Copy of the Relevant Section of Federal Register for Partial Flow Dilution

Direct Final Rule Document ID: EPA-HQ-OAR-2010-0142-0001 Read entire rule...

Page 68452, Part D

D. Revision of 40 CFR 1065.140 To Allow the Use of Partial Flow Dilution Systems for Laboratory Transient Test Cycle PM Measurement

We are taking this opportunity to make changes to 40 CFR 1065.140(d) to allow the use of partial flow sampling systems for measurement of PM during transient test cycles for laboratory testing. PM measurement has been traditionally performed using a full flow dilution tunnel where the entire amount of engine exhaust gas is collected and made available for sampling. With this sampling method, commonly referred to as a constant volume sampler (CVS), the size of the dilution tunnel depends on the exhaust gas volume, thus the greater the volume of exhaust gas emitted from the engine, the larger the dilution tunnel must be. As an alternative, a partial-flow dilution tunnel allows sampling of part of the total exhaust flow, which reduces the size of the sampling system. One of the drawbacks to partial flow sampling systems in the past was that the flow controllers did not have a fast enough response time to accurately respond to the changing exhaust flow rates during a transient cycle. Thus partial flow sampling systems were only allowed for use during steady-state cycle testing. Recent advancements in the development of fast response flow control systems, along with the advancement in the understanding of PM formation characteristics have made partial flow sampling systems a viable technology for use in transient applications when compared to the CVS reference method.

We currently allow the use of partial flow sampling systems for measurement of PM for steady-state and ramped modal cycle (RMC) testing and have put specifications in place in 40 CFR 1065.140(e) with respect to dilution air temperature, minimum dilution ratio, filter face temperature, and residence time to control PM formation. These specifications have further worked to improve the accuracy of partial flow systems when compared to the CVS.

We initially proposed this allowance in the locomotive and compression-ignition marine engines less than 30 liters per cylinder NPRM, but did not finalize it due to concerns over the viability of partial flow systems in transient applications.12 13 Since promulgating that rule, EPA has worked with industry to gain a better understanding of partial flow systems and the improvements that have been made over the past decade.

Page 68453, Part D (Cont.)

We have also reviewed additional data supplied by engine and partial flow system equipment manufacturers showing comparisons between the traditional CVS and partial flow systems for PM measurement.\14\ These data have shown that partial flow measurement of PM is a viable tool for measurement in transient applications and these systems can meet the dilution parameter control requirements in 40 CFR 1065.140 as well as the flow rate linearity requirements in 40 CFR 1065.307, Table 1, and the validation of proportional flow control requirement in 40 CFR 1065.545. Further, correlation testing involving partial flow systems and CVS based systems has shown that the partial flow method is equivalent to the CVS method via t- and f-test analysis. In light of these recent disclosures, EPA will allow the use of this measurement technique.\15\

FOOTNOTES

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    \12\ See ``Proposed Rule: Control of Emissions of Air Pollution from Locomotives and Marine Compression-Ignition Engines Less than 30 Liters per Cylinder'', 72 FR 34594 (April 3, 2007).
    \13\ See ``Final Rule: Control of Emissions of Air Pollution from Locomotives and Marine Compression-Ignition Engines Less Than 30 Liters per Cylinder'', 73 FR (May 6, 2008).
    \14\ See ``Sierra Instruments Model BG-3 vs. CVS Multiple Engine Correlation Study'', dated November 2009. A copy of this list is available in the public docket for this rule. Read study...
    \15\ Compliance evaluation when conducted by the Administrator, independent of the method for dilution, become the official results. Manufacturers should be prepared to demonstrate compliance with the full flow CVS even if initial certification was conducted using a partial flow dilution system. EPA will continue to use the CVS-based PM measurement method for our own compliance testing regardless of what method the manufacturer used to certify the engine.
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