Emissions from off-road heavy-duty vehicles are restricted in the United States, but those regulations have run behind controls for on-road light- and heavy-duty autos. To date the U.S. Environmental Protection Agency and the California Air Resources Board have established limits for pollutants such as nitrous oxides and particulate matter.

Now there is movement to add limits on emissions of greenhouse gases – largely carbon dioxide – as is already being done for on-road cars and trucks. At the Lubricant Expo North America here March 19, Jeff Harmening, senior program manager for the American Petroleum Institute’s Engine Oil Licensing and Certification System, pointed out that CARB has begun work on potential Tier 5 rules that would for the first time regulate CO2 emissions from off-road vehicles.

EPA has yet to tackle such work, but California has often been on the leading edge of environmental regulation in the country. The board aims to introduce its proposal, which would also lower NOx and particulate matter limits, by next year with the idea of implementing it by 2029, Harmening said.

Petro-Canada Lubricants Global Director of Technology Vittorio Lopopolo said there are a variety of ways that greenhouse gas emissions might be reduced and some either involve lubricants or could affect them. Reducing lubricant viscosity has of course been a popular approach for reducing drag, improving fuel economy and thereby reducing CO2 emissions in on-road vehicles and could be used in their off-road counterparts, she said. But that is more likely to lead to wear problems in off-road heavy-duty equipment, given the large loads their engines experience.

Engine design changes could help, but these might change operating conditions – for example raising operating temperatures, which could challenge lubricant durability. Modern emissions control technologies could be employed, as they have in on-road vehicles, but several of these require reductions in lubricant levels of sulfated ash, phosphorus and sulfur, which can create challenges for anti-wear and extreme pressure performance.

As with on-road vehicles, operators of off-road equipment could switch to electric models, but this would likely lead to fragmentation of equipment designs, making product offerings more complex for lube suppliers. Or industry could switch to alternative fuels, such as hydrogen fuel cells, but alternatives often create new requirements for lubricants, so this, too, could complicate product offerings.

Lopopolo added, though, that such challenges present opportunities for the lubricant industry – chances to provide solutions for end users.

“The lubricants industry has had strong success in enabling improvements in other applications and stands ready to bring that track record to heavy-duty off-road,” she said.

Corey Trobaugh, senior director for applied sciences and technology with Cummins, manufacturer of engines for a wide variety of engines, including diesel engines used in on- and off-road heavy-duty applications. He focused on the use of light engine oils to improve fuel economy for on-road trucks, pointing out that some operators have opted not to recommend use of such oils in some engines due to concerns that thin oil films might provide inadequate protection from wear. Such decisions led the American Petroleum Institute to split its most recent heavy-duty diesel oil performance standard into two specifications: API FA-4 for lighter oils and API CK-4 for others that are not as light.

Trobaugh said Cummins has not recommended FA-4 for its off-road engines and has no plans to because customers are prioritizing wear protection over fuel economy.

“For off-highway we still recommend [CK-4] registered oils,” he said. “The main reason is that up to now we haven’t received any customer requests to move to FA-4.”