Heavy-Duty Vehicle Emissions Research pending
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.
Sensor-based Projects
Reducing emissions from mobile sources remains one of the most important environmental challenges in the near term and extending out over the next few decades. The California Air Resources Board (CARB) has been a leader in developing and implementing regulations to deal with air pollutants, such as nitrogen oxides (NOx), particulate matter (PM), and carbon dioxide (CO2) emissions, as the primary greenhouse gas (GHG) of concern. This is being carried out through a range of different regulatory programs that include both increasing tighter emissions standards, as well as the monitoring of heavy-duty vehicle performance and emissions using sensors and the vehicle's on-board diagnostic (OBD) system.
Given the key role that sensors will play in CARB’s future regulatory programs, it is important that these sensors have the accuracy, stability, and durability to meet the requirements of upcoming regulations. For instance, as engine certification limits drop to levels of 0.05 grams per brake horsepower-hour (g/bhp-hr) and below for NOx, it is known that improvements in NOx sensor technology will be needed to meet the challenges of monitoring NOx in-use at such low levels, or over the full range of vehicle operations. There is also going to be a need to monitor real fuel consumption as part of CARB’s updated Heavy Duty (HD) OBD regulations to characterize in-use CO2 emissions.
The objective of this research is to evaluate the potential of state-of-the-art and innovative sensor technologies, such as laser-based systems, in meeting the monitoring needs for recently implemented and future regulatory programs. The research will include the monitoring of NOx, PM, ammonia (NH3), and CO2 emissions from on-road heavy-duty vehicles, by vocation and duty cycles from in-use trucks operating in their natural course of business in California, and off-road equipment.
This research will include both a laboratory and a field-testing component. The laboratory testing will include bench scale testing to evaluate sensor accuracy, precision, linearity, detection limit, measurement range, cross-species interference, and other metrics, as well as testing at CARB laboratories to evaluate the sensor-based monitoring systems as a whole, as well as the specific component sensors. The field testing will include deployment of the sensor-based monitoring systems on 100 heavy-duty diesel vehicles (HDDVs), 100 Optional Low NOx engines that meet the optional 0.02 g/bhp-hr NOx standard, and 20 off-road diesel equipment (ORDEs) to characterize the accuracy, stability, durability, and operation limitations of different types of on-board sensors, with a primary focus on NOx sensors, while measuring real-time real-world diesel vehicle emissions. The real-time datasets collected from both HDDVs and ORDEs during the field testing will be used to characterize emissions and activity patterns that can be used for regulatory programs and emission inventories and identify advantages and limitations of using on-board sensors for regulatory programs.
Activity Data Collection Projects
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 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 on CARB Contract 14-302, including 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.
vocations | Final Report |
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The vocations included, with number of HDVs in parentheses, were:
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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:
- Tan, Y., Henderick, P., Yoon, S., Herner, J., Montes, T., et al.: On-Board Sensor-Based NOx Emissions from Heavy-Duty Diesel Vehicles, Environ. Sci. Technol. (2019), 53 (9), 5504-5511, doi:10.1021/acs.est.8b07048.
- Collier, S., Ruehl, C., Yoon, S., Boriboonsomsin, K., Durbin, T.D., Scora, G., Johnson, K., Herner, J.: Impact of Heavy-Duty Diesel Truck Activity on Fuel Consumption and Its Implication for the Reduction of Greenhouse Gas Emissions, Transport. Res. Rec. (2019), doi:10.1177/0361198119834548.
- Scora, G., Boriboonsomsin, K., Durbin, T., Johnson, K., Yoon, S., Collins, J., Dai, Z.: Variability in Real-World Activity Patterns of Heavy-Duty Vehicles by Vocation, Transport. Res. Rec. (2019), doi:10.1177/0361198119844247.
Emissions Characterization 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.
Engine Technologies | McCaffery et al., Sci. Tot. Environ. (2021) |
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Several different engine technologies are included (with number of HDVs in parentheses):
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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 produced 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, or in the following publication:
NOx Emissions of In-Use Trucks
The estimated contribution of on-road heavy-duty diesel vehicles to the total NOx emission in California was ~32% in 2016, which is considerably higher than the US average (~16-18% in the past decade). This work used on-board NOx sensor data to assess the real-world nitrogen oxides (NOx) emissions from heavy-duty diesel vehicles equipped with Selective Catalytic Reduction (SCR). Two separate datasets were analyzed: records from a set of 72 California HDDVs obtained with OBD dataloggers by contract 13-301 (below left), and from a set of 277 HDDVs with Portable Emissions Measurement Systems (PEMS) by various CARB programs (below right).
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). Measurements at the Caldecott Tunnel were most recently made in August 2021, and future campaigns at this site are planned for 2022 and 2023.
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:
- Ruehl, C., Misra, C., Yoon, S., Smith, J., Burnitzki, M., Hu, S., Collins, J., Tan, Y., Huai, T., Herner, J: Evaluation of Heavy-Duty Vehicle Emission Controls with a Decade of California Real-World Observations, J. Air Waste Manage. (2021), doi:10.1080/10962247.2021.1890277.
- Preble, C.V., Harley, R.A., Kirchstetter, T.W.: Control Technology-Driven Changes to In-Use Heavy-Duty Diesel Truck Emissions of Nitrogenous Species and Related Environmental Impacts, Environ. Sci. & Technol. (2019), 53 (24), 14568 – 14576, doi:10.1021/acs.est.9b04763.
- Haugen, M., Bishop, G.: Long-Term Fuel-Specific NOx and Particle Emission Trends for In-Use Heavy-Duty Vehicles in California, Environ., Sci., Technol. (2018), 52 (10), 6070 – 6076, doi:10.1021/acs.est.8b00621.
- Preble, C.V., Cados, T.E., Harley, R.A., Kirchstetter, T.W.: In-Use Performance and Durability of Particle Filters on Heavy-Duty Diesel Trucks, Environ. Sci. & Technol. (2018), 52 (20), 11913 – 11921, doi:10.1021/acs.est.8b02977.
- Haugen, M., Bishop, G., Repeat Fuel Specific Emission Measurements on Two California Heavy-Duty Truck Fleets, Environ. Sci. Technol. (2017), 51 (7), 4100-4107, doi:10.1021/acs.est.6b06172.
- Preble, C.V, Dallmann, T.R., Kreisberg, N.M., Hering, S.V., Harley, R.A., Kirchstetter, T.W.: Effects of Particle Filters and Selective Catalytic Reduction on Heavy-Duty Diesel Drayage Truck Emissions at the Port of Oakland, Environ. Sci. Technol. 49.14 (2015), 49 (14), 8864 – 8871, doi:10.1021/acs.est.5b01117.
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
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.
More information can be found in the Final Reports (stage 1 and stage 2), and the following peer-reviewed publications:
- Smith, J.D., Ruehl, C., Burnitzki, M., Sobieralski, W., Ianni, R., Quiros, D., Hua, S., Chernich, D., Collins, J., Huai, T., Dwyer, H.: Real-time particulate emissions rates from active and passive heavy-duty diesel particulate filter regeneration, Sci. Total Environ. (2019).
- Ruehl, C., Smith J.D., Ma Y., Shields, J., Burnitzkim M., Sobieralski, W., Ianni, R., Chernich, D., Chang, M-C., Collins, J., Yoon, S., Quiros, D., Hu, S., Dwyer, H.: Emissions During and Real-world Frequency of Heavy-duty Diesel Particulate Filter Regeneration, Environ. Sci. Technol. (2018).
- Yoon, S., Quiros, D., Dwyer, H., Collins, J., Burnitzki, M., Chernich, D., Herner, J.: Characteristics of Particle Number and Mass Emissions during Heavy-Duty Diesel Truck Parked Active DPF Regeneration in an Ambient Air Dilution Tunnel, Atmos. Environ. (2015), 122, 58-64, doi:10.1016/j.atmosenv.2015.09.032.
- Dwyer, H., Yoon, S., Quiros, D., Burnitzki, M., et al.: Ambient Emission Measurements from Parked Regenerations of 2007 and 2010 Diesel Particulate Filters, SAE Technical Paper 2014-01-2353 (2014), doi:10.4271/2014-01-2353.
- Quiros, D., Yoon, S., Dwyer, H., Collins, J., Zhu, Y., Huai, T.: Measuring Particulate Matter Emissions During Parked Active Diesel Particulate Filter Regeneration of Heavy-Duty Diesel Trucks, J Aerosol Sci. (20140< 73, 48-62, doi:10.1016/j.jaerosci.2014.03.002.