Laser-spectroscopic analysis of burners and incinerators

The second type of emissions on a large scale are the flue gases from external combustion processes, and there are differences in opinion as to whether these are more serious than the emissions from the internal combustion sources (see Section 29.1). External combustion is encountered in any type of boiler, using premixed fuel flames (e.g. domestic gas boilers, industrial-scale boilers, gas- and oil-fired power generation) and in incinerators (e.g. waste incinerators). In both cases, one of the major concerns is related to the emission of greenhouse gases, like CO2, and environmentally harmful pollutants, like oxides of nitrogen. In addition, people have also become 

Whatever the process of external combustion, it has been shown that the amount of harmfid emission can be minimized by carefid control of the fuel mixtures and the burning conditions (e.g. the combustion temperature). Flames near the sooting limit (i.e. those from fuel-rich mixtures whose conditions just define the onset of the release elemental carbon aerosol) exhibit a large number of intermediate species, such as H2 and CO, rather than H2O and CO2. Furthermore, depending on the fuel, incomplete combustion will lead to the likely production of a variety of hydrocarbons or aromatic compounds. 

Therefore, the analysis of the nature and behaviour of combustion products in hydrocarbon-rich flames, for example, is important, since the findings help to understand the detailed processes in flame formation and efficient combustion. In this section we will discuss selected examples related to the aforementioned external combustion, and the most influential measurement quantities, namely flame temperature and the detection of molecular intermediates. 

Monitoring low-pressure flames using cavity ring-down spectroscopy 

Combustion diagnostics today relies on a number of analytical and optical techniques, depending on the species under investigation. For the detection of molecular components with more than two or three atoms, mass spectrometry is usually applied with different ionization techniques. For smaller reactive intermediates, optical techniques are the methods of choice because of their non-invasive natme. One of the most widespread experimental approaches to combustion chemistry is through the measurement of the spatial concentration profiles of the intermediate products of combustion the results from such measurements are then compared with model calculations. 

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