Engine manufacturers take note as EPA revisits NOx emissions threshold


Through its just-announced Cleaner Trucks Initiative (CTI), the U.S. Environmental Protection Agency aims to further decrease nitrogen oxide (NOx) emissions from on-highway heavy-duty trucks and update a current engine exhaust standard in an early-2020 rulemaking. Set in 2001, the standard culminated in 2010 with a 0.2-gram brake-horsepower-hour NOx threshold for which engine manufacturers deployed selective catalytic reduction (SCR) equipment and urea-based diesel exhaust fluid (DEF). SCR injects DEF into the engine exhaust stream; the ensuing chemical reaction converts NOx into nitrogen, water vapor and traces of carbon dioxide.

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