SOLID SCR ^® : Demonstrating an Improved Approach to NOx Reduction via a Solid Reductant 2011-01-2207

Stringent global emissions legislation demands effective NOx reduction strategies, particularly for the aftertreatment, and current typical liquid urea SCR systems achieve efficiencies greater than 90% [1]. However, with such high-performing systems comes the trade-off of requiring a tank of reductant (urea water solution) to be filled regularly, usually as soon as the fuel fillings or as far as oil changes. Advantages of solid reductants, particularly ammonium carbamate, include greater ammonia densities, enabling the reductant refill interval to be extended several multiples versus a given reductant volume of urea, or diesel exhaust fluid (DEF) [2]. An additional advantage is direct gaseous ammonia dosing, enabling reductant injection at lower exhaust temperatures to widen its operational coverage achieving greater emissions reduction potential [3], as well as eliminating deposits, reducing mixing lengths, and avoiding freeze/thaw risks and investments.

Smaller diesel engine applications (2 - 3L) have been demonstrated with such solid reductant, but its scalability to larger applications is uncertain, demanding much greater reductant dosing rates, which in turn necessitates greater ammonia production and release rates [4, 5]. A Dodge Ram with a 5.9L Cummins engine is applied in this demonstration, illustrating scaling and transient response capability for larger truck applications. The Solid SCR (SSCR) system design and its initial capability are described, as well as the proposed catalyst layout and dosing integration. Emissions and temperatures are measured, illustrating feasibility to significantly reduce NOx emissions, even with the relatively high engine-out NOx emissions and overall little optimization effort. Emissions performance is compared across many operational points of the engine, as well as within transient cycles, completed using a chassis dynamometer, applying the FTP72, comparing cold and warm start response, and US06 transient drive cycles.