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.

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(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

SymbolQuantityUnitUnit symbolUnits in terms of SI base units
?atomic hydrogen-to-carbon ratiomole per molemol/mol1.
Aareasquare meterm2m2.
a0intercept of least squares regression
a1slope of least squares regression
agacceleration of Earth’s gravitymeter per square secondm/s2m· s?2.
?ratio of diametersmeter per meterm/m1.
?atomic oxygen-to-carbon ratiomole per molemol/mol1.
C#number of carbon atoms in a molecule
cpower-specific carbon mass error coefficientgram per kilowatt-hourg/(kW·hr)3.6?1 · 10?9 · m?2 · s2.
Cddischarge coefficient
Cfflow coefficient
?atomic nitrogen-to-carbon ratiomole per molemol/mol1.
ddiametermetermm.
dpower-specific carbon mass rate absolute error coefficentgram per kilowatt-hourg/(kW·hr)3.6?1 · 10?9 · m?2 · s2.
DRdilution ratiomole per molemol/mol1.
?error between a quantity and its reference
?difference or error quantity
ebrake-specific emission or fuel consumptiongram per kilowatt hourg/(kW·hr)3.6?1 · 10?9 · m?2 · s2.
FF-test statistic
Æ’frequencyhertzHzs?1.
Æ’nangular speed (shaft)revolutions per minuter/min? · 30?1 · s?1.
?ratio of specific heats(joule per kilogram kelvin) per (joule per kilogram kelvin)(J/(kg·K))/(J/(kg·K))1.
?atomic sulfur-to-carbon ratiomole per molemol/mol1.
?opacity
Kcorrection factor1.
Kvcalibration coefficientm4 · s · K0.5/kgm4 · kg?1 · s · K0.5.
llengthmetermm.
Llimit
µviscosity, dynamicpascal secondPa·sm?1 · kg · s?1.
Mmolar mass 1gram per moleg/mol10?3 · kg · mol?1.
mmasskilogramkgkg.
mmass ratekilogram per secondkg/skg · s?1.
vviscosity, kinematicmeter squared per secondm2/sm2 · s?1.
Ntotal number in series
namount of substancemolemolmol.
namount of substance ratemole per secondmol/smol · s?1.
PpowerkilowattkW103 · m2 · kg · s?3.
PFpenetration fraction
ppressurepascalPam?1 · kg · s?2.
?mass densitykilogram per cubic meterkg/m3m?3 · kg.
?pdifferential static pressurepascalPam?1 · kg · s?2.
rratio of pressurespascal per pascalPa/Pa1.
r2coefficient of determination
Raaverage surface roughnessmicrometerµm10?6 · m.
Re#Reynolds number
RFresponse factor
RHrelative humidity
?non-biased standard deviation
SSutherland constantkelvinKK.
SEEstandard error of the estimate
Tabsolute temperaturekelvinKK.
TCelsius temperaturedegree Celsius °CK?273.15.
Ttorque (moment of force)newton meterN·mm2 · kg · s?2.
?plane angledegrees°rad.
ttimesecondss.
?ttime interval, period, 1/frequencysecondss.
Vvolumecubic meterm3m3.
Vvolume ratecubic meter per secondm3/sm3 · s?1.
Wworkkilowatt-hourkW·hr3.6 · 106 · m2 · kg · s?2.
wCcarbon mass fractiongram per gramg/g1.
xamount of substance mole fraction.2mole per molemol/mol1.
Xflow-weighted mean concentrationmole per molemol/mol1.
ygeneric variable
Zcompressibility 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:

Table 2 of § 1065.1005—Symbols for Chemical Species and Exhaust Constituents

SymbolSpecies
Arargon.
Ccarbon.
CH2Oformaldehyde.
CH2O2formic acid.
CH3OHmethanol.
CH4methane.
C2H4Oacetaldehyde.
C2H5OHethanol.
C2H6ethane.
C3H7OHpropanol.
C3H8propane.
C4H10butane.
C5H12pentane.
COcarbon monoxide.
CO2carbon dioxide.
Hatomic hydrogen.
H2molecular hydrogen.
H2Owater.
H2SO4sulfuric acid.
HChydrocarbon.
Hehelium.
85Krkrypton 85.
N2molecular nitrogen.
NH3ammonia.
NMHCnonmethane hydrocarbon.
NMHCEnonmethane hydrocarbon equivalent.
NMNEHCnonmethane-nonethane hydrocarbon.
NOnitric oxide.
NO2nitrogen dioxide.
NOXoxides of nitrogen.
N2Onitrous oxide.
NMOGnonmethane organic gases.
NONMHCnon-oxygenated nonmethane hydrocarbon.
NOTHCnon-oxygenated total hydrocarbon.
O2molecular oxygen.
OHCoxygenated hydrocarbon.
210Popolonium 210.
PMparticulate matter.
Ssulfur.
SVOCsemi-volatile organic compound.
THCtotal hydrocarbon.
THCEtotal hydrocarbon equivalent.
ZrO2zirconium dioxide.

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

Table 3 of § 1065.1005—Prefixes

SymbolPrefix nameFactor
µmicro10?6
mmilli10?3
ccenti10?2
kkilo103
Mmega106

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

Table 4 of § 1065.1005—Superscripts

SuperscriptMeaning
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

SubscriptMeaning
aabsolute (e.g., absolute difference or error).
absabsolute quantity.
actactual condition.
airair, dry.
ambambient.
atmosatmospheric.
bkgndbackground.
Ccarbon mass.
calcalibration quantity.
CFVcritical flow venturi.
combcombined.
compcomposite value.
corcorrected quantity.
dildilution air.
dewdewpoint.
dexhdiluted exhaust.
drydry condition.
dutycycleduty cycle.
?related to a difference or error quantity.
exhraw exhaust.
expexpected quantity.
fluidfluid stream.
fnfeedback speed.
frictfriction.
fuelfuel consumption.
hi,idlecondition at high-idle.
ian individual of a series.
idlecondition at idle.
inquantity in.
initinitial quantity, typically before an emission test.
intintake air.
jan individual of a series.
mappedconditions over which an engine can operate.
maxthe maximum (i.e., peak) value expected at the standard over a test interval; not the maximum of an instrument range.
measmeasured quantity.
mediaPM sample media.
mixmixture of diluted exhaust and air.
normnormalized.
outquantity out.
Ppower.
partpartial quantity.
PDPpositive-displacement pump.
postafter the test interval.
prebefore the test interval.
prodstoichiometric product.
rrelative (e.g., relative difference or error).
raterate (divided by time).
recordrecord rate.
refreference quantity.
revrevolution.
satsaturated condition.
sslip.
spanspan quantity.
SSVsubsonic venturi.
stdstandard condition.
strokeengine strokes per power stroke.
Ttorque.
testtest quantity.
test,altalternate test quantity.
uncoruncorrected quantity.
vacvacuum side of the sampling system.
weightcalibration weight.
zerozero quantity

(f) Constants.

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

Table 6 of § 1065.1005—Constants

SymbolQuantitymol/mol
?Arairamount of argon in dry air0.00934
?CO2airamount of carbon dioxide in dry air0.000375
?N2airamount of nitrogen in dry air0.78084
?O2airamount of oxygen in dry air0.209445

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

Table 7 of § 1065.1005—Molar Masses

SymbolQuantityg/mol
(10-3·kg·mol-1)
Mairmolar mass of dry air 128.96559
MArmolar mass of argon39.948
MCmolar mass of carbon12.0107
MCH3OHmolar mass of methanol32.04186
MC2H5OHmolar mass of ethanol46.06844
MC2H4Omolar mass of acetaldehyde44.05256
MCH4N2Omolar mass of urea60.05526
MC2H6molar mass of ethane30.06904
MC3H8molar mass of propane44.09562
MC3H7OHmolar mass of propanol60.09502
MCOmolar mass of carbon monoxide28.0101
MCH4molar mass of methane16.0425
MCO2molar mass of carbon dioxide44.0095
MHmolar mass of atomic hydrogen1.00794
MH2molar mass of molecular hydrogen2.01588
MH2Omolar mass of water18.01528
MCH2Omolar mass of formaldehyde30.02598
MHemolar mass of helium4.002602
MNmolar mass of atomic nitrogen14.0067
MN2molar mass of molecular nitrogen28.0134
MNH3molar mass of ammonia17.03052
MNMHCeffective C1 molar mass of nonmethane hydrocarbon 213.875389
MNMHCEeffective C1 molar mass of nonmethane hydrocarbon equivalent 213.875389
MNMNEHCeffective C1 molar mass of nonmethane-nonethane hydrocarbon 213.875389
MNOxeffective molar mass of oxides of nitrogen 346.0055
MN2Omolar mass of nitrous oxide44.0128
MOmolar mass of atomic oxygen15.9994
MO2molar mass of molecular oxygen31.9988
MSmolar mass of sulfur32.065
MTHCeffective C1 molar mass of total hydrocarbon 213.875389
MTHCEeffective C1 molar mass of total hydrocarbon equivalent 213.875389

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, ?, of 1.85 (with ?, ?, and ? 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:

Table 8 of § 1065.1005—Molar Gas Constant for Ideal Gases

SymbolQuantityJ/(mol·K)
(m2·kg·s?2·mol?1·K?1)
Rmolar gas constant8.314472

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

Table 9 of § 1065.1005—Ratios of Specific Heats for Dilution Air and Diluted Exhaust

SymbolQuantity[J/(kg·K)]/[J/(kg·K)]
?airratio of specific heats for intake air or dilution air1.399
?dilratio of specific heats for diluted exhaust1.399
?exhratio of specific heats for raw exhaust1.385

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

Table 10 of § 1065.1005—Other Acronyms and Abbreviations

AcronymMeaning
ABSacrylonitrile-butadiene-styrene.
ASTMASTM International.
BMDbag mini-diluter.
BSFCbrake-specific fuel consumption.
CARBCalifornia Air Resources Board.
CFRCode of Federal Regulations.
CFVcritical-flow venturi.
CIcompression-ignition.
CITTCurb Idle Transmission Torque.
CLDchemiluminescent detector.
CVSconstant-volume sampler.
DEFdiesel exhaust fluid.
DFdeterioration factor.
ECMelectronic control module.
EFCelectronic flow control.
e.g.exempli gratia, for example.
EGRexhaust gas recirculation.
EPAEnvironmental Protection Agency.
FELFamily Emission Limit.
FIDflame-ionization detector.
FTIRFourier transform infrared.
GCgas chromatograph.
GC-ECDgas chromatograph with an electron-capture detector.
GC-FIDgas chromatograph with a flame ionization detector.
HEPAhigh-efficiency particulate air.
IBPinitial boiling point.
IBRincorporated by reference.
i.e.id est, in other words.
ISOInternational Organization for Standardization.
LPGliquefied petroleum gas.
MPDmagnetopneumatic detection.
NDIRnondispersive infrared.
NDUVnondispersive ultraviolet.
NISTNational Institute for Standards and Technology.
NMCnonmethane cutter.
PDPpositive-displacement pump.
PEMSportable emission measurement system.
PFDpartial-flow dilution.
PLOTporous layer open tubular.
PMDparamagnetic detection.
PMPPolymethylpentene.
pt.a single point at the mean value expected at the standard.
psipounds per square inch.
PTFEpolytetrafluoroethylene (commonly known as TeflonTM).
RErounding error.
RESSrechargeable energy storage system.
RFPFresponse factor penetration fraction.
RMCramped-modal cycle.
rmsroot-mean square.
RTDresistive temperature detector.
SAWsurface acoustic wave.
SEEstandard error of the estimate.
SSVsubsonic venturi.
SIspark-ignition.
THC-FIDtotal hydrocarbon flame ionization detector.
TINVinverse student t-test function in Microsoft Excel.
UCLupper confidence limit.
UFMultrasonic 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; 88 FR 4689, Jan. 24, 2023]
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