The report, authored by Dr. Kent Johnson (PI), College of Engineering-Center for Environmental Research and Technology (CE-CERT) at the University of California Riverside, evaluated the Cummins Westport ISL G near-zero (NZ) engine emissions during typical in-use conditions.

The testing for the report was done on duty cycles that represent operations in the South Coast Air Basin. These cycles included the urban dynamometer driving schedule (i.e., city driving conditions); port cycles (including near dock, local and regional); refuse cycles; and central business district cycles. Refuse and central business district duty cycles show similar in-use emissions performance to the local and near-dock port cycles, while urban dynamometer driving schedule (UDDS) represents the standard cycle the EPA uses for vehicle and fuel emissions testing.

The engine was certified in the fall of 2016 by the EPA and the California Air Resources Board (CARB) to 0.02 g/bhp-hr, which is 90% cleaner than EPA’s current NO_x emission standard and 90% cleaner than the cleanest available diesel engine.

The report concludes that ISL G near-zero natural gas engines perform with NO_x emissions below the optional 0.02 g/bhp-hr emission target and averaged between 0.014 and 0.002 g/bhp-hr. The report also found that methane emissions were notably lower than previous versions of the same engine, likely due to the closed crankcase ventilation system.

Cycle averaged NOx emissions for the ISL G NZ 8.9 liter equipped vehicle. Source: “Ultra-Low NOx Natural Gas Vehicle Evaluation ISL G NZ” Click to enlarge.

The report concludes that ISL G near-zero natural gas engines perform with NOx emissions below their certification level and that emissions decrease as the duty cycles decrease, meaning that in lower speed scenarios, such as stop-and-go traffic commonly found throughout the South Coast region, the emissions decreased.

When comparing the data of the cleanest available heavy-duty diesel vehicles versus the cleanest available heavy-duty natural vehicles, it is clear that natural gas vehicles provide unmatched reductions of smog-forming emissions. These near-zero emission natural gas vehicles are especially effective in applications that require low speeds, such as short-haul goods movement.

—Dr. Kent Johnson, author of the report

Diesel-fueled medium- and heavy-duty vehicles are the number one source of smog-forming emissions of nitrogen oxides (NO_x) in almost every single metropolitan region in the country. NO_x emissions lead to the formation of ozone and small particulate matter (PM_2.5), each of which contributes to significant health impacts, including asthma and heart disease. In areas with the most severe air quality problems—such as southern and central California—achieving healthy air quality will require a transition of heavy-duty vehicles to ones that emit zero or near-zero emissions.

The Environmental Protection Agency (EPA) has systematically reduced the allowable emissions of NO_x from new heavy-duty engines since 1994 through application of progressively lower federal standards. With the 2010 NO_x certification limit of 0.2g/bhp-hr, NO_x emissions dropped 90% compared to 2006 and older heavy-duty vehicles. Additional NO_x reductions of another 90% are desired for the South Coast Air Basin to meet its 2023 NO_x inventory requirements.

A separate report published in 2013 by the same author evaluated the in-use emissions of heavy-duty diesel vehicles with modern emission control systems in the same duty cycles found that the diesel engines performed with up to 5 times higher NO_x emissions on average than their EPA certification standard and emissions increased as the duty cycle decreased. A report released in October 2016 by the California Air Resources Board (CARB) reported similar findings—that in-use NO_x emissions from heavy-duty diesel trucks were 1.7 to 9 times higher than the NO_x certification standard. As the UCR and CARB reports found, these high in-use NO_x emissions occurred primarily during low speed operations, which is a concern in California where low speed operations are common, such as near port operations.

Resources

• Ultra-Low NO_x Natural Gas Vehicle Evaluation ISL G NZ