Reducing no_x emissions from an engine while maximizing fuel economy

摘要

Exhaust gas recirculation and selective catalytic reduction with urea or other NOx- reducing reagent are employed to enable good fuel economy and low emissions from diesel and lean-burn gasoline engines. EGR is operated at low-load, as well as when problems are experienced with reagent supply or the SCR unit. The SCR is run at its optimum operating conditions of normal to high load, supplanting the need for EGR. The net effect is a circumvention of the known tradeoff between NOx and poor fuel economy. The novel application of SCR and EGR in combination will provide engines that meet low emissions requirements with existing technology.