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The thesis regards the CFD numerical modelling of a novel cyclonic burner that operates under the innovative MILD Combustion regime. In particular, this work aims to point out the main features of such a combustion regime by means of a combined numerical and experimental activity. The main modelling approach adopted was based on tabulated chemistry (FGM model). The author compared the numerical results to the measurements on the cyclonic burner for a wide range of operating conditions in order to assess the predictivity of the model and the key characteristics of the combustion system. The main weaknesses of the numerical methodology were highlighted. In particular the tabulated approach used was not able to predict the internal exhaust recirculation (internal dilution) for this kind of system. Therefore, by adopting a reactor approach, a novel tabulation procedure was designed and validated. Moreover, the role of the radiative heat transfer was investigated in detail. To summarize, the main results achieved can be listed as: The experimental campaign carried out for a wide range of operational conditions showed that the MILD features of the system (uniform thermal field, absence of flame, low emissions, etc.) are slightly affected by the boundary conditions; “Standard” FGM model predicts with a very good agreement the conditions at low reactivity at inlets but is not able to fit the data properly for inlet conditions far from those related to MILD definition (high preheating and dilution) because of the internal dilution; The radiative heat transfer is crucial in this kind of system because of the cavity effect of the walls and the radiative reabsorption of the exhausts. Such effect is much higher compared to a traditional system both for the higher residence times (combustion products recirculating) and for the high heat loss at walls (small scale system); Results showed the influence of the elementary configuration used for the thermochemical manifold tabulation; An analysis made on the heat loss and the dilution level led to define a new tabulation methodology and to associate a fixed MILD operative condition of the burner to a reduced manifold of the thermochemical variables. |
