1065.275—N 2 O measurement devices.
(a) General component requirements.
We recommend that you use an analyzer that meets the specifications in Table 1 of § 1065.205. Note that your system must meet the linearity verification in § 1065.307.
(1) Nondispersive infra-red (NDIR) analyzer.
You may use an NDIR analyzer that has compensation algorithms that are functions of other gaseous measurements and the engine's known or assumed fuel properties. The target value for any compensation algorithm is 0.0% (that is, no bias high and no bias low), regardless of the uncompensated signal's bias.
(2) Fourier transform infra-red (FTIR) analyzer.
You may use an FTIR analyzer that has compensation algorithms that are functions of other gaseous measurements and the engine's known or assumed fuel properties. The target value for any compensation algorithm is 0.0% (that is, no bias high and no bias low), regardless of the uncompensated signal's bias. Use appropriate analytical procedures for interpretation of infrared spectra. For example, EPA Test Method 320 is considered a valid method for spectral interpretation (see http://www.epa.gov/ttn/emc/methods/method320.html ).
(3) Photoacoustic analyzer.
You may use a photoacoustic analyzer that has compensation algorithms that are functions of other gaseous measurements. The target value for any compensation algorithm is 0.0% (that is, no bias high and no bias low), regardless of the uncompensated signal's bias. Use an optical wheel configuration that gives analytical priority to measurement of the least stable components in the sample. Select a sample integration time of at least 5 seconds. Take into account sample chamber and sample line volumes when determining flush times for your instrument.
(4) Gas chromatograph analyzer.
You may use a gas chromatograph with an electron-capture detector (GC-ECD) to measure N2 O concentrations of diluted exhaust for batch sampling.
(i)
You may use a packed or porous layer open tubular (PLOT) column phase of suitable polarity and length to achieve adequate resolution of the N2 O peak for analysis. Examples of acceptable columns are a PLOT column consisting of bonded polystyrene-divinylbenzene or a Porapack Q packed column. Take the column temperature profile and carrier gas selection into consideration when setting up your method to achieve adequate N2 O peak resolution.
(ii)
Use good engineering judgment to zero your instrument and correct for drift. You do not need to follow the specific procedures in § 1065.530 and § 1065.550(b) that would otherwise apply. For example, you may perform a span gas measurement before and after sample analysis without zeroing. Use the average area counts of the pre-span and post-span measurements to generate a response factor (area counts/span gas concentration), which you then multiply by the area counts from your sample to generate the sample concentration.
(c) Interference validation.
Perform interference validation for NDIR, FTIR, and photoacoustic analyzers using the procedures of § 1065.375. Interference validation is not required for GC-ECD. Certain interference gases can positively interfere with NDIR, FTIR, and photoacoustic analyzers by causing a response similar to N2 O. When running the interference verification for these analyzers, use interference gases as follows:
(1)
The interference gases for NDIR analyzers are CO, CO2, H2 O, CH4 and SO2. Note that interference species, with the exception of H2 O, are dependent on the N2 O infrared absorption band chosen by the instrument manufacturer and should be determined dently for each analyzer.
(2)
Use good engineering judgment to determine interference gases for FTIR. Note that interference species, with the exception of H2 O, are dependent on the N2 O infrared absorption band chosen by the instrument manufacturer and should be determined independently for each analyzer.