When used with injecting urea-water solution forming ammonia, Selective Catalytic Reduction (SCR) catalyst is a proven technology for greatly reducing tailpipe emission of nitrogen oxides (NOx) from Diesel engines. However, one major shortcoming of an SCR-based system is forming damaging urea deposits (crystals) in low temperature exhaust operations, especially exacerbated during lower exhaust temperature operations or higher injection rates. Deposits reduce SCR efficiency, damage exhaust components, and induce high concentration ammonia slips.
We describe here an Electrically Heated Mixer (EHM™) demonstrated on a Diesel engine markedly inhibiting deposit formation in urea SCR systems, both in low (near 200 °C) and higher exhaust temperature operations and for both low and high urea injection rates in various, realistic engine operations. Engine test runs were conducted in long durations, 10 to 20 hours each, for a total of nearly 100 hours. In nearly all operation modes, EHM maintained deposits below 1% of the total injected DEF mass; most were below 0.5%, practically non-existent, including when in higher injection rates. To further gain confidence in and validate the deposit-free outcome due to the EHM impact, CFD simulations of the same exhaust conditions were performed, which further confirmed EHM’s capability in substantially inhibiting urea deposits observed on the engine.
Along with prior publications, this work forms a trilogy demonstrating EHM enabling rapid heat-up making available several-fold lower tailpipe NOx, meeting ultra-stringent NOx regulations (e.g., Californian/EPA 2027 meeting 0.02 gr/bhp.hr), reducing tailpipe NOx in various regulatory and non-regulatory cycles [Frontier, 2022] while enabling highly efficient NOx conversion in low-load cycles and in fast transients [Topics in Catalysis, 2022, COMVEC, 2022].