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:
| 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:
| Symbol | Quantity | Unit | Unit symbol | Unit in terms of SI base units |
|---|---|---|---|---|
| a | atomic hydrogen-to-carbon ratio | mole per mole | mol/mol | 1. |
| b | atomic oxygen-to-carbon ratio | mole per mole | mol/mol | 1. |
| CdA | drag area | meter squared | m2 | m2. |
| Crr | coefficient of rolling resistance | kilogram per metric ton | kg/tonne | 10−3. |
| D | distance | miles or meters | mi or m | m. |
| e | mass weighted emission result | grams/ton-mile | g/ton-mi | g/kg-km. |
| Eff | efficiency. | |||
| Em | mass-specific net energy content | megajoules/kilogram | MJ/kg | m2·s−2. |
| fn | angular speed (shaft) | revolutions per minute | r/min | π·30·s−1. |
| i | indexing variable. | |||
| ka | drive axle ratio. | |||
| ktopgear | 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. |
| Mrotating | inertial mass of rotating components | kilogram | kg | kg. |
| N | total number in a series. | |||
| P | power | kilowatt | kW | 103·m2·kg·s−3. |
| 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. |
| wC | carbon mass fraction | gram/gram | g/g | 1. |
| wCH4N2O | urea mass fraction | gram/gram | g/g | 1. |
| x | amount of substance mole fraction | mole per mole | mol/mol | 1. |
| xb | brake energy fraction. | |||
| xbl | brake energy limit. |
(c) Superscripts. This part uses the following superscripts to define a quantity:
| Superscript | Quantity |
|---|---|
| overbar (such as y̅) | arithmetic mean. |
| overdot overdot (such as ẏ) | quantity per unit time. |
(d) Subscripts. This part uses the following subscripts to define a quantity:
| Subscript | Quantity |
|---|---|
| 65 | 65 miles per hour. |
| A | A speed. |
| acc | accessory. |
| app | approved. |
| axle | axle. |
| B | B speed. |
| C | C speed. |
| Ccombdry | carbon from fuel per mole of dry exhaust. |
| CD | charge-depleting. |
| CO2DEF | CO2 resulting from diesel exhaust fluid decomposition. |
| comb | combustion. |
| cor | corrected. |
| CS | charge-sustaining. |
| cycle | test cycle. |
| DEF | diesel exhaust fluid. |
| engine | engine. |
| exh | raw exhaust. |
| 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. |
| record | record. |
| ref | reference quantity. |
| speed | speed. |
| stall | stall. |
| test | test. |
| tire | tire. |
| transient | transient. |
| vehicle | vehicle. |
(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:
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
CS charge-sustaining
DF deterioration factor
DOT Department of Transportation
E85 gasoline blend including nominally 85 percent denatured ethanol
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
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
rpm revolutions per minute
SCR Selective catalytic reduction
SI spark ignition
U.S. United States
U.S.C. United States Code
(f) Prefixes. This part uses the following prefixes to define a quantity:
| 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]
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