40 CFR § 1065.365 - Nonmethane cutter penetration fractions and NMC FID response factors.
(a) Scope and frequency. If you use a FID analyzer and an NMC to measure methane (CH4), verify that the catalytic activity of the NMC has not deteriorated as described in this section. Determine the NMC's penetration fractions (PF) of CH4 and ethane (C2H6) and, if applicable, the FID analyzer response factors using the appropriate procedures of paragraph (d), (e), or (f) of this section. 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 NMC and repeat this verification within 185 days of testing. Note that because NMCs 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 an NMC's penetration fractions more frequently. Use the most recently determined penetration fraction from this section to calculate HC emissions according to § 1065.660 as applicable.
(b) Measurement principles. An NMC is a heated catalyst that removes nonmethane hydrocarbons from an exhaust sample stream before the FID analyzer measures the remaining hydrocarbon concentration. An ideal NMC 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 require that you limit NMC penetration fractions to a certain range. However, we recommend that you optimize an NMC by adjusting its temperature to achieve a PFC2H6 <0.02, as determined by paragraph (d), (e), or (f) of this section, as applicable, using dry gases. If adjusting NMC temperature does not result in achieving the recommended PFC2H6 level, we recommend that you replace the catalyst material. Note that, if we use an NMC for testing, we will optimize it to achieve a PFC2H6 <0.02.
(d) Procedure for a FID calibrated with the NMC. The following procedure describes the recommended method for verifying NMC performance and the required method for any gaseous-fueled engine, including dual-fuel and flexible-fuel engines.
(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 NMC 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 NMC as you would during emission testing. Span the FID through the NMC by using CH4 span gas.
(6) Introduce the C2H6 analytical gas mixture upstream of the NMC. 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 NMC 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 the analytical gas mixture.
(9) Calculate a reference concentration of C2H6, by converting C2H6 to a C1 basis and adjusted for water content, if necessary. Calculate the combined C2H6 response factor and penetration fraction, RFPFC2H6[NMC-FID], by dividing the mean C2H6 concentration from paragraph (d)(8) of this section by the reference concentration of C2H6. For any gaseous-fueled engine, including dual-fuel and flexible-fuel engines, you must determine RFPFC2H6[NMC-FID] as a function of the molar water concentration in the raw or diluted exhaust using paragraph (g) of this section. Use RFPFC2H6[NMC-FID] at the different setpoints to create a functional relationship between RFPFC2H6[NMC-FID] 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. For any other engine you may use the same procedure or you may determine RFPFC2H6[NMC-FID] at zero molar water concentration.
(10) For any gaseous-fueled engine, including dual-fuel and flexible-fuel engines, repeat the steps in paragraphs (d)(6) through (9) of this section, but with the CH4 analytical gas mixture instead of C2H6 and determine RFPFCH4[NMC-FID] as a function of the molar water concentration in the raw or diluted exhaust using paragraph (g) of this section. Note that RFPFCH4[NMC-FID] is set equal to 1.0 only for zero molar water concentration. For any other engine you may use the same procedure, or you may set RFPFCH4[NMC-FID] equal to 1.0.
(11) Use RFPFC2H6[NMC-FID] and RFPFCH4[NMC-FID] in emission calculations according to § 1065.660(b)(2)(i) and (d)(1)(i).
(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 NMC 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 NMC and by using C3H8 span gas. Note that you must span the FID on a C1 basis. For example, if your span gas has a propane reference value of 100 µmol/mol, the correct FID response to that span gas is 300 µmol/mol because there are three carbon atoms per C3H8 molecule.
(6) Introduce the C2H6 analytical gas mixture upstream of the NMC. 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 NMC 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 the analytical gas mixture.
(9) Reroute the flow path to bypass the NMC, introduce the C2H6 analytical gas mixture, and repeat the steps in paragraphs (e)(7) and (8) of this section.
(10) Divide the mean C2H6 concentration measured through the NMC by the mean C2H6 concentration measured after bypassing the NMC. The result is the C2H6 penetration fraction, PFC2H6[NMC-FID]. Use this penetration fraction according to § 1065.660(b)(2)(ii) and (d)(1)(ii).
(11) Repeat the steps in paragraphs (e)(6) through (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) 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 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 NMC 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 NMC and by using CH4 span gas.
(6) Introduce the C2H6 analytical gas mixture upstream of the NMC. 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 NMC 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 the analytical gas mixture.
(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 penetration fraction according to § 1065.660(b)(2)(iii) and (d)(1)(iii).
(10) Introduce the CH4 analytical gas mixture upstream of the NMC. 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 NMC 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 NMC, 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 NMC by the mean CH4 concentration measured after bypassing the NMC. The result is the CH4 penetration fraction, PFCH4[NMC-FID]. Use this CH4 penetration fraction according to § 1065.660(b)(2)(iii) and (d)(1)(iii).
(g) Test gas humidification. If you are generating gas mixtures as a function of the molar water concentration in the raw or diluted exhaust according to paragraph (d) of this section, 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. Determine the mole fraction of H2O in the humidified calibration gas, xH2Oref, as an average value over intervals of at least 30 seconds. We recommend that you design your system to maintain temperatures at least 5 °C above the local calibration gas dewpoint in any transfer lines, fittings, and valves between the point at which you determine xH2Oref and the analyzer. Verify the humidity generator's uncertainty upon initial installation, within 370 days before verifying response factors and penetration fractions, and after major maintenance. Use the uncertainties from the calibration of the humidity generator's measurements and follow NIST Technical Note 1297 (incorporated by reference, see § 1065.1010) to verify that the amount of H2O in xH2Oref is determined within ±3% uncertainty, UxH2O, for one of the options described in § 1065.750(a)(6). If the humidity generator requires assembly before use, after assembly follow the instrument manufacturer's instructions to check for leaks.
(1) 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.
(2) If 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.