You may correct NOX emissions for intake-air humidity as described in this section if the standard-setting part allows it. See Sec. 1066.605(c) for the proper sequence for applying the NOX 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:[GRAPHIC] [TIFF OMITTED] TR19FE15.027 Where: MH2O = molar mass of H2O.pd = saturated vapor pressure at the ambient dry bulb
temperature.RH = relative humidity of ambient airMair = molar mass of air.patmos = atmospheric pressure.
Example: MH2O = 18.01528 g/molpd = 2.93 kPaRH = 37.5%Mair = 28.96559 g/molpatmos = 96.71 kPa[GRAPHIC] [TIFF OMITTED] TR19FE15.028
(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:[GRAPHIC] [TIFF OMITTED] TR19FE15.029
Where: [chi]NOx = measured NOX emission concentration in
the sample, after dry-to-wet and background corrections.Hs = 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[chi]NOx = 1.21 ppm[GRAPHIC] [TIFF OMITTED] TR19FE15.030
(b) For vehicles above 14,000 pounds GVWR, apply correction factors as described in 40 CFR 1065.670. [80 FR 9121, Feb. 19, 2015]