Abstract
The generalised Eddy Dissipation Concept (EDC) developed in the first part of this article is thoroughly validated against twelve flames from the Delft and Adelaide jet-in-hot-coflow (JHC) burners. These flames emulate Moderate or Intense Low Oxygen Dilution (MILD) conditions. Modelling of turbulence-chemistry interactions in this regime is a non trivial problem and many standard combustion models may fail. Recent Direct Numerical Simulation studies revealed a distributed appearance of the reaction zone indicating non-flamelet regime, which justified the use of reactor type modelling approaches. Those kind of models are of empirical nature and are sometimes criticized for being dependent on a number of tunable parameters. Also, most of new concepts are validated against a limited number of experiments. In this study, using the same modelling setup, twelve flames with different jet Reynolds number, level of oxidizer dilution with various fuel mixture were simulated. It turned out that the generalised EDC model considerably improved predictions with respect to the standard model for all the considered flames. Even though the predictions of the other EDC extensions provided better results in some regions, only the proposed generalised approach could cover the broad tange of operating conditions, proving its “universality” and reliability.
Highlights
Moderate or Intense Low Oxygen Dilution (MILD) combustion is gaining increasing interest for the development of new technologies, as explained in the first part of this study [1]
Based on our previous research [5,25], in the first part of this study [1] we have extended the range of applicability of the Eddy Dissipation Concept (EDC) model by ensuring proper behaviour under extremely low Reynolds and Damköhler numbers conditions
In the first modelling study of EDC analysis, the flame denoted as DJHC-I [20,2] was considered with three different fuel mass flow rates resulting in a jet Reynolds numbers of 2500, 4100 and 8800
Summary
Moderate or Intense Low Oxygen Dilution (MILD) combustion is gaining increasing interest for the development of new technologies, as explained in the first part of this study [1]. Series of measurements with various jet Reynolds numbers, levels of coflow dilution and fuel types are analysed to test the models for wide range of operating conditions. This is especially important for the Reynolds Averaged Navier-Stokes (RANS)-based models, which may encounter problems at low and high turbulence. Perpignan et al [4] presented a complete review of modelling approaches applied to the JHC configuration They pointed out that, due to the uncertainties related to the underlying physics of MILD combustion, most of the known turbulence-chemistry interaction (TCI) approaches have been already assessed in this regime. The present formulation is based on functional expressions where the model parameters are adjusted to the local conditions in terms of Reynolds and Damköhler numbers, contrary to the usually proposed ad hoc tuning of the global EDC constants
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