40 CFR § 86.117-96 - Evaporative emission enclosure calibrations.
The calibration of evaporative emission enclosures consists of three parts: initial and periodic determination of enclosure background emissions (hydrocarbons and methanol); initial determination of enclosure internal volume; and periodic hydrocarbon and methanol retention check and calibration. Ethanol retention checks may be performed instead of methanol retention checks. Alcohol retentions may be omitted if no alcohol-fueled vehicles will be tested in the evaporative enclosure. For evaporative and refueling emission tests with ethanol-gasoline blends that have less than 25% ethanol by volume, if you account for ethanol with a mathematical adjustment as described in § 86.1813-17(a)(1)(iv) instead of measuring ethanol, the testing specifications and diagnostic requirements in this part 86 that are specific to ethanol-gasoline blends do not apply. Alternate calibration methods may be used if shown to yield equivalent or superior results, and if approved in advance by the Administrator; specifically, more extreme temperatures may be used for determining calibration without affecting the validity of test results.
(a) Initial and periodic determination of enclosure background emissions. Prior to its introduction into service, annually thereafter, and after any repair that can affect the enclosure background emissions, the enclosure shall be checked to determine that it does not contain materials that will themselves emit hydrocarbons or methanol. When methanol as well as hydrocarbons are present in the evaporative enclosure, the HFID hydrocarbon concentration measurement includes the partial response of the HFID to methanol plus the hydrocarbons. Determination of the HFID response to methanol, § 86.121, prior to its being placed in service is required for the determination of hydrocarbons. Proceed as follows:
(1) Prepare the enclosure. (i) Variable-volume enclosures may be operated in either latched or unlatched volume configuration, as described in paragraph (b)(1) of this section. Ambient temperatures shall be maintained at 96±3 °F throughout the 4-hour period.
(ii) Fixed-volume enclosures may be operated with inlet and outlet flow streams either closed or open; if inlet and outlet flow streams are open, the air flowing into and out of the enclosure must be monitored in accordance with § 86.107-96(a)(1)(ii)(B). Ambient temperatures shall be maintained at 96±3 °F throughout the 4-hour period.
(iii) For running loss enclosures ambient temperatures shall be maintained at 95±3 °F throughout the 4-hour period. For running loss enclosures designed with a vent for makeup air, the enclosure shall be operated with the vent closed.
(2) The enclosure may be sealed and the mixing fan operated for a period of up to 12 hours before the 4-hour background sampling period begins.
(3) Zero and span (calibrate if required) the hydrocarbon analyzer.
(4) Prior to the background determination, purge the enclosure until a stable background hydrocarbon reading is obtained.
(5) Turn on the mixing blower (if not already on).
(6) Seal enclosure and measure background hydrocarbon concentration, background methanol, temperature, and barometric pressure.
These are the initial readings CHCi, CCH3OHi, and PBi, Ti for the enclosure background determination.
(7) Allow the enclosure to stand undisturbed for four hours.
(8) Measure the hydrocarbon concentration on the same FID and the methanol level. These are the final concentrations, CHCf and CCH3OHf. Also measure final temperature and barometric pressure.
(9) Calculate the mass change of methanol, hydrocarbons, and hydrocarbons plus methanol in the enclosure according to the equations in paragraph (d) of this section.
(i) Diurnal enclosures. The enclosure background emissions (hydrocarbons plus methanol) shall not be greater than 0.05g for the 4 hours.
(ii) Running loss enclosures. The enclosure background emissions (hydrocarbons plus methanol) shall not be greater than 0.2 grams for the 4 hours.
(b) Initial determination of enclosure internal volume. Prior to its introduction into service the enclosure internal volume shall be determined by the following procedure:
(1) Carefully measure the internal length, width and height of the enclosure, accounting for irregularities (such as braces) and calculate the internal volume. For variable-volume enclosures, latch the enclosure to a fixed volume when the enclosure is held at a constant temperature; this nominal volume shall be repeatable within ±0.5 percent of the reported value.
(c) Hydrocarbon and methanol (organic gas) retention check and calibration. The hydrocarbon and methanol (if the enclosure is used for methanol-fueled vehicles) retention check provides a check upon the calculated volume and also measures the leak rate. The enclosure leak rate shall be determined prior to its introduction into service, following any modifications or repairs to the enclosure that may affect the integrity of the enclosure, and at least monthly thereafter. The methanol retention check must be performed only upon initial installation and after major maintenance, consistent with good engineering judgment. If six consecutive monthly retention checks are successfully completed without corrective action, the enclosure leak rate may be determined quarterly thereafter as long as no corrective action is required.
(1) An enclosure to be used for the diurnal emission test (see § 86.133-96) shall be calibrated according to the following procedure. Calibration for hydrocarbon and methanol may be conducted simultaneously or in sequential test runs.
(i) Zero and span (calibrate if required) the hydrocarbon analyzer.
(ii) Purge the enclosure until a stable background hydrocarbon reading is obtained.
(iii) Turn on the mixing blowers (if not already on).
(v) Turn on the ambient temperature control system (if not already on) and adjust it for an initial temperature of 96 °F (36 °C). On variable-volume enclosures, latch the enclosure to the appropriate volume position for the set temperature. On fixed-volume enclosures close the outlet and inlet flow streams.
(vi) When the enclosure stabilizes at 96±3 °F (36±2 °C), seal the enclosure and measure background hydrocarbon concentration, background methanol, temperature, and barometric pressure. These are the initial readings CHCi, CCH3OHi, Ti, and PBi for the enclosure calibration.
(vii) Inject into the enclosure 0.5 to 1.0 grams of pure methanol at a recommended temperature of at least 150 °F (65 °C) and/or 0.5 to 1.0 grams of pure propane at lab ambient temperature. The injected quantity may be measured by volume flow or by mass measurement. The method used to measure the quantity of methanol and propane must have an accuracy of ±0.5 percent of the measured value (less accurate methods may be used with the advance approval of the Administrator).
(viii) After a minimum of 5 minutes of mixing, analyze the enclosure atmosphere for hydrocarbon and methanol content, also record temperature and pressure. These measurements are the final readings for the enclosure calibration as well as the initial readings for the retention check.
(ix) To verify the enclosure calibration, calculate the mass of propane and the mass of methanol using the measurements taken in paragraphs (c)(1)(vi) and (viii) of this section. See paragraph (d) of this section. This quantity must be within ±2 percent of that measured in paragraph (c)(1)(vii) of this section for propane and ±5 percent for methanol. Evaluate long-term trends using good engineering judgment to minimize measurement bias. Keep records to document such evaluations and make them available to EPA upon request.
(x) For variable-volume enclosures, unlatch the enclosure from the nominal volume configuration. For fixed-volume enclosures, open the outlet and inlet flow streams.
(xi) Start cycling the ambient temperature from 96 °F to 72 °F and back to 96 °F over a 24-hour period, according to the profile specified in § 86.133-96 and appendix II of this part, within 15 minutes of sealing the enclosure.
(xii) At the completion of the 24-hour cycling period, analyze the enclosure atmosphere for hydrocarbon and methanol content; determine the net withdrawn methanol (in the case of diurnal emission testing with fixed volume enclosures); record temperature and barometric pressure. These are the final readings for the hydrocarbon and methanol retention check. The final hydrocarbon and methanol mass, calculated in paragraph (d) of this section, shall be within three percent of that determined in paragraph (c)(1)(viii) of this section. (For 1991-1995 calendar years, the difference may exceed ±3 percent for methanol, provided it does not exceed ±6 percent.)
(3) Enclosures calibrated according to the procedures specified in either paragraph (c)(1) or (c)(2) of this section may be used for hot soak testing (see § 86.138).
(1) The calculation of net methanol and hydrocarbon mass change is used to determine enclosure background and leak rate. It is also used to check the enclosure volume measurements. The methanol mass change is calculated from the initial and final methanol samples, the net withdrawn methanol (in the case of diurnal emission testing with fixed-volume enclosures), and initial and final temperature and pressure according to the following equation:
(i) MCH3OH = Methanol mass change, µg.
(ii) V = Enclosure volume, ft 3, as measured in paragraph (b)(1) of this section.
(v) VE = Volume of sample withdrawn, ft 3. Sample volumes must be corrected for differences in temperature to be consistent with determination of Vn, prior to being used in the equation.
(vi) PB = Barometric pressure at time of sampling, in. Hg.
(vii) CMS = GC concentration of test sample.
(viii) AV = Volume of absorbing reagent in impinger (ml).
(ix) i = Initial sample.
(x) f = Final sample.
(xii) 1 = First impinger.
(xiii) 2 = Second impinger.
(xiv) MCH3OH,out = mass of methanol exiting the enclosure, in the case of fixed volume enclosures for diurnal emission testing, µg.
(xv) MCH3OH,in = mass of methanol exiting the enclosure, in the case of fixed volume enclosures for diurnal emission testing, µg.
(2) The hydrocarbon mass change is calculated from the initial and final FID readings of hydrocarbon concentration, methanol concentration with FID response to methanol, the net withdrawn hydrocarbon and methanol (in the case of diurnal emission testing with fixed-volume enclosures), and initial and final temperature and pressure according to the following equation:
(i) MHC = Hydrocarbon mass change, g.
(ii) CHC = FID hydrocarbon concentration as ppm carbon, that is, ppm propane × 3, including FID response to methanol in the sample.
(iii) CCH3OH = Methanol concentration as ppm carbon
(iv) V = Enclosure volume ft 3 (m 3), as measured in paragraph (b)(1) of this section.
(v) r = FID response factor to methanol.
(vi) PB = Barometric pressure, in. Hg. (kPa).
(vii) T = Enclosure ambient temperature, R(K).
(viii) i = Indicates initial reading.
(ix) f = Indicates final reading.
(A) k = 3.05.
(B) For SI units, k = 17.60.
(xi) MHC, out = mass of hydrocarbon exiting the enclosure, in the case of fixed-volume enclosures for diurnal emission testing, g.
(xii) MHC, in = mass of hydrocarbon entering the enclosure, in the case of fixed-volume enclosures for diurnal emission testing, g.
(3) For variable-volume enclosures, defined in § 86.107(a)(1)(i), the following simplified form of the hydrocarbon mass change equation may be used:
(e) Calibration of equipment for point-source testing of running losses. For the point-source method, the running loss fuel vapor sampling system shall be calibrated as a CVS system, as specified in § 86.119, with the additional specification that the vapor sampling system verification be conducted as follows:
(1) The following “gravimetric” technique can be used to verify that the vapor sampling system and analytical instruments can accurately measure a mass of gas that has been injected into the system. If the vapor sampling system will be used only in the testing of petroleum-fueled engines, the system verification may be performed using propane. If the vapor sampling system will be used with methanol-fueled vehicles as well as petroleum-fueled vehicles, the system verification performance check must include a methanol check in addition to the propane check. (Verification can also be accomplished by constant flow metering using critical flow orifice devices.)
(i) Obtain a small cylinder that has been charged with pure propane gas. Obtain another small cylinder that has been charged with pure methanol if the system will be used for methanol-fueled vehicle testing. Since this cylinder will be heated to 150-155 °F, care must be taken to ensure that the liquid volume of methanol placed in the cylinder does not exceed approximately one-half of the total volume of the cylinder.
(ii) Determine a reference cylinder weight to the nearest 0.01 grams.
(iii) Operate the vapor sampling system in the normal manner and release a known quantity of pure propane into the most frequently used fuel vapor collector during the sampling period (approximately 5 minutes).
(iv) Continue to operate the vapor sampling system in the normal manner and release a known quantity of pure methanol into the system during the sampling period (approximately 5 minutes).
(v) The calculations of § 86.144 are performed in the normal way, except in the case of propane. The density of propane (17.30 g/ft 3/carbon atom (0.6109 kg/m 3/carbon atom)) is used in place of the density of exhaust hydrocarbons. In the case of methanol, the density of 37.71 g/ft 3 (1.332 kg/m 3) is used.
(vi) The gravimetric mass is subtracted from the vapor sampling system measured mass and then divided by the gravimetric mass to determine the percent accuracy of the system.
(vii) The cause for any discrepancy greater than ±2 percent must be found and corrected.
(2) This procedure shall be conducted in the point-source running loss test environment with the collector installed in a vehicle in the normal test configuration. The fuel of the test vehicle shall either be diesel, or it shall be kept under 100 °F (38 °C). Two to six grams of pure propane and two to six grams of pure methanol shall be injected into the collector while the vehicle is operated over one Urban Dynamometer Driving Schedule (UDDS), as described in § 86.115 and appendix I of this part. The propane and methanol injections shall be conducted at the ambient temperature of 95±5 °F (35±3 °C).