Engine Emission Monitoring Systems in Vehicles: A Comprehensive Playbook

Engine emission monitoring systems in vehicles are crucial for controlling and reducing air pollution, especially from road traffic. These systems employ various monitoring methodologies, including on-board and laboratory-based measurements under real-world conditions, to ensure compliance with stringent emission standards.

CARB’s Certification Process: Ensuring Compliance

The California Air Resources Board (CARB) oversees the certification and compliance process for vehicles and engines. Manufacturers must submit detailed technology and test data to demonstrate that their vehicles and engines meet the required emission standards.

On-Board Diagnostics (OBD) Monitoring

OBD systems are required to run frequently enough during real-world operation to detect and report any malfunctions that could lead to increased emissions. Manufacturers must collect and report in-use monitoring performance data representative of every test group to CARB no later than twelve months after the start of production. Failure to meet the minimum acceptable monitoring performance ratios may result in CARB issuing deficiencies or requiring recalls of affected vehicles.

Heavy-Duty Engine Certification and Compliance

Heavy-duty engines (i.e., engines for use in vehicles greater than 14,000 lbs GVWR) are subject to Manufacturer Self-Testing (MST) to ensure that OBD systems on in-use aged engines can detect faults before emissions exceed malfunction criteria. Prior to receiving certification for an engine family, manufacturers must conduct durability demonstration engine (DDE) testing on at least one engine family. For MST, manufacturers then conduct the same tests three years later, but on a procured real-world aged engine and aftertreatment system.

Heavy-Duty In-Use Testing and Audits

Heavy-duty in-use testing and audits are essential for demonstrating compliance over the useful life of engines. CARB’s regulatory framework for the Not-To-Exceed (NTE) requirements, introduced in 2004, includes on-board portable emission measurement systems (PEMS) during over-the-road operations. This framework paved the way for CARB’s heavy-duty in-use compliance (HDIUC) program, which began in 2016.

Collaboration and Oversight

National oversight of heavy-duty diesel engines is critical, considering the million trucks that operate on-road in California. Collaboration with the US EPA and internal CARB partners, such as staff from OBD, certification, warranty, and PEMS testing, is vital for successful execution of a heavy-duty testing program.

Since the program’s inception in 2007, CARB, in partnership with the USEPA, has issued test orders for 125 engine families to be tested directly by the engine manufacturers. As of December 2021, 623 individual engines/vehicles have been tested as part of this program.

Monitoring Methodologies and Technologies

Engine emission monitoring systems in vehicles employ a variety of monitoring methodologies and technologies to ensure compliance with emission standards. These include:

1. On-Board Diagnostics (OBD): OBD systems continuously monitor the performance of various engine and emission control components, detecting and reporting any malfunctions that could lead to increased emissions.

2. Portable Emission Measurement Systems (PEMS): PEMS are used for in-use testing of heavy-duty vehicles, allowing for the measurement of emissions under real-world driving conditions.

3. Remote Sensing: Remote sensing technology can be used to measure emissions from individual vehicles as they pass by, providing a large-scale, automated approach to emission monitoring.

4. Laboratory-Based Testing: Manufacturers must conduct extensive laboratory-based testing to demonstrate that their vehicles and engines meet the required emission standards.

5. Manufacturer Self-Testing (MST): Heavy-duty engine manufacturers must conduct MST to ensure that OBD systems on in-use aged engines can detect faults before emissions exceed malfunction criteria.

6. Durability Demonstration Engine (DDE) Testing: Prior to receiving certification for an engine family, manufacturers must conduct DDE testing on at least one engine family to demonstrate the durability of the emission control system.

Conclusion

Engine emission monitoring systems in vehicles are a critical component of the effort to control and reduce air pollution from road traffic. The certification and compliance process, as well as the various monitoring methodologies and technologies employed, ensure that vehicles and engines meet stringent emission standards throughout their useful life. Collaboration between regulatory agencies, manufacturers, and research partners is essential for the successful implementation and continuous improvement of these systems.

References:

• Mobile Source Certification and Compliance Program 2022 Report. (2022-12-31). Retrieved from https://ww2.arb.ca.gov/sites/default/files/2022-12/MOBILE%20SOURCE%20CERTIFICATION%20AND%20COMPLIANCE%20PROGRAM%202022%20Report.pdf
• Real-world automotive emissions: Monitoring methodologies, and control measures. (2021-03-01). Retrieved from https://www.sciencedirect.com/science/article/abs/pii/S1364032120309084
• Large-scale automated emission measurement of individual vehicles using remote sensing. (2024-04-23). Retrieved from https://amt.copernicus.org/articles/17/2481/2024/amt-17-2481-2024.pdf