DYNAMIC RESPONSE OF ACOUSTICALLY FORCED TURBULENT PREMIXED BIOGAS FLAMES

Increasing demand for energy and the need for diversification offuels used in gas turbine power generation is continuing to drive forward the development offuel-flexible combustion systems, with particularfocus on biomass derived sustainable fuels. The technical challenges arising from burning sustainable fuels are largely associated with the change in the chemical, thermal and transport properties of these fuels due to the variation of the constituents and their impact on the performance of the combustor including emissions, static and dynamic stabilities. There is a lack of detailed understanding on the effect offuel composition on the flame sensitivity to acoustic and flow perturbations. This paper describes an experimental study investigating the acoustic flame response of simulated biogas (methane/carbon dioxide/air mixtures) turbulent premixed flames. The effect of variation in carbondioxide, CO2, content on the flame response was quantified. Special emphasis was placed on understanding the dependence of this flame response on the amplitude of the acoustic forcing. The flame was subjected to strong velocity perturbations using loud speakers. It was observed that the addition of CO2 had considerable influence on the magnitude of heat release response. The magnitude and the phase offlame describing function indicated that the mechanism of saturation in these flames for all conditions tested were the same. The difference in magnitude could been attributed to dilution effect and hence further investigation were carried out with N2 andAr to clarify the role of CO2. The results indicate that the thermal capacity of the diluent gases could be playing a significant role in nonlinear flame dynamics.