| Heat release |
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A key parameter governing the appearance of self-excited combustion oscillations is unsteady heat-release from the flame, i.e. temporal fluctuation of the combustion process. In many cases, modulated infeed of the fuel-air mixture to the combustion zone is the cause of fluctuating combustion power. The scope for quantifying these fluctuations is a key prerequisite for the analysis of any unstable combustion characteristics which may be present, and for the classification of these as self-excited or externally excited combustion instability.
Combustion of hydrocarbon in oxygen or air does not take place in a single reaction step, but is instead the outcome of a multitude of intermediate reactions (in some cases as many as several hundred), during which a large number of intermediate products are created. Many of these intermediate reactions occur very rapidly and the associated intermediate products are correspondingly short-lived, e.g. the OH radical, with a lifetime of less than 600 ns. IfTA offers spatial-integral measurement of OH radiation (total combustion power) as well as 1-D and 2-D measurements of defined flame areas or zones on the combustion front. For the integral measurement, we use special kinds of photomultipliers. These 1-D and 2-D measurements are implemented by means of special fibre-optic elements. To obtain the time-related link between heat-induced oscillations and oscillation from simultaneously occurring acoustic field parameters, these measurements are evaluated within the frequency range. As well as direct analysis, data of this kind can also be used for calculating the Rayleigh index. |