Urea selective catalytic reduction

Testing by Ford researchers of a small-diesel emissions-control system proved successful in meeting ULEV emissions standards.

Oxides of nitrogen (NOx) and particulate matter (PM) emissions are of primary concern for diesel vehicles to meet future emissions standards. Diesel vehicles potentially have a 40% better fuel economy with 20% lower carbon dioxide (CO₂) emissions than current gasoline vehicles. However, removal of NOx from lean exhaust gas is difficult without reducing compounds in the exhaust stream.

Selective catalytic reduction (SCR) with ammonia has been used extensively for NOx control in stationary sources. The high selectivity of ammonia for reaction with NOx in high O₂ environments makes SCR attractive for use on light-duty diesel vehicles. Compared to ammonia, aqueous urea is much safer for use on board a vehicle.