VALIDATION OF COMBUSTION MODELS ON A LABORATORY-SCALE FURNACE OPERATING IN DILUTED COMBUSTION REGIME

Diluted combustion, also called flameless or MILD combustion, is one of the most efficient techniques developed to reduce NOx emission in high temperature air combustion systems. Its modeling issue lies in the fact that chemical kinetics has to be taken into account in the combustion model to capture the change of mixing and kinetic time scales compared with a classical flame. The validation of the numerical modeling on industrial scale furnaces is quite difficult since detailed in-furnace experimental data are necessary and because the large computational domain requires important computational resources. That is why this work proposes to validate the combustion models on a 30kW natural gas furnace, i.e. at laboratory scale, but with a configuration similar to industrial furnaces (geometry, injection system, variable load). Experimental data are collected considering air preheated at 800°C and for two equivalence ratios. The progress of the reaction is observed in UV from OH self-emission and is quantified thanks to the distribution of temperature and species content (O2, CH4, CO, CO2) measured inside the furnace. The system is then modeled using the commercial code ANSYS Fluent with the Eddy-Dissipation/Finite Rate model or with the Eddy Dissipation Concept model, two combustion models differing in the way they consider chemical kinetics. Only the latter, which allows including a detailed reaction mechanism, is able to predict the correct order of magnitude of NOx emission and to reproduce the shape and position of the reaction zone.