Heavy-duty on-road diesel vehicles are among the top sources of oxides of nitrogen (NOx) emissions in the South Coast Air Basin. The Cummins Westport Inc. ISB6.7 G is a low-emission 6.7-liter natural gas engine that can support school bus, shuttle bus, transit bus, medium-duty truck, and yard tractor applications as an alternative to diesel engines. The ISB6.7 G is certified to emit 50 percent lower NOx emissions than the current standard for diesel engines.
For 2018 model year natural gas engines, heavy-duty on-board diagnostics are required to monitor engine system or component parameters to identify malfunctions or deterioration that can cause increases in emissions. This project further developed the ISB6.7 G with the addition of heavy-duty on-board diagnostics, conducted vehicle integration and demonstration, and laid the foundation for future work to reduce NOx emissions by an additional 80 percent. Heavy-duty on-board diagnostics protect the environment from excess emissions resulting from engine issues that may arise during the useful lives, which will assist regions like the South Coast Air Basin in attaining and maintaining ambient air quality standards.
The project culminated with an engine (B6.7N), receiving certification to the United States Environmental Protection Agency’s current criteria pollutant and greenhouse gas emission standards, the California Air Resources Board’s Optional Low NOx Standard of 0.10 grams per brake horsepower-hour, and heavy-duty on-board diagnostics compliance. The project team demonstrated 11 vehicles—including delivery trucks, shuttle buses, and yard tractors—for more than six months, and they accumulated more than 357,000 miles. The University of California, Riverside, conducted chassis dynamometer testing to evaluate real-world emissions. The B6.7N began commercial production in January 2018 and was offered in the market segments of school buses and yard tractors.
