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Near-Zero Natural Gas Engine Exceeds EPA Standard, UC Report Says

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February 13, 2017

Heavy-duty vehicles equipped with the 8.9-liter Cummins Westport ISL G Near Zero natural gas engine exceeded EPA certification standards during a full range of duty cycles, according to a new report by the University of California, Riverside’s College of Engineering—Center for Environmental Research and Technology (CE-CERT). The CE-CERT study shows that the recently introduced ultralow-NOx natural gas engines run 90 percent cleaner than the 2010 EPA NOx standard of 0.2 grams per brake horsepower-hour (g/bhp-hr).

In comparison, previously released CE-CERT data found that heavy-duty diesel trucks emitted NOx at levels as much as five times higher than their certification standards in the same duty cycles used to test the ISL G Near Zero natural gas engine.

The new report concludes that the ISL G Near Zero NOx natural gas engine performs with NOx emissions even lower than the optional 0.02 g/bhp-hr emission certification standard, averaging between 0.014 and 0.002 g/bhp-hr. It also says that methane emissions were “notably lower” compared with those of previous versions of the same engine, probably due to the closed-crankcase ventilation system. Because the study demonstrates the engine’s near-zero-emission performance, CE-CERT expects that NGVs with this engine could play an important role in reducing NOx emissions in the South Coast Air Basin in the immediate future.

The near-zero-NOx engine was evaluated during typical in-use conditions for heavy-duty vehicles operating in the South Coast Air Basin, including city and central business district driving conditions, as well as port and refuse cycles. Researchers found not only that the ISL G Near Zero natural gas engine produces NOx emissions below its certification standard, but also that emissions decrease as the duty cycles decrease (for example, in low-speed, stop-and-go, and idling traffic patterns).

“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,” said Dr. Kent Johnson, author of the report. “These near-zero-emission natural gas vehicles are especially effective in applications that require low speeds, such as short-haul goods movement.”

The CEC, the South Coast AQMD, and SoCalGas provided funding for the emissions testing work.

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