40 CFR § 1065.1005 - Symbols, abbreviations, acronyms, and units of measure.

§ 1065.1005 Symbols, abbreviations, acronyms, and units of measure.

The procedures in this part generally follow the International System of Units (SI), as detailed in NIST Special Publication 811, which we incorporate by reference in § 1065.1010. See § 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 § 1065.1005 - Symbols for Quantities

Symbol Quantity Unit Unit symbol Units 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 0 intercept of least squares regression
a 1 slope of least squares regression
a g acceleration of Earth's gravity meter per square second m/s2 m· s 2.
β ratio of diameters meter per meter m/m 1.
β atomic oxygen-to-carbon ratio mole per mole mol/mol 1.
C # number of carbon atoms in a molecule
c power-specific carbon mass error coefficient gram per kilowatt-hour g/(kW·hr) 3.6 1 · 10 9 · m 2 · s2.
C d discharge coefficient
C f flow coefficient
δ atomic nitrogen-to-carbon ratio mole per mole mol/mol 1.
d diameter meter m m.
d power-specific carbon mass rate absolute error coefficent gram per kilowatt-hour g/(kW·hr) 3.6 1 · 10 9 · m 2 · s2.
DR dilution ratio mole per mole mol/mol 1.
ε error between a quantity and its reference
difference or error quantity
e brake-specific emission or fuel consumption gram per kilowatt hour g/(kW·hr) 3.6 1 · 10 9 · m 2 · s2.
F F-test statistic
ƒ frequency hertz Hz s 1.
ƒn angular speed (shaft) revolutions per minute r/min π · 30 1 · s 1.
γ ratio of specific heats (joule per kilogram kelvin) per (joule per kilogram kelvin) (J/(kg·K))/(J/(kg·K)) 1.
γ atomic sulfur-to-carbon ratio mole per mole mol/mol 1.
K correction factor 1.
K v calibration coefficient m4 · s · K0.5/kg m4 · kg 1 · s · K0.5.
l length meter m m.
L limit
µ viscosity, dynamic pascal second Pa·s m 1 · kg · s 1.
M molar mass 1 gram per mole g/mol 10 3 · kg · mol 1.
m mass kilogram kg kg.
m mass rate kilogram per second kg/s kg · s 1.
v viscosity, kinematic meter squared per second m2/s m2 · s 1.
N total number in series
n amount of substance mole mol mol.
n amount of substance rate mole per second mol/s mol · s 1.
P power kilowatt kW 103 · m2 · kg · s 3.
PF penetration fraction
p pressure pascal Pa m 1 · kg · s 2.
ρ mass density kilogram per cubic meter kg/m3 m 3 · kg.
Δ p differential static pressure pascal Pa m 1 · kg · s 2.
r ratio of pressures pascal per pascal Pa/Pa 1.
r 2 coefficient of determination
Ra average surface roughness micrometer µm 10 6 · m.
Re # Reynolds number
RF response factor
RH relative humidity
σ non-biased standard deviation
S Sutherland constant kelvin K K.
SEE standard error of the estimate
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.
θ plane angle degrees ° rad.
t time second s s.
Δ t time interval, period, 1/frequency second s s.
V volume cubic meter m3 m3.
V volume rate cubic meter per second m3/s m3 · s 1.
W work kilowatt-hour kW·hr 3.6 · 106 · m2 · kg · s 2.
w C carbon mass fraction gram per gram g/g 1.
x amount of substance mole fraction.2 mole per mole mol/mol 1.
X flow-weighted mean concentration mole per mole mol/mol 1.
y generic variable
Z compressibility factor

1 See paragraph (f)(2) of this section for the values to use for molar masses. Note that in the cases of NOX and HC, the regulations specify effective molar masses based on assumed speciation rather than actual speciation.

2 Note that mole fractions for THC, THCE, NMHC, NMHCE, and NOTHC are expressed on a C1-equivalent basis.

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

Symbol Species
Ar argon.
C carbon.
CH2O formaldehyde.
CH2O2 formic acid.
CH3OH methanol.
CH4 methane.
C2H4O acetaldehyde.
C2H5OH ethanol.
C2H6 ethane.
C3H7OH propanol.
C3H8 propane.
C4H10 butane.
C5H12 pentane.
CO carbon monoxide.
CO2 carbon dioxide.
H atomic hydrogen.
H2 molecular hydrogen.
H2O water.
H2SO4 sulfuric acid.
HC hydrocarbon.
He helium.
85Kr krypton 85.
N2 molecular nitrogen.
NH3 ammonia.
NMHC nonmethane hydrocarbon.
NMHCE nonmethane hydrocarbon equivalent.
NMNEHC nonmethane-nonethane hydrocarbon.
NO nitric oxide.
NO2 nitrogen dioxide.
NOX oxides of nitrogen.
N2O nitrous oxide.
NMOG nonmethane organic gases.
NONMHC non-oxygenated nonmethane hydrocarbon.
NOTHC non-oxygenated total hydrocarbon.
O2 molecular oxygen.
OHC oxygenated hydrocarbon.
210Po polonium 210.
PM particulate matter.
S sulfur.
SVOC semi-volatile organic compound.
THC total hydrocarbon.
THCE total hydrocarbon equivalent.
ZrO2 zirconium dioxide.

(c) Prefixes. This part uses the following prefixes for units and unit symbols:

Table 3 of § 1065.1005 - Prefixes

Symbol Prefix name Factor
µ micro 10 6
m milli 10 3
c centi 10 2
k kilo 103
M mega 106

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

Table 4 of § 1065.1005 - Superscripts

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

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

Table 5 of § 1065.1005 - Subscripts

Subscript Meaning
a absolute (e.g., absolute difference or error).
abs absolute quantity.
act actual condition.
air air, dry.
amb ambient.
atmos atmospheric.
bkgnd background.
C carbon mass.
cal calibration quantity.
CFV critical flow venturi.
comb combined.
comp composite value.
cor corrected quantity.
dil dilution air.
dew dewpoint.
dexh diluted exhaust.
dry dry condition.
dutycycle duty cycle.
related to a difference or error quantity.
exh raw exhaust.
exp expected quantity.
fluid fluid stream.
fn feedback speed.
frict friction.
fuel fuel consumption.
hi,idle condition at high-idle.
i an individual of a series.
idle condition at idle.
in quantity in.
init initial quantity, typically before an emission test.
int intake air.
j an individual of a series.
mapped conditions over which an engine can operate.
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.
media PM sample media.
mix mixture of diluted exhaust and air.
norm normalized.
out quantity out.
P power.
part partial quantity.
PDP positive-displacement pump.
post after the test interval.
pre before the test interval.
prod stoichiometric product.
r relative (e.g., relative difference or error).
rate rate (divided by time).
record record rate.
ref reference quantity.
rev revolution.
sat saturated condition.
s slip.
span span quantity.
SSV subsonic venturi.
std standard condition.
stroke engine strokes per power stroke.
T torque.
test test quantity.
test,alt alternate test quantity.
uncor uncorrected quantity.
vac vacuum side of the sampling system.
weight calibration weight.
zero zero quantity

(f) Constants.

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

Symbol Quantity mol/mol
x Arair amount of argon in dry air 0.00934
x CO2air amount of carbon dioxide in dry air 0.000375
x N2air amount of nitrogen in dry air 0.78084
x O2air amount of oxygen in dry air 0.209445

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

Table 7 of § 1065.1005 - Molar Masses

Symbol Quantity g/mol
M air molar mass of dry air 1 28.96559
M Ar molar mass of argon 39.948
M C molar mass of carbon 12.0107
M CH3OH molar mass of methanol 32.04186
M C2H5OH molar mass of ethanol 46.06844
M C2H4O molar mass of acetaldehyde 44.05256
M CH4N2O molar mass of urea 60.05526
M C2H6 molar mass of ethane 30.06904
M C3H8 molar mass of propane 44.09562
M C3H7OH molar mass of propanol 60.09502
M CO molar mass of carbon monoxide 28.0101
M CH4 molar mass of methane 16.0425
M CO2 molar mass of carbon dioxide 44.0095
M H molar mass of atomic hydrogen 1.00794
M H2 molar mass of molecular hydrogen 2.01588
M H2O molar mass of water 18.01528
M CH2O molar mass of formaldehyde 30.02598
M He molar mass of helium 4.002602
M N molar mass of atomic nitrogen 14.0067
M N2 molar mass of molecular nitrogen 28.0134
M NH3 molar mass of ammonia 17.03052
M NMHC effective C1 molar mass of nonmethane hydrocarbon 2 13.875389
M NMHCE effective C1 molar mass of nonmethane hydrocarbon equivalent 2 13.875389
M NMNEHC effective C1 molar mass of nonmethane-nonethane hydrocarbon 2 13.875389
M NOx effective molar mass of oxides of nitrogen 3 46.0055
M N2O molar mass of nitrous oxide 44.0128
M O molar mass of atomic oxygen 15.9994
M O2 molar mass of molecular oxygen 31.9988
M S molar mass of sulfur 32.065
M THC effective C1 molar mass of total hydrocarbon 2 13.875389
M THCE effective C1 molar mass of total hydrocarbon equivalent 2 13.875389

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

2 The effective molar masses of THC, THCE, NMHC, NMHCE, and NMNEHC are defined on a C1 basis and are based on an atomic hydrogen-to-carbon ratio, α, of 1.85 (with β, γ, and δ equal to zero).

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

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

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

(4) This part uses the following ratios of specific heats for dilution air and diluted exhaust:

Symbol Quantity [J/(kg · K)]/[J/(kg · K)]
g air ratio of specific heats for intake air or dilution air 1.399
g dil ratio of specific heats for diluted exhaust 1.399
g exh ratio of specific heats for raw exhaust 1.385

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

Table 10 of § 1065.1005 - Other Acronyms and Abbreviations

Acronym Meaning
ABS acrylonitrile-butadiene-styrene.
ASTM ASTM International.
BMD bag mini-diluter.
BSFC brake-specific fuel consumption.
CARB California Air Resources Board.
CFR Code of Federal Regulations.
CFV critical-flow venturi.
CI compression-ignition.
CITT Curb Idle Transmission Torque.
CLD chemiluminescent detector.
CVS constant-volume sampler.
DEF diesel exhaust fluid.
DF deterioration factor.
ECM electronic control module.
EFC electronic flow control.
e.g. exempli gratia, for example.
EGR exhaust gas recirculation.
EPA Environmental Protection Agency.
FEL Family Emission Limit.
FID flame-ionization detector.
FTIR Fourier transform infrared.
GC gas chromatograph.
GC-ECD gas chromatograph with an electron-capture detector.
GC-FID gas chromatograph with a flame ionization detector.
HEPA high-efficiency particulate air.
IBP initial boiling point.
IBR incorporated by reference.
i.e. id est, in other words.
ISO International Organization for Standardization.
LPG liquefied petroleum gas.
MPD magnetopneumatic detection.
NDIR nondispersive infrared.
NDUV nondispersive ultraviolet.
NIST National Institute for Standards and Technology.
NMC nonmethane cutter.
PDP positive-displacement pump.
PEMS portable emission measurement system.
PFD partial-flow dilution.
PLOT porous layer open tubular.
PMD paramagnetic detection.
PMP Polymethylpentene.
pt. a single point at the mean value expected at the standard.
psi pounds per square inch.
PTFE polytetrafluoroethylene (commonly known as TeflonTM).
RE rounding error.
RESS rechargeable energy storage system.
RFPF response factor penetration fraction.
RMC ramped-modal cycle.
rms root-mean square.
RTD resistive temperature detector.
SAW surface acoustic wave.
SEE standard error of the estimate.
SSV subsonic venturi.
SI spark-ignition.
THC-FID total hydrocarbon flame ionization detector.
TINV inverse student t-test function in Microsoft Excel.
UCL upper confidence limit.
UFM ultrasonic flow meter.
U.S.C. United States Code
[79 FR 23815, Apr. 28, 2014, as amended at 81 FR 74191, Oct. 25, 2016; 86 FR 34575, June 29, 2021; 87 FR 64866, Oct. 26, 2022]