stabilize the CVS.
(5) Preheat or pre-cool any heat exchangers in the sampling system.
(6) Allow heated and cooled components such as sample lines, filters, chillers, and pumps to stabilize at operating temperature.
(7) You may purge the HC sampling system during stabilization.
(c) If you performed the vacuum-side leak verification of the HC sampling system as described in paragraph (b)(8) of this section, you may use the HC contamination procedure in § 1065.520(f) to verify HC contamination. Otherwise, zero, span, and verify contamination of the HC sampling system, as follows:
(1) Select the lowest HC analyzer range that can measure the C3H8 concentration expected for the CVS and C3H8 flow rates.
(4) Overflow zero air at the HC probe inlet or into a tee near the outlet of the probe.
(5) Measure the stable HC concentration of the HC sampling system as overflow zero air flows. For batch HC measurement, fill the batch container (such as a bag) and measure the HC overflow concentration.
(6) If the overflow HC concentration exceeds 2 µmol/mol, do not proceed until contamination is eliminated. Determine the source of the contamination and take corrective action, such as cleaning the system or replacing contaminated portions.
(7) When the overflow HC concentration does not exceed 2 µmol/mol, record this value as xTHCinit and use it to correct for HC contamination as described in § 1065.660.
(d) Perform the propane check as follows:
(1) For batch HC sampling, connect clean storage media, such as evacuated bags.
(2) Operate HC measurement instruments according to the instrument manufacturer's instructions.
(3) If you will correct for dilution air background concentrations of HC, measure and record background HC in the dilution air.
(4) Zero any integrating devices.
(5) Begin sampling, and start any flow integrators.
(6) Release the contents of the C3H8 reference cylinder at the rate you selected. If you use a reference flow rate of C3H8, start integrating this flow rate.
(7) Continue to release the cylinder's contents until at least enough C3H8 has been released to ensure accurate quantification of the reference C3H8 and the measured C3H8.
(8) Shut off the C3H8 reference cylinder and continue sampling until you have accounted for time delays due to sample transport and analyzer response.
(9) Stop sampling and stop any integrators.
(e) Perform post-test procedure as follows:
(1) If you used batch sampling, analyze batch samples as soon as practical.
(2) After analyzing HC, correct for contamination and background.
(3) Calculate total C3H8 mass based on your CVS and HC data as described in § 1065.650 (40 CFR 1066.605 for vehicle testing) and § 1065.660, using the molar mass of C3H8, MC3H8, instead the effective molar mass of HC, MHC.
(4) If you use a reference mass, determine the cylinder's propane mass within ±0.5% and determine the C3H8 reference mass by subtracting the empty cylinder propane mass from the full cylinder propane mass.
(5) Subtract the reference C3H8 mass from the calculated mass. If this difference is within ±2% of the reference mass, the CVS passes this verification. If not, take corrective action as described in paragraph (f) of this section.
(f) A failed propane check might indicate one or more problems requiring corrective action, as follows:
Table 1 of § 1065.341 - Troubleshooting Guide for Propane Checks
|Problem||Recommended corrective action|
|Incorrect analyzer calibration||Recalibrate, repair, or replace the FID analyzer.|
|Leaks||Inspect CVS tunnel, connections, fasteners, and HC sampling system. Repair or replace components.|
|Poor mixing||Perform the verification as described in this section while traversing a sampling probe across the tunnel's diameter, vertically and horizontally. If the analyzer response indicates any deviation exceeding ±2% of the mean measured concentration, consider operating the CVS at a higher flow rate or installing a mixing plate or orifice to improve mixing.|
|Hydrocarbon contamination in the sample system||Perform the hydrocarbon-contamination verification as described in § 1065.520.|
|Change in CVS calibration||Perform a calibration of the CVS flow meter as described in § 1065.340.|
|Flow meter entrance effects||Inspect the CVS tunnel to determine whether the entrance effects from the piping configuration upstream of the flow meter adversely affect the flow measurement.|
|Other problems with the CVS or sampling verification hardware or software||Inspect the CVS system and related verification hardware, and software for discrepancies.|
(g) You may verify flow measurements in a PFD (usually dilution air and diluted exhaust streams) for determining the dilution ratio in the PFD using the following method:
(1) Configure the HC sampling system to extract a sample from the PFD's diluted exhaust stream (such as near a PM filter). If the absolute pressure at this location is too low to extract an HC sample, you may sample HC from the PFD's pump exhaust. Use caution when sampling from pump exhaust because an otherwise acceptable pump leak downstream of a PFD diluted exhaust flow meter will cause a false failure of the propane check.
(2) Perform the propane check described in paragraphs (b), (c), and (d) of this section, but sample HC from the PFD's diluted exhaust stream. Inject the propane in the same exhaust stream that the PFD is sampling from (either CVS or raw exhaust stack).
(3) Calculate C3H8 mass, taking into account the dilution from the PFD.
(4) Subtract the reference C3H8 mass from the calculated mass. If this difference is within ±2% of the reference mass, all PFD flow measurements for determining PFD dilution ratio pass this verification. If not, take corrective action as described in paragraph (f) of this section. For PFDs sampling only for PM, the allowed difference is ±5%.
(h) Table 2 of § 1065.307 describes optional verification procedures you may perform instead of linearity verification for certain flow-measurement systems. Performing carbon balance error verification also replaces any required propane checks.