### U.S. Code of Federal Regulations

Regulations most recently checked for updates: Jun 02, 2023

§ 1066.610 - Dilution air background correction.

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

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. 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.

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

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.

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

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 DF1 = 14.40 t1 = 505 s DF2 = 24.48 t2 = 867 s DF3 = 17.28 t3 = 505 s [79 FR 23823, Apr. 28, 2014, as amended at 86 FR 34583, June 29, 2021]