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Show - 7- 4.2.2 Models used and main results In addition to the equations of fluid mechanics described in section 3.2.2, we also solve : - the transport equation of enthalpy, - radiation using the six-flow model (or Spalding model) [6], - combustion by the conserved scalar combustion model [7]. The conserved scalar model is based on the hypothesis of non-premixed combustion and an infinitely fast global reaction such that : Fuel + s oxidizers----> (1 + s) products. The temperature is calculated on the basis of enthalpy. For the purposes of calculation, we introduced variations in the average heating capacities according to the temperature and the chemical species present. The results of the first simulations point to significant differences between reactive flows and non-reactive flows. In particular, the main recirculation zone in the quarl moves from the side towards the centre. The fuel and oxidizer do not seem to mix correctly. This could explain the length of the simulated flame as compared with the test flame. The results of numerical simulation show the difficulties of modelling industrial burners. In view of the complexity of phenomena, it is necessary to perform exhaustive validation work on each of the models used. This work relies notably on the results of detailed flame analysis as set out in section 4.1. 5. Conclusions Reacting to the new environmental protection regulations, Gaz de France and the company Stein-Heurtey are pooling their experience to develop a tool that will be able to forecast and reduce NOx emissions from industrial burners. In pursuit of the above objective, major studies have been undertaken to acquire more detailed knowledge of flows and combustion in burners using preheated air (8SI-1) and also to constitute a data base for the validation of models. The first results of nLHllerical simulation illustrate the limits of the models used at present. However, pending the development of more detailed methods for the numerical simulation of turbulent combustion, the analysis of results must provide qualitative information on the influence of geometric parameters and burner operating conditions on NOx emissions. As a result, we are pursuing work on models at the same time as the parametric study of the burner. Notably, we are looking at how fluctuations in temperature and chemical species concentrations can be taken into account and how we can develop a radiation moder that is better adapted to radiative transfer in a semi-transparent environment. ... 1 .. |