Response to More-Rigid NOx and GHG Regs

EPA’s new NOx rule combined with its upcoming GHG Phase 3 standard could prove challenging for HD truck and diesel-engine manufacturers.

Cummins' on-highway product roadmap for aftertreatment technology from 2007 to 2020. Its development work continues. (Cummins)

In the waning days of 2022, the U.S. EPA delivered news that likely dimmed the good cheer of the season for many manufacturers in the heavy-duty (HD) truck industry. Not that it was unexpected, but the agency’s final rule on HD diesel engine NOx emissions is stringent – more than 80% stricter than current standards and covering a wider range of engine operating conditions. The new limits – which also target particulate matter, hydrocarbons and carbon monoxide – begin with model year 2027 HD trucks.

Cummins Emission Solutions has developed a close-coupled SCR with dual-dosing system that it claims takes advantage of residual heat from the engine to increase the effectiveness of NOx conversion, reducing levels to “well below” current EPA and EU regulations and “complying with anticipated reductions in the coming years.” (Cummins)

The “two-phased approach” first increases stringency in NOx emissions from 0.2 to 0.035 g/bhp-hr by 2027 and again from 0.035 to 0.02 g/bhp-hr in MY 2031 – a 90% reduction in total. The new rule also increases useful life of governed vehicles by 1.5 to 2.5 times and extends emissions-related warranty requirements by 2.8 to 4.5 times, the EPA says.

The new low-NOx standards are part of the EPA’s Clean Trucks Plan (CTP) that also includes “Phase 3” greenhouse gas (GHG) standards for HD vehicles beginning in MY 2027. The proposal for Phase 3 is due in March, with the final rule expected in December 2023.

Despite the deep NOx reductions, the CTP rule remains less demanding than California Air Resources Board’s (CARB) HD Omnibus regulation, which tightens NOx limits to 0.050 g/bhp-hr from 2024 and to 0.02 g/bhp-hr from 2027.

“We’re very excited about [EPA’s new standard, but] the two rules aren’t the same,” Bill Robertson, CARB vehicle program specialist, said at the recent SAE Government/Industry Meeting in Washington, DC. “We recognize that having a single national program does have a lot of benefits to production and cost of administrating programs and managing parts and designs. We’re interested in where that alignment discussion can go.”

While manufacturers overwhelmingly desire a unified national standard – and the new EPA limits move much closer to that goal – “excited” is not the word to describe how the Truck and Engine Manufacturers Association (EMA) sees the situation, particularly when factoring in GHG Phase 2 in 2027 and Phase 3 beyond that.

The EPA's final rule takes a “two-phased approach” that first increases stringency in NOx emissions from 0.2 to 0.035 g/bhp-hr by 2027 and again from 0.035 to 0.02 g/bhp-hr in MY 2031 – a 90% reduction in total. (U.S. EPA)

“We believe the NOx rule will require a little bit of fuel consumption, which increases greenhouse-gas emissions. So, the 2027 GHG standard will become more challenging,” Timothy Blubaugh, executive VP at EMA, said at the SAE G/I Meeting. GHG Phase 3 must consider impacts of the new ultra-low NOx regulation to ensure its success, he added.

Regardless of the stances policymakers or manufacturers take, it’s the purchasing decisions of fleets that ultimately will determine the success or failure of the new standards.

“Diesel is dominant because of its reliability and its durability. A diesel engine can last a million miles, and it can be rebuilt to extend its life,” Blubaugh said. “If trucking fleets look at the product we’re providing them and it’s too expensive or costs too much in operation, they may simply decide to invest in maintaining their existing vehicles longer. This is not something we want because we need to sell our products to recoup our investments, and it’s not what the EPA wants.”

Without fleet turnover, older generations of diesel technology with relatively higher emissions stay in service longer, negatively impacting air quality.

Unintended consequences – that’s a lesson learned from the last time EPA enacted stricter NOx standards for HD highway engines, phased in from 2007-2010. “What happened in 2009-2010? Lots of people bought lots of engines right before the rules,” reminded Aymeric Rosseau, director of vehicle and mobility systems at Argonne National Laboratory.

History could be repeated leading up to 2027. Rosseau noted the potential hit to fuel efficiency when engineering to reduce NOx emissions: “Because of this 1- or 2- or 3-percent efficiency loss that you may get, that’s hundreds of thousands of dollars [to fleets].”

And business is business, after all.