[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: 40CFR1065.240]



[Page 706-707]

 

                   TITLE 40--PROTECTION OF ENVIRONMENT

 

         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)

 

PART 1065_ENGINE-TESTING PROCEDURES--Table of Contents

 

                    Subpart C_Measurement Instruments

 

Sec.  1065.240  Dilution air and diluted exhaust flow meters.



    (a) Application. Use a diluted exhaust flow meter to determine 

instantaneous diluted exhaust flow rates or total diluted exhaust flow 

over a test interval. You may use the difference between a diluted 

exhaust flow meter and a dilution air meter to calculate raw exhaust 

flow rates or total raw exhaust flow over a test interval.

    (b) Component requirements. We recommend that you use a diluted 

exhaust flow meter that meets the specifications in Table 1 of Sec.  

1065.205. Note that your overall system for measuring diluted exhaust 

flow must meet the linearity verification in Sec.  1065.307 and the 

calibration and verifications in Sec.  1065.340 and Sec.  1065.341. You 

may use the following meters:

    (1) For constant-volume sampling (CVS) of the total flow of diluted 

exhaust, you may use a critical-flow venturi (CFV) or multiple critical-

flow venturis arranged in parallel, a positive-displacement pump (PDP), 

a subsonic venturi (SSV), or an ultrasonic flow meter (UFM). Combined 

with an upstream heat exchanger, either a CFV or a PDP will also 

function as a passive flow controller in a CVS system. However, you may 

also combine any flow meter with any active flow control system to 

maintain proportional sampling of exhaust constituents. You may control 

the total flow of diluted exhaust, or one or more sample flows, or a 

combination of these flow controls to maintain proportional sampling.

    (2) For any other dilution system, you may use a laminar flow 

element, an ultrasonic flow meter, a subsonic venturi, a critical-flow 

venturi or multiple critical-flow venturis arranged in



[[Page 707]]



parallel, a positive-displacement meter, a thermal-mass meter, an 

averaging Pitot tube, or a hot-wire anemometer.

    (c) Flow conditioning. For any type of diluted exhaust flow meter, 

condition the flow as needed to prevent wakes, eddies, circulating 

flows, or flow pulsations from affecting the accuracy or repeatability 

of the meter. For some meters, you may accomplish this by using a 

sufficient length of straight tubing (such as a length equal to at least 

10 pipe diameters) or by using specially designed tubing bends, orifice 

plates or straightening fins to establish a predictable velocity profile 

upstream of the meter.

    (d) Exhaust cooling. You may cool diluted exhaust upstream of a raw-

exhaust flow meter, as long as you observe all the following provisions:

    (1) Do not sample PM downstream of the cooling.

    (2) If cooling causes exhaust temperatures above 202 [deg]C to 

decrease to below 180 [deg]C, do not sample NMHC downstream of the 

cooling for compression-ignition engines, 2-stroke spark-ignition 

engines, and 4-stroke spark-ignition engines below 19 kW.

    (3) If cooling causes aqueous condensation, do not sample 

NOX downstream of the cooling unless the cooler meets the 

performance verification in Sec.  1065.376.

    (4) If cooling causes aqueous condensation before the flow reaches a 

flow meter, measure dewpoint, Tdew and pressure, ptotal at the flow 

meter inlet. Use these values in emission calculations according to 

Sec.  1065.650.