§ 1065.370 CLD CO2 and H2O quench verification.

(a) Scope and frequency. If you use a CLD analyzer to measure NO_X, 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 NO_X response by collisional quenching, which inhibits the chemiluminescent reaction that a CLD utilizes to detect NO_X. 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) CO₂quench 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 NO_X, 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.