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  • Commercial vehicles: Planning for new CO2 and NOx emission regulations

Diesel engines have powered medium- and heavy-duty commercial vehicles for the last 100-plus years. And while electrification is on the rise, diesel will remain the dominant player in commercial vehicle transportation for the next few decades.

The Environmental Protection Agency (EPA), along with local and regional regulators, will soon increase already stringent carbon dioxide (CO2) and oxides of nitrogen (NOx) emissions regulations. This will create new challenges for truck manufacturers in terms of cold engine start-up and low-load operation. With that, OEMs will need a plan to incorporate new technologies into their diesel engines and to adopt new electric commercial vehicle (ECV) powertrain options that champion greater fuel efficiency, lower transportation costs and reduce toxic emissions for a healthier, more sustainable environment.

The state of the trucking industry

Future changes in truck powertrains are distinguished by two key rationale—the need to reduce emissions and the drive to lower transportation costs. For over 20 years, the reduction of diesel emissions focused on two components: particulate matter (PM) and NOx.  
Future changes in truck powertrains are distinguished by two key rationale—the need to reduce emissions and the drive to lower transportation costs.
Karl Sievertsen, Vice President and Chief Technology Officer, Eaton's Vehicle Group
Since the 1990s, a series of stringent polluting emissions limits set by the federal government has significantly reduced both PM and NOx tailpipe emissions from diesel engines through complex but effective exhaust aftertreatment systems. As a result, today’s diesel-powered trucks produce almost no PM and very low levels of NOx when running at steady-state highway travel. However, low-engine load cycles that are seen at idle and during stop-and-go traffic challenge aftertreatment system function and result in levels of NOx well above the steady-state limits set by federal standards. In populated urban settings with high concentrations of vehicles and slow-moving congested road systems, higher NOx levels contribute to ozone formation and its associated health risks. Furthermore, in terms of greenhouse gas emissions, since 2017 the transportation sector has become the largest CO2 emitter, overtaking the electrical power sector. While light-duty CO2 emissions are being driven down through ever more stringent fuel economy standards, commercial vehicle CO2 emissions are in fact growing in step with GDP and e-commerce growth. These two trends are the driving forces behind regulations driving simultaneous NOx and CO2 reductions in the commercial vehicle segment.

EPA Phase 2 CO2 reductions

per ton mile —a 13.8% CO2 reduction by 2021.
75.7g
per ton mile —a 13.8% CO2 reduction by 2021.
per ton mile —a 19.5% CO2 reduction by 2024.
70.7g
per ton mile —a 19.5% CO2 reduction by 2024.
per ton mile —a 26.8% CO2 reduction by 2027.
64.3g
per ton mile —a 26.8% CO2 reduction by 2027.

The Cleaner Trucks Initiative

As PM and NOx emissions were reduced over the last two decades, awareness of greenhouse gas (GHG) emission impacts on global warming grew. The EPA responded with additional GHG rules. Phase 1 set CO2 emissions at 87.8g per ton mile, and many in the industry felt acceptable CO2 efficiencies were achieved. Some in the industry were surprised when Phase 2 set three new regulatory benchmarks: a 13.8% reduction to 75.7g in 2021, a 19.5% reduction to 70.7g in 2024 and a 26.8% reduction to 64.3g in 2027.

The EPA agreed to launch the Cleaner Trucks Initiative in 2018 and is currently in the rulemaking process, targeting a new rule in early 2021 with new limits as of 2027. Working in concert with the CO2 Phase 2 program, the initiative sets a single national NOx requirement to meet the needs of states across the country. In parallel, the California Air Resources Board (CARB) is regulating to further reduce NOx to 0.05g, or 75%, by 2024 and to 0.02g, or 90%, by 2027, and the EPA is trying to achieve similar targets in 2027. I believe these efforts will influence regulations in Europe, the Middle East and Africa (EMEA), where regulators have already started working on NOx reductions, and Asia-Pacific (APAC) regions and expect to see a convergence of standards across the world.

The 0.05g NOx, which is at the heart of the CARB/EPA proposal, is not what is hard about emissions reduction. Cutting CO2 or improving NOx independently of each other is a manageable engineering challenge. But reducing both in parallel has never happened before. Some OEMs currently wrestle with meeting 2021 emission reduction mandates, and the ‘24 and ‘27 challenges that loom are more daunting. In my opinion, OEMs will not meet the '24 and' 27 regulations without rethinking their approach to improvement. To this end, enabling refined powertrain efficiency and applying vehicle electrification where appropriate makes the most sense.

I believe a cut in NOx at low load when an aftertreatment system is cold, coupled with dramatic reductions in CO2, will do two things. First, it will force new thinking for diesel powertrains. Secondly, it will inspire engineers to apply electric technologies where they make sense.

Red long-haul semi-trick

"OEMs will not meet the '24 and '27 regulations without rethinking their approach to improvement."

Electrification must be incremental

For commercial fleet buyers and manufacturers, electrification isn’t as simple as flipping a switch. First and foremost, any commercial vehicle—including ECVs—must have a reasonable payback period. Typically, that’s 12 to 18 months. OEM truck manufacturers understand this and won’t jeopardize sales with high-cost additions, such as fully-electric commercial vehicles, that aren’t yet financially viable.

The fact is, current advancements don’t support cost-effective solutions for fully electric commercial vehicles. Today’s long-haul ECVs are hampered by battery weight, range limits, recharging times and charging station infrastructure. In short, batteries can’t match the hauling power of diesel as their weight, energy density and recharging options significantly limit the amount of freight that can be carried. That’s why thousands of Class 8 semis on the road today are 20 to 30 years old. The technology is proven, trusted and cost-effective. Fleets will use them until they can't be driven anymore or until new technologies demonstrate benefits either in terms of better fuel economy or reduced maintenance. In my opinion, incremental options are the best way of justifying costs passed to buyers.

Eaton's cylinder deactivation technology

"Incremental options are the best way of justifying costs passed to buyers."

Mobilizing tomorrow: Advancing technology the trucking industry

Reducing emissions at the source—the diesel engine—is our primary focus. We look to improve engine breathing, bring more control to valve management, make exhaust gas recirculation more efficient and create other opportunities to reduce fuel consumption and related tailpipe emissions.

Addressing air-quality and GHG truck emissions offers manufacturers the opportunity to consider multiple powertrain options: 

  • Cylinder deactivation

Cylinder deactivation (CDA) aids in optimizing selective catalytic reduction (SCR) temperatures. Thermal aftertreatment is only effective at reducing NOx above 250°C. This is problematic for two reasons: first, staying hot during low load is difficult as a cold engine sends cool gas into the aftertreatment system; second, an aftertreatment system typically takes 10 to 30 minutes to get hot. Large amounts of NOx are released in the meantime.

But by heating the catalyst, Eaton’s one-minute get-hot CDA technology significantly reduces NOx. In partnership with the Southwest Research Institute, we’ve extensively tested a 15L heavy-duty diesel engine equipped with an Eaton CDA. Results have shown a 33% to 86% NOx reduction and a 3% to 8% CO2 reduction, depending on the test cycle. These are representative of both new low-load in-use compliance and real-world benefits. As part of the same study, the aftertreatment was replaced with an improved close-coupled system. The combination of the Eaton CDA and improved aftertreatment allowed a sub 0.02 g/hp-hr NOx on the EPA Federal Test Procedure and sub 0.24 g/hp-hr on the proposed low-load cycle, essentially meeting the NOx requirement for 2027. Simultaneously, CO2 emissions were reduced by 5% and 0.5% compared to baseline, respectively.

Such impressive NOx reductions are due to an increased exhaust temperature at low load, which keeps the NOx aftertreatment system at peak efficiency (250-400°C). At low load, limiting the number of active cylinders minimizes airflow to reduce the air-fuel ratio, which drives exhaust temperatures higher. Carefully selecting the number of active cylinders (two through six), depending on the load and speed condition, maximizes the CDA benefit.

  • Internal decompression engine braking

Internal decompression engine braking quickly shifts individual cylinders from combustion to braking in a single engine cycle and also provides higher braking force at low engine speeds as it activates the exhaust valve to produce one compression brake event for every two piston strokes. This is particularly important for OEMs looking to improve fuel efficiency, lower displacement engines running at lesser RPMs and reduce vehicle aerodynamic drag. 

  • Exhaust gas recirculation

Exhaust gas recirculation (EGR) technology is used to reduce NOx in the combustion cycle. Injecting the exhaust into the intake flow reduces the amount of oxygen in the air-fuel mix to lower NOx. The remaining NOx is then further reduced by the SCR aftertreatment system to meet current federal standards.

While effective, EGR systems have drawbacks. Since exhaust manifold pressures are lower than intake pressures, backpressure must be created to flow exhaust gas into the intake. Variable geometry turbochargers are typically used to generate that backpressure, but they do so at the expense of fuel efficiency losses (pumping losses) as high as 5%. However, Eaton’s separate TVS EGR pump, driven by a 48V electric motor, allows the engine to recover those pumping losses.

  • Mild hybrids

Mild hybrids pass some engine work to other sources and generate electric power when the diesel is under load. The engine in a long-haul tractor is always on when the vehicle is moving, but on average, a truck coasts 20% of that time. When coasting, the engine isn’t needed for forward motion, just powering accessories. Mild hybrids store power in batteries for electrically driven accessories (water pumps, AC compressors) dependent on a running diesel engine.

With continued improvements in aerodynamics and tire rolling resistance that are key to reducing fuel consumption and CO2 emissions, time spent coasting should rise to 30%. With the right mild hybrid, an opportunity exists to shut down the diesel at that time. Our solution is a 48V mild hybrid that replaces the alternator and engine-driven AC compressor with an electric motor/generator and integrated AC compressor mounted on the transmission power take-off opening. The system acts as a generator to power those loads and recharges batteries any time the transmission gears are running. When the truck enters a coasting mode, the diesel is shut down and the turning wheels continue to generate power for the truck’s electrical infrastructure and AC system. Replacing the traditional starter motor, the 48V mild hybrid also enables engine stop/start functionality. This delivers a 1.5% to 2% fuel efficiency improvement under highway driving conditions.

When to expect new technologies in market

Forecasting adoption timelines for developing technologies is always a guessing game. Add in proposed regulations that are still in flux and predictions become even more difficult. But one thing is clear—manufacturers must embrace new thinking to keep pace with regulatory changes on the horizon.

The first reduction step of the EPA’s three-stage plan for trucks in 2021 will likely be met with incremental changes to current truck technology. However, the steep reductions in 2024 and 2027 will drive significant levels of truck electrification, with OEMs needing to produce high numbers of zero-emission light- and medium-duty trucks, as well as heavy-duty trucks with efficiency-improving technologies like mild hybrids. Both regional and federal efforts to reduce truck NOx emissions are also proceeding along a similar timeline, creating an impetus for diesel efficiency improvements and zero-emission truck adoption wherever practical. And I believe local mandates for truck electrification, various incentive programs and general market conditions will all also align over the next decade to increase ECV volumes, which in turn will lead to lower EV hardware costs and expansion of the charging network.

No matter the final timeline, all participants in the commercial vehicle market must provide trucks that deliver the most reliable, durable service at the lowest cost possible. That starts with incremental change and the movement toward vehicle electrification.