(a) Scope and frequency. If you use a CLD analyzer to measure NOX, verify the amount of H2O and CO2 quench after installing the CLD analyzer and after major maintenance.
(b) Measurement principles. H2O and CO2 can negatively interfere with a CLD's NOX response by collisional quenching, which inhibits the chemiluminescent reaction that a CLD utilizes to detect NOX. This procedure and the calculations in § 1065.675 determine quench and scale the quench results to the maximum mole fraction of H2O and the maximum CO2 concentration expected during emission testing. If the CLD analyzer uses quench compensation algorithms that utilize H2O and/or CO2 measurement instruments, evaluate quench with these instruments active and evaluate quench with the compensation algorithms applied.
(c) System requirements. A CLD analyzer must have a combined H2O and CO2 quench of ±2% or less, though we strongly recommend a quench of ±1% or less. Combined quench is the sum of the CO2 quench determined as described in paragraph (d) of this section, plus the H2O quench determined in paragraph (e) of this section.
(d) CO2 quench verification procedure. Use the following method to determine CO2 quench by using a gas divider that blends binary span gases with zero gas as the diluent and meets the specifications in § 1065.248, or use good engineering judgment to develop a different protocol:
(1) Use PTFE or stainless steel tubing to make necessary connections.
(2) Configure the gas divider such that nearly equal amounts of the span and diluent gases are blended with each other.
(3) If the CLD analyzer has an operating mode in which it detects NO-only, as opposed to total NOX, operate the CLD analyzer in the NO-only operating mode.
(4) Use a CO2 span gas that meets the specifications of § 1065.750 and a concentration that is approximately twice the maximum CO2 concentration expected during emission testing.
(5) Use an NO span gas that meets the specifications of § 1065.750 and a concentration that is approximately twice the maximum NO concentration expected during emission testing.
(6) Zero and span the CLD analyzer. Span the CLD analyzer with the NO span gas from paragraph (d)(5) of this section through the gas divider. Connect the NO span gas to the span port of the gas divider; connect a zero gas to the diluent port of the gas divider; use the same nominal blend ratio selected in paragraph (d)(2) of this section; and use the gas divider's output concentration of NO to span the CLD analyzer. Apply gas property corrections as necessary to ensure accurate gas division.
(7) Connect the CO2 span gas to the span port of the gas divider.
(8) Connect the NO span gas to the diluent port of the gas divider.
(9) While flowing NO and CO2 through the gas divider, stabilize the output of the gas divider. Determine the CO2 concentration from the gas divider output, applying gas property correction as necessary to ensure accurate gas division, or measure it using an NDIR. Record this concentration, xCO2act, and use it in the quench verification calculations in § 1065.675. Alternatively, you may use a simple gas blending device and use an NDIR to determine this CO2 concentration. If you use an NDIR, it must meet the requirements of this part for laboratory testing and you must span it with the CO2 span gas from paragraph (d)(4) of this section.
(10) Measure the NO concentration downstream of the gas divider with the CLD analyzer. Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response. While the analyzer measures the sample's concentration, record the analyzer's output for 30 seconds. Calculate the arithmetic mean concentration from these data, xNOmeas. Record xNOmeas, and use it in the quench verification calculations in § 1065.675.
(11) Calculate the actual NO concentration at the gas divider's outlet, xNOact, based on the span gas concentrations and xCO2act according to Eq. 1065.675-2. Use the calculated value in the quench verification calculations in Eq. 1065.675-1.
(12) Use the values recorded according to this paragraph (d) and paragraph (e) of this section to calculate quench as described in § 1065.675.
(e) H2 O quench verification procedure. Use the following method to determine H2O quench, or use good engineering judgment to develop a different protocol:
(1) Use PTFE or stainless steel tubing to make necessary connections.
(2) If the CLD analyzer has an operating mode in which it detects NO-only, as opposed to total NOX, operate the CLD analyzer in the NO-only operating mode.
(3) Use an NO span gas that meets the specifications of § 1065.750 and a concentration that is near the maximum concentration expected during emission testing.
(4) Zero and span the CLD analyzer. Span the CLD analyzer with the NO span gas from paragraph (e)(3) of this section, record the span gas concentration as xNOdry, and use it in the quench verification calculations in § 1065.675.
(5) Create a humidified NO span gas by bubbling a NO gas 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, humidify your test gas to an H2O level approximately equal to the maximum mole fraction of H2O expected during emission testing. If the humidified NO span gas sample does not pass through a sample dryer, the quench verification calculations in § 1065.675 scale the measured H2O quench to the highest mole fraction of H2O expected during emission testing. If the sample passes through a dryer during emission testing, you must humidify your test gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer. For this case, the quench verification calculations in § 1065.675 do not scale the measured H2O quench.
(6) Introduce the humidified NO test gas into the sample system. You may introduce it upstream or downstream of any sample dryer that is used during emission testing. Note that the sample dryer must meet the sample dryer verification check in § 1065.342.
(7) Measure the mole fraction of H2O in the humidified NO span gas downstream of the sample dryer, xH2Omeas. We recommend that you measure xH2Omeas as close as possible to the CLD analyzer inlet. You may calculate xH2Omeas from measurements of dew point, Tdew, and absolute pressure, ptotal.
(8) Use good engineering judgment to prevent condensation in the transfer lines, fittings, or valves from the point where xH2Omeas is measured to the analyzer. We recommend that you design your system so the wall temperatures in the transfer lines, fittings, and valves from the point where xH2Omeas is measured to the analyzer are at least 5 °C above the local sample gas dew point.
(9) Measure the humidified NO span gas concentration with the CLD analyzer. Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response. While the analyzer measures the sample's concentration, record the analyzer's output for 30 seconds. Calculate the arithmetic mean of these data, xNOwet. Record xNOwet and use it in the quench verification calculations in § 1065.675.
(f) Corrective action. If the sum of the H2O quench plus the CO2 quench is less than −2% or greater than + 2%, take corrective action by repairing or replacing the analyzer. Before running emission tests, verify that the corrective action successfully restored the analyzer to proper functioning.
(g) Exceptions. The following exceptions apply:
(1) You may omit this verification if you can show by engineering analysis that for your NOX sampling system and your emission calculation procedures, the combined CO2 and H2O interference for your NOX CLD analyzer always affects your brake-specific NOX emission results within no more than ±1% of the applicable NOX standard. If you certify to a combined emission standard (such as a NOX + NMHC standard), scale your NOX results to the combined standard based on the measured results (after incorporating deterioration factors, if applicable). For example, if your final NOX + NMHC value is half of the emission standard, double the NOX result to estimate the level of NOX emissions corresponding to the applicable standard.
(2) You may use a NOX CLD analyzer that you determine does not meet this verification, as long as you try to correct the problem and the measurement deficiency does not adversely affect your ability to show that engines comply with all applicable emission standards.
[73 FR 59328, Oct. 8, 2008, as amended at 73 FR 73789, Dec. 4, 2008; 75 FR 23041, Apr. 30, 2010; 76 FR 57447, Sept. 15, 2011; 79 FR 23771, Apr. 28, 2014; 81 FR 74168, Oct. 25, 2016; 86 FR 34545, June 29, 2021]