(a) Scope and frequency. If you use FID analyzers for raw exhaust measurements from engines that operate in a non-stoichiometric mode of combustion (e.g., compression-ignition, lean-burn), verify the amount of FID O2 interference upon initial installation and after major maintenance.

(b) Measurement principles. Changes in O2 concentration in raw exhaust can affect FID response by changing FID flame temperature. Optimize FID fuel, burner air, and sample flow to meet this verification. Verify FID performance with the compensation algorithms for FID O2 interference that you have active during an emission test.

(c) System requirements. Any FID analyzer used during testing must meet the FID O2 interference verification according to the procedure in this section.

(d) Procedure. Determine FID O2 interference as follows, noting that you may use one or more gas dividers to create the reference gas concentrations that are required to perform this verification:

(1) Select three span reference gases that contain a C3H8 concentration that you use to span your analyzers before emission testing. Use only span gases that meet the specifications of §1065.750. You may use CH4 span reference gases for FIDs calibrated on CH4 with a nonmethane cutter. Select the three balance gas concentrations such that the concentrations of O2 and N2 represent the minimum, maximum, and average O2 concentrations expected during testing. The requirement for using the average O2 concentration can be removed if you choose to calibrate the FID with span gas balanced with the average expected oxygen concentration.

(2) Confirm that the FID analyzer meets all the specifications of §1065.360.

(3) Start and operate the FID analyzer as you would before an emission test. Regardless of the FID burner's air source during testing, use zero air as the FID burner's air source for this verification.

(4) Zero the FID analyzer using the zero gas used during emission testing.

(5) Span the FID analyzer using a span gas that you use during emission testing.

(6) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of sampled data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, then proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(7) Check the analyzer response using the span gas that has the minimum concentration of O2 expected during testing. Record the mean response of 30 seconds of stabilized sample data as xO2minHC.

(8) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of stabilized sample data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, then proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(9) Check the analyzer response using the span gas that has the average concentration of O2 expected during testing. Record the mean response of 30 seconds of stabilized sample data as xO2avgHC.

(10) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of stabilized sample data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(11) Check the analyzer response using the span gas that has the maximum concentration of O2 expected during testing. Record the mean response of 30 seconds of stabilized sample data as xO2maxHC.

(12) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of stabilized sample data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, then proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(13) Calculate the percent difference between xO2maxHC and its reference gas concentration. Calculate the percent difference between xO2avgHC and its reference gas concentration. Calculate the percent difference between xO2minHC and its reference gas concentration. Determine the maximum percent difference of the three. This is the O2 interference.

(14) If the O2 interference is within ±2%, the FID passes the O2 interference verification; otherwise perform one or more of the following to address the deficiency:

(i) Repeat the verification to determine if a mistake was made during the procedure.

(ii) Select zero and span gases for emission testing that contain higher or lower O2 concentrations and repeat the verification.

(iii) Adjust FID burner air, fuel, and sample flow rates. Note that if you adjust these flow rates on a THC FID to meet the O2 interference verification, you have reset RFCH4 for the next RFCH4 verification according to §1065.360. Repeat the O2 interference verification after adjustment and determine RFCH4.

(iv) Repair or replace the FID and repeat the O2 interference verification.

(v) Demonstrate that the deficiency does not adversely affect your ability to demonstrate compliance with the applicable emission standards.

(15) For analyzers with multiple ranges, you need to perform the procedure in this paragraph (d) only on a single range.

[70 FR 40516, July 13, 2005, as amended at 73 FR 37309, June 30, 2008; 79 FR 23770, Apr. 28, 2014]