Watch Now

Solving for NOx: Can the industry meet a new EPA standard?

When current NOx limits were set in 2010, there wasn’t as much focus on fuel economy. Now, with truck and engine makers required to meet Phase 2 fuel economy mandates, the possible addition of a lower NOx limit could complicate design. ( Photo: Shutterstock )

On Tuesday, the U.S. Environmental Protection Agency (EPA) took a step to reduce oxides of nitrogen (NOx) emissions from commercial heavy-duty vehicles. The EPA said it would begin a rulemaking, likely in 2020, to address NOx for the first time since a rulemaking in 2001 set the current levels at 0.20 grams per brake horsepower-hour (g/bhp-hr).

“The Cleaner Trucks Initiative will help modernize heavy-duty truck engines, improving their efficiency and providing cleaner air for all Americans,” said Acting EPA Administrator Andrew Wheeler in a statement. “The U.S. has made major reductions in NOx emissions, but it’s been nearly 20 years since EPA updated these standards. Through rulemaking and a comprehensive review of existing requirements, we will capitalize on these gains and incentivize new technologies to ensure our heavy-duty trucks are clean and remain a competitive method of transportation.”

The incentive to review and possibly set new NOx levels is not being driven by any statutory timeline, but rather in response to petitions from 20 state and local government agencies, including the California Air Resources Board (CARB) and the San Joaquin Valley Air Pollution Control District.

CARB, in a 2016 comment to the Phase 2 greenhouse gas emissions regulation, “estimated that heavy-duty on-highway vehicles currently contributed about one-third of all NOx emissions in California. In order to achieve the 2008 National Ambient Air Quality Standard for ozone … the state’s South Coast Air Basin would need an 80% reduction in NOx emissions by 2031.”

EPA, in response to petitioners’ requests to set a new national NOx standard to avoid each state setting its own limits, noted that over the past 40 years, emissions standards have become “progressively more stringent,” but with 70% of heavy-duty vehicles on the road today still pre-2007 vehicles – more work could be done.

“EPA believes that opportunity exists to develop, in close coordination with CARB and other stakeholders, a new, harmonized and comprehensive national NOx reduction strategy for heavy-duty on-highway engines. Therefore, EPA intends to initiate a rulemaking to propose revisions to the federal on-highway heavy-duty NOx emissions control program,” it said in the response.

Tuesday’s announcement is the formal acknowledgement that a rulemaking will likely go forward.

“Today’s announcement makes clear that reducing NOx emissions from heavy-duty vehicles is a clean air priority for this administration,” said EPA Office of Air and Radiation Assistant Administrator Bill Wehrum. “EPA’s Cleaner Trucks Initiative is an important signal to all interested stakeholders that we will work hard on reducing emissions while producing a more effective and efficient program.”

There is no timeline for implementation of any rulemaking, but as the industry starts to debate the benefits and challenges lower NOx limits present, there are a couple of key questions that must be answered, and they are not much different than what they were in 2007 or 2010, the last two years that new levels were mandated.


What will the limit be?

No one knows for sure, although CARB has been pushing a 0.02 g/bhp-hr limit – a 90% reduction from today’s current 0.20 standard.

“Zero point two (0.02) has been a discussion for a long time, so it’s a point out there that people have been working towards,” Mike Roeth, executive director of the North American Council for Freight Efficiency (NACFE), tells FreightWaves. “It’s out there with natural gas engines … but it’s been a target for a long time.”

In fact, CARB notes that four engines – two from Cummins (NYSE: CMI) and two from Roush CleanTech – currently meet its voluntary 0.02 limit. But getting there with diesel engines is a bit trickier. Can the technology do it? Likely. What will the impact be on fuel economy and what will be the cost? Those are more complicated questions.

“In 2009, we didn’t have EPA’s and NHTSA fuel economy rules that set the bar,” Allen Schaeffer, executive director of the Diesel Technology Forum, explains to FreightWaves.  

To meet the EPA 2010 limit of 0.20, it has been estimated to have added $10,000 to the base cost of the average Class 8 tractor. At this point, it’s just too early to know what the cost this round will be.


What impact will a new NOx limit have on fuel economy?

Schaeffer notes that in 2007, the first step in the two-step process to meet the 2001 NOx regulations, fuel economy took a back seat to meeting the rule. Exhaust gas recirculation (EGR) was the chosen technology for most to meet the 2007 standard, but when 2010’s 0.20 limit was instituted, most engine makers utilized selective catalytic reduction (SCR) technology to meet the limits that didn’t have the same negative impact on fuel economy. Since then, engines have become even more fuel efficient.

“In 2011, the introduction of SCR allowed [engine makers] to design engines that not only lower emissions but also improve fuel economy,” Schaeffer says.

“There was history of [one truck maker] trying to meet the 0.20 NOx standard and really struggling with it in regards to fuel economy,” Roeth notes. “It is a big challenge and it is a big challenge for many reasons. One is the negative effect on fuel economy, but also there is reliability, durability, costs issues. The wide range of truck applications that you have to build to [is another].”

With that said, Roeth believes lower limits are achievable and without much negative effect on fuel economy, if there is any at all. EPA appears to be “pretty wide in what they are looking at here,” he says, indicating he believes the agency is reviewing previous steps taken during the 2007 and 2010 NOx rules and Phase 1 and Phase 2 GHG regulations for lessons that can be applied in the next phase. EPA has also suggested it will review real-world testing results as part of any new proposed rule.


How will it be achieved?

In addition to what the final NOx limit will be, this is the greatest unknown. After using EGR and SCR to meet the earlier limits, the question is now whether SCR can significantly lower NOx levels potentially down to 0.02 g/bhp-hr. Schaeffer doesn’t know if that is possible yet but is confident that the industry will develop the necessary technologies to meet the limit, wherever that bar is set.

“A whole range of things could roll into that,” he says. “How are they going to meet further reductions in NOx emissions? We’ve got SCR today. We’ve got a couple of things, we’re into the second or third generation of SCR technology.

“This new rule will push a broader window of [technological] performance to ensure systems are working at [full efficiency to reduce NOx],” Schaeffer adds, noting that more aggressive and more tightly controlled SCR systems are but one possibility. He also noted waste heat recovery, which turns wasted engine heat into useful power, as a possibility as those systems continue to develop. There is also more advanced air management techniques that engine makers continue to refine that could help, or maybe even a technology that is not currently available.

One thing Schaeffer points to is not to get wrapped up in what the eventual number is.

“It’s not clear to me that there is a uniform path for everyone to reach the levels. … It depends on what level the standard is set at,” he says. “It just depends on how stringent the numbers get, but the number is just one part of this thing.”

He notes considerations such as warranty, durability and lifecycle management. “The industry has a pretty strong track record and I think you have to look back over time and the track record of how these regulations come together to find a middle ground,” Schaeffer says. “But there is also a track record of making these engines cleaner.”


What about the Phase 2 GHG rules?

When EPA first regulated NOx in 2001, the industry wasn’t dealing with meeting stricter fuel economy measures. This time around, engine makers will need to balance NOx levels with Phase 2 GHG regulations that set a goal of reducing CO2 emissions by about 24% (depending on vehicle type and application) by 2027. The Environmental Defense Fund, in 2016, determined that to achieve that, the average line-haul tractor would have to achieve a 9.5 mpg, compared to 6 mpg in 2010.

Because of the unknowns – such as what the limit will be and what kind of technologies will be needed to meet it – knowing how it will impact Phase 2 adherence is difficult to gauge. One positive, though, is that the industry will be working both programs at the same time, which could help engine makers choose and balance the best possible paths forward.

“You’ve got a good history of processes, a good history of delivering on pretty stringent mandates, and a good history of pushing the envelope on development [of improving combustion technologies],” Schaeffer notes. “I’m optimistic. I’ve been watching the process for a number of years and seen great success.”

In the end, Schaeffer points out that EPA has “two big balls to juggle, that is to not lose any ground but improve fuel economy, reduce CO2 [and] also to ratchet down NOx.

“Fuel efficiency is number one on the mind of fleets, and number two and number three,” he concludes.

Brian Straight

Brian Straight leads FreightWaves' Modern Shipper brand as Managing Editor. A journalism graduate of the University of Rhode Island, he has covered everything from a presidential election, to professional sports and Little League baseball, and for more than 10 years has covered trucking and logistics. Before joining FreightWaves, he was previously responsible for the editorial quality and production of Fleet Owner magazine and Brian lives in Connecticut with his wife and two kids and spends his time coaching his son’s baseball team, golfing with his daughter, and pursuing his never-ending quest to become a professional bowler. You can reach him at [email protected]