696 / 2019-04-30 19:43:34

Simulation of combustion instability of a premixed model combustor with heat exchanger in the combustion chamber

combustion instability,heat exchangers,flame transfer function,system identification

全体主题 > 数值模拟、建模与CFD

Heat exchangers are essential parts of a condensing boiler system. Combustion instability in the furnace considering heat exchangers has not gained much attention which leads to a lack of knowledge of the interactions between the burner and heat changer. The analysis of combustion instabilities caused by the interactions between the burner and the heat changer in a simplified model combustor is presented with CFD method. The reactive Scale Adaptive Simulation (SAS) approach is utilized to describe flame dynamics coupled with acoustic field. An academic CFD model of Limousine combustor is used to simulate the combustion instability properties as the method validation. And then the system was added with 2 different heat changers in the combustion chamber. The self-excited instability of the 3D slice model is modelled and compared in terms of oscillation frequencies and amplitudes. In order to obtain the response of the system to small perturbations, a simplified truncated 2D computational domain is used and broadband velocity excitation is utilized to study the thermoacoustic reflection behavior for a wide range of frequencies. Flame transfer function (FTF) by CFD/system identification (SI) and single frequency excitation method are utilized to study the influence of the burner and heat exchanger to the combustion dynamics. Results show that the existence of heat exchanger can influence the thermoacoustic property significantly in terms of FTF gain and phase for changing the acoustic characteristics of the combustion domain and flow field. The self-sustained fluctuation amplitude is reduced to a value quite low for both the two types of heat exchangers. When inlet velocity excitation is added, the two combustion system show different frequency response too. The results of the paper provide a theoretical guidance for designing stable combustion system in a condensing boiler system.