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91.419—Raw emission sampling calculations.
(b)
Air and fuel flow method. If both air and fuel flow mass rates are measured, the following equations are used to determine the weighted emission values for the test engine:
Where:
WHC = Mass rate of HC in exhaust [g/hr],
GAIRD = Intake air mass flow rate on dry basis [g/hr],
GFUEL = Fuel mass flow rate [g/hr],
MHCexh = Molecular weight of hydrocarbons in the exhaust; see the following equation:
MHCexh = 12.01 1.008 × α
Where:
α=Hydrocarbon/carbon atomic ratio of the fuel.
Mexh=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
WNOX = NO volume concentration in exhaust, ppm 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 × K, where K is:
DH2 = H2 percent concentration in exhaust, dry, calculated from the following equation:
WCO = Mass rate of CO in exhaust, [g/hr]
MCO = Molecular weight of CO = 28.01
WNOx = Mass rate of NOX in exhaust, [g/hr]
MNO2 = Molecular weight of NO2 = 46.01
KH = Factor for correcting the effects of humidity on NO2 formation for four-stroke gasoline engines; see the equation below:
Where:
H = specific humidity of the intake air in grams of moisture per kilogram of dry air.
For two-stroke gasoline engines, KH should be set to 1.
(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:
WHC = Mass rate of HC in exhaust, [g/hr]
MF = Molecular weight of test fuel; see following equation:
GFUEL = Fuel mass flow rate, [g/hr]
TC = Total carbon; see following equation:
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
WNOX = NO volume concentration in exhaust, ppm 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 × K, where K is:
DH2 = H2 percent concentration in exhaust, dry, calculated from the following equation:
WCO = Mass rate of CO in exhaust, [g/hr]
MCO = Molecular weight of CO = 28.01
WNOx = Mass rate of NOX in exhaust, [g/hr]
MNO2 = Molecular weight of NO2 = 46.01
KH = Factor for correcting the effects of humidity on NO2 formation for four-stroke gasoline engines; see the equation below:
Where:
H = specific humidity of the intake air in grams of moisture per kilogram of dry air.
For two-stroke gasoline engines, KH should be set to 1.
(d)
The final reported emission test results must be computed by using the following formula for each individual gas component:
Where:
Ywm = Weighted mass emission level (HC, CO, NOX) for a test [g/kW-hr].
Wi = Average mass flow rate (WHC, WCO, WNOx) of an emission from the test engine during mode i, [g/hr].
fi = Weighting factors for each mode according to § 91.410(a)
Pi = Average power measured during mode i, [kW], calculated according to the formula given in § 91.423(b). Power for the idle mode shall always be zero for this calculation.
(e)
The final reported weighted brake-specific fuel consumption (WBSFC) shall be computed by use of the following formula:
Where:
WBSFC = Weighted brake-specific fuel consumption in grams of fuel per kilowatt-hour (g/kW-hr).
Fi = Fuel mass flow rate of the engine during mode i, [g/hr].
fi = Weighting factors for each mode according to § 91.410(a)
Pi = Average power measured during mode i, [kW], calculated according to the formula given in § 91.423(b). Power for the idle mode shall always be zero for this calculation.
Code of Federal Regulations
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