Nitrous oxide emissions from a medium-duty diesel truck exhaust system

Abstract

Starting in 2010, medium-duty diesel trucks in the USA were introduced with aftertreatment systems that contained precious metal oxidation catalysts, soot filters, and selective catalytic reduction (SCR) systems for control of nitrogen oxides (NO, NO2). While modern diesel aftertreatment systems have high performance for meeting hydrocarbons, carbon monoxide (CO), NOx, and particulate matter, there is some concern over emission of nitrous oxide (N2O) that can be formed within the exhaust system. N2O has an atmospheric lifetime of approximately 114 years and is 298 times more effective than CO2 at trapping heat in the atmosphere. In this study, the sources of N2O were compared in the laboratory flow reactor and at the system level on diesel trucks. The interactions of HC with NOx on the DOC and NOx with NH3 within the SCR catalyst were the predominant mechanisms for N2O formation. The composite N2O mass emission was calculated to be approximately 43 mg/mi, resulting in an equivalent CO2 penalty of about 2%, similar to the 1% to 3% penalty estimated for the global light-duty vehicle fleet.