[Code of Federal Regulations]

[Title 40, Volume 31]

[Revised as of July 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 40CFR1065.20]



[Page 682-683]

 

                   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 683]]



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.