The generation and chemistry of pollutants from combustion sources

The brown cloud of smog that hangs over many of the world's major cities arises from the pollutants emerging from the combustion processes taking place in cars, aeroplanes and power plant. These compounds are generated within an engine or furnace and then expelled into the atmosphere, where they combine with other elements such as water vapour and other atmospheric gases to produce brown gaseous smog.

Although it is possible to filter out pollutants from the exhaust gases by cleaning, this is an expensive option involving lots of hardware, chemicals and disposal problems. Far better to prevent the noxious compounds forming in the first instance. With this aim in mind, Dr Nondas Mastorakos is examining how pollutants are generated inside combustion engines.

He explains: "The exhaust gases from combustion processes typically contain a mixture of pollutants, both of the NOx type and other volatile organic compounds (VOCs). The chemical processes that go on are very complex, so the first step is to simplify the processes so that they can be modelled using a CFD approach. We can then analyse what is going on in the combustion chambers to cause the pollutants to form. Engine designers can use our results to improve the way engines operate and thus decrease pollutant generation directly.

Small changes in design can make a large difference. Once the pollutants are generated, there is nothing to be done about them. The modelling techniques that we apply to combustion are also useful for atmospheric scientists, who must predict how the pollutants will disperse and evolve and can then warn people where and when pollution levels are likely to get critical. This is very important for people living in the vicinity of, say, large-scale power plant."

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