Code of Federal Regulations Title 40. Protection of Environment § 40.90.419 Raw emission sampling calculations—gasoline fueled engines

(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:

Where:

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

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

G_FUEL=Fuel mass flow rate [g/hr],

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

M_HCexh=12.01+α1.008+β16.00

Where:

α=Hydrogen/carbon atomic ratio of the fuel

β=Oxygen/carbon atomic ratio of the fuel

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

Where:

WHC=HC volume concentration in exhaust, ppmC wet

WCO=CO percent concentration in the exhaust, wet

DCO=CO percent concentration in the exhaust, dry

WCO₂=CO₂ percent concentration in the exhaust, wet

DCO₂=CO₂ percent concentration in the exhaust, dry

WNO_X=NO volume concentration in exhaust, ppm wet

WO₂=O₂ percent concentration in the exhaust, wet

WH₂=H₂ percent concentration in exhaust, wet

K=correction factor to be used when converting dry measurements to a wet basis. Therefore, wet concentration=dry concentration x K,

where K is:

DH₂=H₂ percent concentration in exhaust, dry, calculated from the following equation:

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

M_co=Molecular weight of CO=28.01

W_NOx=Mass rate of NO_X in exhaust, [g/hr]

M_NO2=Molecular weight of NO₂=46.01

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

K_H = (9.953 x H + 0.832)

Where:

H = the amount of water in an ideal gas;  40 CFR 1065.645 describes how to determine this value (referred to as x_H2O).

K_H = 1 for two-stroke gasoline engines.

(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.

Where:

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

M_{HC exh}=Molecular weight of hydrocarbons in the exhaust, see following equation:

M_HCexh=M_C+αM_H+βM_O

M_C=Molecular weight of carbon=12.01 [g/mole]

M_H=Molecular weight of hydrogen=1.008 [g/mole]

M_O=Molecular weight of oxygen=16.00 [g/mole]

α=Hydrogen to carbon ratio of the test fuel

β=Oxygen to carbon ratio of the test fuel

M_F=Molecular weight of test fuel

G_FUEL=Fuel mass flow rate, [g/hr]

TC=Total carbon in exhaust, see following equation:

WCO=CO percent concentration in the exhaust, wet

WCO₂=CO₂ percent concentration in the exhaust, wet

DCO=CO percent concentration in the exhaust, dry

DCO₂=CO₂ percent concentration in the exhaust, dry

WHC=HC volume concentration in exhaust, ppmC wet

WNO_X=NO_X volume concentration in exhaust, ppm wet

K=correction factor to be used when converting dry measurements to a wet basis. Therefore, wet concentration=dry concentration x K, where K is:

DH₂=H₂ percent concentration in exhaust, dry, calculated from the following equation:

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

M_CO=Molecular weight of CO=28.01

WNO_X=Mass rate of NO_X in exhaust, [g/hr]

MNO₂=Molecular weight of NO₂=46.01

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

K_H = (9.953 x H + 0.832)

Where:

H = the amount of water in an ideal gas;  40 CFR 1065.645 describes how to determine this value (referred to as x_H2O).

K_H = 1 for two-stroke gasoline engines.

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

Where:

A_WM=Final weighted brake-specific mass emission rate (HC, CO, NO_X) [g/kW-hr]

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

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

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

Where:

speed=average engine speed measured during mode i [rev./minute]

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