Trucks and vehciles in traffic

Mobile Source Emissions Research - Heavy Duty Vehicles

CARB's Mobile Source Emissions Research on heavy-duty vehicles

Heavy-duty vehicles include line-haul trucks, vocational trucks, drayage trucks and buses, to name a few. They are an important part of the economy and perform a wide variety of revenue services which is reflected in the large range of vehicle sizes and operational characteristics. The complexity of this vehicle category presents a challenge in reducing greenhouse gases and criteria pollutants which requires a large effort on researching various aspects of heavy-duty vehicles including their operation, their in-use emissions and the effectiveness of aftertreatment devices. Below is a list of recent and current projects related to heavy-duty vehicles.

Activity Data Collection Projects

Measurement of In-Use Emissions and Fuel Consumption from Vocational Heavy-Duty Vehicles with Conventional and Alternative Engine and Fuel Technologies in Southern California (16RD012)

This project, supported both by CARB and the South Coast Air Quality Management District, is collecting several types of data from heavy-duty vehicles. This includes OBD-based real-world activity data from over 200 trucks, portable emissions measurement system (PEMS) data from 100 trucks, 60 chassis dynamometer tests, and 10 real-world test with a mobile trailer. Several different engine technologies are included (with number of HDVs in parentheses):

  • Compressed Natural Gas, 0.2g (80)
  • Compressed Natural Gas, 0.02g (33)
  • Diesel, 0.2g (70)
  • Diesel, no SCR (6)
  • HPDI (4)
  • Diesel-electric (6)
  • Electric (7)
  • Propane (6)
  • Propane, 0.02 g (1)
  • H2 / Fuel Cell (1)
  • Total (214)

Results from this study will be used to benchmark CARB’s emissions inventories, inform State Implementation Plans (SIPs), characterize activity patterns from different HDV vocations, and evaluate the performance and deterioration of different engine technologies and emissions certification levels. CARB staff have produces a fact sheet describing emissions from the CNG HDVs in this set.

More information on this study can be found in the RD contract catalog (link), or in the following publication:

 

Real‐World Activity of Heavy‐Duty Tractors Hauling Container Chassis, Flatbed Trailer, and Tank Trailer (14-302)

This study was completed in 2018. Major findings include:

  • Most fleets had over two-thirds of VMT at speeds above 45 mph
  • Most fleets would benefit from aerodynamic technologies on their trailers
  • Expansion Tractor-Trailer GHG Regulations could exempt lower-speed fleets

The Tractor-Trailer Greenhouse Gas Regulation requires that box type trailers 53 feet or longer be equipped with approved aerodynamic devices (below) and low-rolling resistance tires. These requirements have been shown to result in a significant fuel savings which impacts their GHG emissions. However, other types of trailers including curtainside, container-chassis, tanker and flatbed have not been studied extensively and should be examined to understand whether their typical operational behavior includes extensive high speed driving and large cumulative vehicle miles traveled (VMT) per year. At higher speeds aerodynamic devices induce a more significant fuel savings.

Diagram of typical heavy duty truck and aerodynamic devices

Diagram of a typical heavy duty truck with various aerodynamic devices installed

In this project a survey was sent out to fleet operators which utilized curtainside, flatbed, tanker, and container-chassis type trailers. Fleets within California with tractors pulling tanker, flatbed, and container-chassis were also logged for at least a month to study their operational behavior. It was found through both survey results and vehicle activity logging that:

This study was completed in 2018. Major findings include:

  • Most fleets had over two-thirds of VMT at speeds above 45 mph
  • Most fleets would benefit from aerodynamic technologies on their trailers
  • Expansion Tractor-Trailer GHG Regulations could exempt lower-speed fleets

The results of this study have been used to inform regulatory activities related to the Tractor-Trailer Greenhouse Gas Regulation. More information on this study can be found in its Final Report (link) and its Research Seminar (link), or in the following journal article:

More information in the final report and the seminar.

 

Real-World Activity Patterns of Heavy-Duty Vehicles and Their Implications on In-Use Emissions (13-301)

    This study collected OBD-based activity data from 90 HDVs in California. The sample was selected to represent common HDV vocations in the state. Results were used to benchmark CARB’s emissions inventories and characterize the activity of different HDV vocations. This included vocations, with number of HDVs in parentheses, were:

    • Line haul (6)
    • Drayage (6)
    • Agricultural (8)
    • Construction (6)
    • Cement mixers (5)
    • Food distribution (11)
    • Moving (1)
    • Shuttle (5)
    • Refuse (6)
    • Buses (11)
    • Municipal work (13)
    • Towing (7)
    • Utility Repair (5)
    • Total (90)

    This study was completed in 2017. Major findings include:

    • SCR temperature is sub-optimal (< 200°C) 11 – 87% of the time, depending on vocation
    • Real-world SCR NOx conversion ranges from 11 – 87%, again depending on vocation
    • Results were used to develop vocation-specific chassis dynamometer drive cycles

    More information on this study can be found in its Final Report (link) and its Research Seminar (link), a detailed resource document (link) or in the following journal articles:

     

    Emissions Characterization Projects

    Low-NOx Demo (13-312)

    Background

    2010 emission standards for heavy-duty engines have established a limit for oxides of nitrogen (NOx) emissions of 0.20 g/bhp-hr, a 90% reduction from the previous emission standards. However, it is projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with the 2010 emission standards, the upcoming National Ambient Air Quality Standards (NAAQS) requirements for ambient particulate matter and ozone will not be achieved in California without further significant reductions in NOx emissions from the heavy duty vehicle fleet. There is currently little incentive for manufacturers to pursue emission reductions beyond the current standards, and so the potential for further reductions is unclear. To address this lack of information, CARB is funding a research program to explore and investigate the feasibility of significantly reducing NOx emissions below today's standard.

    Objective

    This study investigated the feasibility of achieving NOx emissions significantly lower than the current engine standard. We evaluated improved engine emission control calibration, enhanced aftertreatment technology choices and configurations, improved and more efficient catalyst, improved aftertreatment thermal management, urea dosing strategies, and engine management practices for two heavy-duty engines: one natural gas engine with a three-way catalyst (TWC); and one diesel engine with a diesel particulate filter (DPF) and selective catalytic reduction (SCR). The target NOx emission rate for this project over the heavy-duty Federal Test Procedure (FTP) was 0.02 g/bhp-hr.

    Project Plan

    The project team refined a research plan identifying specific engines, test cycles, and aftertreatment technologies for consideration in the screening and final demonstration efforts.

    The project team characterized the emission performance of the two stock engines using procedures following Title 40, Code of Federal Regulations, Part 1065 (40 CFR 1065), determined stock engine characteristics for cold starts, hot starts, normal operation, and low-load-low-temperature operation, and defined possible engine control strategies.

    Based on the engine performance and engine control strategies, the project team selected candidate aftertreatment technologies and engine control strategies for screening. The candidate emission reduction strategies were screened using low-cost exhaust emission sources and test benches. The best emission reduction strategy was identified for the final system demonstration.

    Finally, the project team performed engine dynamometer tests following reference methods specified in 40 CFR 1065 for the selected emission reduction strategies. The tests measured performance over the heavy-duty FTP, World Harmonized Transient Cycle (WHTC), ramped mode cycle (RMC), extended Idle, and three low-load-low-temperature cycles such as the Orange County Transit Authority (OCTA) bus cycle, New York bus cycle (NYBC), and CARB Creep cycle.

    Project deliverables were a final report and emission test data sets. The report describes NOx emission reduction strategies, test methods, and test results, as well as summaries of data and findings from the research. The data sets are in spreadsheet or database format and include second-by-second test data from the demonstration testing, data tables reporting integrated emissions and other key parameters from each individual test, and tables summarizing overall test results.

    Program Advisory Group

    CARB invited representatives from heavy-duty engine and aftertreatment industries, and from federal, state, and local governmental agencies to form a Low NOx Advisory Group. The representatives are able to speak for their organizations and to coordinate the comments, suggestions, and advice of their members. Representatives from the following organizations accepted the invitation and have served as an advisory panel for the study:

    • The Truck and Engine Manufacturers Association (EMA) and their members
    • The Manufacturers of Emission Controls Association (MECA)
    • Environmental Protection Agency (EPA)
    • Department of Energy (DOE)
    • Oak Ridge National Laboratory (ORNL)
    • South Coast Air Quality Management District (SCAQMD)
    • California Energy Commission (CEC)

    Results

    This study was completed in 2017. Major findings include:

    • Final system was able to achieve 99% conversion efficiency on composite FTP / WHTC fully aged
    • 0.02 g/hp-hr was very challenging - system complexity and GHG impact higher due to very low temperatures
    • Significant potential for low NOx levels on vocational and field cycles

    More information can be found in the Final Report (link), the Research Seminar (link), or in the following publications:

    Peer-Reviewed Publications

    Sharp, C., Webb, C., Yoon, S., Carter, M. et al. Achieving Ultra Low NOx Emissions Levels with a 2017 Heavy-Duty On-Highway TC Diesel Engine - Comparison of Advanced Technology Approaches. SAE Int. J. Engines, 10(4): 2017, doi:10.4271/2017-01-0956

    Sharp, C., Webb, C., Neely, G., Yoon, S., Carter, M. et al. Achieving Ultra Low NOx Emissions Levels with a 2017 Heavy-Duty On-Highway TC Diesel Engine and an Advanced Technology Emissions System - Thermal Management Strategies. SAE Int. J. Engines. 10(4): 2017, doi:10.4271/2017-01-0954

    Sharp, C., Webb, C., Neely, G., Sarlashkar, J., Yoon, S. et al. Achieving Ultra Low NOx Emissions Levels with a 2017 Heavy-Duty On-Highway TC Diesel Engine and an Advanced Technology Emissions System - NOx Management Strategies. SAE Int. J. Engines. 10(4): 2017, doi:10.4271/2017-01-0958

    Smith, I., Briggs, T., Sharp, C., and Webb, C. Achieving 0.02 g/bhp-hr NOx Emissions from a Heavy-Duty Stoichiometric Natural Gas Engine Equipped with Three-Way Catalyst. SAE Technical Paper 2017-01-0957, 2017, doi:10.4271/2017-01-0957

     

    Plume capture measurements (various contracts)

    In contrast to PEMS measurements, which provide extensive records from individual trucks, stationary emission measurement systems can be used to record emissions “snapshots” of passing vehicles, each one lasting only a few seconds. While these snapshots only capture a single point in the drive cycle, they can be obtained for larger, representative samples of the on-road fleet. CARB has sponsored several projects over the past decade that use plume capture methods to sample exhaust from passing vehicles. These measurements have been made at four field sites in California: the Port of L.A., the Port of Oakland, the Caldecott Tunnel, and the Cottonwood weight station (below).

    Photographs taken at four roadside locations - (1) the Port of Oakland, (2) the Caldecott Tunnel, (3) the Port of Los Angeles, and (4) the Cottonwood weigh station.

    These results have been used to benchmark CARB’s emissions inventories, quantify the benefits of regulations such as the Truck and bus Rule, and inform the development of CARB’s Heavy-duty Inspection and Maintenance program. More information on these studies can be found in its Final Reports (links for Caldecott, the Port of Oakland, and Port of L.A./Cottonwood) and its Research Seminars (links for Caldecott, the Port of Oakland, and Port of L.A./Cottonwood), a detailed resource document (link), or in the following journal articles:

     

      Heavy-duty On-Road Vehicle Inspection and Maintenance Program (15RD022)

      California Senate Bill 210, passed in 2019, authorizes CARB to develop a first-of-its-kind Inspection and Maintenance (I/M) program for HDVs. To inform the development of this program, CARB conducted a 50 vehicle pilot I/M study in conjunction with an HDV repair shop in southern California, in which emissions were measured before and after repair. Major findings of this study were:

      • Substantial reductions for NOx were seen after repair
      • No significant PM reductions were observed due to low pre-repair emission levels.
      • A full-scale program could use OBD scans and RSD/PEAQS roadside emissions measurements in a cost-effective manner

      These results will help CARB establish a more comprehensive HD I/M program. More information on this study can be found in its Final Report (link) and its Research Seminar (link), or in the following journal articles:

       

      Measurement of Emissions from both Active and Parked Regenerations of a Diesel Particulate Filter from Heavy Duty Trucks

      Diesel Particulate Filters (DPFs) prevent almost all particulate matter (PM) emitted by a truck’s engine during normal operation, but they must be regenerated periodically and PM emissions during these events are not as well characterized. A series of 11 regenerations were performed on 2 DPFs in which emissions were quantified, and the total mass lost from the DPF was measured gravimetrically. Major findings include:

      • Nearly all of the mass lost from the DPF was oxidized to CO2
      • The small amount emitted was primarily sulfate.
      • DPFs are working as intended, and are serving a crucial role in meeting California’s Diesel Risk Reduction Plan.

       

      Picture of experimental setup
      Experimental setup where diesel particle filter outlet was connected to a custom built air tunnel used for sampling and characterization of the particulate and gas-phase emissions.

      More information can be found in the Final Reports (stage 1 and stage 2), and the following peer-reviewed publications:

       

      Other Projects