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Code of Federal Regulations (Last Updated: April 5, 2024) |
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Title 40 - Protection of Environment |
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Chapter I - Environmental Protection Agency |
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SubChapter C - Air Programs |
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Part 86 - Control of Emissions from New and in-Use Highway Vehicles and Engines |
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Subpart D - XXX |
§ 86.345-79 - Emission calculations.
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(a) The following abbreviations (and units) are used in this section.
α = atomic hydrogen/carbon ratio of the fuel
φ = dry fuel-air ratio (measured)/fuel-air ratio (stoichiometric)
BARO = Barometric pressure (in. H gA)
BHP = Brake horsepower
BSCO = Brake specific carbon monoxide emissions, (gm/BHP-HR)
BSFC = Brake specific fuel consumption (lb/BHP-HR)
BSHC = Brake specific hydrocarbon emissions (gm/BHP-HR)
BSNOX = Brake specific oxides of nitrogen emissions (gm/BHP-HR)
DCO = CO volume concentration in exhaust, ppm (dry)
DCO2 = CO2 volume concentration in exhaust, percent (dry)
DHC = HC volume carbon concentration in exhaust, ppmC (dry)
DKNO = NO volume concentration in exhaust, in ppm (dry and humidity corrected)
EIP = engine intake pressure (in. H gA) = BARO − inlet depression
f/a = measured dry fuel-air ratio
G = humidity of the inlet air in grains of water per pound of dry air = (453.59/0.0648) H, (see §86.344)
K = water − gas equilibrium constant = 3.5
KNOx = Humidity correction factor for oxides of nitrogen
Kw = Wet to dry correction factor
MC = Atomic weight of carbon
(MC + MH) = mean molecular weight of the fuel per carbon atom
MCO = Molecular weight of CO
MF = Mass flow-rate of fuel used in the engine in lb/hr = Wf/453.59
MH = Atomic weight of hydrogen
MNO2 = Molecular weight of nitrogen dioxide (NO2)
T = Temperature of inlet air (°F)
WCO = Mass rate of CO in exhaust, grams/hr
Wf = Mass flow-rate of fuel used in the engine, in grams/hr = (453.59)×(Wf lbs/hr)
WHC = HC volume concentration in exhaust, ppm C(wet)
WHC = Mass rate of HC in exhaust, grams/hr
WNOx = Mass rate of NOX in exhaust, grams/hr
Y = H2O volume concentration of intake air (See §86.344)
(b) Determine the exhaust species volume concentration for each mode.
(c)(1) Convert wet basis measurements to a dry basis by the following:
Dry concentrations = 1/KW×wet concentrations. KW is defined by the equation in Figure D79-6.
(2) For Diesel engines, for each mode use the measured engine (f/a) entering the combustion chamber when calculating φ. If applicable bleed air, etc. must be subtracted from the measured air flow (see §86.313).
(3) For gasoline-fueled engines, optional for Diesel engines, calculate φ for each mode by substituting WHC for DHC in the (f/a) equations in paragraph (d) of this section.
(4) Calculate a Y value for each gasoline-fueled engine test from the pre-test data. Apply the Y value to the KW equation for the entire test.
(5) Calculate a separate Y value for each Diesel test segment from the pretest-segment data. Apply the Y value to the KW equation for the entire test-segment.
Figure D79-6. Kw—Wet to Dry Correction Factor
(d) Compute the dry (f/a) if required as follows:
(e) Data validation—(1) Diesel engines only. Compare the calculated dry (f/a) with the measured fuel and air flow. For a valid test the emission calculated (f/a) must agree within 10 percent of the measured (f/a) for each mode. Diesel engine idle and 2 percent modes do not have to meet this requirement.
(2) Fuel/Air ratio comparison. When comparing measured (f/a) ratio to an emissions calculated (f/a) ratio, the measured air flow (in terms of mass) is the total mass of air entering the exhaust pipe. This may include additions of air mass to the exhaust pipe by an air injection system.
(3) Other methods of data validation may be used if prior approval is obtained from the Administrator.
(4) Data validation techniques that have obtained prior approval from the Administrator for use on gasoline-fueled engines may be used to determine void tests.
(f) Multiply the dry nitric oxide volume concentrations by the following humidity correction factor to obtain DKNO:
(1) Gasoline-fueled engines:
KNOx + 0.6272 = 0.00629G − 0.0000176G2
(2) Diesel engines:
A = 0.044 (f/a) − 0.0038
B = − 0.116(f/a) + 0.0053
T = Temperature of inlet air, °F.
(g) Calculate the mass emissions of each species in grams per hour for each mode as follows:
(h)(1) For gasoline-fueled engines, weight the mass values of BHIP, WHC, WCO, Mf, and WNOx for each mode by multiplying the modal mass values by the appropriate modal weighting factor prescribed by §86.335.
(2) For Diesel engines, weight the values of BHP, WHC, WCO, WNOx, and Mf as follows:
(i) Weight the values from each idle mode by multiplying the values by (0.067);
(ii) Weight the remaining modes by multiplying the values by 0.08.
(i) Calculate the brake specific emissions for:
(1) Each gasoline-fueled engine test cycle, and
(2) Each Diesel engine test by summing the weighted values (BHP, WHC, WCO, and WNOx) from each mode as follows:
(t) = Test cycle number (t = 1, 2) (gasoline-fueled engines only).
(j)(1) Calculate the brake-specific fuel consumption (BSFC) from the nonweighted BHP and Mf for each mode. Gasoline-fueled engine idle and CT modes, and Diesel idle modes are excluded.
(2) For gasoline-fuel engines use:
(3) For Diesel engines use:
(4) Other methods of correcting power to determine BSFC may be used only with prior approval of the Administrator.
(k) Calculate the weighted brake-specific fuel consumption (WBSFC) for
(1) Each gasoline engine test cycle by:
t = Test cycle number (t = 1,2)
(2) Each Diesel engine test by:
(l) For gasoline-fueled engines, calculate the brake-specific emissions and fuel consumption for the complete test as follows:
BSHC(T) = 0.35 BSHC(1) = 0.65 BSHC(2)
BSCO(T) = 0.35 BSCO(1) = 0.65 BSCO(2)
BSNOx(T) = 0.35 BSNOx(1) = 0.65 BSNOx(2)
WBSFC(T) = 0.35 WBSFC(1) = 0.65 WBSFC(2)