627 / 2019-01-20 16:57:07

Simulation of combustion instability of a partially premixed model combustor considering heat exchanger as active acoustic elements

Combustion instability; Partially premixed flame; Heat exchanger; Flame description function; Transfer matrix

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 exchanger 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. 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 a heat changer near the outlet of the combustion chamber. The reactive Scale Adaptive Simulation (SAS) approach is utilized to describe flame dynamics coupled with acoustic field. The self-excited instability and the response of the system to small amplitude broadband velocity perturbations are simulated to study the combustion and acoustic coupling between the burner and heat exchanger. A method of combining Transfer Matrix (TM) and Flame Description Function (FDF) is introduced to study the influence of the burner and heat exchanger separately. Results show that the modelling methods can effectively illustrate the mutual interactions between pressure perturbations and unsteady heat release in the unsteady LIMOUSINE combustor. The existence of heat exchanger can influence the thermoacoustic property significantly in terms of frequency and amplitude of oscillations for changing the flow field and temperature field. Comparison analysis was implemented by changing the distance between flames and heat exchanger. When flames do not impinge on the heat exchanger, linear network modelling approach can be applied to construct the response of the burner and heat exchanger separately through selecting a suitable intermediate plane. But when flames impinge on the heat exchanger, flame and heat exchanger cannot be seen as individual element and should be analyzed as a coupled element. The results of the paper provide a theoretical guidance for designing stable combustion system in a condensing boiler system.