40 CFR § 1037.805 Symbols, abbreviations, and acronyms | Code of Federal Regulations | US Law

40 CFR § 1037.805

Symbols, abbreviations, and acronyms

June 9, 2020

CFR

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 §1037.810). 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:

Open Table

Symbol	Species
C	carbon.
CH4	methane.
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.
THC	total hydrocarbon.
THCE	total hydrocarbon equivalent.

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

Open Table

Symbol	Quantity	Unit	Unit symbol	Unit in terms of SI base units
A	vehicle frictional load	pound force or newton	lbf or N	kg·m·s−2.
a	axle position regression coefficient
α	atomic hydrogen-to-carbon ratio	mole per mole	mol/mol	1.
α	axle position regression coefficient
α0	intercept of air speed correction
α1	slope of air speed correction
ag	acceleration of Earth's gravity	meters per second squared	m/s²	m·s−2.
a0	intercept of least squares regression
a1	slope of least squares regression
B	vehicle load from drag and rolling resistance	pound force per mile per hour or newton second per meter	lbf/(mi/hr) or N·s/m	kg·s−1.
b	axle position regression coefficient
β	atomic oxygen-to-carbon ratio	mole per mole	mol/mol	1.
β	axle position regression coefficient
β0	intercept of air direction correction
β1	slope of air direction correction
C	vehicle-specific aerodynamic effects	pound force per mile per hour squared or newton-second squared per meter squared	lbf/mph² or N·s²/m¹	kg·m−1.
c	axle position regression coefficient
ci	axle test regression coefficients
Ci	constant
ΔCdA	differential drag area	meter squared	m²	m².
CdA	drag area	meter squared	m²	m².
Cd	drag coefficient
CF	correction factor
Crr	coefficient of rolling resistance	kilogram per metric ton	kg/tonne	10−2.
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
F	adjustment factor
F	force	pound force or newton	lbf or N	kg·m·s−2.
fn	angular speed (shaft)	revolutions per minute	r/min	π·30·s−1.
G	road grade	percent	%	10−2.
g	gravitational acceleration	meters per second squared	m/s²	m·s−2.
h	elevation or height	meters	m	m.
i	indexing variable
ka	drive axle ratio			1
kd	transmission gear ratio
ktopgear	highest available transmission gear
L	load over axle	pound force or newton	lbf or N	kg·m·s−2.
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.
Me	vehicle effective mass	kilogram	kg	kg.
Mrotating	inertial mass of rotating components	kilogram	kg	kg.
N	total number in series
n	number of tires
ṅ	amount of substance rate	mole per second	mol/s	mol·s−1.
P	power	kilowatt	kW	10³·m²·kg·s−3.
P	tire inflation pressure	pascal	Pa	kg·m−1·s−2.
p	pressure	pascal	Pa	kg·m−1·s−2.
ρ	mass density	kilogram per cubic meter	kg/m³	kg·m−3.
PL	payload	tons	ton	kg.
ϕ	direction	degrees	°	°.
1	direction	degrees	°	°.
r	tire radius	meter	m	m.
r²	coefficient of determination
Re#	Reynolds number
SEE	standard estimate of error
σ	standard deviation
TRPM	tire revolutions per mile	revolutions per mile	r/mi
TRRL	tire rolling resistance level	kilogram per metric ton	kg/tonne	10−3.
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.
t	time	hour or second	hr or 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	weighting factor
w	wind speed	miles per hour	mi/hr	m·s−1.
W	work	kilowatt-hour	kW·hr	3.6·m²·kg·s−1.
wC	carbon mass fraction	gram/gram	g/g	1.
WR	weight reduction	pound mass	lbm	kg.
x	amount of substance mole fraction	mole per mole	mol/mol	1.

Open Table

Superscript	Quantity
overbar (such as y̅)	arithmetic mean.
Double overbar (such	arithmetic mean of
=	arithmetic mean.
as y)
overdot (such as ẏ)	quantity per unit time.

(d) Subscripts. This part uses the following subscripts to define a quantity:

Open Table

Subscript	Quantity
±6	±6° yaw angle sweep.
A	A speed.
air	air.
aero	aerodynamic.
alt	alternative.
act	actual or measured condition.
air	air.
axle	axle.
B	B speed.
brake	brake.
C	C speed.
Ccombdry	carbon from fuel per mole of dry exhaust.
CD	charge-depleting.
circuit	circuit.
CO2DEF	CO2 resulting from diesel exhaust fluid decomposition.
CO2PTO	CO2 emissions for PTO cycle.
coastdown	coastdown.
comp	composite.
CS	charge-sustaining.
cycle	test cycle.
drive	drive axle.
drive-idle	idle with the transmission in drive.
driver	driver.
dyno	dynamometer.
effective	effective.
end	end.
eng	engine.
event	event.
fuel	fuel.
full	full.
grade	grade.
H2Oexhaustdry	H2O in exhaust per mole of exhaust.
hi	high.
i	an individual of a series.
idle	idle.
in	inlet.
inc	increment.
lo	low.
loss	loss.
max	maximum.
meas	measured quantity.
med	median.
min	minimum.
moving	moving.
out	outlet.
P	power.
pair	pair of speed segments.
parked-idle	idle with the transmission in park.
partial	partial.
ploss	power loss.
plug-in	plug-in hybrid electric vehicle.
powertrain	powertrain.
PTO	power take-off.
rated	rated speed.
record	record.
ref	reference quantity.
RL	road load.
rotating	rotating.
seg	segment.
speed	speed.
spin	axle spin loss.
start	start.
steer	steer axle.
t	tire.
test	test.
th	theoretical.
total	total.
trac	traction.
trac10	traction force at 10 mi/hr.
trailer	trailer axle.
transient	transient.
TRR	tire rolling resistance.
urea	urea.
veh	vehicle.
w	wind.
wa	wind average.
yaw	yaw angle.
ys	yaw sweep.
zero	zero quantity.

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

Open Table


ABT	averaging, banking, and trading.
AECD	auxiliary emission control device.
AES	automatic engine shutdown.
APU	auxiliary power unit.
CD	charge-depleting.
CFD	computational fluid dynamics.
CFR	Code of Federal Regulations.
CITT	curb idle transmission torque.
CS	charge-sustaining.
DOT	Department of Transportation.
EPA	Environmental Protection Agency.
FE	fuel economy.
FEL	Family Emission Limit.
GAWR	gross axle weight rating.
GCWR	gross combination weight rating.
GEM	greenhouse gas emission model.
GVWR	gross vehicle weight rating.
Heavy HDV	Heavy heavy-duty vehicle (see §1037.140).
HVAC	heating, ventilating, and air conditioning.
ISO	International Organization for Standardization.
Light HDV	Light heavy-duty vehicle (see §1037.140).
Medium HDV	Medium heavy-duty vehicle (see §1037.140).
NARA	National Archives and Records Administration.
NHTSA	National Highway Transportation Safety Administration.
PHEV	plug-in hybrid electric vehicle.
PTO	power take-off.
RESS	rechargeable energy storage system.
rpm	revolutions per minute.
SAE	Society of Automotive Engineers.
SEE	standard error of estimate.
SKU	stock-keeping unit.
TRPM	tire revolutions per mile.
TRRL	tire rolling resistance level.
U.S.C.	United States Code.
VSL	vehicle speed limiter.

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

Open Table

Symbol	Quantity	Value
g	gravitational constant	9.81 m·s−2.
R	specific gas constant	287.058 J/(kg·K).

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

Open Table

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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