Abstract
KEYWORDS - urea, NOx, light-duty diesel, Tier 2, LEV II
Emission regulations for diesel vehicles in the U.S. are very stringent, especially for particulate matter (PM) and nitrogen oxides (NOx). The two leading technologies for high NOx reduction on diesel vehicles are Selective Catalytic Reduction (SCR) and Lean NOx Traps (LNT). LNTs have the advantage of requiring no new infrastructure, and do not pose any new customer compliance issues. However, Urea SCR has several technical advantages, including a high and durable NOx conversion in a wider temperature window, a lower equivalent fuel penalty, and lower system and operating costs. In this paper, high efficiency NOx and PM control are discussed. Mathematical simulations are used to come to sound, technical judgment for business decisions when all desired experimental data are not available.
Through application of advanced SCR coating on cordierite channel flow and high porosity filter substrates, Ford Motor Company has developed several innovative emission control systems for diesel vehicles. The focus on diesel engine emissions was a direct result of the improved volumetric fuel economy (up to 50%) and lower CO2 emissions (up to 25%) over comparable gasoline engines shown in Europe. SCR with aqueous urea was chosen as the primary emission approach for the NOx emission control component. Challenging the standard approach, the program applied SCR washcoating to high porosity filters (SCRF) to reduce the complexity of the exhaust layout for U.S. diesel applications. Migration of the SCR coating to the filter also increased the importance of an overall high efficiency diesel oxidation catalyst (DOC) package to provide HC/CO control during standard driving and the thermal energy to conduct active filter regenerations with good control to maintain SCR function. The program expected to demonstrate more than 90% reduction in PM and NOx emissions on a light-duty truck with aging on the road up to 50k mi. Finally, new system concepts were studied to further enhance the conversion of NOx using SCRFs.