- WEB EXCLUSIVE
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The EPA is requesting comment on draft guidance and related interpretations concerning the application of certain emission certification regulations to those on-highway heavy-duty diesel engines that are using selective catalytic reduction (SCR) systems to meet federal emission standards. The agency will review the comments and provide final guidance and interpretations in a future Federal Register document. This Federal Register document describes and seeks public comment on draft guidance for complying with adjustable parameter regulations at 40 CFR 86.094-22 as they apply to certification of on-highway heavy-duty diesel engines using selective catalytic reduction (SCR) technology to meet emission standards for NOX. This draft guidance includes EPA's interpretation of relevant regulatory provisions in light of available information on current and developing approaches for effective SCR controls. After considering any public comments received, the EPA will issue the guidance and interpretations in the Federal Register, and will use them in reviewing any application for certification application involving SCR received on or after the effective date of the guidance. The draft guidance contained in this document reflects the fact that manufacturers of heavy-duty engines and operators of trucks have gained significant experience in the design and use of SCR systems for these engines, and this experience should be reflected in the certification process. We invite public comment on the draft guidance and interpretations in the Federal Register. Any parties may submit comments by July 7, 2011.
Until the effective date of the final guidance and interpretations, manufacturers should continue to refer to the regulations and existing guidance documents and to work with their certification representatives. The EPA recognizes that SCR technology will continue to mature, and they anticipate that appropriate designs for heavy-duty diesel vehicles and heavy-duty diesel engines using SCR systems may continue to evolve as additional experience with the technology is gained.
The draft document provides specific examples of how the EPA interprets existing certification regulations and how they intend to apply the regulations to heavy-duty diesel engines using SCR systems, based on the information available. The examples are not exclusive and are to be considered examples. Manufacturers remain able to present their own unique strategies that are not the same as the examples provided, and such strategies will remain subject to agency review and approval under the certification regulations. Manufacturers must still show the EPA that they meet all statutory and regulatory requirements when they apply for certification.
In promulgating the 0.20 gram per brake horsepower-hour NOX standard for 2010 model year heavy-duty diesel engines, based on a specified regulatory test procedure, the EPA recognized SCR technology as one potential approach for achieving the required emission reductions. The agency identified several issues for manufacturers to address in developing and applying SCR technology. Those issues related largely to the technology's use of a chemical reducing agent to reduce NOX emissions. The reductant is generally in liquid form, which is referred to in this document as DEF (diesel exhaust fluid). DEF is stored in a tank located on the vehicle and is injected into the exhaust downstream of the engine. SCR technologies require drivers to refill DEF on a regular basis and are dependent on appropriately broad availability of DEF.\1\ EPA regulations governing certification of engines generally require manufacturers to show that emission control technologies are adequately designed to limit adjustments that may increase emissions ("adjustable parameters,'' discussed in detail below). SCR is unique among emission controls in that it requires on-going driver interaction to ensure proper operation of the system.
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