The carbon content of fly ash is the major determinant of combustion efficiency for coal-fired boilers.  Carbon content is presently measured offline by a Loss-On-Ignition (LOI) test.  The LOI test is typically performed by collecting a sample of fly ash from the boiler, weighing the sample, heating the sample to a temperature sufficient to drive moisture from the sample, reweighing the sample to determine the moisture content in the sample when collected, reheating the sample in an air stream to a temperature sufficient to oxidize the carbon in the sample to carbon dioxide, and weighing the remaining sample to determine the carbon content by the difference in weight between the sample prior to oxidation of the carbon and after the oxidation step. 
There are a number of disadvantages associated with the typical LOI test.  One disadvantage is the tedious and time consuming steps necessary to treat the sample to provide the relevant dam.  Furthermore, the LOI test may introduce inaccuracies into the data if mineral matte, such as limestone or other substances, are present which exhibit weight changes upon heating in addition to the changes caused by carbon oxidation.