A predictive control approach to diesel Selective Catalytic Reduction

Reduction of oxides of nitrogen (NOx) emitted from diesel exhaust systems is a current problem due to increased stringency in worldwide emissions legislation. One of the most successful approaches to reduce tailpipe NOx is to reduce NOx by ammonia over a catalyst, known as Selective Catalytic Reduction (SCR). Control of the ammonia injection in such systems is typically a map-based approach, often augmented by feedback from NOx sensors to account for mechanical variation and ageing. We show that a predictive control approach to this system yields several compelling improvements over such industry standard controllers during a representative test cycle. These include better NOx conversion performance whilst simultaneously minimising the quantity of ammonia released to the environment, along with reduced design effort.