[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: 40CFR1065.225]

[Page 706]
 
                   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.