(a) Scope and frequency. If you use a FID analyzer and a nonmethane cutter (NMC) to measure methane (CH4), determine the nonmethane cutter's penetration fractions of methane, PFCH4, and ethane, PFC2H6. As detailed in this section, these penetration fractions may be determined as a combination of NMC penetration fractions and FID analyzer response factors, depending on your particular NMC and FID analyzer configuration. Perform this verification after installing the nonmethane cutter. Repeat this verification within 185 days of testing to verify that the catalytic activity of the cutter has not deteriorated. Note that because nonmethane cutters can deteriorate rapidly and without warning if they are operated outside of certain ranges of gas concentrations and outside of certain temperature ranges, good engineering judgment may dictate that you determine a nonmethane cutter's penetration fractions more frequently.
(b) Measurement principles. A nonmethane cutter is a heated catalyst that removes nonmethane hydrocarbons from an exhaust sample stream before the FID analyzer measures the remaining hydrocarbon concentration. An ideal nonmethane cutter would have a CH4 penetration fraction, PFCH4, of 1.000, and the penetration fraction for all other nonmethane hydrocarbons would be 0.000, as represented by PFC2H6. The emission calculations in § 1065.660 use the measured values from this verification to account for less than ideal NMC performance.
(c) System requirements. We do not limit NMC penetration fractions to a certain range. However, we recommend that you optimize a nonmethane cutter by adjusting its temperature to achieve a PFCH4 >0.85 and a PFC2H6 <0.02, as determined by paragraphs (d), (e), or (f) of this section, as applicable. If we use a nonmethane cutter for testing, it will meet this recommendation. If adjusting NMC temperature does not result in achieving both of these specifications simultaneously, we recommend that you replace the catalyst material. Use the most recently determined penetration values from this section to calculate HC emissions according to § 1065.660 and § 1065.665 as applicable.
(d) Procedure for a FID calibrated with the NMC. The method described in this paragraph (d) is recommended over the procedures specified in paragraphs (e) and (f) of this section and required for any gaseous-fueled engine, including dual-fuel and flexible-fuel engines. If your FID arrangement is such that a FID is always calibrated to measure CH4 with the NMC, then span that FID with the NMC using a CH4 span gas, set the product of that FID's CH4 response factor and CH4 penetration fraction, RFPFCH4[NMC-FID], equal to 1.0 for all emission calculations, and determine its combined C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID], as follows. For any gaseous-fueled engine, including dual-fuel and flexible-fuel engines, you must determine the CH4 penetration fraction, PFCH4[NMC-FID], and C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID], as a function of the molar water concentration in the raw or diluted exhaust as described in paragraphs (d)(10) and (12) of this section. Generate and verify the humidity generation as described in paragraph (d)(11) of this section. When using the option in this paragraph (d), note that the FID's CH4 penetration fraction, PFCH4[NMC-FID], is set equal to 1.0 only for 0% molar water concentration. You are not required to meet the recommended lower limit for PFCH4 of greater than 0.85 for any of the penetration fractions generated as a function of molar water concentration.
(1) Select CH4 and C2H6 analytical gas mixtures and ensure that both mixtures meet the specifications of § 1065.750. Select a CH4 concentration that you would use for spanning the FID during emission testing and select a C2H6 concentration that is typical of the peak NMHC concentration expected at the hydrocarbon standard or equal to the THC analyzer's span value. For CH4 analyzers with multiple ranges, perform this procedure on the highest range used for emission testing.
(2) Start, operate, and optimize the nonmethane cutter according to the manufacturer's instructions, including any temperature optimization.
(3) Confirm that the FID analyzer meets all the specifications of § 1065.360.
(4) Start and operate the FID analyzer according to the manufacturer's instructions.
(5) Zero and span the FID with the nonmethane cutter as you would during emission testing. Span the FID through the cutter by using CH4 span gas.
(6) Introduce the C2H6 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.
(7) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.
(8) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.
(9) Divide the mean C2H6 concentration by the reference concentration of C2H6, converted to a C1 basis. The result is the C2H6 combined response factor and penetration fraction, RFPFC2H6[NMC-FID]. Use this combined C2H6 response factor and C2H6 penetration fraction and the product of the CH4 response factor and CH4 penetration fraction, RFPFCH4[NMC-FID], set to 1.0 in emission calculations according to § 1065.660(b)(2)(i) or (d)(1)(i) or § 1065.665, as applicable.
(10) Determine the combined C2H6 response factor and C2H6 penetration fraction as a function of molar water concentration and use it to account for C2H6 response factor and C2H6 penetration fraction for NMHC determination as described in § 1065.660(b)(2)(iii) and for CH4 determination in § 1065.660(d)(1)(iii). Humidify the C2H6 analytical gas mixture as described in paragraph (d)(11) of this section. Repeat the steps in paragraphs (d)(6) through (8) of this section until measurements are complete for each setpoint in the selected range. Divide each mean measured C2H6 concentration by the reference concentration of C2H6, converted to a C1-basis and adjusted for water content to determine the FID analyzer's combined C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID]. Use RFPFC2H6[NMC-FID] at the different setpoints to create a functional relationship between the combined response factor and penetration fraction and molar water concentration, downstream of the last sample dryer if any sample dryers are present. Use this functional relationship to determine the combined response factor and penetration fraction during the emission test.
(11) Create a humidified test gas by bubbling the analytical gas mixture that meets the specifications in § 1065.750 through distilled H2O in a sealed vessel or use a device that introduces distilled H2O as vapor into a controlled gas flow. If the sample does not pass through a dryer during emission testing, generate at least five different H2O concentrations that cover the range from less than the minimum expected to greater than the maximum expected water concentration during testing. Use good engineering judgment to determine the target concentrations. For analyzers where the sample passes through a dryer during emission testing, humidify your test gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer and determine a single wet analyzer response to the dehumidified sample. Heat all transfer lines from the water generation system to a temperature at least 5 °C higher than the highest dewpoint generated. Determine H2O concentration as an average value over intervals of at least 30 seconds. Monitor the humidified sample stream with a dewpoint analyzer, relative humidity sensor, FTIR, NDIR, or other water analyzer during each test or, if the humidity generator achieves humidity levels with controlled flow rates, validate the instrument within 370 days before testing and after major maintenance using one of the following methods:
(i) Determine the linearity of each flow metering device. Use one or more reference flow meters to measure the humidity generator's flow rates and verify the H2O level value based on the humidity generator manufacturer's recommendations and good engineering judgment. We recommend that you utilize at least 10 flow rates for each flow-metering device.
(ii) Perform validation testing based on monitoring the humidified stream with a dewpoint analyzer, relative humidity sensor, FTIR, NDIR, or other water analyzer as described in this paragraph (d)(11). Compare the measured humidity to the humidity generator's value. Verify overall linearity performance for the generated humidity as described in § 1065.307 using the criteria for other dewpoint measurements or confirm all measured values are within ±2% of the target mole fraction. In the case of dry gas, the measured value may not exceed 0.002 mole fraction.
(iii) Follow the performance requirements in § 1065.307(b) if the humidity generator does not meet validation criteria.
(12) Determine the CH4 penetration fraction as a function of molar water concentration and use this penetration fraction for NMHC determination in § 1065.660(b)(2)(iii) and for CH4 determination in § 1065.660(d)(1)(iii). Repeat the steps in paragraphs (d)(6) through (11) of this section, but with the CH4 analytical gas mixture instead of C2H6. Use this functional relationship to determine the penetration fraction during the emission test.
(e) Procedure for a FID calibrated with propane, bypassing the NMC. If you use a single FID for THC and CH4 determination with an NMC that is calibrated with propane, C3H8, by bypassing the NMC, determine its penetration fractions, PFC2H6[NMC-FID] and PFCH4[NMC-FID], as follows:
(1) Select CH4 and C2H6 analytical gas mixtures and ensure that both mixtures meet the specifications of § 1065.750. Select a CH4 concentration that you would use for spanning the FID during emission testing and select a C2H6 concentration that is typical of the peak NMHC concentration expected at the hydrocarbon standard and the C2H6 concentration typical of the peak total hydrocarbon (THC) concentration expected at the hydrocarbon standard or equal to the THC analyzer's span value. For CH4 analyzers with multiple ranges, perform this procedure on the highest range used for emission testing.
(2) Start and operate the nonmethane cutter according to the manufacturer's instructions, including any temperature optimization.
(3) Confirm that the FID analyzer meets all the specifications of § 1065.360.
(4) Start and operate the FID analyzer according to the manufacturer's instructions.
(5) Zero and span the FID as you would during emission testing. Span the FID by bypassing the cutter and by using C3H8 span gas.
(6) Introduce the C2H6 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.
(7) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.
(8) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.
(9) Reroute the flow path to bypass the nonmethane cutter, introduce the C2H6 analytical gas mixture, and repeat the steps in paragraph (e)(7) through (e)(8) of this section.
(10) Divide the mean C2H6 concentration measured through the nonmethane cutter by the mean C2H6 concentration measured after bypassing the nonmethane cutter. The result is the C2H6 penetration fraction, PFC2H6[NMC-FID]. Use this penetration fraction according to § 1065.660(b)(2)(ii), § 1065.660(d)(1)(ii), or § 1065.665, as applicable.
(11) Repeat the steps in paragraphs (e)(6) through (e)(10) of this section, but with the CH4 analytical gas mixture instead of C2H6. The result will be the CH4 penetration fraction, PFCH4[NMC-FID]. Use this penetration fraction according to § 1065.660(b)(2)(ii), § 1065.660(c)(1)(ii), or § 1065.665, as applicable.
(f) Procedure for a FID calibrated with CH4 , bypassing the NMC. If you use a FID with an NMC that is calibrated with CH4, by bypassing the NMC, determine its combined ethane (C2H6) response factor and penetration fraction, RFPFC2H6[NMC-FID], as well as its CH4 penetration fraction, PFCH4[NMC-FID], as follows:
(1) Select CH4 and C2H6 analytical gas mixtures and ensure that both mixtures meet the specifications of § 1065.750. Select a CH4 concentration that you would use for spanning the FID during emission testing and select a C2H6 concentration that is typical of the peak NMHC concentration expected at the hydrocarbon standard or equal to the THC analyzer's span value. For CH4 analyzers with multiple ranges, perform this procedure on the highest range used for emission testing.
(2) Start and operate the nonmethane cutter according to the manufacturer's instructions, including any temperature optimization.
(3) Confirm that the FID analyzer meets all the specifications of § 1065.360.
(4) Start and operate the FID analyzer according to the manufacturer's instructions.
(5) Zero and span the FID as you would during emission testing. Span the FID by bypassing the cutter and by using CH4 span gas. Note that you must span the FID on a C1 basis. For example, if your span gas has a methane reference value of 100 µmol/mol, the correct FID response to that span gas is 100 µmol/mol because there is one carbon atom per CH4 molecule.
(6) Introduce the C2H6 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.
(7) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.
(8) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.
(9) Divide the mean C2H6 concentration by the reference concentration of C2H6, converted to a C1 basis. The result is the combined C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID]. Use this combined C2H6 response factor and C2H6 penetration fraction according to § 1065.660(b)(2)(iii) or (d)(1)(iii) or § 1065.665, as applicable.
(10) Introduce the CH4 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.
(11) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.
(12) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.
(13) Reroute the flow path to bypass the nonmethane cutter, introduce the CH4 analytical gas mixture, and repeat the steps in paragraphs (e)(11) and (12) of this section.
(14) Divide the mean CH4 concentration measured through the nonmethane cutter by the mean CH4 concentration measured after bypassing the nonmethane cutter. The result is the CH4 penetration fraction, PFCH4[NMC-FID]. Use this CH4 penetration fraction according to § 1065.660(b)(2)(iii) or (d)(1)(iii) or § 1065.665, as applicable.
[73 FR 37310, June 30, 2008, as amended at 74 FR 56513, Oct. 30, 2009; 79 FR 23770, Apr. 28, 2014; 81 FR 74168, Oct. 25, 2016; 86 FR 34543, June 29, 2021]