Improved catalysers could reduce nitrogen oxides in diesel exhausts
18 September 2014
It is fully doable to reduce environmentally harmful nitrogen oxide emissions from diesel engines by improving the aftertreatment system in catalysers. This is demonstrated in a thesis by Soma Tayamon at Uppsala University.
Today’s transports are to a large extent propelled by diesel engines which have low fuel consumption and are relatively efficient. These engines are used in lorries, busses, boats as well as in cars.
However, diesel engines still produce large quantities of harmful particles, soot, carbon dioxide, carbon monoxide and nitrogen oxides. These emissions have a negative effect on the environment, and among other things cause acidification of lakes and forests. Nitrogen oxides are also cause harm to humans and animals by affecting our respiratory systems.
Decreasing these emissions is necessary for sustainable environmental development and for our survival. Reducing nitrogen oxides is accomplished through engine optimization, but also by installing external catalysers. Such aftertreatment systems work by injecting ammonia (in the form of urea) into the catalyser, where it reacts with the nitrogen oxides. The end result is water, unreacted nitrogen oxide and/or ammonia. Today excess ammonia is reduced by oxidation. This process produces nitrous oxide, which directly affects global warming. Nitrous oxide is a 200 times stronger greenhouse gas than carbon dioxide.
In her thesis, Soma Tayamon has developed and used mathematical models to reduce the amount of nitrogen oxides from diesel engines. Her findings show that it is possible to acheive a reduction by optimizing the amount of urea injected into the system. The models are relatively simple, which should contribute to keeping down the cost of development of such systems.
Soma Tayamon also shows that an even larger reduction of nitrogen oxides can be acheived by increasing the exhaust temperature.
‘The results indicate that it is possible to develop good regulatory systems for nitrogen oxide reduction in these aftertreatment systems, at a relatively low cost’, she says.
She now hopes that her model will be put to use in the development of more environmentally friendly transports, to avoid the process of oxidizing excess ammonia.
The study has been conducted in collaboration with Scania.