[Code of Federal Regulations]
[Title 40, Volume 31]
[Revised as of July 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR1065.20]

[Page 683-684]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 1065_ENGINE-TESTING PROCEDURES--Table of Contents
 
             Subpart A_Applicability and General Provisions
 
Sec.  1065.20  Units of measure and overview of calculations.

    (a) System of units. The procedures in this part generally follow 
the International System of Units (SI), as detailed in NIST Special 
Publication 811, 1995 Edition, ``Guide for the Use of the International 
System of Units (SI),'' which we incorporate by reference in Sec.  
1065.1010. This document is available on the Internet at http://
physics.nist.gov/Pubs/SP811/contents.html. Note the following 
exceptions:
    (1) We designate rotational frequency, fn, of an engine's crankshaft 
in revolutions per minute (rev/min), rather than the SI unit of 
reciprocal seconds (1/s). This is based on the commonplace use of rev/
min in many engine dynamometer laboratories. Also, we use the symbol fn 
to identify rotational frequency in rev/min, rather than the SI 
convention of using n. This avoids confusion with our usage of the 
symbol n for a molar quantity.
    (2) We designate brake-specific emissions in grams per kilowatt-hour 
(g/(kW[middot]hr)), rather than the SI unit of grams per megajoule (g/
MJ). This is based on the fact that engines are generally subject to 
emission standards expressed in g/kW[middot]hr. If we specify engine 
standards in grams per horsepower[middot]hour (g/(hp[middot]hr)) in the 
standard-setting part, convert units as specified in paragraph (d) of 
this section.
    (3) We designate temperatures in units of degrees Celsius ( [deg]C) 
unless a calculation requires an absolute temperature. In that case, we 
designate temperatures in units of Kelvin (K). For conversion purposes 
throughout this part, 0 [deg]C equals 273.15 K.
    (b) Concentrations. This part does not rely on amounts expressed in 
parts per million or similar units. Rather, we express such amounts in 
the following SI units:
    (1) For ideal gases, [micro]mol/mol, formerly ppm (volume).
    (2) For all substances, [micro]m\3\/m\3\, formerly ppm (volume).
    (3) For all substances, mg/kg, formerly ppm (mass).
    (c) Absolute pressure. Measure absolute pressure directly or 
calculate it as the sum of atmospheric pressure plus a differential 
pressure that is referenced to atmospheric pressure.
    (d) Units conversion. Use the following conventions to convert 
units:
    (1) Testing. You may record values and perform calculations with 
other units. For testing with equipment that involves other units, use 
the conversion factors from NIST Special Publication 811, as described 
in paragraph (a) of this section.
    (2) Humidity. In this part, we identify humidity levels by 
specifying dewpoint, which is the temperature at which pure water begins 
to condense out of air. Use humidity conversions as described in Sec.  
1065.645.
    (3) Emission standards. If your standard is in g/(hp[middot]hr) 
units, convert kW to hp before any rounding by using the conversion 
factor of 1 hp ( 550 ft[middot]lbf/s) = 0.7456999 kW. Round the final 
value for comparison to the applicable standard.
    (e) Rounding. Unless the standard-setting part specifies otherwise, 
round only final values, not intermediate values. Round values to the 
number of significant digits necessary to match the number of decimal 
places of the applicable standard or specification. For information not 
related to standards or specifications, use good engineering judgment to 
record the appropriate number of significant digits.
    (f) Interpretation of ranges. In this part, we specify ranges such 
as ``10% of maximum pressure'', ``(40 to 50) 
kPa'', or ``(30 10) kPa''. Interpret a range as a 
tolerance unless we explicitly identify it as an accuracy, 
repeatability, linearity, or noise specification. See Sec.  1065.1001 
for the definition of Tolerance.
    (g) Scaling of specifications with respect to a standard. Because 
this part 1065 is applicable to a wide range of engines and emission 
standards, some of the specifications in this part are scaled with 
respect to an engine's emission standard or maximum power. This ensures 
that the specification will be adequate to determine compliance, but not 
overly burdensome by requiring unnecessarily high-precision equipment. 
Many of these specifications are given with respect to a ``flow-weighted 
mean'' that is expected at the standard. Flow-weighted mean is the mean 
of a quantity after it is weighted proportional to a corresponding flow 
rate. For example, if a gas concentration is

[[Page 684]]

measured continuously from the raw exhaust of an engine, its flow-
weighted mean concentration is the sum of the products of each recorded 
concentration times its respective exhaust flow rate, divided by the sum 
of the recorded flow rates. As another example, the bag concentration 
from a CVS system is the same as the flow-weighted mean concentration, 
because the CVS system itself flow-weights the bag concentration. Refer 
to Sec.  1065.602 for information needed to estimate and calculate flow-
weighted means.