40 CFR § 1066.610 - Dilution air background correction.

§ 1066.610 Dilution air background correction.

(a) Correct the emissions in a gaseous sample for background using the following equation:

x [ emission ] = x [emission]dexh x [emission]bkgnd · ( 1 ( 1 DF ) ) Eq. 1066.610-1

Where:
x[emission]dexh = measured emission concentration in dilute exhaust (after dry-to-wet correction, if applicable).
x[emission]bkgnd = measured emission concentration in the dilution air (after dry-to-wet correction, if applicable).
DF = dilution factor, as determined in paragraph (b) of this section.

Example: x NOxdexh = 1.08305 ppm x NOxbkgnd = 0.12456 ppm D F = 9.14506 x NOx = 1.08305 0.12456 · ( 1 ( 1 9.14506 ) ) = 0.97211 ppm (b) Except as specified in paragraph (c) of this section, determine the dilution factor, D F , over the test interval using the following equation: D F = 1 ( 1 + α 2 + 3.76 · ( 1 + α 4 β 2 ) ) · ( x CO 2 + x NMHC + x CH 4 + x CO ) Eq. 1066.610-2

Where:
xCO2 = amount of CO2 measured in the sample over the test interval.
xNMHC = amount of C1-equivalent NMHC measured in the sample over the test interval.
xCH4 = amount of CH4 measured in the sample over the test interval.
xCO = amount of CO measured in the sample over the test interval.
a = atomic hydrogen-to-carbon ratio of the test fuel. You may measure a or use default values from Table 1 of 40 CFR 1065.655.
b = atomic oxygen-to-carbon ratio of the test fuel. You may measure b or use default values from Table 1 of 40 CFR 1065.655.

Example: x CO 2 = 1.456 % = 0.01456 x NMHC = 0.84 ppm = 0.00000084 x CH 4 = 0.26 ppm = 0.00000026 x CO = 80.4 ppm = 0.0000804 α = 1.92 β = 0.03 D F = 1 ( 1 + 1.92 2 + 3.76 · ( 1 + 1.92 4 0.03 2 ) ) · ( 0.01456 + 0.00000084 + 0.00000026 + 0.0000804 ) = 9.14506

(c) Determine the dilution factor, DF, over the test interval for partial-flow dilution sample systems using the following equation:

D F = V dexhstd V exhstd Eq. 1066.610-3

Where:

Vdexhstd = total dilute exhaust volume sampled over the test interval, corrected to standard reference conditions.

Vexhstd = total exhaust volume sampled from the vehicle, corrected to standard reference conditions.

Example: V dexhstd = 170.9 m 3 V exhstd = 15.9 m 3 DF = 170.9 15.4 = 11.1

(d) Determine the time-weighted dilution factor, DFw, over the duty cycle using the following equation:

D F w = i = 1 N t i i = 1 N 1 D F i · t i Eq. 1066.620-4

Where:
N = number of test intervals.
i = test interval number
t = duration of the test interval.
DF = dilution factor over the test interval.
Example:

N = 3 DF 1 = 14.40 t 1 = 505 s DF 2 = 24.48 t 2 = 867 s DF 3 = 17.28 t 3 = 505 s DF w = 505 + 867 + 505 ( 1 14.40 · 505 ) + ( 1 24.48 · 867 ) + ( 1 17.28 · 505 ) = 18.82