U.S. Code of Federal Regulations
Regulations most recently checked for updates: Mar 27, 2023
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:
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. |
area | square meter | m | m | |
vehicle frictional load | pound force or newton | lbf or N | m·kg·s | |
acceleration of Earth's gravity | meters per second squared | m/s | m·s | |
calculated vehicle frictional load | pound force or newton | lbf or N | m·kg·s | |
intercept of least squares regression. | ||||
slope of least squares regression. | ||||
acceleration | feet per second squared or meters per second squared | ft/s | m·s | |
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 | |
β | ratio of diameters | meter per meter | m/m | 1. |
β | atomic oxygen to carbon ratio | mole per mole | mol/mol | 1. |
conversion factor. | ||||
vehicle-specific aerodynamic effects | pound force per mile per hour squared or newton-second squared per meter squared | lbf/(mi/hr) | m | |
number of carbon atoms in a molecule | number of carbon atoms in a molecule | |||
discharge coefficient. | ||||
drag area | meter squared | m | m | |
flow coefficient. | ||||
heat capacity at constant pressure | joule per kelvin | J/K | m | |
heat capacity at constant volume | joule per kelvin | J/K | m | |
diameter | meters | m | m. | |
distance | miles or meters | mi or m | m. | |
slope correlation | pound force per mile per hour squared or newton second squared per meter squared | lbf/(mi/hr) | m | |
dilution factor. | 1. | |||
mass weighted emission result | grams/mile | g/mi. | ||
force | pound force or newton | lbf or N | kg·s | |
ƒ | frequency | hertz | Hz | s |
ƒn | angular speed (shaft) | revolutions per minute | r/min | π·30·s |
friction compensation error | horsepower or watt | W | m | |
road-load force | pound force or newton | lbf or N | kg·s | |
γ | ratio of specific heats | (joule per kilogram kelvin) per (joule per kilogram kelvin) | (J/(kg·K))/(J/(kg·K)) | 1. |
ambient humidity | grams water vapor per kilogram dry air | g H | g H | |
Δ | change in height | meters | m | m. |
inertia | pound mass or kilogram | lbm or kg | kg. | |
current | ampere | A | A. | |
indexing variable. | ||||
inertia work rating. | ||||
correction factor | 1. | |||
calibration coefficient | m | m | ||
µ | viscosity, dynamic | pascal second | Pa·s | m |
M | molar mass | gram per mole | g/mol | 10-3·kg·mol |
effective mass | kilogram | kg | kg. | |
mass | pound mass or kilogram | lbm or kg | kg. | |
total number in series. | ||||
total number of pulses in a series. | ||||
pressure | pascal | Pa | m | |
Δ | differential static pressure | pascal | Pa | m |
saturated vapor pressure at ambient dry bulb temperature | kilopascal | kPa | m | |
penetration fraction. | ||||
ρ | mass density | kilogram per cubic meter | kg/m | m |
dynamometer roll revolutions | revolutions per minute | rpm | π·30 | |
ratio of pressures | pascal per pascal | Pa/Pa | 1. | |
r | coefficient of determination. | |||
Reynolds number. | ||||
response factor. | ||||
relative humidity. | ||||
Sutherland constant | kelvin | K | K. | |
standard error of the estimate. | ||||
specific gravity. | ||||
Δ | distance traveled during measurement interval | meters | m | m. |
absolute temperature | kelvin | K | K. | |
Celsius temperature | degree Celsius | °C | K−273.15. | |
torque (moment of force) | newton meter | N·m | m | |
time | hour or second | hr or s | s. | |
Δ | time interval, period, 1/frequency | second | s | s. |
voltage | volt | V | m | |
speed | miles per hour or meters per second | mi/hr or m/s | m·s | |
volume | cubic meter | m | m | |
flow volume rate | cubic feet per minute or cubic meter per second | ft | m | |
volume percent. | ||||
concentration of emission over a test interval | part per million | ppm. | ||
generic variable. | ||||
compressibility factor. |
(b) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:
Symbol | Species |
---|---|
CH | methane. |
CH | methanol. |
CH | formaldehyde. |
C | acetaldehyde. |
C | ethanol. |
C | ethane. |
C | propanol. |
C | propane. |
C | butane. |
C | pentane. |
CO | carbon monoxide. |
CO | carbon dioxide. |
H | water. |
HC | hydrocarbon. |
N | molecular nitrogen. |
NMHC | nonmethane hydrocarbon. |
NMHCE | nonmethane hydrocarbon equivalent. |
NMOG | nonmethane organic gas. |
NO | nitric oxide. |
NO | nitrogen dioxide. |
NO | oxides of nitrogen. |
N | nitrous oxide. |
O | 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:
Table 3 of § 1066.1005 - Superscripts
Superscript | Meaning |
---|---|
overbar (such as | arithmetic mean. |
overdot (such as | quantity per unit time. |
(d) Subscripts. This part uses the following subscripts for modifying quantity symbols:
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 ( |
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:
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:
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 CO |
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:
Table 6 of § 1066.1005 - Densities of Chemical Species
Symbol | Quantity | g/m | g/ft |
---|---|---|---|
density of methane | 666.905 | 18.8847 | |
density of methanol | 1332.02 | 37.7185 | |
C | 957.559 | 27.1151 | |
C | 915.658 | 25.9285 | |
density of propane | 611.035 | 17.3026 | |
C | 832.74 | 23.5806 | |
density of carbon monoxide | 1164.41 | 32.9725 | |
density of carbon dioxide | 1829.53 | 51.8064 | |
effective density of hydrocarbon - gaseous fuel | (see 3) | (see 3) | |
density of formaldehyde | 1248.21 | 35.3455 | |
effective density of hydrocarbon - liquid fuel | 576.816 | 16.3336 | |
effective density of nonmethane hydrocarbon - gaseous fuel | (see 3) | (see 3) | |
effective density of nonmethane hydrocarbon - liquid fuel | 576.816 | 16.3336 | |
effective density of nonmethane equivalent hydrocarbon - gaseous fuel | (see 3) | (see 3) | |
effective density of nonmethane equivalent hydrocarbon - liquid fuel | 576.816 | 16.3336 | |
effective density of oxides of nitrogen | 1912.5 | 54.156 | |
density of nitrous oxide | 1829.66 | 51.8103 | |
effective density of total hydrocarbon - liquid fuel | 576.816 | 16.3336 | |
effective density of total equivalent hydrocarbon - liquid fuel | 576.816 | 16.3336 |
(g) Constants. (1) This part uses the following constants for the composition of dry air:
Symbol | Quantity | mol/mol |
---|---|---|
amount of argon in dry air | 0.00934 | |
amount of carbon dioxide in dry air | 0.000375 | |
amount of nitrogen in dry air | 0.78084 | |
amount of oxygen in dry air | 0.209445 |
(2) This part uses the following molar masses or effective molar masses of chemical species:
Symbol | Quantity | g/mol
(10 |
---|---|---|
molar mass of dry air ^{1} | 28.96559 | |
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:
Symbol | Quantity | J/(mol · K)
(m ^{2} · kg · s |
---|---|---|
molar gas constant | 8.314472 |
(h) Prefixes. This part uses the following prefixes to define a quantity:
Symbol | Quantity | Value |
---|---|---|
n | nano | 10 |
µ | micro | 10 |
m | milli | 10 |
c | centi | 10 |
k | kilo | 10 ^{3} |
M | mega | 10 ^{6} |