engleski

A comprehensive modelling of NOx formation in combustion systems based on reduced chemical reaction mechanisms

The nitrogen oxides (NOx) are among the main pollutants in the atmosphere. Nitrogen oxides emitted from combustion systems are a major environmental problem since they contribute to photochemical smog, acid rain, corrosion problems, global warming and depletion of stratospheric ozone. As a consequence, formation of nitrogen oxides in combustion systems presents a topic of growing public concern and subject to increasingly stringent regulations in order to protect human health, air quality and vegetation. With the development of increasingly affordable and powerful computers, computer modelling of the NOx chemical reaction processes has become a valuable tool that can be used to provide insights and understanding of nitrogen pollutants formation process. This paper presents a review of modelling work performed at Power Engineering Department (PED) concerning the prediction of nitrogen oxides in combustion of gaseous and liquid hydrocarbon fuels. The model for nitrogen oxides formation is based on reduced chemical reaction mechanisms, which is implemented in commercial CFD code FIRE. This approach of modelling is required a joint solution of detailed CFD equations for turbulent reacting flow, combined with reduced mechanisms. Two chemical reaction mechanisms, the extended Zeldovich and prompt, are incorporated in the model in order to predict NO formation rate from atmospheric nitrogen. For liquid fuel with chemical bound nitrogen additional reaction mechanism is incorporated. Chemistry-turbulent interactions are modelled by integration of chemical kinetic rates with respect to fluctuating temperature and appropriate probability density function (PDF). The nitrogen oxides formation is calculated decoupled from the generalized combustion model in a post-processor step using converged solution of a pre-calculated flame structure.

Pollution; Combustion; Modelling; NOx; CFD; AVL FIRE; Post-processing

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