Spontaneous oscillations in lean premixed combustors

In this paper a mathematical model of the oscillating behaviour observed in lean premixed combustors is developed. The combustor is modelled as a WSR and only mass and energy balances are taken into account. Model results show that oscillations can be foreseen also in absence of coupling between heat release and acoustics. The simulated oscillations are the result of reactor instabilities induced by heat losses and the strong dependence of reaction rate on temperature and concentrations. Theoretical stability maps of the combustor have been generated by means of the bifurcation theory. Bifurcation diagrams have been built as function of the most important operating parameters (heat transfer coefficient and residence time) at different values of equivalence ratio and mixing degree. Model results suggest that oscillations are likely to occur at lean condition. Oscillations amplitudes and frequencies trends have shown to be qualitatively in agreement with the experimental results reported in literature.