40 CFR § 86.140-94 - Exhaust sample analysis.
The following sequence shall be performed in conjunction with each series of measurements:
(a) For CO, CO2, CH4, NOX, and for Otto-cycle and methanol-fueled, natural gas-fueled and liquefied petroleum gas-fueled (if non-heated FID option is used) diesel vehicle HC:
(1) Zero the analyzers and obtain a stable zero reading. Recheck after tests.
(2) Introduce span gases and set instrument gains. In order to avoid errors, span and calibrate at the same flow rates used to analyze the test sample. Span gases should have concentrations equal to 75 to 100 percent of full scale. If gain has shifted significantly on the analyzers, check the calibrations. Show actual concentrations on chart.
(3) Check zeroes; repeat the procedure in paragraphs (a) (1) and (2) of this section if required.
(4) Check flow rates and pressures.
(5) Measure THC, CO, CO2, CH4, and NOX concentrations of samples.
(6) Check zero and span points. If difference is greater than 2 percent of full scale, repeat the procedure in paragraphs (a) (1) through (5) of this section.
(b) For petroleum-fueled, natural gas-fueled and liquefied petroleum gas-fueled (if HFID is used) diesel vehicle HC:
(1) Zero HFID analyzer and obtain a stable zero reading.
(2) Introduce span gas and set instrument gains. Span gas should have concentration equal to 75 to 100 percent of full scale.
(3) Check zero as in paragraph (b)(1) of this section.
(4) Introduction of zero and span gas into the analyzer can be accomplished by either of the following methods:
(i) Close heated valve in THC sample (see Figures B94–5 or B94–6) and allow gases to enter HFID. Extreme care should be taken not to introduce gases under high pressure.
(ii) Connect zero and span line directly to THC sample probe and introduce gases at a flow rate greater than 125 percent of the HFID flow rate with the CVS blower operating (see Figures B94–5 or B94–6). Excess flow must be allowed to exit probe inlet.
In order to minimize errors, HFID flow rate and pressure during zero and span (and background bag reading) must be exactly the same as that used during testing.
(5) Continuously record (integrate electronically if desired) dilute THC emission levels during test. Background samples are collected in sample bags and analyzed as in paragraphs (b)(4) (i) or (ii) of this section.
(6) Check zero and span as in paragraphs (b) (1) through (4) of this section. If difference is greater than 2 percent of full scale, void test and check for THC “hangup” or electronic drift in analyzer.
(c) For CH3OH (methanol-fueled vehicles), introduce test samples into the gas chromatograph and measure the concentration. This concentration is CMS in the calculations.
(d) For HCHO (methanol-fueled vehicles), introduce formaldehyde test samples into the high pressure liquid chromatograph and measure the concentration of formaldehyde as a dinitrophenylhydrazine derivative in acetonitrile. This concentration is CFS in the calculations.
(e) For CH4 analysis:
(1) In the event that the procedure results in negative NMHCwm values (as may occur with high methane fractions), any negative NMHCwm value whose absolute value is less than 10 percent of the NMHC standard shall be rounded to zero. Negative NMHCwm values whose absolute value is more than 10 percent of the NMHC standard shall require sample remeasurement. If the 10 percent criterion cannot be met after remeasurement, the test will be void.
(2) Other sampling procedures may be used if shown to yield equivalent or superior results and if approved in advance by the Administrator.