Understanding how electric fields make flames cleaner could improve power stations

Burning hydrocarbons is a more complex process than it seems. If combustion is complete, then the products are carbon dioxide and water vapour, which may be undesirable in the atmosphere but are at least well understood and non-toxic. However, if the hydrocarbon is not completely consumed in the flame, then other products may form. These include carbon monoxide, oxides of nitrogen and soot, all of which are hazardous to health.

One technique that is used in power stations to ensure the combustion is clean is to apply an electrical field across the flame; this has been found to reduce the production of pollutants, although the mechanism for this is not clear. This led researchers at KAUST’s clean combustion research centre to embark on a study of exactly what compounds are formed when methane burns in air.

The team, led by Aamir Farooq, set up a device called a McKenna burner, which produces a flat flame from a well-mixed stream of methane, oxygen and argon; and above this they set a specially-designed molecular beam mass spectrometer, with which they hoped to detect positively-charged particles within the combustion products. There are much less of these than there are of neutral atoms and molecules, but tend to be reactive and so are undesirable.