[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: 40CFR1065.230]

[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.  1065.230  Raw exhaust flow meter.

    (a) Application. You may use measured raw exhaust flow, as follows:
    (1) Use the actual value of calculated raw exhaust in the following 
cases:
    (i) Multiply raw exhaust flow rate with continuously sampled 
concentrations.
    (ii) Multiply total raw exhaust with batch sampled concentrations.

[[Page 707]]

    (2) In the following cases, you may use a raw exhaust 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 a raw-exhaust 
flow meter that meets the specifications in Table 1 of Sec.  1065.205. 
This may involve using an ultrasonic flow meter, a subsonic venturi, an 
averaging Pitot tube, a hot-wire anemometer, or other measurement 
principle. This would generally not involve a laminar flow element or a 
thermal-mass meter. Note that your overall system for measuring raw 
exhaust flow must meet the linearity verification in Sec.  1065.307 and 
the calibration and verifications in Sec.  1065.330. Any raw-exhaust 
meter must be designed to appropriately compensate for changes in the 
raw exhaust's thermodynamic, fluid, and compositional states.
    (c) Flow conditioning. For any type of raw 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. 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 raw 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.