# 40 CFR 91.426 - Dilute emission sampling calculations.

Where:

A

*wm*=Weighted mass emission level (HC, CO, CO*2*, or NO*X*) for a test [g/kW-hr].W

*i*=Average mass flow rate of an emission from a test engine during mode i [g/hr].WF

*i*= Weighting factor for each mode i as defined in § 91.410(a).P

*i*= Gross average power generated during mode i [kW] calculated from the following equation (power for the idle mode shall always be zero for this calculation):speed = average engine speed measured during mode i [rev./minute]

torque = average engine torque measured during mode i [N-m]

K

*Hi*= Humidity correction factor for mode i. This correction factor only affects calculations for NO*X*and is equal to one for all other emissions. K*Hi*is also equal to one for all two-stroke engines.Where:

Q

*i*= Volumetric flow rate of the dilute exhaust through the CVS at standard conditions [m^{3}/hr at STP].D = Density of a specific emission (D

*HC*, D*CO*, D*CO2*, D*NOx*) in the exhaust [g/m^{3}].DF

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

*Di*= Concentration of the emission (HC, CO, NO*X*) in the dilute exhaust extracted from the CVS during mode i [ppm].C

*Bi*= Concentration of the emission (HC, CO, NO*X*) in the background sample during mode i [ppm].STP = Standard temperature and pressure. All volumetric calculations made for the equations in this section are to be corrected to a standard temperature of 20 °C and 101.3 kPa.

D

*HC*= 576.8 g/m^{3}DNO

*X*= 1912 g/m^{3}D

*CO*= 1164 g/m^{3}D

*CO2*= 1829 g/m^{3}
(1)
The value of D

*HC*above is calculated based on the assumption that the fuel used has a carbon to hydrogen ratio of 1:1.85. For other fuels, D*HC*can be calculated from the following formula:Where:

M

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

*STP*= Ideal gas constant for a gas at STP = 0.024065 [m^{3}-mole].
(2)
The idealized molecular weight of the exhaust hydrocarbons, ie., the molecular weight of the hydrocarbon molecule divided by the number of carbon atoms in the molecule, M

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

M

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

*H*= Molecular weight of hydrogen = 1.008 [g/mole].α = Hydrogen to carbon ratio of the test fuel.

(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:

Where:

C

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

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

*DCO2*= Concentration of CO*2*in the dilute sample [ppm].
(e)
The humidity correction factor K

*H*is an adjustment made to the measured NO*X*. 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:Where:

H = Absolute humidity of the engine intake air [grams of water per kilogram of dry air].

Where:

P

*dew*= Saturated vapor pressure at the dew point temperature [kPa].P

*b*= Barometric pressure [kPa].Where:

M

*f*= Mass of fuel consumed by the engine during the mode [g].T = Duration of the sampling period [hr].

(h)
The mass of fuel consumed during the mode sampling period, M

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

G

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

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

HC

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

*mass*= mass of carbon monoxide emissions for the mode sampling period [g].CO

*2mass*= mass of carbon dioxide emissions for the mode sampling period [g].α = The atomic hydrogen to carbon ratio of the fuel.

**Title 40 published on 2013-07-01**

no entries appear in the Federal Register **after** this date.