Production of Ammonia from Diesel Exhaust Fluid for Low Temperature Diesel Emissions Control

Randal  Goffe, PACCAR Technical Center

Title: Production of Ammonia from Diesel Exhaust Fluid for Low Temperature Diesel Emissions Control

Authors: Randal A. Goffe¹, Andy Yiu², Shehab Gherfal², Emad Al-Ibrahim², Omar Altoaimi², Phu Phan², Ziwen Guo², Yifei Guan², Alberto Aliseda²

¹PACCAR Technical Center, 12479 Farm to Market Road, Mount Vernon, WA 98273, USA,

²Department of Mechanical Engineering, MS 352600, University of Washington, Seattle, WA 98195-2600

Over 60% of hydrocarbons and nitrogen oxides (NOx) in heavy duty exhaust are emitted in an untreated state during the first 60 seconds on cold start as a result of catalysts not being active. The fundamental challenge addressed in this paper is the ability to dose Diesel Exhaust Fluid (DEF) during portions of the drive cycle where the exhaust temperature is too low for ammonia thermolysis to occur.  This research project uses electro-oxidation to active NH₃ formation that can replace thermolysis to address low temperature emissions challenges.  There are two features that distinguish this work from previous work on the electro-oxidation of urea to form ammonia: (i) DEF effectively contains no ionic electrolyte in solution; and (ii) the flow regime under which dosing is carried out (1.2 -168 mL/min) will severely limit the residence time for urea molecules at the electrode interface involved in the charge transfer reaction.  To address this challenge, a cylindrical electrochemical flow-cell was designed, built and used to investigate the impact of the following parameters on the electro-oxidative production of NH₃ gas at room temperature: flow rate (between 27 – 42 mL/min); steady state voltage (0 – 5V); pulsed voltage; electrode material (stainless steel vs nickel); flow-cell geometry (both length and the separation distance between electrodes); and prolonged application of steady state voltage to investigate formation of potential secondary product(s).  Finally, a computational fluid dynamics simulation was used to determine the relative efficiency of the electro-oxidation process for gaseous NH₃ production at room temperature, providing a validated computational tool that can be used in design and optimization of electro-chemical urea-to-ammonia production. This has the potential to offer a solution to the low temperature emissions challenge for heavy duty diesel trucks.