(a)Schematic drawings. Figure B90-7 is a schematic drawing of the exhaust gas analytical system for analysis of hydrocarbons (HC) (hydrocarbons plus methanol in the case of methanol-fueled vehicles), carbon monoxide (CO), carbon dioxide (CO2), and oxides of nitrogen (NOX). The schematic diagram of the hydrocarbon analysis train for diesel vehicles (and for hydrocarbons plus methanol for methanol-fueled diesel vehicles if continuous HFID analysis is employed) is shown as part of Figure B90-5 (or Figure B90-6). Since various configurations can produce accurate results, exact conformance with either drawing is not required. Additional components such as instruments, valves, solenoids, pumps and switches may be used to provide additional information and coordinate the functions of the component systems.
(b)Major component description. The exhaust gas analytical system for HC, CO, CO2, and NOX, Figure B90-7, consists of a flame ionization detector (FID) (heated, 235°±15 °F (113°±8 °C) for methanol-fueled vehicles) for the determination of hydrocarbons, non-dispersive infrared analyzers (NDIR) for the determination of carbon monoxide and carbon dioxide and a chemiluminescence analyzer (CL) for the determination of oxides of nitrogen. A heated flame ionization detector (HFID) is used for the continuous determination of hydrocarbons from petroleum-fueled diesel vehicles (may also be used with methanol-fueled diesel vehicles), Figure B90-5 (or B90-6). The analytical system for methanol consists of a gas chromatograph (GC) equipped with a flame ionization detector. The analysis for formaldehyde is performed using high pressure liquid chromatography (HPLC) of 2,4-dinitrophenylhydrazine (DNPH) derivatives using ultraviolet (UV) detection. The exhaust gas analytical system shall conform to the following requirements:
(1) The CL requires that the nitrogen dioxide present in the sample be converted to nitric oxide before analysis. Other types of analyzers may be used if shown to yield equivalent results and if approved in advance by the Administrator.
(2) The carbon monoxide (CO) NDIR analyzer may require a sample conditioning column containing CaSO4, or indicating silica gel to remove water vapor and containing ascarite to remove carbon dioxide from the CO analysis stream.
(i) If CO instruments which are essentially free of CO2 and water vapor interference are used, the use of the conditioning column may be deleted, see §§ 86.122 and 86.144.
(ii) A CO instrument will be considered to be essentially free of CO2 and water vapor interference if its response to a mixture of 3 percent CO2 in N2 which has been bubbled through water at room temperature produces an equivalent CO response, as measured on the most sensitive CO range, which is less than l percent of full scale CO concentration on ranges above 300 ppm full scale or less than 3 ppm on ranges below 300 ppm full scale, see § 86.122.
(3) For petroleum-fueled diesel vehicles (and if selected, for methanol-fueled diesel vehicles) a continuous hydrocarbon sample shall be measured using a heated analyzer train as shown in Figure B90-5 (or B90-6). The train shall include a heated probe, a heated continuous sampling line, a heated particulate filter and a heated hydrocarbon instrument (HFID) complete with heated pump, filter and flow control system.
(i) The response time of this instrument shall be less than 1.5 seconds for 90 percent of full scale response.
(ii) The continuous HC sample system may use an “overflow” zero and span system; see § 86.140-82(b)(4). In this type of system (figures B82-3A and B82-4A), zero or span gas is introduced into the heated sample line at a flow rate that exceeds the sample flow rate to the HFID. The excess gas overflows the sample probe into the dilution tunnel. This method assures that the reference gas enters HFID in the same concentration as the injected reference gas and at the same rate as the sample exhaust gas. In addition to zero and span checks, it may also be used to calibrate the HC analyzer per § 86.121-82(b). The overflow gas flow rate into the sample line shall be greater than 125 percent of the HFID flow rate with the CVS blower operating. A lower flow rate may be used if it has been experimentally shown to produce equivalent results and current dccumentation is maintained. The overflow gases shall enter the heated sample line as close as practicable to the outside surface of the dilution tunnel.
(iii) No other analyzers may draw a sample from the continuous HC sample probe, line or system, unless a common sample pump is used of all analyzers and the single sample line system design reflects good engineering practice.
(iv) Sample transport time from sampling point to inlet of instrument shall be less than 4 seconds.
(v) For petroleum-fueled diesel vehicles, the sample line and filter shall be heated to maintain a sample gas temperature of 375°±10 °F (191°±6 °C) before the filter and before the HFID.
(vi) For methanol-fueled diesel vehicles, the sample line and filter shall be heated to maintain a sample gas temperature of 235°±15 °F (113°±8 °C) before the filter and before the HFID.
(c)Other analyzers and equipment. Other types of analyzers and equipment may be used if shown to yield equivalent results and if approved in advance by the Administrator.
[54 FR 14512, Apr. 11, 1989]
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