40 CFR 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.

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

Table 1 to Paragraph (a) of § 1036.805—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.
NMNEHC	nonmethane nonethane hydrocarbon.
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:

Table 2 to Paragraph (b) of § 1036.805—Symbols for Quantities

Symbol	Quantity	Unit	Unit symbol	Unit in terms of SI base units
?	atomic hydrogen-to-carbon ratio	mole per mole	mol/mol	1
?	Area	square meter	m²	m²
?	atomic oxygen-to-carbon ratio	mole per mole	mol/mol	1
Cd?	drag area	meter squared	m²	m²
Crr	coefficient of rolling resistance	newton per kilonewton	N/kN	10?³
D	distance	miles or meters	mi or m	m
e	efficiency
?	Difference or error quantity
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	?·30·s?¹
g	gravitational acceleration	meters per second squared	m/s²	m·s?²
i	indexing variable
ka	drive axle ratio			1
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	total number in a series
M	vehicle mass	kilogram	kg	kg
Mrotating	inertial mass of rotating components	kilogram	kg	kg
N	total number in a series
Q	total number in a series
P	Power	kilowatt	kW	10³·m²·kg·s?³
?	mass density	kilogram per cubic meter	kg/m³	m?³·kg
r	tire radius	meter	m	m
SEE	standard error of the estimate
?	standard deviation
T	torque (moment of force)	newton meter	N·m	m²·kg·s?²
t	Time	second	s	s
?t	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

Table 3 to Paragraph (c) of § 1036.805—Superscripts

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

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

Table 4 to Paragraph (d) of § 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	cycle.
D	distance.
D	D speed.
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.
int	test interval.
j	an individual of a series.
k	an individual of a series.
m	mass.
max	maximum.
mapped	mapped.
meas	measured quantity.
MY	model year.
neg	negative.
pos	positive.
R	range.
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.
UF	utility factor.
vehicle	vehicle.

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

Table 5 to Paragraph (e) of § 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.
ECM	Electronic Control Module.
EGR	exhaust gas recirculation.
EPA	Environmental Protection Agency.
FCL	Family Certification Level.
FEL	family emission limit.
FTP	Federal Test Procedure.
GEM	Greenhouse gas Emissions Model.
g/hp·hr	grams per brake horsepower-hour.
GPS	global positioning system.
GVWR	gross vehicle weight rating.
Heavy HDE	heavy heavy-duty engine (see § 1036.140).
Heavy HDV	heavy heavy-duty vehicle (see 40 CFR 1037.140).
Light HDE	light heavy-duty engine (see § 1036.140).
Light HDV	light heavy-duty vehicle (see 40 CFR 1037.140).
LLC	Low Load Cycle.
LPG	liquefied petroleum gas.
Medium HDE	medium heavy-duty engine (see § 1036.140).
Medium HDV	medium heavy-duty vehicle (see 40 CFR 1037.140).
NARA	National Archives and Records Administration.
NHTSA	National Highway Traffic Safety Administration.
NTE	not-to-exceed.
PEMS	portable emission measurement system.
RESS	rechargeable energy storage system.
SCR	selective catalytic reduction.
SEE	standard error of the estimate.
SET	Supplemental Emission Test.
Spark-ignition HDE	spark-ignition heavy-duty engine (see § 1036.140).
SI	spark-ignition.
UL	useful life.
U.S	United States.
U.S.C	United States Code.

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

Table 6 to Paragraph (f) of § 1036.805—Constants

Symbol	Quantity	Value
g	gravitational constant	9.80665 m·s?².
R	molar gas constant	8.314472 J/(mol·K) (m²·kg·s?²·mol?¹·K?¹).

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

Table 7 to Paragraph (g) of § 1036.805—Prefixes

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

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