The Paul Scherrer Institute (PSI) in Switzerland has developed a new type of catalytic conversion system that filters nearly all nitrogen oxides out of diesel exhaust gases using a refined control technology. The process requires a non-toxic urea solution, which can be incorporated into future diesel engine vehicles via a separate refillable tank.
Diesel engines are looked upon as relatively economic and environment-friendly because they have a better fuel efficiency than petrol engines. But burning diesel also produces nitrogen oxides, which enhance the build-up of hazardous ozone during periods of high solar radiation.
“In the end, diesel engines today are the main cause for high ozone values during summer”, said Oliver Kroecher, Exhaust Gas Aftertreatment Group Manager at PSI. By 2005, exhaust gas standards for diesel engines are to be tightened throughout Europe.
To comply with the new threshold values, engine manufacturers are now focussing on SCR (Selective Catalytic Reduction) technology. Here, nitrogen oxides are transformed into nitrogen and water vapour using a catalytic converter and by adding a urea solution.
PSI scientists have now developed a practicable SCR catalytic converter that disposes over 90% of the nitrogen oxides in exhaust gases.
“Our converter has minimal dimensions and can prevent the escape of ammonia generated during the reaction, thanks to an ingenious regulating system,” said Kroecher.
To optimise the disposal of nitrogen oxide, the amount of urea added adapts continuously to different drive phases. “Our regulator system all but anticipates the engine activity and can therefore react fast enough to changes”, added Kroecher.
“In the long run, we’re working on zero-emission concepts, in order to develop combustion types creating no other pollutants than carbon dioxide,” said Kroecher.