# 40 CFR 90.426 - Dilute emission sampling calculations

*WM*= Final weighted brake-specific mass emission rate for an emission (HC, CO, CO

*2*, or NO

*X*) [g/kW-hr]

*i*= Average mass flow rate of an emission (HC, CO, CO

*2*, NO

*X*) from a test engine during mode i [g/hr]

*i*= Weighting factor for each mode i as defined in § 90.410(a).

*i*= Gross average power generated during mode i [kW], calculated from the following equation,

*Hi*= NO

*X*humidity correction factor for mode i. This correction factor only affects calculations for tion factor only affects calculations for NO

*X*and is equal to one for all other emissions. K

*Hi*is also equal to 1 for all two-stroke engines.

*i*in g/hr, of an emission for mode i is determined from the following equation:

*I*= Volumetric flow rate [m

^{3}/HR at stp].

*2*, Density NO

*X*) [g/m

^{3}].

*i*= Dilution factor of the dilute exhaust during mode i.

*Di*= Concentration of the emission (HC, CO, NO

*X*) in dilute exhaust extracted from the CVS during mode i [ppm].

*Bi*= Concentration of the emission (HC, CO, NO

*X*) in the background sample during mode i [ppm].

*HC*= 576.8 g/m

^{3}

*NOX*= 1912 g/m

^{3}

*CO*= 1164 g/m

^{3}

*CO2*= 1829 g/m

^{3}

*HC*above is calculated based on the assumption that the fuel used has a hydrogen to carbon ratio of 1:1.85. For other fuels Density

*HC*can be calculated from the following formula:

*HC*= The molecular weight of the hydrocarbon molecule divided by the number of carbon atoms in the molecule [g/mole].

*STP*= Ideal gas constant for a gas at STP = 0.024065 [m

^{3}·mole]

*HC*, can be calculated from the following formula:

*C*= Molecular weight of carbon=12.01 [g/mole]

*H*= Molecular weight of hydrogen=1.008 [g/mole]

*O*= Molecular weight of oxygen=16.00 [g/mole]

*DHC*= Concentration of HC in the dilute sample [ppm].

*DCO*= Concentration of CO in the dilute sample [ppm].

*DCO2*= Concentration of CO

*2*in the dilute sample [ppm].

*H*is an adjustment made to measured NO

*X*values. This corrects for the sensitivity that a spark-ignition engine has to the humidity of its combustion air. The following formula is used to determine K

*H*for NO

*X*calculations:

*H*= (9.953 H 0.832)

*H*

*2*

*O*).

*H*= 1 for two-stroke gasoline engines.

*FUEL*= Mass of fuel consumed by the engine during the mode [g]

*FUEL*, can be calculated from the following equation:

*S*= Mass of carbon measured during the mode sampling period [g].

*2*= The fuel carbon weight fraction, which is the mass of carbon in fuel per mass of fuel [g/g].

*S*, can be calculated from the following equation:

*mass*= mass of hydrocarbon emissions for the mode sampling period [grams].

*mass*mass of carbon monoxide emissions for the mode sample period [grams].

*2mass*= mass of carbon dioxide emissions for the mode sample period [grams].

(a) The final reported emission test results must be computed by use of the following formula:

KHi = NOX humidity correction factor for mode i. This correction factor only affects calculations for tion factor only affects calculations for NOX and is equal to one for all other emissions. KHi is also equal to 1 for all two-stroke engines.

(b) The mass flow rate, Wi in g/hr, of an emission for mode i is determined from the following equation:

(c) Densities for emissions that are to be measured for this test procedure are:

(1) The value of DensityHC above is calculated based on the assumption that the fuel used has a hydrogen to carbon ratio of 1:1.85. For other fuels DensityHC can be calculated from the following formula:

(2) The idealized molecular weight of the exhaust hydrocarbons, i.e., the molecular weight of the hydrocarbon molecule divided by the number of carbon atoms in the molecule, MHC, can be calculated from the following formula:

(3) The value of DensityNOX above assumes that NOX is entirely in the form of NO2

(d) The dilution factor, DF, is the ratio of the volumetric flow rate of the background air to that of the raw engine exhaust. The following formula is used to determine DF:

(e) The humidity correction factor KH is an adjustment made to measured NOX values. This corrects for the sensitivity that a spark-ignition engine has to the humidity of its combustion air. The following formula is used to determine KH for NOX calculations:

(f)-(g) [Reserved]

(h) The fuel mass flow rate, Fi, can be either measured or calculated using the following formula:

(i) The mass of fuel consumed during the mode smpling period, MFUEL, can be calculated from the following equation:

(j) The grams of carbon measured during the mode, GS, can be calculated from the following equation: