Exhausting exercise

A new exhaust treatment system to reduce nitrous oxide (NOx) emissions will improve fuel efficiency in diesel engines, according to its UK developer.

The Sigma system, designed by engineers at IMI Vision, injects ammonia gas directly into the engine’s exhaust, instead of using a liquid urea spray as in existing systems.

Harmless vapour Current ‘wet’ Selective Catalytic Reduction (SCR) systems spray AdBlue - a water and urea solution - into the exhaust system, where the urea is converted into ammonia. This reacts with NOx in the catalytic converter to produce harmless nitrogen and water vapour.

When urea is added to the exhaust pipe the water evaporates and the remaining solid pellets of AdBlue melt, leaving equal amounts of ammonia and isocyanic acid. The acid is only converted to ammonia once it enters the converter, a process which uses up to 30 per cent of the converter’s capacity.