# Calculations.

Calculations.
(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 The methanol mass change is calculated from the initial and final methanol samples, the net withdrawn methanol (in the case of diurnal emission testing with fixed-volume enclosures), and initial and final temperature according to the following equation:
(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and final FID readings of hydrocarbon concentration, methanol concentration with FID response to methanol, the net withdrawn hydrocarbon and methanol (in the case of diurnal emission testing with fixed-volume enclosures), and initial and final temperature and pressure according to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.
(x)
(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:
(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 The methanol mass change is calculated from the initial and final methanol samples, the net withdrawn methanol (in the case of diurnal emission testing with fixed-volume enclosures), and initial and final temperature according to the following equation:
(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and final FID readings of hydrocarbon concentration, methanol concentration with FID response to methanol, the net withdrawn hydrocarbon and methanol (in the case of diurnal emission testing with fixed-volume enclosures), and initial and final temperature and pressure according to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.
(x)
(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).

## Source

40 CFR § 86.117-96

## Scoping language

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 86.181317(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.

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