40 C.F.R. § 1066.615

Current through September 30, 2024

Section 1066.615 - NO[X] intake-air humidity correction

You may correct NO_X emissions for intake-air humidity as described in this section if the standard-setting part allows it. See § 1066.605(c) for the proper sequence for applying the NO_X intake-air humidity correction.

(a) For vehicles at or below 14,000 pounds GVWR, apply a correction for vehicles with reciprocating engines operating over specific test cycles as follows:

(1) Calculate a humidity correction using a time-weighted mean value for ambient humidity over the test interval. Calculate absolute ambient humidity, H, using the following equation:

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Where:

M_H2O = molar mass of H₂O.

p_d = saturated vapor pressure at the ambient dry bulb temperature.

RH = relative humidity of ambient air

M_air = molar mass of air.

p_atmos = atmospheric pressure.

Example:

M_H2O = 18.01528 g/mol

p_d = 2.93 kPa

RH = 37.5% = 0.375

M_air = 28.96559 g/mol

p_atmos = 96.71 kPa

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(2) Use the following equation to correct measured concentrations to a reference condition of 10.71 grams H₂O vapor per kilogram of dry air for the FTP, US06, LA-92, SC03, and HFET test cycles:

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Where:

[XI]_NOx = measured NO_X emission concentration in the sample, after dry-to-wet and background corrections.

H_s = humidity scale. Set = 1 for FTP, US06, LA-92, and HFET test cycles. Set = 0.8825 for the SC03 test cycle.

H = ambient humidity, as determined in paragraph (a)(1) of this section.

Example:

H = 7.14741 g H₂O vapor/kg dry air time weighted over the FTP test cycle

[XI]_NOx = 1.21 ppm

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(b) For vehicles above 14,000 pounds GVWR, apply correction factors as described in 40 CFR 1065.670 .

40 C.F.R. §1066.615

80 FR 9121, Feb. 19, 2015, as amended at 81 FR 74207, Oct. 25, 2016

81 FR 74207, 12/27/2016