Symbols, abbreviations, and acronyms.

  1. Law
  2. CFR 40
  3. Protection of Environment
  4. Environmental Protection Agency
  5. Air Pollution Controls
  6. Control of Emissions from New and In-Use Heavy-Duty Highway Engines
  7. Definitions and Other Reference Information
  8. Symbols, abbreviations, and acronyms.

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§ 1036.805 Symbols, abbreviations, and acronyms.

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 (incorporated by reference in § 1036.810). 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 chemical species. This part uses the following symbols for chemical species and exhaust constituents:

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Symbol Species
C carbon.
CH4 methane.
CH4N2O urea.
CO carbon monoxide.
CO2 carbon dioxide.
H2O water.
HC hydrocarbon.
NMHC nonmethane hydrocarbon.
NMHCE nonmethane hydrocarbon equivalent.
NO nitric oxide.
NO2 nitrogen dioxide.
NOX oxides of nitrogen.
N2O nitrous oxide.
PM particulate matter.

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

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Table 2 to § 1036.805 - 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.
Α Area square meter m2 m2.
β atomic oxygen-to-carbon ratio mole per mole mol/mol 1.
C d Α drag area meter squared m2 m2.
C rr coefficient of rolling resistance kilogram per metric ton kg/tonne 10−3.
D distance miles or meters mi or m m.
ε efficiency
∈ Difference or error quantity
e mass weighted emission result grams/ton-mile g/ton-mi g/kg-km.
Eff efficiency
E m mass-specific net energy content megajoules/kilogram MJ/kg m2·s−2.
f n angular speed (shaft) revolutions per minute r/min π·30·s−1.
g gravitational acceleration meters per second squared m/s2 m·s−2.
i indexing variable
k a drive axle ratio 1.
k topgear highest available transmission gear
m Mass pound mass or kilogram lbm or kg kg.
M molar mass gram per mole g/mol 10−3·kg·mol−1.
M vehicle mass kilogram kg kg.
M rotating inertial mass of rotating components kilogram kg kg.
N total number in a series
P Power kilowatt kW 103·m2·kg·s−3.
ρ mass density kilogram per cubic meter kg/m3 m−3·kg.
r tire radius meter m m.
SEE standard error of the estimate
σ standard deviation
T torque (moment of force) newton meter N·m m2·kg·s−2.
t Time second s s.
Δt time interval, period, 1/frequency second s s.
UF utility factor
v Speed miles per hour or meters per second mi/hr or m/s m·s−1.
W Work kilowatt-hour kW·hr 3.6·m2·kg·s−1.
w C carbon mass fraction gram/gram g/g 1.
w CH4N2O urea mass fraction gram/gram g/g 1.
x amount of substance mole fraction mole per mole mol/mol 1.
x b brake energy fraction
x bl brake energy limit

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

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Table 3 to § 1036.805 - 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:

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Table 4 to § 1036.805 - Subscripts

Subscript Meaning
65 65 miles per hour.
A A speed.
A absolute (e.g., absolute difference or error).
Acc accessory.
App approved.
Axle axle.
B B speed.
C C speed.
C carbon mass.
Ccombdry carbon from fuel per mole of dry exhaust.
CD charge-depleting.
CO2DEF CO2 resulting from diesel exhaust fluid decomposition.
comb combustion.
comp composite.
Cor corrected.
CS charge-sustaining.
Cycle test cycle.
DEF diesel exhaust fluid.
engine engine.
Exh raw exhaust.
Front frontal.
Fuel fuel.
H2Oexhaustdry H2O in exhaust per mole of exhaust.
Hi high.
I an individual of a series.
Idle idle.
M mass.
Max maximum.
mapped mapped.
Meas measured quantity.
Neg negative.
Pos positive.
R relative (e.g., relative difference or error).
Rate rate (divided by time).
Rated rated.
record record.
Ref reference quantity.
speed speed.
Stall stall.
Test test.
Tire tire.
transient transient.
Μ vector.
vehicle vehicle.

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

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Table 5 to § 1036.805 - Other Acronyms and Abbreviations

Acronym Meaning
ABT averaging, banking, and trading.
AECD auxiliary emission control device.
ASTM American Society for Testing and Materials.
BTU British thermal units.
CD charge-depleting.
CFR Code of Federal Regulations.
CI Compression-ignition.
COV coefficient of variation.
CS charge-sustaining.
DEF diesel exhaust fluid.
DF deterioration factor.
DOT Department of Transportation.
E85 gasoline blend including nominally 85 percent denatured ethanol.
ECU Electronic Control Unit.
EPA Environmental Protection Agency.
FCL Family Certification Level.
FEL Family Emission Limit.
GEM Greenhouse gas Emissions Model.
g/hp-hr grams per brake horsepower-hour.
GVWR gross vehicle weight rating.
HDV heavy-duty vehicle.
LPG liquefied petroleum gas.
NARA National Archives and Records Administration.
NHTSA National Highway Traffic Safety Administration.
NTE not-to-exceed.
RESS rechargeable energy storage system.
RMC ramped-modal cycle.
SCR selective catalytic reduction.
SEE standard error of the estimate.
SET Supplemental Emission Test.
SI spark-ignition.
U.S. United States.
U.S.C. United States Code.

(f) Constants. This part uses the following constants:

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Table 6 to § 1036.805 - Constants

Symbol Quantity Value
g gravitational constant 9.80665 m·s−2

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

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Table 7 to § 1036.805 - Prefixes

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

[81 FR 74011, Oct. 25, 2016; 82 FR 29761, June 30, 2017; 86 FR 34404, June 29, 2021]


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