Symbols, abbreviations, acronyms, and units of measure.

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§ 1066.1005 Symbols, abbreviations, acronyms, and units of measure.

The procedures in this part generally follow either the International System of Units (SI) or the United States customary units, as detailed in NIST Special Publication 811, which we incorporate by reference in § 1066.1010. See 40 CFR 1065.20 for specific provisions related to these conventions. This section summarizes the way we use symbols, units of measure, and other abbreviations.

(a) Symbols for quantities. This part uses the following symbols and units of measure for various quantities:

Expand Table

Table 1 of § 1066.1005 - Symbols for Quantities

Symbol Quantity Unit Unit symbol Unit in terms of SI base units
α atomic hydrogen to carbon ratio mole per mole mol/mol 1.
A area square meter m2 m2.
A vehicle frictional load pound force or newton lbf or N m·kg·s−2.
a g acceleration of Earth's gravity meters per second squared m/s2 m·s−2.
a m calculated vehicle frictional load pound force or newton lbf or N m·kg·s−2.
a 0 intercept of least squares regression.
a 1 slope of least squares regression.
a acceleration feet per second squared or meters per second squared ft/s2 or m/s2 m·s-2.
B vehicle load from drag and rolling resistance pound force per mile per hour or newton second per meter lbf/(mi/hr) or N·s/m kg·s-1.
β ratio of diameters meter per meter m/m 1.
β atomic oxygen to carbon ratio mole per mole mol/mol 1.
c conversion factor.
C vehicle-specific aerodynamic effects pound force per mile per hour squared or newton-second squared per meter squared lbf/(mi/hr)2 or N·s2/m2 m-1·kg.
C # number of carbon atoms in a molecule C # number of carbon atoms in a molecule C #.
C d discharge coefficient.
C d A drag area meter squared m2 m2.
C f flow coefficient.
C p heat capacity at constant pressure joule per kelvin J/K m2·kg·s-2·K-1.
C v heat capacity at constant volume joule per kelvin J/K m2·kg·s-2·K-1.
d diameter meters m m.
D distance miles or meters mi or m m.
D slope correlation pound force per mile per hour squared or newton second squared per meter squared lbf/(mi/hr)2 or N·s2/m2 m−2·kg.
DF dilution factor. 1.
e mass weighted emission result grams/mile g/mi.
F force pound force or newton lbf or N kg·s−2.
ƒ frequency hertz Hz s−1.
ƒn angular speed (shaft) revolutions per minute r/min π·30·s−1.
FC friction compensation error horsepower or watt W m2·kg·s−3.
FR road-load force pound force or newton lbf or N kg·s−2.
γ ratio of specific heats (joule per kilogram kelvin) per (joule per kilogram kelvin) (J/(kg·K))/(J/(kg·K)) 1.
H ambient humidity grams water vapor per kilogram dry air g H2O vapor/kg dry air g H2O vapor/kg dry air.
Δh change in height meters m m.
I inertia pound mass or kilogram lbm or kg kg.
I current ampere A A.
i indexing variable.
IR inertia work rating.
K correction factor 1.
K v calibration coefficient m4·s·K0.5/kg m4·kg−1·s·K0.5.
µ viscosity, dynamic pascal second Pa·s m−1·kg·s−1.
M molar mass gram per mole g/mol 10-3·kg·mol−1.
M e effective mass kilogram kg kg.
m mass pound mass or kilogram lbm or kg kg.
N total number in series.
n total number of pulses in a series.
p pressure pascal Pa m−1·kg·s−2.
Δp differential static pressure pascal Pa m−1·kg·s−2.
p d saturated vapor pressure at ambient dry bulb temperature kilopascal kPa m−1·kg·s−1.
PF penetration fraction.
ρ mass density kilogram per cubic meter kg/m3 m−3·kg.
R dynamometer roll revolutions revolutions per minute rpm π·30−1·s−1.
r ratio of pressures pascal per pascal Pa/Pa 1.
r2 coefficient of determination.
Re # Reynolds number.
RF response factor.
RH relative humidity.
S Sutherland constant kelvin K K.
SEE standard error of the estimate.
SG specific gravity.
Δs distance traveled during measurement interval meters m m.
T absolute temperature kelvin K K.
T Celsius temperature degree Celsius °C K−273.15.
T torque (moment of force) newton meter N·m m2·kg·s-2.
t time hour or second hr or s s.
Δt time interval, period, 1/frequency second s s.
U voltage volt V m2·kg·s-3·A-1.
v speed miles per hour or meters per second mi/hr or m/s m·s-1.
V volume cubic meter m3 m3.
V̇ flow volume rate cubic feet per minute or cubic meter per second ft3/min or m3/s m3·/s−1.
VP volume percent.
x concentration of emission over a test interval part per million ppm.
y generic variable.
Z compressibility factor.

(b) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:

Expand Table
Symbol Species
CH4 methane.
CH3OH methanol.
CH2O formaldehyde.
C2H4O acetaldehyde.
C2H5OH ethanol.
C2H6 ethane.
C3H7OH propanol.
C3H8 propane.
C4H10 butane.
C5H12 pentane.
CO carbon monoxide.
CO2 carbon dioxide.
H2O water.
HC hydrocarbon.
N2 molecular nitrogen.
NMHC nonmethane hydrocarbon.
NMHCE nonmethane hydrocarbon equivalent.
NMOG nonmethane organic gas.
NO nitric oxide.
NO2 nitrogen dioxide.
NOX oxides of nitrogen.
N2O nitrous oxide.
O2 molecular oxygen.
OHC oxygenated hydrocarbon.
PM particulate matter.
THC total hydrocarbon.
THCE total hydrocarbon equivalent.

(c) Superscripts. This part uses the following superscripts for modifying quantity symbols:

Expand Table

Table 3 of § 1066.1005 - Superscripts

Superscript Meaning
overbar (such as ȳ) arithmetic mean.
overdot (such as ẏ) quantity per unit time.

(d) Subscripts. This part uses the following subscripts for modifying quantity symbols:

Expand Table

Table 4 of § 1066.1005 - Subscripts

Subscript Meaning
0 reference.
abs absolute quantity.
AC17 air conditioning 2017 test interval.
act actual or measured condition.
actint actual or measured condition over the speed interval.
adj adjusted.
air air, dry.
atmos atmospheric.
b base.
bkgnd background.
c cold.
comp composite.
cor corrected.
cs cold stabilized.
ct cold transient.
cUDDS cold-start UDDS.
D driven.
dew dewpoint.
dexh dilute exhaust quantity.
dil dilute.
e effective.
emission emission specie.
error error.
EtOH ethanol.
exh raw exhaust quantity.
exp expected quantity.
fil filter.
final final.
flow flow measurement device type.
gas gaseous.
h hot.
HFET highway fuel economy test.
hs hot stabilized.
ht hot transient.
hUDDS hot-start UDDS.
i an individual of a series.
ID driven inertia.
in inlet.
int intake.
init initial quantity, typically before an emission test.
IT target inertia.
liq liquid.
max the maximum (i.e., peak) value expected at the standard over a test interval; not the maximum of an instrument range.
meas measured quantity.
mix dilute exhaust gas mixture.
out outlet.
PM particulate matter.
record record.
ref reference quantity.
rev revolution.
roll dynamometer roll.
s settling.
s slip.
s stabilized.
sat saturated condition.
SC03 air conditioning driving schedule.
span span quantity.
sda secondary dilution air.
std standard conditions.
T target.
t throat.
test test quantity.
uncor uncorrected quantity.
w weighted.
zero zero quantity.

(d) Subscripts. This part uses the following subscripts to define a quantity:

Expand Table
Subscript Quantity
0 reference.
abs absolute quantity.
AC17 air conditioning 2017 test interval.
act actual or measured condition.
actint actual or measured condition over the speed interval.
adj adjusted.
air air, dry.
atmos atmospheric.
b base.
bkgnd background.
c cold.
comp composite.
cor corrected.
cs cold stabilized.
ct cold transient.
cUDDS cold-start UDDS.
D driven.
dew dewpoint.
dexh dilute exhaust quantity.
dil dilute.
e effective.
emission emission specie.
error error.
EtOH ethanol.
exh raw exhaust quantity.
exp expected quantity.
fil filter.
final final.
flow flow measurement device type.
gas gaseous.
h hot.
HFET highway fuel economy test.
hs hot stabilized.
ht hot transient.
hUDDS hot-start UDDS.
i an individual of a series.
ID driven inertia.
in inlet.
int intake.
init initial quantity, typically before an emission test.
IT target inertia.
liq liquid.
max the maximum (i.e. peak) value expected at the standard over a test interval; not the maximum of an instrument range.
meas measured quantity.
mix dilute exhaust gas mixture.
out outlet.
PM particulate matter.
record record.
ref reference quantity.
rev revolution.
roll dynamometer roll.
s settling.
s slip.
s stabilized.
sat saturated condition.
SC03 air conditioning driving schedule.
span span quantity.
sda secondary dilution air.
std standard conditions.
T target.
t throat.
test test quantity.
uncor uncorrected quantity.
w weighted.
zero zero quantity.

(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:

Expand Table

Table 5 of § 1066.1005 - Other Acronyms and Abbreviations

Acronym Meaning
A/C air conditioning.
AC17 air conditioning 2017 test interval.
ALVW adjusted loaded vehicle weight.
ASME American Society of Mechanical Engineers.
CFR Code of Federal Regulations.
CFV critical-flow venturi.
CNG compressed natural gas.
CVS constant-volume sampler.
EPA Environmental Protection Agency.
ETW equivalent test weight.
EV electric vehicle.
FID flame-ionization detector.
FTP Federal test procedure.
GC gas chromatograph.
GEM greenhouse gas emissions model.
GHG greenhouse gas (including CO2, N2O, and CH4).
GPS global positioning system.
GVWR gross vehicle weight rating.
HEV hybrid electric vehicle, including plug-in hybrid electric vehicles.
HFET highway fuel economy test.
HLDT heavy light-duty truck.
HPLC high pressure liquid chromatography.
IBR incorporated by reference.
LA-92 Los Angeles 1992 driving schedule.
MDPV medium-duty passenger vehicle.
NIST National Institute for Standards and Technology.
NMC nonmethane cutter.
PDP positive-displacement pump.
PHEV plug-in hybrid electric vehicle.
PM particulate matter.
RESS rechargeable energy storage system.
ppm parts per million.
SAE Society of Automotive Engineers.
SC03 air conditioning driving schedule.
SEA selective enforcement audit.
SFTP Supplemental Federal Test Procedure.
SI International System of Units.
SSV subsonic venturi.
UDDS urban dynamometer driving schedule.
US06 aggressive driving schedule.
U.S.C. United States Code.
WWV NIST radio station call sign.

(f) Densities of chemical species . This part uses the following densities of chemical species:

Expand Table

Table 6 of § 1066.1005 - Densities of Chemical Species

Symbol Quantity a b g/m3 g/ft3
ρ CH4 density of methane 666.905 18.8847
ρ CH3OH density of methanol 1332.02 37.7185
ρ C2H5OH C1-equivalent density of ethanol 957.559 27.1151
ρ C2H4O C1-equivalent density of acetaldehyde 915.658 25.9285
ρ C3H8 density of propane 611.035 17.3026
ρ C3H7OH C1-equivalent density of propanol 832.74 23.5806
ρ CO density of carbon monoxide 1164.41 32.9725
ρ CO2 density of carbon dioxide 1829.53 51.8064
ρ HC-gas effective density of hydrocarbon - gaseous fuel c (see 3) (see 3)
ρ CH2O density of formaldehyde 1248.21 35.3455
ρ HC-liq effective density of hydrocarbon - liquid fueld 576.816 16.3336
ρ NMHC-gas effective density of nonmethane hydrocarbon - gaseous fuel c (see 3) (see 3)
ρ NMHC-liq effective density of nonmethane hydrocarbon - liquid fuel d 576.816 16.3336
ρ NMHCE-gas effective density of nonmethane equivalent hydrocarbon - gaseous fuel c (see 3) (see 3)
ρ NMHCE-liq effective density of nonmethane equivalent hydrocarbon - liquid fuel d 576.816 16.3336
ρ NOx effective density of oxides of nitrogen e 1912.5 54.156
ρ N2O density of nitrous oxide 1829.66 51.8103
ρ THC-liq effective density of total hydrocarbon - liquid fuel d 576.816 16.3336
ρ THCE-liq effective density of total equivalent hydrocarbon - liquid fuel d 576.816 16.3336

a Densities are given at 20 °C and 101.325 kPa.

b Densities for all hydrocarbon containing quantities are given in g/m3-carbon atom and g/ft3-carbon atom.

c The effective density for natural gas fuel and liquefied petroleum gas fuel are defined by an atomic hydrogen-to-carbon ratio, α, of the hydrocarbon components of the test fuel. ρHCgas = 41.57·(12.011 + (α·1.008)).

d The effective density for gasoline and diesel fuel are defined by an atomic hydrogen-to-carbon ratio, α, of 1.85.

e The effective density of NOX is defined by the molar mass of nitrogen dioxide, NO2.

(g) Constants.

(1) This part uses the following constants for the composition of dry air:

Expand Table
Symbol Quantity mol/mol
xArair amount of argon in dry air 0.00934
xCO2air amount of carbon dioxide in dry air 0.000375
xN2air amount of nitrogen in dry air 0.78084
xO2air amount of oxygen in dry air 0.209445

(2) This part uses the following molar masses or effective molar masses of chemical species:

Expand Table
Symbol Quantity g/mol
(10−3 · kg · mol−1)
Mair molar mass of dry air1 28.96559
MH2O molar mass of water 18.01528

1 See paragraph (g)(1) of this section for the composition of dry air.

(3) This part uses the following molar gas constant for ideal gases:

Expand Table
Symbol Quantity J/(mol · K)
(m2 · kg · s−2 · mol−1 · K−1)
R molar gas constant 8.314472

(h) Prefixes. This part uses the following prefixes to define a quantity:

Expand Table
Symbol Quantity Value
n nano 10−9
µ micro 10−6
m milli 10−3
c centi 10−2
k kilo 103
M mega 106

[79 FR 23823, Apr. 28, 2014, as amended at 80 FR 9124, Feb. 19, 2015; 81 FR 74215, Oct. 25, 2016; 86 FR 34585, June 29, 2021]


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