[Title 40 CFR 90.420]
[Code of Federal Regulations (annual edition) - July 1, 1996 Edition]
[Title 40 - PROTECTION OF ENVIRONMENT]
[Chapter I - ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)]
[Part 90 - CONTROL OF EMISSIONS FROM NONROAD SPARK-IGNITION ENGINES]
[Subpart E - Gaseous Exhaust Test Procedures]
[Sec. 90.420 - CVS concept of exhaust gas sampling system.]
[From the U.S. Government Publishing Office]




  40
  PROTECTION OF ENVIRONMENT
  9
  1996-07-01
  1996-07-01
  false
  
  90.420
  Sec. 90.420
  
    PROTECTION OF ENVIRONMENT
    ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
    CONTROL OF EMISSIONS FROM NONROAD SPARK-IGNITION ENGINES
    Gaseous Exhaust Test Procedures
  


Sec. 90.420  CVS concept of exhaust gas sampling system.

    (a) A dilute exhaust sampling system is designed to directly measure 
the true mass of emissions in engine exhaust without the necessity of 
measuring either fuel flow or intake air flow. This is accomplished by 
diluting the exhaust produced by a test engine with ambient background 
air and measuring the total diluted exhaust flow rate and the 
concentration of emissions within the dilute flow. Total mass flow of an 
emission is then easily calculated.
    (b) A constant volume sampler (CVS) is typically used to control the 
total amount of dilute flow through the system. As the name implies, a 
CVS restricts flow to a known value dependent only on the dilute exhaust 
temperature and pressure.
    (c) For the testing described in this subpart, a CVS must consist 
of: a mixing tunnel into which the engine exhaust and dilutant 
(background) air are dumped; a dilute exhaust flow metering system; a 
dilute exhaust sample port; a background sample port; a dilute exhaust 
sampling system; and a background sampling system.
    (1) Mixing tunnel. The mixing tunnel must be constructed such that 
complete mixing of the engine exhaust and background air is assured 
prior to the sampling probe.

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    (2) Exhaust flow metering system. A dilute exhaust flow metering 
system must be used to control the total flow rate of the dilute engine 
exhaust as described in Sec. 90.421.
    (3) Exhaust sample port. A dilute exhaust sample port must be 
located in or downstream of the mixing tunnel at a point where complete 
mixing of the engine exhaust and background air is assured.
    (4) Background sample port. A dilute exhaust sample port must be 
located in the stream of background air before it is mixed with the 
engine exhaust. The background probe must draw a representative sample 
of the background air during each sampling mode.
    (5) Exhaust sampling system. The dilute exhaust sampling system 
controls the flow of samples from the mixing tunnel to the analyzer 
system. This could be either a continuous sampling system or grab (bag) 
sampling system. If a critical flow venturi (CFV) is used on the dilute 
exhaust sample probe, this system must assure that the sample CFV is in 
choke flow during testing. If no CFV is used, this system must assure a 
constant volumetric flow rate through the dilute exhaust sample probe or 
must incorporate electronic flow compensation.
    (6) Background sampling system. The background sampling system 
controls the flow of samples from the background air supply to the 
analyzer system. This could be either a continuous sampling system or 
grab (bag) sampling system. This system must assure a constant 
volumetric flow rate through the background sample probe.