[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: 40CFR1065.225]



[Page 705]

 

                   TITLE 40--PROTECTION OF ENVIRONMENT

 

         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)

 

PART 1065_ENGINE-TESTING PROCEDURES--Table of Contents

 

                    Subpart C_Measurement Instruments

 

Sec.  1065.225  Intake-air flow meter.



    (a) Application. You may use an intake-air flow meter in combination 

with a chemical balance of carbon (or oxygen) between the fuel, inlet 

air, and raw exhaust to calculate raw exhaust flow as described in Sec.  

1065.650, as follows:

    (1) Use the actual value of calculated raw exhaust in the following 

cases:

    (i) For multiplying raw exhaust flow rate with continuously sampled 

concentrations.

    (ii) For multiplying total raw exhaust flow with batch-sampled 

concentrations.

    (2) In the following cases, you may use an intake-air flow meter 

signal that does not give the actual value of raw exhaust, as long as it 

is linearly proportional to the exhaust flow rate's actual calculated 

value:

    (i) For feedback control of a proportional sampling system, such as 

a partial-flow dilution system.

    (ii) For multiplying with continuously sampled gas concentrations, 

if the same signal is used in a chemical-balance calculation to 

determine work from brake-specific fuel consumption and fuel consumed.

    (b) Component requirements. We recommend that you use an intake-air 

flow meter that meets the specifications in Table 1 of Sec.  1065.205. 

This may include a laminar flow element, an ultrasonic flow meter, a 

subsonic venturi, a thermal-mass meter, an averaging Pitot tube, or a 

hot-wire anemometer. Note that your overall system for measuring intake-

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

calibration in Sec.  1065.325.

    (c) Flow conditioning. For any type of intake-air 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. 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.