Engine Technology Forum webinar clarifies role of SCR, DEF amid recent US EPA guidance

The Engine Technology Forum announced the availability of the recorded version of its April 20 webinar, “Making Diesel Clean: What You Need to Know About SCR and DEF,” which brought together technical experts and industry leaders to explain the role of selective catalytic reduction (SCR) and diesel exhaust fluid (DEF) in modern diesel engines and to address recent U.S. EPA guidance affecting these systems.

The webinar comes amid increased public and policy attention on SCR and DEF systems used in trucking, agriculture, construction and other heavy‑duty sectors.

Presenters emphasized that SCR and DEF are proven, widely deployed emissions‑control technologies that have delivered major reductions in nitrogen oxides (NOx) while also enabling improved fuel efficiency, performance and engine durability.

“SCR and DEF have been central to more than a decade of clean‑air progress in the United States,” said Allen Schaeffer, executive director of the Engine Technology Forum. “Recent EPA guidance is focused on improving real‑world operability and reliability—not on rolling back emissions standards. Our goal with this webinar was to provide policymakers with a clear, fact‑based understanding of how these systems work and why they matter.”

Proven technology with real‑world benefits

The webinar reviewed the policy context that led to SCR adoption, including EPA rules requiring more than 95 percent reductions in NOx and particulate matter from diesel engines.

Since 2010 for on‑highway vehicles and approximately 2014 for most off‑road equipment, SCR systems using DEF have become standard across millions of engines operating billions of miles and hours.

Louise Arnold, Johnson Matthey’s director of government affairs for the Americas, explained that SCR allows manufacturers to overcome the traditional tradeoff between efficiency and emissions.

“Diesel engines are inherently efficient, but the conditions that improve efficiency also generate more NOx,” Arnold said. “SCR makes it possible to optimize engines for fuel efficiency and performance, while managing NOx downstream in the exhaust. That flexibility is why SCR has become the globally favored solution for heavy‑duty, off‑road and stationary engines.”

Speakers emphasized that no commercially available alternative technology matches SCR’s emissions-control capability at comparable cost and performance across the full range of heavy‑duty applications.

Mature, reliable DEF supply chain

The webinar also addressed misconceptions about DEF availability and quality.

Industry experts described a robust North American DEF supply chain built over the past 16 years, supported by major investments in nitrogen production, dilution plants, distribution networks and retail infrastructure.

Alan Smith, the senior director of focus industries at Brenntag North America, highlighted the scale and resilience of the DEF market.

“DEF infrastructure was built to meet regulatory requirements, but it has matured into a highly reliable, nationwide supply system,” Smith said. “Today, DEF is widely available through retail outlets, bulk delivery, and on‑site fueling for fleets and equipment operators, with strong industry quality controls at every level.”

In 2026, North American DEF consumption is projected at approximately 1.46 billion gallons, supported by thousands of retail locations and more than a thousand distributors.

Quality incidents have remained rare, reflecting industry‑wide stewardship and testing practices.

EPA guidance provides flexibility, not a rollback

A central focus of the webinar was EPA guidance issued in August 2025 and March 2026 addressing how manufacturers may implement SCR and DEF compliance strategies.

The guidance provides manufacturers with:

• Additional time and mileage before engine derates occur.

• Reduced severity of final derates.

• Flexibility to rely on NOx sensors rather than DEF quality sensors, where appropriate.

Presenters stressed that the guidance does not eliminate DEF, weaken emissions standards or permit tampering or disabling of emissions controls.

“Emissions standards remain fully in place, including more stringent NOx requirements coming for future model years,” Schaeffer said. “EPA’s guidance gives manufacturers flexibility in how compliance is achieved, while preserving the environmental and public‑health benefits of SCR.”

Addressing myths, misunderstandings

The webinar directly addressed several common misconceptions, including claims that DEF is being phased out or that EPA has authorized permanent disabling of SCR systems.

Speakers emphasized that such claims are incorrect and noted that tampering with emissions controls can lead to significant penalties, reduced engine durability and loss of warranty or resale value.

Webinar recording now available

The full webinar recording, including the presentation and a live question‑and‑answer session, is now available on the Engine Technology Forum website.

To view the recorded webinar and related materials, click here.