Ngọn lửa rối khuếch tán

MÔ HÌNH TOÁN HỌC

TÍNH TOÁN NGỌN LỬA RỐI KHUẾCH TÁN

Turbulence diffusion flames are widely used in industry because of their safety. Nevertheless, their efficiency and the pollution emission depend on the organization of the combustion medium and this fact needs the knowledge on the structure of flame. The experimental measurement of the instantaneous and local values of oxygen and fuel is very difficult, and sometime, is impossible inside the combustion chamber. So the prediction by the mathematical model is very helpful.
 
In this paper a model for calculating of turbulent diffusion flames in the air and in the Diesel Engines is presented. The model includes the k-e turbulence model. The turbulent nonpremixed combustion process is modeled via the conserved scalar model where the fraction mixture f is chosen as conserved scalar. The laminar concept is used for instantaneous thermochemical state of the combustion mixture. With this approach, the species concentration as well as the temperature of combustion can be calculated thanks to their relations with the fraction mixture f.

Thus the basic problem of the model is determination of f. The local value of this scalar depends on the turbulence intensity which is a random phenomena. In the model, this phenomena is modeled by a probability density function (pdf) of f. The formulation of the function is completely determined by the mean value of f and its fluctuation. Two pdf (Beta function and Polynomial function) are chosen and the comparison of the results is presented.

For the first stage of research a one-dimensional equations system is established. The results given by the model is validated against the experimental data.

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