The FID hydrocarbon analyzer shall receive the following initial and periodic calibrations.
(a)Initial and periodic optimization of detector response. Prior to its introduction into service and at least annually thereafter, the FID hydrocarbon analyzer shall be adjusted for optimum hydrocarbon response. (The HFID used with methanol-fueled vehicles shall be operated at 235° ±15 °F (113° ±8 °C)). Analyzers used with gasoline-fuel and liquefied petroleum gas-fuel shall be optimized using propane. Analyzers used with natural gas-fuel may be optimized using methane, or if calibrated using propane the FID response to methane shall be determined and applied to the FID hydrocarbon reading. Alternate methods yielding equivalent results may be used, if approved in advance by the Administrator.
(1) Follow the manufacturer's instructions or good engineering practice for instrument startup and basic operating adjustment using the appropriate FID fuel and zero-grade air.
(2) Optimize on the most common operating range. Introduce into the analyzer a propane (or methane as appropriate) in air mixture with a propane (or methane as appropriate) concentration equal to approximately 90 percent of the most common operating range.
(3) Select an operating FID fuel flow rate that will give near maximum response and least variation in response with minor fuel flow variations.
(4) To determine the optimum air flow, use the FID fuel flow setting determined above and vary air flow.
(5) After the optimum flow rates have been determined, record them for future reference.
(b)Initial and periodic calibration. Prior to its introduction into service and monthly thereafter the FID hydrocarbon analyzer shall be calibrated on all normally used instrument ranges, and, if applicable, the methanol response factor shall be determined (paragraph (c) of this section). Use the same flow rate as when analyzing sample.
(1) Adjust analyzer to optimize performance.
(2) Zero the hydrocarbon analyzer with zero-grade air.
(3) Calibrate on each normally used operating range with propane in air (or methane in air as appropriate) calibration gases having nominal concentrations of 15, 30, 45, 60, 75 and 90 percent of that range. For each range calibrated, if the deviation from a least squares best-fit straight line is two percent or less of the value at each data point, concentration values may be calculated by use of a single calibration factor for that range. If the deviation exceeds two percent at any point, the best-fit non-linear equation which represents the data to within two percent of each test point shall be used to determine concentration.
(c)FID response factor to methanol. When the FID analyzer is to be used for the analysis of hydrocarbon samples containing methanol, the methanol response factor of the analyzer shall be established. The methanol response factor shall be determined at several concentrations in the range of concentrations in the exhaust sample, using either bag samples or gas bottles meeting the requirements of § 86.114.
(1) The bag sample of methanol for analysis in the FID, if used, shall be prepared using the apparatus shown in Figure M90-1. A known volume of methanol is injected, using a microliter syringe, into the heated mixing zone (250 °F (121 °C) of the apparatus. The methanol is vaporized and swept into the sample bag with a known volume of zero grade air measured by a gas flow meter with an accuracy of ±2 percent.
(2) The bag sample is analyzed using the FID.
(3) The FID response factor, r, is calculated as follows:
r = FIDppm/SAMppm
(i) r = FID response factor.
(ii) FIDppm = FID reading in ppmC.
(iii) SAMppm=methanol concentration in the sample bag, or gas bottle, in ppmC. SAMppm for sample bags:
(iv) 0.02406 = Volume of one mole at 29.92 in Hg and 68 °F, m3.
(v) Fuel injected = Volume of methanol injected, ml.
(vi) Fuel density = Density of methanol, 0.7914 g/ml.
(vii) Air volume = Volume of zero grade air, m3.
(viii) Mol. Wt. CH3OH = 32.04.
(d) The gas chromatograph used in the analysis of methanol samples shall be calibrated at least monthly following manufacturers' recommended procedures (certain equipment may require more frequent calibration based on use and good engineering judgment).
(e)FID response factor to methane. When the FID analyzer to be used for the analysis of natural gas-fueled vehicle hydrocarbon samples has been calibrated using propane, the methane response factor of the analyzer shall be established. To determine the total hydrocarbon FID response to methane, known methane in air concentrations traceable to National Institute of Standards and Technology (NIST) shall be analyzed by the FID. Several methane concentrations shall be analyzed by the FID in the range of concentrations in the exhaust sample. The total hydrocarbon FID response to methane is calculated as follows:
rCH4 = FIDppm/SAMppm
(1) rCH4 = FID response factor to methane.
(2) FIDppm = FID reading in ppmC.
(3) SAMppm = the known methane concentration in ppmC.
[54 FR 14566, Apr. 11, 1989, as amended at 59 FR 48523, Sept. 21, 1994; 60 FR 34361, June 30, 1995]
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