# 40 CFR 90.419 - Raw emission sampling calculations

*Air and fuel flow method.*If both air and fuel flow mass rates are measured, use the following equations to determine the weighted emission values for the test engine:

*HC*= Mass rate of HC in exhaust [g/hr],

*AIRD*= Intake air mass flow rate on dry basis [g/hr],

*FUEL*= Fuel mass flow rate [g/hr],

*HCexh*= Molecular weight of hydrocarbons in the exhaust, see the following equation:

*exh*= Molecular weight of the total exhaust, see the following equation:

*2*= CO

*2*percent concentration in the exhaust, wet

*2*= CO

*2*percent concentration in the exhaust, dry

*X*= NO volume concentration in exhaust, ppm wet

*2*= O

*2*percent concentration in the exhaust, wet

*2*= H

*2*percent concentration in exhaust, wet

*2*= H

*2*percent concentration in exhaust, dry, calculated from the following equation:

*co*= Mass rate of CO in exhaust, [g/hr]

*co*= Molecular weight of CO=28.01

*NOx*= Mass rate of NO

*X*in exhaust, [g/hr]

*NO2*= Molecular weight of NO

*2*=46.01

*H*= Factor for correcting the effects of humidity on NO

*2*formation for 4-stroke gasoline small engines, as follows:

*H*= (9.953 × H 0.832)

*H*

*2*

*O*).

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

*Fuel flow method.*The following equations are to be used when fuel flow is selected as the basis for mass emission calculations using the raw gas method.

*HC*= Mass rate of HC in exhaust, [g/hr]

*HCexh*= Molecular weight of hydrocarbons in the exhaust, see following equation:

*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]

*F*= Molecular weight of test fuel

*FUEL*= Fuel mass flow rate, [g/hr]

*2*= CO

*2*percent concentration in the exhaust, wet

*2*= CO

*2*percent concentration in the exhaust, dry

*X*= NO

*X*volume concentration in exhaust, ppm wet

*2*= H

*2*percent concentration in exhaust, dry, calculated from the following equation:

*CO*= Mass rate of CO in exhaust, [g/hr]

*CO*= Molecular weight of CO = 28.01

*X*= Mass rate of NO

*X*in exhaust, [g/hr]

*2*= Molecular weight of NO

*2*=46.01

*H*= Factor for correcting the effects of humidity on NO

*2*formation for 4-stroke gasoline small engines, as follows:

*H*= (9.953 × H 0.832)

*H*

*2*

*O*).

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

*WM*= Final weighted brake-specific mass emission rate (HC, CO, NO

*X*) [g/kW-hr]

*i*= Mass emission rate during mode i [g/hr]

*i*= Weighting factors for each mode according to § 90.410(a)

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

(a) Derive the final weighted brake-specific mass emission rates (g/kW-hr) through the steps described in this section.

(b) Air and fuel flow method. If both air and fuel flow mass rates are measured, use the following equations to determine the weighted emission values for the test engine:

(c) Fuel flow method. The following equations are to be used when fuel flow is selected as the basis for mass emission calculations using the raw gas method.

KH = Factor for correcting the effects of humidity on NO2 formation for 4-stroke gasoline small engines, as follows:

KH = (9.953 × H 0.832)

(d) Calculate the final weighted brake-specific emission rate for each individual gas component using the following equation: