Improved SCR Systems for Heavy Duty Applications

This paper describes the function and application of the preoxidation, hydrolysis and SCR catalysts individually and as a combined system for urea SCR both in model gas and engine bench tests. Using the basic system and a non-optimized urea injection strategy 45% NO_x conversion was achieved in the ESC engine test. Adding a preoxidation catalyst significantly improved the NO_x conversion in the low temperature region of the engine mapping. NO_x conversions over 75% can be achieved in the ESC test using this improved system. With a 50% reduced SCR catalyst volume still a NO_x conversion of over 65% could be achieved. Tests after 200 hours engine aging show that the activity of the system is stable.