The direct implementation into CFD codes of large kinetic mechanisms for the prediction of pollutant emissions is still unfeasible, due to computer time limitations which become particularly relevant when considering the typical scale of the industrial applications. Therefore, simplified modeling approaches are generally adopted, as they allow reducing the computational effort associated with the numerical simulations. With regard to NO formation, simple one-step mechanisms are used to describe each of the relevant routes contributing to the overall generation of NO, i.e., thermal, prompt. The main drawback associated to a simplified NO formation approach lies, however, in the extreme sensitivity of the lumped rates on the thermo chemical state which define the combustion system of interest. Then, a proper description of turbulence/chemistry interactions must be employed in the CFD model, to provide a realistic background for the estimation of NO emissions. This becomes particularly important in MILD combustion regime, which generally requires an accurate description of the gas-phase oxidation, due to the kinetic control on the overall combustion process. The present paper discusses key aspects and requisite for predicting NO formation in MILD combustion regime. The approach is based on the direct coupling of simplified NO mechanisms to the CFD calculation and is applied to different MILD conditions. Simulations are carried out for a set of experimental runs performed on a self-recuperative MILD burner, varying the hydrogen content in the fuel stream from 0% up to 50% by wt. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A simplified approach for predicting NO formation in MILD combustion of CH4–H2 mixtures

GALLETTI, CHIARA;TOGNOTTI, LEONARDO
2011

Abstract

The direct implementation into CFD codes of large kinetic mechanisms for the prediction of pollutant emissions is still unfeasible, due to computer time limitations which become particularly relevant when considering the typical scale of the industrial applications. Therefore, simplified modeling approaches are generally adopted, as they allow reducing the computational effort associated with the numerical simulations. With regard to NO formation, simple one-step mechanisms are used to describe each of the relevant routes contributing to the overall generation of NO, i.e., thermal, prompt. The main drawback associated to a simplified NO formation approach lies, however, in the extreme sensitivity of the lumped rates on the thermo chemical state which define the combustion system of interest. Then, a proper description of turbulence/chemistry interactions must be employed in the CFD model, to provide a realistic background for the estimation of NO emissions. This becomes particularly important in MILD combustion regime, which generally requires an accurate description of the gas-phase oxidation, due to the kinetic control on the overall combustion process. The present paper discusses key aspects and requisite for predicting NO formation in MILD combustion regime. The approach is based on the direct coupling of simplified NO mechanisms to the CFD calculation and is applied to different MILD conditions. Simulations are carried out for a set of experimental runs performed on a self-recuperative MILD burner, varying the hydrogen content in the fuel stream from 0% up to 50% by wt. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Parente, A; Galletti, Chiara; Tognotti, Leonardo
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/202393
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