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MECA report assesses technology feasibility for heavy-duty diesel trucks to meet lower NOx standards by 2024

The Manufacturers of Emission Controls Association (MECA) released a report assessing market-ready technologies being commercialized by suppliers of emission control and efficiency components for heavy-duty diesel vehicles to meet lower intermediate standards for oxides of nitrogen (NOx) by 2024 as a transition to final standards in 2027.

The report presents dynamometer test results and emission models from fully aged aftertreatment systems installed on heavy-duty on-road engines to offer several compliance paths that are achievable by model year 2024 without significant changes to today’s engines or aftertreatment systems.

The models used have been optimized over decades of testing of accelerated aged commercial catalysts and validated against real world emission control systems. The technologies outlined are either commercial or market-ready options that can be deployed on vehicles by model year 2024 to achieve 0.05 gram per brake horsepower hour (g/bhp-hr) on the heavy-duty FTP certification cycle and approximately 0.2 g/bhp-hr in low load operation using the proposed low load certification cycle being developed at Southwest Research Institute under a contract from the California Air Resources Board (CARB).

The MECA assessment is based on the implementation timeline presented by CARB staff at a January 2019 public workshop as well as the assumptions laid out in the CARB staff white paper released in April 2019. In the latter, CARB staff signaled a plan to align the regulatory provisions for the first phase of NOx tightening with the second implementation stage of the Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles - Phase 2 in 2024.

Assumptions include that the OEMs will have to meet a Federal Test Procedure (FTP) certification standard with current cold start and hot start weightings, a Ramped Modal Cycle Supplemental Emission Test (RMC-SET) and the proposed Low Load Cycle (LLC) based on profile LLC-7 (CARB, 2019).

Included, as part of future requirements, is a revised heavy-duty in-use testing (HDIUT) protocol that replaces the current not-to-exceed (NTE) based protocol with a moving average windows method with a 10% low power exclusion, similar to that required under Euro VI-D. Finally, the technologies considered in the assessment were assumed to be designed to meet a 435,000-mile full-useful life (FUL) and a 350,000-mile or 5-year warranty, with the latter going into effect in 2022 in California.

The main conclusions in the report include:

  • Several advanced technology options can be deployed on heavy-duty engines and vehicles to reduce NOx emissions by 75% below today’s heavy-duty FTP NOx standards while also meeting the 2024 heavy-duty Phase 2 greenhouse gas limits and reducing the total cost of ownership of trucks.

    Technologies such as cylinder deactivation (CDA), high efficiency variable geometry turbochargers with exhaust gas by-pass, and start-stop systems are only some of the commercially available fuel saving technologies that can be implemented by 2024.

    Some of these strategies can be deployed on cold-start to heat up aftertreatment and keep it hot under low engine load operation. Other technologies that are being demonstrated on vehicles include 48V electrical architectures combined with regenerative braking and small batteries that can electrify auxiliary components on the engines such as air conditioning compressors, water and oil pumps, EGR pumps, electric assist turbochargers, electrically heated catalysts, 48V motor-generators, 48V electric fans and auxiliary power units to take the load off the engines.

    Technologies such as CDA and 48V mild hybridization can enable simultaneous NOx and CO2 reduction, and once implemented, these technologies will deliver fuel savings to truck owners.

  • Strategies for reducing emissions during cold start and low load operation, combined with improved engine calibration and control of urea dosing, can be implemented to enable heavy-duty trucks to achieve an FTP NOx emission limit of 0.05 g/bhp-hr and a low-load cycle limit below 0.2 g/bhp-hr. These same technologies will deliver low temperature NOx conversion in the real world as part of the newly proposed moving average windows-based compliance program.

  • The cost of controlling NOx to 0.05 g/bhp-hr in 2024 and to 0.02 g/bhp-hr by 2027 will be less than the cost of emission control technology in 2010 because, over the past nine years, ingenuity and innovation have downsized emission controls by 60% and substantially lowered their cost.


CO2 and NOx certification test data for heavy-duty diesel engines certified from 2002 through 2019. Credit: MECA. Source of data: US EPA (2019).

Both the US EPA and the California ARB have announced rulemakings focused on strengthening the current heavy-duty emission standards. Getting to ultra-low NOx and greenhouse gas emission levels will require a systems approach of advanced aftertreatment technologies, efficient engines, and clean fuels.

MECA and our member companies have played an important role in the environmental success story associated with mobile sources in the US for over 40 years. To achieve our country’s air quality goals, we must ensure trucks are as clean as possible as the heavy-duty fleet moves toward electrification. MECA members are committed to delivering the technology solutions and supporting the regulatory policies to continue to reduce emissions from this sector.

—MECA’s Executive Director, Rasto Brezny

Founded in 1976, MECA is a nonprofit trade association of the world’s leading manufacturers of clean mobility technologies for all mobile sources.



Pretty much expected that the NOx limit could be met. No surprise either that the cost would not escalate. The question is if the measures against cold start emissions will have any significant impact on street level emissions, simply because cold starts are rare for HD vehicles?

If we would draw a parallel from this study to diesel-fuelled LD vehicles, it is likely that (the anticipated...) Euro 7 level could be met already today and a potential Euro 8 level in a few more years.

It appears as we do not need EVs to reduce emissions.

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