§ 86.1243-90 - Calculations; evaporative emissions.

(a) The calculation of the net hydrocarbon, methanol and hydrocarbon plus methanol mass change in the enclosure is used to determine the diurnal and hot soak mass emissions. The mass changes are calculated from initial and final hydrocarbon and methanol concentrations in ppm carbon, initial and final enclosure ambient temperatures, initial and final barometric pressures, and net enclosure volume using the following equations:

(1) For methanol:

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(i) MCH3OH=Methanol mass change, μ g.

(ii) Vn=Net enclosure volume, ft3, as determined by subtracting 50 ft3 (1.42 m3) (volume of vehicle with trunk and windows open) from the enclosure volume. A manufacturer may use the measured volume of the vehicle (instead of the nominal 50 ft3) with advance approval by the Administrator: Provided, the measured volume is determined and used for all vehicles tested by that manufacturer.

(iii) TE=Temperature of sample withdrawn, °R.

(iv) VE=Volume of sample withdrawn, ft3.

(v) TSHED=Temperature of SHED, °R

(vi) PB=Barometric pressure at time of sampling, in. Hg.

(vii) CMS=GC concentration of sample.

(viii) AV=Volume of absorbing reagent in impinger.

(ix) i=Initial sample.

(x) f=Final sample.

(xi) 1=First impinger.

(xii) 2=Second impinger.

(2) For hydrocarbons:

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Where:

(i) MHC=Hydrocarbon mass change, g.

(ii) CHC=FID hydrocarbon concentration as ppm carbon including FID response to methanol in the sample.

(iii) CCH23OH=Methanol concentration as ppm carbon.

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(iv) Vn = Net enclosure volume ft3 (m3), as determined by subtracting 50 ft3 (1.42 m3) (volume of vehicle with trunk and windows open) from the enclosure volume. A manufacturer may use the measured volume of the vehicle (instead of the nominal 50 ft3) with advance approval by the Administrator: Provided, the measured volume is determined and used for all vehicles tested by that manufacturer.

(v) r = FID response factor to methanol.

(vi) PB = Barometric pressure, in Hg (kPa).

(vii) T = Enclosure temperature, °R(°K).

(viii) i = initial reading.

(ix) f = final reading.

(x) 1 = First impinger.

(xi) 2 = Second impinger.

(xii)(A) k = 0.208 (12 + H/C).

(B) For SI units, k = 1.2 (12 + H/C).

Where:

(xiii) H/C = hydrogen carbon ratio.

(A) H/C = 2.33 for diurnal emissions.

(B) H/C = 2.2 for hot soak emissions.

(3) For total evaporative emissions:

Total Evaporative Emissions =

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(b) The final reported results shall be computed by summing the individual evaporative emission results determined for the diurnal breathing-loss test, running-loss test and the hot-soak test.