Numerical analysis of flameless combustion in a compact chamber burning hydrous ethanol

Abstract

This paper presents the numerical simulation of a compact laboratory-scale combustion chamber designed to operate with flameless combustion technology, using hydrous ethanol as fuel. The purpose of the study is to validate the combustion modeling to perform a more in-depth analysis of the combustion atmosphere based on the temperature profiles, velocity fields and emissions of UHC, CO and NO to verify the development of the flameless combustion regime from burning liquid biofuels. In this paper, two different combustions models had their results of the numerical simulations analyzed: the Eddy Dissipation Concept (EDC) and the hybrid model Finite Rate / Eddy Dissipation (FRED). The temperature profiles and UHC, CO and NO concentrations obtained in the numerical simulations showed good agreement with the experimental results for the combustion modeling by the FRED model, with maximum deviations between 1.0 and 12.5% between the numerical and experimental temperature profiles and maximum deviations of 6% for the UHC, CO and NO numerical and experimental emission rates, allowing the validation of the developed numerical procedure. The EDC model hasn’t satisfactorily reproduced the turbulent and chemical interactions of the combustion reactions that occur in the flameless of hydrous ethanol, significantly affecting the temperature distribution in the combustion atmosphere which presented maximum deviations of the order of 25% in relation to the experimental results. The validation of the combustion modeling by the FRED model allowed a global analysis of the combustion atmosphere and the numerical results revealed that during the experiment the combustion chamber used in the present study didn’t operate in the flameless regime, but in the transition regime between conventional combustion and the flameless combustion regime. The numerical analysis showed that a longer operation time of the experimental combustion system is necessary for the development of the flameless.