On-board Ammonia Generation using Reformate
Mark Hemingway, Delphi
A diesel exhaust with a Lean NOx Trap (LNT) followed by a Selective Catalytic Reduction (SCR) catalyst is used to reduce NOx. Initially, exhaust is channel into the LNT where the NOx is selectively stored by the trap. When LNT regeneration is necessary, a 3-way valve bypasses the LNT while the stored NOx is converted to ammonia through injection of a hydrogen/carbon monoxide mixture known as reformate. The SCR is able to continue NOx reduction during this regeneration by utilizing stored ammonia from a previous cycle. Once the LNT regeneration is complete, exhaust flow resumes through the LNT pushing the ammonia into the SCR. NOx conversion exceeding 85% have been achieved over a wide range of temperatures and exhaust flows.