A new study on ultra-low emission natural gas heavy-duty engines found that the new Cummins-Westport 11.9-liter engine achieved California’s lowest smog-forming emissions standard, and maintained those emissions during all types of driving.

Cycle averaged NO_x emissions for the ISX12N 400 equipped truck. Source: UCR.

The study, prepared by researchers at the University of California, Riverside Bourns College of Engineering Center for Environmental Research and Technology (CE-CERT) was sponsored in part by the California Energy Commission (Commission), the South Coast Air Quality Management District (SCAQMD), Southern California Gas Company (SoCalGas) and Clean Energy.

The results underscore the importance of the near-zero truck engines for cleaning the air. Most heavy-duty vehicles on roads today are diesel-powered and represent one of the largest sources of NO_x emissions and fuel consumption in North America. By contrast, the new near-zero emissions 12-liter engine, made by Cummins Westport, is the only heavy-duty engine in the category to not only meet, but exceed, the California Air Resources Board’s cleanest optional low-NO_x standard of 0.02 g/bhp-hr.

The ISX12N 400 NG engine met and exceeded the target NO_x emissions of 0.02 g/bhp-hr and maintained those emissions during in-use duty cycles found in the South Coast Air Basin. The other gaseous and particulate matter were below the standards and/or similar to previous levels. Particle number, ammonia emissions, and methane emissions were higher than current 2010 certified diesel engines on similar drive cycles. These higher emissions should be considered for health and environmental impact studies. In general, it is expected NG vehicles could play a significant role in achieving the NO_x inventory goals given the near zero emission factors demonstrated.

—“ Ultra-Low NO_x Near-Zero Natural Gas Vehicle Evaluation ISX12N 400”

Kent Johnson, associate research engineer at CE-CERT, led the tests on the near-zero emissions natural gas engine. The evaluation included regulated and non-regulated emissions, ultrafine particles, global warming potential, and fuel economy.

Testing was performed on a dynamometer that simulated various types of driving conditions, from pulling into a loading dock to regional hauling. Johnson performed similar testing on an 8.9-liter near-zero natural gas engine last year. Those results found the smaller engine had even lower emissions than California standards will require in the near future—in some driving conditions, almost zero.

The first study was a smaller engine intended for use in school buses and trash trucks, which are only about 30 percent of the heavy-duty inventory. The new engine is for drayage and movement of goods, or 70 percent of the inventory. This engine technology is good not only for the smaller work-force applications of transit and refuse, but also for hauling loads around Southern California.

—Kent Johnson

About 41% of the state’s greenhouse gas (GHG) emissions come from transportation. When near-zero emission natural gas trucks are fueled by renewable natural gas, GHG emissions can be reduced by at least 80%. Already, close to 70% of natural gas fleets in California are fueled with renewable natural gas. This number is expected to continue to climb.