To meet 2010 emissions standards set out by the United States Environmental Protection Agency (EPA), diesel engines apply advanced engine technologies, including cooled exhaust gas recirculation (EGR) and exhaust aftertreatment components such as diesel particulate filters (DPF) and selective catalytic reduction (SCR).
These aftertreatment components are not required for Cummins Westport natural gas engines.
The ISL G met EPA 2010 emissions standards three years ahead of schedule when it was introduced in 2007. Both the ISL G and the ISX12 G engines meet current US EPA and California Air Resources Board (CARB) emissions standards, and 2014 EPA greenhouse gas and US Department of Transportation fuel-economay regulations. They use spark ignited cooled stoichiometric EGR combustion which allows for the use of a Three-Way Catalyst (TWC). TWCs are effective, simple, passive aftertreatment devices packaged as part of the muffler that provide consistent emissions control performance and are maintenance-free.
The Cummins Westport ISL G also meets Euro EEV emissions standards.
The Cummins Westport B Gas Plus and C Gas Plus engines, available outside of North America, use lean burn spark ignited technology and an oxidation catalyst to meet Euro V/EEV and Euro III/IV emission standards respectively.