Southwest Research Institute (SwRI) demonstrated the effectiveness of its patented and award-winning CAT-DEF technology during the WCX World Congress Experience in Detroit in April. CAT-DEF—Catalyzed Diesel Exhaust Fluid—is an SwRI-developed catalyst- and surfactant-modified diesel exhaust fluid (DEF) solution.
The internally funded advancement successfully reduced heavy-duty diesel engine nitrogen oxide (NOx) emissions to meet the California Air Resources Board (CARB) 2027 standards.
Today’s diesel engines use selective catalytic reduction (SCR) to abate NOx emissions. DEF—a 32.5 wt. % urea-water solution—is injected into the exhaust stream and ideally decomposes to form ammonia, which reacts with NOx on the SCR catalyst to form N2 and H2O.
Although the current process is relatively efficient at temperatures greater than 250 °C, at temperatures below 250 °C, urea-derived deposits form within the aftertreatment system. These deposits severely limit low-temperature NOx conversion and increase fuel consumption as high-temperature engine operations are required to remove the deposits.
SwRI’s novel technology decreases NOx and carbon dioxide emissions for diesel engines by significantly reducing undesirable deposit formation in exhaust systems.
Previous work has sufficiently demonstrated that the addition of surfactant and a urea/isocyanic acid (HNCO) decomposition catalyst to UWS can significantly decrease deposit formation within an aftertreatment system. The objective of this work was to further optimize the modified UWS formulation by investigating different types and concentrations of surfactants and titanium-based urea/HNCO catalyst.
Because there is a correlation between surface tension and water evaporation, it was theorized that minimizing the surface tension of UWS would result in decreased deposit formation. Eighteen surfactants underwent a surface tension evaluation study to determine what type and concentration of surfactant is required to maximize surface tension reduction. Surfactant concentration was able to be reduced by 94% while maintaining surface tension reduction of over 50%.
Six distinct catalysts were evaluated for urea decomposition activity utilizing SwRI’s Universal Synthetic Gas Reactor (USGR) to measure CO2 and NH3 evolution from solid mixtures of catalyst and urea. At a minimum, CO2 production increased by 298% when a titanium-based catalyst was present with urea with the highest performing catalyst increasing CO2 production by 540% compared to pure urea. Deposit generation evaluations were then conducted utilizing the optimized catalyst and surfactant to determine the impact of catalyst and surfactant in UWS on deposit formation.
Tailpipe NOx and PM emissions of the optimized UWS were compared against a conventional UWS on a 15 L low NOx engine. Both formulations met the CARB 2027 PM standards, but only the modified UWS met the CARB 2027 low NOX 0.02 g/hp-hr standard. The NOX composite FTP of the modified UWS and conventional UWS were 0.019 g/hp-hr NOX and 0.051 g/hp-hr respectively.
Using internal funding, SwRI engineers studied the technology’s effectiveness for reducing NOx emissions at the new standards set by CARB through a head-to-head comparison of diesel engines operated with and without CAT-DEF.
We demonstrated that using CAT-DEF allowed an engine to meet or exceed upcoming CARB 2027 NOx requirements, while using standard DEF did not meet the new standard. Our findings show that DEF can now be utilized over a much broader range of engine operation, decreasing overall NOx emissions.
SwRI’s CAT-DEF technology is currently available to license. The novel innovation is backward-compatible and can be used in existing engines as a deposit reduction solution. For future applications, which will be required to meet more stringent regulatory requirements, the CAT-DEF solution competes with higher-cost engine hardware modifications currently being considered by the diesel engine industry and DEF manufacturers.
Wheeler, S., Seuser, G., Zavala, B., and Henry, C. (2022) “Optimization of Surfactant and Catalyst Modified Urea-Water Solution Formulation for Deposit Reduction in SCR Aftertreatment Systems,” SAE Technical Paper 2022-01-0541